Pseudomonas aeruginosa Infection Models

Pseudomonas aeruginosa (P. aeruginosa) is an ESKAPE pathogen defined less by a single resistance gene than by a stack of hard-to-treat traits: a poorly permeable outer membrane, constitutive and inducible efflux, an inducible AmpC-type cephalosporinase (the Pseudomonas-derived cephalosporinase, or PDC), biofilm-associated tolerance, and the speed with which it acquires further mechanisms in the host and in the hospital. That combination is why multidrug-resistant P. aeruginosa has been designated a serious threat by the CDC, and why carbapenem-resistant P. aeruginosa remains on the WHO Bacterial Priority Pathogens List. An efficacy package that reports only a broth MIC is incomplete. TransPharm Preclinical Solutions evaluates candidates against P. aeruginosa in vivo across three validated infection models and produces the quantitative burden and survival data that a development program needs.

P. aeruginosa is a Gram-negative, non-fermenting rod that lives in moist environments and readily colonizes healthcare water, devices, and damaged mucosa. It is an opportunistic, predominantly nosocomial pathogen. In ventilated, catheterized, neutropenic, burned, or otherwise immunocompromised patients it causes pneumonia, bloodstream infection, urinary tract infection, and wound and device-related disease. In people with cystic fibrosis and other chronic airway disease it establishes long-term lung infection that is rarely eradicated once biofilm is established.

Carbapenem-resistant P. aeruginosa was a critical-priority pathogen on the WHO’s 2017 list; the 2024 update moved it to the high-priority tier, a change that WHO attributed to reported declines in global resistance rates. It remains a high-burden healthcare pathogen and a core target for new antibacterials.

The scientific problem in a P. aeruginosa study is matching the challenge to the question. A laboratory strain such as ATCC 15692 (PAO1) or a susceptibility reference strain such as ATCC 27853 answers a different question than a mucoid cystic-fibrosis isolate or a difficult-to-treat resistant (DTR) clinical strain – one already non-susceptible to piperacillin-tazobactam, the antipseudomonal cephalosporins, aztreonam, the carbapenems, and the fluoroquinolones. Biofilm and persistence in the lung or on a device can dissociate in vitro susceptibility from in vivo effect. Strain choice, infection site, and whether the readout is lethality or organ burden therefore determine whether a study is interpretable.

The resistance route matters as much as the resistance category. In P. aeruginosa, carbapenem resistance is most often chromosomal and mutational – loss of the OprD porin that admits carbapenems, derepression of the PDC cephalosporinase, and overexpression of efflux systems such as MexAB-OprM – rather than the acquired carbapenemases that dominate in the Enterobacterales; metallo-β-lactamases such as VIM and IMP are a less common but transferable route. Because these mechanisms differ in which agents they spare, the resistance profile of the challenge strain, not just a “carbapenem-resistant” label, shapes what an efficacy study can show.

TransPharm Preclinical Solutions evaluates candidates against P. aeruginosa in vivo and 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 on request.

Every study parameter is configurable to the scientific question: challenge strain, host species and 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

Peritonitis is inflammation of the peritoneal lining and a standard severe Gram-negative challenge for systemic agents. Intra-abdominal P. aeruginosa supports both lethality- and burden-based readouts and is a practical screen when the question is whether a candidate holds up in a rapidly progressive infection.

Animals are challenged by intraperitoneal injection, with gastric mucin often used to help establish infection. Test article may be administered by oral gavage or by subcutaneous, intravenous, or intraperitoneal injection. Endpoints include survival and CFU burden in harvested organs and/or blood. Validated in mice and rats.

Pulmonary infection is the setting in which P. aeruginosa is most consequential: hospital-acquired and ventilator-associated pneumonia, and chronic airway infection in structurally abnormal lung. A lung challenge is the appropriate model when the question is reduction of pulmonary burden, survival after airway infection, or delivery of an inhaled or systemically dosed agent to infected lung.

Animals are challenged by intranasal or intratracheal instillation. Test article may be administered by nebulization, oral gavage, intranasal or intratracheal instillation, or by intravenous, intraperitoneal, intramuscular, or subcutaneous injection. Endpoints include survival and CFU burden in harvested organs and/or blood. Validated in mice and rats.

A urinary tract infection may remain limited to the urethra and bladder or ascend to the kidney. Hospital-acquired UTIs are frequently device-associated, and P. aeruginosa is a familiar, often resistant isolate in that setting. An ascending UTI model tests clearance from the urinary tract and supports dosing strategy.

Animals are challenged by intraurethral administration. Test article may be administered by oral gavage or by intraurethral, subcutaneous, intraperitoneal, or intravenous injection. The primary endpoint is CFU burden in harvested organs (kidney, bladder) and/or blood. Validated in mice. Validated isolates include P. aeruginosa ATCC 27853 and ATCC 15692 (PAO1).

In vitro susceptibility testing complements the in vivo models. 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 MDR and DTR isolates, where combination regimens are frequently required.