LIVESTOCK-ASSOCIATED STAPHYLOCOCCUS AUREUS (CC398) AS A CAUSE OF HUMAN INFECTION IN ISRAEL

Staphylococcus aureus isolates of clonal complex 398 (CC398) have been reported globally as a cause of colonization in livestock workers. Recently, several reports documented symptomatic infections with these strains in patients reporting no livestock exposure. Though distinct human-origin and livestock-adapted lineages have been described within CC398, the reservoir of these infections still remains unclear. We aimed to determine the presence and prevalence of CC398 strains in Israel among 3,782 S. aureus isolates from human bacteremia and skin and soft tissue infections (SSTI), analyzed at the national reference center.

During 2011-2015, 56 individual human infections were caused by CC398-associated strains. The strains were isolated from bloodstream infections (46), and from SSTI (10) in 15 health care centers. Most of the cases (50) were caused by methicillin susceptible S. aureus (MSSA). The MRSA strains included spa types t011 and t1451, while the MSSA strains included t6605, t937, t571, t1149, t1255. Representative isolates were confirmed as ST398 and ST291 - a variant of ST398. The PVL toxin gene was detected in a single strain (t571). Resistance rates among the strains were noted for erythromycin (43%), clindamycin (45%), tetracycline (11%), ciprofloxacin (5%), gentamicin (5%), fusidic acid (2%), SXT (2%), linezolid (2%). Lineage variety was analyzed by Pulsed-Field Gel Electrophoresis, spa typing and an assay for the scn, chp and φ3 loci. CC398 comprised 2.2% of bacteremia strains analyzed at the national reference center, and the prevalence remained steady during the period analyzed.

Since its emergence in the previous decade, CC398 has become a frequent cause of colonization and disease in Europe. Further epidemiological and molecular analyses are required in order to clearly determine the reservoir of CC398 infections in Israel, and investigate the possible link to livestock.