Enterobacteriaceae & Campylobacter
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Questions and Answers

What is the result of the interaction between hydrogen sulphide (H2S) and iron in the Triple Sugar Iron (TSI) test?

  • A white precipitate is formed
  • A black precipitate is formed (correct)
  • The agar turns yellow
  • No reaction occurs

    • Fimbriae are used for swarming motility.

    False

    What is the role of urease in the pathogenesis of UTIs?

    Urease converts urea in urine to ammonia and carbon dioxide, leading to the formation of struvite stones.

    The swarming motility of Proteus mirabilis aids in its _______________ along catheter surfaces.

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

    Match the following infections with the corresponding site of infection:

    <p>Urethritis = Urethra Cystitis = Bladder Prostatitis = Prostate Pyelonephritis = Kidneys</p> Signup and view all the answers

    What is the consequence of the formation of struvite stones in the urinary tract?

    <p>Both A and B</p> Signup and view all the answers

    Proteus mirabilis is commonly found in the urinary tract of healthy individuals.

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

    The bacteria Proteus mirabilis can differentiate into elongated swarm cells, which express many _______________, allowing the bacteria to move and form multicellular rafts.

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

    What is the minimum number of bacteria required to cause Shigella infection?

    <p>10</p> Signup and view all the answers

    Shigella can survive the acidic environment of the stomach.

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

    What is the primary method of transmission of Shigella?

    <p>Fecal-oral transmission</p> Signup and view all the answers

    Shigella can cause a severe complication called _______________ Syndrome (HUS).

    <p>Hemolytic Uremic</p> Signup and view all the answers

    What is the primary site of infection for Proteus mirabilis?

    <p>Urinary tract</p> Signup and view all the answers

    Proteus mirabilis is a lactose fermenter.

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

    What is the result of thrombus formation in kidney damage?

    <p>Ischemic kidney damage</p> Signup and view all the answers

    Heat-stable enterotoxin (ST) activates adenylate cyclase.

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

    What is the outcome of ETEC infection?

    <p>Watery diarrhea, possible fever, and bloating</p> Signup and view all the answers

    EIEC attaches to and invades intestinal epithelial cells using _______________.

    <p>none (uses no specific structure for attachment)</p> Signup and view all the answers

    Match the following E. coli types with their corresponding mechanisms:

    <p>ETEC = Activates adenylate cyclase, increasing cAMP EIEC = Invades and multiplies within epithelial cells EPEC = Injects effector proteins via a Type III secretion system</p> Signup and view all the answers

    What is the result of pedestal formation and microvilli effacement in EPEC infection?

    <p>Effacement of microvilli</p> Signup and view all the answers

    EPEC uses fimbriae to attach to intestinal epithelial cells.

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

    What is the outcome of thrombocytopenia?

    <p>Decreased platelet count</p> Signup and view all the answers

    Campylobacter spp. are gram-positive bacteria.

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

    What is the primary source of energy for Campylobacter spp.?

    <p>Amino acids</p> Signup and view all the answers

    Campylobacter spp. grow at a temperature of _______________________.

    <p>42°C</p> Signup and view all the answers

    What is a symptom of pyelonephritis?

    <p>All of the above</p> Signup and view all the answers

    Match the following UTI symptoms with their corresponding type of UTI:

    <p>Cystitis = Dysuria, pyuria, and suprapubic pain Pyelonephritis = Fever, chills, and flank pain Urethritis = Dysuria, urinary frequency, and urinary urgency</p> Signup and view all the answers

    Struvite stones are radiolucent.

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

    Urinalysis of a UTI patient may show _______________________ in the urine.

    <p>pyuria (pus)</p> Signup and view all the answers

    What is the primary cause of watery diarrhea in children under two years of age due to E. coli?

    <p>Impaired absorption</p> Signup and view all the answers

    UPEC can colonize the periurethral area and ascend the urinary tract.

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

    What is the primary purpose of type 1 fimbriae and P fimbriae in UPEC?

    <p>Adhesion to uroepithelial cells</p> Signup and view all the answers

    Salmonella enterica is a _______________________ anaerobe.

