The Occurrence of Antibiotic-Resistant Strains of Streptococci in the Ingesta of Calves

Veterinarni Medicina 38, 1993, 75-81

The occurrence and antibiotic-resistance spectrum of some strains of rumen strepto-cocci were investigated in calves of four age categories in the milk diet period at 1-3, 4-7, 8-14 days of age and 6-8 weeks of age. More than 75 % of the strains isolated from the calves of all age categories were resistant to more than one tested antibiotic (tetracycline, neomycin, erythromycin, streptomycin, chloramphenicol). The average number of streptococci isolated from the ingesta of calves during the period of observation was 10(5) per ml. The per cent of resistant strains showed an increasing trend from birth to the age of 8-14 days (Tab. I). The occurrence of resistant strains in 6-8 week calves was even lower than in the calves of the youngest age category. A four-marker type of resistance (41.6 -50 %) prevailed within 14 days of age. Two-marker types of resistance (42.6 %) occurred most frequently in the calves of the oldest age category. Tab. II shows the spectrum of resistant strains. Tetracycline-resistant amylolytic strains of Streptococcus bovis were selected from among the isolated strains to be used as donor strains in conjugation experiments. Successful resistance transmission was observed in solid-surface conjugation. The transmission frequency ranged within the transconjugate values of 10(-3) to 10(-5) per donor cell within the species (Tab. III). A chromosomally rifampicin-resistant strain of Streptococcus bovis BM114 was used as a recipient as it did not contain any plasmids and was sensitive to the tested antibiotics. Agarose-gel electrophoresis was used to visualize the presence of plasmid DNA in donor strains (Fig. 1)

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