Diversity and variation in antimicrobial susceptibility patterns over time in Mycoplasma agalactiae isolates...

Mycoplasma agalactiae is responsible for Contagious Agalactia, a severe syndrome affecting small ruminants worldwide and resulting in significant economic losses in countries with an important dairy industry. The aim of this study was to examine the antimicrobial susceptibility patterns of M. agalactiae isolates in France, their evolution over the last 25 years and their relationships with the genetic diversity of isolates and their origin (geographical and animal host).

Susceptibility patterns were determined by measuring minimal inhibitory concentrations (MICs) of several antimicrobials used against mycoplasmas. Caprine M. agalactiae strains showed increased MICs over time for most of the antimicrobials tested, except fluoroquinolones. This susceptibility loss was homogeneous despite the considerable genetic and geographical heterogeneity of the isolates. In contrast, all the ovine isolates originating from a single clone and the same region showed increased MICs only to some macrolides.

MICs have evolved differently depending on the origin of the isolates but the overall loss in susceptibility has remained far more moderate than that of Mycoplasma bovis, a cattle pathogen closely related to M. agalactiae.

Several hypotheses are proposed to explain the differences in susceptibility patterns, such as local, specific, nonmycoplasma-targeting antibiotic treatments and the genetic background of isolates in connection with their animal host.