Resistance Profiles and Biological Characteristics of Rifampicin-Resistant Small-Colony Variants.

BACKGROUND

() is a major contributor to nosocomial and community-acquired infections. small colony variants (SCVs) which changed in relevant phenotype have made more limited and difficult for therapeutic options against infections increasingly. Rifampicin is considered as the "last-resort" antibiotic against . Our study investigated resistance profiles and biological characteristics of rifampicin-resistant SCVs.

METHODS

We collected SCVs that were selected from 41 rifampicin-resistant clinical isolates. Then, biological characteristics, resistance spectrum, and rifampicin resistance mechanisms of tested SCVs and corresponding parental strains were investigated by classic microbiological methods, agar dilution method, polymerase chain reaction (PCR). Moreover, the fitness cost of SCVs, including growth, biofilm formation ability, and virulence profile, was also determined by bacterial growth curve assay, biofilm formation assay, and infection model.

RESULTS

There were three SCVs (JP310 SCVs, JP1450 SCVs, JP1486 SCVs) that were selected from 41 rifampicin-resistant SCVs colonies were tiny, with decreased pigmentation, and the hemolysis circle was not obvious compared with corresponding parental strains. And SCVs could not be restored to normal-colony phenotype after hemin, menaquinone, or thymidine supplementation. Different mutations occurred in JP1486 SCVs. Antimicrobial susceptibility testing revealed MICs of SCVs were higher than corresponding parental strains. Besides, the growth ability and virulence of SCVs were lower, and biofilm formation ability of which increased compared with parental strains.

CONCLUSION

SCVs share the rifampicin resistance mechanisms with parental strains, although there were some differences in the position of mutations. Moreover, we found that the biological characteristics of SCVs were significantly different from corresponding parental strains. In contrast, decreased susceptibility to other antibiotics of SCVs was observed during phenotype switch. Furthermore, SCVs incur the fitness cost.