As a leading non-fermentative opportunistic bacterium, Pseudomonas aeruginosa (P. aeruginosa) plays a major role in healthcare-associated infections. The emergence of carbapenem-resistant strains is a serious clinical threat, often associated with integrons and carbapenemases such as blaIMP. The present study aimed to assess the distribution of class 1 and 2 integrons and the blaIMP gene among clinical isolates of carbapenem-resistant P. aeruginosa from hospitals in Shiraz.
Seventy clinical isolates of P. aeruginosa were collected from different hospital wards. The identification of the isolates was performed using common microbiology methods. The disk diffusion method was used to evaluate the antimicrobial susceptibility. Minimum inhibitory concentration (MIC) values for imipenem in carbapenem-resistant strains were obtained using E-test strips. Polymerase chain reaction (PCR) was used to identify the resistance determinants including intI1, intI2, and blaIMP.
Of the 70 clinical isolates, 35 (50%) isolates were imipenem-resistant. MIC testing showed that 34 isolates had a resistant MIC (MIC ≥ 8 μg/mL). PCR results showed that 33 (94.3%) isolates carried the intI1 gene and 17 (48.6%) isolates carried the blaIMP gene. Co-existence of intI1 and blaIMP genes was observed in 17 (48.6%) isolates. The intI2 gene was not detected in any of the samples. The prevalence of the intI1 and blaIMP genes was higher among the isolates obtained from intensive care units (ICU) and internal medicine wards.
The high prevalence of class 1 integrons and the blaIMP gene among carbapenem-resistant isolates suggests the key function of mobile genetic elements in the horizontal spread of resistance factors.