Macrolide-resistant genes of Streptococcus pyogenes isolated from the upper respiratory tract by polymerase chain reaction.

The growing number of macrolide-resistant strains of Streptococcus pyogenes is an increasing problem worldwide. This study evaluated 300 clinical isolates obtained from the upper respiratory tract. Minimal inhibitory concentrations (MICs) of erythromycin (EM), azithromycin (AZM), and clindamycin (CLDM), serotypes, and macrolide resistance genes of mefA, ermB, and ermTR were determined. The genetic relationship of EM-resistant and susceptible strains were also analyzed by pulsed-field gel electrophoresis (PFGE). Twenty-nine (9.7%) EM-resistant S. pyogenes were identified. Of the 29 strains showing resistance to EM, 22 isolates (7.3%, MIC 3.13-12.5 microg/ml) expressed the mefA gene. The predominant serotypes among the mefA-positive isolates were T12, emm9 or T25, emm75-1. The two isolates (0.1%) that possessed the ermB gene were highly resistant to EM (MIC > 100 microg/ml). The remaining five strains (1.6%) possessed the ermTR gene (MIC 3.13-100 microg/ml). Restriction fragment polymorphism analyzed by pulsed-field gel electrophoresis (PFGE) by SmaI and ApaI digestions showed several clones among the mefA-positive S. pyogenes. Our findings suggest that the mefA gene is the predominant mechanism for macrolide resistance and that this gene is horizontally transmitted among M phenotype strains of S. pyogenes. Consequently, macrolides would not be the first drug of choice for treatment of tonsillitis and other S. pyogenes-related diseases. Physicians and researchers need to take into consideration the macrolide resistance of some strains of S. pyogenes.

[Usefulness of arbitrarily primed polymerase chain reaction (AP-PCR) method for DNA fingerprinting analysis of Mycobacterium tuberculosis (MTB); comparison between DNA restriction fragment-length polymorphism (RFLP) method and AP-PCR method].

We have been analyzing cases suspected as outbreak of Mycobacterium tuberculosis in Tokyo using RFLP method. This time we analyzed 27 strains of MTB from 5 cases in two hospitals, a family, member of social activity and stuff of a corporation using both RFLP and AP-PCR methods. At 4 cases, over 80% of strains were same pattern in each cases with RFLP and AP-PCR and were identified as a patient to patients transmission of MTB. At one case, in a hospital, each strains were completely different patterns at both methods, which showed it was not a outbreak case. Results of RFLP and AP-PCR were completely same, which indicates AP-PCR is also useful and rapid method for epidemiological analysis of MTB infection as well as RFLP.