Microbiology Week Fifteen

Enterotoxigenic E Coli (ETEC)

Major cause of traveler's diarrhea and infant diarrhea in developing countries, both are watery diarrheas. Non-invasive (stays outside cell) and causes severe diarrhea due to heat-labile toxin and heat-stable toxin (which enter small intestines)- stimulate secretion and fluid loss. Transmitted in developing countries through poor sanitation and use of human feces as fertilizer on food crops.

Norovirus

A highly contagious naked, RNA virus that is thought to be the cause of almost 90% of all viral gastroenteritis infections. It is the most common cause of food-borne illness in the United States, sickening nearly 21 million people each year. Norovirus is transmitted by coming in contact with an infected person, consuming contaminated food or water, or by coming in contact with contaminated surfaces. The virus causes inflammation in your stomach and/or small intestine, leading to stomach pain, nausea, diarrhea, and vomiting. Symptoms usually appear within 12 to 48 hours of exposure and patients recover within 1 to 3 days. Norovirus is easily transmitted in crowded situations, such as schools, cruise ships, nursing homes, or restaurants, and is not restricted to particular age groups. i.e. stomach bug. Can spread even after your symptoms go away. Can avoid it by bleaching items, cleaning shellfish. #1 cause of diarrhea in kids. Because the Norovirus is so contagious, it commonly crops up as an epidemic in people that are in close contact with one another like school children.

Rotavirus

A naked, RNA virus that is most common in infants and young children, and is the leading cause of severe diarrhea in these age groups. Older children and adults can be infected with rotavirus, but they will typically exhibit milder symptoms. Symptoms appear approximately 2 days after exposure to infected individuals or contaminated surfaces and include severe watery diarrhea, vomiting, fever, and abdominal pain. Rotavirus is a very serious illness and is responsible for the deaths of over 500,000 infants and children each year, worldwide. The CDC recommends an oral vaccine be given to infants in the US. Almost every child has by age 5, but breastfeeding helps. No way to treat, just need to hydrate. Avoid infection by vaccination.

Giardia Intestinalis

A protist in the supergroup Excavata, more specifically the Diplomonads. Many Diplomonads are parasites, thrive in oxygen poor environments, and are symmetrical - with two equal-sized nuclei and four flagella on each side. This symmetry can be seen in the image above of Giardia, the two dark circles are the nuclei of the cell. Giardiasis is the most common intestinal parasite found in the United States, although the majority of infections are asymptomatic. Human infection is often seen in campers and hikers who drink water from rivers and streams without proper filtering or boiling the contaminated water. Symptoms such as loss of appetite, diarrhea, stomach cramps and upset, projectile vomiting, excessive gas, and lactose intolerance, can arise within one to three weeks of exposure to contaminated water. The symptom of lactose intolerance is typically temporary, but can become permanent. Cysts are shed in the fecal matter of infected vertebrates, which can survive in cold water for up to three months. Diagnosis is achieved through examination of the patient's stool for trophozoites (pictured above) and cysts.

Enterohemorrhagic E Coli (EHEC)

Also called STEC (shiga toxin-producing E coli) and VTEC (verotoxic E coli). Non-invasive but causes attaching and effacing lesions, similar to EPEC but this one is only in the LARGE INTESTINE (i.e. colon). Produces a hemorrhagic toxin called shiva-like toxin or verotoxin, which nicks the colon cells' 60S ribosomes, shutting down eukaryotic protein synthesis. Includes O157:H7 and O104:H4 which are found in food or water contaminated by catal feces (mainly hamburger), sometimes through sewage contaminating water. Person to person transmission also occurs. Less than 100 cells needed for infection. Shiga-like toxin can also enter the bloodstream and travel to the kidney, whose cells are particularly vulnerable to the toxin. Disease may progress to hemolytic uremic syndrome (HUS) and acute renal failure, can cause many complications and should be treated quickly.

Enteroinvasive E Coli (EIEC)

Invades intestinal wall and causes inflammatory disease of the large intestine leading to bloody diarrhea and pus. virulence due to invasion of intestinal epithelium (via invasion proteins). Transmission may be associated with contaminated food.