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

    Match the following diagnoses with their corresponding tests:

    <p>Gram Staining = Diagnosis of UTIs Culture = Diagnosis of Salmonella infections HUS Diagnosis = Identifying Shiga toxin in the blood</p> Signup and view all the answers

    What is the primary treatment for diarrhea caused by E. coli?

    <p>Hydration and rest</p> Signup and view all the answers

    Salmonella enterica has a Vi antigen specific to non-typhoidal strains.

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

    What is a characteristic of Escherichia coli?

    <p>Gram-negative bacilli</p> Signup and view all the answers

    Escherichia coli is a lactose non-fermenter.

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

    What enzyme does Escherichia coli produce?

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

    Escherichia coli can reduce _______________________ to nitrite.

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

    Match the following characteristics of Escherichia coli with their descriptions:

    <p>Motile = Ability to move Facultative anaerobe = Ability to grow in aerobic and anaerobic conditions Catalase +ve = Production of catalase enzyme Lactose fermenter = Production of beta-galactosidase and cleavage of lactose into glucose and galactose</p> Signup and view all the answers

    Which pathotype of E. coli produces Shiga-like toxins and causes bloody diarrhea?

    <p>Shiga-like toxin-producing E. coli (STEC)</p> Signup and view all the answers

    Enterotoxigenic E. coli (ETEC) causes urinary tract infections (UTIs).

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

    What is the outcome of hemolytic uremic syndrome (HUS)?

    <p>Ischemic kidney damage, reduced filtration, and uremia</p> Signup and view all the answers

    Uropathogenic E. coli (UPEC) causes _______________________ in the urinary tract.

    <p>urinary tract infections (UTIs)</p> Signup and view all the answers

    Match the following E. coli pathotypes with their corresponding diseases:

    <p>Enteropathogenic E. coli (EPEC) = Watery diarrhea in children under two years old Shiga-like toxin-producing E. coli (STEC) = Bloody diarrhea and hemolytic uremic syndrome (HUS) Uropathogenic E. coli (UPEC) = Urinary tract infections (UTIs) Enterotoxigenic E. coli (ETEC) = Watery diarrhea</p> Signup and view all the answers

    What is the mechanism of action of Heat-labile Enterotoxin (LT)?

    <p>Activates adenylate cyclase, increasing cAMP</p> Signup and view all the answers

    EIEC causes bloody diarrhea by triggering a strong inflammatory response.

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

    What is the primary outcome of EPEC infection?

    <p>Impairs absorption, causing watery diarrhea</p> Signup and view all the answers

    UPEC produces alpha and beta _______________, causing lysis of urinary tract cells.

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

    Match the following E. coli types with their corresponding mechanisms of infection:

    <p>EIEC = Attaches to and invades intestinal epithelial cells, causing cell destruction EPEC = Injects effector proteins via a Type III secretion system, causing actin cytoskeleton rearrangement UPEC = Uses type 1 fimbriae and P fimbriae to adhere to uroepithelial cells ETEC = Produces heat-labile and heat-stable enterotoxins, leading to watery diarrhea</p> Signup and view all the answers

    What is the function of fimbriae/pili in E. coli?

    <p>Attachment to the host cells</p> Signup and view all the answers

    Lipid A is a component of LPS in E. coli.

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

    What is the function of haemolysins in E. coli?

    <p>Haemolysins are exotoxins that lyse red blood cells.</p> Signup and view all the answers

    The K antigens in E. coli are composed of _______________ acid.

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

    Match the following E. coli virulence factors with their functions:

    <p>Capsule = Attachment to host cells Fimbriae/pili = Attachment to host cells Flagella = Motility Lipid A = Component of LPS</p> Signup and view all the answers

    What is a characteristic of Salmonella enterica?

    <p>Facultative intracellular pathogen</p> Signup and view all the answers

    Salmonella enterica can ferment lactose.

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

    What is the type of antigen specific to Salmonella spp.?

    <p>Vi antigen (capsular polysaccharide, only found in typhoidal strains)</p> Signup and view all the answers

    Salmonella enterica is a _______________________ anaerobe.

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

    Where does Salmonella enterica subsp. enterica serovar typhi reach after ingestion?

