Antimicrobial-resistance and enterotoxin-encoding genes among staphylococci isolated from expressed human breast milk

Disciplina de Microbiologia e Imunologia, Faculdade de Ciências Médicas, Universidade do Estado do Rio de Janeiro, Avenida 28 de Setembro, 87, Fundos – 3o andar, 20551-030, Rio de Janeiro, Brazil Correspondence Vânia L. C. Merquior merquior{at}uerj.br Received September 3, 2003 Accepted March 4, 2004 Resistance traits and the presence of enterotoxin-encoding genes were investigated in staphylococcus isolates obtained from expressed human breast milk. A total of 54 staphylococcal isolates identified as Staphylococcus epidermidis (53.6 %), Staphylococcus warneri (20.4 %), Staphylococcus haemolyticus (13 %) and Staphylococcus aureus (13 %) were investigated. By using a disc-diffusion method, higher rates of resistance, including intermediate resistance, were observed for penicillin (87 %) and erythromycin (59.3 %). All strains were susceptible to clindamycin and vancomycin. Minimal inhibitory concentration (MIC) was determined by a macrodilution method for four clinically relevant antimicrobial drugs. High rates of resistance or intermediate resistance were observed for erythromycin, gentamicin and oxacillin. Additionally, three isolates showed reduced susceptibility to vancomycin (MIC, 8 µg ml –1 ). Genetic determinants of resistance were detected by using PCR and the results showed good correlation with the macrodilution tests. Moreover, in four staphylococcus isolates, the presence of enterotoxin-encoding genes ( seg , seh and sea ) was identified. The results demonstrated that expressed human breast milk can be a reservoir of multiresistant staphylococci that may also harbour important virulent determinants. Abbreviations: CNS, coagulase-negative staphylococci; EHM, expressed human breast milk; SE, staphylococcal enterotoxins.