Protistan Infections That Can Cause Diarrhea

These protistan infections that can also impact the GI tract. These protists are from different supergroups, but share the distinction of causing diarrhea and the most common route of infection is via fecally-contaminated water. Cryptosporidium spp. Entamoeba histolytica Giardia intestinalis

Gram - Vibrios causing Acute Diarrhea

Vibrio cholera Vibrio parahaemolyticus andVibrio vulnificus Vibrio pathogens are salt-tolerant inhabitants of coastal waters, associate with marine invertebrates (warmer waters of the atlantic). Campylobacter jejuni Helicobacter pylori (close relative to campylobacter)

Entamoeba Histolytica

An Amoebozoan, a protistan supergroup we first learned about when discussing amoebic encephalitis. Amebiasis symptoms include loose stool, abdominal pain, weight loss, and fatigue, but only 10 to 20% of infected individuals will display these symptoms. Amebic dysentery is the term given to severe E. histolytica infections, with the added symptoms of bloody diarrhea and fever. Symptoms typically take one to two weeks to arise, although there has been cases of symptoms taking longer to develop. Diagnosis is achieved through microscopical analysis of stool samples. During diagnosis, it is important not to confuse E. histolytica with another amoeba, Entamoeba coli which is a non-pathogenic amoeba that may be found in the human GI tract. To distinguish the two, the E. histolyticatrophozoite often presents with ingested human red blood cells. Cysts released in the feces of infected vertebrates can persist in soil or water for weeks up to several months.

Cryptosporidium Spp.

An Apicomplexan, a protistan group of animal parasites we first encountered when learning about malaria. The most common way to be infected with cryptosporidiosis is through the consumption of water contaminated with Cryptosporidium spp. cysts. The cysts enter the water when fecal matter from infected vertebrates is introduced, and they can last for several days to weeks in the water. Common sources of human outbreaks are in water parks or municipal water systems. Cryptosporidium is resistant to chlorine and oftentimes swimming pools have to be shut down and drained when fecally-contaminated. Symptoms arise within 2 to 10 days of consuming the contaminated water, and can last for a week or more. The illness is most severe for immuno-compromised patients, and healthy patients may not experience any symptoms. The primary symptom is watery diarrhea, but other symptoms include stomach pain, nausea, vomiting, fever, weight loss, and dehydration. Proper diagnosis is made by examining the patient's stool. The stool can be examined for cysts via microscopy using an acid fast stain, or it can be checked for Cryptosporidium anitgens via ELISA.

Bacillus Cereus Exotoxins

Bacillus cereus is an endospore-forming gram-positive bacilli that is a common soil microbe that can be an airborne and dust-borne contaminant. As a result, it is a common resident on vegetables and food products in close contact with soil. B. cereus multiplies very readily in cooked foods, most notably fried rice. In fact, oubreaks of food poisoning from this bacterium are often associated with Chinese restaurants. Other foods implicated with B. cereus are cooked potatoes and meat and vegetable dishes. Bacillus cereus spores and toxins survive short periods of cooking and reheating; when the food is stored at room temperature, the spores germinate and release exotoxins. B. cereus produces two exotoxins, one of which causes an emetic (or vomiting) disease, the other causes a diarrheal-type disease. The emetic form of the disease is the most frequently linked to fried rice and food intoxication results from ingestion of a heat-stable exotoxin that causes acute vomiting, usually within 1-4 hours post-ingestion. The diarrheal form of the disease is associated with cooked meats or vegetables that are held at warm temperatures for long periods of times. These conditions cause B. cereus to produce a heat-labile (or heat-sensitive) exotoxin that causes watery, profuse diarrhea, nausea, and abdominal cramps. The symptoms generally disappear in 24 hours with no lasting effects or required treatments.

Escherichia coli

Best known fecal coliform and most abundant intestinal facultative anaerobe. Most species are nonpathogenic and motile. Causes an opportunistic infection when it enters the urethra and is the most common cause of urinary tract infections (UTIs). Some strains are pathogens with differing virulence factors and effects. True pathogenic strains are all spread via fecal-oral route, from poor sanitation and fecal contamination; enterotoxigenic E coli, enteroinvasive E coli, enteropathogenic E coli, and enterohemorrhagic E coli.

