Microbiology lab final

Describe the lytic cycle of a virus.

1. Attachment 2. Penetration 3. Injection 4. Biosynthesis 5. Maturation 6. Release

Obligate aerobes

1. Obligate aerobes need oxygen because they cannot ferment or respire anaerobically. They gather at the top of the tube where the oxygen concentration is highest.

What are two possibilities if a nitrate broth does not turn red after adding dimethyl-alpha-naphthylamine and sulfanilic acid?

1. the mircoorganism is unable to use nitrate as a final electron acceptor in it's energy metabolism and nitrate in the broth is still present after incubation. 2. the microorganism was able to reduce the nitrate to nitrite and further reduced the nitrite to ammonia or nitrogen gas. Therefore after incubation the nitrate is not present in the broth

Obligate anaerobes

2. Obligate anaerobes are poisoned by oxygen, so they gather at the bottom of the tube where the oxygen concentration is lowest.

what is the catalase reaction?

2H2O2 ------------>2H2O + O2 Hydrogen Perox catalase water oxygen

Facultative anaerobes

3. Facultative anaerobes can grow with or without oxygen because they can metabolise energy aerobically or anaerobically. They gather mostly at the top because aerobic respiration generates more ATP than either fermentation or anaerobic respiration.

Microaerophiles

4. Microaerophiles need oxygen because they cannot ferment or respire anaerobically. However, they are poisoned by high concentrations of oxygen. They gather in the upper part of the test tube but not the very top.

Aerotolerant organisms

5. Aerotolerant organisms do not require oxygen as they metabolise energy anaerobically. Unlike obligate anaerobes however, they are not poisoned by oxygen. They can be found evenly spread throughout the test tube.

If no starch is present in the plate after incubation, what will you see after applying Gram's iodine?

A clear area around the growth of the microorganism

What are proglottids?

A long chain of segments produced by the head of a tapeworm

What is a reservoir of infection?

A physical site such as soil or an animal where viable infectious agents remain alive and from which infection of individuals may occur

What is a pandemic?

A world wide distributed epidemic

Define and give an example of each of the following Carbohydrate: Monosaccharide: Disacchardie: Polysaccharide:

Carbohydrate: Organic compounds utilized by microorganism as an energy source and a source of carbon Monosaccharide: Glucose Disacchardie: Sucrose Polysaccharide: Starch

What are antiseptics and disinfectants?

Chemical agents used to control the growth of microorganisms under different conditions.

why is it not possible to test for ammonia as evidence of nitrate reduction to ammonia in the nitrate broth culture?

If the organism was able to reduce the nitrate to nitrite and further reduced the nitrite to ammonia or nitrogen gas; the nitrate will no longer be present in the broth.

What is the ecological advantage of having the enzyme amylase?

In order to utilize starch, a microorganism must be able to produce the enzyme amylase and secrete it extracellularly. When amylase is excreted by organism, amylase is able to hydrolyze the starch molecule to smaller units that can pass through the cell membrane.

Where is hookworm disease usually found?

In the southern US

What is the product produced by a microorganism when it catabolizes tryptophan?

Indole. Trytophan----------->Indole+Pyruvic acid+Ammonia tryptophanase

What are nosocomial infections?

Infections acquired in the hospital

Where do flukes reside in the host?

Intestine, liver, blood, or lung

Where do the eggs of flukes eventually work their way into after being deposited into the host tissue?

Into the feces or bladder

What is the relevance of bromthymol blue pH indicator in the Simmons agar?

It is green at a neutral pH and blue in an alkaline environment such as when citrate is metabolized. An excess of ammonia ions are produced which causes the pH of the medium to increase into the alkaline range

why is gelatin not used as a solidifying agent in the microbiology lab?

because it melts at low temperature

what is the color of a positive test for H2S production?

black

What does the H2S test use as an agent to determine if a bacteria is positive or negative for the production of H2S? What is the reaction?

iron sulfate. If the test is positive, a black precipitate will be formed (FeS

What is special about each proglottid?

it is monoecious and will break off the terminal end as they reach maturity and shed in the feces

What does Escherichia coli produce when it ferments glucose?

lots of acid to the point where pH is losered to 4.5 and growth stops

What do antiseptics control the growth of?

microorganisms on living surfaces

what type of microorganisms have the enzyme oxidase?

microorganisms which have type c cytochromes in their electron transport chain

All members of the family Enterobacteriaceae, which includes Escherichia coli are oxidase _______________

negative

How does Salmonella test for Urea hydrolysis?

negative

What enzyme catalyzes the reaction of using nitrate as the final electron acceptor in their anaerobic respiration as an alternative to oxygen?

nitrate reductase

What is nitrate reduced to when catalyzed by nitrate reductase?

nitrite (NO2-). And in some microorganisms nitrite is further reduced to either nitrigen gas (N2) or ammonia (NH3).

