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

Abstract

Objectives: To investigate the role of a plasmid bearing the erm(B) gene on the prevalence of the macrolide, lincosamide and group B streptogramin (MLS B ) phenotype of group A streptococci (GAS) and to characterize the plasmid and determine the clonal relation between the erythromycin-resistant isolates.Methods: Two hundred and five erythromycin-resistant GAS isolates were collected from 1990 to 2006. Colony hybridization, PCR, plasmid curing and PFGE techniques were used to analyse the mechanisms behind the phenotypes.Results: Among the 56 isolates with constitutive MLS B (cMLS B ) resistance, 53 isolates harboured a plasmid, pA15, of 19 kb. erm(B) was on pA15 and it confered a cMLS B resistance phenotype. The prevalence rate of the pA15-containing isolates was 36.3% from 1993 to 1995, but the plasmid could not be detected from 2004 to 2006. To link the high-level resistance to pA15, clinical isolate A15 was selected and pA15 was cured by novobiocin. In the plasmid-cured strain SW503, the erythromycin MIC decreased from 256 to 0.032 mg/L. By electroporation, pA15 was re-introduced into the plasmid-cured erythromycin-susceptible strain, and the high-level erythromycin resistance was restored. Plasmid pA15 was also transferred to group B streptococci and group C streptococci by electroporation. In all the pA15-containing isolates, emm1 type was present and pulse type J was predominant (48 of 54 isolates). Conclusions:The plasmid pA15 mediated cMLS B resistance in the mid-1990s, but pA15 was not detected in the clinical isolates from 2004 onwards, which correlates with the absence of cMLS B resistance in this region.

The Prevalence of Erythromycin Resistance in Group B Streptococcal Isolates at a University Hospital in Taiwan

“…In Taiwan, the prevalence rate of erythromycin resistance in S. pyogenes was between 40% and 70% before 2000, but currently, it is < 20%. 10,13 During decrease in MLS B resistance rate, shift in predominance of genotype from erm(B) to mef(A) was observed in S. pyogenes isolates. 13,17 In contrast, the percentage of erm(B) in GBS isolates is increasing, while the percentage of isolates with mef(A) is decreasing.…”

“…Few genes present on plasmid pA15 are erm(B) gene, zeta gene (toxin of epsilon-zeta postsegregational killing system), delta gene (hypothetical protein, similar to ATPases involved in plasmid active partitioning), omega gene (transcriptional repressor), and epsilon gene (antidote of epsilon-zeta postsegregational killing system). 13 The probe was labeled with Gene Images AlkPhos Direct Labeling and Detection System according to the manufacturer's instructions (Amersham Biosciences, Piscataway, NJ). After hybridization, CDP-StarÔ chemiluminescent detection reagent (Amersham Biosciences) was used for signal detection.…”

“…10 Based on previous reports from Taiwan, factors influencing decrease in erythromycin resistance rate in S. pyogenes include (1) reduced erythromycin consumption, (2) shift in genotype from erm(B) to mef(A), and (3) decrease in isolates carrying plasmid pA15 that mediate cMLS B phenotype. 10,13,20 The objectives of the present study were (1) to determine the prevalence rate of erythromycin and clindamycin resistance and MIC of the GBS clinical isolates, and (2) to investigate the mechanism(s) responsible for the MLS B resistance.…”

“…pA15 is similar to well-studied GAS plasmid pSM19035. 13 Colony hybridization and PCR data showed that the zeta gene present on pA15 was present in 81 (13%) of the 612 erythromycin-resistant GBS isolates along with erm(B), while the erythromycin MIC range was between 1 and 256 mg=ml. In addition, of the 42 erm(B)-positive isolates that were randomly selected from 1997 to 2001, zeta gene was present in the 19% of the isolates.…”

Omega (ParB) binding sites together with the RNA polymerase-recognized sequence are essential for centromeric functions of the Pω region in the partition system of pSM19035

“…Plasmids of this family are found in enterococci, lactococci, staphylococci and streptococci (Liu et al, 2007;O'Connor et al, 2007;Zhu et al, 2010). The partition system of plasmid pSM19035 is encoded by genes d and !, which encode a Walker-type ATPase (ParA-like) and an RHH DNA-binding protein (ParB-like), respectively.…”