LAUSR

OBJECTIVES Sub-inhibitory concentrations (sub-MICs) of antibiotics reflect the conditions bacteria encounter in tissues and the natural environment. Sub-MICs of antibiotics can induce stress and alter the expression of different bacterial genes. Bacteria react to stress conditions using different mechanisms one of which is Toxin-Antitoxin (TA) systems. This study investigated the expression of TA system genes under oxidative and antibiotic stresses in Klebsiella pneumoniae. METHODS To determine the effects of sub-MICs of gentamicin, nalidixic acid, and ceftazidime, as well as certain concentrations of H2O2 on bacterial survival and growth, colony forming unit was quantitated and turbidity was assessed following the treatment of K. pneumoniae with ½ MICs of antibiotics and 5 mM H2O2 at different time intervals. Moreover, the expression of TA system genes in K. pneumoniae was evaluated one hour after treatment using qRT-PCR method. RESULTS Our results revealed the reduced K. pneumoniae growth in the presence of sub-MICs of antibiotics and 5 mM H2O2 compared to the control. Furthermore, according to the results of qRT-PCR assay, only the presence of gentamicin could increase the expression of TA system genes. CONCLUSION Although the exact role of the TA systems in response to stress is still unclear, our study provided information on the effect of the type II TA systems under the oxidative and antibiotic stress conditions.