Food Microbiology Test 1 (Lecture 1-5)

How much does food borne disease cost the U.S.?

$77 billion annually

What are the shelf life endpoints representing the levels of microorganisms?

-7 logs of bacteria causes spoilage of food -5 logs of yeast causes spoilage of food -If there is visible mold, the food is spoiled

Thermal Processing: General and 1795 French Government

-Associated with larger, growing populations. Allows food to be shipped longer distances, etc. -Observation of effects/cause unknown -1795: Award for food preservation method. Nicholas Appert noticed that foods didn't spoil if they were heated in sealed containers (i.e. canned). Glass bottles, corked, boiling water. Insistance of Napoleon I, published in 1810. 1700s to mid-1800s there was the development of

Thermal processing: Solomon

-Baltimore canning -Adding Calcium Chloride to water to raise boiling point (100C-->116 C). Need less thermal energy to get benefits from food.

Describe the mechanisms of plant product spoilage.

-Breakdown of primary structural components (cellulose, pectin, cutin) -Degraditive enzymes (pectinases [borytis cinerea, penicillium, erwinia carotovora], cellulases, proteases, phosphatidases, dehydrogenases)

Can you eat moldy bread?

-Can't remove moldy part because the mold you see is just tip of the iceberg. Mycella grows deep into foods. Toxins found near mycelia. -Exceptions: good molds= Pencicillum reoqueforti (ex. blue cheeses) . Hard cheeses and dry salami.

What is soft rot?

-Caused by erwinia carotovora -Tissues become damaged and Erwinia invades, reduces acids. -Most common post harvest disease we see -Softening due to reduction of pectin -Salmonella can grow 5 logs on a food that has soft rot in comparison to not being able to grow on these foods.

Describe the organoleptic changes to food based on bacterial levels.

-Certain breaking points where if you have a certain number of bacteria that you can actually taste it. Yet it is impossible to get rid of ALL bacteria in food. Spoilage can be reduced if you can control the GROWTH of the microorganisms. -Less than 10^6=microbial spoilage generally not recognized -10^6-10^7=may taste "off" taste in food -10^7-10^8= good smells bad. We perceive this food is spoiled before even tasting. -10^8-10^9= All food products display obvious signs of spoilage -Above 10^9= food becomes liquid and this state is very unnatural to find in nature. Able to be seen in lab.

What was occurring in the realm of Food Microbiology during the year 20,000-10,000 B.C.?

-Evidence of agriculture (grain). -Domestication of plants and animals -Cause of disease/spoilage still unknown (killed animals for food; mold destroying grains, breakdown of meats)

How can food safety be increased/ensured?

-Extend lag phase -Slow growth rate so population is too small to cause illness -Increase death phase

What was occurring in the realm of Food Microbiology during the year 30,000 B.C.?

-Foods hunted and stored -Little ability to store food or find enough food. Therefore, preservation wasn't a problem -Cause of disease/spoilage were unknown

Describe sour rot.

-Geotrichum candidum causes sour rot of fruits -Also caused by other fungi and tactics -Associated with a sweet flavor

Thermophiles

-Grow at hotter temperatures -Example: geobacillus stearothermophilus and alicyuclobacillus acidoterrestris

Effects of water activity on microbial growth

-Increase lag phase by lowering water activity -Decrease growth rate -Decrease number of stationary phase cells. In stationary phase, cells are more resistant to thermal processing and the hurdles we put in place. Maintain enough processes that keep them alive so they can persist for awhile. -Minimal to no effects on microbial survival, being to grow once water is again available. water activity on its own isn't a lethality treatment (just stopping it from replicating it at that time; microorganisms aren't killed), salmonella is resistant to low water activity...once it gets into the stomach/small intestine they now have all the water they need to persist

Post-harvest decay from mold

-Moldy berries [don't wash them before packaging because washing them increases the rate of spoilage], moldy bread, cucumbers, moldy cheese -Blue cheese, etc. are good molds because they don't produce any bad toxins

Mesophiles

-Most foodborne microorganisms are mesophiles -Mild temperatures

What lies ahead for Food Microbiology?

-Moving from "what" to "why" -Era of molecular biology and genetics. Genotypic vs. phenotypic. Increased control of pathogens and spoilers. Importance of antimicrobial agents. Developed of alternative processes and improved regulation. Food safety regulations required that when a product was associated with an outbreak that that product is removed from the shelves.

Dilution scheme reminders

-See if original sample is diluted..if it is assign a dilution factor -Putting 1 ml doesn't increase dilution factor only .1 ml does

Describe the effect of initial load of microorganisms on spoilage.

-The higher number of microorganisms you start off with, devoid of temperature, the faster the food with spoil. Thus sanitation and disinfecting processes are very important to ensure that there are less microorganisms in food.

