Enterobacter cloacae Infection Models

Enterobacter cloacae (E. cloacae) is an ESKAPE pathogen best known for a resistance mechanism that can emerge during treatment: an inducible, chromosomal AmpC beta-lactamase that, once derepressed, defeats most beta-lactams, including third-generation cephalosporins. That makes it a distinctive target for antimicrobial development, and one where strain choice and study design determine whether an efficacy study is meaningful. TransPharm Preclinical Solutions evaluates candidates against E. cloacae in vivo and produces the quantitative efficacy data that a development program needs.

E. cloacae is a Gram-negative bacterium of the Enterobacterales order and a member of the Enterobacter cloacae complex. It is a gut commensal and an environmental organism that becomes an opportunistic, predominantly nosocomial pathogen, causing bloodstream, respiratory, surgical-wound, and urinary tract infections, especially in immunocompromised and hospitalized patients. As one of the six ESKAPE pathogens, it combines this nosocomial reach with a strong capacity for beta-lactam resistance.

E. cloacae carries a chromosomal, inducible AmpC beta-lactamase. At baseline this confers resistance to aminopenicillins and early-generation cephalosporins; when it is derepressed by mutation – and derepressed mutants pre-exist in most populations – resistance extends to the third-generation cephalosporins and can produce treatment failure that appears only after therapy has begun. This is the central consideration in an Enterobacter efficacy study: the result depends heavily on whether the challenge strain is wild-type or stably derepressed, and on whether a candidate retains activity against, or selects for, the derepressed phenotype. Matching the strain and the study design to that question is what makes the data meaningful.

TransPharm Preclinical Solutions evaluates candidates against Enterobacter cloacae in vivo, and also maintains an on-site library of hundreds of validated pathogens, including many multidrug-resistant strains. Characterized isolates, including sponsor-supplied or resistant clinical strains, can be sourced and validated to a program’s specifications upon request.

Every study parameter is configurable to the scientific question: challenge strain, route of administration, comparator agents, and dosing schedule. The core readouts are quantitative bacterial burden (CFU/g or CFU/mL) in target tissues, organs, and blood, with survival and mortality tracking where applicable.

The following are available as add-ons to any study:

• Pharmacokinetic profiling and PK/PD analysis
• Blood chemistry
• Additional tissue harvests
• Histopathology

Animals are challenged by intraperitoneal injection, with gastric mucin used to help establish infection where needed. Endpoints include survival (mortality tracking) and CFU burden in harvested organs and blood, supporting both lethality- and burden-based efficacy readouts. Validated in mice and rats.

In vitro susceptibility testing complements the in vivo model. TransPharm Preclinical Solutions runs MIC by agar and broth dilution per CLSI, along with MBC, time-kill kinetics, and checkerboard analysis. Checkerboard analysis is particularly relevant for resistant isolates, where combination regimens are frequently required.