Impact of Azithromycin Resistance Mutations on the Virulence and Fitness of Chlamydia caviae in Guinea Pigs

Abstract

Azithromycin (AZM) is a major drug used in the treatment and prophylaxis of infections caused byChlamydia, yet no significant clinical resistance has been reported for these obligate intracellular bacteria. Nevertheless, spontaneous AZM resistance (Azm r ) arose in vitro at frequencies ranging from 3 ؋ 10 ؊8 to 8 ؋ 10 ؊10 for clonal isolates of Chlamydia caviae, which is a natural pathogen of guinea pigs. Sequencing of the unique 23S rRNA gene copy in 44 independent Azm r isolates identified single mutations at position A 2058 or A 2059 (Escherichia coli numbering system). While SP 6 AZ 1 (A 2058 C) and SP 6 AZ 2 (A 2059 C) Azm r mutants showed growth defects in cell culture and were less pathogenic in the guinea pig ocular infection model than in the parent SP 6 , the three isogenic C. caviae isolates grew equally well in the animal. On the other hand, coinoculation of the C. caviae parent strain with one of the Azm r strains was detrimental for the mutant strain. This apparent lack of association between pathology and bacterial load in vivo showed that virulence of the two Azm r mutants of C. caviae was attenuated. While chlamydial growth in vitro reflects the ability of the bacteria to multiply in permissive cells, survival in the host is a balance between cellular multiplication and clearance by the host immune system. The obligate intracellular nature of Chlamydia may therefore limit emergence of resistance in vivo due to the strength of the immune response induced by the wild-type antibiotic-sensitive bacteria at the time of antibiotic treatment.

Beyond Tryptophan Synthase: Identification of Genes That Contribute to Chlamydia trachomatis Survival during Gamma Interferon-Induced Persistence and Reactivation

“…We also attempted to map the Sip mutants using an antibiotic-driven, positive-selection LGT approach (50). However, the rifampin-and ofloxacin-resistant parents that we isolated for these crosses exhibited altered persistence phenotypes, consistent with previous reports that endogenous C. trachomatis antibiotic resistance alleles can have phenotypic costs (51)(52)(53)(54). Our experience suggests that counterselection LGT performs optimally when mutants have strong phenotypes, and further refinement of the counterselection approach may allow us to map the remaining mutants in the future (41).…”

Molecular Typing of Treponema pallidum in the Czech Republic during 2011 to 2013: Increased Prevalence of Identified Genotypes and of Isolates with Macrolide Resistance

“…Moreover, the decreasing occurrence of the A2059G mutation could reflect its higher fitness cost than that of the A2058G mutation in treponemes. Different fitness costs imposed by the A2058C and A2059C mutations in the 23S rRNA gene have been observed in Chlamydia caviae (35).…”

Macrolide resistance mechanisms inEnterobacteriaceae: Focus on azithromycin

“…Although data regarding Enterobacteriaceae are scarce, probably due to their low clinical relevance, data obtained in other microorganisms possessing a single copy of the rrn operon have shown possible fitness loss as well as lesser virulence of azithromycin-resistant microorganisms due to specific 23S rRNA base changes (Binet et al, 2010;Hao et al, 2009). In the case of E. coli, the A2062G change has shown to strongly affect normal bacterial growth (Cochella & Green, 2004) while other substitutions such as C2610G, or A2503C, A2503U result in non-viability which does not support cell growth in the absence of wild-type ribosomes in E. coli (V azquez- Laslop et al, 2010Laslop et al, , 2011.…”