Functional analysis of pneumococcal drug efflux pumps associates the MATE DinF transporter to quinolone susceptibility

The pneumococcal chromosome encodes about 140 transporters, many of which predicted to be involved in efflux. In order to critically evaluate pneumococcal efflux, a series of transporter mutants were constructed, and their phenotypes were assayed by disk diffusion, microdilution drug susceptibility testing (MIC), growth cultures at subMIC concentrations and Phenotype Microarray analysis. Mutants for seven ABC transporters, three MATE efflux pumps and one MFS transporter were obtained in S. pneumoniae strain DP1004. The susceptibility of these eleven mutants to over 250 different substances was compared to that of the parent strain. Out of the tested transporters, only the ABC transporter PatAB (SP2073-5) presented a clear MDR profile as the mutant showed significantly increased susceptibility to ethidium bromide, acriflavin and berberine. Among the other transporters analysed, the mutants devoid of the MATE efflux pump SP2065 exhibited reduced susceptibility to novobiocin and the DinF MATE family transport system (SP1939) exhibited increased susceptibility to moxifloxacin, ciprofloxacin and levofloxacin. This change in quinolone MIC was found to be independent form the competence mediated effect of quinolones on the cinA-recA-dinF operon. Furthermore the dinF mutant allowed, in contrast to the parental strain, to select for quinolone resistant mutants when exposed to moxifloxacin. These data confirm the clear MDR profile of the PatAB ABC transporter and propose for the MATE DinF a phenotype associated to quinolone susceptibility, in particular for moxifloxacin.