38 Questions
What type of bacteria are predominant in the adult large bowel (colon)?
Anaerobes
What is the ratio of anaerobes to aerobes in the large bowel (colon)?
1000:1
What is the approximate number of bacteria present in 1 gram of stool from a healthy human?
10^11-10^12 CFU/g
What is the term for the inflammation of the stomach and the intestines?
Gastroenteritis
What is the term for an abnormal increase in the number and frequency of bowel movements?
Diarrhea
What is the term for an inflammatory disorder of the GI tract often associated with blood and pus in the faeces?
Dysentery
What is the term for the inflammation of the mucosa of small and large intestines?
Enterocolitis
What type of bacteria are typically present in infants within hours of birth?
Normal human epithelial flora
What is proctitis?
Inflammation of the rectal mucosa
What is food-associated infection (FAI) usually caused by?
Toxins produced by the organisms
Which bacteria causes bacillary dysentery?
Shigella spp.
What is the most important enterohemorrhagic E. coli strain?
O157:H7
Which bacteria causes acute gastroduodenal ulcers?
Helicobacter pylori
What is the most common cause of antibiotic-associated diarrhea?
Clostridium difficile
Which bacteria causes food poisoning?
Bacillus cereus
Which bacteria can cause diarrhea by overgrowing the intestinal flora in patients treated with antibiotics?
Pseudomonas aeruginosa
What is the recommended time frame for transporting stool samples to the lab for viral culture?
Within 2 hours at room temperature
What is the purpose of adding sodium bicarbonate to gastric aspirate specimens?
To neutralize the specimen within 1 hour of collection
What type of agar is used for selective culture of Campylobacter?
Selective Campylobacter agar (Campy)
What is the recommended method for transporting rectal swabs for viral recovery?
In modified Stuart's medium or another viral transport medium
Why are gastric aspirate specimens mostly taken from infants?
For AFB detection
What is not suitable for the detection of parasites, toxins, or viral antigens?
Swabs are not acceptable for the detection
Which of the following parasites is known to attach to intestinal cells by suckers?
Giardia lamblia
What is the primary effect of aflatoxins on the human body?
Carcinogenesis
Which of the following fungal toxins is primarily produced by Amanita mushrooms?
Mushroom toxins
What is the primary advantage of invasion for microorganisms?
Both A and B
Which of the following microorganisms causes minimal invasion?
Norwalk virus
Which of the following routes of infection involves the transmission of bacterial toxins through contaminated food or water?
Ingestion of bacterial toxin-contaminated food or water
What is the primary characteristic of inflammatory diarrhea?
Fever and loose stools
Which of the following microorganisms causes a severe invasion of the intestine?
Entamoeba histolytica
What type of media is used to detect S.aureus or yeast outgrowth?
BAP
What type of medium is used to isolate Campylobacter jejuni subspecies?
Campylobacter Selective Media
What type of examination can help visualize the darting motility of campylobacter spp.?
Unstained saline preps
What is the purpose of enrichment broth in culturing fecal specimens?
To enrich for Salmonella and Shigella
What is the incubation condition for Campylobacter selective media?
Microaerobic conditions at 42°C
What type of media is used to isolate Yersinia entercolitica?
Cefsulodin-irgasan-novobiocin (CIN) agar
What is the purpose of Sorbitol MacConkey (SMAC) agar?
To isolate E.coli O157:H7
What type of examination is used to check for the presence of blood and mucus in a specimen?
Macroscopic examination
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.
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.
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