Are food borne illness statistics reliable?

-There are a variety of agents (bacteria, viruses, parasites, and chemicals) -There are unidentified pathogens where the nature of the disease leads to misdiagnosis. Little investigation of sporadic cases. Many not recognized as food borne pathogens 30 years ago. -There is transmission route confusion--> person to person, recreational water, contact with animals -Underreporting--> only a small fraction of illnesses are confirmed by laboratory testing and reported to public health agencies

Thermal processing: Durand of England

-Tin cans. Expanded thermal processing; expanded canning/shipping; allow European societies to grow

Describe the burden food borne diseases have globally. Give Food safety statistics.

-WHO estimates 1 in 10 people fall ill every year from eating contained food (600 million illnesses) -420,000 die as a result. Diarrheal disease agents caused 230,000 deaths. Salmonella Typhi, Taenia solium, hepatitis A virus, and aflatoxin. Children under 5 years of age are at particularly high risk with 125,000 children dying from food borne diseases every year. -There is a growing concern of aflatoxin because we are bringing in our food from places where aflatoxin is present. -48 million food borne illnesses from consuming contaminated foods/beverages -128,000 hospitalizations from consuming contaminated foods/beverages -3,000 deaths from consuming contaminated foods/beverages -56% of food-borne illnesses in the U.S. we don't know the cause (not enough data, no PCR, etc.) -44% of food-borne illnesses in the U.S. we know where the disease comes from...31 known pathogens to blame. Generally, mortality if higher in bacterial related illnesses (high risk of death) when compared with viruses or parasites.

What are three main ways parasite diagnosis parasite control?

1) Fecal exam (ova and parasite exam). Parasites aren't continuously shed—when people go to the bathroom they aren't always producing an ova. Therefore need to take fecal samples for a 3 day period in order to get an ova. Need compliance from patient for this type of testing. Need skilled individual for examination of ova under microscope. Examined microscopically for ova (eggs) 2)Endoscopy/colonoscopy: used when fecal exam is negative; portion of intestine is taken out (some parasites are too difficult to be obtained through fecal samples) 3)Blood tests: serology=antibodies (popular with toxoplasmic ganidia); blood smear=parasites must begin

Describe the two possible physiological states of cells.

1) Injured cells--> inability of cells exposed to sublethal stress to grow on selective media but still grow on non-selective media. Requires additional nutrients, time for repair. These cells are less resistant to selective agents or have increased nutritional requirement. After exposure number of microorganisms is reduced. Injured microorganism cells have an extended lag phase 2)Viable but not culturable (VBNC)--> cannot cultured on any media, still infectious, non-sporulating bacteria. Number of microorganisms reduces even more drastically.

Name 9 sources of Food Contaminants.

1) Raw Ingredients 2) Food Handlers 3)Surfaces 4)Packaging 5)Water 6)Air 7)Soil 8)Insects 9)Animals **60% of noroviruses come from food handlers **40% of noroviruses come from the air...particles are suspended in the air for 3 days

Name the top five pathogens causing domestically acquired food borne illnesses resulting in death.

1) Salmonella 2)Toxoplasma gondii 3)Listeria monocytogenes 4)Norovirus 5) Campylobacter

Numeric control of Foodborne Microorganisms

1) Vacuum packaging--> restricts oxygen, slows spoilage and oxidation 2)Modified atmosphere packaging --> increased CO2 or N2. CO2 is directly antimicrobial. N2 is relatively inert in food atmosphere. Initial temperature is alter. Affected by oxygen tradition rate of packaging. 4)controlled atmosphere storage. Atmosphere monitored and held at appropriate conditions

What are the biological hazards in foods?

1)Bacteria 2)Viruses 3)Parasites

What are the four main categories of hazards in foods?

1)Biological--> foodborne pathogens, bacteria, diseases 2)Chemicals-->produced by bacteria, toxins that are natural parts of the food (ex. cyanide in the pits of fruit) 3)Physical--> metal shaving from processing, bone (choking hazard) 4) Radiological--> can grow fruits and vegetables in soil that is radioactive

What are the two commercial testing procedures for parasites?

1)ELISA (enzyme linked immunosorbent assays)--> typically used for agglutination. ELISA done in 96 well plate. In the bottom of each well there is antibodies. Antigens could be on the surface. If the antibody and the antigen complex then there's a color change. 2) Real time PCR . Can adapt it to look for specific genes and to characterize virulence. Basically this is DNA replication in a test tube. Two primers necessary to form the beginning of the growing chain in DNA replication. DNA polymerase is a special polymerase that's active at 72 degrees celsius. Three distinct temperatures in the machine (high, low, high-->denature, anneal, and extend) .

What are the four ways to identify viruses?

