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Questions and Answers
What type of bacteria are predominant in the adult large bowel (colon)?
What type of bacteria are predominant in the adult large bowel (colon)?
What is the ratio of anaerobes to aerobes in the large bowel (colon)?
What is the ratio of anaerobes to aerobes in the large bowel (colon)?
What is the approximate number of bacteria present in 1 gram of stool from a healthy human?
What is the approximate number of bacteria present in 1 gram of stool from a healthy human?
What is the term for the inflammation of the stomach and the intestines?
What is the term for the inflammation of the stomach and the intestines?
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What is the term for an abnormal increase in the number and frequency of bowel movements?
What is the term for an abnormal increase in the number and frequency of bowel movements?
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What is the term for an inflammatory disorder of the GI tract often associated with blood and pus in the faeces?
What is the term for an inflammatory disorder of the GI tract often associated with blood and pus in the faeces?
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What is the term for the inflammation of the mucosa of small and large intestines?
What is the term for the inflammation of the mucosa of small and large intestines?
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What type of bacteria are typically present in infants within hours of birth?
What type of bacteria are typically present in infants within hours of birth?
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What is proctitis?
What is proctitis?
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What is food-associated infection (FAI) usually caused by?
What is food-associated infection (FAI) usually caused by?
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Which bacteria causes bacillary dysentery?
Which bacteria causes bacillary dysentery?
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What is the most important enterohemorrhagic E. coli strain?
What is the most important enterohemorrhagic E. coli strain?
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Which bacteria causes acute gastroduodenal ulcers?
Which bacteria causes acute gastroduodenal ulcers?
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What is the most common cause of antibiotic-associated diarrhea?
What is the most common cause of antibiotic-associated diarrhea?
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Which bacteria causes food poisoning?
Which bacteria causes food poisoning?
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Which bacteria can cause diarrhea by overgrowing the intestinal flora in patients treated with antibiotics?
Which bacteria can cause diarrhea by overgrowing the intestinal flora in patients treated with antibiotics?
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What is the recommended time frame for transporting stool samples to the lab for viral culture?
What is the recommended time frame for transporting stool samples to the lab for viral culture?
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What is the purpose of adding sodium bicarbonate to gastric aspirate specimens?
What is the purpose of adding sodium bicarbonate to gastric aspirate specimens?
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What type of agar is used for selective culture of Campylobacter?
What type of agar is used for selective culture of Campylobacter?
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What is the recommended method for transporting rectal swabs for viral recovery?
What is the recommended method for transporting rectal swabs for viral recovery?
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Why are gastric aspirate specimens mostly taken from infants?
Why are gastric aspirate specimens mostly taken from infants?
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What is not suitable for the detection of parasites, toxins, or viral antigens?
What is not suitable for the detection of parasites, toxins, or viral antigens?
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Which of the following parasites is known to attach to intestinal cells by suckers?
Which of the following parasites is known to attach to intestinal cells by suckers?
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What is the primary effect of aflatoxins on the human body?
What is the primary effect of aflatoxins on the human body?
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Which of the following fungal toxins is primarily produced by Amanita mushrooms?
Which of the following fungal toxins is primarily produced by Amanita mushrooms?
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What is the primary advantage of invasion for microorganisms?
What is the primary advantage of invasion for microorganisms?
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Which of the following microorganisms causes minimal invasion?
Which of the following microorganisms causes minimal invasion?
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Which of the following routes of infection involves the transmission of bacterial toxins through contaminated food or water?
Which of the following routes of infection involves the transmission of bacterial toxins through contaminated food or water?
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What is the primary characteristic of inflammatory diarrhea?
What is the primary characteristic of inflammatory diarrhea?
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Which of the following microorganisms causes a severe invasion of the intestine?
Which of the following microorganisms causes a severe invasion of the intestine?
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What type of media is used to detect S.aureus or yeast outgrowth?
What type of media is used to detect S.aureus or yeast outgrowth?
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What type of medium is used to isolate Campylobacter jejuni subspecies?
What type of medium is used to isolate Campylobacter jejuni subspecies?
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What type of examination can help visualize the darting motility of campylobacter spp.?
What type of examination can help visualize the darting motility of campylobacter spp.?
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What is the purpose of enrichment broth in culturing fecal specimens?
What is the purpose of enrichment broth in culturing fecal specimens?
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What is the incubation condition for Campylobacter selective media?
What is the incubation condition for Campylobacter selective media?
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What type of media is used to isolate Yersinia entercolitica?
What type of media is used to isolate Yersinia entercolitica?
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What is the purpose of Sorbitol MacConkey (SMAC) agar?
What is the purpose of Sorbitol MacConkey (SMAC) agar?
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What type of examination is used to check for the presence of blood and mucus in a specimen?
