Prophage association of mef(A) elements encoding efflux-mediated erythromycin resistance in Streptococcus pyogenes.
OBJECTIVE
To compare different mef(A) elements of Streptococcus pyogenes for a possible chimeric genetic nature, i.e. a transposon inserted into a prophage.


METHODS
Eleven S. pyogenes isolates with efflux-mediated erythromycin resistance were used. The isolates were typed using several genotypic approaches. Gene detection was performed by PCR using specific primer pairs. The mef(A) elements of the test strains were induced with mitomycin C and phage DNA was extracted. Induction was monitored by PCR using primers targeting mef(A).


RESULTS
Six tetracycline-susceptible isolates had PCR evidence of all of the eight open reading frames (ORFs) of the Tn1207.1 element; their mef(A) element was consistent with the Tn1207.3 element in four isolates and with the 58.8 kb chimeric element in two. Five tetracycline-resistant isolates had no PCR evidence of orf1 and orf2 and showed variable patterns as to orf3, orf7, and orf8. Three ORFs placed along the conserved region downstream of Tn1207.1 in the 58.8 kb mef(A) chimeric element were detected in the six tetracycline-susceptible, but not in the five tetracycline-resistant isolates. Induction assays with mitomycin C demonstrated that the mef(A) elements of all strains tested were present in culture supernatants in a DNAse-resistant form, such as a phage capsid.


CONCLUSIONS
All recognized mef(A) elements of S. pyogenes appear to be prophage-associated. Whereas the two elements detected in tetracycline-susceptible isolates (Tn1207.3 and the 58.8 kb one) were apparently inserted into the same prophage, the tet(O)-mef(A) element was inserted into a different prophage. Phage transfer is likely to play a critical role in the dissemination of erythromycin resistance in S. pyogenes populations.
Giovanetti
Eleonora
E
Istituto di Microbiologia e Scienze Biomediche, Università Politecnica delle Marche, 60131 Ancona, Italy.
Brenciani
Andrea
A
Vecchi
Manuela
M
Manzin
Aldo
A
Varaldo
Pietro E
PE
D001426:Bacterial Proteins / Q000235:genetics*; D002874:Chromosome Mapping; D004251:DNA Transposable Elements / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D004917:Erythromycin / Q000494:pharmacology*; D015870:Gene Expression / Q000187:drug effects; D008565:Membrane Proteins / Q000235:genetics*; D016685:Mitomycin / Q000494:pharmacology; D016366:Open Reading Frames; D039002:Prophages / Q000235:genetics*; D013297:Streptococcus pyogenes / Q000187:drug effects* / Q000235:genetics*; D013752:Tetracycline / Q000494:pharmacology
D001426:Bacterial Proteins; D004251:DNA Transposable Elements; C117866:MefA protein, Streptococcus; D008565:Membrane Proteins; D016685:Mitomycin; D004917:Erythromycin; D013752:Tetracycline