Detection and quantification of methicillin-resistant Staphylococcus aureus in fresh broiler meat at retail in Germany

• Published in: International journal of food microbiology Vol. 292; pp. 8 - 12
• Main Authors: Pauly, N., Wichmann-Schauer, H., Ballhausen, B., Torres Reyes, N., Fetsch, A., Tenhagen, B.-A.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 02.03.2019; Elsevier BV
• Subjects: Broiler meat; Contamination; Drug resistance; Enrichment; Livestock; Low level; Meat; Methicillin; Most probable number; MPN; MRSA; Multilocus sequence typing; Quantification; Sensitivity; Skin; Specificity; Staphylococcus infections; Sensitivity; Specificity; MPN; Quantification; Broiler meat; MRSA
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2018.11.025

The aim of this study was to detect, to quantify and to characterize MRSA in broiler meat samples with skin. Furthermore, we compared an isolation method using a second selective enrichment step (method A) with a simpler method omitting this step (method B). For quantification we used a direct plating method on selective agar plates and a “Most probable number” (MPN) technique for estimation of low numbers of MRSA. Presumptive MRSA colonies were confirmed by MALDI-TOF and by PCR. After confirmation the isolated MRSA were characterized by spa-typing and, if necessary, by multi-locus sequence typing. Method B detected more MRSA-positive samples (16.7%, n = 215) than method A (12.1%). However, method B also produced more false positive results (28.4%).The highest estimated number of MRSA in fresh broiler meat with skin was 1100 MPN/g, but in most positive samples (80.1%) the estimated numbers of MRSA were lower than 10 MPN/g. Thus, the numbers of MRSA in the samples were too low to detect using the spread plate technique. Ten different spa-types were identified. Six of these with 69% of the isolates were assigned to the clonal complex CC398 (t034; t011; t2576; t571; t5452; t1457). Spa-types t1430, t13177 and t899 can be assigned to CC9. Spa-type t304 was identified as MLST-type ST6. In conclusion, we provide quantitative data on low level contamination of fresh broiler meat with MRSA. Most isolated MRSA were from livestock associated spa-types. Omitting the second enrichment step was associated with an increase in sensitivity but lower specificity of the cultural method. •Using selective enrichment decreased sensitivity but increased specificity of MRSA detection in fresh broiler meat.•16.7% of fresh broiler meat samples contained MRSA.•MRSA-positive samples of fresh broiler meat contained very low numbers of MRSA.•96% of all isolates were assigned to livestock-associated MRSA from CC398 or CC9.•4% of all isolates were spa-type t304 with the MLST-type ST6, a hospital-associated MRSA