13: Enterobacteria

Question 1

Enterobacteria identification based on specialized media

Answer 1

Faculative anaerobes
-glucose fermentation (Lactose fermenter)
-oxidase negative
enterobacteria = red = MacConkey’s Agar
enterobacteria = pink = …

Question 2

Salmonella
-gram -/+
-flagella?
-w/ or w/o O2?
- identification based on specialized media

Answer 2

-ONLY Zoonotic = non-typhyoidal
-Gram (-)
-flagella
-H2S
-Facultative anaerobe
-glucose fermenter
-lactose NON-fermenter

Serovar Typhi found in humans and causes typhoid fever

Question 3

Salomonella Pathogenesis

Answer 3

Infects effector proteins into M cells and intestinal epithelial cells leading to efflux of water and electrolytes (Diarrhea)

-bacteremia: if salmonella penetrates tissue below the epithelium where it’ll have access to the blood stream
-inflammatory response: if salmonella is phagocytized by macrophages

Question 4

NON-TYPHOIDAL SALMONELLA GASTROENTERITIS
Symptoms

Answer 4

-Symptoms develop 12 to 72 hours post-exposure
-nausea and omitting
-abdominal pain/cramping
-diarrhea

Non-typhoidal Salmonella gastroenteritis is an infection caused by strains of Salmonella bacteria other than Salmonella Typhi and Salmonella Paratyphi. These bacteria are primarily associated with foodborne illnesses and are often linked to contaminated poultry, eggs, dairy products, and occasionally fruits and vegetables

Question 5

Salmonellosis
-diagnosis
-treatment

Answer 5

diagnosis
-isolation from feces or blood on selective agar (that inhibits the growth of gram (+) bacteria)

treatment
-Most patients recover w/o antibiotics
-rehydration with fluids and electrolytes
-antibiotics for those at risk for complications- ceftriaxone

Question 6

S.enterica serovar Typhi epidemiology

Answer 6

-Humans are the only reservoir
-contaminated water or food VIA FECAL-ORAL ROUTE

Salmonella enterica serovar Typhi (commonly referred to as S. Typhi) is a specific serovar of Salmonella enterica that causes typhoid fever. This bacterial infection is different from nontyphoidal Salmonella infections (which cause gastroenteritis) because S. Typhi targets the human body systemically, causing prolonged fever and, in severe cases, potentially life-threatening complications.

Question 7

S.enterica serovar Typhi pathogenesis

Answer 7

Typhi follows the same invasion and damage of M cells and epithelial cells as non-typhoidal salmonella.
Induces recruitment of dendritic cells and macrophages instead of inflammatory response

SYSTEMIC DISEASE
-LPS endotoxin induces fever

Pathogenesis chart page 14
-Upon ingestion, S. Typhi bacteria invade the small intestine and enter the bloodstream, disseminating to various organs like the liver, spleen, and bone marrow.
-The bacteria are phagocytosed by macrophages and can survive inside these immune cells, allowing them to spread systemically.
=septicemia
=cholecystitis and carrier state
=diarrhea, hemorrhage, perforation (ulceration/inflammation of Peyer pataches)

Question 8

Typhoid fever treatment

Answer 8

-Ceftriaxone for severe disease
-Ciprofloxacin for uncomplicated enteric fever

Salmonella enterica serovar Typhi (commonly referred to as S. Typhi) is a specific serovar of Salmonella enterica that causes typhoid fever. This bacterial infection is different from nontyphoidal Salmonella infections (which cause gastroenteritis) because S. Typhi targets the human body systemically, causing prolonged fever

Question 9

Which shigella species are common in the U.S.

Answer 9

-S. Flexneri
-S. Sonnei’

S.dysenteriae = more virulent - bacillary dysentery
S. Boydii

Question 10

Shigella Morphology and identification based on specialized media

Answer 10

-gram (-)
-faculative anaerobe
-non-motile
-does NOT ferment lactose
- H2S negative
-ID50 is very low

Question 11

Who are the only reservoirs from shigella?

Answer 11

Humans
-transmission by fecal-oral route

Outbreaks commonly occur in daycares, nursing homes, hospitals/mental institutions

Question 12

Shigellosis pathogenesis

Answer 12

it begins to invade the epithelial cells lining the intestinal mucosa, particularly the colonic mucosa.
The bacteria target M cells (microfold cells) in the Peyer’s patches of the gut, which play a role in sampling antigens and pathogens from the gut lumen.
After being translocated by M cells, Shigella is taken up by macrophages in the underlying tissue, but instead of being killed, the bacteria induce apoptosis in these macrophages, ** leading to inflammatory response.

cell-to-cell spread via actin tail
Create ulcers, bleeding, necrosis of colonic mucosa

Question 13

Shigellosis clinical manifestations

Answer 13

Symptoms developed 24-72 hours

Clinical Manifestations
Watery diarrhea: Early in the infection, watery diarrhea occurs due to the inflammation in the small intestine and colon.
Dysentery: As the bacteria spread and destroy epithelial cells, diarrhea becomes more severe and is accompanied by blood, pus, and mucus due to the destruction of the colonic epithelium. (B/c of Enterotoxin)
Fever, malaise, anorexia, abdominal pain, and tenesmus: These symptoms are common, with the constant urge to defecate being a hallmark of shigellosis.

