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

Simple Summary Staphylococcus aureus is present in the microbiota of both humans and some animal species, being recognized as one of the most important opportunistic human pathogens. S. aureus is responsible for causing a variety of infections. Methicillin-resistant S. aureus (MRSA) is particularly important, as it is becoming increasingly prevalent in the population. MRSA has been increasingly reported among wild free-living animals which may impose a public health concern due to its zoonotic potential. To investigate the prevalence and antimicrobial resistance of S. aureus and MRSA in wild synanthropic rodent populations, we conducted this study on 204 rodents captured in port areas in Portugal. The antimicrobial resistance was investigated in all isolates as well as virulence genes and genetic lineages. Thirty-eight S. aureus were isolated. The results showed that six MRSA were detected with particularly interesting mecC-carrying MRSA isolates which had not yet been found in Portugal. A low frequency of antibiotic resistance and virulence genes was observed among the isolates. Nevertheless, a high diversity of clonal lineages was detected among S. aureus some of which are associated with livestock. The frequent carriage of Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), by wild animals along with its zoonotic potential poses a public health problem. Furthermore, the repeated detection of the mecA gene homologue, mecC, in wildlife raises the question whether these animals may be a reservoir for mecC-MRSA. Thus, we aimed to isolate S. aureus 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 degrees 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 S. aureus. All isolates were characterized by MLST, spa- and agr typing. From 204 samples, 38 S. aureus were isolated of which six MRSA were detected. Among the six MRSA isolates, three harbored the mecC gene and the other three, the mecA gene. All mecC-MRSA isolates were ascribed to sequence type (ST) 1945 (which belongs to CC130) and spa-type t1535 whereas the mecA isolates belonged to ST22 and ST36 and spa-types t747 and t018. Twenty-five S. aureus were susceptible to all antibiotics tested. S. aureus isolates were ascribed to 11 MLST and 12 spa-types. S. aureus presents a great diversity of genetic lineages in wild rodents. This is the first report of mecC-MRSA in Portugal.

Automated summary

The study conducted in wild rodents living in port areas in Portugal revealed the presence of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA), with some MRSA isolates carrying the mecC gene, indicating a high genetic lineage diversity.