Transmission of highly virulent community-associated MRSA ST93 and livestock-associated MRSA ST398 between humans and pigs in Australia

S Sahibzada,S Abraham,G W Coombs,M Hernández-Jover,S Pang,J Heller,D Jordan

doi:10.1038/s41598-017-04789-0

Abstract

Pigs have been recognised as a reservoir of livestock associated methicillin-resistant Staphylococcus aureus (LA-MRSA) in Europe, Asia and North America. However, little is known about the presence and distribution of MRSA in the Australian pig population and pig industry. This study describes the presence, distribution and molecular characteristics of the human adapted Australian CA-MRSA ST93 isolated from pigs, people, and the environment within a piggery. Isolates were subjected to antibiotic susceptibility testing, DNA microarray, whole genome sequencing, multi locus sequence typing, virulence and resistance gene characterization and phylogenetic analysis. MRSA were isolated from 60% (n = 52) of farm workers where 84% of isolates returned ST93 and the rest ST398. Of the thirty-one pig isolates tested further, an equal number of ST398 and ST93 (15 each) and one as ST30-V were identified. Four of six environmental isolates were identified as ST93 and two as ST398. This study has identified for the first time in Australia the occurrence of CA-MRSA ST93 and LA-MRSA ST398 amongst farm workers, pigs, and the farm environment. Comparative genome analysis indicates that ST398 is likely to have been introduced into Australia from Europe or North America. This study also reports the first linezolid resistant MRSA isolated in Australia.

Highlights

Methicillin-resistant Staphylococcus aureus (MRSA), in addition to being resistant to most beta-lactams, are typically resistant to multiple classes of antibiotics
MRSA were isolated from 31 (60%) of the 52 farm workers who participated in the study: 10/19 (53%) on Farm-A and 21/33 (64%) on Farm-B
The three major findings arise from this study are as follow: First, we have identified for the first time in Australia the dissemination of community-associated MRSA (CA-MRSA) ST93-IV and livestock-associated MRSA (LA-MRSA) ST398-V amongst farm workers, pigs and the farm environment; Second, we have found, using comparative genome analysis, that ST398-V was likely to have been introduced into Australia from Europe or North America and the ST93-IV pig MRSA isolates came from humans with subsequent pig adaptation; and third, to the best of our knowledge we report the first linezolid resistant MRSA isolated in Australia

Summary

Introduction

Methicillin-resistant Staphylococcus aureus (MRSA), in addition to being resistant to most beta-lactams, are typically resistant to multiple classes of antibiotics. First reported in a human hospitalised patient in the United Kingdom[1], MRSA are frequently isolated worldwide. MRSA infections were initially exclusively associated with the hospital setting, a change in epidemiology occurred in the 1990s when infections began to emerge amongst people who had no prior hospital association[2]. While CC398 is frequently reported to be associated with nasal carriage or colonization, infections resulting from this strain in humans, rare, may occur[18]. Occupational exposure to pigs is a risk factor for carriage, compared to CA-MRSA and HA-MRSA, CC398 is not transmissible from human to human, and has few virulence-associated genes[23,24,25]. A second Australian study in 2014 isolated CC398 from less than 1% of 324 pigs sampled from five different commercial pig farms and one feral herd located across Australia[30]

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