This work reports the composition and succession of tetracycline- and erythromycin-resistant bacterial communities
in a model cheese, monitored by polymerase chain reaction denaturing gradient gel electrophoresis (PCRDGGE).
Bacterial 16S rRNA genes were examined using this technique to detect structural changes in the cheese
microbiota over manufacturing and ripening. Total bacterial genomic DNA, used as a template, was extracted
from cultivable bacteria grown without and with tetracycline or erythromycin (both at 25 μg ml−1
) on a nonselective
medium used for enumeration of total and viable cells (Plate Count agar with Milk; PCA-M), and
from those grown on selective and/or differential agar media used for counting various bacterial groups;
i.e., lactic acid bacteria (de Man, Rogosa and Sharpe agar; MRSA), micrococci and staphylococci (Baird–Parker
agar; BPA), and enterobacteria (Violet Red Bile Glucose agar; VRBGA). Large numbers of tetracycline- and
erythromycin-resistant bacteria were detected in cheese samples at all stages of ripening. Counts of antibioticresistant
bacteria varied widely depending on the microbial group and the point of sampling. In general, resistant
bacteria were 0.5–1.0 Log10 units fewer in number than the corresponding susceptible bacteria. The PCR-DGGE
profiles obtained with DNA isolated from the plates for total bacteria and the different bacterial groups suggested
Escherichia coli, Lactococcus lactis, Enterococcus faecalis and Staphylococcus spp. as the microbial types resistant to
both antibiotics tested. This study shows the suitability of the PCR-DGGE technique for rapidly identifying and
tracking antibiotic resistant populations in cheese and, by extension, in other foods.