    <p>Distal ileum of the small intestine</p> Signup and view all the answers

    Salmonella enterica subsp. enterica serovar typhi induces recruitment of neutrophils.

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

    What is the function of the Type III secretion system in Salmonella enterica subsp. enterica serovar typhi?

    <p>It injects effector proteins, preventing vacuole-lysosome fusion.</p> Signup and view all the answers

    Salmonella enterica subsp. enterica serovar typhi forms a _______________________ vacuole after being phagocytosed by macrophages.

    <p>salmonella-containing</p> Signup and view all the answers

    Match the following stages of Salmonella enterica subsp. enterica serovar typhi pathogenesis with their descriptions:

    <p>Ingestion and Targeting = Reaches distal ileum of the small intestine and targets epithelial layer of the mucosal lining Immune Evasion = Suppresses neutrophil recruitment and induces recruitment of monocytes and macrophages Survival and Replication = Forms a salmonella-containing vacuole and survives and replicates within it</p> Signup and view all the answers

    How many serotypes are there within the subspecies enterica of Salmonella?

    <p>Over 2,500</p> Signup and view all the answers

    Salmonella enterica subsp. enterica serovar Typhimurium typically causes a systemic infection.

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

    What is the primary site of infection for Salmonella enterica subsp. enterica serovar Typhimurium?

    <p>Distal ileum of the small intestine</p> Signup and view all the answers

    Salmonella enterica subsp. enterica serovar Typhimurium causes _______________________ in the small intestine and colon.

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

    Match the following steps in the pathogenesis of Salmonella enterica subsp. enterica serovar Typhimurium with their descriptions:

    <p>Ingestion and Targeting = Reaches the distal ileum of the small intestine and targets epithelial layer of the mucosal lining Immune Response = Causes enterocolitis and recruits immune cells Potential Spread = Can become invasive and lead to bacteremia</p> Signup and view all the answers

    What is the primary characteristic of Shigella spp.?

    <p>Non-motile and non-lactose fermenter</p> Signup and view all the answers

    Shigella spp. can cause shigellosis, a contagious intestinal infection.

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

    What is the primary virulence factor of Shigella spp. that causes bloody diarrhea?

    <p>Shiga toxin</p> Signup and view all the answers

    Shigella spp. grow on selective media like _______________________ agar.

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

    Match the following virulence factors of Shigella spp. with their descriptions:

    <p>O antigen = required for the bacteria to penetrate the mucosa and epithelial cell of the colon Shiga toxin = causes bloody diarrhea Invasiveness = virulent strains penetrate the mucosa and epithelial cell of the colon</p> Signup and view all the answers

    Shigella spp. are urease and oxidase positive.

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

    What is the primary site of infection for Shigella spp.?

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

    What is the outcome of Shigella infection in the colon?

    <p>Intense inflammation, attracting more immune cells, damaging epithelial cells, and causing ulcerations and abscesses</p> Signup and view all the answers

    Shigella spp. are _______________________ anaerobes.

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

    What is the primary method of identification of Shigella spp.?

    <p>All of the above</p> Signup and view all the answers

    What is the characteristic of Proteus mirabilis that allows it to survive in both aerobic and anaerobic environments?

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

    Proteus mirabilis is a gram-positive bacillus.

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

    What is the function of the enzyme urease produced by Proteus mirabilis?

    <p>Converts urea in urine to ammonia and carbon dioxide.</p> Signup and view all the answers

    Proteus mirabilis forms _______________________________________ colonies on MacConkey agar.

    <p>smooth, pale, or colourless</p> Signup and view all the answers

    What is the primary site of infection for Proteus mirabilis?

    <p>Urinary tract</p> Signup and view all the answers

    Proteus mirabilis is a lactose fermenter.

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

    Match the following characteristics of Proteus mirabilis with their descriptions:

    <p>Non-spore-forming = Does not produce spores Highly motile = Has a high degree of movement Oxidase -ve = Cannot oxidize Urease +ve = Produces the enzyme urease</p> Signup and view all the answers

    What is the result of the swarming motility of Proteus mirabilis in the urinary tract?

