title: Short communication: In vitro antimicrobial susceptibility of Mycoplasma bovis isolates identified in milk from dairy cattle in Belgium, Germany, and Italy.
abstract: The objective of this study was to assess the in vitro antimicrobial susceptibility of 73 isolates of Mycoplasma bovis isolated from milk of dairy cattle herds of Belgium, Germany, and Italy. Minimal inhibitory concentration (MIC) values were determined by the microbroth dilution method for the following antimicrobials: erythromycin, spiramycin, tilmicosin, tylosin, lincomycin, enrofloxacin, doxycycline, oxytetracycline, florfenicol, and tiamulin. Macrolides, florfenicol, oxytetracycline, and enrofloxacin, were chosen because they represent antimicrobials families commonly used in several countries for treatment of M. bovis, and their MIC values in cattle population are reported in several studies, allowing a comparison with previous data. Doxycycline and tiamulin were selected to assess the susceptibility of M. bovis to new antimicrobials, because they are not registered in the European Union for the treatment of dairy cattle. Among the agents of the different antimicrobial classes, the macrolides showed the highest concentration to inhibit 90% of isolates (MIC90), all above the highest concentration tested: >8μg/mL for erythromycin, >16μg/mL for spiramycin, and >32μg/mL for tilmicosin and tylosin. Also the MIC90 of lincomycin was above the highest concentration tested (>32μg/mL), but the distribution of the MIC values was almost perfectly bimodal: 41 isolates had a MIC ≤0.5μg/mL and 30 isolates >32μg/mL. Oxytetracycline had a 2-fold higher concentration to inhibit 50% of isolates (2 vs. 0.5μg/mL) and 1-fold higher MIC90 (4 vs. 2μg/mL) than doxycycline. Enrofloxacin and florfenicol had both a MIC90 of 2μg/mL, whereas tiamulin had a MIC90 of 0.5μg/mL. Significant differences on the MIC values were found among the 3 countries for several antimicrobials: compared with Germany, Belgium and Italy showed significantly higher MIC for lincomycin, spiramycin, and tylosin, and lower for oxytetracycline and florfenicol. The Belgian isolates showed the lowest MIC for enrofloxacin compared with Germany and Italy. The MIC results obtained in our study suggest the presence of a high level of resistance of M. bovis isolates originating from milk to macrolides in all countries involved in this study. On the contrary, a low level of resistance was found against the antimicrobials that are not used in cattle, such as tiamulin and doxycycline, highlighting a possible link between antimicrobial treatments and development of resistance in the studied M. bovis population.
authors.affiliation: Istituto Zooprofilattico Sperimentale delle Venezie, viale dell'Università 10, 3020 Legnaro (PD), Italy; Dipartimento di Medicina Veterinaria, Università degli Studi di Milano, Via Celoria 10, 20133, Milan, Italy. Electronic address: abarberio@izsvenezie.it.
authors.forename: A
authors.initials: A
authors.lastname: Barberio
authors.affiliation: Istituto Zooprofilattico Sperimentale delle Venezie, viale dell'Università 10, 3020 Legnaro (PD), Italy.
authors.forename: B
authors.initials: B
authors.lastname: Flaminio
authors.affiliation: M-team and Mastitis and Milk Quality Research Unit, Department of Reproduction, Obstetrics and Herd Health, Faculty of Veterinary Medicine, Ghent University, B-9820 Merelbeke, Belgium.
authors.forename: S
authors.initials: S
authors.lastname: De Vliegher
authors.affiliation: Flanders Milk Control Center, Hagenbroeksesteenweg 167, 2500 Lier, Belgium.
authors.forename: K
authors.initials: K
authors.lastname: Supré
authors.affiliation: University of Applied Sciences and Arts, Department of Bioprocess Engineering-Microbiology, Heisterbergallee 12, D-30453 Hannover, Germany.
authors.forename: V
authors.initials: V
authors.lastname: Kromker
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Via Bianchi 9, 25124 Brescia, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Garbarino
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Via Bianchi 9, 25124 Brescia, Italy.
authors.forename: N
authors.initials: N
authors.lastname: Arrigoni
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Via Bianchi 9, 25124 Brescia, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Zanardi
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Via Bianchi 9, 25124 Brescia, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Bertocchi
authors.affiliation: Istituto Zooprofilattico Sperimentale delle Venezie, viale dell'Università 10, 3020 Legnaro (PD), Italy; Dipartimento di Medicina Animale, Produzioni e Salute (MAPS), Università degli Studi di Padova, Viale dell'Università 16, 35020 Legnaro, (PD), Italy.
authors.forename: F
authors.initials: F
authors.lastname: Gobbo
authors.affiliation: Istituto Zooprofilattico Sperimentale delle Venezie, viale dell'Università 10, 3020 Legnaro (PD), Italy.
authors.forename: S
authors.initials: S
authors.lastname: Catania
authors.affiliation: Dipartimento di Medicina Veterinaria, Università degli Studi di Milano, Via Celoria 10, 20133, Milan, Italy; Quality Milk Production Services, Animal Health Diagnostic Center, Cornell University, 240 Farrier Road, Ithaca, NY 14853.
authors.forename: P
authors.initials: P
authors.lastname: Moroni
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000890:Anti-Infective Agents / Q000494:pharmacology; D001530:Belgium; D002417:Cattle; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D008892:Milk / Q000187:drug effects / Q000382:microbiology*; D009175:Mycoplasma Infections / Q000662:veterinary; D045682:Mycoplasma bovis
chemical_list: D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents
keywords: Mycoplasma bovis; antimicrobials; dairy cattle; minimum inhibitory concentration