Staphylococcus aureus AbcA transporter enhances persister formation under β-lactam exposure

Abstract

We evaluated the role of Staphylococcus aureus AbcA transporter in bacterial persistence and survival following exposure to the bactericidal agents nafcillin and oxacillin at both the population and single-cell levels. We show that AbcA overexpression resulted in resistance to nafcillin but not oxacillin. Using distinct fluorescent reporters of cell viability and AbcA expression, we found that over 6–14 hours of persistence formation, the proportion of AbcA reporter-expressing cells assessed by confocal microscopy increased sixfold as cell viability reporters decreased. Similarly, single-cell analysis in a high-throughput microfluidic system found a strong correspondence between antibiotic exposure and AbcA reporter expression. Persister cells grown in the absence of antibiotics showed neither an increase in nafcillin MIC nor in abcA transcript levels, indicating that survival was not associated with stable mutational resistance or abcA overexpression. Furthermore, persister cell levels on exposure to 1×MIC and 25×MIC of nafcillin decreased in an abcA knockout mutant. Survivors of nafcillin and oxacillin treatment overexpressed transporter AbcA, contributing to an enrichment of the number of persisters during treatment with pump-substrate nafcillin but not with pump-non-substrate oxacillin, indicating that efflux pump expression can contribute selectively to the survival of a persister population.

Decoding Bacterial Persistence: Mechanisms and Strategies for Effective Eradication

“…When exposed to 1−25× MIC concentration of nafcillin, a subpopulation of S. aureus cells exhibits 1.5-to 2.5-fold increased transcription of the abcA efflux pump, allowing them to persist under a lethal dosage of this antibiotic. 93 In the aquatic pathogen A. veronii, it was observed that the loss of the AcrAB efflux pump reduced persister frequency against β-lactam, tetracycline, and chloramphenicol; in contrast, its overexpression led to the opposite. 94 As lowered antibiotic concentration inside a cell is also achieved by lowered porin expression, reduced influx is also a contributing factor toward bacterial persistence.…”

“…Similar observations have been made in the case of β-lactam persisters of S. aureus and Aeromonas veronii . When exposed to 1–25× MIC concentration of nafcillin, a subpopulation of S. aureus cells exhibits 1.5- to 2.5-fold increased transcription of the abcA efflux pump, allowing them to persist under a lethal dosage of this antibiotic . In the aquatic pathogen A. veronii , it was observed that the loss of the AcrAB efflux pump reduced persister frequency against β-lactam, tetracycline, and chloramphenicol; in contrast, its overexpression led to the opposite .…”