    <p>Aids in migration along catheter surfaces and ascends from the bladder to the kidneys, causing infections.</p> Signup and view all the answers

    Proteus mirabilis produces hydrogen sulphide (H2S), which reacts with iron to form a _______________________________________ precipitate.

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

    What is the consequence of the formation of struvite stones in the urinary tract?

    <p>All of the above</p> Signup and view all the answers

    What is the shape of Campylobacter spp.?

    <p>Long spiral-shaped rod</p> Signup and view all the answers

    Campylobacter spp. can use sugars oxidatively or fermentatively.

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

    Campylobacter spp. grow at a temperature of _______________.

    <p>42°C</p> Signup and view all the answers

    What is the purpose of the motility of Campylobacter spp.?

    <p>To burrow through the mucus layer</p> Signup and view all the answers

    Campylobacter spp. are a common cause of bacterial gastroenteritis worldwide.

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

    What is the primary source of Campylobacter spp. infection?

    <p>Foods like poultry and unpasteurised milk</p> Signup and view all the answers

    Campylobacter spp. possess a _______________ flagellum at one or both ends.

    <p>Single polar unsheathed</p> Signup and view all the answers

    What is the shape of Campylobacter bacteria under microscopy?

    <p>Comma-shaped</p> Signup and view all the answers

    Enterobacteriaceae grows in low oxygen and warmer temperatures.

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

    What is the result of the oxidase test for Campylobacter?

    <p>Oxidase +ve</p> Signup and view all the answers

    Campylobacter requires specialised media, such as _______________________ agar.

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

    Match the following characteristics with the corresponding bacteria:

    <p>Motile = Campylobacter Non-motile = Shigella Rod-shaped = Enterobacteriaceae Comma-shaped = Enterobacteriaceae</p> Signup and view all the answers

    Study Notes

    Proteus mirabilis

    • Gram-negative bacillus, widely distributed in soil and water, and part of the normal human intestinal flora
    • Causes urinary tract infections (UTIs)
    • Non-spore-forming and highly motile
    • Facultative anaerobic, non-lactose fermenter, and oxidase negative
    • Urease positive, producing urease enzyme

    Growth on Agar

    • Blood agar: Exhibits swarming growth, forming thin, filmy layers of concentric circles
    • MacConkey agar: Forms smooth, pale, or colorless colonies; does not swarm
    • Triple Sugar Iron (TSI) test: Produces hydrogen sulphide (H2S), which reacts with iron to form a black precipitate

    Virulence Factors

    • Flagella: Confer motility, aids in swarming motility on surfaces, particularly urinary catheters
    • Fimbriae: Used for attachment to uroepithelium cells
    • Hemolysin: Creates tiny holes in cell membranes, causing cell damage
    • ZapA protease: Destroys immunoglobulin A (IgA) and immunoglobulin G (IgG), neutralizing the immune system's opsonins
    • Urease: Converts urea in urine to ammonia and carbon dioxide, leading to the formation of struvite stones

    Pathogenesis in the Urinary Tract

    • Swarming motility aids in migration along catheter surfaces
    • Ascends from the bladder to the kidneys, causing infections
    • Struvite stones: Formed from phosphate, calcium, magnesium, and ammonium; can lead to staghorn renal calculi or kidney stones
    • Causes urinary stasis, promoting bacterial multiplication and urinary alkalinisation

    Infections Caused

    • Urethritis: Infection of the urethra
    • Cystitis: Infection of the bladder
    • Prostatitis: Infection of the prostate
    • Pyelonephritis: Infection of the kidneys
    • Struvite stones: May lead to xanthogranulomatous pyelonephritis, causing kidney destruction

    Risk Factors

    • Common in elderly hospitalised patients
    • Risk factors include urinary tract procedures (surgery, catheterisation), chronic kidney disease, neurogenic bladder, multiple prior UTIs, prior use of antibiotics, and sexual activity

    Symptoms

    • Urethritis: Dysuria (pain during urination), pyuria (pus in the urine), increased urinary frequency
    • Cystitis: Dysuria, urinary frequency, urgency, suprapubic pain, ammonia-smelling urine
    • Prostatitis: Similar to cystitis; may also include fever, chills, swollen and tender prostate
    • Pyelonephritis: Dysuria, urinary frequency, urgency, flank pain, fever, chills, nausea, vomiting

