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Questions and Answers
What is a characteristic effect of the Vero toxin produced by the EHEC O157:H7 strain?
Which disease syndrome is associated with Enteroaggregative E. coli (EAEC)?
In which group is Enteroinvasive E. coli (EIEC) primarily seen?
What is a primary symptom of the disease caused by EHEC?
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What distinguishes Enterotoxigenic E. coli (ETEC) from other E. coli strains?
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What is the primary reservoir for Clostridium difficile?
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Which toxin produced by Clostridium difficile is responsible for damaging the mucosa?
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Which treatment is recommended for severe cases of Clostridium difficile infection?
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What is a distinguishing feature of Clostridium perfringens?
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What is a recommended measure to prevent Clostridium difficile infections?
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What indicates the fermentation of glucose in a culture medium?
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What color indicates the presence of alkaline conditions after fermentation?
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In which group of bacteria would you expect to see an alkaline slant with an acid butt?
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Which of the following tests is commonly used for rapid identification of indole production?
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What is a common characteristic of Enterobacteriaceae regarding glucose?
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Which species is known for rapid H2S production?
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What does a positive methyl red test indicate?
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Which of the following characteristics distinguishes Escherichia coli?
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Which biochemical test indicates E. coli as a lactose fermenter?
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What is a primary reservoir for Escherichia coli?
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Which type of E. coli is associated with Traveler's diarrhea?
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What mechanism does Enteropathogenic E. coli (EPEC) use to adhere to intestinal cells?
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Which toxin stimulates fluid loss in Enterotoxigenic E. coli (ETEC)?
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What is the main pathogenic effect of Enteroinvasive E. coli (EIEC)?
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In which clinical situation is Enterohemorrhagic E. coli (EHEC) strain most likely transmitted?
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What is the effect of the heat-stable toxin produced by Enterotoxigenic E. coli (ETEC)?
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What is the primary role of gut associated lymphoid tissue (GALT)?
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Which of the following conditions is NOT a predisposing factor for diarrheal diseases?
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What type of pathogen is characterized by producing toxins that lead to disease?
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What sets bacillary dysentery apart from general dysentery?
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Which of the following symptoms is primarily associated with gastroenteritis?
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How are enterobacteriaceae primarily classified?
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What is the main function of O antigens in gram-negative bacteria?
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Which mechanism of GI pathogens causes damage through cellular invasion?
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What is the primary characteristic of enterotoxins?
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Which symptom is least likely to be associated with non-toxigenic bacterial infections?
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What is the primary method of diagnosing Campylobacter jejuni?
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Which characteristic feature is associated with Helicobacter pylori?
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What is the main treatment strategy for infections caused by Helicobacter pylori?
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Which of the following diseases is HELICOBACTER PYLORI associated with?
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What is a distinguishing clinical symptom of Vibrio cholerae infection?
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How is Vibrio cholerae primarily transmitted to humans?
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What type of bacteria is Vibrio species classified as?
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Which statement about Helicobacter pylori is true regarding its classification as a carcinogen?
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Study Notes
Microbial Diseases of the GIT
- The GIT is the gastrointestinal tract.
- Microbial flora in the GIT is important as it helps in the digestion and helps in a variety of other ways.
- The mouth contains millions of bacteria per ml of saliva.
- In the stomach and small intestines, there are few organisms present due to the high acidity (HCl) and rapid movement of food.
- The large intestine has 100 billion bacteria per gram of feces.
- 40% of fecal mass consists of microbial cells.
- Examples of prominent bacteria include: Lactobacilli, Streptococci, Escherichia Coli, Enterococcus Faecalis, Lactic acid bacteria, Bacteroids, Bifidobacterium bifidum, etc.
- The pH varies along the GIT.
- The esophagus pH is 2
- The stomach pH is 2
- The duodenum pH is 4-5
- The jejunum and ileum pH is 4-5
- The colon pH is 7
- The anus pH is 10-12
- Normal microbial flora has antibacterial benefits.