What type of examination is used to check for the presence of blood and mucus in a specimen?
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Study Notes
Resident Microbial Flora
- Infants are colonized by normal human epithelial flora, including Staphylococcus, Corynebacterium spp., and other gram-positive organisms, within a few hours of birth.
- The normal flora of the adult large bowel (colon) is established relatively early in life and consists predominantly of anaerobic species, including Bacteroides, Clostridium, Peptotreptococcus, Bifidobacterium, and Eubactrium.
- Aerobes, including E. coli, other Enterobacteriaceae, Enterococci, and streptococci, are outnumbered by anaerobes (1000:1).
- The number of bacteria/gram of stool within the bowel lumen increases steadily as material approaches the sigmoid colon.
- 80% of the dry weight of feces from healthy humans consists of bacteria, which can be present in numbers as high as 10^11-10^12 CFU/g of stool.
Terms to Know
- Gastritis: inflammation of the stomach
- Gastroenteritis: inflammation of the stomach and intestines, characterized by GI symptoms including nausea, vomiting, diarrhea, and abdominal discomfort
- Enterocolitis: inflammation of the mucosa of small and large intestines
- Diarrhea: abnormal increase in the number and frequency of bowel movements, with fecal material often having a loose to liquid consistency
- Dysentery: inflammatory disorder of the GI tract, often associated with blood and pus in the feces, and accompanied by pain, fever, and abdominal cramps
- Proctitis: inflammation of the rectal mucosa
- Food-Associated Infection (FAI): usually caused by toxins produced by organisms, rather than the direct actions of the organism itself
Diseases
- Causative agents: bacteria, viruses, and parasites
- Bacterial infections:
- Salmonella spp.: common cause of gastroenteritis
- Shigella spp.: cause bacillary dysentery and common cause of diarrhea
- Campylobacter spp.: frequently cause diarrhea in the US
- E. coli: pathogenic E. coli may be enterohemorrhagic, enteroinvasive, enterotoxigenic, or enteropathogenic
- Yersinia enterocolitica: causes enterocolitis, some infections resemble acute appendicitis
- Edwardsiella tarda: relatively uncommon cause of diarrhea
- Vibrio: V. cholerae causes cholera, V. parahaemolyticus causes watery diarrhea
- Helicobacter pylori: causes chronic gastritis and the most common cause of peptic and duodenal ulcers
- Clostridium: C. difficile is an important cause of antibiotic-associated diarrhea and pseudomembranous colitis, C. perfringens produces enterotoxin and is a common cause of food-poisoning
- Staphylococcus aureus: can cause GI disease in two different ways, including Staph. food poisoning and staphylococcal overgrowth
- Pseudomonas aeruginosa: can cause diarrhea by overgrowing the intestinal flora in patients treated with antibiotics
- Bacillus cereus: causes food poisoning
Adherence to Intestinal Cells
- Cryptosporidiosis (Cryptosporidium parvum) and Isospora spp.: disrupt mucosal function, seen in diarrhea of patients with AIDS and in travelers' diarrhea
- Helminths: Flukes, tapeworms (cestodes), and roundworms (nematodes)
- Protozoans: Giardiasis (Giardia lamblia) attaches by suckers, no invasion or toxin production
Fungal Toxins
- Ergot (rye, wheat): can cause hallucinations, can be medicinal
- Aflatoxins (moldy grain, peanuts): strong carcinogens
- Mushroom toxins: mainly produced by Amanita, toxic to liver
Invasion
- Invasion allows the microorganism to reach deeper tissues, access nutrients for growth, and possibly avoid host immune response
- Minimal invasion: Norwalk virus, Rotavirus
- Variable invasion: Aeromonas sp., Campylobacter sp., Salmonella sp., Vibrio parahemolyticus
- Severe invasion: Entamoeba histolytica, enteroinvasive E. coli, Shigella species
Routes of Infection
- Transmission through fecal-oral route
- Ingestion of bacterial toxin-contaminated food or water
- Direct person-to-person contact
- Through animal contact
Symptoms
- Nausea, vomiting, abdominal discomfort, and diarrhea
Diagnostic Procedures
- Visual Examination: macroscopic examination for presence of blood and mucus, microscopic examination for presence of blood, PMNs, bacteria in gram-stained smears
- Cultures: most labs routinely culture fecal specimens for Salmonella, Shigella, Campylobacter, and E. coli O157:H7
- Media used: BAP, MacConkey agar, XLD agar, Campylobacter Selective Media, Enrichment broth, CIN agar, SS agar, SMAC agar
- Incubation conditions: ambient air at 35°C, microaerobic conditions for Campylobacter spp.
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Description
Learn about the normal human epithelial flora that colonize infants, including Staphylococcus and other gram-positive organisms, and how the content of intestinal flora changes over time.
