561. The use of phage typing and penicillin sensitivity tests in studies of staphylococci from bovine mastitis

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Abstract
In three heavily infected herds there were sufficient types of staphylococci to enable phage typing to be of use in distinguishing between strains present before and after intramammary infusions with antibiotics. Two phage types were rarely found in established infections in one quarter even when three or four distinguishable types were present in a herd. But two types were sometimes found in milk samples when the teat apex was unhealthy and truly aseptic sampling by the usual procedure was impractical. In quarters infected for many months phage type and penicillin sensitivity (and resistance) were found to be very stable. There were only two spontaneous replacements of one phage type by another.