- Bacteriocins and colicin.
- Competition for space and nutrients with potentially pathogenic bacteria.
- Benefits to the host
- Release organic acids to help digestion.
- Produce vitamin K and some B vitamins.
- Stimulates the immune system.
- Normal flora becomes pathogenic when the host is immunocompromised or when chronic antibiotic use weakens good intestinal bacteria.
Gastrointestinal Defenses
- Mechanical barriers like tight junctions between epithelial cells prevent entry into tissues.
- Mechanical actions like peristalsis, GI secretions (electrolytes and mucus), and intestinal fluids flush away pathogens; and important in inhibiting gram (-) bacilli.
- Immune cells are located in GALT, Peyer's patches, leukocytes, and IgA.
Predisposing Factors for Diarrheal Diseases
- Extremes of age (young and old)
- Recent travel
- Unsafe water
- Unclean food
- Malnutrition
- Poor personal hygiene/sanitation
- Prolonged antibiotic use
- Underlying illnesses
- Institutionalization
General Mechanisms of GI Pathogens
- Toxigenic effects due to toxins released from gut bacteria.
- Enteroinvasive effects due to multiplication and invasion of gut tissues.
- Interference of secretion and absorption.
- Spread to contiguous and distant sites.
- Obstruction of the lumen due to large numbers of intestinal worms.
Gastroenteritis
- A bacterial, parasitic, or viral disease of the gastrointestinal tract, causing inflammation within the G.I. tract.
Definition of Terms
- Enterotoxin: an exotoxin with enteric activity.
- Dysentery: inflammation of the intestines with severe abdominal cramps, tenesmus and low-volume stools containing blood, mucus, and leukocytes.
- Bacillary dysentery: caused by bacterial infection with invasion of host cells/tissues and/or production of exotoxins.
- Diarrhea: loose, watery stools.
- Bloody or mucus-containing stools = dysentery.
- Abdominal cramps, nausea, vomiting: a defense mechanism to rid the body of harmful material.
- Gastroenteritis: inflammation of the stomach or intestinal mucosa.
Bacterial Diseases of the Lower GI
- Infections: pathogens enter GIT and multiply; bacteria may penetrate intestinal mucosa or pass to other systemic organs; delay in symptom appearance while pathogen increases in number.
- Toxins: ingestion of pre-formed toxin; sudden onset of symptoms few hours later; fever not always present.
Gram-Negative Bacilli
- Gram-negative rods and curved; 42°C; TCBS; oxidase; lactose; H2S; motility; urease; indole; etc. (refer to specific tables for detailed information of each bacteria.)
Enterobacteriaceae
- Large family of short, non-spore-forming gram-negative rods.
- Inhabit soil, water, decaying matter, bowel of animals.
- Most frequent cause of diarrhea, almost 50% of nosocomial infection, facultative anaerobes growing best in air; ferment glucose; reduce nitrates into nitrites; oxidase and catalase.
Antigenic Structure
- Endotoxin; some produce exotoxins.
- Antigens
- O: cell envelope (O antigens)
- H: flagellar (H antigens); motile cells only
- K: capsular polysaccharide (K antigens)
- Vi (virulence): Salmonella capsular antigen.
Morphology and Identification
- Typical organisms: short rods or short rods with a capsule.
- Klebsiella species: large, regular capsule.
- Enterobacter species: less regular, less prominent capsule.
Culture
- E. Coli colonies: circular, convex, smooth colonies with distinct edges.
- Enterobacter colonies: similar but mucoid.
- Klebsiella: large and mucoid.
- Salmonellae and Shigellae: colonies similar to E. coli but do not ferment lactose.
- Blood agar; Eosin methylene blue or MacConkey agar (to differentiate lactose fermentation).
- Triple sugar iron (TSI) agar (complex media) - glucose, sucrose, lactose, ferrous sulfate, tissue extracts, indicator (phenol red).
