Screening of antibiotic residues in pork meat in Ho Chi Minh City, Vietnam, using a microbiological test kit and liquid chromatography/tandem mass spectrometry

The screening and monitoring of residual antibiotics in pork meat were conducted in Ho Chi Minh City, Vietnam, from 2014 to 2015. One hundred samples collected from a wholesale market were screened on-site using a microbiological kit, and eighteen samples were determined as positive for residual antibiotics. Once transferred to the lab, all the samples were analyzed for 28 antibiotics using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Sulfamethazine residues (11-1600 μg/kg) were detected in 23 samples by LC-MS/MS. Notably, 11 samples with sulfamethazine concentrations ranging from 310 to 1600 μg/kg were detected as “positive” in the initial screening, whereas 12 other samples with sulfamethazine levels below 200 μg/kg were screened as “negative”. No other targeted antibiotics were identified among the remaining positive samples. These results show the potential and limitations of a monitoring system combining on-site microbiological tests and an LC-MS/MS method.