1)Electron microscopy--> shape, size, single or double stranded, number of nucleic acid pieces, types of vector for spread and serological characteristics of the coat/coat protein 2)Serology: antibody-antisera interaction (blood sample or induce an antibody response) 3)Spectroscopy: detecting light scattering "signatures". Determining a type of signature of a virus based on the type of light that the virus scatters. Rapid tests are used for classification of viruses. 4)Molecular based methods (PCR /sequence)

What are the four major cultural methods?

1)Media types (broths and agars). Non selective=if microorganism can grow under those conditions then it will grow Selective=something in media to deter growth of certain organisms under those conditions (contains agents that restrict or prevent the growth of non-target microorganisms). Examples are antibiotics, bile salts, and acids. Differential=something added to media to cause colonies to be distinctive from each other. Allow differentiation of microorganisms (ex. pH indicators, hydrogen sulfide). H2S indicator has a distinct black color in the medium. These colonies will normally be surrounded by clear zones, a result of proteolysis or lipolysis. Occasionally, opaque zones will form within this clear zone, a result of lipase or lecithinase activity. 2)Enrichment: Detection method and 2 steps (pre enrichment, selective enrichment) 3) Plating: streak for isolation, pour plate, spread plate. Pour plate advantage=put sample directly (undiluted) so you limit the number of microorganisms you can see (10 is max) Spread plate you will always have 100 microorgansisms Enrichment is giving microorganisms specific things to make them grow better. Or keeping them at specific temperatures. Uses selective agents to promote pathogen growth to high levels while inhibiting growth of the competing organisms 4)Most probable number: estimates number of organisms present. Uses dilution technique. estimate based on number of organisms present. Tedious. Used only when low levels of a sample are present

Name the top five pathogens causing domestically acquired food borne illnesses.

1)Norovirus 2) Salmonella 3)Clostrium perfringens 4)Campylobacter 5)Staphylococcus aureus

Name the top five pathogens causing domestically acquired food borne illnesses resulting in hospitalization.

1)Salmonella 2)Norovirus 3) Campylobacter 4)Toxoplasma gondii 5)E. Coli

What are the 2 methods of direct plate counting?

1)Spread plate method= colonies form on surface of the agar. Normally used for solid samples and detecting microorganisms which require much oxygen for growth 2)Pour plate method= colonies form throughout agar, used for liquid samples, detect microorganisms that don't require much oxygen for growth, and lower limit of detection

Give an example of rapid screening (immunoprecipitate method)

1)short 8 hour selective enrichment 2)heat kill sample 3)drop onto sample port 4)wait 15 minutes 5) record results You have a sample, you place it onto the center, once the enzyme detects the antibody you get a color change type of reaction. Typically fast. For bacteria, it requires an enrichment phase and takes about 8 hours.

Emergence of Food Microbiology

1665: Robert Hooke published Micrographic, the first illustrated book on microscopy that detailed the structure of Mucor (a microscopic fungus) 1670s: Lee Wenhoek recorded observations of "animalcules" 1854-1864: Louis Pasteur thermal processing. "Pasteurization of wine" Association of certain bacteria types with spoilage and disease. Mid-1700s: Lazzaro Spallanzani showed that boiled meat placed in a sealed container did not spoil Development of Microbiology in mid-1800s.

Timeline Review

20,000 B.C. to 1700's A.D.: Development of agriculture, crude preservation, and association between food and disease 1700's to Mid-1800's: Development of thermal processing Mid-1800's to present: Development of microbiology 1890's to 1940's: Era of Preservation 1950's to 1980's: Era of Food Science. Chemistry and Engineering. 1980's to present: Growth of Food Microbiology. Increased recognition of causes. Improvement of detection and enumeration. Improvement of processing and handling

What is the temperature danger zone for food born pathogens?

40-140 F; bacteria grow most rapidly

What is the normal gas composition of the atmosphere?

78% nitrogen 21% oxygen Other gases are less than 1% (CO2, argon, ozone, etc.)

Describe the spoilage of plant products.

Active spoilage: Plant pathogenic microorganisms Passive or wound-induced spoilage: opportunistic microorganisms Don't typically see spoilage when a plant is growing in a field. After harvesting or processing it, it is post-harvest decay (active spoilage). Could be opportunistic.

What do microorganisms that cause food spoilage do to the food?

Affects aroma, texture, and or appearance of food. Only laboratory testing can tell if harmful microorganisms or toxins are present. Yet some are difficult to detect or cannot be detected.

Sublethal injury

Allow for a recovery period (up to 12 hours). Associated with things that have a very low water activity or were processed under very high heat.

Define microbiology.

An artificial subdiscipline of biology based on size

Describe spoilage and disease.