Clostridium Difficile

Can cause pseudomembranous colitis (also called antibiotic-associated colitis) after antibiotic therapy kills the competing microflora of the gut. Gram + spore-formign anaerobic bacillus. Normal resident fo colon, in low numbers. Treatment with antibiotics eliminates C. difficile's competition and it can cause pseudomembranous colitis (antibiotic-associated colitis) when it grows unchecked. Spread via fecal-oral route, organism is infested either as the vegetative form or as hardy spores, which can survive for long periods in the environment and can traverse the acidic stomach. In small intestine, spores germinate into vegetative form. In large intestine, C. difficile-associated disease can arise if the normal flora has been disrupted by antibiotic therapy. C. difficile reproduces in the intestinal crypts, releasing toxins A and B causing severe inflammation, mucous and cellular debris are expelled, leading to formation of pseudomembranes. Toxin A attracts neutrophils and monocytes, and toxin B degrades the colonic epithelial cells, both leading to colitis, pseudomembrane formation, and watery diarrhea. Produces entertoxins that damage the intestine and can cause the "pseudomembrane" development. Major symptom is severe diarrhea with cramps and possible fever. Colon perforation and death are possible. Highest risk patients are those on broad spectrum antibiotics for an extended time period (nursing home patients #1). Treatment by removing the antibiotics in weak cases, using a strong antibiotic targeted to anaerobes is possible, probiotics and even fecal transplantation to restore normal flora.

Campylobacter jejuni

Causes bacterial gastroenteritis. Transmitted by food (raw poultry and unpasteurized dairy). Adheres to intestine, burrows through the mucus and multiplies, secretes C. jujuni enterotoxin which causes watery/bloody diarrhea, headache, fever, abdominal pain, and possible vomiting. Usually self limiting within a week. Often undiagnosed and untreated, possibly most common food infection, cross contamination with just one drop of raw chicken juice is so common. Very rare to have complications, if there are any, it's a high risk group and antibiotics and rehydration therapy can help fix.

Enteropathogenic E Coli (EPEC)

Causes chronic diarrhea and infantile diarrhea in developing countries (though rotavirus is more common). Attachment and subsequent injections of proteins directly into small intestine epithelia leads to small intestine microvilli damage and surface effacement, causing watery diarrhea.

Listeria Monocytogenes

Causes listeriosis upon ingestion of contaminated foods which starts with diarrhea and can progress to septicemia and meningitis by entering lymph then bloodstream, particularly in high risk groups like pregnant women, immunocompromised adults and the elderly. Non-spore-forming, gram + bacillus. Resistant to cold, heat, salt, pH extremes, and bile. Primary reservoir is soil and water, contaminates produce and dairy products. Variety in bacillus structure. Results in food poisoning particularly after refrigeration of unpasteurized dairy products, poultry and prepared foods. Outbreaks have been traced to contaminated foods such as produce, deli meats, soft cheeses, and other dairy products. Individual cases arise from the organism growing in the fridge. Treat with antibiotics. High risk groups need careful monitoring because complications and death are possible.

Vibrio Cholera

Causes the disease cholera resulting in rice-water stools when the bacteria is ingested in contaminated water or from fecal contamination from infected people. Comma-shaped bacterium that causes cholera. In some humid environments and infected people are the reservoirs. Ingested with food or water or contact with feces of someone suffering from cholera. Attaches to intestinal cells. Infects surface of small intestine, noninvasive. Cholera toxin causes electrolyte and water loss through secretory diarrhea, resulting dehydration leads to muscle, circulatory, and neurological symptoms. Can lose as much as one liter of fluid per hour, many patients die from dehydration. Rice water stools, bits of intestinal mucosa coming off with diarrhea.

Adenovirus Serotypes 40-42

Classified as the enteric adenoviruses because they primarily infect the gastrointestinal tract. Infection by these serotypes can be attributed to 5-20% of hospitalizations for childhood diarrhea worldwide, but they can infect any age group. Adenoviruses 40-42 are the only DNA viruses that cause viral gastroenteritis. Symptoms last 7 to 8 days and include diarrhea, vomiting, and fever. Transmission is thought to be contact with contaminated food, water, or surfaces.