- Differentiates Salmonella, Shigella from other enteric gram-negative rods in stool cultures.
- Specific procedures are given for each type of culture.
Growth Characteristics
- Identified further by biochemical differentiation (carbohydrate fermentation patterns, amino acid decarboxylase activities, other enzymes).
- Glucose and acid production – all Enterobacteriaceae.
- H2S - Proteus mirabilis & Salmonella; no precipitate for negative.
- Indole test (indole production from tryptophan).
- Methyl Red (MR) Test
- Voges-Proskauer Test
- Citrate Utilization Test
Motility Test
- Principle: semi-solid agar media to determine motility by diffusion.
- Positive test = growth away from line of inoculation
- Negative test = growth occurred only at the line of inoculation.
- This test distinguishes between motile and nonmotile bacteria based on flagella.
Urea Test
- Principle: Urease hydrolyzes urea to ammonia, which raises the pH, and the color change will be from an initial yellow to a bright pink.
- Positive test = color change from yellow to bright pink.
- Negative test = no color change. (The test tube should remain yellow.)
Presumptive Identification
- Table with lactose-fermented and lactose-slowed bacteria.
- Table can be used for presumptive identification of gram-negative enteric bacteria.
Escherichia Coli
- Distinguishing Features: Gram-negative rod, facultative anaerobic, oxidase negative, lactose fermenter, iridescent green sheen on EMB.
- Triple-sugar iron (TSI) agar: A/A, gas (+), H2S (-).
- Reservoir - humans, colon; may colonize vagina or urethra, crops.
- Transmission: endogenous; fecal-oral; enteric strains: bovine fecal contamination (raw or undercooked beef, milk, apple juice)
Escherichia Coli: Disease Syndromes
- Enteropathogenic E. coli (EPEC)
- Enterotoxigenic E. coli (ETEC)
- Enteroinvasive E. coli (EIEC)
- Enterohemorrhagic E. coli (EHEC)
- Enteroaggregative E. coli (EAEC)
- Detailed descriptions for each type.
Klebsiella Pneumoniae
- Distinguishing Features: gram-negative rods, large polysaccharide capsule, mucoid, lactose-fermenting colonies, oxidase negative.
- Reservoir: human colon and upper respiratory tract.
- Pathogenesis: capsule (impedes phagocytosis); endotoxin.
- Diseases: pneumonia, urinary tract infection, septicemia.
- Diagnosis: culture of sputum or clean catch urine sample.
- Treatment: third-generation cephalosporin, aminoglycoside, carbapenem for ESBL-producing strains.
- Prevention: good catheter care, limit use of antibiotics.
Serratia Marcescens
- Distinguishing Features: produces a characteristic red pigment called prodigiosin.
- Diseases: meningitis, pneumonia, UTI.
- Treatment: cephalosporins (3rd generation)
Proteus Mirabilis/Proteus Vulgaris
- Distinguishing Features: gram-negative rods, non-lactose fermenting, highly motile, urease-positive, facultative anaerobe, oxidase negative.
- Pathogenesis: Urease raises urine pH- kidney stones.
- Diseases: urinary tract infection, septicemia.
- Diagnosis: culture of blood or urine, lactose-negative organisms, swarming motility.
- Treatment: fluoroquinolone; TMP-SMX; third-generation cephalosporin (uncomplicated UTIs).
Yersinia Pestis
- Distinguishing Features: small gram-negative rods with bipolar staining, facultative intracellular parasite, coagulase positive.
- Transmission: wild rodents fleas.
- Pathogenesis: coagulase-contaminated mouth parts, endotoxin and exotoxin, envelope antigen, type III secretion system.
- Disease: bubonic plague, pneumonic plague.
- Diagnosis: clinical specimens and cultures, "safety pin" staining.
- Treatment: aminoglycosides.
Yersinia Enterocolitica
- Distinguishing Features: motile at 25°C, non-motile at 37°C, cold growth.
- Reservoir: zoonotic.
