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Antimicrobial Agents and Chemotherapy, August 2008, p. 2767-2770, Vol. 52, No. 8
0066-4804/08/$08.00+0     doi:10.1128/AAC.00481-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

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

Service de Microbiologie and EA 2128 Relations hôte et microorganismes des épithéliums, Hôpital Côte de Nacre, Université de Caen, 14033 Caen cedex, France,¹ Université de Lyon, Université Lyon 1, Laboratoire de Biométrie et Biologie Evolutive (UMR5558), CNRS, Faculté de Médecine Lyon sud, 69921 Oullins cedex, France,² Laboratoire de Microbiologie de l'Environnement, USC INRA EA956, IRBA, Université de Caen, Caen, France³

Received 11 April 2008/ Returned for modification 16 May 2008/ Accepted 22 May 2008

Streptococcus uberis UCN60 was resistant to spiramycin (MIC = 8 µg/ml) but susceptible to erythromycin (MIC = 0.06 µg/ml), azithromycin (MIC = 0.12 µg/ml), josamycin (MIC = 0.25 µg/ml), and tylosin (MIC = 0.5 µg/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 µg/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.

Published ahead of print on 2 June 2008.