Group A Streptococci; Epidemiology and Genetics of Antibiotic Resistance

Abstract: Group A streptococci (GAS) cause throat and skin infections, severe invasive diseases as well as the non-suppurative complications acute rheumatic fever and glomerulonephritis. GAS have retained susceptibility to betalactam drugs, but resistance to alternative antibiotics is of concern. In a large Iranian survey the carrier rates among symptom-free children and those with pharyngotonsillitis were 20% and 34%, respectively. There were no macrolide resistant strains, but 42% were tetracycline resistant; of these, 406 isolates were typed by different methods. Though half of the strains were T- and M-nontypeable, more than 20 M types were represented. Non-typeable strains could mostly be typed genetically by a PCR-capture-ELISA procedure. Fingerprinting by PFGE disclosed further strain heterogeneity, suggesting tetracycline resistance to be disseminated among Iranian GAS strains. Among Swedish isolates from 1980-99, a new, non-inducible (NI) resistance phenotype, due to efflux was predominant during the 80ies. Classical MLS resistance, both inducible (IR) and constitutive (CR), seemed to appear only during the late 90-ies. In addition, three novel subphenotypes of MLS resistance were demonstrated. Resistance determinants were traced by PCR and invariably showed ermB in IR and CR strains but mefA in NI strains. Novel subphenotype strains mostly showed both erm and mef genes. Most IR strains were also tetracycline resistant, and typing of 100 such strains serologically as well as by PCR-capture-ELISA and emm-sequencing showed almost all to be of M-type 77, not previously reported from Sweden. In addition, five different clones of such multi-resistant strains were distinguished by PFGE. Thus, new molecular methods represent potent tools for epidemiological typing of antibiotic resistant and other GAS.