As time went on there was an increased knowledge of factors. These factors included air (spoilage microorganisms need 02 to thrive), light, and moisture. Yet there still was no knowledge of the cause of spoilage/disease. There were prohibitions on eating certain foods (Ex. Pork because it was associated with acquiring Trichinellosis). Prohibitions on handling of food (ex. leaving rice out overnight--> helped reduce Bacillus Serus). Often in religious documents they ban certain foods (religious sanctions imposed, fundamental regulations of hygiene).

Define Infection. Gives examples of Foodborne infections.

Attachment and growth of pathogenic microorganisms on or within the body of a human or animal (bacteria, viruses, and parasites). Must consume living microorganism (although disease may be toxin mediated). Examples: Salmonella enterica, E. Coli, Listeria monocytogenes [very dangerous to pregnant women, elderly and children less than 1 can be lethal], Norovirus [needs to grow and divide in beta cells which are immune system cells; 58% of diseases in U.S. are from norovirus], Hepatisis A [needs to get through intestinal epithelium but then moves/grows and divides into the liver. Destroys liver cells and the body can't detoxify itself], Cryptosporidium pram [colonizes (attaches) and invades in small intestine and causes diarrhea]

How are biofilms made?

Biofilm formation begins with attachment of the primary species to surface and encasement within polysaccharide matrix to which additional bacterial groups become encased and persist and/or contribute to growth of the biofilm Typically the organisms making the matrix aren't human pathogens. Human pathogens that come in are usually the secondary bacterial species—taking advantage of the biofilm formers that are nearby.

Describe the early regulations in civil law of Emperor Leo VI of Byzantium in 1,000 A.D.

Blood sausage that caused botulism (clostridium botulinum--> results in large number of deaths; organism uses all the oxygen). Prohibition was placed on eating and preparing. Punishments included loss of property and exile.

Facultative anaerobes

Both aerobic and anaerobic growth; greater growth in presence of oxygen. More growth at surface of food.

Outbreaks vs. Cases

Case: an instance of a particular disease Outbreak: an inccident in which 2 more cases of a similar illness result from eating the same food Outbreaks receive most attention but sporadic cases are estimated to be 10 times greater than the number of cases in identified outbreaks.

Intrinsic factors

Characteristics of the food itself pH, water activity, oxidation-reduction potential, nutrients, antimicrobial substances, biological structures

How is water activity measured?

Chilled Mirror Dewpoint Sample placed in cup enclosed in meter Vapor pressure detected by chilling water in food and allowing it to condenses on a chilled mirror Dewpoint of "air" above sample is determined Condensation vapor pressure at dewpoint Saturation vapor pressure at sample temperature Referenced to product temperature Make sure that product is broken up (grind up solid food) because there's more likely to be food on the inside of food versus on the outside of it so you want to evenly distribute the water Water collects on a mirror. Compare vapor pressure to the saturation vapor pressure at a sample temperature Need to have sample at a close range of temperatures (can't be too hot because you will have more vapor being produced as it cools so you'll get an inaccurate reading due to chilled mirror); system won't take temperature until it starts cooling down

Biofilm

Complex multi-cellular communities encased within self-produced biopolymers attached to solid surfaces. Majority of the earth's microbial biomass likely resides with biofilms. Biofilm components: carbohydrates such as cellulose, proteins such as flagella, pili, fimbriae and extracellular DNA act as adhesives to surface Biofilm attachment to human cells important in meany biofilm mediated infections for instance Salmonella Typhi carrier state associated with biofilm formation on gallstones in majority of carriers. Biofilms also common on majority of manmade materials (plastics, rubber, cement glass, stainless steel) including materials used in food processing plants Biofilms are complex multicellular communities (bacteria with fungi or yeasts, bacteria with algae or other types of eukaryotes). All biofilms are self-produced biopolymers attached to surfaces (surrounded by carbohydrates).

Microbes have different water activity requirements

Cross protection (look it up) Majority of bacteria will grow within .99-.88 water activity. For most yeasts, minimum is .88 water activity. Few other specific spoilage microorganisms that can grow at .86. Cutoff for shelf stability is .85 because of the few exceptions. Regular molds= .8 water minimum Halophilic bacteria= salt loving (increased solute), .75 water activity minimum Xerotolerent=tolerant of desiccation High water activity=low shelf life As water activity is decreased, the number of microorganisms that can grow is reduced so the shelf life increases Lower water activity means slower replication Relative vapor pressure is what water activity is Below 0.5 you aren't concerned with microbial growth because there isn't enough water for replication...they are NOT dead though. Microorganisms still persist at this low of a water activity, but they just don't replicate. If you dehydrate everything it won't be good because certain foods that you expect to be crispy won't (ex. Potato chips). Loss of structure As you increase water activity, enzyme activity increases (overall likelihood of staling, etc.), mold/yeast/bacteria growth increases

Describe classical microbiology.

