Deciphering the Growth Phase-Dependent Degradation Kinetics of Antibiotic Resistance Gene of Methicillin-Resistant Staphylococcus aureus during Chlorination

Abstract

Degradation kinetics of the intracellular antibiotic resistance gene (i-ARG) during chlorination, specifically the mecA gene (i-mecA) in methicillin-resistant Staphylococcus aureus (MRSA), exhibit complexities influenced by bacterial growth stages. This study systematically investigated the i-mecA degradation kinetics in MRSA cultured in log and stationary phases. Using quantitative polymerase chain reaction, amplicons within i-mecA were measured, and markedly different i-mecA degradation behaviors under different growth conditions were observed. In log phase MRSA, i-mecA rapidly depleted at low chlorine exposures, contrasting with minimal loss in the stationary phase MRSA. This initial rapid loss in log phase could not be entirely accounted for by the decreased DNA recovery rate from MRSA following chlorination. Severe DNA damage, such as strand breaks, occurred more rapidly in log phase MRSA through investigations using flow cytometry, consistent with the initial rapid loss of i-mecA. Tailing kinetics were observed for both log and stationary phase MRSA, where i-mecA degradation slowed with prolonged chlorine exposure. The formation of MRSA aggregate and the emergence of a chlorine-resistant phenotype were proposed as responsible for the tailing kinetics in log and stationary phase MRSA, respectively. These findings provide valuable insights for evaluating and interpreting the i-ARG degradation kinetics during water chlorination. © 2024 American Chemical Society.