    Diagnosis

    • Urine culture: Identifies Proteus mirabilis
    • Urinalysis: Shows pyuria (WBCs in urine), bacteriuria, and urinary pH above 7
    • Complete blood count (CBC): Shows leucocytosis in pyelonephritis or prostatitis
    • X-ray: Struvite stones appear radiopaque

    Treatment

    • Cystitis: Trimethoprim-sulfamethoxazole (TMP-SMX), quinolones, or fosfomycin
    • Pyelonephritis: Fluoroquinolones, cephalosporins, or gentamicin
    • Struvite stones: Surgery may be required for removal

    Campylobacter spp.

    • Gram-negative, slender, curved, long spiral-shaped rods, may be coccoid in really old culture
    • Motile, with a single polar unsheathed flagellum at one or both ends
    • Non-spore former, oxidase positive, and microaerophilic and capnophilic
    • Grows at 42°C, adapted to chickens with higher body temperature
    • Unable to use sugars either oxidatively or fermentatively; derives energy from amino acids
    • Not grown on MAC or NA; grows on chocolate agar

    Uropathogenic E. coli (UPEC)

    • Colonization: UPEC can colonize the periurethral area and ascend the urinary tract
    • Adhesion and Invasion: Uses type 1 fimbriae and P fimbriae to adhere to uroepithelial cells
    • Invasion: Invades and replicates within bladder cells
    • Toxin Production: Produces alpha and beta hemolysins, causing lysis of urinary tract cells
    • Ascending Infection: Can ascend to the kidneys, causing flank pain and more severe symptoms

    Diagnosis

    • General Diagnosis: Gram staining, culture, and HUS diagnosis
    • HUS Diagnosis: Identifying Shiga toxin in the blood

    Treatment

    • Diarrhea: Hydration and rest, antibiotics in severe cases (e.g., doxycycline, cotrimoxazole)
    • Hemolytic Uremic Syndrome (HUS): Supportive care, dialysis, corticosteroids, blood transfusions, plasmapheresis
    • UTIs: Antibiotics, such as cotrimoxazole, nitrofurantoin, and fluoroquinolones (e.g., ciprofloxacin)

    Salmonella enterica

    • Gram-negative bacilli, motile, facultative anaerobe, and non-spore former
    • Encapsulated, can ferment glucose but not lactose, oxidase negative, and H2S positive
    • Frequently found in sewage, river, seawater, and certain food; pathogen of animals (poultry, cows, pigs)
    • O, H, Vi antigens, with Vi specific to Salmonella spp.
    • Virulence factors: Endotoxin, enterotoxin, and cytotoxin

    Symptoms and Complications

    • Symptoms last about seven days
    • Infected person can be a carrier for infection up to 4 weeks after the onset of symptoms
    • Typical Symptoms: Severe abdominal and rectal cramping and pain, high fever, vomiting, loss of appetite, and watery, mucus-like diarrhea, potentially containing blood or pus
    • Complications: Hemolytic Uremic Syndrome (HUS), tonic-clonic seizures, sepsis, and reactive arthritis

    Transmission

    • Fecal-oral transmission
    • Sources: Contaminated water or food, flies carrying stool particles, contact with contaminated objects or hands, and sexual contact (occasionally)

    Virulence and Survival

    • Extremely virulent, with as few as 10 bacteria able to cause an infection
    • Can survive the acidic environment of the stomach

    Diagnosis

    • Fecal Sample: Cultured on selective media like MacConkey agar
    • Stool Stains: Methylene blue may show polymorphonuclear leukocytes
    • PCR Testing: For direct identification of Shigella DNA

    Treatment

    • General Treatment: Fluid and electrolyte replenishment
    • Antibiotics: Beta-lactams (penicillins and cephalosporins), macrolides, and quinolones

