Variability of SCCmec elements in livestock-associated CC398 MRSA.

The most common livestock-associated lineage of methicillin-resistant Staphylococcus aureus (MRSA) in Western Europe is currently clonal complex (CC) 398. CC398-MRSA spread extensively across livestock populations in several Western European countries, and livestock-derived CC398-MRSA strains can also be detected in humans. Based on their SCCmec elements, different CC398 strains can be distinguished. SCCmec elements of 100 veterinary and human CC398-MRSA isolates from Germany and Austria were examined using DNA microarray-based assays. In addition, 589 published SCC and/or genome sequences of CC398-MRSA (including both, fully finished and partially assembled sequences) were analysed by mapping them to the probe sequences of the microarrays. Several isolates and sequences showed an insertion of a large fragment of CC9 genomic DNA into the CC398 chromosome. Fifteen subtypes of SCCmec elements were detected among the 100 CC398 isolates and 41 subtypes could be discerned among the published CC398 sequences. Eleven of these were also experimentally detected within our strain collection, while four subtypes identified in the isolates where not found among the sequences. A high prevalence of heavy metal resistance genes, especially of czrC, was observed among CC398-MRSA. A possible co-selection of resistances to antibiotics and zinc/copper supplements in animal feed as well as a spill-over of SCCmec elements that have evolved in CC398-MRSA to other, possibly more virulent and/or medically relevant S. aureus lineages might pose public health problems in future.

In vitro activity of ceftaroline against mecC-positive MRSA isolates.

Ceftaroline is a new cephalosporin with activity against methicillin-resistant Staphylococcus aureus (MRSA). A collection of 17 clinical and veterinary mecC-positive MRSA isolates was tested to evaluate the in vitro efficacy of ceftaroline against recently emerged mecC-MRSA isolates. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of ceftaroline for the 17 isolates were determined by broth microdilution using the methodology and interpretive criteria of the Clinical and Laboratory Standards Institute (CLSI). Additional susceptibility tests were performed using ceftaroline M.I.C.Evaluator (M.I.C.E.™) strips. All isolates showed susceptibility according to CLSI breakpoints, with MICs of ceftaroline ranging from 0.125mg/L to 0.25mg/L. MBCs were identical or up to a twofold dilution step higher. In conclusion, all tested isolates, from various sources and belonging to several clonal complexes (CCs), but predominantly to CC130, were found to be susceptible to ceftaroline. Ceftaroline could thus be an option for the treatment of mecC-MRSA infections.

[Phenotyping and microarray based genotyping of the antibiotic resistance of MRSA and MSSA from quarter milk samples of clinically healthy dairy cows]. / Phänotypisierung und Microarray- basierte Genotypisierung des Antibiotika- Resistenzverhaltens von MRSA und MSSA aus Viertelgemelksproben klinisch gesun- der Milchkühe.

The aim of this investigation was the comprehensive characterization of the in vitro antibiotic resistance profile and of the detectable resistance determinants in a systematic sampling of Staphylococcus aureus isolates from raw milk from clinically healthy cows. Quarter milk samples from all asymptomatic, milk producing cows from 34 Thuringian dairy herds were taken twice (n = 10421 and 10 417 respectively) and investigated bacteriologically. 189 out of the 1902 detected Staphylococcus aureus isolates were selected and established in terms of their resistance pattern using DNA-microarray analysis and agar diffusion test (AVID 1998) for the determination of the genotypic and phenotypic resistance, respectively. 135 isolates (71.4%) did not carry any resistance gene represented on the array. The penicillin resistance gene blaZ was found in 21 isolates (11.1%), which were tested resistant to penicillin by agar diffusion test. Only four isolates (2.1%) harboured the methicillin resistance gene mecA and were thus defined as methicillin-resistant Staphylococcus aureus (MRSA). They belonged to the clonal complex CC398 and possessed, beside mecA, also tetracycline resistance genes. Other resistance markers were very rare, with macrolide and aminoglycoside resistance genes being found in only one isolate (0.5%) each. On one hand, the present survey shows the (still) limited antimicrobial resistance of Staphylococcus aureus isolated from clinically healthy dairy cows. On the other hand, the study demonstrates that MRSA can be detected in raw milk in small quantities, but these strains show only few additional resistance properties.

Leukocidin genes lukF-P83 and lukM are associated with Taphylococcus aureus clonal complexes 151, 479 and 133 isolated from bovine udder infections in Thuringia, Germany.

Staphylococcus aureus is one of the most important causal agents of bovine mastitis. Population studies on bovine Staphylococcus aureus isolates have identified considerable genetic heterogeneity among strains causing mastitis. The aim of this study was to investigate the contribution of different clonal complexes and the occurrence of virulence factors and resistance determinants within bovine Staphylococcus aureus isolates.A total of 189 Staphylococcus aureus isolates obtained from milk samples of 34 dairy herds in the German Federal State of Thuringia were characterised by microarray technology.The isolates were assigned to eleven different clonal complexes with CC151, CC479 and CC133 being dominant (together 80.5%). The methicillin resistance gene mecA was found in four isolates (2.1%), which belonged to CC398. Enterotoxin genes could be detected in 79.3% of analysed Staphylococcus aureus and 19 isolates (10.1%) harboured a distinct allele of the toxic shock syndrome toxin gene, tst-RF122. The most striking finding of the present study was that almost all except one isolate (151/152) belonging to CC151, CC479 and CC133 harboured the leukocidin genes lukF-P83 and lukM, whereas no further isolates from other lineages possessed these genes.The consistent occurrence of lukF-P83/lukM in the dominating clonal complexes suggests an essential role of this leukocidin in the etiology of bovine mastitis.