Enterohemorrhagic E. coli (EHEC) Infections

E. coli O157:H7

Primary strain of EHEC

Hemorrhagic diarrhea

Significant clinical manifestation of EHEC infections

Colitis

Significant clinical manifestation of EHEC infections

Hemolytic uremic syndrome (HUS)

Severe complication that can develop from EHEC infections, characterized by low platelet count, hemolytic anemia, and kidney failure

Contaminated food

Primary mode of transmission for EHEC infection to humans

Stool appearance

In EHEC infection, stool contains no leukocytes

Fever

Characteristic of fever in patients with EHEC infection is low grade fever or absence of fever

Abdominal cramps

Common symptom associated with EHEC infection

Watery diarrhea

Common symptom associated with EHEC infection

Bloody diarrhea

Common symptom associated with EHEC infection

Stool culture

Laboratory diagnosis method for EHEC involving highly differential media and serotyping

Verotoxin

To diagnose EHEC, detect this in stool filtrates

Verotoxin-neutralizing antibody titer

Laboratory diagnosis method for EHEC involving demonstrating a fourfold or greater increase in this titer

Laboratory Diagnosis EHEC

Stool culture on highly differential media, followed by serotyping
Detecting the verotoxin in stool filtrates
• Demonstration of fourfold or greater increase in verotoxin-neutralizing antibody titer

What type of culture media is typically used for detecting EHEC in stool samples?

SMAC (Sorbitol MacConkey) plates may be used instead of traditional MAC (MacConkey agar containing lactose).

What do traditional MAC contain

MacConkey agar containing lactose).

How does the use of SMAC plates aid in the identification of E. coli O157?

E. coli O157:H7 cannot ferment sorbitol, allowing for its differentiation from other E. coli strains.

What two specific serological tests are used for identifying E. coli O157;H7in clinical settings?

ELISA test for O157:7 antigen and latex agglutination test for O157;H7 antigen.

Waht test can verotoxin be detected in stool samples of suspected EHEC cases?

ELISA tests designed for Shiga toxin

How is verotoxin similar with a toxin produced by Shigella species?

Verotoxin is structurally identical to Shiga toxin.

Who and Where is Enterotoxigenic E. coli (ETEC) commonly associated with causing diarrhea?

ETEC is associated with diarrhea in adults and children in tropical and subtropical climates

What is one of the major causes of infant bacterial diarrhea in developing countries?

ETEC

What is the primary cause of traveler's diarrhea in Western industrialized nations, including the US?

ETEC

How does ETEC primarily spread to cause infection?

ETEC spreads via consumption of contaminated food and water.

What characteristic regarding infective dose is notable for ETEC infections in immunocompetent hosts?

A high infective dose is needed to cause disease in immunocompetent hosts.

What are the typical symptoms of Enterotoxigenic E. coli (ETEC) infection?

AWatery diarrhea, abdominal cramps, and sometimes nausea.

How would you describe the disease severity of ETEC?

ETEC causes mild, self-limiting disease.

Are vomiting and fever common symptoms in ETEC infections?

No, vomiting and fever are rare in ETEC infections.

How is ETEC primarily diagnosed in clinical settings?

Diagnosis is primarily made by the presence of lactose-fermenting organisms on differential media and characteristic symptoms.

What additional testing may be performed in reference laboratories to confirm ETEC infection?

Testing for toxins or colonizing factors may be conducted.And Molecular testing for fecal specimens is in development

Which E. coli straine produces dysentery

EIEC (Enteroinvasive E. coli

What is the primary pathogenic mechanism of Enteroinvasive E. coli (EIEC)?

EIEC produces dysentery by directly penetrating, invading, and destroying the intestinal mucosa.

How does Enteroinvasive E. coli (EIEC) typically spread to cause infection?

Infection occurs via the fecal-oral route.

EIEC Clinical Presentation

Fever

Severe abdominal cramps

Malaise

Watery diarrhea

Which E Coli strain does not ferment sorbitol?

EHEC

EHEC may develop into

hemolytic uremic syndrome (HUS),

hemolytic uremic syndrome (HUS) is associated with what

low platelet count, hemolytic anemia, and kidney failure

How common is Enteroinvasive E. coli (EIEC) in the US and other developed countries?

EIEC is rare in the US and other developed countries.

With which age group is Enteropathogenic E. coli (EPEC) primarily associated?

Infants, causing infantile diarrhea.

Where have outbreaks of EPEC been documented?

Hospital nurseries and daycare centers.

EPEC Clinical Presentation

Low-grade fever,
-malaise,
-vomiting,
-diarrhea with large amounts of mucus but no blood

How is EPEC primarily diagnosed

Based on clinical symptoms.•
Serological typing of O/H antigens

What serological tests are used for diagnosing EPEC, and for what purpose are they typically performed?

• Serological typing of O/H antigens

What are the two kinds of human diseases associated with Enteroadherent or Enteroaggregative E. coli (EAEC)?

Diarrheal syndromes and urinary tract infections (UTIs).

In which populations are uropathogenic strains of EAEC particularly associated with cystitis and acute pyelonephritis?

Cystitis in children and acute pyelonephritis in pregnant women.

EAEC Clinical Presentation

Watery diarrhea

• Vomiting

• Dehydration

• Occasionally abdominal pain

What specific patient group in developed countries has been associated with EAEC-related diarrhea?

HIV patients.

EHEC

Enterohemorrhagic E. coli

ETEC

Enterotoxigenic E. coli

EIEC

Enteroinvasive E. coli

EPEC

Enteropathogenic E. coli

EAEC

Enteroaggregative E. coli

What symptoms does a patient with typhoid fever develop during the first week of the disease?