Culture based (i.e. living microorganisms) Selective/differential media for isolation Biochemical assays Identify or population density in days or weeks Isn't practical if the food your working with spoils quickly Influenced by the growth requirements of the microbes. 99% of the world bacteria have not been cultured Provides a challenge for detection of "new" disease agents or spoilage bacteria

Purposes of methods (rapid and classical)

DETECTION: determine presence or absence. Useful for diagnosis and treatment CHARACTERIZATION: subtyping (need to link illnesses to each other or a particular source; not necessary to treat an individual. Dominated by molecular methods. Differences in DNA backbone used to discriminate between two different isolates. Only ways to subtype many viruses and many clonal food borne bacteria). Virulence (need to know what strain of bacteria and if it will respond to antibiotics/santitizers.) Resistance to stress. QUANTIFICATION: not always needed...sometimes only done to see that it hasn't passed certain thresholds.

How do we identify Norovirus in biofilms?

Electron microscopy, etc.

Explain the early regulation in civil Law among the Greeks and Romans.

Ergot (claviceps purpurea)--> halucigenic properties; thrive in wet/warm conditions. Consumption of spoiled grains. Precautions were taken to avoid contaminated grain.

Drying beef jerky to a water activity of 0.85 will eliminate risk of Salmonella infection. True or false?

FALSE; unless Salmonella is killed completely within the system it will still cause an issue within the system. 0.85 prevents growth of Salmonella but if they are still there then they still will cause illness when ingested

Your company manufactures ready to eat refrigerated meals. A good way to track microbial quality is by performing plate counts and incubating at 37 degrees Celsius. True or false?

FALSE; what you are going to be concerned about are the psychrotophic or psychrophilic bacteria you are going to prohibit their growth if you get to 37 degrees. So the temperature you should store them at is 4 degrees because they will most likely be growing at this temperature in this particular product.

Describe Extrinsic Factors

Factors external to the food product Not substrate dependent Primary extrinsic factors: temperature of storage, relative humidity of environment, and presence of concentration of gases Temperature of food itself can be different but it's considered extrinsic because the food temp and the storage temp should equilibrate High relative humidity's can increase spoilage or growth of microorganisms Reducing amount of oxygen (increasing nitrogen) to decrease microbial growth

How do we identify parasites in biofilms?

Fecal exam, ELISA, etc.

As agriculture was beginning early on in history what were some food storage techniques as well as preservation methods?

Food storage techniques: 1) Fermentation: early form of preservation. Could be alcoholic or acidic. 2)Drying: putting food in the sun for days before helped preservation 3) Salting: adding salt allows food to last longer 4)Smoking: put food in smoke of fire food lasted longer 5)Cold temperatures: food stores at cold temperatures lasted longer Preservation: salt as money.

Oxidation Reduction Potential (Eh)

Generally, the ease with which a substance gains or loses electrons Measured in millivolts (mV) Increasingly oxidized = more positive electrical potential (millivolts increasing) Increasingly reduced = more negative electrical potential (millivolts decreasing)-->obligate anaerobes; anaerobic High Eh favors aerobic microorganisms Low Eh favors anaerobic microorganisms Eh affected by: 1) Atmosphere ([by having oxygen in the environment this means you have more electrons that are available [higher Eh values]) 2) Heating drive off oxygen and you reduce the amount of Eh [making more negative]) 3) Microorganism growth (the more microorganisms growing in a system they are changing the redox potential of the product they are in)

Define microbiological spoilage of food.

Growth of bacteria, yeasts, and/or molds that leads to the production of microbial metabolic by-products which make the food product unacceptable. -Yeasts/molds need lower moisture levels, lower pH. They are typically not pathogenic. -Bacteria are more likely to be pathogenic. Usually only associated with spoilage.

Acid Stress Responses of Salmonella

Homeostatic Response--> Cell attempts to maintain intracellular pH Activates proton pumps to expel H+ ions. yeast cells attempting to maintain their intracellular neutral pH of 7. Proton pumps expel hydrogen ions Acid Tolerance Response--> Triggered at pH 5.5 to 6.0 Induction of acid tolerant proteins. change membrane structure and the frequency of the proton pumps (pumps work harder or there are additional protein pumps being turned on). More chaperone proteins (stabilize membrane and make sure pumps keep working). Acid Shock Proteins--> Triggered at pH 3.0 to 5.0 Regulatory proteins distinct from ATR proteins. mostly regulatory proteins; growth rate doesn't happen but can happen for particular strains or is very, very low. Things associated with repair of the cell.

Injury used as a tool for extending shelf

In cured lunch meat, refrigeration extends the lag phase of spoilage bacteria.

