Genetic Diversity among Staphylococcus aureus Isolates Showing Oxacillin and/or Cefoxitin Resistance Not Linked to the Presence of mec Genes.

Methicillin-resistant Staphylococcus aureus isolates lacking mec genes (n = 32), collected from Belgian hospitals, were characterized for their ß-lactamase production and the presence of mutations in pbp genes, the pbp4 promoter, and genes involved in penicillin-binding protein 4 overproduction (gdpP and yjbH). Twelve isolates were ß-lactamase hyperproducers (BHPs), while 12 non-BHP isolates might produce an incomplete GdpP protein. Most isolates showed nucleotide missense mutations in pbp genes. A few isolates also showed mutations in the pbp4 promoter.

CC398 Staphylococcus aureus subpopulations in Belgian patients.

Studies based on genome-wide single nucleotide polymorphisms (SNPs) supported the existence of two subpopulations in clonal complex (CC) 398 Staphylococcus aureus: an ancestral human-adapted clade (HC) and an animal-associated clade (AC). In this study, we have investigated the occurrence of genetic markers that allow discrimination of these subpopulations among CC398 isolates collected during 2014 to 2016 from human patients in Belgium. A collection of isolates was investigated by means of spa-typing and 16S-mecA-nuc PCR. CC398 isolates were classified as belonging to the human or the animal clade by using a canonical SNPs PCR and further studied by antimicrobial susceptibility and the presence of toxins, immune evasion cluster (IEC), and resistance genes. A total of 124 (7.8%) human isolates belonged to CC398. They were grouped into HC (n = 58) or AC (n = 66). The genes erm(T), pvl, chp, and scn were predominantly found in HC-CC398, while AC-CC398 isolates carried more frequently than the mecA, erm(C), tet(K), tet(M), and tet(L) genes. Different combinations of gene profiles were observed according to the clade. CC398 isolates from Belgian patients belonged to different subpopulations including typical HC and AC-isolates. Few HC-strains with mecA and AC-isolates harboring IEC were found. CC398 isolates from Belgian patients belonged to different subpopulations including typical HC and AC-isolates, as well as new emerging subpopulations that underline the ability of this lineage to acquire resistance and virulence genes. Further research is needed to evaluate the emergence of these subpopulations in the clinical setting.

Mutations at the Ribosomal S10 Gene in Clinical Strains of Staphylococcus aureus with Reduced Susceptibility to Tigecycline.

Mutations on the tip of the extended loop of the ribosomal S10 protein have been associated to tigecycline (TGC) resistance in passaged mutants of different bacteria species. This study described the first two clinical TGC-resistant Staphylococcus aureus isolates with these mutations. One strain (TGC MIC = 2 mg/liter) had a 12-nucleotide deletion affecting residues 56 to 59 (HKYK) of the S10 protein. The second strain (TGC MIC = 1 mg/liter) had amino acid substitutions (K57M and Y58F) previously described in S. aureus passaged mutants.

In vitro activity of ceftaroline against clinical Staphylococcus aureus isolates collected during a national survey conducted in Belgian hospitals.

OBJECTIVES: The aim of this study was to estimate the in vitro activity of ceftaroline against clinical Staphylococcus aureus isolates collected during national surveillance in Belgian acute-care hospitals. Ceftaroline-resistant isolates were further investigated for their resistance mechanisms. METHODS: From October 2013 to March 2014, 155 laboratories of Belgian acute-care hospitals were invited to send to the National Reference Centre-Staphylococcus aureus (Belgium) up to five non-duplicate S. aureus including three MRSA and two MSSA from hospitalized patients. Isolates were analysed by spa typing, SCCmec typing (for MRSA) and PCR for detection of 16S-mecA-nuc and 16S-mecC. MICs of oxacillin, cefoxitin and ceftaroline were determined by the broth microdilution method. The nucleotide sequences of mecA, native pbp and gdpP genes of isolates with reduced susceptibility to ceftaroline were analysed for the presence of mutations responsible for amino acid substitutions. RESULTS: Ninety-nine percent of isolates, including MRSA (n = 284) and MSSA (n = 131), were susceptible to ceftaroline. Only four MRSA isolates showed resistance to ceftaroline (MIC = 2 mg/L). These four isolates belonged to lineages CC5 (n = 1), CC22 (n = 2) and CC8 (n = 1). Two isolates (CC22 and CC8) carried mutations in mecA, as well as in other pbp genes. The remaining isolates carried mutations in native pbp genes or in gdpP. CONCLUSIONS: This is the first Belgian in vitro survey on ceftaroline activity against S. aureus. This antibiotic showed excellent activity against MRSA and MSSA, and only a few MRSA isolates with resistance were found. Reduced susceptibility to ceftaroline seems a complex phenomenon due to the accumulation of mutations in genes involved in ß-lactam tolerance.

