Methicillin-resistant
Recently, pigs were shown to be a major reservoir for MRSA multilocus sequence type 398 (ST398). Because this sequence type has also been isolated from other animal species, it is referred to as livestock-associated MRSA (
In 2007, from randomly selected farms in Belgium, we sampled 5 laying hens from each of 10 farms and 5 broiler chickens from each of 14 farms. One broiler farm was sampled twice (4 months apart, from different flocks in the same house, leaving 1 production round unsampled). Samples were taken from the cloaca and nasal cavity of these 50 laying hens and 75 broiler chickens.
Samples were first incubated in a brain–heart infusion broth supplemented with nalidixic acid and colistin, each at a concentration of 10 µg/mL. After overnight incubation at 37°C, 1 µL of this broth was streaked onto an MRSA ChromID plate (bioMérieux, Marcy l’Etoile, France) and incubated for 24–48 h at 37°C. To differentiate phenotypes of
The phenotypically identified MRSA strains were then confirmed by 16S rRNA-
Disk susceptibility of the strains was tested by using the Kirby-Bauer disk-diffusion method. Clinical Laboratory Standards Institute guidelines (M31-A3) were followed for inoculum standardization. After plates were incubated for 18 h, inhibition zones were measured in millimeters and interpreted according to Neo-Sensitabs manufacturer’s instructions (http://rosco.dk).
MRSA was not isolated from any laying hen samples. This finding may indicate that MRSA is absent or present only in low numbers in laying hens, possibly because of the limited use of antimicrobial drugs in these animals. Use of certain antimicrobial drugs in human hospitals has been shown to be a risk factor for acquiring MRSA infection, especially when the chosen treatment is inappropriate or insufficient (
MRSA was isolated from 8 broiler chickens from 2 of the 14 farms sampled. Low prevalence in poultry has also been found by Kitai et al. (
In the MRSA-positive flocks, the number of positive samples varied between 1/5 (20%) and 5/5 (100%). From the 1 MRSA-positive farm that was sampled twice, MRSA was isolated on both occasions. This finding indicates that MRSA may persist on a farm and colonize future flocks. MRSA was found in nearly equal numbers from the nares samples and the cloaca samples. Of the 8 MRSA-positive animals (16 samples), MRSA was found in all samples except for 1 cloacal swab, for a total of 15 MRSA isolations.
Susceptibility testing showed that all 15 isolated strains were resistant to erythromycin, kanamycin, tobramycin, lincomycin, tylosin, tetracycline, and trimethoprim. All strains were susceptible to chloramphenicol, ciprofloxacin, linezolid, mupirocin, quinopristin-dalfopristin, rifampin, and sulfonamides.
Molecular typing showed that the strains all belonged to
| Source | Composition† | |
|---|---|---|
| Pig | t011 | 008 – 16 – 02 – 25 – – – – – 34 – 24 – 25 |
| Pig | t034 | 008 – 16 – 02 – 25 – 02 – 25 – 34 – 24 – 25 |
| Pig | t108 | 008 – 16 – 02 – 25 – – – – – – – 24 – 25 |
| Pig | t567 | 008 – – – 02 – 25 – – – – – – – 24 – 25 |
| Pig | t943 | 008 – 16 – 02 – 25 – – – 25 – – – 24 – 25 |
| Pig | t1254 | 106 – 16 – 02 – 25 – – – – – 34 – 24 – 25 |
| Pig | t1255 | 008 – 16 – – – – – – – – – 34 – 24 – 25 |
| Poultry | t1456 | 008 – 16 – 02 – 25 |
*All
We confirmed the presence of MRSA in broiler chickens, but we were unable to find it in laying hens. All isolates belonged to 1
This research was supported by the Belgian Antibiotics Policy Coordinating Committee, Federal Public Service, Brussels, Belgium.
Dr Persoons is a researcher at the Faculty of Veterinary Medicine of Ghent University, Merelbeke, Belgium. His main research interest is antimicrobial drug resistance in indicator and zoonotic bacteria in poultry.