RESUMEN
The prevalence of bacteriophages infecting Staphylococcus aureus in dairy samples was assessed. Fourteen Staph. aureus strains were used in enrichment cultures of 75 dairy samples. All samples grew specific Staph. aureus bacteriophages. According to the host range, 8 different phages were isolated. Three of them, phages PhiH5, PhiG7, and PhiA72, were found in 89% of the samples; all the isolated phages were temperate. Phages PhiH5 and PhiA72 were used in preliminary bacterial challenge tests against Staph. aureus in milk. A phage mixture (1:1) was more effective than each single phage, most likely by preventing the survival of lysogenized cells. Phages inhibited Staph. aureus in UHT and pasteurized whole-fat milk. However, the phages were less active in semi-skimmed raw milk and little inhibition was achieved in whole, raw milk. Killing of Staph. aureus was observed at room temperature and at 37 degrees C, but not at refrigeration temperature.
Asunto(s)
Productos Lácteos/microbiología , Productos Lácteos/virología , Fagos de Staphylococcus/fisiología , Staphylococcus aureus/virología , Animales , Antiinfecciosos/aislamiento & purificación , Antiinfecciosos/metabolismo , Bovinos , Femenino , Conservación de Alimentos/métodos , Mastitis Bovina/microbiología , Leche/microbiología , Leche/virología , Filogenia , Prevalencia , Técnica del ADN Polimorfo Amplificado Aleatorio , Fagos de Staphylococcus/crecimiento & desarrollo , Fagos de Staphylococcus/aislamiento & purificación , Staphylococcus aureus/clasificación , Staphylococcus aureus/genética , TemperaturaRESUMEN
Pseudomonas syringe PB-5123, a producer of fosfomycin, is resistant to high concentrations of the antibiotic. Two possible mechanisms of resistance have been detected: (i) impermeability to exogenous fosfomycin, even in the presence of sugar phosphate uptake inducers, and (ii) antibiotic phosphorylation. The gene responsible for this last activity, fosC, encodes a ca. 19,000-Da protein and is immediately followed by a second open reading frame, which shows sequence similarities to glutathione S-transferases. FosC uses ATP as a cosubstrate in an inactivation reaction that can be reversed with alkaline phosphatase. Other nucleotide triphosphates cannot be substituted for ATP in this reaction. No relationship between fosC and the previously described genes of fosfomycin resistance was found.