Detection of macrolide resistance genes in culture-negative specimens from Bangladeshi children with invasive pneumococcal diseases

Objectives In recent years, an increasing prevalence of macrolide resistance among pneumococci in Bangladesh has been observed. However, the scenario remains incomplete, as few isolates (<1%) are available from pneumonia cases and most pneumococcal meningitis cases (>80%) are culture-negative. This study optimised a triplex PCR method to detect macrolide resistance genes (MRGs) (mefA and ermB) and cpsA from culture-negative pneumococcal cases to predict the prevalence and level of macrolide resistance. Methods The presence of MRGs among pneumococcal strains (n = 153) with a wide range of erythromycin MICs (<0.5 to ≥256 mg/L) was determined by PCR. Triplex PCR was validated by simultaneous detection of MRG(s) and cpsA in culture-negative clinical specimens and corresponding isolates. The known impact of the presence of specific MRG(s) on MICs of strains was used to predict the MICs of non-culturable strains based on the presence/absence of MRG(s) in the specimens. Results None of the erythromycin-susceptible isolates possessed any of the MRGs, and all non-susceptible strains had ≥1 MRG. MICs were 2–16 mg/L and ≥256 mg/L for 93% of strains with mefA and ermB, respectively, whereas 100% of isolates with both genes had MICs ≥ 256 mg/L. PCR for body fluids showed 100% concordance with corresponding isolates when tested for MRG(s) in parallel. Conclusions Erythromycin MICs can be predicted for non-culturable strains with 93–100% precision based on detection of ermB and/or mefA. This method will be useful for establishing comprehensive surveillance for macrolide resistance among pneumococci, specifically in the population with prior antibiotic use.