During the first week, a patient with typhoid fever develops fever accompanied by malaise, anorexia, lethargy, myalgia, and a continuous dull headache.

Describe the initial invasion process of the typhoid fever organism in the body.

The organism first invades the intestinal mucosa, then gains access to the lymphatic system.he organism reaches the bloodstream and spreads to the liver, bone marrow, and spleen, where it is re-dispersed into the blood and continues to disseminate throughout the body.

What happens to a patient during the second and third weeks of typhoid fever infection?

During the second and third weeks of infection, the patient experiences sustained fever with prolonged bacteremia.

Which organs does the typhoid fever organism invade during the later stages of infection?

The organism invades the gallbladder and Peyer's patches, as well as the intestinal tract via the biliary tract.

How is typhoid fever diagnosed during the first week of infection?

During the first week, typhoid fever is diagnosed by isolating the organism in the bloodstream.

How is typhoid fever diagnosed during the second and third weeks of infection?

isolating the organism from stool samples.

What antimicrobial agents are commonly used to treat typhoid fever?

Quinolones, chloramphenicol, and advanced generation cephalosporins are commonly used to treat typhoid fever.

What organism causes typhoid fever?

Typhoid fever is caused by Salmonella typhi.

What organisms cause paratyphoid fevers?

Paratyphoid fevers are caused by Salmonella paratyphi A, B, or C.

What are the main symptoms of enteric fevers?

prolonged fever, bacteremia, involvement of the reticuloendothelial system (RES) (liver, spleen, intestines, and mesentery), and dissemination to multiple organs.

What type of Salmonella causes bacteremia and extraintestinal infections?

Non-typhoidal Salmonella causes bacteremia and extraintestinal infections.

What is the clinical presentation of non-typhoidal Salmonella bacteremia in general?

The clinical presentation includes prolonged fever and intermittent bacteremia.

What is the recommended treatment for bacteremia and extraintestinal infections caused by non-typhoidal Salmonella?

The recommended treatment is an antimicrobial drug regimen, often involving third generation cephalosporins.

What causes gastroenteritis and diarrhea?

Gastroenteritis and diarrhea are caused by a variety of serotypes.

How are gastroenteritis and diarrhea transmitted?

They are transmitted by ingestion of contaminated food and water.

How long do most cases of gastroenteritis and diarrhea last?

Most cases are self-limiting and resolve within a few days with no complications

What is the primary treatment for gastroenteritis and diarrhea?

The primary treatment is supportive care and rehydration.

Salmonella Virulence factors

Resistant to stomach acids and phagocytosis

• Able to adhere and invade mucosal cells

• Produces enterotoxins

Salmonella Infections

Gastroenteritis & Diarrhea

• Bacteremia and Extraintestinal Infections

• Enteric Fever Called “Typhoid Fever” or “Typhoid”

Yersinia enterocolitica Culture Characteristics:

Optimal growth at 25-30º C

What is the optimal growth temperature range for Yersinia enterocolitica?

is 25-30º C

Which selective agar plates are best for growing Yersinia enterocolitica?

Yersinia Selective Agar (YSA) and CIN agar are best for growing Yersinia enterocolitica.

Is Yersinia enterocolitica a lactose-fermenting organism?

No, Yersinia enterocolitica is a non-lactose fermenting organism.

Describe the motility characteristics of Yersinia enterocolitica.

is motile at 25ºC and non-motile at 37ºC.

Is Yersinia enterocolitica urease positive or negative?

Yersinia enterocolitica is urease positive.

What test is done on Yersinia enterocolitica

Yersinia pestis Gram stain

• Gram negative, short plump bacilli that exhibit bipolar staining – described as “safety-pin” appearance

Yersinia pestis Culture

Typically not performed, due to highly virulent nature of organism

Yersinia pestis Biochemical Testing

not performed due to virulent nature of organism and low level of metabolic activity

Yersinia pestis Unique feature

organism is motile at 25oC and non-motile at 37oC

Yersinia pestis Serological Testing

Immunoassays performed on serum or biopsy tissue sample

Yersinia pestis Virulence Factor

Potent endotoxins and exotoxins

Production of antiphagocytic capsule

Production of enzymes such as coagulase and fibrinolysin

Yersinia pestis Three presentations in humans

Bubonic • Septicemic • Pneumonic

Yersinia pestis Bubonic Form symptoms

“Black Death” - Killed 14 million in the 14th century

Clinical symptoms include high fever and painful swollen regional lymph nodes (known as buboes)

Yersinia pestis Pneumonic Plague Clinical Presentation

Occurs secondary to bubonic or septicemic presentation when organism proliferates and spreads into respiratory system

Can occur as primary infection if bacteria are inhaled

Which polyvalent antisera groups are used for preliminary serotyping of Salmonella?

Polyvalent antisera for groups A, B, C1, C2, D, E, and Vi are used.

Which capsular antigen is specific to Salmonella typhi?

The Vi capsular antigen

Where is H antigen typing for Salmonella typically performed?

H antigen typing is typically performed at reference laboratories.

Salmonella Laboratory Diagnosis

TSI: K/A, H2S+ • Key feature to distinguish from Shigella

Motility+ Key feature to distinguish from Shigella

Indole -

MR +/ VP

Salmonella TSI

K/A, H2S+

Salmonella Motility

+

Salmonella Indole

Neg

Salmonella MR/VP

MR pos

Salmonella

Salmonella on HE/XLD/SS:

Medium/large non-lactose fermenting colonies that produce black pigment (H2S)

Salmonella on MAC

Medium/large non-lactose fermenting colonies

Salmonella on BAP

Large, gray, non-hemolytic colonies

Shigella Treatment

Oral rehydration

Antimicrobial drug therapy may limit clinical course of infection