Livestock-Associated Methicillin Resistant Staphylococcus aureus (LA-MRSA) Clonal Complex (CC) 398 Isolated from UK Animals belong to European Lineages.

In recent years, there has been an increase in the number of livestock-associated methicillin resistant Staphylococcus aureus (LA-MRSA) clonal complex (CC) 398 recovered from S. aureus isolated animals in the UK. To determine possible origins of 12 LA-MRSA CC398 isolates collected after screening more than a thousand S. aureus animal isolates from the UK between 2013 and 2015, whole genome sequences (WGS) of CC398 European, including UK, and non-European isolates from diverse animal hosts were compared. Phylogenetic reconstruction applied to WGS data to assess genetic relatedness of all 89 isolates, clustered the 12 UK CC398 LA-MRSA within the European sub-lineages, although on different nodes; implicating multiple independent incursions into the UK, as opposed to a single introduction followed by clonal expansion. Three UK isolates from healthy pigs and one from turkey clustered within the cassette chromosome recombinases ccr C S. aureus protein A (spa)-type t011 European sub-lineage and three UK isolates from horses within the ccrA2B2 t011 European sub-lineage. The remaining UK isolates, mostly from pigs, clustered within the t034 European lineage. Presence of virulence, antimicrobial (AMR), heavy metal (HMR), and disinfectant (DR) resistance genes were determined using an in-house pipeline. Most, including UK isolates, harbored resistance genes to ≥3 antimicrobial classes in addition to ß-lactams. HMR genes were detected in most European ccrC positive isolates, with >80% harboring czrC, encoding zinc and cadmium resistance; in contrast ~60% ccrC isolates within non-European lineages and 6% ccrA2B2 isolates showed this characteristic. The UK turkey MRSA isolate did not harbor φAVß avian prophage genes (SAAV_2008 and SAAV_2009) present in US MSSA isolates from turkey and pigs. Absence of some of the major human-associated MRSA toxigenic and virulence genes in the UK LA-MRSA animal isolates was not unexpected. Therefore, we can conclude that the 12 UK LA-MRSA isolates collected in the past 2 years most likely represent separate incursions into the UK from other European countries. The presence of zinc and cadmium resistance in all nine food animal isolates (pig and poultry), which was absent from the 3 horse isolates may suggest heavy metal use/exposure has a possible role in selection of some MRSA.

Heavy metal and disinfectant resistance genes among livestock-associated methicillin-resistant Staphylococcus aureus isolates.