    Escherichia coli Characteristics

    • Classified as Gram-negative bacilli, a type of bacteria
    • Motile, meaning they can move on their own
    • Facultative anaerobe, meaning they can thrive in both aerobic and anaerobic environments
    • Produces catalase enzyme, making it catalase-positive (+ve)
    • Ferments lactose, producing beta-galactosidase and breaking it down into glucose and galactose
    • Some strains have a capsule, making them encapsulated
    • Capable of reducing nitrate to nitrite
    • Can grow on basic, non-enriched media, such as:
      • Nutrient Agar (NA)
      • Peptone water (a water-soluble mixture of peptides and amino acids)
      • Nutrient broth
    • This ability to grow on non-enriched media helps differentiate E. coli from Campylobacter

    E. coli Pathotypes

    • E. coli pathotypes classified based on disease-causing mechanisms and virulence factors.

    Shiga-like Toxin-Producing E. coli (STEC)

    • Produces Shiga toxins, causing bloody diarrhea and hemolytic uremic syndrome (HUS).
    • Attaches to intestinal cells using fimbriae.
    • Toxins cause intestinal injury, inflammation, and blood leakage.
    • Systemic toxin release leads to HUS, characterized by:
      • Kidney damage and proteinuria
      • Inflammatory response and clot formation
      • Thrombocytopenia and hemolytic anemia
      • Ischemic kidney damage and uremia

    Enterotoxigenic E. coli (ETEC)

    • Produces heat-labile and heat-stable enterotoxins, causing watery diarrhea.
    • Uses fimbriae to adhere to intestinal mucosa.
    • Heat-labile toxin activates adenylate cyclase, increasing cAMP and chloride secretion.
    • Heat-stable toxin activates guanylate cyclase, increasing cGMP and electrolyte secretion.
    • Causes watery diarrhea without damaging the intestinal wall.

    Enteroinvasive E. coli (EIEC)

    • Attaches to and invades intestinal epithelial cells.
    • Invades and multiplies within epithelial cells, causing cell destruction.
    • Triggers a strong inflammatory response, leading to widespread epithelial damage and bloody diarrhea.

    Enteropathogenic E. coli (EPEC)

    • Uses bundle-forming pili to attach to intestinal epithelial cells.
    • Injects effector proteins, causing actin cytoskeleton rearrangement and pedestal formation.
    • Impairs absorption, causing watery diarrhea, primarily in children under two years old.

    Uropathogenic E. coli (UPEC)

    • Colonizes the periurethral area and ascends the urinary tract.
    • Uses type 1 fimbriae and P fimbriae to adhere to uroepithelial cells.
    • Invades and replicates within bladder cells.
    • Produces alpha and beta hemolysins, causing lysis of urinary tract cells.
    • Causes cystitis and pyelonephritis.

    Virulence Factors of E. coli

    • The capsule of E. coli is composed of polysialic acid and is referred to as the K antigen.
    • Fimbriae, also known as pili, are structures involved in the attachment of E. coli to host cells.
    • Flagella are responsible for the motility of E. coli and are associated with the H antigens.
    • Adhesins are a type of virulence factor that facilitate the adhesion of E. coli to host cells.
    • O antigens are a component of the lipopolysaccharide (LPS) layer of E. coli's outer membrane.
    • Lipid A is a toxic component of the LPS layer of E. coli.
    • Enterotoxins are exotoxins produced by E. coli that can cause gastrointestinal symptoms.
    • Haemolysins are exotoxins produced by E. coli that can lyse red blood cells.
    • Cytotoxic necrotising factor (CNF) is an exotoxin produced by E. coli that can cause cell death and tissue damage.

    Salmonella enterica Characteristics

    • Gram-negative bacilli, motile and facultative anaerobe
    • Non-spore former
    • Facultative intracellular pathogens, encapsulated
    • Ferments glucose but not lactose
    • Oxidase-negative and H2S-positive

    Habitat and Sources

    • Frequently found in sewage, river, seawater, and certain food
    • Pathogen of animals (poultry, cows, pigs), a common source of non-typhoidal Salmonella infections in humans

    Antigens

    • O, H, and Vi antigens
    • Vi antigen is specific to Salmonella spp., a capsular polysaccharide (only typhoidal strains)

    Virulence Factors

    • Endotoxin
    • Enterotoxin (Exo)
    • Cytotoxin (Exo)