Gram + Bacilli causing Acute Diarrhea

Clostridium difficile Listeria monocytogenes

Clostridium Perfringens Exotoxin

Clostridium perfringens as being the causative agent of gas gangrene, but the endospores of this gram positive bacillus can also contaminate many kinds of foods. The foods most likely to cause food intoxication from this organism are meat dishes, stews and gravies that are improperly reheated. When these foods are cooled, kept only warm for long periods of time, or left unrefrigerated, spores can germinate and the cells begin to multiply. If the food is eaten without adequate reheating, C. perfringens enters the small intestines and releases exotoxin. The C. perfringens exotoxin is an enterotoxin that acts upon the epithelial cells of the small intestines, causing watery diarrhea, nausea (usually without vomiting), and severe abdominal cramping and pain. Symptoms begins to arrive in 8 to 16 hours post-ingestion of contaminated food. The recovery is rapid and no treatment is required as deaths are extremely rare.

The Enterics: Gram Negative Bacilli causing Acute Diarrhea

Enterobacteriaceae family. All small, gram - rods. Facultative anaerobes. Ferment glucose, reduce nitrates to nitrites, oxidase negative, and catalase positive. Many inhabit soil and water and some are common occupants of the large intestine. Enteric pathogens are most frequent cause of diarrheal illnesses through action of enterotoxins. Divided into fecal coliforms (lactose fermenters and non-coliforms (non-lactose fermenters). MacConkey Agar is selective (only gram -) and differential (lactose fermenting or not) media for distinguishing between lactose and nonlactose fermenting Enterobacteriaceae. Classified by 2 surface antigens; O - cell wall antigen, H - flagella antigen, and K - capsule/fimbrial antigen. Virulence factors; fimbriae (for adherence), endotoxin (LPS), exotoxins (mostly enterotoxins causing gastroenteritis. Escherichia coli (coliform) Salmonella (non-coliform) Shigella (non-coliform)

Bacterial Infections with Acute Diarrhea and Vomitting

Food poisoning, also called foodborne illness, refers to symptoms in the gastrointestinal tract that are caused by a preformed exotoxin produced by a pathogen. Symptoms include severe nausea, frequent vomiting accompanied by diarrhea, and abdominal cramping. Three bacteria in particular cause acute diarrhea and vomiting. By acute we mean symptoms present within one to a few hours post-ingestion of the contaminated food. These bacteria include: Staphylococcus aureus Bacillus cereus Clostridium perfringens

Vibrio Vulnificus

Gastroenteritis from raw oysters, cutting yourself opening up an oyster. If it gets into the skin, can cause a necrotizing fasciitis. Watery diarrhea.

Vibrio Parahaemolyticus

Gastroenteritis from raw seafood. Watery diarrhea.

Salmonella

Non-coliform member. Highly motile, encapsulated organisms. Over 1700 serotypes. Of all serotypes, salmonella typhi is unique in having no nonhuman animal reservoirs, only human to human. Produces hydrogen sulfide, H2S (how it is differentiated from shigella). Salmonella Typhi is the most serious pathogen, etiological agent of typhoid fever, humans are only host and reservoir. Fecal-oral transmission. Some people are permanent carriers, i.e. Typhoid Mary, a cook who infected 51 people, 3 died. Infections are uncommon in developed countries (about 500 cases yearly in the USA), versus underdeveloped world (17 million cases/year with 600,000 deaths). Feces-contaminated food or water is ingested and motile bacilli attaches to intestinal cells. Gradual onset of headache, loss of appetite, lethargy, fever, abdominal pain, followed by few short bouts of diarrhea after second week. Disease varies from prolonged, mild, self-resolving fever, but can lead to perforations in small intestine leading to death. Salmonella enteritidis has about 1700 serotypes (including S. typhimurium). Normal animal intestinal flora (cows, chickens, rodents, reptiles). Transmission mainly from raw poultry or eggs, reptilian pets, or raw milk. One of the leading causes of gastroenteritis and acute diarrhea. Bacteria is ingested and they invade small intestine epithelial cells. Usually self-limiting in the healthy, causing fever and an inflammatory but watery diarrhea with abdominal pain, nausea, and vomiting.