Gama hemolysis

no hemolysis which produces no change in the area around the colonial growth

is blood agar a selective medium? why?

no, because blood agar inhibits the growth of various microbes at a time

synthetic or chemically defined medium

one whose exact chemical composition is known

Many microorganisms are able to use nitrate (NO3-)as the final electron acceptor in their anaerobic respiration as an alternative to ______________.

oxygen.

How does Proteus test for Urea hydrolysis?

positive

Neisseria gonorrhoea (causative agent of gonorrhea) is oxidase __________________

positive

In a positive urea hydrolysis result, what makes the medium alkaline?

The accumulation of ammonia which reacts with water to form ammonium hydroxide

what factors influence the gram reaction?

The chemical makeup of their cell walls

What will you observe in a positive coagulase test?

The clumping of bacterial cells

What happens if an organism in the Simmons agar can transport citrate into the cell?

The culture will grow and turn the medium from green to blue due to the presence of bromthymol blue pH indicator.

Where do tapeworms attach to their hosts?

The intestinal wall

What ingredients in the MSA media enable them to be selective? Differential?

The naCl makes the media selective. The presence of mannitol and pH indicator phenol red makes the media differential.

What is epidemiology?

The study of the occurence, distribution, and control of infectious disease in populations

what is the purpose of the indicator used in the thioglycollate broth and the Brewer anaerobe jar?

The thioglycollate broth allows indication of the oxygen requirement of the microorganism. The ox/red indicator in the Brewer anaerobe jar is resazurin which is pink when oxidized and colorless when the oxygen is removed from the jar.

How do tapeworms get their nutrients?

They absorb nutrients through their cuticle (skin), they can not ingest, because they have no digestive system

What is the platyhelminthes further grouped into?

Two classes, Trematoda (flukes) and the Cestoda (tapeworms

urea hydrolysis reaction

Urea + H20 -------------> 2NH3 + CO2 Urea Urease ammonia

What antiseptics and disenfectants usually effective against?

Vegetative cells, but not endospores

What are bacteriophage?

Viruses that infect bacteria

Define epidemic.

When a disease occurs in an unusually high number of individuals in a community at the same time

How is the anaerobic environment produced in the Brewer anaerobe jar?

When an anaerogen sachet is placed in a sealed jar, the oxygen in the jar is rapidly absorbed with the simultaneous generation of carbon dioxide.

How does the generalized life cycle of a fluke begin?

With the egg of the parasite deposited in the tissues of the intestinal wall, bladder, or other site of the host

what is gelatin? what does it break down to and what enzyme catalyzes gelatin?

a protein. breaks down to amino acids. Catalyzed by gelatinase

what does Entereobacter produce when if ferments glucose?

acetoin and growth never stops until all medium is used

What happens in a positive urea hydrolysis test?

after incubation the medium will be deep red if positive. Red color is the result of the pH indicator, Phenol red, turing red in an alkaline environment (pH 8.1)

what are the most prominent organisms in the human throat?

alpha hemolytic streptococci

what opportunistic pathogen exists in the throat as normal flora?

alpha hemolytic streptococcus pneumonia and Candida albicans

What are some examples of antiseptics?

Alcohol, iodine, and bactine

What do some flukes require in order to complete their life cycle?

An additional host, like an aquatic snail or clam

Exoenzyme

An enzyme generated by a cell that functions outside of the cell

What is coagulase?

An enzyme that coagulates (clots) the fibrin in some bloods and aids S. aureas in its ability to cause disease

Endoenzyme

An enzyme that functions within the cell in which it was generated

What is the miracidium?

An intermidiate stage of larve, that takes place after the eggs hatch in water

What helps inhibit bacterial growth on the skin?

Anitmicrobial substances such as sebum, secreted by oil glands

Why is EMB agar less effective than MAC agar in inhibiting the growth of Gram positive bacteria?

Because crystal violet in the MAC agar is so potent. We keep EMB agar because of the green sheen produced E. Coli, making it easier to identify.

Why can the number of bacteriophage (plaque forming units) present per ml of the original suspension be calculated?

Because each plaque is the result of the replication of a single bacteriophage

If the MR indicator is added first, it is possible to perform both tests in the same tube. Why?

