Novel Organization of the Staphylococcal Cassette Chromosome Composite Island in Clinical Staphylococcus haemolyticus and Staphylococcus hominis Subspecies Isolates from Dogs.

Staphylococcus haemolyticus and Staphylococcus hominis subsp. are common coagulase-negative staphylococcus opportunistic pathogens. In Thailand, the clinical strains 1864 and 48 and S. hominis subsp. 384 and 371 have been recovered from sick dogs. These strains were methicillin resistant with the nontypeable staphylococcal cassette chromosome (NT-SCC). The SCC element distribution in the clinical isolates from dogs was analyzed using whole-genome sequencing, which revealed the presence of different SCC composite islands (CIs) and gene structure. The SCC-CIs of ψSCC (13 kb) and ψSCC (11 kb) with a class C1 complex but no gene were discovered in 1864. The CIs of ψSCC with a C1 complex (28 kb), SCC with (23 kb), and ψSCC (2.6 kb) were discovered in 48. In SCC, insertion sequence IS contained an aminoglycoside-resistant gene []. Two copies of IS containing the tetracycline-resistant gene (K) were found downstream of ψSCC. In S. hominis subsp. , the SCC-CI in strain 384 had two separate sections: ψSCC (20 kb) and SCC (23 kb). ψSCC lacked the gene complex but carried the class A complex. Trimethoprim-resistant dihydrofolate reductase () was discovered on ψSCC between two copies of IS. In strain 371, SCC VIII (4A) (37 kb) lacking a direct repeat at the chromosomal end was identified. This study found SCC elements in clinical isolates from dogs that were structurally complex and varied in their genetic content, with novel organization. In Thailand, the staphylococcal cassette chromosome (SCC) element, which causes methicillin resistance through acquisition of the gene, has been studied in clinical coagulase-negative Staphylococcus isolates from various companion animals, and Staphylococcus haemolyticus and Staphylococcus hominis subsp. were found to have the most nontypeable (NT)-SCC elements. These species are more prone to causing illness and more resistant to a variety of antimicrobials than other coagulase-negative staphylococci. However, full characterization of NT-SCC in clinical and S. hominis subsp. isolates from such animals has been limited. Our findings support the use of full nucleotide sequencing rather than PCR designed for Staphylococcus aureus in further research of novel SCC elements. Moreover, several antimicrobial resistance and heavy metal resistance genes were identified on the SCC elements; these are important as they could limit the therapeutic options available in veterinary medicine.