CHARACTERIZATION OF A METHICILLIN-RESISTANT STAPHYLOCOCCUS EPIDERMIDIS FOUND IN THE OCEAN

Staphylococcus epidermidis is a coagulase-negative, commensal bacterium that lives on the skin of humans. Although on human skin, it is considered an opportunistic pathogen, as well as a source of resistance genes for closely related Staphylococcus aureus. Methicillin resistant S. epidermidis (MRSE) is a group of S. epidermidis that is resistant to beta-lactam antibiotics. Beta-lactam antibiotics contain a beta-lactam ring and bind to penicillin binding proteins (PBP) making them nonfunctional. PBP are responsible for transpeptidation of the bacteria’s peptidoglycan wall. MRSE contain SCCmec, a chromosomal cassette that contains the mecA gene that codes for PBP2a that does not have the same affinity toward beta-lactam antibiotics which allows normal cell function to continue. MRSE are associated with nosocomial infections, which are commonly multidrug resistant. We hypothesized that MRSE carrying plasmid-mediated antibiotic resistance genes may be present in the environment, which could constitute a reservoir of multidrug-resistant MRSE. To test this hypothesis, a systematic sampling from environmental water sources was done. One strain isolated from Laguna Beach, CA was identified as a MRSE by disk diffusion test using cefoxitin and MALDI-TOF. The disk susceptibility test demonstrated phenotypic resistance to penicillin, doxycycline, trimethoprim/sulfamethoxazole, lincomycin, and erythromycin. The SCCmec was classified as type IVb due to IS431, mecA, ∆mecR, and IS1272. Five plasmids with sizes of 45kb, 6.4kb, 4.3kb, and two at 2kb were determined to be present by gel electrophoresis. Three plasmids were assembled with the sizes of 45kb, 4.4kb and 2.5kb. The 45kb plasmid was void of resistance. The 4.4kb plasmid had tetracycline resistance (tetK). It was 98% similar to an S.epidermidis plasmid in a Russian hospital patient. The 2.5kb plasmid had lincosamide resistance (lnuA). It was 84% similar to a S. epidermidis plasmid found in Germany from a cow with preclinical mastitis. Two plasmidic contigs were assembled. The first contained IS431mec, msrA, mphA and qacA. The blast comparisons showed 19 Staphylococci plasmid regions similar to the msrA, mphA and the qacA region: 1 in Australia and 18 in the USA. The second contig contained IS431mec, blaZ, bla, and blaR. The blast comparisons showed 7 Staphylococci plasmids similar to the blaZ contig found in Germany, China, Denmark, France, Norway and two from the USA. In conclusion, this is the first record of an environmentally isolated type IVb SCCmec MRSE carrying plasmid-encoded antibiotic resistance genes from an aquatic environment. The resistance regions on the environmental isolate were similar to clinical strains of Staphylococci species found throughout the world which could indicate an environmental gene pool for Staphylococci.