Unusual occurrence of M type 77, antibiotic-resistant group a streptococciin southern Sweden

For many years group A streptococci of T type 28 (T28) have been common in southern Sweden; however, since 1995 resistance to both macrolide-lincosami de-streptogramin B (MLS) antibiotics and tetracycline was observed among T2 8 isolates, which prompted the present studies on clonal relatedness of ant ibiotic-resistant T28 strains. By extended T typing, 95 of 100 examined tet racycline-resistant strains showed the combination T9-T13-T28; of these, 93 belonged to M type 77 (M77) and one belonged to M73. Three strains were T2 8-M28 and two were T28-M nontypeable. The serological M77 was confirmed by PCR capture enzyme-linked immunosorbent assay, emm amplicon restriction pro filing, and emm sequence typing, Fifty strains were examined for superantig en genes: speA was detected in three blood isolates only, whereas all isola tes harbored speB, and only two of the strains were negative for speC. Eigh ty-nine of the 100 strains were also macrolide resistant, of which 59 were inducibly MLS resistant (LR) and 21 were constitutively MLS resistant (CR), 6 were noninducibly resistant (NI), and 3 had novel subphenotypes recently reported by our group. Resistance genes were determined by PCR and hybridi zation methods. Eighty-four of the 100 strains harbored tetM. ermB was dete cted in all CR and IR strains, and mefA was found in all NI strains; both e rmB and mefA were identified in to two strains with novel subphenotypes. Pu lsed-field gel electrophoresis showed that these antibiotic-resistant M77 s trains belonged to at least five different clones.