Shigella

Non-motile gram - rods. Do not produce H2S. Etiological agent of bactillary dysentery, a disease marked by crippling abdominal cramps and frequent diarrhea with mucus and blood. Important species are S. dysenteriae (severest form), S. boydii and both S. sonnei and S. flexneri (found in US) Only found in human and ape gastrointestinal tract. Transmission through fecal-oral spread. Feces-contaminted food or water is ingested and the non-motile shigella is phagocytosed into the large intestines where they survive in the phagosome and multiply. They are invasive and spread to adjacent cells and stimulate an inflammatory immune response that causes extensive tissue destruction. Also release endotoxin and exotoxin (shiga toxin). Shiga toxin cleaves the 60S ribosome, inhibiting protein synthesis. Shigellosis symptoms vary widely, depending on the patient's nutritional status and age, the infective strain, and dose.

Urinary Tract Infections

One of the most common bacterial infections in humans. By the age of 30, at least 20% of all women have experienced an episode of UTI, and over 50% have one or more lifetime UTIs. The greater frequency of UTI in women is attributable to a shorter urethra compared to males, and a closer proximity of the urethra to the anus, where fecal material harboring enteric bacteria can contaminate the urethral opening. A shorter urethra makes it more likely that bacteria can quickly make its way to the bladder, resulting in a urinary tract infection. A lower urinary tract infection is an infection or the urethra, bladder, or both. Bladder infection leads to burning sensation, pressure, frequent urination, and unpleasant smelling urine that may have blood; most common cause is bacteria. Colds can't cause bladder infections. Antibiotics can help speed up getting better. To prevent infections, drink 2 liters daily, urinate frequently, and don't resist the urge to go to bathroom, always completely empty all urine, and urinate after sex. Causes are not enough fluid intake, sexual intercourse, bad hygiene, bladder or kidney stones, pregnancy, menopause, diabetes mellitus, a catheter, birth defects, and chemicals. Urinary tract infections usually occur when normal flora in the gastrointestinal tract ascend up the urethra into the bladder. Normally, the flushing action of urine helps to keep infections at bay but if urine flow is reduced or bacteria are introduced into the bladder, a bladder infection (known as cystitis) can occur. If the infection then spreads to the kidneys it is called pyelonephritis. Signs and symptoms of cystitis include burning pain upon urination (dysuria), frequent urges to urinate even when the bladder is empty, pain in the pubic area, fever and nausea. Cloudy urine is indicative of the presence of bacteria and white blood cells, and an orange or red tinge from the presence of red blood cells (hematuria) may be found in the urine. If back pain is present, this is a sign that the kidneys are now involved in the infection (pyelonephritis). The main causes of bacterial UTIs (which combined account for 95% of all cystitis and pyelonephritis cases) are the following opportunistic normal flora: Escherichia coli - Escherichia coli (a gram negative bacillus) is by far the most common cause of urinary tract infection, accounting for 80-85% of acute cystitis. The species of E. coli that cause UTIs are different from those that cause diarrhea and are known as UPEC - Uropathogenic E. coli. UPEC strains do exist as normal flora in the GI tract and they have a variety of virulence factors that facilitates their infection in the urinary tract. These include: 1) numerous fimbriae with adhesins that specifically attach to the epithelial cells lining the urinary tract, and 2) motility that is adapted to allow UPEC to ascend the urinary system quickly. Other factors promoting UTI with E. coli include sexual intercourse and urinary catheters, the latter accounting for UTIs being the most common of nosocomial infections. Staphylococcus saprophyticus - Staphylococcus saprophyticus is an opportunistic gram positive staphylococci that is responsible for 5-15% of acute cystitis. S. saprophyticus can be a resident of the skin, gastrointestinal tract, and vagina. UTIs caused by this organism is found almost exclusively in sexually active young woman and is the second most common cause of urinary infections in this age group. Cultures of S. saprophyticus can be differentiated from Staphylococcus aureus because they lack Coagulase (thus referred to as Coagulase-negative staphylococci) and S. saprophyticusis Novobiocin resistant, unlike S. aureus which is sensitive to Novobiocin. Proteus mirabilis - Proteus mirabilis is a gram (-) bacillus and an opportunistic non-coliform enteric that can also cause urinary infection. P. mirabilis is of particular importance because it can lead to the formation of kidney stones in patients through its production of urease. Urease is an enzyme that catalyzes urea (a major solute in urine) into CO2 and ammonia. Proteus can grow well in urine and its urease activity causes an increase in ammonia which in turn increases the urine pH (alkaline). Ammonia and the alkaline environment are factors in the formation of kidney stones. Has fimbriae for attachment to epithelial cells of the urinary tract and is highly motile, especially when hyperflagellated. P. mirabilis can swarm on the surface of moist agar and create distinguishing concentric rings which can be used for laboratory identification. Proteus can also be identified by testing positive for urease and H2S(hydrogen sulfide) production. All UTIs are treated with antibiotics and prevention comes by way of basic practices such as emptying the bladder frequently and (especially for females) wiping from front to back after a bowel movement. Scientific studies have found that components in cranberry juice discourage attachment of UPEC to the urinary tract, hence drinking cranberry juice is encouraged for people who are predisposed to UTIs. Another bacterium that we are including in this UTI section is Leptospira interrogans, a spirochete with very tight coils and characteristic hooked ends. An infection with this organism is known as Leptospirosis. Leptospirosis is a zoonotic infection (primarily an animal disease accidentally transmitted to humans) that is transmitted to humans via contact with contaminated animal urine. L. interrogans can affect the kidneys, along with the liver, brain, and eyes. In infected domesticated or wild animals, Leptospira interrogans invades and grows inside the kidney. Animals shed the spirochete in their urine and contaminate water (rivers, streams, swimming pools). Once in the water, humans can come in contact with Leptospira interrogans through broken skin or the mucous membranes. Leptospirosis is an occupational hazard of sewer workers, rice farmers, slaughterhouse workers, veterinarians, dairy farmers and military personnel. There has even been a case of athletes competing in the swimming phase of a triathlon contracting leptospirosis from the water. The incidence of Leptospirosis increases in times of natural disasters like hurricanes and floods where humans and animals are wading in water. Leptospirosis has two phases: 1) an early phase where L. interrogans can be found in the blood and CSF. Symptoms include fever, headache, muscle aches, conjunctivitis and vomiting; 2) the immune phase which causes meningitis, and Weil's Syndrome, a condition characterized by kidney invasion, liver disease, jaundice, anemia, and neurological disturbances. Death can result if left untreated due to severe kidney and liver damage. Leptospirosis can be treated with antibiotics, the sooner the better. Prevention includes a vaccine only made available for military personnel who train in jungle regions and animal care and livestock workers. For the general population, the best prevention is wearing protective clothing and avoid swimming and wading in natural water sources that are frequented by livestock.

