Molecular Epidemiology of Livestock-Associated Methicillin Resistant Staphylococcus aureus (LA MRSA) clonal complex CC398 in Israel

Livestock associated methicillin resistant Staphylococcus aureus (LA-MRSA) has recently emerged in hospital and community-acquired infections in several European countries and globally. CC398, the most prevalent LA-MRSA clade, caused infections among humans in close contact with animals, as well as in patients reporting no livestock exposure. Molecular typing reflects diversity among CC398 (spa types, SCCmec types and PFGE). Nevertheless, human-origin CC398 and livestock origin can be distinguished by the presence of an immune evasion cluster (IEC), encoding human innate immune modulators, that are rare in livestock associated isolates. In addition tetracycline resistance has been postulated as a LA-MRSA marker. We aimed to determine the prevalence of CC398 strains in Israel among 10,005 S. aureus isolates from human bacteremia and skin and soft tissue infections (SSTI), analyzed at the national reference center. In addition we examined the possible origin and the likely link to livestock.

During 2011-2018, 135 (1% of all cases) individual human infections were caused by CC398-associated strains. The strains were isolated from bloodstream infections (65), and from SSTI (70) in 20 health care centers. Most of the cases (106) were caused by methicillin susceptible S. aureus (MSSA). The MRSA strains included spa types t011, t034, t190, t937 and t1451, while the MSSA strains included t6605, t571, t937, t1451, t1149 and t1255. Representative isolates were confirmed as ST398 and ST291 - a variant of ST398. The PVL toxin gene was detected in a 9 strains. In general, the results imply to several lineages that may be associated with multiple sources, while most of the isolates are apparently of a human origin, isolates of spa type t011 are of livestock origin.