Microbial based assay for specific detection of β-lactam group of antibiotics in milk

Abstract

The spore forming Bacillus cereus (66) was screened for the induction of β-lactamase in presence of an inducer using iodometric assay. A significant induction in marker enzyme was observed in B. cereus 66 at maximum residual limit (MRL) of penicillin, ampicillin, cloxacillin, amoxicillin, cefalexin, and cephazolin belonging to β-lactam group of antibiotics. A microbial based assay, where enzyme induction was optimized at pH 7.0, temperature 30°C, and whey powder (0.25%) after 4 h of incubation. The spore based assay was tested with milk samples spiked with 6 different β-lactam antibiotics. The results were 100 and 83.33% in correlation with microbial receptor and inhibition based assay, respectively. Overall, spore based assay can be a useful and cost effective tool for the specific detection of β-lactam group of antibiotics in milk.

Keywords: Assay; Bacillus; Induction; Spore; β-lactam; β-lactamase.

Fig. 1

Disc assay result on comparative inhibitory effect of antibiotic on B.cereus 66; A = Minimum Inhibitory concentration and B = European Union/ Codex Alimentarius Commission Maximum Residual Limit (EU/Codex MRL) (n = 3)