Staphylococcus aureus Enterotoxin

Staphylococcus aureus is responsible for numerous infections throughout the human body. S. aureus is also one of the most common causes of acute food poisoning, especially from eating foods that are rich in carbohydrates such as custards, cream pastries, and especially potato salad. It is also associated with processed meats, chicken salad, and ham (recall that Staphylococcus are halotolerant). Staph food poisoning is caused by release of an enterotoxin. Enterotoxins are a type of exotoxin that act upon the gastrointestinal tract of humans which induce nausea, vomiting, and diarrhea. The illness does not require the actual bacteria to be present or alive in the contaminated food as the toxin alone is sufficient for causing symptoms. If the bacterium is allowed to multiply in the food, it produces its toxin. Even if the bacteria are subsequently destroyed by heating or reheating, the preformed toxin will act quickly once it is ingested. The Staph enterotoxin is heat-stable; inactivation requires 100 degrees C for at least 30 minutes. As a result, heating food after toxin production may not prevent disease. Ingestion of the enterotoxin causes acute symptoms of vomiting, diarrhea and abdominal cramping within 1-6 hours post-ingestion. Recovery is also rapid, usually within 24 hours. Often, a single food source will cause disease in several people, leading to a mini-outbreak. Prevention comes from proper food handling which includes washing hands, fruits and vegetables, and keeping cooked hot foods hot [140°F (60°C) or above] and cold foods cold [40°F (4°C) or below].