Lactoperoxidase System

Inhibitory system that occurs naturally in milk: Lactoperoxidase (0.5 - 1.0 ppm required ; 30 ppm natural) Thiocyanate (0.25 mM required; 0.02 - 0.25 mM natural) Hydrogen peroxide (100 U/ml required; 1 - 2 U/ml natural) Particularly effective against some Gram negatives Used in countries where refrigeration is limited Typically, must add thiocyanate and hydrogen peroxide May extend shelf-life from 2 days to 5 days These compounds are all naturally occurring in milk. All milk contains these three compounds. Together these compounds are particularly effective against gram negative organisms. Gram negative organisms can use fat in the milk for growth. By adding thiocyanate and hydrogen peroxide (specific amounts), you can use it to extend the shelf life of the product in areas that refrigeration isn't available (3rd world countries use this) -Will extend shelf-life from 2-5 days

Standard Plate count

Intended to determine the concentration of microorganisms within a food product. Only recover viable bacteria capable of growth at select conditions. Conditions exclude non-viable microorganisms and microorganisms with specific growth requirements.

Development of Food Microbiology

Koch: late 1800s established criteria for proving that a bacterium caused a disease. Established 3 postulates: 1) isolate the suspected bacterium to pure culture from the diseased animal 2) expose a healthy animal to the bacterium and make it sick 3) reisolate the bacterium from the newly infected animal) Petri: invented Petri dish to improve upon Koch's postulates Lister: father of antiseptic surgery; paved the way for safer medical procedures E. Van Ermengein: discovered Clostridium botulinum in 1896 1920's Botulism commission: public health service, 1922 there was a published guide for thermal processing, consumer education increased -First half of the 20th century was marked by the discovery of the "traditional" foodborne pathogens. Salmonella--> came from warm blooded animals. Clostridium botulinum--> came from improperly canned foods. Staphylococcus aureus--> associated with poor hygiene. Bacillus aureus--> contaminated starchy foods. Viruses were first crystalized and associated with disease in the 1930s and are a major cause of food borne illness. James Watson and Francis Crick: Discovered the structure of DNA....allowed for increased understanding as to how bacteria caused illness. 1/3 of the world's supply is lost to spoilage Probiotic bacteria may help people maintain health through their diet

Describe the spoilage of processed products.

MAJOR FACTORS: nature of the product and ingredients used SLIMY SPOILAGE: Yeasts; Lactobacillus, Enterococcus; B. Thermosphacta Souring: Lactics utilize sugars to make acids (Lactobacillus) Greening: Fresh meats make hydrogen sulfide [chemical process]. Cured meats= Lactobacillus viridescens [microbial activity]. Non-spoilage greening=misaligned muscle fibers from slicing

Water

Major component of many foods Water in foods profoundly affects Structure Appearance Taste Susceptibility to spoilage Growth of foodborne pathogens Removal of water (dehydration) is a major means of controlling microorganisms in foods Water activity (aw) is the best predictor of food stability, food safety, and other properties In many vegetables about 90% of their mass are water Processing (baking, drying, etc.) can change how much water is in food By removing water, structure/appearance of food changes (ex. Cabbage sauerkraut; cake battercake) Adding salt or sugars changes the amount of water available (gelation reaction; liquid to looking like jello) Water effects taste (allows flavorful compounds to be distributed around the mouth; if water isn't there then the taste distribution is different and thus the taste is different) Molds and yeasts and bacteria require water to maintain their homeostatic potential Water is important for regulating growth of foodborne pathogens...most foodborne pathogens aren't capable of growing in high salt/high sugar environments; most need a certain water content 2 main ways of controlling water activity: dehydration or adding another solute into the mix

Describe food-borne pathogens in biofilms.

Majority of food borne disease causing bacteria are able to adhere to or form biofilms in environmental conditions Isolated from naturally occurring biofilms in processing plants The majority of FB disease causing bacteria are able to be primary colonizers or adhere to established biofilms. unclear if some of these pathogens (Camplylobacter, Vibrio) can begin formation of the biofilms. Exposure to stress promotes formation of biofilms Stress=anything we do to the organism that makes the environment less hospitable to the biofilms (ex. Temp change, adding sanitizer, etc.) Stress kills a lot of the biofilms but some persist. Stress never kills all biofilms. There are several recent reviews that compile original research indicting that encasement within biofilms is associated with improved resistance to environmental stress. However, a fair amount of vairability in biofilm formation is associated with the strain. Desiccation=drying Ones that are surviving UV stress are likely on the inside of the biofilm opposed to the outside (Only want to determine presence. Pulse field gel electrophoresis is used for characterization so it isn't necessary here.)

What do microorganisms that cause food borne illness do to the food?

May or may not affect sensory characteristics of the food. Only laboratory testing can tell if harmful microorganisms or toxins are present. Yet some are difficult to detect or cannot be detected.

Describe rapid methods. Give examples of all the types of methods.

