Title: Methicillin-resistant Staphylococcus aureus in farm animals: detection, prevalence, transmission routes and disinfection strategy.
Other Titles: Methicilline resistente Staphylococcus aureus bij landbouwhuisdieren: detectie, prevalentie, transmissieroutes en desinfectie strategie.
Authors: Pletinckx, Larissa
Issue Date: 26-Jun-2013
Abstract: Staphylococcus aureus is an important human and animal pathogen with a spectacular adaptive capacity. Overuse and misuse of methicillin and other similar penicillins caused different outbreaks of methicillin-resistant S. aureus (MRSA) in hospitals in the sixties, giving rise to hospital-associated MRSA (HA-MRSA). In the late 1990s, MRSA strains began to show up in the community, causing community- associated infections (CA-MRSA). However, it did not stop with these two main types. Mid 2000¬ís, a new MRSA lineage clonal complex (CC) 398 was described and titled livestock-associated MRSA (LA-MRSA). This type was mainly reported in pigs, but also in other food producing animals and in people in close contact with these animals. In order to define prevalence and characterize the problem of LA-MRSA, the literature concerning S. aureus, antimicrobials and the emergence of antimicrobial resistance, identification and typing of LA-MRSA and non-antibiotic remediation, was reviewed and resulted in several goals for our study.A first objective was to define the suitable media and correct animal sampling sites for maximal detection of MRSA in pigs and poultry. Two different salt concentrations (2.5% or 7.5% NaCl) were evaluated and three selective chromogenic media (ChromID MRSA, BrillianceMRSA and MRSASelect) for their ability to detect MRSA in swabs from pigs obtained from three different anatomical sampling sites (anterior nares, skin behind both ears and perineum). ChromID MRSA showed the highest relative sensitivity and specificity after enrichment in 7.5% NaCl. The skin behind the ears was the anatomical site with the highest relative sensitivity (91.4%) for MRSA detection compared to perineum and anterior nares, with a relative sensitivity of 76.5% and 75.3%, respectively. An increased relative sensitivity could be achieved when combining two anatomical sites. Sampling of anterior nares and skin behind the ears appeared to be the most sensitive combination with a relative sensitivity of 98.2%. These results show that sampling of only the anterior nares underestimates the real pig MRSA prevalence. In chickens however, BrillianceMRSA 2 Agar outperformed MRSASelect and ChromID MRSA. ChromID MRSA had the highest isolation rates, BrillianceMRSA 2 agar demonstrated the highest relative sensitivity while MRSASelect and BrillianceMRSA 2 agar the highest relative specificity. MRSA was most frequently isolated from the cloaca (8) and nose shell (6) and to a lesser extent from the skin beneath the wing (3) and the pharynx (1). The relative sensitivity of the different anatomical sites was 44.4% for the cloaca, 33.3% for the nose shell, 16.7% for the skin beneath the wing and 5.6% for the pharynx. Combining cloaca and nose shell (77.8%) increased the chance of MRSA detection. Furthermore, also the within flock prevalence of MRSA in various broiler flocks was compared with the MRSA prevalence in pigs, the colonization of the farmer and the contamination in the barn environment. A rather low within flock prevalence of MRSA between 0 and 28% was detected in broilers, varying between flocks, whereas in pigs on the same farms the within herd prevalence varied between 82 and 92%. No MRSA contamination in the direct barn environment of the broilers was found, this in contrast to the environment of the pigs, indicating a relationship between MRSA prevalence and contamination in the environment. Two farmers were continuously colonized, while the third one was only once. In conclusion, a major difference was seen in MRSA occurrence between broilers and pigs from the same farm. This may suggest that broilers are naturally less susceptible to MRSA ST398 colonization than pigs. In addition, short production time in broilers, vacancy of the barn environment during one week and the higher frequency of disinfection might also explain the lower prevalence in broilers. In order to know more about the transmission routes of MRSA ST398 between different animal species, the barn environment and people residing on the same farm, two pig farms, two poultry-pig farms and two dairy-pig farms were investigated for presence of MRSA and obtained spa-, SCCmec- type and antimicrobial susceptibility profiles were compared. Multilocus sequence typing (MLST) showed that MRSA ST398 was found in all animal species, in farmers and also in the pig barn environment. The presence of MRSA with the same spa-, SCCmec- type and antibiotic profile in the different animal species in direct or indirect contact with pigs suggests MRSA transfer. Weaned piglets had the highest MRSA prevalence (86.3%) and a high correlation (r=0.86, p=0.03) was observed between sows and pre-weaned piglets. The results also indicated that barn environment, companion animals, rats, mice and farmers could play an important role in the dissemination of MRSA, emphasizing the importance of internal biosecurity. However, external biosecurity is equally important because other spa-, SCCmec- types or antimicrobial resistances can be introduced through purchase of gilts. This study demonstrated that MRSA likely spreads between animal species, humans and the pig barn environment, which is why it is important to accurately implement control practices, in which not only pigs should be targeted, but also all other animal species present on farms. Therefore a disinfection strategy was tested on two pig farms. The disinfection strategy of the test groups consisted of washing the sows with a shampoo to remove dirt before entry in the farrowing unit followed by disinfection of the skin during six days prior to farrowing by spraying a solution containing chlorhexidine digluconate and isopropanol. On the first day of disinfection and six days after stopping the disinfection a significant decrease (P<0.01) of on average 68% and 66% in sow MRSA prevalence was observed on both farms, whereas no decrease was seen in the control groups. Just before weaning, 21/28 days after the end of the disinfection strategy, the difference in MRSA prevalence between both groups was reduced to 4% and was no longer significant (P=0.20). The MRSA prevalence of the piglets in the test groups was significantly lower (26%; P<0.01) six days after the end of disinfection. Just before weaning this difference was reduced to 5% but was still significant (P<0.01). In the swine nursery unit, no significant difference (P=0.99) was seen between both groups. Based on semi-quantitative counts, a relationship (r2>0.6; P<0.01) was seen between MRSA contamination in the barn environment and the MRSA prevalence in pigs. The results show that the tested disinfection strategy reduces temporary the sow- and piglet-MRSA status, but does not result in a final reduction of MRSA at weaning or in the nursery unit. In conclusion our study illuminates once more that MRSA CC398 is abundantly present in animals, but also in humans in close contact with livestock. If the disinfection strategy would be applied several times with intervals and in combination with nasal wash, it might limit pig-pig, pig-human and pig-environment transmission, as the results clearly indicate a decrease in MRSA prevalence. However, further research is needed to find measures that manage to decrease MRSA. As it is really difficult to reduce LA-MRSA from pig farms, MRSA negative farms should concentrate even more on maintaining their MRSA negative status, as prevention is better and much easier than remediation.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Division of Gene Technology (-)
Studiegebied Gezondheidszorg VIVES-Zuid

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