Effect of a disinfection strategy on the methicillin-resistant Staphylococcus aureus CC398 prevalence of sows, their piglets and the barn environment.

AIMS: To assess, in a cleaned and disinfected barn environment, the efficacy of an animal disinfection strategy to reduce the livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) prevalence in sows, their offspring and the barn environment. METHODS AND RESULTS: On each farm, six sow rounds were sampled; sows were divided into either a test or control group. Per round, 20 sows and 40 of their piglets were sampled at different time points together with the barn environment. The disinfection strategy of the test groups consisted of washing the sows with a shampoo followed by disinfection of the skin with a solution containing chlorhexidine digluconate and isopropanol. On the first day of disinfection and 6 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 no longer significant (P = 0·20). The MRSA prevalence of the piglets in the test groups was significantly lower (26%; P < 0·01) 6 days after the end of disinfection. Just before weaning, this difference was reduced to 5% but 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 (r(2)  > 0·6; P < 0·01) was seen between MRSA contamination in the barn environment and the MRSA prevalence in pigs. CONCLUSION: Results show that the tested disinfection strategy reduces temporarily the sow and piglet MRSA status, but does not result in a final reduction in MRSA at weaning or in the nursery unit. SIGNIFICANCE AND IMPACT OF THE STUDY: First report on the efficacy of an animal disinfection strategy to reduce LA-MRSA prevalence in sows, their offspring and the barn environment.

Evaluation of different chromogenic media for the detection of methicillin-resistant Staphylococcus aureus CC398 in broilers.

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) has emerged in a wide variety of animal species, including poultry. The objective of this study was to evaluate three different chromogenic media for MRSA clonal complex (CC) 398 detection in broilers. On three Belgian poultry farms, 50 broiler chickens were sampled per farm from both nose shell and cloaca. All swab specimens were enriched and inoculated the following day on three chromogenic media: chromID MRSA (bioMérieux), Brilliance MRSA 2 Agar (Oxoid) and MRSASelect (Bio-Rad). ChromID had the highest isolation rates, yet, Brilliance MRSA 2 Agar demonstrated the highest relative sensitivity, while MRSASelect and Brilliance MRSA 2 Agar showed the highest relative specificity. A subset of MRSA isolates was confirmed to be CC398 by the polymerase chain reaction (PCR) targeting sau1-hsdS1. In conclusion, Brilliance MRSA 2 Agar outperformed MRSASelect and chromID MRSA for the detection of MRSA in broilers.

Methicillin-resistant Staphylococcus aureus (MRSA) ST398 in pig farms and multispecies farms.

During the last few years, methicillin-resistant Staphylococcus aureus (MRSA) ST398 has been isolated frequently from livestock, especially from pigs and to a lesser extent from cattle and poultry. To gain insight into the distribution of this bacterium in pig farms versus multispecies farms, 30 Belgian farms (10 pig, 10 pig/poultry and 10 pig/cattle farms) were screened for the presence of MRSA. On each farm, 10 nasal swabs were taken from pigs. When present, cattle (n=10) were sampled in the nares and poultry (n=10) in the nares, earlobes and cloaca. A selection of the obtained isolates were further characterized using multilocus sequence typing (MLST), spa typing, SCCmec typing, pulsed field gel electrophoresis (PFGE), multiple-locus variable-number tandem repeat analysis (MLVA) and antimicrobial susceptibility testing. On 26 of 30 farms, MRSA was isolated from pigs. Furthermore, MRSA was also isolated from poultry and cattle on one pig/poultry and five pig/cattle farms, respectively. All tested MRSA isolates belonged to ST398. Eight spa types (t011, t034, t567, t571, t1451, t2974, t3423 and t5943) were detected, among which t011 predominated. SCCmec cassettes type IVa and V were present in 20% and 72% of the isolates, respectively. When combining the results of the two remaining typing methods, PFGE and MLVA, eighteen genotypes were obtained of which one genotype predominated (56% of the positive farms). All MRSA isolates were resistant to tetracycline. Resistance to trimethoprim, aminoglycosides, macrolides, lincosamides, fluoroquinolones and chloramphenicol was also observed. In conclusion, there was no effect of the farm type on the MRSA status of the pigs. A statistically significant difference was observed when comparing the pig/poultry or the pig/cattle MRSA status on the multispecies farms. Additionally, a wide variety of MRSA ST398 strains was found within certain farms when combining different typing methods.

Evaluation of salt concentrations, chromogenic media and anatomical sampling sites for detection of methicillin-resistant Staphylococcus aureus in pigs.

The performance of chromogenic media for the detection of methicillin-resistant Staphylococcus aureus (MRSA) in humans, has been evaluated in numerous studies. However, few comparative studies have been performed for the detection of MRSA in pigs. In this study two different salt concentrations (2.5% or 7.5% NaCl) were evaluated in the enrichment nutrient broth and three selective chromogenic media (chromID MRSA, BrillianceMRSA and MRSASelect) for their ability to detect MRSA in swabs from 29 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, followed by MRSASelect and BrilianceMRSA. For all chromogenic media more MRSA-positive results were obtained for specimens collected from skin behind the ears than for specimens taken from both nares and perineum. The results with regard to the anatomical sampling sites were confirmed in a larger study on three different pig farms involving 60 pigs per farm. 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.

Screening of poultry-pig farms for methicillin-resistant Staphylococcus aureus: sampling methodology and within herd prevalence in broiler flocks and pigs.

Many reports described the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in different livestock animals from one-species farms. However, in no published reports the prevalence on mixed poultry-pig farms was mentioned, nor the possible relation in MRSA colonization between those two species on one farm, and the possible role of the farmer in the dissemination of MRSA between those two species. Furthermore, no data is available on the optimal sampling site to detect MRSA in broilers. Therefore this study aimed to determine the most suitable sample location in broiler chickens for MRSA and the within flock prevalence of MRSA in various broiler flocks and compared this with the MRSA prevalence in pigs, the colonization of the farmer and the contamination in the barn environment in three mixed poultry-pig farms. MRSA was most frequently isolated from the cloaca and nose shell and to a lesser extent from the skin beneath the wing and the pharynx. 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. Based upon these relative sensitivities combining cloaca and nose shell would increase the chance of MRSA detection. A rather low within flock prevalence of MRSA varying between 0% and 28% was detected in broilers, 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. Conversely, 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. The farmer may play an important role in the dissemination of MRSA from pigs to poultry, especially in mixed farms where pigs are highly colonized and may act as a reservoir for MRSA ST398 carriage in humans.