Livestock associated methicillin-resistant Staphylococcus aureus (LA-MRSA) has emerged in animal production worldwide. Most LA-MRSA in Europe belong to the clonal complex (CC) 398. The reason for the LA-MRSA emergence is not fully understood. Besides antimicrobial agents used for therapy, other substances with antimicrobial activity applied in animal feed, including metal-containing compounds might contribute to their selection. Some of these genes have been found in various novel SCCmec cassettes. The aim of this study was to assess the occurrence of metal-resistance genes among a LA-S. aureus collection [n=554, including 542 MRSA and 12 methicillin-susceptible S. aureus (MSSA)] isolated from livestock and food thereof. Most LA-MRSA isolates (76%) carried at least one metal-resistance gene. Among the LA-MRSA CC398 isolates (n=456), 4.8%, 0.2%, 24.3% and 71.5% were positive for arsA (arsenic compounds), cadD (cadmium), copB (copper) and czrC (zinc/cadmium) resistance genes, respectively. In contrast, among the LA-MRSA non-CC398 isolates (n=86), 1.2%, 18.6% and 16.3% were positive for the cadD, copB and czrC genes, respectively, and none were positive for arsA. Of the LA-MRSA CC398 isolates, 72% carried one metal-resistance gene, and the remaining harboured two or more in different combinations. Differences between LA-MRSA CC398 and non-CC398 were statistically significant for arsA and czrC. The czrC gene was almost exclusively found (98%) in the presence of SCCmec V in both CC398 and non-CC398 LA-MRSA isolates from different sources. Regarding the LA-MSSA isolates (n=12), some (n=4) were also positive for metal-resistance genes. This study shows that genes potentially conferring metal-resistance are frequently present in LA-MRSA.

Dissemination of metal resistance genes among animal methicillin-resistant coagulase-negative Staphylococci.

The use of metals as feed supplement has been recognized as a potential driver for co-selection of methicillin-resistant Staphylococcus aureus in pigs. However, the prevalence of these determinants in methicillin-resistant coagulase-negative staphylococci (MRCoNS) is largely unknown. In this study, a collection of 130 MRCoNS from pigs and veal calves were investigated for the presence of metal-resistance genes (czrC, copB, cadD, arsA) associated to SCCmec. Near half of the isolates carried metal resistance genes (czrC 5.4%, copB 38.5%, cadD 7.7%, arsA 26.2%) regardless of their SCCmec type. The increased use of metals in livestock animals, especially zinc in pigs in several European countries may co-select for methicillin-resistance in several staphylococcal species.

Antimicrobial resistance and population structure of Staphylococcus aureus recovered from pigs farms.

Staphylococcus aureus is a burden in human and veterinary medicine. During the last decade, an increasing number of studies reported the presence of livestock-associated methicillin-resistant S. aureus (LA-MRSA) clonal complex (CC) 398 in pigs. During 2013, a survey was performed in pig farms (n=328) randomly selected over Belgium, to monitor the current epidemiological situation of LA-MRSA among asymptomatic pigs and compare with former data to determine possible evolutions. Per farm, nose swabs were taken from 20 animals and pooled. MRSA was detected in 215 farms. Most isolates belonged to CC398 (n=211), and the remaining were ST9/t337 (n=1), ST80/t044 (n=2) and ST239/t4150 (n=1). A large diversity (n=19) of spa-types was found in the CC398 isolates. More than 90% of the isolates were non-wild type (NWT) to tetracycline and trimethoprim. NWT isolates were also found for ciprofloxacin (61.1%), clindamycin (64.4%), erythromycin (57.8%), kanamycin (43.1%) and gentamicin (45.5%). Microarray analysis showed that most CC398 isolates carried genes encoding resistance to tetracycline [tet(M)], macrolide-lincosamide-streptogramin group [erm(B), erm(C), lnu(A), vga(A)], aminoglycosides (aacA-aphD,aa dD, aphA3, sat) and/or phenicols (fexA). One CC398 isolate carried the multi-resistance gene cfr. The non-CC398 isolates carried virulence genes, as the egc-like cluster. The ST80 strain carried the Panton-Valentine leukocidin gene and corresponded to the community-acquired (CA-)MRSA ST80-IV European clone. The MRSA prevalence among pigs in Belgium remains similar to previous studies but a larger diversity in spa-types has been detected in this study. The recovery of CA-MRSA from livestock indicates that one should remain vigilant to the evolution of LA-MRSA in pigs.

Antimicrobial resistance and population structure of Staphylococcus epidermidis recovered from animals and humans.

