Concerns regarding the presence of drug residues
in foods include allergic reactions, toxicity, technological
problems in fermented products and the development of
antibiotic resistance in human pathogens. The analysis of
antimicrobial residues in foods is generally carried out, in a
first step, through microbiological screening tests. These
tests commonly use Geobacillus stearothermophilus as
target specie but show a low ability to detect quinolones.
The goal of our study was to evaluate the performance of a
new microbiological test (Equinox) for detection of
quinolone residues in muscle. The kit contains an ampoule
with a standardized number of freeze-dried Escherichia coli
and must be diluted with a specific detection medium
containing a redox indicator. Microbial growth will modify
the redox potential of the medium being observed through a
colour change (from blue to brown/orange). Equinox limits
of detection for most of tested quinolones (enrofloxacin,
norfloxacin, sarafloxacin, marbofloxacin, ciprofloxacin,
danofloxacin and difloxacin) were below or around
maximum residue limit (MRL) UE and CCβ values
obtained corresponded with the determined sensitivities.
In contrast, flumequine could not be detected at MRL UE
levels. Moreover, Equinox displayed a low sensitivity to
other antimicrobials. Sensitivity data obtained in vitro were
consistent when testing incurred muscle samples. Matrix
constituents, test batch and animal species did not affect the
performance of the test. Equinox could be easily automated
enabling a large numbers of simultaneous analysis, and a
photometric reading can be applied for a precise interpretation.
The results obtained in this study prove that Equinox
is a useful tool when screening for quinolone residues or
can be combinedwith othermethods for screening of unknown
sample