-complications = rectal prolapse

Question 14

Shigella
-diagnosis
-treatment

Answer 14

Diagnosis
-Stool culture is the gold standard for diagnosing shigellosis.
(Will find RBC and WBC)

Treatment
-self-limiting
-rehydration with fluids and electrolytes
-antibiotics are rarely given, ciprofloxacin for severe disease

Question 15

Which are the strains of E.coli that cause gastroenteritis in humans? (5 strains)

Answer 15

The strains that cause gastroenteritis in humans are not the same as the E.coli strains in the normal human gut flora.

EHEC - Hemorrhagic colitis
ETEC - Traveler’s diarrhea
EIEC - gastroenteritis
EPEC - gastroenteritis in children
EAEC - persistent diarrhea in children

Question 16

E.Coli Morphology/physiology and identification based on specialized media

Answer 16

-Gram (-) rod
-All have fimbriae, some have flagella (H antigen)
-Lactose fermentation w/ acid (+)
-sorbitol fermentation w/ acid (+)
EXCEPT for EHEC which is acid (-)
-H2S (-) = helps distinguish b/w E.coli and Salmonella
Facultative anaerobe

Question 17

Enterotoxigenic E.coli (ETEC)
-referred to what?
-produces what enterotoxin

Answer 17

Travelers diarrhea

Causes diarrhea in infants and travelers in regions of poor sanitation.

Produces 2 enterotoxins
-LT - heat- labile toxin (destroyed by heating/cooking)
-ST - heat-stable toxin (remains stables after heating/cooking)

Question 18

Enteroinvasive E.coli (EIEC)
-referred to what
-symptoms
-pathogenesis

Answer 18

Gastroenteritis

Blood and pus in stool with fever (bloody diarrhea) = Diarrhea results from cell death due to growth of bacteria w/n the cells

Similar to shigella, these bacteria can spread directly from cell-to-cell through actin polymerization

Question 19

Enteropathogenic E.coli (EPEC)
-referred to as
-symptoms
-pathogenesis

Answer 19

Epidemic infantile diarrhea
Produces a profuse watery diarrhea containing mucus (NON-bloody) w/ vomiting and fever
=Diarrhea due to cellular invasion and cell death

Causes alteration of cellular structures similar to EHEC pedestal formation

Question 20

Enteroaggregative E.coli (EAEC)
-referred to as
-symptoms
-pathogenesis

Answer 20

Acute diarrhea in healthy individuals

Persistent/chronic diarrhea in young children and AIDS patient (especially malnourished)

Persistent watery NON-bloody diarrhea (>14 days in duration) due to formation of a thick mucus-bacteria biofilm

Colonize in aggregates

Question 21

Which E.COLI strain invades and multiplies within the epithelial cells of the colon, leading to cell death and inflammation. It causes tissue damage and disrupts the intestinal lining by escaping the vacuole and spreading intracellularly.

Answer 21

EIEC (Enteroinvasive E.coli)

SIMILAR TO SHIGELLA

Causes dysentery-like symptoms, including bloody diarrhea, severe abdominal cramps, and fever. EIEC typically causes invasive inflammatory diarrhea, similar to shigellosis.

Target: LI (COLON)

Question 22

Which E.COLI strain produces two types of toxins: heat-labile toxin (LT), which activates adenylate cyclase, increasing cAMP levels, and heat-stable toxin (ST), which activates guanylate cyclase, increasing cGMP. These toxins disrupt ion transport in intestinal cells, leading to increased water and electrolyte secretion.

Answer 22

Enterotoxigenic E. coli (ETEC)

ETEC is the most common cause of traveler’s diarrhea and childhood diarrhea in developing countries. It causes watery diarrhea without blood, along with nausea, vomiting, and abdominal cramping.

Question 23

Which E.COLI strain produces two types of toxins: heat-labile toxin (LT), which activates adenylate cyclase, increasing cAMP levels, and heat-stable toxin (ST), which activates guanylate cyclase, increasing cGMP. These toxins disrupt ion transport in intestinal cells, leading to increased water and electrolyte secretion.

Answer 23

Enterotoxigenic E. coli (ETEC)

ETEC is the most common cause of traveler’s diarrhea and childhood diarrhea in developing countries. It causes watery diarrhea without blood, along with nausea, vomiting, and abdominal cramping.

Question 24

Which E.COLI strain causes non-bloody watery diarrhea, primarily in infants and young children in developing countries.

Answer 24

Enteropathogenic E. coli (EPEC)
EPEC - gastroenteritis in children

Causes non-bloody watery diarrhea, primarily in infants and young children in developing countries. The diarrhea can be prolonged and accompanied by vomiting and fever.

Question 25

Which E.COLI strain forms biofilm-like aggregations on the surface of the intestinal mucosa. It adheres to the intestinal epithelium in a “stacked-brick” pattern, mediated by aggregative adherence fimbriae (AAF).

Answer 25

Enteroaggregative E. coli (EAEC)

Typically associated with persistent diarrhea, especially in children and immunocompromised individuals. The diarrhea is often watery, and may be accompanied by mucus, low-grade fever, and abdominal pain.