Is E coli (Escherichia coli) O157:H7 a variant of E coli (Escherichia coli) O157?

E. coli O157:H7 and E. coli O157 Relationship

Yes, E. coli O157:H7 is a specific variant of E. coli O157, distinguished by its H7 flagellar antigen. 1, 2

Serotyping Classification System

E. coli serotypes are named according to their somatic (O) and flagellar (H) antigens:

• The "O157" designation refers to the specific somatic (O) antigen on the bacterial cell surface
• The "H7" designation identifies the specific flagellar (H) antigen 1

E. coli O157 Family

• E. coli O157:H7 is the most clinically significant and well-studied member of the O157 serogroup
• Other variants within the O157 group include:
  • E. coli O157:NM (non-motile strains that do not express the H antigen) 1, 3
  • These non-motile strains can still produce Shiga toxins and cause disease 3

Clinical Significance

• E. coli O157:H7 is the most frequently isolated diarrheagenic type of E. coli in North America 4
• It is responsible for approximately 73,000 cases annually in the United States 2
• The infectious dose is very low (<100 organisms) 2
• It can cause:
  • Diarrhea (bloody and non-bloody)
  • Hemorrhagic colitis
  • Hemolytic uremic syndrome (HUS) 1, 2

Laboratory Identification

The CDC case definition for E. coli O157:H7 infection includes:

• Isolation of E. coli O157:H7 from a specimen, OR
• Isolation of Shiga toxin-producing E. coli O157:NM from a clinical specimen 1

PCR-restriction fragment length polymorphism (PCR-RFLP) testing can identify the gene encoding the H7 antigen (fliC) in E. coli, which is useful for confirming E. coli O157:H7 and related strains that may not express immunoreactive H antigen 3.

Broader Context

While E. coli O157:H7 is the most renowned Shiga toxin-producing E. coli (STEC), it's important to note that:

• Over 200 different types of STEC have been documented in meat and animals
• At least 60 STEC serotypes have been linked with human disease
• Six non-O157 serogroups (O26, O45, O103, O111, O121, and O145) account for the majority of reported non-O157 STEC infections in the United States 2, 5

Clinical Management Implications

The specific identification of E. coli O157:H7 (versus other E. coli O157 variants) is clinically important because:

• Prompt, accurate diagnosis is critical for appropriate management
• Antibiotics should not be used to treat E. coli O157:H7 infections due to increased risk of developing HUS
• Antimotility agents should be avoided
• Early parenteral volume expansion may decrease renal damage 2

The distinction between E. coli O157:H7 and other E. coli O157 variants has important implications for laboratory testing, epidemiological surveillance, and outbreak investigation.