May or may not be cultured based. Serology (antigen/antibody; can determine if they are present ) Genetics, etc. Identify in minutes or hours Antibody-based methods: enzyme immunoassays, immunoflourescence, immunmagnetic seperation (separates target organisms from sample. Magnetic beads coated with a specific antibody are added to a sample and the sample is incubated to facilitate binding of the target cells to the antibody and then the complex is isolated from the sample by using a magnet. These methods are losing popularity because you have to have live animals to make antibodies and many people disagree using animals for this purpose Nucleic acid-based methods: hybridization (color change of fluorescence) and PCR application Others: miniaturized biochemical test kits (ex. API; more rapid than culturing but not rapid). Impedance, conductance.

What were the first inhabitants of the earth?

Microbes; they will always exist. .They are the foundation of the biosphere. • Food microbiologists can only create foods that microbes do not "like", manipulate the growth of microbes that are in food, kill them, or exclude them by physical barriers

Why are dilutions necessary?

Microorganisms grow to very high concentrations in order for one to count the number of microorganisms present you must dilute the sample

Nutrients

Microorganisms need food to grow and repair cellular structures Microorganism require various substances for growth: Water Source of energy Source of nitrogen Vitamins and related growth factors Minerals Gram positive bacteria: Least synthetic Growth more readily limited by limited nutrients (ex. B vitamins) Gram negative bacteria and molds: Able to synthesize most or all of required B vitamins

Antimicrobial Constituents

Naturally occurring substances in food that have antimicrobial effects: Essential oils (Eugenol in cloves and Allicin in garlic).-->Eugenol is good against staph aureous Iron-binding substances: (Lactoferrin in milk and Ovotransferrin in eggs).-->. Ovotransferrin in eggs prevents microorganisms that may have gotten in through the shell from growing. Antimicrobial enzymes: Lysozyme in eggs and milk.--> target cell membranes. makes it less likely for microorganisms to thrive Other: Glucosinolates in cruciferous vegetables (cabbage, broccoli, etc.)-- >associated with taste

Microaerophiles

Only aerobic growth, oxygen is required in low concretion.

Obligate aerobes

Only aerobic growth. Oxygen required.

Aerotolerant Anaerobes

Only anaerobic growth, but continues in presence of oxygen

Obligate anaerobes

Only anaerobic growth. Ceases in presence of oxygen.

How do we identify Salmonella in biofilm?

Presence/absence=PCR, UV light detection, enrichment

Aerobic plate count (APC)

Provides an estimation of the number of microorganisms in a food. Strict anaerobes don't grow on it. Drawbacks: coalescence of colonies and growth of spreaders

Temperature of Storage

Refrigeration: 4C (-40F) maximum. Studies indicate up to 50% of home refrigerators are too warm which is an issues because pathogenic microorganisms are replicating and spoilage microorganisms are present

Expansion of Processing Methods

Refrigeration: extended shelf-life, emergence of frozen foods was by Clarence Birdseyes in 1929 when he created method to quickly package frozen vegetables. Speed is key because it makes a smaller ice crystal which helps maintain a better quality of the vegetable. Maintains color, consistency, etc. Wide use began in 1950s. Ionizing radiation: began in 1925. Ludwig and Hopf from Germany. MIT U.S. Army Major setback in 1953...associated with how the public perceives radiation; poisoning issue where the public was exposed to high levels of radiation Prions: basically proteins that have gone bad. In 1953, irradiation came under food additive regulations.

Microbial growth growth and production of metabolites in food are associated with which of the following?

SPOILAGE OF STRAWBERRIES and STAPHYLOCOCCUS AUEREUS INTOXICATION

Which method would you use to determine if Listeria is present in lunchmeat?

Selective and differential media and PCR.

Microbial Growth Curve

Stationary phase=maintaining cellular processes, can have spoilage at this phase, can have pathogens that are still virulent Lag phase=many extrinsic factors are designed to extend the lag time (amount of time it takes them to begin replicating) or decreases the growth rate (decrease in slope of log line; will take longer to get growing because of the response to stress in the lag phase) Overall the majority of things we'll take about don't influence the death rate

Define Food Microbiology.