    Salmonella Typhi Pathogenesis

    • Reaches the distal ileum of the small intestine after ingestion
    • Targets the epithelial layer of the mucosal lining
    • Adheres to and is phagocytosed by M cells, then spit into underlying Peyer's patches

    Immune Evasion

    • Vi capsular polysaccharide antigen protects against antibody tagging
    • Suppresses neutrophil recruitment
    • Induces recruitment of monocytes and macrophages
    • Can cause hypertrophy, necrosis, and potentially ileal perforation

    Survival and Replication

    • Phagocytosed by macrophages, forming a Salmonella-containing vacuole
    • Type III secretion system injects effector proteins, preventing vacuole-lysosome fusion
    • Survives and replicates within the vacuole

    Salmonella enterica subsp. enterica serovar Typhimurium

    • Salmonella enterica subsp. enterica has over 2,500 serotypes
    • Common serotypes include Salmonella enteritidis and typhimurium

    Pathogenesis

    • Ingestion: Salmonella reaches the distal ileum of the small intestine
    • Targeting: Adheres to and is phagocytosed by M cells in the epithelial layer of the mucosal lining
    • Further action: Spit into underlying Peyer's patches

    Immune Response

    • Strong pro-inflammatory cytokine response occurs
    • Immune cells (especially neutrophils) are recruited
    • Causes enterocolitis (inflammation of the small intestine and colon)
    • Can lead to mucosal damage and ulcers

    Potential Spread

    • Typically limited to the mucosa and destroyed by local immune cells
    • In some cases, can become invasive and cause bacteremia

    Shigella spp. General Information

    • Shigella spp. consists of four species: Shigella dysenteriae, Shigella flexneri, Shigella boydii, and Shigella sonnei.
    • All species can cause shigellosis, a contagious intestinal infection, which can progress to dysentery.

    Anatomy and Physiology

    • Shigella spp. are gram-negative bacilli.
    • They are facultative anaerobes, meaning they can survive with or without oxygen.
    • They are non-motile, lacking flagella.
    • They are non-spore forming and non-encapsulated.
    • They are non-lactose fermenters and urease and oxidase negative.
    • They do not produce H2S.

    Virulence Factors

    • Shigella spp. have an O antigen, which is a key virulence factor.
    • Shigella dysenteriae produces Shiga toxin, which can also be found in EHEC and causes bloody diarrhea.
    • Invasiveness is a key virulence factor, as virulent strains penetrate the mucosa and epithelial cells of the colon.

    Identification

    • Shigella spp. can be grown on selective media like MacConkey agar.
    • They form white, non-lactose fermenting, non-hydrogen sulfide-producing colonies.
    • Methylene blue staining of stool samples may show polymorphonuclear leukocytes.
    • PCR testing can be used for direct identification of Shigella DNA.

    Pathogenesis

    • Ingestion and initial infection: Shigella is ingested and multiplies in the small intestine before passing into the colon.
    • Targets epithelial cells of the mucosal lining, particularly M-cells.
    • Invasion and immune response: M-cells phagocytose Shigella, which then releases it into mucosa-associated lymphoid tissues (MALT).
    • Macrophages in MALT engulf Shigella, but Shigella induces apoptosis in macrophages.
    • Release of cytokines triggers intense inflammation, attracting more immune cells, damaging epithelial cells, and causing ulcerations and abscesses.
    • Spread within the host: Shigella disrupts cellular junctions, allowing it to enter enterocytes.
    • It uses a type III secretory system to inject proteins into enterocytes, inducing phagocytosis.
    • Inside enterocytes, Shigella escapes the phagosome into the cytoplasm, using actin-based motility to move and spread infection.
    • Shiga toxin: An AB toxin that binds to the host cell membrane, is engulfed into the phagosome, and then cleaves 28S rRNA in ribosomes, halting protein synthesis and causing cell death.
    • Can reach the bloodstream and cause hemolytic uremic syndrome (HUS).

    Proteus Mirabilis Overview

    • Gram-negative bacillus, widely distributed in soil and water, and part of the normal human intestinal flora.
    • Causes urinary tract infections (UTIs).

