Antibiotic residues when present in animal tissues, through food chain, can
enter human body, causing allergic reactions or facilitating the development
of resistant bacterial strains. In order to determine the presence of
antibiotics in animal tissues, it is appropriate to use convenient, reliable
and sensitive methods. Microbiological methods applied for the detection of
antibiotic residues in primary products of animal origin are based on the
sensitivity of specific bacterial strains to a particular group of
antibiotics. Regulatives on the amount of pesticides, metals and metalloids
and other toxic substances, chemotherapeutics, anabolics and other substances
which can be found in food ("Off. Gazette", No. 5/92, 11/92 - corr. and
32/02), state that milk and milk products can be used in commercial purposes
only if not contain antibiotics in quantities that can be detected by
reference methods. The applied method is modified STAR (Screening test for
detection of antibiotics) protocol, regulated by the CRL (Community Reference
Laboratory) Fougeres, France, in which the initial validation of the method
had been carried out. In accordance with the demands of Regulative Commission
EC No657/2002, the sensitivity of modified STAR protocol for beta lactam
antibiotics group was examined , that is, there was carried out a contracted
validation of the method, which initial validation had been performed at CRL.
In a couple of series of experiments, 20 blank samples of raw cow milk
originating from animals not treated by antibiotics, had been examined. By
the beginning of the experiment samples were stored in a freezer at -20?C.
Samples of raw cow milk enriched by working solutions of seven beta-lactam
antibiotics, in order to obtain concentrations at the level of 0.5, 1 and 1.5
MRL (Maximmum Residue Limit) for each given antibiotic (Commission Regulation
EC No. 37/2010). For detection of beta-lactam antibiotics, there was used
Kundrat agar test with previously inoculated G.stearothermophilus ATCC 10149
strain. Aliquots of 30 _l of working solution at 0.5, 1 and 1.5 MRL
concentration level, for each antibiotic, were inflicted on two paper disks
placed on inoculated Kundrat agar surface. Petri plates with Kundrat agar
previously inoculated with G.stearothermophilus , on which the samples were
deposited, were incubated for 12-15h at 55oC. The obtained width of
microorganisms growth inhibition zone, that is supposed to be at least 2.0
mm, measured from the disc edge, demonstrated the capability to detect all
the tested 7 antibiotics from the beta lactam group at a level below the
MRLs. Consequently, this proves that use of this method it is possible to
meet the demands of Regulative Commission EC No. 37/2010.
Evaluation of sensitivity of modified star protocol microbiological method for beta-lactame antibiotics detection in raw cow milk