Because if the MR indicator is added first, it will turn red in color (pH 4.5 or lower) identifying as Escherichia. Or it will appear yellow in color (pH 6.0 or higher) identifying as Enterobacter.

In the citrate utilization test, why must the test medium be chemically defined?

Because in order to determine if an organism can metabolize citrate, citrate must be the only carbon source present in test medium

Why would an organism be resistant to antimicrobial agents?

Because in the hospital environment, they are frequently exposed to a variety of antimicrobial agents

Why are the plates with 30-300 plaques the only plates counted?

Because less than 30 is too few, there could be anomolies, and 300 is too much because you may have more than 1 viral particle per plaque, the plate is too crowded

Why are only certain organisms able to colonize on the skin?

Because of high salt concentration due to perspiration, and the very dry environment

Why is it important to incubate cultures at least 48 hours if not longer when testing for the presence of acetoin?

Because the conversion of acid products to acetoin doesn't take place until the 48 hour mark.

Why is phenol red such an excellent pH indicator for the fermentation of glucose/lactose?

Because the pH indicator phenol red is red at neutral pH but turns yellow at pH < 6.8 and a magenta hot pink at pH > 8.4

Why is the sterile mineral oil added to some cupules in the API 20E test strip?

Because the reaction requires an anaerobic environment.

What type of flukes are dioecious, and what does this mean?

Blood flukes, they have separate male and female animals

How does transmission take place of the human schitosomes?

By contact with water containing human waste and aquatic snails

How is trichinosis usually acquired?

By eating undercooked pork or bear meat containing larvae

How is the Clonorchis sinensis (Chinese liver fluke) diagnosed?

By finding eggs in feces

Describe how a viral plaque is formed in a bacterial lawn.

By going through the lytic cycle

How is the presence of a virus determined in a viruses bacteriophage assay?

By the presence of plaques

What chemical compound is the source of the indole in the test for indole production?

amino acid tryptophan

What color is Kovac's reagent when it reacts with tryptophan?

Cherry red

What are some examples of disenfectants?

Chlorox and lysol

How are streptococci antigenically classified, and what are their classifications based on?

Classified into Lancefield groups A through O, based on the presence of certainantigens on their cell walls

Beta hemolysis

Complete hemolysis of the RBC's which produces a clear zone around the colonial growth

Which tapeworm is found widely in the US?

Diphyllobothrium latum (the fish tapeworm) and is found in bears, cats, dogs, man and other fish-eating animals

How can cercariae penetrate a vertebrae host?

Directly through the skin, and migrate via the bloodstream to the bloodvessels of the intestinal wall and liver where they develop into an adult animal

What are the products of protein hydrolysis?

amino acids

What does the color orange represent in the MR-VP test?

Enterobacter produce more neutral end (pH 5.1)

What are the two parts of human skin? Which is more superficial, more deep?

Epidermis is superficial to the dermis

What does the color red represent in the MR-VP test?

Escheria ferment glucose, produce more acids (4.5 pH)

microorganisms negative for oxidase reaction:

Escherichia coli, Klebsiella pneumonia

The citrate utilization test is used to distinguish between which two microorganisms?

Escherichia coli--CANNOT utilize citrate Enterobacter--CAN utilize citrate

word reaction that illustrates gelatin hydrolysis

Gelatin----------------->amino acids gelatinase

what sugar is likely to be fermented?

Glucose. Because it is the smallest monomer and does not need to be broken down prior to fermenting

How do you differentiate between gram + and gram - stain?

Gram + retains purple color Gram - decolorize and counter-stain pink

What Lancefield group is Streptococcus pyogenes assigned to, and what does it cause?

Group A, causitive agent of strep throat

What does the SIM Agar test for?

H2S production, indole production and motility

What is the scolex?

Head of tapeworms

What must happen for a pathogenic organism to continue to exist in nature?

It must be able to transmit from one host to another

How are cercariae created?

Large numbers of larvae, created by miracidium infecting aquatic snails

Where does pinworm reside in the host, and how does it spread?

Lives in the intestine, migrating to the anal area at night to lay eggs. During the night eggs can spread to bedding or night clothes spreading the worm.

What does skin act as a physical barrier to?

Microbial invasion of the body

What do disenfectants control the growth of?

Microorganisms on non-living surfaces

What are transient organisms? .

Microorganisms temporarily acquired from the environment, they are not permanent inhabitants of our skin

What type of animals are helminths?

Multicellular, eukaryotic

What are symptoms of trichinosis?

