Research Article: Livestock-associated Staphylococcus aureus on Polish pig farms

Date Published: February 2, 2017

Publisher: Public Library of Science

Author(s): Aneta Mroczkowska, Jacek Żmudzki, Natalia Marszałek, Monika Orczykowska-Kotyna, Iga Komorowska, Agnieszka Nowak, Anna Grzesiak, Ewelina Czyżewska-Dors, Arkadiusz Dors, Zygmunt Pejsak, Waleria Hryniewicz, Tomasz Wyszomirski, Joanna Empel, Karsten Becker.


Livestock-associated Staphylococcus aureus (LA-SA) draws increasing attention due to its particular ability to colonize farm animals and be transmitted to people, which in turn leads to its spread in the environment. The aim of the study was to determine the dissemination of LA-SA on pig farms selected throughout Poland, characterize the population structure of identified S. aureus, and assess the prevalence of LA-SA carriage amongst farmers and veterinarians being in contact with pigs.

The study was conducted on 123 pig farms (89 farrow-to-finish and 34 nucleus herds), located in 15 out of 16 provinces of Poland. Human and pig nasal swabs, as well as dust samples were analyzed. S. aureus was detected on 79 (64.2%) farms from 14 provinces. Amongst these farms LA-SA-positive farms dominated (71/79, 89.9%, 95% CI [81.0%, 95.5%]). The prevalence of LA-MRSA-positive farms was lower than LA-MSSA-positive (36.6% of LA-SA-positive farms, 95% CI [25.5%, 48.9%] vs. 74.6%, 95% CI [62.9%, 84.2%]). In total, 190 S. aureus isolates were identified: 72 (38%) MRSA and 118 (62%) methicillin-susceptible S. aureus (MSSA), of which 174 (92%) isolates were classified to three livestock-associated lineages: CC398 (73%), CC9 (13%), and CC30/ST433 (6%). All CC398 isolates belonged to the animal clade. Four LA-MRSA clones were detected: ST433-IVa(2B) clone (n = 8, 11%), described to the best of our knowledge for the first time, and three ST398 clones (n = 64, 89%) with the most prevalent being ST398-V(5C2&5)c, followed by ST398-V(5C2), and ST398-IVa(2B).

The prevalence of LA-MRSA-positive pig farms in Poland has increased considerably since 2008, when the first MRSA EU baseline survey was conducted in Europe. On Polish pig farms CC398 of the animal clade predominates, this being also reflected in the prevalence of CC398 nasal carriage in farmers and veterinarians. However, finding a new ST433-IVa(2B) clone provides evidence for the continuing evolution of LA-MRSA and argues for further monitoring of S. aureus in farm animals.

Partial Text

Staphylococcus aureus is one of the major human opportunistic pathogens responsible for wide range of infections [1]. Of particular concern remain methicillin-resistant S. aureus (MRSA) strains causing severe infections with treatment limitations. Initially, MRSA strains had been restricted to the hospital environment (hospital-associated MRSA, HA-MRSA), but later they also emerged in the community (community-associated, CA-MRSA) [2]. During the past decade, a new subpopulation of S. aureus, so-called livestock-associated S. aureus (LA-SA), has been described. The first LA-SA strains were reported amongst pigs and pig farmers in France and the Netherlands; livestock-associated MRSA (LA-MRSA) strains were represented exclusively by clonal complex (CC) 398, whereas livestock-associated methicillin-susceptible S. aureus (LA-MSSA) were more diverse and encompassed S. aureus of both CC398 and sequence type (ST) 9 or 433 [3, 4]. In subsequent years CC398-MRSA strains were identified in pigs all over the world [5–8]. Although different MRSA lineages adapted to pigs have been reported, only two of them are recognized as the most prevalent: CC398 in Europe, and CC9 in Asia [9–11]. CC398-MRSA strains are drawing increased attention on grounds of their particular ability to colonize livestock animals, and be transmitted to persons being in contact with colonized animals and their environment [12–15]. Despite suggestions that CC398 is less virulent than other MRSA lineages, a number of studies demonstrate infections caused by CC398-MRSA in humans, especially in pig farmers and their family members [16–19] and indicate food-producing animals as a potential source of their origin.

The epidemiology of S. aureus in Western and Central Europe has changed significantly in the past decade due to the emergence of genetic lineages adapted to livestock animals, especially to pigs. Here we present the results of the first structured survey conducted on pig farms in Poland, which partially fill the gap concerning the prevalence and molecular characteristics of livestock-associated S. aureus, both MRSA and MSSA, in the central and eastern EU countries.




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