Clonal complex (CC) 398 methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) are associated with carriage and infection among animals and humans but only a single case of CC398 MRSA has been reported in the Republic of Ireland (ROI). The present study investigated the molecular epidemiology of CC398 MRSA (n = 22) and MSSA (n = 10) from animals and humans in the ROI from 2010–2014. Isolates underwent antimicrobial susceptibility testing, spa typing, DNA microarray profiling and PCR for CC398-associated resistance genes. All MRSA underwent SCCmec IV or V subtyping. Four distinct CC398-MRSA incidents were identified from (i) a man in a nursing home (spa type t011-SCCmec IVa, immune evasion complex (IEC) negative), (ii) a horse and veterinarian who had recently travelled to Belgium (t011-IVa, IEC positive), (iii) pigs (n = 9) and farm workers (n = 9) on two farms, one which had been restocked with German gilts and the other which was a finisher farm (t034-VT, IEC negative, 3/9 pigs; t011- VT, IEC negative, 6/9 pigs & 9/9 farm workers), and (iv) a child who had worked on a pig farm in the UK (t034-VT, IEC negative). Isolates also carried different combinations of multiple resistance genes including erm(A), erm(B), tet(K), tet(M) & tet(L), fexA, spc, dfrG, dfrK aacA-aphD and aadD further highlighting the presence of multiple CC398-MRSA strains. CC398 MSSA were recovered from pigs (n = 8) and humans (n = 2). CC398 MSSA transmission was identified among pigs but zoonotic transmission was not detected with animal and human isolates exhibiting clade-specific traits. This study highlights the importation and zoonotic spread of CC398 MRSA in the ROI and the spread of CC398 MSSA among pigs. Increased surveillance is warranted to prevent further CC398 MRSA importation and spread in a country that was considered CC398 MRSA free.
22The emergence of methicillin-resistant Staphylococcus aureus (MRSA) in livestock has 23 refocused attention on S. aureus colonization and transmission in pigs. This study 24 investigated the effect of the S. aureus colonization status of a sow on the colonization status 25 of her piglets, and whether pigs carry the same strain of S. aureus throughout production. 26 Nasal swabs were collected from the piglets of six healthy sows two days after birth and two 27 days before and two days after they were moved into each production stage. The average 28 prevalence of S. aureus colonization varied between 26% and 73%. The odds of being S. 29 aureus positive were almost 12 times higher for piglets born to nasal-positive sows than for 30 those born to nasal-negative sows, and three times higher again for piglets born to sows that 31 were both nasal-and vaginal-positive. Isolates recovered from piglets immediately after birth 32 were indistinguishable from those of the dam as determined by phenotypic and molecular 33 typing, including microarray analysis and optical mapping. All isolates belonged to clonal 34 complex 9 and the majority exhibited a novel spa type, t10449. The findings show that the S. 35 aureus colonization status of the sow influences the colonization status of her piglets in the 36 early production stages but strains carried by pigs change over time. Multiresistant S. aureus 37 was detected, in particular post-weaning. Results suggest that sow status and management 38 practices, including mixing of pigs and antimicrobial usage at weaning, should be considered 39 when implementing control measures for S. aureus on a farm. 40Word count: 249 41
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