Addressing the Antimicrobial Resistance of Ruminant Mycoplasmas Using a Clinical Surveillance Network

Abstract

Antimicrobial resistance (AMR) surveillance of mycoplasmas of veterinary importance has been held back for years due to lack of harmonized methods for antimicrobial susceptibility testing (AST) and interpretative criteria, resulting in a crucial shortage of data. To address AMR in ruminant mycoplasmas, we mobilized a long-established clinical surveillance network called “Vigimyc.” Here we describe our surveillance strategy and detail the results obtained during a 2-year monitoring period. We also assess how far our system complies with current guidelines on AMR surveillance and how it could serve to build epidemiological cut-off values (ECOFFs), as a first attainable criterion to help harmonize monitoring efforts and move forward to clinical breakpoints. Clinical surveillance through Vigimyc enables continuous collection, identification and preservation of Mycoplasma spp. isolates along with metadata. The most frequent pathogens, i.e., M. bovis and species belonging to M. mycoides group, show stable clinicoepidemiological trends and were included for annual AST. In the absence of interpretative criteria for ruminant mycoplasmas, we compared yearly minimum inhibitory concentration (MIC) results against reference datasets. We also ran a SWOT (Strengths, Weaknesses, Opportunities, Threats) analysis on the overall service provided by our AMR surveillance strategy. Results of the 2018–2019 surveillance campaign were consistent with the reference datasets, with M. bovis isolates showing high MIC values for all antimicrobial classes except fluoroquinolones, and species of the Mycoides group showing predominantly low MIC values. A few new AMR patterns were detected, such as M. bovis with lower spectinomycin MICs. Our reference dataset partially complied with European Committee on Antimicrobial Susceptibility Testing (EUCAST) requirements, and we were able to propose tentative epidemiological cut-off values (TECOFFs) for M. bovis with tilmicosin and spectinomycin and for M. mycoides group with tilmicosin and lincomycin. These TECOFFs were consistent with other published data and the clinical breakpoints of Pasteurellaceae, which are often used as surrogates for mycoplasmas. SWOT analysis highlighted the benefit of pairing clinical and antimicrobial resistance surveillance despite the AST method-related gaps that remain. The international community should now direct efforts toward AST method harmonization and clinical interpretation.

Efflux Might Participate in Decreased Susceptibility to Oxytetracycline in Contagious Agalactia-Causative Mycoplasma spp.

“…Our observations suggest that the efflux system in mycoplasma allows tetracycline resistance up to 4 µg/mL and might facilitate the acquisition of a target mutation for higher resistance. This is consistent with the fact that the M. putrefaciens species, which has remained so far mostly susceptible to tetracycline [ 6 ], exhibits no or a weak efflux. On the experimental basis proposed here, it would be interesting to further test the contribution of efflux in other Mycoplasma species with high tetracycline MICs and the corresponding mutations in the target genes, such as M. bovis .…”

“…In a previous study, we observed a moderate decrease in susceptibility to oxytetracycline in some Mycoplasma strains belonging to species involved in contagious agalactia syndrome of small ruminants, M. agalactiae , Mmc and Mcc [ 10 ]. Only Mput did not show any in vitro increased tetracycline MICs, which was recently confirmed [ 6 ]. Three main mechanisms, namely target protection, target modification, and efflux extrusion, are known to result in tetracycline resistance in bacteria.…”

“…capricolum (Mcc), and M. putrefaciens (Mput) , which belong or are related to the M. mycoides cluster [ 4 ] and are seldom isolated from sheep. Mmc is the main etiological agent responsible for clinical caprine CA in France [ 5 , 6 ].…”

“…Among the few antimicrobials with marketing authorization for small ruminants, the convenient broad-spectrum, low-cost tetracyclines are often used [ 9 ]. The activity of oxytetracycline against CA-causing mycoplasmas has been demonstrated in vitro in several studies, but isolates with increased minimal inhibitory concentration (MIC) suggest emerging resistance in the field [ 6 , 8 , 10 , 11 , 12 , 13 , 14 ].…”

Integrating the Human and Animal Sides of Mycoplasmas Resistance to Antimicrobials

“…In the meanwhile, epidemiological cut-off values (ECOFFs), i.e., the highest MIC that defines the upper end of the wild-type (WT) MIC distribution, could be used as surrogates, i.e., thresholds for early warning of acquired phenotypic resistance, but not for guiding therapy, as non-WT isolates are not always clinically resistant. Furthermore, the process of setting ECOFFs is also challenging, as, according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST, https://www.eucast.org, accessed on 1 September 2021) standard operating procedures, it requires aggregation of MIC data obtained in different laboratories using standardized AST methods [98]. Today, if more and more results are regularly published, they are hardly comparable, even when comparing MIC data, as there might be an influence of the method [27].…”