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

Abstract

Staphylococcus haemolyticus and Staphylococcus hominis subsp. hominis are common coagulase-negative staphylococcus opportunistic pathogens. In Thailand, the clinical strains S. haemolyticus 1864 and 48 and S. hominis subsp. hominis 384 and 371 have been recovered from sick dogs. These strains were methicillin resistant with the nontypeable staphylococcal cassette chromosome mec (NT-SCCmec). The SCCmec element distribution in the clinical isolates from dogs was analyzed using whole-genome sequencing, which revealed the presence of different SCCmec composite islands (CIs) and gene structure. The SCCmec-CIs of c SCCmec1864 (13 kb) and c SCC1864 (11 kb) with a class C1 mec complex but no ccr gene were discovered in S. haemolyticus 1864. The CIs of c SCCmec48 with a C1 mec complex (28 kb), SCC48 with ccrA4B4 (23 kb), and c SCC48 (2.6 kb) were discovered in S. haemolyticus 48. In SCC48, insertion sequence IS256 contained an aminoglycoside-resistant gene [aph(20)-Ia]. Two copies of IS431 containing the tetracycline-resistant gene tet(K) were found downstream of c SCC48. In S. hominis subsp. hominis, the SCCmec-CI in strain 384 had two separate sections: c SCCmec384 (20 kb) and SCCars (23 kb). c SCCmec384 lacked the ccr gene complex but carried the class A mec complex. Trimethoprim-resistant dihydrofolate reductase (dfrC) was discovered on c SCCmec384 between two copies of IS257. In strain 371, SCCmec VIII (4A) (37 kb) lacking a direct repeat at the chromosomal end was identified. This study found SCCmec elements in clinical isolates from dogs that were structurally complex and varied in their genetic content, with novel organization.