Phenotype, genotype, and serotype distribution of macrolide resistant invasive and non-invasive Streptococcus pneumoniae strains, in Sousse, Tunisia.

OBJECTIVE

We determined the macrolide resistance phenotypes and genotypes in Streptococcus pneumoniae isolates in Sousse and assessed the serotype distribution.

METHODS

We included S. pneumoniae strains isolated at our laboratory (2010-2013). The antimicrobial susceptibility was tested according to CA-SFM specifications. Serotyping was performed by agglutination of latex particles, to identify a subset of serotypes included in pneumococcal conjugate vaccines. The presence of macrolide resistance genes (ermB, mefA, mel) was detected by PCR.

RESULTS

A total of 52.8% of 140 S. pneumoniae isolates were macrolide-resistant: MLSB (89.2%) and M (10.8%). The MLSB phenotypes were genotypically confirmed by ermB gene presence. 62% had decreased susceptibility to penicillin. The serotypes were: 14, 1, 23F, and 19A. Serotype coverage by PCV7, PCV10 and PCV13 was 44.2%, 73.6%, and 75.6% respectively.

CONCLUSION

50% of S. pneumoniae isolates were macrolide resistant. The MLSB phenotype encoded by the ermB gene was the most frequent. Serotype coverage seems inadequate.