Enterobacteriaceae Overview

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Questions and Answers

What life-threatening complication may arise from E.coli infections due to verotoxin?

Haemolytic Uraemic Syndrome (correct)

Meningitis

Respiratory failure

Septicemia

Why are antibiotics not recommended for treating E.coli infections caused by strain O157:H7?

They increase the risk of haemolytic uremic syndrome (correct)

They can worsen diarrhea symptoms

They promote the growth of E.coli

They have no effect on the bacteria

What color do E.coli colonies turn on MacConkey’s agar due to lactose fermentation?

Blue

Green

Yellow

Rose pink (correct)

What is a characteristic of Klebsiella pneumoniae?

Non-motile with a large polysaccharide capsule Signup and view all the answers

Which test is used for serology of Klebsiella pneumoniae?

Slide agglutination test Signup and view all the answers

What is the result of the IMVC test for Klebsiella pneumoniae?

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What is a common feature of Salmonella compared to other bacteria?

Motile with peritrichous flagella Signup and view all the answers

What diagnostic result is expected for E.coli on TSI medium?

Yellow slant and yellow butt Signup and view all the answers

What is the primary mode of transmission for Enterohaemorrhagic E. coli (EHEC)?

Faeco-oral route Signup and view all the answers

Which toxin produced by Enterotoxigenic E. coli (ETEC) stimulates the secretion of fluids to the gut lumen?

Heat-stable toxin (ST) Signup and view all the answers

What is the characteristic effect of Enteropathogenic E. coli (EPEC) infection on intestinal cells?

Destruction of intestinal microvilli Signup and view all the answers

What type of diarrhea is associated with Enteroinvasive E. coli (EIEC)?

Dysentery-like diarrhea Signup and view all the answers

What is the primary virulence factor for Enteroaggregative E. coli (EAggEC)?

Pili for adherence Signup and view all the answers

Which E. coli strain is specifically known for causing hemorrhagic colitis?

Enterohaemorrhagic (EHEC) Signup and view all the answers

What is the role of the heat-labile toxin (LT) produced by Enterotoxigenic E. coli (ETEC)?

Cause watery diarrhea by increasing cAMP Signup and view all the answers

Which of the following groups is most likely to suffer persistent diarrhea from Enteroaggregative E. coli (EAggEC)?

Children and HIV patients Signup and view all the answers

What is a common characteristic of Enterobacteriaceae?

They ferment glucose but have varying fermentation of other sugars. Signup and view all the answers

Which of the following genera in Enterobacteriaceae are known to be pathogenic?

Salmonella and Shigella Signup and view all the answers

What is the significance of LPS in Enterobacteriaceae?

It acts as an endotoxin released after bacterial cell death. Signup and view all the answers

E. coli is primarily known for its role in which disease?

Urinary Tract Infection Signup and view all the answers

Which type of E. coli is known for producing enterotoxins?

Enterotoxigenic E. coli Signup and view all the answers

Which of the following is NOT a characteristic of non-lactose fermenters in Enterobacteriaceae?

Ferment lactose abundantly. Signup and view all the answers

What virulence factor is primarily responsible for E. coli adherence to mucosal surfaces?

Pili Signup and view all the answers

How is E. coli primarily transmitted to cause urinary tract infections?

From its own fecal flora to the urethra. Signup and view all the answers

What is the primary mode of transmission for typhoid fever?

Fecal-oral route Signup and view all the answers

Which group is more commonly affected by typhoid fever?

Children and young adults Signup and view all the answers

Which of the following is a nontyphoidal serotype of Salmonella commonly associated with foodborne gastroenteritis?

S.enteritidis Signup and view all the answers

What is the incubation period for typhoid fever?

5-21 days Signup and view all the answers

What characterizes the systemic disease of typhoid fever?

Life-threatening systemic disease with multiple organ involvement Signup and view all the answers

Which symptom is commonly associated with typhoid fever?

Abdominal symptoms Signup and view all the answers

What type of carriers are primarily responsible for the transmission of Salmonella after recovery?

Gall bladder and urinary carriers Signup and view all the answers

Which of the following is NOT a complication of typhoid fever?

Chronic fatigue syndrome Signup and view all the answers

What type of colonies are observed on Bismuth sulphite agar for Enteric Fever diagnosis?

Brown to black colonies Signup and view all the answers

Which organism demonstrates H2S production in sugar fermentation tests?

S. Paratyphi B Signup and view all the answers

In which week does the Widal test become significant for detecting antibodies in the serum?

Second week Signup and view all the answers

What does a high titre of O and H antibodies (>1/160) indicate?

Recent active infection Signup and view all the answers

What is one reason the Widal test may yield false negative results during the first week?

Antibodies are not present yet Signup and view all the answers

Which of the following vaccines contains live attenuated bacteria?

Oral living attenuated typhoid vaccine (Vivotif) Signup and view all the answers

What type of agar shows pale yellow non-lactose fermenting colonies for Enteric Fever culture?

MacConkey's agar Signup and view all the answers

What should be expected when using tetrathionate broth for Enteric Fever diagnosis?

