| Summary: | Subinhibitory concentrations (subMIC) of antibiotics, although not able to kill bacteria, can modify their physicochemical characteristics and may interfere with some bacterial functions. This study aimed to investigate the effect of subMIC of imipenem and piperacillin on the transcriptional expression of virulence-related genes toxA and exoS in Pseudomonas auroginosa. Five clinical isolates of P. aeruginosa were screened for the presence of toxA and exoS genes and MICs of imipenem and piperacillin were determined using broth macrodilution. The expression levels of toxA and exoS at subMIC concentrations of antibiotics were measured by real-time PCR. Our results showed that the expression of toxA decreased at all subinhibitory concentrations of imipenem, especially at concentrations 2, 4 and 8 mg/L (p < 0.05). Whereas, exoS expression was increased 4.1- to 7-fold at subinhibitory concentrations of imipenem. The increase of toxA expression was measured at concentrations 16, 4, 2, 0.25 and 0.125 mg/L of piperacillin. However, piperacillin had no significant influence on exoS expression (p > 0.05). Further studies will be required to assess whether subMIC of imipenem can improve the outcomes of severe and serious infections caused by P. aeruginosa. Keywords: Exoenzyme S, exotoxin A, Pseudomonas aeruginosa, Subinhibitory concentrations, Imipenem, Piperacillin
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