While Staphylococcus epidermidis, as part of the commensal flora, is a well-known human opportunistic pathogen, only little is known about the genetic relatedness of S. epidermidis carriage isolates from animal and human origin. This study aimed to compare S. epidermidis recovered from livestock, livestock-farmers and humans associated with the hospital environment. A total of 193 S. epidermidis isolates from three populations [animals (n=33), farmers (n=86) and hospital-associated (n=74)] were characterized by broth microdilution antimicrobial susceptibility testing, staphylococcal cassette chromosome mec (SCCmec) typing, pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). The overall S. epidermidis nasal colonization rate was low in animals (1-9%) but high among farmers (75%). High levels of multi-resistance were found in all populations. Tetracycline resistance was high in animal and farmer isolates; resistance to erythromycin, clindamycin and trimethoprim was high in animal and hospital-associated isolates. Methicillin-resistant S. epidermidis - MRSE isolates were found in all collections, with 22 (67%) MRSE in animals, 44 (51%) MRSE in farmers and 42 (57%) MRSE associated with the hospital-setting. Known SCCmec types and variants were detected in 79% of MRSE; the rest were non-typeable cassettes. In total 79 PFGE-types were found, of which 22 were shared between livestock, farmers and the hospital settings. Clonal complex 2 was predominant in all three populations and most STs corresponded to types previously observed in community and nosocomial S. epidermidis populations. S. epidermidis isolates from livestock, farmers and hospital-setting showed a high level of diversity, but some clones can be found in humans as well as in animals.

Diversity of antimicrobial resistance and virulence genes in methicillin-resistant non-Staphylococcus aureus staphylococci from veal calves.

In this study we determined whether methicillin-resistant non-Staphylococcus aureus (MRNAS) from veal calves may be a potential reservoir of antimicrobial-resistance and virulence genes. Fifty-eight MRNAS were studied by means of DNA-microarray and PCR for detection of antimicrobial resistance and virulence genes. The isolates carried a variety of antimicrobial-resistance genes [aacA-aphD, aadD, aph3, aadE, sat, spc, ampA, erm(A), erm(B), erm(C), erm(F), erm(T), lnu(A), msr(A)-msr(B), vga(A), mph(C), tet(K), tet(M), tet(L), cat, fexA, dfrA, dfrD, dfrG, dfrK, cfr, fusB, fosB, qacA, qacC, merA-merB]. Some isolates carried resistance genes without showing the corresponding resistance phenotype. Most MRNAS carried typical S. aureus virulence factors like proteases (sspP) and enterotoxins (seg) genes. Most Staphylococcus epidermidis isolates carried the arginine catabolic element, and nearly 40% of the Staphylococcus sciuri isolates carried leukocidins, and/or fibronectin-binding protein genes. MRNAS were highly multi-resistant and represent an important reservoir of antimicrobial resistance and virulence genes.

Antimicrobial resistance and population structure of Staphylococcus epidermidis recovered from pig farms in Belgium.

Pigs are known to harbour a variety of staphylococcal bacteria, including Staphylococcus epidermidis, in the upper respiratory tract. The aim of the present study was to determine the prevalence, genetic diversity, virulence and antimicrobial resistance of S. epidermidis in healthy pigs, as well as to identify the potential role of pigs as a reservoir of zoonotic infection. The overall prevalence of S. epidermidis carriage was 28%, with approximately half of the pigs tested (13.5%) carrying methicillin-resistant S. epidermidis (MRSE). Some isolates belonged to multilocus sequence types, associated with healthy human carriers or healthcare personnel (ST88, ST210) whereas others were related to animal or environmental strains (ST100, ST273). Most MRSE isolates carried SCCmec type IV, with SCCmec type V or a non-typeable SCCmec detected in the remaining isolates. Both MRSE and methicillin-susceptible S. epidermidis isolates showed a degree of antimicrobial resistance, with most resistant to tetracycline and/or trimethoprim antimicrobial drugs. Isolates subjected to micro-array analysis carried the antimicrobial resistance genes tet(K), tet(M) and dfrS1, while half carried the arginine catabolic element (ACME) associated with colonisation. Some MRSE ST273 strains also carried the ica operon involved in biofilm formation. These research findings provide insight into the population structure and characteristics of S. epidermidis carried by healthy pigs, suggesting a role for these strains as a potential reservoir for antimicrobial and virulence genes and indicating that exchange of strains might occur between pigs and humans.

