Question 11

Are there any temporal trends in regards to the relative incidence of the two major mechanisms of macrolide resistance [erm (B) and mef (A)]?

We performed a study in Spain investigating 45 mef -positive S. pneumoniae isolates. Of these 45 isolates, 17 carried the mef gene alone while the other 28 carried both the mef gene and erm (B) gene (62.2%). 82.2% of mef -positive S. pneumoniae was resistant to penicillin G, while none were resistant to levofloxacin. It was also important to note that when S. pneumoniae isolates were positive for both erm (B) and mef genes the resistance rates to penicillin G, tetracycline and clindamycin increased markedly (13).

Our results have been supported by the latest data from the PROTEKT survey which has demonstrated that mef (A)-mediated macrolide resistance continues to decrease while the more highly resistant isolates with double resistant mechanisms erm (B) and mef (A) increased to 25% (Table2) (11).

Table 2. Rates of resistance to individual antimicrobials among mef -positive Streptococcus pneumoniae