Inactivation Kinetics of Methicillin Resistant Staphylococcus Aureus (MRSA) and its Resistance Genes by Monochloramine

Abstract

Methicillin-resistant staphylococcus aureus (MRSA), responsible for several critical infections in humans are often found in aquatic environment. The resistance of MRSA is originated from mecA gene located within staphylococcal chromosome cassette mec. As a transposon, mecA gene can be transferred to another bacteria by horizontal gene transfer (HGT). Therefore, not only MRSA itself but also mecA gene could be a potential concern for public health. The objective of this study was to determine the kinetics of inactivation of MRSA and its mecA gene during water disinfection with chloramine (NH2Cl). Cultivability, flow cytometry (FCM), and quantitative polymerase chain reaction (qPCR) were used to determine various types of damages of MRSA and its mecA gene. During treatment of MRSA with 2mg/L of NH2Cl, 6-log reduction in the concentration of cultivable cells was achieved at the chlorine exposure of 14 mgCl2/Lmin at pH 7.0. The membrane damage of MRSA determined by FCM with SYBR/PI staining analysis was relatively slower and 6-log reduction in the concentration of membrane-damaged cells required a chlorine exposure of 186 mgCl2/Lmin. Finally, the mecA gene was highly resistant to NH2Cl and little degradation of mecA gene was achieved even at the chlorine exposure of 2000 mgCl2/Lmin. Overall, our data show that chloramine can achieve significant inactivation of MRSA but is not effective for the degradation of mecA gene in typical conditions of water disinfection.