- Transmission: unpasteurized milk, pork, prominent in northern climates.
- Diseases: enterocolitis, pseudoappendicitis, reactive arthritis.
- Diagnosis: stool culture, 25.c cold enrichment.
- Treatment: supportive care, fluoroquinolone, third-generation cephalosporin.
Shigella Species
- Distinguishing Features: gram-negative rods, non-motile, non-lactose fermenters.
- Reservoir: human colon.
- Transmission: fecal-oral.
- Diseases: enterocolitis/shigellosis.
- Diagnosis: isolation from stool during illness and culture on selective media.
- Treatment: fluid and electrolyte replacement; antibiotics; strains are ampicillin-resistant.
Salmonella Enterica Typhi
- Distinguishing Features: gram-negative rods, highly motile, Vi capsular, facultative anaerobe, non-lactose fermenting, produces H2S, sensitive to acid.
- Reservoir: humans only.
- Transmission: fecal-oral route.
- Pathogenesis: typhoid fever (enteric/paratyphoid).
- Diagnosis: isolated from blood, bone marrow, urine, and tissue biopsy, rose spots, antigens in patient's serum.
- Treatment: fluoroquinolones, third-generation cephalosporins.
Salmonella Subspecies other than typhi
- Distinguishing Features: facultative Gram negative rods, non-lactose fermenting, produces H2S, speciated with biochemical reactions and serotyped with O,H, Vi antigens.
- Reservoir: enteric tracts of humans, domestic animals.
- Transmission: raw chicken and eggs, foodborne, reptile pets.
- Pathogenesis: invades mucosa in ileocecal region, invasive to lamina propria, increased PG, increased cAMP.
- Diseases: enterocolitis, gastroenteritis.
- Diagnosis: culture on Hektoen agar, H2S production.
- Treatment: antibiotics (self-limiting gastroenteritis); third-generation cephalosporins, fluoroquinolone, TMP-SMX
Pseudomonas Aeruginosa
- Distinguishing Features: oxidase-positive, gram-negative rods, non-fermenting, pigments (pyocyanin, fluorescein), grape-like odor, slime layer, non-lactose fermenting colonies.
- Pathogenesis: endotoxin-gram negative shock, inhibits protein synthesis like diphtheria toxin, forms pulmonary microcolonies difficult to remove by phagocytosis.
- Diseases: various, including colonizations of healthy people, burn patients, patients.
- Diagnosis: Gram stain and culture.
- Treatment: antipseudomonal penicillin, aminoglycoside, or fluoroquinolones.
- Prevention: pasteurization, disinfection, hand washing, prompt removal of catheters, avoid flowers and raw vegetables.
Campylobacter Jejuni
- Distinguishing Features: Gram-negative curved rods with polar flagella, oxidase-positive, microaerophilic, grows at 42 °C.
- Reservoir: intestinal tracts of humans, cattle, sheep.
- Transmission: fecal-oral.
- Pathogenesis: low infectious dose, invades mucosa of the colon, destroying mucosal surfaces, inflammatory diarrhea.
- Diseases: gastroenteritis.
- Complications: Guillain-Barré syndrome, reactive arthritis.
- Diagnosis: culture on Campylobacter or Skirrow agar at 42.0 °C.
- Treatment: mostly supportive care, electrolyte replacement; erythromycin, fluoroquinolones, resistant to penicillin.
Helicobacter Pylori
- Distinguishing Features: Gram-negative spiral gastric bacteria, oxidase-positive, urease-positive, microaerophilic, grows at 37°C.
- Reservoir: humans.
- Transmission: fecal-oral/oral-oral.
- Pathogenesis: urease-positive, neutralizes stomach acid, allows survival, mucinase aids in penetration, invasive, marked inflammation.
- Diseases: chronic gastritis, duodenal ulcers, associated with gastric cancer, mucosa-associated lymphoid tissue, lymphoma.