Characterization of methicillin-resistant Staphylococcus sciuri isolates from industrially raised pigs, cattle and broiler chickens.

OBJECTIVES: This study aimed at assessing the epidemiology and genetic diversity of methicillin-resistant Staphylococcus sciuri (MRSS) from different farm animal species. METHODS: Nasal swabs were collected from 200 pigs, 100 dairy cows, 100 beef cows, 150 veal calves and 200 broilers. Colonies were isolated on selective media containing cefoxitin and the mecA gene was detected by PCR. Antimicrobial resistance was determined by broth microdilution. The genetic diversity was assessed by PFGE and resistance and virulence genes were detected by microarray analysis. RESULTS: The total MRSS prevalence at the animal level was estimated at 9.5%, varying from ∼10% in veal (13.3%), broilers (12.5%) and dairy cows (10.0%) to 6.5% in pigs and 3.0% in beef cows. mecA was detected in all isolates. SCCmec elements of type III and non-typeable ones were seen most frequently. More than 90% of isolates were non-wild-type (NWT) for gentamicin, penicillin, tiamulin, clindamycin and quinupristin/dalfopristin. The frequency of NWT isolates for fusidic acid and trimethoprim ranged between 78% and 87%. PFGE analysis allowed distinction between two major clusters. Most isolates tested by microarray carried erm and tet genes. Virulence genes were also detected, including an isa gene encoding an immune-evasion factor and the hsdS2 gene encoding a site-specific deoxyribonuclease. CONCLUSIONS: This study shows that multiresistant MRSS is carried by different farm animal species. Although some animals shared the same strain, PFGE showed different patterns, indicating high diversity among the MRSS isolates recovered. The absence of clusters associated with a certain animal species suggests low host specificity.

Epidemiology and molecular characterization of methicillin-resistant Staphylococcus aureus nasal carriage isolates from bovines.

BACKGROUND: Staphylococcus aureus is a common bacterium usually found on skin and mucous membranes of warm blooded animals. Resistance in S. aureus has been increasingly reported though depending on the clonal lineage. Indeed, while hospital acquired (HA)-methicillin resistant S. aureus (MRSA) are typically multi-resistant, community associated (CA)-MRSA are by large more susceptible to many antibiotics. Although S. aureus isolated from animals are often susceptible to most antibiotics, multi-resistant livestock associated (LA)-MRSA have been recovered from bovine mastitis.In this study, we investigated the prevalence and types of MRSA present in the nose of healthy bovines of different age groups and rearing practices. Since no validated methods for MRSA isolation from nasal swabs were available, we compared two isolation methods. Molecular characterization was performed by means of spa-typing, MLST, SCCmec typing and microarray analysis for the detection of antimicrobial resistance and virulence genes. RESULTS: MRSA between herd prevalence in bovines was estimated at 19.8%. There was a marked difference between rearing practices with 9.9%, 10.2% and 46.1% of the dairy, beef and veal calve farms respectively being MRSA positive. No significant difference was observed between both isolation methods tested. Most isolates were ST398 spa type t011 or closely related spa types. Few ST239 spa type t037 and t388 and ST8 spa type t121 were also found. SCCmec types carried by these strains were mainly type IV(2B), IV(2B&5) and type V. Type III and non-typeable SCCmec were recovered to a lesser extent. All isolates were multi-resistant to at least two antimicrobials in addition to the expected cefoxitin and penicillin resistance, with an average of resistance to 9.5 different antimicrobials. Isolates selected for microarray analysis carried a broad range of antimicrobial resistance and virulence genes. CONCLUSION: MRSA were mainly present in veal farms, compared to the lower prevalence in dairy or beef farms. Multi-resistance in these strains was high. Though mainly CC398 spa t011 was found, the genetic diversity was higher than what was found for pigs in Belgium. CC8 strains, a typically human lineage but also recently found also in association with bovines, has been retrieved here also.

