Resistance phenotypes and genotypes of methicillin-resistant Staphylococcus aureus isolates from broiler chickens at slaughter and abattoir workers.

OBJECTIVES: To comparatively investigate the resistance phenotypes and genotypes of various methicillin-resistant Staphylococcus aureus (MRSA) isolates from broilers at slaughter and workers at the respective poultry slaughterhouses. METHODS: Forty-six MRSA isolates (28 from broilers and 18 from humans) obtained at four different slaughterhouses were included. In addition to previously determined sequence types (STs) and spa types, the isolates were characterized by dru typing, SCCmec typing and PFGE. Resistance phenotypes were determined by broth microdilution. Resistance genes and clonal complexes (CCs) were detected by DNA microarray or specific PCR assays. RESULTS: MRSA of CC398, spa type t011 and varying dru types represented 23/28 broiler isolates and 12/18 human isolates. Three ST9/t1430/dt10a isolates were each seen among the isolates from the abattoir workers and the broilers. In addition, two human CC398/ST1453/t4652/dt3c isolates, a single human CC398/t034/dt6j isolate and two chicken CC398/t108/dt11a isolates were detected. All CC398 isolates (including ST1453) and some of the ST9 isolates from chickens and humans showed resistance to four to nine classes of antimicrobial agents and carried a wide range of resistance genes. While the resistance phenotypes and genotypes of the chicken isolates of the same flock were closely related, they usually differed from the resistance phenotypes and genotypes of the isolates from the workers at the respective slaughterhouse. CONCLUSIONS: The apparent homogeneity of MRSA isolates from the same flock suggests exchange of isolates between the respective animals. The apparent heterogeneity of MRSA isolates from abattoir workers might reflect their occupational contact with animals from numerous chicken flocks.

Longitudinal study on transmission of MRSA CC398 within pig herds.

UNLABELLED: ABSBACKGROUND: Since the detection of MRSA CC398 in pigs in 2004, it has emerged in livestock worldwide. MRSA CC398 has been found in people in contact with livestock and thus has become a public health issue. Data from a large-scale longitudinal study in two Danish and four Dutch pig herds were used to quantify MRSA CC398 transmission rates within pig herds and to identify factors affecting transmission between pigs. RESULTS: Sows and their offspring were sampled at varying intervals during a production cycle. Overall MRSA prevalence of sows increased from 33% before farrowing to 77% before weaning. Overall MRSA prevalence of piglets was>60% during the entire study period. The recurrent finding of MRSA in the majority of individuals indicates true colonization or might be the result of contamination. Transmission rates were estimated using a Susceptible-Infectious-Susceptible (SIS-)model, which resulted in values of the reproduction ratio (R0) varying from 0.24 to 8.08. Transmission rates were higher in pigs treated with tetracyclins and ß-lactams compared to untreated pigs implying a selective advantage of MRSA CC398 when these antimicrobials are used. Furthermore, transmission rates were higher in pre-weaning pigs compared to post-weaning pigs which might be explained by an age-related susceptibility or the presence of the sow as a primary source of MRSA CC398. Finally, transmission rates increased with the relative increase of the infection pressure within the pen compared to the total infection pressure, implying that within-pen transmission is a more important route compared to between-pen transmission and transmission through environmental exposure. CONCLUSION: Our results indicate that MRSA CC398 is able to spread and persist in pig herds, resulting in an endemic situation. Transmission rates are affected by the use of selective antimicrobials and by the age of pigs.

Persistence of livestock-associated methicillin-resistant Staphylococcus aureus in field workers after short-term occupational exposure to pigs and veal calves.

The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) carriage in pig and veal calf farmers in the Netherlands is estimated at 25 to 35%. However, no information is available about MRSA carriage in humans after short-term occupational exposure to pigs or veal calves. This study examines the prevalence and duration of MRSA acquisition after short-term intensive exposure to pigs or veal calves for persons not exposed to livestock on a daily basis. The study was performed with field workers who took samples from the animals or the animal houses in studies on MRSA prevalence in pig and veal farms. They were tested for MRSA by taking nasal samples before, directly after, and 24 h after they visited the farms. There were 199 sampling moments from visits to 118 MRSA-positive farms. Thirty-four of these visits (17%) resulted in the acquisition of MRSA. Thirty-one persons (94%) appeared negative again after 24 h. There were 62 visits to 34 MRSA-negative farms; none of the field workers acquired MRSA during these visits. Except for that from one person, all spa types found in the field workers were identical to those found in the animals or in the dust in animal houses and belonged to the livestock-associated clone. In conclusion, MRSA is frequently present after short-term occupational exposure, but in most cases the strain is lost again after 24 h.

Quantification of transmission of livestock-associated methicillin resistant Staphylococcus aureus in pigs.

Antimicrobial resistance in pigs becomes a public health issue when resistant organisms transfer from pigs to humans. Pigs are a large reservoir for livestock-associated (LA-)MRSA and people in contact with pigs are at risk for infection with LA-MRSA. Transmission and persistence of LA-MRSA within a pig population contributes to the maintenance of this zoonotic reservoir. Current knowledge on colonization and transmission of LA-MRSA in pigs is limited and mainly based on observational field surveys. Two experiments were performed to colonize pigs and quantify transmission of LA-MRSA between pigs. In the first experiment, colonization of six-week old piglets failed after intranasal inoculation, confirming the complexity of MRSA-colonization. In the second experiment, naive pigs got colonized after exposure to orally inoculated pigs. Subsequently, these contact-infected pigs transmitted MRSA to a new group of naive pigs. The reproduction ratio, R(0), was estimated with a SIS-model to quantify transmission between the first and second contact pigs as this resembles more the natural transmission. Two scenarios were evaluated, with different assumptions regarding infection status of individual pigs. R(0) varied between 3.7 and 4.3 and was significantly above 1, indicating a high probability of persistence of LA-MRSA, even without antimicrobial use.

Transmission of methicillin resistant Staphylococcus aureus among pigs during transportation from farm to abattoir.

The prevalence of methicillin resistant Staphylococcus aureus (MRSA) in pigs at abattoirs is higher than in pigs sampled on farms. This study investigated whether MRSA negative pigs can become MRSA positive during transportation from the farm to the abattoir after exposure to other pigs and environmental sources of MRSA. Nasal swabs were collected from four batches of pigs during loading at the farm, on arrival at the abattoir and after stunning. Environmental wipes were taken from lorries after transporting pigs and from lairages after holding pigs. All pigs (n=117) tested MRSA negative before transportation. On arrival at the abattoir, 12/117 (10.3%) pigs in two batches tested MRSA positive. In lorries that tested positive after transportation, the prevalence of MRSA positive pigs was 21.1%, whereas no MRSA was detected in pigs that had been transported in lorries that tested negative after transportation. At stunning, all batches and 70/117 (59.8%) pigs tested MRSA positive. Pigs can become MRSA positive in the short period of time during transportation from the farm to stunning at the abattoir.