EFFECTS OF DIFFERENT TEST CONDITIONS ON MICS OF FOOD ANIMAL GROWTH-PROMOTING ANTIBACTERIAL AGENTS FOR ENTEROCOCCI

The influence of the addition of sheep blood to Mueller-Hinton II agar and the effects of aerobic incubation with or without CO2 and of anae robic incubation were tested with bacitracin, tylosin, avoparcin, virg iniamycin, avilamycin, narasin, and flavomycin on enterococci, The ant ibacterial activity of bambermycin (Flavomycin) was strongly inhibited by the addition of blood, except with the species Enterococcus faeciu m, Enterococcus mundtii, Enterococcus hirae, Enterococcus casseliflavu s, and Enterococcus gallinarum, which were not susceptible to this ant ibiotic on blood-free medium. With all other antimicrobials except avo parcin and tylosin, the presence of blood resulted in MIC increases of 1 to 3 log(2) differences. Incubation in aerobic or anaerobic atmosph eres enriched with CO2 lowered the susceptibility of enterococci to ty losin and increased their susceptibility to avilamycin, narasin, and a voparcin, This effect was most pronounced in tests on blood-free media , Results of susceptibility tests incubated under anaerobiosis and in a CO2-enriched atmosphere did not differ, For all enterococcal species , the preferred conditions for testing the susceptibility are Mueller- Hinton II medium supplemented with blood and incubation in a CO2-enric hed atmosphere. However, when only E. faecium and Enterococcus faecali s are being tested, Mueller-Hinton II medium without blood incubated a erobically gives satisfactory results.