Abstract
Bacterial tolerance, especially in Staphylococcus aureus (S. aureus), may arise under intermittent antibiotic regimens and act as a stepping stone toward resistance development. However, the transition from tolerance to resistance and its contributing factors remain poorly understood. This study explores the role of the efflux pump gene abcA in this process. abcA mutants (overexpression, knockout, and complementation) were constructed via homologous recombination. These strains were subjected to 21 cycles of intermittent exposure to oxacillin at 20× MIC, and the resistance evolution was monitored. Spontaneous mutation frequencies and survival abilities in these mutants were also measured to determine their involvement in resistance development. The abcA overexpression mutant exhibited a faster development of resistance compared to the wildtype strain. Conversely, the abcA knockout mutant maintained susceptibility to oxacillin, with no significant changes in the relative MIC. Increased mutation frequency and enhanced survival were observed in the overexpression strain, whereas both were reduced in the knockout. abcA overexpression significantly accelerated the development of oxacillin resistance in S. aureus by promoting spontaneous mutations and bacterial survival. Disrupting abcA may offer a novel strategy to prevent the evolution of antibiotic resistance.