Genotypic diversity and virulent factors of Staphylococcus epidermidis isolated from human breast milk

Staphylococcus epidermidis strains were isolated from the expressed human breast milk (EHM) of 14 healthy donor mothers. Genetic diversity was evaluated using RAPD-PCR REP-PCR and pulse-field gel electrophoresis (PFGE). PFGE allowed the best discrimination of the isolates, since it provided for the greatest diversity of the analyzed genomes. Among the S. epidermidis strains, resistance to gentamicin, tetracycline, erythromycin, clindamycin or vancomycin was detected, whilst four isolates were multiresistant. The results from our study demonstrate that staphylococci from EHM could be reservoirs of resistance genes, since we showed that tetK could be transferred from EHM staphylococci to Gram-negative Escherichia coli. Most of the staphylococcal strains displayed excellent proteolytic and lipolytic activities. Additionally, the presence of ica genes, which was related to their ability to form a biofilm on tissue culture plates, and the presence of virulence factors including autolysin/adhesin AtLE, point to their pathogenic potential.