Antimicrobial Resistance and Genetic Lineages of Staphylococcus aureus from Wild Rodents: First Report of mecC-Positive Methicillin-Resistant S. aureus (MRSA) in Portugal

Abstract

The frequent carriage of <i>Staphylococcus aureus</i>, including methicillin-resistant <i>S. aureus</i> (MRSA), by wild animals along with its zoonotic potential poses a public health problem. Furthermore, the repeated detection of the <i>mec</i>A gene homologue, <i>mec</i>C, in wildlife raises the question whether these animals may be a reservoir for <i>mec</i>C-MRSA. Thus, we aimed to isolate <i>S. aureus</i> and MRSA from wild rodents living in port areas and to characterize their antimicrobial resistance and genetic lineages. Mouth and rectal swab samples were recovered from 204 wild rodents. The samples were incubated in BHI broth with 6.5% of NaCl and after 24 h at 37 °C the inoculum was seeded onto Baird-Parker agar, Mannitol Salt agar and ORSAB (supplemented with 2 mg/L of oxacillin) plates. Species identification was confirmed by MALDI-TOF MS. The antimicrobial susceptibility testing was performed by the Kirby-Bauer disc diffusion method against 14 antibiotics. The presence of virulence and resistance genes was performed by PCR. The immune evasion cluster (IEC) system was investigated in all <i>S. aureus</i>. All isolates were characterized by MLST, <i>spa</i>- and <i>agr</i> typing. From 204 samples, 38 <i>S. aureus</i> were isolated of which six MRSA were detected. Among the six MRSA isolates, three harbored the <i>mec</i>C gene and the other three, the <i>mec</i>A gene. All <i>mec</i>C-MRSA isolates were ascribed to sequence type (ST) 1945 (which belongs to CC130) and <i>spa</i>-type t1535 whereas the <i>mec</i>A isolates belonged to ST22 and ST36 and <i>spa</i>-types t747 and t018. Twenty-five <i>S. aureus</i> were susceptible to all antibiotics tested. <i>S. aureus</i> isolates were ascribed to 11 MLST and 12 <i>spa</i>-types. <i>S. aureus</i> presents a great diversity of genetic lineages in wild rodents. This is the first report of <i>mec</i>C-MRSA in Portugal.