Understanding E. coli Strains and Effects
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Questions and Answers

What is a characteristic effect of the Vero toxin produced by the EHEC O157:H7 strain?

  • Inhibits 60S Ribosome (correct)
  • Increases mucus secretion
  • Promotes intestinal absorption
  • Causes fever and chills

    • Which disease syndrome is associated with Enteroaggregative E. coli (EAEC)?

  • Hemolytic Uremic Syndrome
  • Persistent watery diarrhea (correct)
  • Severe bloody diarrhea
  • Acute renal failure

    • In which group is Enteroinvasive E. coli (EIEC) primarily seen?

  • Infants in developing countries
  • Travelers
  • Infants and toddlers
  • Older children and adults (correct)

    • What is a primary symptom of the disease caused by EHEC?

    <p>Thrombocytopenia</p> Signup and view all the answers

    What distinguishes Enterotoxigenic E. coli (ETEC) from other E. coli strains?

    <p>It produces choleralike watery diarrhea.</p> Signup and view all the answers

    What is the primary reservoir for Clostridium difficile?

    <p>Human colon/gastrointestinal tract</p> Signup and view all the answers

    Which toxin produced by Clostridium difficile is responsible for damaging the mucosa?

    <p>Toxin A</p> Signup and view all the answers

    Which treatment is recommended for severe cases of Clostridium difficile infection?

    <p>Metronidazole</p> Signup and view all the answers

    What is a distinguishing feature of Clostridium perfringens?

    <p>Double zone of hemolysis</p> Signup and view all the answers

    What is a recommended measure to prevent Clostridium difficile infections?

    <p>Use of narrow-spectrum antibiotics only</p> Signup and view all the answers

    What indicates the fermentation of glucose in a culture medium?

    <p>Yellow slant and yellow butt</p> Signup and view all the answers

    What color indicates the presence of alkaline conditions after fermentation?

    <p>Red</p> Signup and view all the answers

    In which group of bacteria would you expect to see an alkaline slant with an acid butt?

    <p>Salmonellae and shigellae</p> Signup and view all the answers

    Which of the following tests is commonly used for rapid identification of indole production?

    <p>Indole Test</p> Signup and view all the answers

    What is a common characteristic of Enterobacteriaceae regarding glucose?

    <p>Glucose and acid production</p> Signup and view all the answers

    Which species is known for rapid H2S production?

    <p>Proteus mirabilis</p> Signup and view all the answers

    What does a positive methyl red test indicate?

    <p>Strong acid production</p> Signup and view all the answers

    Which of the following characteristics distinguishes Escherichia coli?

    <p>Facultative anaerobic, oxidase negative</p> Signup and view all the answers

    Which biochemical test indicates E. coli as a lactose fermenter?

    <p>Triple sugar iron agar: A/A, gas (+), H2S (-)</p> Signup and view all the answers

    What is a primary reservoir for Escherichia coli?

    <p>Human colon and vaginal flora</p> Signup and view all the answers

    Which type of E. coli is associated with Traveler's diarrhea?

    <p>Enterotoxigenic E. coli (ETEC)</p> Signup and view all the answers

    What mechanism does Enteropathogenic E. coli (EPEC) use to adhere to intestinal cells?

    <p>Bundle forming pilus encoded by EAF</p> Signup and view all the answers

    Which toxin stimulates fluid loss in Enterotoxigenic E. coli (ETEC)?

    <p>Heat-labile toxin</p> Signup and view all the answers

    What is the main pathogenic effect of Enteroinvasive E. coli (EIEC)?

    <p>Causes inflammatory disease of the large intestine</p> Signup and view all the answers

    In which clinical situation is Enterohemorrhagic E. coli (EHEC) strain most likely transmitted?

    <p>Consuming raw or undercooked beef</p> Signup and view all the answers

    What is the effect of the heat-stable toxin produced by Enterotoxigenic E. coli (ETEC)?

    <p>Increases secretion of water and ions</p> Signup and view all the answers

    What is the primary role of gut associated lymphoid tissue (GALT)?

    <p>To serve as a defense mechanism against pathogens</p> Signup and view all the answers

    Which of the following conditions is NOT a predisposing factor for diarrheal diseases?

    <p>Excessive exercise</p> Signup and view all the answers

    What type of pathogen is characterized by producing toxins that lead to disease?

    <p>Toxigenic pathogens</p> Signup and view all the answers

    What sets bacillary dysentery apart from general dysentery?

    <p>It is specifically caused by bacterial infection with tissue invasion.</p> Signup and view all the answers

    Which of the following symptoms is primarily associated with gastroenteritis?

    <p>Inflammation of the stomach or intestinal mucosa</p> Signup and view all the answers

    How are enterobacteriaceae primarily classified?

    <p>As lactose fermenters and non-lactose fermenters</p> Signup and view all the answers

    What is the main function of O antigens in gram-negative bacteria?

    <p>To act as a target for immune response through agglutination</p> Signup and view all the answers

    Which mechanism of GI pathogens causes damage through cellular invasion?

    <p>Enteroinvasive</p> Signup and view all the answers

    What is the primary characteristic of enterotoxins?

    <p>They are exotoxins with enteric activity.</p> Signup and view all the answers

    Which symptom is least likely to be associated with non-toxigenic bacterial infections?

    <p>Sudden onset of symptoms</p> Signup and view all the answers

    What is the primary method of diagnosing Campylobacter jejuni?

    <p>Culture on Campylobacter or Skirrow agar at 42°C</p> Signup and view all the answers

    Which characteristic feature is associated with Helicobacter pylori?

    <p>Gram-negative spiral bacteria with flagella</p> Signup and view all the answers

    What is the main treatment strategy for infections caused by Helicobacter pylori?

    <p>Combination therapy including a proton pump inhibitor and antibiotics</p> Signup and view all the answers

    Which of the following diseases is HELICOBACTER PYLORI associated with?

    <p>Chronic gastritis and duodenal ulcers</p> Signup and view all the answers

    What is a distinguishing clinical symptom of Vibrio cholerae infection?

    <p>Rice-water diarrhea</p> Signup and view all the answers

    How is Vibrio cholerae primarily transmitted to humans?

    <p>Fecal-oral route from contaminated water</p> Signup and view all the answers

    What type of bacteria is Vibrio species classified as?

    <p>Curved rod</p> Signup and view all the answers

    Which statement about Helicobacter pylori is true regarding its classification as a carcinogen?

    <p>It is classified as a type I carcinogen by the WHO.</p> Signup and view all the answers

    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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