Typing of Islands in Genetically Diverse Methicillin-Resistant Strains from Cattle.

belongs to the normal bacterial flora of dairy cows and does not usually cause disease. However, methicillin-resistant strains were isolated from bovine mastitis milk. These bacteria had acquired a chromosomal island (McRI -1 or McRI -2) carrying the methicillin resistance gene To gain insight into the distribution of McRI types in from cattle, 33 -containing strains from Switzerland were characterized using molecular techniques, including multilocus sequence typing, antibiotic resistance gene identification, and PCR-based McRI typing. In addition, the same genetic features were analyzed in 27 -containing strains isolated from bovine bulk milk in England/Wales using publicly available whole-genome sequences. The 60 strains belonged to 24 different sequence types (STs), with strains belonging to ST5, ST6, ST21, and ST26 observed in both Switzerland and England/Wales. McRI -1 was found in different STs from Switzerland ( = 19) and England/Wales ( = 4). McRI -2 was only found in 7 strains from Switzerland, all of which belonged to ST6. A novel island, McRI -3, which contains a complete operon ( [where the subscript indicates ]) combined with the left part of McRI -2 and the right part of McRI -1, was found in heterogeneous STs from both collections (Switzerland,  = 7; England/Wales,  = 21). Two strains from England/Wales carried a truncated McRI -3. Phylogenetic analyses revealed no clustering of strains according to geographical origin or carriage of McRI -1 and McRI -3. Circular excisions were also detected for McRI -1 and McRI -3 by PCR. The analyses indicate that these islands are mobile and may spread by horizontal gene transfer between genetically diverse strains. Since its first description in 2017, the methicillin resistance gene has been detected in strains from different cattle sources and countries. Our study provides new insights into the molecular diversity of -carrying strains by using two approaches to characterize elements: (i) multiplex PCR for molecular typing of McRI and (ii) read mapping against reference sequences to identify McRI types In combination with multilocus sequence typing, this approach can be used for molecular characterization and surveillance of carrying .