Inhibition of E. coli growth Signup and view all the answers

Study Notes

General Characteristics of Enterobacteriaceae

Gram-negative bacilli, primarily normal commensals in the colon.
Includes pathogenic genera (e.g., Salmonella, Shigella) and commensals (e.g., E. coli, Klebsiella).
Facultative anaerobes capable of fermenting glucose; other sugar fermentations vary.
Oxidase negative and reduce nitrates to nitrites.
Features lipopolysaccharides (LPS) in cell walls; LPS can cause septic shock upon bacterial death.
Can cause intestinal and extraintestinal diseases, depending on the genus.
Antigenic composition: somatic (O) antigen, flagellar (H) antigen, and capsular (K) antigen present in varying degrees.

Classification of Enterobacteriaceae

Divided into lactose fermenters (e.g., E. coli, Klebsiella) and non-lactose fermenters (e.g., Salmonella, Shigella).
Lactose fermenters create rose-pink colonies on MacConkey agar; non-lactose fermenters display pale yellow colonies.

E. coli

Normal intestinal inhabitants; some strains are pathogenic.
Morphology: Gram-negative bacilli, motile, some encapsulated.
Virulence factors include:
- Pili for mucosal adherence.
- K antigen, which is antiphagocytic.
- LPS as an endotoxin causing fever and shock.
- Two enterotoxins (heat labile LT and heat stable ST) from enterotoxigenic strains.
- Verotoxin from enterohaemorrhagic strains.

Diseases Associated with E. coli

Extraintestinal Diseases:
- Most common cause of urinary tract infections (UTIs); colonizes vaginal and periurethral areas.
- Nosocomial infections are frequently associated with urinary catheterization.
- Neonatal septicemia and meningitis.
Intestinal Diseases (Gastroenteritis):
- Diarrhea types include watery (ETEC, EPEC) and bloody (EIEC, EHEC).
- Transmission primarily through the fecal-oral route.

Specific E. coli Pathotypes

Enterotoxigenic E. coli (ETEC):
- Causes traveler's diarrhea; produces profuse watery diarrhea through LT and ST toxins.
Enteropathogenic E. coli (EPEC):
- Causes infantile diarrhea; adheres to intestinal mucosa and affects absorption.
Enteroinvasive E. coli (EIEC):
- Causes dysentery-like diarrhea; invades the colonic mucosa leading to bloody diarrhea.
Enteroaggregative E. coli (EAggEC):
- Causes persistent diarrhea in children and HIV patients with patchy adherence to the intestinal mucosa.
Enterohaemorrhagic E. coli (EHEC O157:H7):
- Causes hemorrhagic colitis; linked to undercooked hamburgers; complications can include hemolytic uremic syndrome.

Diagnosis of E. coli Infections

Sample type depends on infection site (e.g., stool, urine).
Gram stain shows motile, Gram-negative bacilli.
Culture on MacConkey agar yields rose-pink colonies; E. coli also ferments multiple sugars.
IMVC testing typically results in positive Indole, Methyl Red, and negative Voges-Proskauer and Citrate Utilization.

Treatment for E. coli Infections

Rehydration is critical for traveler's diarrhea; trimethoprim-sulfamethoxazole may be beneficial.
Antibiotics given for diarrhea with fever, blood, or pus; careful consideration for O157:H7, where antibiotics may worsen the condition.

Klebsiella pneumoniae

Causes lobar pneumonia, UTIs (often nosocomial), and septicemia in immunocompromised patients.
Morphological traits include Gram-negative bacilli, non-motile, and a large polysaccharide capsule.
Culture characteristics show rose-pink colonies on MacConkey agar; mucoid colonies on EMB agar due to extracellular slime.

Salmonella

Morphology: Gram-negative bacilli with peritrichous flagella, non-capsulated.
Common species include Salmonella enterica, which has numerous serotypes, notably those causing typhoid (e.g. S. Typhi) and nontyphoidal gastroenteritis (e.g. S. enteritidis, S. typhimurium).

Typhoid Fever (Enteric Fever)

Characterized by severe systemic illness due to bacteria in the bloodstream.
Symptoms include chills, fever, headache, and abdominal pain; can lead to complications like intestinal hemorrhage.
Mode of transmission is fecal-oral; primarily from human carriers.
Chronic carriers can excrete the pathogen intermittently.

Diagnosis of Enteric Fever

Blood culture in the first week identifies the organism.
Subsequent analysis includes stool and urine samples, revealing specific culture characteristics and H2S production.
Serological tests (e.g., Widal test) assess antibody levels in response to infection.

Vaccines for Typhoid Fever

TAB vaccine: heat-killed vaccine targeting S. Typhi and S. Paratyphi.
Oral typhoid vaccine (Vivotif) is a live attenuated option.
Inactivated single-dose Vi polysaccharide vaccine available as well.

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Description

This quiz covers the general characteristics of the Enterobacteriaceae family, which includes important genera like Salmonella, Shigella, E. coli, and Klebsiella. You will learn about their gram-negative properties, metabolic functions, and ecological roles as either pathogens or commensals.