Muscle pain, difficulty breathing, diarrhea

Mannitol Salt Agar

Nutrient agar base Mannitol 7..5% NaCl Phenol red (pH indicator-yellow at 6.8 and lower and red at 8.4 and above)

Flukes are generally monoecious, what does this mean?

One animal is both male and female

What is an endemic disease?

One which is constantly present, usually low in incidence, in a population

What is miracisium infectious to?

Only a certain species of aquatic snails in which a complex series of generations occurs.

The high salt concentration in Mannitol Salt Agar makes it selective for:

Staphylococcus because they are able to grow in environments, like the surface of our skin, that have a high NaCl concentration. Conversely, it inhibits growth of gram negative bacteria because they are not able to grow in environments high in salt.

H2S test overview

Tests for bacteria that produces enzymes necessary to metabolize amino acids that contain sulfur like cytine, cysteine and methionine. They do this by producing H2S.

What are helminths?

Parasitic roundworms or flatworms

What are carriers?

People that are infected with the disease causing agent but show few or no symptoms

MAC agar

Peptone lactose bile salts NaCl agar neutral red dye crystal violet

EMB Agar ingredients

Peptone lactose sucrose dipotassium phosphate agar eosin methylene blue

How does Taenia solium (Pork tapeworm) infect pigs? How are humans infected?

Pigs are infected when eggs are ingested with food contaminated with human feces. Humans get infected when they eat raw or undercooked infected tissues of a pig.

What is the most common helminth infection caused by roundworms in the United States?

Pinworm (Enteriobius vermicularis)

What two phyla are helminths grouped into?

Platyhelminths (flatworms) and Nematoda (roundworms)

What is the name of the group of enzymes that catalyze protein hydrolysis?

Proteolytic enzymes

microorganisms positive for oxidase reaction:

Pseudomonas aeruginosa

what is the reaction that happens when an organism can use amylase for the hydrolysis of starch?

STARCH---------->MALTOSE----------->GLUCOSE amylase maltase

What ingredients in the MAC media enable them to be selective? Differential?

Selective: Dyes (crystal violet, neutral red) Differential: lactose dyes

What ingredients in the EMB media enable them to be selective? Differential?

Selective: eosin (methylene blue) Differential: lactose dyes

What organisms are selected / selected against for in EMB agar?

Selects for gram + Selects against gram -

What organisms are selected / selected against for in MAC agar?

Selects for gram - Selects against gram +

What organisms are selected / selected against for in MSA agar (green sheen)?

Selects for gram - Selects against gram +

What medium is used to test for motility?

Sim agar 0.3% (semi-solid)

what is the medium used in the citrate utilization test?

Simmons citrate agar, a chemically defined(synthetic) medium

Name 5 microoraganisms that can colonize on the skin.

Stahylococcus Micrococcus Propinobacterium acnes Corynebacterium yeast

Name two organisms that commonly cause nosocomial infections.

Staphylococcus aureas and Escherichia coli

What does a coagulase test help to distinguish?

Staphylococcus aureas from othere staph species

What is special about the eggs of flukes?

They have a hook which can cause damage to the intestinal wall or bladder which can result in bloody urine or blood in the fecal matter

what is the purpose of the citrate utilization test?

To determine if a microorganism produces a transport protein that enables them to carry citrate across their cell membrane and utilize it as a carbon and energy source.

what is the API 20E multiple test strip used for?

To identify an unknown member of the Enterobacteriaceae family and other gram negative rods

What is the purpose of the control plate in the Bacteriophage plaque assay lab?

To make sure that the E. coli is not already infected with the virus

What is the role of the nitrate in the broth in the metabolism of the organism giving a positive test for nitrate reduction?

To test the ability of the organism to reduce the nitrate to nitrite or further reduce it to ammonia or nitric oxide. [use nitrate as the final electron acceptor in their anaerobic respiration as an alternative to oxygen]

What type of medium are EMB and Mac Agar

both selective and differential. They inhibit growth of gram positive bacteria due to presence of dyes but gram negative bacteria are able to grow. They are differential because colonies of gram negative bacteria that can ferment lactose, which is present in the media, will be pink to red and those unable to ferment lactose will be colorless.

How is the presence of Indole detected in the Sim agar?

by adding Kovac's reagent.

How is the catalase test performed?

by placing a drop of 3% H2O2 on the inoculum and observing for the release of O2 bubbles. The release of O2 bubbles indicates a positive test

In the action of bacteria on simple carbohydrates, how is gas production shown?

by the formation of bubbles in the Durham tube

In the hydrolysis of starch experiment, how is the presence of extracellular amylase detected?

by using gram's iodine to form a blue/brown color complex where the starch is present

what is the color of a positive indole test?

cherry red

what must happen for the citrate utilization test to be positive?

citrate must be the only carbon source in the medium

what is a source of gelatin?

collagen, a component of connective tissue and tendons of animals

Define complex medium

culture medium made up of nutrients including extracts from yeasts, meat or plants, or digests of these proteins.

