Characterization of an erythromycin resistance (erm) plasmid in Streptococcus pyogenes

Abstract

Three erythromyxin‐resistant Swedish isolates of Streptococcus pyogenes, representing different T‐types, were studied. Two of the strains showed constitutive high‐level (MIC>200 μg/ml) and one showed moderate (MIC 6.4 μg/ml) resistance; the latter strain was sensitive to lincosamide and clindamycin, and resistance was not induced by erythromycin. In each of the strains, a plasmid with an estimated Mw of 17.6±0.9×106 was isolated in addition to smaller cryptic plasmids. The three plasmids pSE701, pSE702 and pSE703 had very similar restriction enzyme cleavage patterns. Novobiocin curing of the high‐level resistance strain ER559 showed the resistance to be linked to its 17.6×106 plasmid, pSE703. Furthermore, by electroporation this rather large plasmid was reintroduced into an erythromycin‐sensitive cured derivative, acquiring resistance, and the plasmid was again recovered from the transconjugant. One of the plasmids, pSE702, was shown by filter mating to be conjugative within S. pyogenes. DNA‐DNA hybridization showed that the resistance determinant of the present three isolates was related to the erm gene on plasmid pAMpl of Enterococcus faecalis but not to that of plasmid pE194 of Staphylococcus aureus. The copy numbers of pSE702 and pSE703, derived from the two high‐level resistant strains, were 11±3 and 17±5 compared to 2±1 for pSE701, derived from the moderately resistant strain, possibly accounting for the phenotypic variation observed. The plasmids pSE702 and pAMpM showed about 80% homology in DNA‐DNA hybridization tests and high similarity in their restriction maps.

Presence of erm gene classes in Gram-positive bacteria of animal and human origin in Denmark

“…For di¡erent staphylococci and for enterococci and streptococci identical erm gene classes were observed. S. pyogenes and S. pneumoniae of human origin have previously been found to harbor ermB (class IV) [22,20,23,8] and transfer of genes between enterococci and S. suis of animal origin to these bacteria could take place. However, in Denmark the frequency of macrolide resistance among these bacteria is low, making it di¤cult to obtain resistant isolates.…”

Genetic Basis of Erythromycin Resistance in Oral Bacteria

“…In humans, macrolides are used for the treatment of respiratory tract infections or as an alternative to penicillin in patients who are allergic to that antibiotic (23). During the last two decades there have been increases in the levels of resistance to erythromycin among clinical as well as commensal isolates, and these increases correlate with the increased use of this class of antibiotics (9,11,19,25,32,33). The oral cavity is one of the most densely colonized environments in humans.…”

Presence of plasmid pA15 correlates with prevalence of constitutive MLSB resistance in group A streptococcal isolates at a university hospital in southern Taiwan

“…7,13 We demonstrated that plasmid pA15 can transform erythromycin-susceptible GAS and other Streptococcus species in vitro, including GBS and GCS, conferring erythromycin resistance. Our study is the first such publication from Taiwan and we show that the plasmid pA15 may spread easily to other strains and contribute to an increase in erythromycin resistance prevalence under constant antibiotic selection.…”

“…Plasmid curing and transformation of GAS, group B streptococci (GBS) and group C streptococci (GCS) were performed according to the method described by Schalen et al 7 GAS isolates were also screened for the presence of plasmid pA15 by colony hybridization according to the method described by Sambrook and Russell. 8 The zeta gene (GI:63021982, locus_tag ¼ 'pSM19035_009') was used as a probe to screen the GAS isolates for the presence of plasmid pA15.…”