Emergence of Macrolide Resistance Gene mph (B) in Streptococcus uberis and Cooperative Effects with rdmC -Like Gene

Abstract

Streptococcus uberis UCN60 was resistant to spiramycin (MIC ‫؍‬ 8 g/ml) but susceptible to erythromycin (MIC ‫؍‬ 0.06 g/ml), azithromycin (MIC ‫؍‬ 0.12 g/ml), josamycin (MIC ‫؍‬ 0.25 g/ml), and tylosin (MIC ‫؍‬ 0.5 g/ml). A 2.5-kb HindIII fragment was cloned from S. uberis UCN60 DNA on plasmid pUC18 and introduced into Escherichia coli AG100A, where it conferred resistance to spiramycin by inactivation. The sequence analysis of the fragment showed the presence of an rdmC-like gene that putatively encoded a protein belonging to the alpha/beta hydrolase family and of the first 196 nucleotides of the mph(B) gene putatively encoding a phosphotransferase known to inactivate 14-, 15-, and 16-membered macrolides in E. coli. The entire mph(B) gene was then identified in S. uberis UCN60. The two genes were expressed alone or in combination in E. coli, Staphylococcus aureus, and Enterococcus faecalis. Analysis of MICs revealed that rdmC-like alone did not confer resistance to erythromycin, tylosin, and josamycin in those three hosts. It conferred resistance to spiramycin in E. coli and E. faecalis but not in S. aureus. mph(B) conferred resistance in E. coli to erythromycin, tylosin, josamycin, and spiramycin but only low levels of resistance in E. faecalis and S. aureus to spiramycin (MIC ‫؍‬ 8 g/ml). The combination of mph(B) and rdmC-like genes resulted in a resistance to spiramycin and tylosin in the three hosts that significantly exceeded the mere addition of the resistance levels conferred by each resistance mechanism alone.

Occurrence of antibiotic resistance genes and mobile genetic elements in enterococci and genomic DNA during anaerobic digestion of pharmaceutical waste sludge with different pretreatments

“…In addition, it confers resistance by inactivation to erythromycin, josamycin, tylosin, and spiramycin in E. coli AG100A but only to spiramycin in E. faecalis JH2-2 and Staphylococcus aureus RN4220 (Achard et al, 2008). Unlike other genes, which tend to decrease during pretreatment and rebound during AD, mphB slightly increased during pretreatment and decreased during all AD processes.…”

Functional characterization and phylogenetic analysis of acquired and intrinsic macrolide phosphotransferases in the Bacillus cereus group

“…Macrolide antibiotics are widely used to treat various infections caused by a number of clinically important Gram-positive pathogens, as well as some Gram-negative pathogens, such as Legionella and Chlamydia. Accordingly, resistance to macrolides has shown an increasing trend in the last two decades, especially in Gram-positive bacteria (Leclercq, 2002;Achard et al, 2008). The resistance may be promoted by several distinct mechanisms, including mutations in 23S rRNA or ribosomal proteins, methylation of ribosomal 23s rRNA by methylases, active efflux by pump proteins and inactivation of antibiotics by specific enzymes (Roberts, 2008).…”

The TetR Family of Regulators

“…MphR regulates expression of mphA, encoding a macrolide phosphotransferase, and mrx, encoding a membrane protein required for high-level resistance (101,102). Another, unnamed TFR is found upstream of genes encoding a macrolide phosphotransferase (mphB) and a putative methyl esterase (rdmC-like) required for high-level macrolide resistance in some strains of E. coli as well as Streptococcus uberis (103). Despite the fact that they both regulate macrolide resistance genes, this unnamed TFR and MphR were found in separate groups in our analysis (25).…”