Molecular basis of antimicrobial drug resistance in Staphylococcus aureus isolates recovered from young healthy carriers in Spain.

The frequency and genetic bases of antimicrobial drug resistance was determined for 111 Staphylococcus aureus recovered from young healthy carriers in a Spanish region. Resistances to ampicillin (84.7%), kanamycin (27%), erythromycin (25.2%), clindamycin (22.5%), tetracycline (11.7%), amikacin and tobramycin (6.3% each), gentamicin (5.4%), chloramphenicol (2.7%), ciprofloxacin (0.9%; MIC 4 µg/ml), moxifloxacin (0.9%) and mupirocin (0.9%; MIC 60 µg/ml) were found, and all were susceptible to methicillin (MSSA). Nearly 50% of the isolates were resistant to one antibiotic, 30% to two, 15.3% to three and 1.8% to four, while only 6.3% remained fully susceptible. A total of 31 profiles were found. For each phenotypic resistance, at least one gene accounting for it was identified. The detected genes were blaZ; erm(A)-erm(B)-erm(C)-msr(A)-msr(B)-lnu(A), aphA-aadE-sat4-aacA + aphD-aadD, tet(K), cat, and qacA/B, for resistance to ampicillin, macrolides and/or lincosamides, aminoglycosides, tetracycline, chloramphenicol, and quaternary ammonium compounds, respectively. In all isolates carrying cat genes, in all except one of the isolates positive for tet(K), and in most isolates with blaZ, erm(C), msr(A), or msr(B), the gene(s) mapped on resistance plasmids, which were detected in 69.2% of the resistant isolates (65% of the total). The S. aureus from young healthy carriers analysed in the present study do not constitute a reservoir of MRSA, but they represent a repository of multiple determinants conferring resistance to "old" antimicrobials. Some of these have still clinical applications and, considering the increasing resistance to recently introduced antimicrobials, none of them can be disregarded.

Molecular epidemiology of methicillin-resistant Staphylococcus sciuri in healthy chickens.

Staphylococcus sciuri is commonly found on the skin of animals and humans as well as in the environment. However, little is known on its prevalence, resistance and epidemiology. Therefore, we investigated the prevalence of methicillin resistant S. sciuri (MRSS) strains in poultry, as they may represent a reservoir of resistance genes for other strains. In 2011, 281 poultry farms were sampled by taking nasal swabs of 20 animals. The swabs were pooled and MRSS were selectively isolated. Genus and methicillin resistance were determined by PCR and species identification was performed using transfer RNA-intergenic spacer analysis. MRSS were further characterised by SCCmec typing, PFGE, microarray and susceptibility testing. Eighty-seven MRSS were isolated resulting in an estimated prevalence of 31.0%. The prevalence in broilers did not significantly differ from that in layers. Most isolates harboured a non-typeable SCCmec and a little less than 40% carried SCCmec type III. Isolates from broiler farms carried mostly the SCCmec type III, while isolates from layer farms carried mostly the non-typeable SCCmec cassette. The 87 isolates generated 47 different SmaI-PFGE profiles that grouped in two main clusters corresponding to the two farm types. All isolates were resistant to fusidic acid, tiamulin and gentamicin and were sensitive to rifampicin and vancomycin. Isolates selected for microarray analysis carried a broad range of antimicrobial resistance and virulence genes. This study showed that MRSS is carried by healthy chickens at the same level in both broilers and layers. They represent a large reservoir for resistance and virulence genes. Strains from layers and broilers represent different clusters.

The ecological importance of the Staphylococcus sciuri species group as a reservoir for resistance and virulence genes.

