<i>Pseudomonas aeruginosa</i> Response to Acidic Stress and Imipenem Resistance

Abstract

The present study aimed to unveil the phenotypic heterogeneity and heteroresistance of P. aeruginosa to acidic stress and imipenem. Furthermore, the growth, morphology, and potential for biofilm formation of the subject isolates at different pHs were assessed. Isolates of P. aeruginosa were recovered from juice samples and confirmed by molecular analysis. Antibiotics sensitivity was evaluated using the Kirby–Bauer-disk diffusion method, and the MIC for imipenem was determined, followed by a biofilm formation assay and population analysis. Scanning electron microscopy (SEM) was used to visualize biofilm formation. The subject isolates persisted in an acidic environment and adopted a biofilm lifestyle. The population analysis assay indicated the presence of two distinct phenotypes, i.e., a normal colony phenotype (NCP) and slow growing colony phenotype (SGCP). NCP showed visible colonies after 48 h, while SGCP colonies appeared after 72 h of incubation. Both displayed heteroresistance to imipenem and susceptibility to other antibiotics. Biofilm formation at acidic pH was observed in both phenotypes. Interestingly, the recovery of SGCP was increased in an acidic environment. Biofilm consortia were highly resistant to imipenem. The present study indicated that P. aeruginosa persisted for a long time in an acidic environment, through phenotypic alteration. The subject isolates adopted a biofilm lifestyle and reduced metabolism, to neutralize the effects of acidic pH and imipenem toxicity. Interestingly, the biofilm consortia harbored metabolically active (NCP), as well as inactive populations, of (SGCP), to maintain an active growth and persistency. SGCP retained the potential to revert to NCP upon subsequent sub-culturing in plentiful nutrients and optimum conditions.

Keywords

• heterogeneity
• pH stress
• biofilm formation
• imipenem resistance