    Characteristics

    • Non-spore-forming and highly motile.
    • Facultative anaerobic, able to survive in both aerobic and anaerobic environments.
    • Non-lactose fermenter and oxidase negative.
    • Urease positive, producing urease enzyme.
    • Hydrogen sulfide (H2S) positive.

    Growth on Agar

    • Blood agar: Exhibits swarming growth, forming thin, filmy layers of concentric circles.
    • MacConkey agar: Forms smooth, pale, or colorless colonies, without swarming.
    • Triple Sugar Iron (TSI) test: Produces hydrogen sulfide (H2S), which reacts with iron to form a black precipitate.

    Virulence Factors

    • Flagella: Confer motility, aiding in swarming motility on surfaces, particularly urinary catheters.
    • Fimbriae: Tiny projections used for attachment to uroepithelium cells.
    • Hemolysin: Creates tiny holes in cell membranes, causing cell damage.
    • ZapA protease: Destroys immunoglobulin A (IgA) and immunoglobulin G (IgG), neutralizing the immune system's opsonins.
    • Urease: Converts urea in urine to ammonia and carbon dioxide, leading to the formation of struvite stones.

    Pathogenesis in the Urinary Tract

    • Swarming motility aids in migration along catheter surfaces.
    • Ascends from the bladder to the kidneys, causing infections.
    • Struvite stones: Formed from phosphate, calcium, magnesium, and ammonium, can lead to staghorn renal calculi or kidney stones.
    • Causes urinary stasis, promoting bacterial multiplication and urinary alkalinization.

    Diagnosis

    • Urine culture: Identifies Proteus mirabilis.
    • Urinalysis: Shows pyuria (WBCs in urine), bacteriuria, and urinary pH above 7.
    • Complete blood count (CBC): Shows leucocytosis in pyelonephritis or prostatitis.
    • X-ray: Struvite stones appear radiopaque.

    Campylobacter spp. Characteristics

    • Gram-negative, slender, curved, and spiral-shaped rods that may appear coccoid in older cultures.
    • Motile due to single polar unsheathed flagellum at one or both ends.
    • Non-spore forming and oxidase positive, using oxygen to create ATP.
    • Microaerophilic and capnophilic, requiring reduced oxygen and increased CO2 for growth.

    Growth and Culture

    • Grows at 42°C, adapted to high body temperature of chickens.
    • Unable to use sugars oxidatively or fermentatively, and derives energy from amino acids.
    • Does not grow on MAC or NA, but grows on chocolate agar.

    Virulence Factors

    • Motility allows for burrowing through the mucus layer.
    • Heat-labile enterotoxin is a virulence factor.

    Epidemiology

    • One of the most common causes of bacterial gastroenteritis worldwide.
    • Commonly found in foods like poultry and unpasteurized milk.

    Diagnosis and Identification

    • Grows on blood agar varieties like Skirrow, Butzler, and Campy-BAP.
    • Stool sample examination reveals Gram-negative, comma-shaped bacteria and presence of white and red blood cells.

    Pathogenesis and Virulence Factors

    • Uses fimbri-like filaments and cell surface proteins like PEV-1 and CADF for attachment to mucosa.
    • Invades mucosa using spiral shape and long flagella, releasing cytotoxins like cytolethal distending toxins (CDT), causing cell damage and inflammation.

    Distinguishing Campylobacter from Enterobacteriaceae

    • Campylobacter has a comma-shaped morphology, differing from the rod-shaped Enterobacteriaceae.
    • Campylobacter exhibits motility, distinguishing it from non-motile Shigella.

    Incubation Conditions

    • Campylobacter requires low oxygen and warmer temperatures for growth.
    • Enterobacteriaceae do not have specific growth requirements.

    Growth Requirements

    • Campylobacter requires specialized media, such as chocolate agar, for growth.
    • Enterobacteriaceae can grow on a wider range of media.

    Oxidase Test

    • Campylobacter is oxidase positive (oxidase +ve).
    • Enterobacteriaceae are oxidase negative (oxidase -ve).

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    This quiz tests your knowledge of H2S producing bacteria, its growth on different agar, and its virulence factors.

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