The presence of nitrites in a broth can be detected by adding________________.

dimethyl-alpha-naphthylamine and sulfanilic acid. Red is positive for the presence of nitrities.

Purpose of the gram stain

dividie bacteria into two groups: gram positive and gram negative

what type of environment do complex medias serve for microorganisms?

energy, carbon, nitrogen, and sulfur requirements of growing microorganisms are provided by proteins.

What are the end products of starch hydrolysis?

glucose

What is Proteus sp.?

gram negative rod that is normal flora in human intestines

what is Salmonella sp.?

gram negative rod which is an intestinal pathogen in humans

Alpha hemolysis

incomplete hemolysis which produces a green cloudy zone around the colonial growth

In the action of bacteria on simple carbohydrates, microorganisms UNABLE to ferment glucose or lactose will show a

red (alkaline) reaction

In what age group is pinworm usually found?

school age children K-3

bacteriophage parts

see lab book

why is it important not to shake the thioglycollate broth?

shaking can disturb the growth pattern of the bacteria and alter results

What ingredients present in blood agar make it a differential medium?

sheep red blood cells

The catalase reaction is used to distinguish between the two genera:

staphyloccocus and streptococcus or Bacillus and Clostridium Staphyloccocus and Bacillus are catalase positive. Streptococcus and Clostridium are catalase negative.

List four organisms found as normal microbiota (flora) in the human respiratory tract

staphylococcus, streptococcus, Neisseria, Hemophilus, yeast

micoorganisms positive for catalase:

staphylococus aureus Klebsiella pneumonia

microorganisms negative for catalase:

streptococcus viridans

what chemical compunds are the source for H2S in the test for H2S production?

sulfur-containing amino acids

If gelatinase is produce by the bacteria what will happen?

the gelatin will be liquified

If gelatinase is NOT produced by the bacteria what will happen?

the gelatin will remain solid

What makes Mannitol Salt Agar differential?

the presence of mannitol and the pH indicator phenol red make this medium differential. Staphylococcus aureus is able to grow on this medium and ferment mannitol. When it ferments mannitol, acid bi-products are formed and the pH indicator penol red will be yellow (halo) Staphylococcus epidermidis can grow in this medium but it cannot ferment mannitol. So staph. epidermidis will NOT have a yellow halo around the growth

what indicates a positive test for catalase?

the release of O2 bubbles after placing a drop of H2O2 on the inoculum

In the action of bacteria on simple carbohydrates, what causes the alkaline reaction?

the utilization of beef extract and peptone as the carbon source for the microorganisms

what are Salmonella and Proteus easily confused?

they are both non-lactose fermenters

how does the normal flora of the throat prevent more serious organisms from establishing themselves?

they outcompete for nutrients and space, or create conditions that inhibit growth

What is the Urea Hydrolysis test use for clincially?

to differentiate between two bacterial genera, Salmonella sp. and Proteus sp.

What is the purpose of the Gelatin Hydrolysis test?

to test bacteria for the ability to produce proteolytic enzymes

How is the oxidase test perfomred?

using an applicator stick place inoculumon the oxidase reagent strip. Observe for a change in color to deep purple. Change in color to deep purple = positive test for oxidase

why is it important for some bacteria to produce the enzyme catalase?

when electrons are transferred to oxygen in aerobic respiration in the electron transport chain, H2O2 can be formed which is lethal to the cell. most microorganisms have the enzyme catalase which breaks down hydrogen peroxide to water. 2H2O2 ---->2H2O + O2

In the action of bacteria on simple carbohydrates, microorganisms fermenting glucose or lactose will show a

yellow (acid) reaction

If the nitrate broth does not turn red after the addition of dimethyl-alpha-naphthylamine and sulfanilic acid, resulting in a negative test, what can be added to the broth to determine which of two possiblities occured?

zinc dust. If the nitrate has been reduced to N2 or NH3, no red color will form after the addition of the zinc dust because there is no nitrate present in the broth to be reduced. If the microorganism was not able to reduce titrate to nitrite, the nitrate will still be present in the broth. The zinc dust will reduce the nitrate to nitrite and because the dimethyl -alpha-naphthylamine and sulfanilic acid reagent are in the tube, a red color will develop.