Characterisation of Acquired Resistance to Macrolides of <em>Mycoplasma gallisepticum</em> Strains

Researchers in Israel have reported the recent emergence of acquired resistance to both the macrolide and fluoroquinolone classes of antibiotics in M. gallisepticum.

19 August 2011

3 minute read

The macrolide class of antibiotics, including tylosin and tilmicosin, is widely used in the veterinary field for prophylaxis and treatment of mycoplasmosis, explain Irena Gerchman of Kimron Veterinary Institute in Israel and co-authors there and at CIRAD in France. Their paper has recently been published online in the journal, Veterinary Research.

The researchers continue that they carried out in vitro susceptibility testing on 50 strains of M. gallisepticum isolated in Israel during the period 1997-2010.

Acquired resistance to tylosin and tilmicosin was present in 50 per cent of them. Moreover, 72 per cent (13/18) of the strains isolated from clinical samples since 2006 showed acquired resistance to enrofloxacin, tylosin and tilmicosin.

Molecular typing of the field isolates, performed by gene-target sequencing (GTS), detected 13 molecular types (I-XIII). Type II was the predominant type prior to 2006 whereas type X, first detected in 2008, is currently prevalent. All 10 type X strains were resistant to both fluoroquinolones and macrolides, suggesting selective pressure leading to clonal dissemination of resistance. However, this was not a unique event since resistant strains with other GTS molecular types were also found.

Concurrently, the molecular basis for macrolide resistance in M. gallisepticum was identified.

The scientists says that their results revealed a clear-cut correlation between single point mutations A2058G or A2059G in domain V of the gene encoding 23S rRNA (rrnA, MGA_01) and acquired macrolide resistance in M. gallisepticum. Indeed, all isolates with MIC greater than or equal to 0.63µg/mL to tylosin and with MIC greater than or equal to 1.25µg/mL to tilmicosin possess one of these mutations, suggesting an essential role in decreased susceptibility of M. gallisepticum to 16-membered macrolides.

Reference

Gerchman I, S. Levisohn, I. Mikula, L. Manso-Silvan and I. Lysnyansky. 2011. Characterization of in vivo-acquired resistance to macrolides of Mycoplasma gallisepticum strains isolated from poultry. Veterinary Research (article in press) doi:10.1186/1297-9716-42-90