Carbapenemase Detection in Pseudomonas aeruginosa: Phenotypic vs. Genotypic Methods

Detecting carbapenemase-producing Pseudomonas aeruginosa, a bacterium increasingly resistant to antibiotics, requires careful consideration of both phenotypic and genotypic methods, according to a review published in Cureus on May 1, 2026. The study highlights the importance of accurate detection for effective treatment and infection control in healthcare settings.

P. Aeruginosa is a significant threat in hospital infections due to its multidrug resistance. Carbapenemase enzymes allow the bacteria to resist carbapenems, a class of antibiotics often used as a last resort. Accurate and timely identification of these carbapenemase-producing strains is crucial for guiding appropriate antibiotic therapy and preventing further spread.

Phenotypic and Genotypic Methods Compared

The review details the use of both phenotypic and genotypic methods for detecting carbapenemase production. Phenotypic methods assess the observable characteristics of the bacteria, such as its resistance to antibiotics, while genotypic methods identify the specific genes responsible for carbapenemase production.

Two commonly used phenotypic tests are the double-disk synergy test (DDST) and the combined disk synergy test (CDST). These tests evaluate the interaction between carbapenem antibiotics and other inhibitors to detect carbapenemase activity. Genotypic methods, directly detect the presence of genes encoding various carbapenemases, including blaKPC, blaNDM-1, blaIMP, blaVIM, blaSIM, blaSPM, blaGIM, and blaOXA-48.

Study Findings on Prevalence and Gene Detection

A study detailed in the Cureus review analyzed 559 isolates of P. Aeruginosa and found that 102 (18.24%) were resistant to carbapenems. Of these carbapenem-resistant isolates, 87.25% (89/102) tested positive using the DDST, and 93.17% (95/102) tested positive using the CDST.

Genotypic analysis revealed the following distribution of carbapenemase genes: blaVIM was detected in 30 isolates (29.1%), blaNDM-1 in 29 isolates (28.4%), and blaSIM and blaGIM in 6 isolates each (5.8%). Notably, 12 isolates harbored a combination of two carbapenemase genes, with six containing both blaVIM and blaNDM-1. Four isolates were found to carry a combination of three carbapenem-resistant genes.

The Challenge of Coproducers and Optimizing Patient Management

The presence of isolates coproducing multiple carbapenemases is a significant concern, as it can lead to increased resistance and treatment challenges. The review emphasizes that a thorough understanding of the molecular mechanisms of resistance is essential for optimizing patient management and implementing effective hospital infection control strategies.

The study suggests that algorithms based on susceptibility test results could potentially reduce the workload and time required for carbapenemase detection in the laboratory, contributing to improved resistance prevention efforts. Predicting carbapenemase presence based on susceptibility profiles could allow clinicians to select more appropriate therapies based on local phenotypic profiling of non-carbapenemase-producing, carbapenem-resistant P. Aeruginosa.

The increasing prevalence of carbapenemase-producing P. Aeruginosa underscores the need for continued surveillance, improved diagnostic methods, and the development of new antimicrobial agents to combat this growing public health threat.