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Unusual occurrence of M type 77, antibiotic-resistant group A streptococci in southern Sweden
A Jasir1, A Tanna, A Efstratiou
1Department of Infectious Diseases, University of Lund, Lund, Sweden.
Abstract:
For many years group A streptococci of T type 28 (T28) have been common in southern Sweden; however, since 1995 resistance to both macrolide-lincosamide-streptogramin B (MLS) antibiotics and tetracycline was observed among T28 isolates, which prompted the present studies on clonal relatedness of antibiotic-resistant T28 strains. By extended T typing, 95 of 100 examined tetracycline-resistant strains showed the combination T9-T13-T28; of these, 94 belonged to M type 77 (M77) and one belonged to M73. Three strains were T28-M28 and two were T28-M nontypeable. The serological M77 was confirmed by PCR capture enzyme-linked immunosorbent assay, emm amplicon restriction profiling, and emm sequence typing. Fifty strains were examined for superantigen genes: speA was detected in three blood isolates only, whereas all isolates harbored speB, and only two of the strains were negative for speC. Eighty-nine of the 100 strains were also macrolide resistant, of which 59 were inducibly MLS resistant (IR) 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 hybridization methods. Eighty-four of the 100 strains harbored tetM. ermB was detected in all CR and IR strains, and mefA was found in all NI strains; both ermB and mefA were identified in two strains with novel subphenotypes. Pulsed-field gel electrophoresis showed that these antibiotic-resistant M77 strains belonged to at least five different clones.
Insights
Group A Streptococcus T28 strains in Sweden have developed resistance to macrolide-lincosamide-streptogramin B (MLS) antibiotics and tetracycline. Pulsed-field gel electrophoresis revealed these antibiotic-resistant strains belong to at least five distinct clones.
Area of Science:
- Microbiology
- Molecular Biology
- Epidemiology
Background:
- Group A Streptococcus (GAS) T type 28 (T28) strains have been prevalent in southern Sweden.
- Since 1995, an increase in T28 isolates exhibiting resistance to macrolide-lincosamide-streptogramin B (MLS) antibiotics and tetracycline has been observed.
Purpose of the Study:
- To investigate the clonal relatedness of antibiotic-resistant T28 strains of Group A Streptococcus.
- To characterize the genetic basis of antibiotic resistance in these strains.
Main Methods:
- Extended T typing, emm typing (PCR capture enzyme-linked immunosorbent assay, emm amplicon restriction profiling, emm sequence typing), superantigen gene detection (speA, speB, speC), antibiotic resistance gene analysis (tetM, ermB, mefA) using PCR and hybridization, and pulsed-field gel electrophoresis (PFGE).
Main Results:
- Ninety-five of 100 tetracycline-resistant strains were T9-T13-T28, predominantly M type 77 (M77).
- Eighty-nine strains were macrolide resistant, with varying MLS resistance phenotypes (inducible, constitutive, noninducible, novel subphenotypes).
- Resistance genes tetM, ermB, and mefA were identified corresponding to the observed resistance patterns. PFGE indicated at least five distinct clones among the antibiotic-resistant M77 strains.
Conclusions:
- The emergence of antibiotic resistance in T28 GAS strains in Sweden is associated with specific M types and is driven by the acquisition of resistance genes like tetM, ermB, and mefA.
- The presence of multiple clones suggests different evolutionary pathways for antibiotic resistance acquisition in these strains.
- Continued surveillance is crucial to monitor the spread and evolution of antibiotic-resistant GAS.