Florence Crombé

Prevalence and Antimicrobial Susceptibility of Methicillin-Resistant Staphylococcus aureus Among Pigs in Belgium

The prevalence, distribution, and antimicrobial susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) in Belgian pig farms has been investigated. To that end, nasal samples were collected from 1,500 pigs on 50 farms randomly selected over Belgium. Both closed (breeding or farrow-to-finish) and open (fattening) farms were included. Within closed farms different age groups were investigated. A total number of 663 (44%) pigs belonging to 34 (68%) farms carried MRSA. According to their management practice, MRSA was detected on 94% of the open farms and 56% of the closed farms. Focusing on the in-herd prevalence among fattening pigs for both management systems, a significantly higher rate was found in open farms (72%) compared to closed farms (26%). Within the closed farms, piglets (41%) showed a higher MRSA prevalence than sows (26%) and fattening pigs (26%). All strains tested were ST398 and showed mainly spa-type t011, as commonly found on pig herds in Europe. Less dominating spa-types were t034, t567, and t2970. The MRSA strains carried two SCCmec-types, type IVa or V. All 643 MRSA strains were resistant to tetracycline and additional resistances to trimethoprim (97%), lincosamides (73%), macrolides (56%), aminoglycosides (48%), and fluoroquinolones (32%) were found. Multiresistance (defined as resistance to four or more non-β-lactam antimicrobial classes) was found in 63% of the tested strains. In conclusion, a high prevalence of MRSA was found in Belgian pig farms, with the highest prevalence in open farms. In accordance with other European countries, age-related and management-related differences in MRSA prevalence were observed that should be considered when control strategies are outlined.

Transmission Dynamics of Methicillin-Resistant Staphylococcus aureus in Pigs

From the mid-2000s on, numerous studies have shown that methicillin-resistant Staphylococcus aureus (MRSA), renowned as human pathogen, has a reservoir in pigs and other livestock. In Europe and North America, clonal complex (CC) 398 appears to be the predominant lineage involved. Especially worrisome is its capacity to contaminate humans in close contact with affected animals. Indeed, the typical multi-resistant phenotype of MRSA CC398 and its observed ability of easily acquiring genetic material suggests that MRSA CC398 strains with an increased virulence potential may emerge, for which few therapeutic options would remain. This questions the need to implement interventions to control the presence and spread of MRSA CC398 among pigs. MRSA CC398 shows a high but not fully understood transmission potential in the pig population and is able to persist within that population. Although direct contact is probably the main route for MRSA transmission between pigs, also environmental contamination, the presence of other livestock, the herd size, and farm management are factors that may be involved in the dissemination of MRSA CC398. The current review aims at summarizing the research that has so far been done on the transmission dynamics and risk factors for introduction and persistence of MRSA CC398 in farms.

Evidence of possible methicillin-resistant Staphylococcus aureus ST398 spread between pigs and other animals and people residing on the same farm

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged in a wide variety of animal species. However, little is known about the transmission routes of MRSA ST398 between different animal species, the barn environment and people residing on the same farm. In this study, two pig farms, two poultry-pig and two dairy-pig farms were investigated with respect to the presence of MRSA. On each farm, samples were collected from all animal species present, the barn environment, the farmer, household members and the herd veterinarians. Besides the MRSA prevalence, the obtained spa-, SCCmec-type and antimicrobial susceptibility profiles were also compared. Multilocus sequence typing (MLST) showed that MRSA ST398 was found in all animal species, in humans present on the farms 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. Furthermore, different pig age categories were investigated, with weaned piglets having the highest MRSA prevalence (86.3%). The herd-level prevalence was highly correlated (r=0.86, p=0.03) between sows and pre-weaned piglets. The results also indicate that 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. In this study we 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.

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.

Species and staphylococcal cassette chromosome mec (SCCmec) diversity among methicillin-resistant non-Staphylococcus aureus staphylococci isolated from pigs.

While methicillin-resistant Staphylococcus aureus (MRSA) ST398 is known to be widespread in pig farms, few studies have investigated the species diversity and SCCmec types of methicillin-resistant non-S. aureus staphylococci (MRNAS) residing in the nose of pigs. We examined nasal swab samples of 200 pigs originating from 10 Belgian pig farms previously found positive for MRSA ST398. Suspected staphylococcal isolates were subjected to a 16S rRNA-mecA-nuc PCR. Confirmed MRNAS were genotypically identified to the species level and investigated with a SCCmec typing PCR. MRNAS (n=72) were detected on all 10 farms and were carried by 29.5% of the pigs. Seven MRNAS species were found: Staphylococcus epidermidis (38.9%), Staphylococcus sciuri (18.1%), Staphylococcus pasteuri (18.1%), Staphylococcus rostri (12.5%), Staphylococcus warneri (8.3%), Staphylococcus haemolyticus (2.7%) and Staphylococcus hominis (1.4%). SCCmec cassettes were of type IVa (29.2%), type IVc (25%), type III (22.2%), type V (5.6%) or could not be assigned to any of the known types (NT types) (18.1%). Five distinct NT types were found. The predominance of methicillin-resistant S. epidermidis (MRSE) in our samples is remarkable, as MRSE is mainly associated with humans. The finding of three different SCCmec elements (IVa, V, NT type 1) in MRNAS that also prevail or predominate in MRSA ST398 shows that MRNAS might be an important SCCmec reservoir for MRSA in pigs. Yet, the occurrence of multiple other SCCmec types illustrates that further studies are required to understand the presence and spread of SCCmec in methicillin-resistant staphylococci from animals.