Studies microbes that grow in food and how food environments influence microbes. Field has changed radically in the last 20 yrs. Number of recognized foodborne pathogens has doubled. Genetic and immunological probes have replaced biochemical tests and reduced testing time. Food micro still in the early stages→only study the microbes that we see under the microscope and grow on agar media in petri dishes but experts suggest that only 1% of all the bacteria in the biosphere can be detected by cultural methods

Relative Growth Rates of Bacteria

Temperature is effective at controlling the overall growth rate of bacteria Depending on what the temperature is this effects the overall time of bacteria to replicate Take more energy for psychrophile to replicate so their growth rate is lower than a psychrotroph or mesophile. When your closer to the end of the scale the growth rate is lower than the other types of bacteria but they are still growing. At warmer temperatures for mesophiles its easier to replicate so the growth rates are higher at 25 degrees Celsius. Difficult for mesophiles to repair membranes at certain high temperatures so this is when their growth rate declines. Slower growth rates and different genes expressed. Most membrane fluidity through increased unsaturated fatty acids preventing membrane from solidifying. Different expression of virulence and motility associated genes. Membranes being changed due to increase of fatty acids. Important at low temperatures because as you reduce the temperature the amount of molecular movement decreases (more rigid). Increasing saturated fats makes membrane solid which makes it impossible to have transport throughout the cell. Compatible solutes= can be taken into the cell, if you have a food product high in these compounds then the likelihood of spoilage is higher than foods with low levels of these (sugars help stabilize membrane and prevent freezing in the internal portions of the cells) By being exposed to low temperatures, it may reduce likelihood of virulence Motility is affected at low temperatures -Important for biofilms...if they are unable to move as quickly then you have less biofilm accumulation in these environments

What is one way we can control spoilage bacteria?

Temperature; most organisms that cause spoilage grow more slowly at lower temperatures. Temperature severely effects microbial growth.

Define intoxication. Give examples of Foodborne intoxications.

Toxins disrupt the functioning of the intestinal cells; they may be absorbed into the blood stream. Symptoms include headache, dizziness, vomiting, diarrhea, stomach pains, neurological symptoms, paralysis, and death. The toxin is pre-formed in the food; doesn't require ingestion of living cells; toxins may be very resistant to food processing measures. Have to ingest performed toxin to get sick. Examples= Clostridium botulinum has anaerobic growth and causes botulism. Staphylococcus aureus.

What is RT-PCR?

Uses reverse transcriptase Starting template is RNA instead of DNA RNA viruses are common amongst food borne viruses (ex. Norovirus, Hepatitis A, Hepatitis E)

Water Activity Fundamentals

Water content is not a reliable predictor Chemically bound water is not available to microorganisms aw is most relevant for safety and quality aw is affected by Solute type Temperature Ice has lower aw than liquid water Humidity of storage Desorption or resorption Jams and jellies have lots of water in them but it isn't available to microorganisms due to the fact that is it chemically bound to sugars Certain types of molecules will bind to water more tightly (salts and sugars) Ice has a higher vapor pressure so it has a lower water activity that liquid water because in an ice cube there are fewer molecules that are actually available As your humidifying something your adding more water to a system. So this can change the water activity of a food product. Desorption= you are doing a physical process (baking, freezing, dehydration, etc.) that are physically removing water because the water is sublemating (liquidgas) Resorption=what happens when you are trying to add water back or you are changing it in some way as part of your next processing step. Changing structure of food matrix itself Different moisture levels in the same food may have the same water activity depending on whether the moisture content was achieved by removing water (desorption) or adding water (respiration) hot air=evaporation freeze drying=sublimation Reduction in water activity for cured meats because salts are added Self stability=0.85 water activity (doesn't need to be refrigerated)

Water activity

Water content measures the amount of water in a food Water activity is a measure of the intensity of the association of water with non-aqueous components of foods Amount of water available for biological use Ex. Salt (NaCl) holds water very tightly in solution Definition: P is vapor pressure of water in food Po is the vapor pressure of pure water aw=P/P0 aw Scale = 0.0 (bone dry) to 1.0 (pure water). Adding salt or sugar to water it binds tightly to water molecules which changes the amount of water that's able to be bound or used by other microorganisms

Psychrotrophs

grow fastest under warmer temperature but CAN still grow at low temperatures but isn't optimal (ex. Pseudomonas, Enterococcus, Listeria, and Yersinia)

pH

pH=-log10[H+] H+ and OH- ions pH scale=0-14; logarithmic (10-fold) When bleach encounters cells, it dissolves the membranes and causes cells to lyse Very alkaline things don't contain food products, pH of 8.5 is where food products begin to be seen (egg whites) Most food products are acidic Weak acids are more lethal than strong acids. Strong acids completely dissociate into H+ and A-. Weak acids do not completely dissociate and this undissociated form enters cell. Thus, undissociated ones are better at killing microorganisms because they can actually infiltrate the cell. Lower the pH the more energy the cell must expend to maintain intracellular neutrality in order for the membranes to stay intact and the enzymes to keep working. Most foodborne pathogens cannot grow below pH 4.4. Still persist, die-off is very slow. Die off more rapidly once pH reaches 2. Some spoilage/fermentation microbes can grow as low as pH 3.0 Vinegar used for pickling cucumbers

Define a D-value.

time required, at a given condition, to kill 90% (reduce by 1 log of bacteria) Lower D value=it seems easier to kill microorganisms