- Diagnosis: biopsy with culture, histology, Giemsa, urea breath test, serology (measure antibodies in serum.)
- Treatment: myriad of regimens, omeprazole + amoxicillin + clarithromycin or quadruple therapy.
- Prevention/caution: broad-spectrum antibiotics.
Vibrio Species
- Genus Features: gram-negative curved rods with polar flagella, oxidase-positive, vibrionaceae.
- Species of Medical Importance: cholerae, parahaemolyticus, vulnificus.
- Reservoir - humans, no vertebrate animal carriers, copepods, shellfish (in contaminated water.)
- Transmission: fecal-oral (sensitive to stomach acid), human-to-human.
- Pathogenesis: motility, mucinase, and toxin coregulated pili (attach to intestinal mucosa); cholera enterotoxin similar to LT, ADP ribosylates, activates adenylate cyclase, increased cAMP -> efflux of Cl- and H2O.
- Diseases: cholera, tremendous fluid loss, hypovolemic shock.
- Diagnosis: culture stool on TCBS producing yellow colonies; oxidase-positive.
- Treatment: fluid and electrolyte replacement, reducing disease, doxycycline or ciprofloxacin.
- Prevention: Proper sanitation, new vaccines.
Clostridium Difficile
- Reservoir: human colon/gastrointestinal tract.
- Pathogenesis: Toxin A - enterotoxin, damaging mucosa, increasing fluid; Toxin B - cytotoxin, cytopathic.
- Diseases: antibiotic-associated diarrhea, colitis, pseudomembranous colitis.
- Diagnosis: culture not diagnostic, stool exam for toxin production.
Clostridium Perfringens
- Distinguishing Features: large gram-positive, spore-forming rods, anaerobic, "stormy fermentation", double zone of hemolysis.
- Reservoir: soil/colon
- Transmission: foodborne, traumatic implantation.
- Pathogenesis: spores germinate, produce alpha toxin, enterotoxin produced in intestines, food poisoning.
- Diseases: gas gangrene, myonecrosis (rare), food poisoning.
- Treatment: debridement, delayed closure, antibiotic use.
Clostridium Botulinum
- Distinguishing Features: anaerobic, gram-positive spore-forming rods.
- Reservoir: soil/dust.
- Transmission: foodborne/traumatic implantation.
- Pathogenesis: spores germinate, produce A-B toxin, highly toxic.
- Botulinum toxin: heat-labile, absorbed by gut, blocks acetylcholine release at myoneural junction, flaccid paralysis.
- Diseases/Symptoms in adults and infants: see Table II-2-14 for details.
Bacillus Cereus
- Distinguishing Features: spores
- Reservoir: found in nature
- Transmission: foodborne intoxication
- Pathogenesis: emetic toxins, similar to S. aureus; diarrheal toxins produced in vivo (similar to E. coli LT).
- Diseases: gastroenteritis
- Diagnosis: clinical grounds, culture and Gram stain of implicated food.
- Treatment: self-limiting; vancomycin for eye infection.
Staphylococcus Aureus
- Distinguishing Features: small, yellow colonies on blood agar, B-hemolytic, coagulase positive, ferments mannitol on mannitol salt agar.
- Pathogenesis: enterotoxins: fast acting, heat-stable (2-6 hours symptoms).
- Diseases: gastroenteritis.
- Treatment: self-limiting.
Typhoid Assay
- (Prelab discussion) This information is not sufficient to generate study notes.
Salmonella Enterica Typhi
- (Information taken from pre-lab discussion regarding the microbiology of Salmonella)
- Identification information.
- Additional information about the organism (pathogenesis, diseases, diagnosis, treatment).
- Additional studies of typhoid fever are needed.
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Test your knowledge on various strains of E. coli, including the characteristics of Vero toxin and the diseases they cause. This quiz covers Enteroaggregative E. coli, Enteroinvasive E. coli, and Enterotoxigenic E. coli, and their associated symptoms. Perfect for students studying microbiology or health sciences.