Colonization and Transmission of Methicillin-Resistant Staphylococcus aureus ST398 in Nursery Piglets

ABSTRACT A transmission experiment was performed to evaluate the spread of methicillin-resistant Staphylococcus aureus (MRSA) ST398 in nursery piglets. Reproduction ratios (R0) in three experimental groups were found to vary between 3.92 and 52.54, indicating that after introduction, MRSA ST398 will spread easily among weaned piglets, with a tendency to become established.

Characterization of methicillin-resistant non-Staphylococcus aureus staphylococci carriage isolates from different bovine populations.

OBJECTIVES This study aimed at investigating bovine non-Staphylococcus aureus staphylococci for their role as a potential reservoir for methicillin resistance. METHODS Nasal swab samples were collected from 150 veal calves on 15 veal farms, 100 dairy cows on 10 dairy farms and 100 beef cows on 10 beef farms. Suspected staphylococcal isolates were investigated by PCR for the presence of the classic mecA and mecA(LGA251). Methicillin-resistant non-S. aureus staphylococci (MRNAS) were genotypically identified and were characterized by broth microdilution antimicrobial susceptibility testing and staphylococcal cassette chromosome mec (SCCmec) typing. RESULTS The MRNAS (n = 101) carriage rate was estimated as 30.29% (95% CI 6.14%-74.28%) in veal calves, 13.1% (95% CI 1.28%-63.72%) in dairy cows and 24.8% (95% CI 11.97%-44.42%) in beef cows. Carriage rates were not significantly different between the three populations (P > 0.05). mecA(LGA251) was not detected. Most (n = 80) MRNAS were identified as Staphylococcus sciuri, Staphylococcus lentus or Staphylococcus fleurettii. Resistance to aminoglycosides, macrolide-lincosamide-streptogramin antimicrobials, tetracycline and ciprofloxacin was frequently detected. Two linezolid-resistant MRNAS from veal calves carried the multidrug-resistance gene cfr. SCCmec cassettes of type III predominated (n = 46); another 40 SCCmec cassettes harboured a class A mec complex without identifiable ccr complex; type IVa, type V and several other non-typeable cassettes were detected in low frequencies, especially in methicillin-resistant Staphylococcus epidermidis. CONCLUSIONS The SCCmec types predominating in bovine MRNAS differ from those mostly detected in livestock-associated methicillin-resistant S. aureus strains. Yet, the detection of cfr and the high level of other antimicrobial resistances suggest a potentially important role of bovine MRNAS as a reservoir for resistance determinants other than SCCmec.

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.

Methicillin-resistant Staphylococcus aureus (MRSA) on the skin of long-term hospitalised horses

Given the significance of methicillin-resistant Staphylococcus aureus (MRSA) infections for both horses and staff in equine veterinary hospitals, protocols are required to minimise the risk of nosocomial transmission, including the screening of the skin and nasal chambers of equine patients for evidence of infection. The objective of this study was to clarify the potential existence and extent of MRSA on the skin of horses requiring long-term hospitalisation (≥ 6 months). Thirty such horses were sampled at eight different locations on their skin and from their nasal chambers. MRSA was isolated from 12 animals (40%), with all sample sites testing positive on at least one occasion. Organisms were most frequently detected in the nasal chambers (relative sensitivity, 83.3%; 34.5% positive horses; isolation rate 33.3%). Skin presence was found in 30% of animals with the highest isolation rates found at the carpus (16.7%), neck, withers and croup (13.3% each). To achieve a relative screening sensitivity of >90%, at least one skin site was required in addition to nasal sampling. This evidence of skin as well as nasal reservoirs of MRSA in long-term hospitalised horses should facilitate the design of effective screening and containment protocols.

Screening for methicillin-resistant staphylococci in dogs admitted to a veterinary teaching hospital

This study investigated the nasal carriage of methicillin-resistant staphylococci (MRS) in dogs (n=177) prior to medical examination or surgery in a veterinary teaching hospital. Nasal swab samples were collected after induction of anaesthesia and incubated overnight in salt enriched trypticase-soy broth. Cultures were analysed on two different agar media containing cefoxitin. Suspected MRS isolates were genotypically identified and characterised by antimicrobial susceptibility testing and staphylococcal cassette chromosome mec (SCCmec)-typing. Methicillin-resistant Staphylococcus aureus (MRSA) isolates were additionally characterised by spa-typing and multilocus sequence typing. The presence of Panton-Valentine leukocidin (pvl) genes was determined by PCR. MRS carriage was compared between animals with or without an infectious process. Two MRSA were isolated, both belonging to typical Belgian human hospital clones and lacking pvl. Additionally a methicillin-resistant Staphylococcus haemolyticus carrying a type V SCCmec was detected. No relationship was observed between MRS carriage and presence of infections. The results suggest that MRS are present in dogs originating from the community, albeit at a low prevalence. This could pose risks for cross contamination of dogs and their owners.