Infectious Disease and Microbiology – Leclercia adecarboxylata

Overview

Leclercia adecarboxylata is a Gram-negative bacillus belonging to the Enterobacterales. It is widely distributed in the environment but is a rare cause of human infection.

When clinically significant infection occurs, it is often opportunistic and may present as bacteremia, respiratory tract infection, or part of a polymicrobial soft-tissue or abscess infection.

Classification

Genus: Leclercia

Species: Leclercia adecarboxylata

Group: Enterobacterales

Historically, this organism has sometimes been confused with Escherichia coli because of similarities in biochemical characteristics.

Microbiologic Characteristics

L. adecarboxylata is:

• Gram-negative bacillus

• Facultatively anaerobic, although older sources may describe it as aerobic

• Motile

• A member of Enterobacterales

• Generally considered an opportunistic organism

Accurate identification may require modern biochemical or molecular laboratory methods because it can resemble other enteric Gram-negative bacilli.

Incubation Period

The incubation period is:

Unknown

There is no characteristic incubation period because infections can arise from several different routes and clinical circumstances.

Epidemiology

L. adecarboxylata has a:

Worldwide distribution

but is a:

Rare cause of human infection

The organism has been recovered from environmental sources such as:

• Water

• Soil

• Other environmental material

Opportunistic Infection

Clinically important disease has particularly been described in patients with:

• Immunosuppression

• Serious underlying disease

• Invasive medical devices

• Disrupted skin or mucosal barriers

• Traumatic wounds

However, infection can occasionally occur in immunocompetent individuals as well.

Bacteremia

L. adecarboxylata can cause:

Bacteremia

Bloodstream infection may occur as an isolated infection or secondary to another infectious focus.

Possible manifestations include:

• Fever

• Chills

• Systemic inflammatory response

• Sepsis in severe cases

Catheter-Associated Infection

Because opportunistic Gram-negative organisms can colonize or infect intravascular devices, L. adecarboxylata has also been reported in association with:

Catheter-related bloodstream infection

When a device-associated infection is suspected, appropriate source control may be necessary in addition to antimicrobial therapy.

Respiratory Tract Infection

The source identifies:

Respiratory tract infections

as another clinical manifestation.

These infections are uncommon and are more clinically significant when the organism is isolated from an appropriate lower respiratory specimen in a patient with compatible signs of infection.

Polymicrobial Infection

An important characteristic is that L. adecarboxylata may occur as part of:

Polymicrobial infections

rather than as the only pathogen.

Examples include:

• Abscesses

• Wound infections

• Soft-tissue infections

Therefore, treatment may need to cover other organisms isolated from the same infectious focus.

Wound and Soft-Tissue Infection

Environmental exposure combined with disruption of the skin barrier can permit L. adecarboxylata to enter tissues.

A useful clinical pattern is:

Traumatic wound

• ●

Environmental contamination

• ●

Gram-negative bacillus isolated from wound/abscess

→ Consider Leclercia adecarboxylata among the uncommon environmental pathogens.

Diagnosis

The principal diagnostic method is:

Culture

Depending on the clinical syndrome, specimens may include:

• Blood

• Respiratory secretions

• Wound cultures

• Abscess material

• Tissue specimens

Laboratory Identification

Because L. adecarboxylata can resemble other Enterobacterales, particularly E. coli, accurate species-level identification may occasionally be challenging.

Modern methods such as:

MALDI-TOF mass spectrometry

can facilitate reliable identification.

Treatment

The source lists:

Fluoroquinolones

as a treatment option.

Additional Treatment

The source also lists:

• Trimethoprim-sulfamethoxazole (TMP-SMX)

• Beta-lactam/beta-lactamase inhibitor combinations

These may be effective depending on the susceptibility of the isolate.

Antimicrobial Susceptibility

Many reported L. adecarboxylata isolates have been susceptible to multiple antimicrobial classes.

However, resistance can occur, including isolates with clinically important beta-lactam resistance mechanisms.

Therefore, treatment of invasive disease should be guided by:

Culture and antimicrobial susceptibility testing

rather than assuming universal susceptibility.

Treatment Principle

For significant L. adecarboxylata infection:

Confirm clinical significance

↓

Determine whether infection is monomicrobial or polymicrobial

↓

Perform susceptibility testing

↓

Choose an active antimicrobial

↓

Provide source control when an abscess or infected device is present

This is particularly important because many reported infections involve wounds, abscesses, or medical devices.

Colonization vs. True Infection

Because L. adecarboxylata is an uncommon organism and can occur in polymicrobial specimens, its clinical significance should be interpreted carefully.

Evidence supporting true infection includes:

• Isolation from a normally sterile site

• Repeated positive cultures

• Compatible clinical manifestations

• Isolation from a deep wound or abscess

• Clinical response to targeted treatment

Leclercia vs. Escherichia coli

Leclercia adecarboxylata

→ Rare opportunistic pathogen

→ Environmental distribution

→ Bacteremia, respiratory and wound infections

→ Frequently encountered in polymicrobial infection

→ Can resemble E. coli in the laboratory

Escherichia coli

→ Common human intestinal flora

→ Very common human pathogen

→ UTI, bacteremia, intra-abdominal infection, and diarrheal disease

→ Much more frequently encountered clinically

High-Yield Clinical Pattern

Rare Gram-negative bacillus

• ●

Immunocompromised patient or disrupted tissue barrier

• ●

Bacteremia, respiratory infection, wound infection, or abscess

• ●

Possible polymicrobial infection

→ Think Leclercia adecarboxylata

Exam Essentials

Organism: Leclercia adecarboxylata

Morphology: Gram-negative bacillus

Group: Enterobacterales

Distribution: Worldwide

Frequency: Rare human pathogen

Environmental association: Soil and water

Incubation: Unknown

Major infection: Bacteremia

Other infections: Respiratory tract, wound, and soft-tissue infections

Important pattern: May occur in polymicrobial abscesses

Important hosts: Often opportunistic, especially with impaired host defenses or disrupted barriers

Diagnosis: Culture

Laboratory issue: May be confused with E. coli

Source treatment: Fluoroquinolone

Additional source treatments: TMP-SMX and beta-lactam/beta-lactamase inhibitor combinations

Management principle: Susceptibility-guided therapy and appropriate source control

Key clinical pearl: Leclercia adecarboxylata is a rare environmental Gram-negative bacillus that should be considered a potential opportunistic pathogen when recovered from blood, deep wounds, or abscesses. It is particularly notable for appearing in polymicrobial infections and for its laboratory resemblance to Escherichia coli.