The Staphylococcus sciuri species group includes five species that are most often presented as commensal animal-associated bacteria. The species of this group are Staphylococcus sciuri (with three subspecies), Staphylococcus lentus, Staphylococcus vitulinus, Staphylococcus fleurettii and Staphylococcus stepanovicii. Members of these group are commonly found in a broad range of habitats including animals, humans and the environment. However, those species have been isolated also from infections, both in veterinary and human medicine. Members of this group have been shown to be pathogenic, though infections caused by these species are infrequent. Furthermore, members of the S. sciuri species group have also been found to carry multiple virulence and resistance genes. Indeed, genes implicated in biofilm formation or coding for toxins responsible of toxic shock syndrome and multi-resistance, similar to those carried by Staphylococcus aureus, were detected. This group may thereby represent a reservoir for other bacteria. Despite its recognized abundance as commensal bacteria and its possible role as reservoir of virulence and resistance genes for other staphylococci, the S. sciuri species group is often considered harmless and, as such, not as well documented as, for example, S. aureus. More investigation into the role of the S. sciuri species group as commensal and pathogenic bacteria is required to fully assess its medical and veterinary importance.

Genotyping and antimicrobial resistance of Staphylococcus aureus isolates from diseased turkeys.

Staphylococcus aureus is a highly versatile pathogen in a large number of domestic animals, including avian species. To gain deeper insight into the epidemiology and diversity of S. aureus associated with articular disease in domestic turkeys, isolates were collected from infected foot joints of turkeys in Brittany (France). A total of 34 isolates were recovered and characterized by means of antimicrobial resistance, staphylococcal protein A typing, macrorestriction pulsed-field gel electrophoresis and micro-array analysis. Thirty isolates were identified as clonal complex (CC) 398 and methicillin-susceptible S. aureus (MSSA), one was identified as a methicillin-resistant S. aureus (MRSA) CC398 isolate, and the remaining were also MSSA and belonged to CC5, CC101, and CC121. Eleven different antimicrobial resistance patterns were detected, with most isolates resistant to penicillin and tetracycline. Based on all typing methods used, the 34 isolates could be divided into 22 different strains. Results on selected isolates, genotyped using microarrays, indicated a high homogeneity among pathogenic MSSA isolates from turkeys. Moreover, all isolates, except the unique MRSA isolate, carried specific φAvß prophage avian-niche-specific genes, demonstrating the versatility of S. aureus to adapt to the specific ecological poultry niche.

Characterization of methicillin-resistant Staphylococcus aureus from healthy carrier chickens.

Methicillin-resistant Staphylococcus aureus (MRSA) has long been recognized as an important pathogen in human medicine leading to hospital and community-acquired infections. However, it is now also considered a growing problem in veterinary medicine, although causing little or no disease. Although MRSA has already been detected in livestock including poultry, little is known about the epidemiology of MRSA in broiler and layer chickens. We therefore investigated 372 poultry farms in Belgium. We also compared the isolation method recommended by the European Food Safety Authority using two enrichment steps with an isolation method using only one enrichment step. Isolated MRSA was characterized by means of antimicrobial resistance profiling, spa typing, multi-locus sequence typing, and SCCmec typing. MRSA prevalence was 0.8% using the double broth enrichment method, while using the single broth enrichment method it was 1.8%. Five MRSA strains belonged to the livestock-associated (LA) MRSA ST398 (four with spa type t011 and one with t899), and three to the hospital-acquired MRSA ST239 spa type t037. The ST239 strains carried SCCmec type III while those belonging to ST398 carried SCCmec type IV or V. All isolates showed additional resistance to erythromycin and tetracycline apart from the expected resistance to cefoxitin and penicillin. All strains were susceptible to linezolid, mupirocin and vancomycin. In conclusion, a higher sensitivity for the isolation of LA-MRSA was obtained using only one enrichment step. While the typical LA-MRSA ST398 was present at low prevalence in poultry, human-associated strains have also been found.