Infectious Disease and Microbiology – Edwardsiella tarda

Overview

Edwardsiella tarda is an aerobic, Gram-negative bacillus that is an uncommon cause of human infection. It is found worldwide and is associated with the intestinal flora of various animals, including snakes.

The major human infections are gastroenteritis and bacteremia.

Microbiologic Characteristics

Edwardsiella tarda is an:

• Aerobic Gram-negative bacillus

• Enteric bacterium

• Organism associated with the gastrointestinal tracts of various animals

It can be isolated using standard bacterial culture techniques.

Epidemiology

Human E. tarda infection is rare but occurs worldwide.

The organism may be part of the normal intestinal flora of various animals, particularly:

• Reptiles, including snakes

• Fish and other aquatic animals

• Other animal species

Human infection may therefore have an environmental or animal-associated source.

Transmission and Exposure

Exposure may occur through contact with colonized animals or contaminated aquatic environments and through consumption of contaminated food.

Because of its association with aquatic animals and reptiles, a history of fish, water, or reptile exposure may provide an important epidemiologic clue.

Clinical Infections

The two principal clinical manifestations described for E. tarda are:

1. Gastroenteritis

2. Bacteremia

Most infections remain gastrointestinal, but invasive bloodstream infection can occur and requires more aggressive management.

Gastroenteritis

E. tarda can cause an acute gastrointestinal illness characterized primarily by diarrhea and abdominal symptoms.

Possible manifestations include:

• Diarrhea

• Abdominal pain or cramping

• Nausea and vomiting

• Fever

The clinical presentation may resemble gastroenteritis caused by other enteric Gram-negative organisms.

Bacteremia

E. tarda can occasionally invade the bloodstream and produce bacteremia.

This represents a more serious form of infection and may be associated with systemic manifestations such as:

• Fever

• Chills

• Hypotension in severe disease

• Sepsis

Recognition of bloodstream infection is important because intravenous antimicrobial treatment is required.

Diagnosis

Diagnosis is established by bacterial culture.

Depending on the clinical syndrome, appropriate specimens include:

• Stool culture for gastroenteritis

• Blood cultures for suspected bacteremia

• Cultures from other infected sites when appropriate

Identification of the organism should be accompanied by antimicrobial susceptibility testing in serious infections.

Treatment

The primary antimicrobial treatment described in the source is a:

Fluoroquinolone

For patients with E. tarda bacteremia, the source specifically recommends intravenous treatment with a quinolone.

Additional Treatment Options

Other antimicrobial agents with potential activity include:

• Ampicillin

• Aminoglycosides

• Cephalosporins

For invasive infection, antimicrobial selection should be guided by the isolate’s susceptibility pattern and the clinical severity of disease.

High-Yield Clinical Pattern

Animal, reptile, fish, or aquatic exposure

• ●

Gastroenteritis

or

Bacteremia/sepsis

• ●

Aerobic Gram-negative bacillus isolated by culture

→ Consider Edwardsiella tarda

Exam Essentials

Organism: Edwardsiella tarda

Type: Aerobic Gram-negative bacillus

Distribution: Worldwide

Frequency: Rare human pathogen

Reservoir: Intestinal flora of animals, including snakes

Important exposures: Reptiles and aquatic environments/animals

Major infections: Gastroenteritis and bacteremia

Diagnosis: Culture

Primary treatment: Fluoroquinolone

Bacteremia: Intravenous antimicrobial therapy is required

Additional options: Ampicillin, aminoglycosides, or cephalosporins

Key clinical pearl: Think of Edwardsiella tarda when gastroenteritis or bacteremia occurs after aquatic-animal or reptile exposure; invasive bloodstream infection is the major serious manifestation and requires systemic antimicrobial therapy.