Fitness Cost of Rifampin Resistance in Neisseria meningitidis:In VitroStudy of Mechanisms Associated withrpoBH553Y Mutation

Abstract

ABSTRACTRifampin chemoprophylaxis againstNeisseria meningitidisinfections led to the onset of rifampin resistance in clinical isolates harboring point mutations in therpoBgene, coding for the RNA polymerase β chain. These resistant strains are rare in medical practice, suggesting their decreased fitness in the human host. In this study, we isolated rifampin-resistantrpoBmutants from hypervirulent serogroup C strain 93/4286 and analyzed their different properties, including the ability to grow/survive in different culture media and in differentiated THP-1 human monocytes and to compete with the wild-type strainin vitro. Our results demonstrate that differentrpoBmutations (H553Y, H553R, and S549F) may have different effects, ranging from low- to high-cost effects, on bacterial fitnessin vitro. Moreover, we found that the S549F mutation confers temperature sensitivity, possibly explaining why it is observed very rarely in clinical isolates. Comparative high-throughput RNA sequencing analysis of bacteria grown in chemically defined medium demonstrated that the low-cost H553Y substitution resulted in global transcriptional changes that functionally mimic the stringent response. Interestingly, many virulence-associated genes, including those coding for meningococcal type IV pili, porin A, adhesins/invasins, IgA protease, two-partner secretion system HrpA/HrpB, enzymes involved in resistance to oxidative injury, lipooligosaccharide sialylation, and capsular polysaccharide biosynthesis, were downregulated in the H553Y mutant compared to their level of expression in the wild-type strain. These data might account for the reduced capacity of this mutant to grow/survive in differentiated THP-1 cells and explain the rarity of H553Y mutants among clinical isolates.