Abstract
Mycoplasma synoviae (MS) is a highly prevalent bacterial species in poultry causing disease and severe economic losses. Antibiotic treatment is one of the control strategies that can be applied to contain clinical outbreaks in MS-free flocks, especially because this bacterium can be transmitted in ovo. It becomes, then, very important for veterinarians to know the antibiotic susceptibility of the circulating strains in order to choose the most appropriate first-line antibiotic molecule as a proactive role in fighting antibiotic resistance. We evaluated the Minimum Inhibitory Concentrations (MICs) of enrofloxacin, oxytetracycline, doxycycline, erythromycin, tylosin, tilmicosin, spiramycin, tiamulin, florfenicol and lincomycin for MS isolates collected between 2012 and 2017 in Italy. A total of 154 MS isolates from different poultry commercial categories (broiler, layer, and turkey sectors) was tested using commercial MIC plates. All MS isolates showed very high MIC values of erythromycin (MIC90 ≥8 μg/mL) and enrofloxacin (MIC90 ≥16 μg/mL). MIC values of doxycycline and oxytetracycline obtained were superimposable to each other with only a one-fold dilution difference. Discrepancies between MIC values of tylosin and tilmicosin were observed. Interestingly, seven isolates showed very high MIC values of lincomycin and tilmicosin, but not all of them showed very high MIC values of tylosin. Most of the MS isolates showed low MIC values of spiramycin, but seven strains showed a MIC ≥16 μg/mL. In the observation period, the frequency of the different MIC classes varied dependently on the tested antibiotic. Interestingly, tilmicosin MICs clearly showed a time-dependent progressive shift towards high-concentration classes, indicative of an on-going selection process among MS isolates. Until standardized breakpoints become available to facilitate data interpretation, it will be fundamental to continue studying MIC value fluctuations in the meantime in order to create a significant database that would facilitate veterinarians in selecting the proper drug for treating this impactful Mycoplasma.
Highlights
Several Mycoplasma species are considered significant pathogens for the poultry industry, among which Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS) are considered the most relevant
A total of 154 MS isolates was selected from the isolates collection of the Mycoplasma Unit of the Istituto Zooprofilattico Sperimentale delle Venezie on the base of the following criteria: year of isolation, avian species, poultry sector and genotype
Minimum Inhibitory Concentrations (MICs) results sorted by drug are shown in Table 2 and Fig 1
Summary
Several Mycoplasma species are considered significant pathogens for the poultry industry, among which Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS) are considered the most relevant. A lot of attention was focused on MG, leaving to MS the role of a minor pathogen in some poultry categories; specific eradication programs were applied worldwide especially against MG in order to decrease its prevalence [1]. Despite all these efforts, MS prevalence remains high in the poultry industry suggesting there may be a lack of knowledge in their epidemiology or in the application of appropriate control measures. Several European authors have been reporting outbreaks more frequently involving MS rather than MG, pointing out the real impact of MS on the poultry industry [2]
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