Prevalence and characterization of -methicillin-resistant Macrococcus spp. in food producing animals and meat in Switzerland in 2019

The prevalence of methicillin-resistant Macrococcus spp. in calves and pigs at slaughterhouses and in retail beef and pork meat was determined using samples taken in 2019 within the framework of the national monitoring of methicillin-resistant Staphylococcus aureus in food producing animals in Switzerland. The isolates were submitted to antimicrobial susceptibility testing of 19 antibiotics and to molecular techniques (e.g. PCR, microarray, WGS) for the identification of resistance genes, elements containing the methicillin resistance genes mec and sequence type (ST). Methicillin-resistant Macrococcus spp. (M. caseolyticus (n=38), M. bohemicus (n=4) and Macrococcus spp. (n=2)) were isolated in 40 of 299 nasal swabs from calves representing a prevalence of 13,38 % (95 % CI, 9,98 % - 17,70 %), and in four of 303 nasal swabs from pigs [1,32 % (95 % CI, 0,36 % - 3,35 %)]. One of 311 samples of Swiss pork meat contained a Macrococcus sp. [0,32 % (95 % CI, 0,01 % - 1,78 %)], and four of 309 beef meat samples (260 domestic and 49 imported) contained M. caseolyticus [1,29 % (95 % CI, 0,35 % - 3,28 %)]. The M. caseolyticus strains belonged to diverse STs, with ST21 being the most common in both pigs and calves. The mecD gene was located on Macrococcus resistance island mecD (McRImecD) in 42 strains and on staphylococcal cassette chromosome mec (SCCmecD) in three strains, while mecB was found on plasmids in four strains. In addition to resistance to β-lactams, the strains also exhibited resistance to tetracycline (n=17; tet(L), tet(K), tet(M)), streptomycin (n=13; str, ant(6)-Ia, rpsL mutation [K56R in ribosomal protein S12]), kanamycin (n=10; aac(6')-Ie - aph(2'')-Ia, aph(2')-Ib, aph(2')-Ic, ant(4')-Ia), clindamycin (n=9; erm(B), erm(45)), erythromycin (n=9; erm(B), msr(G), erm(45)), fusidic acid (n=9; fusC) and gentamicin (n=1; aac(6')-Ie - aph(2'')-Ia). This study represents the first national prevalence study of methicillin-resistant Macrococcus spp. in pigs, calves, pork and beef meat in Switzerland and revealed a reservoir of genetically diverse strains carrying several resistance traits.