Aerobic Gram-Negative Rods Isolated from Bovine Udder Infections

SUMMARY Seventy cultures of aerobic gram-negative rods isolated from bovine udder infections in a mastitis research herd were studied. Nearly one-half (45.7%) of the isolates were Escherichia coli. Twenty-nine of the 32 E. coli isolates were unrelated serotypes. Most of the remaining isolates were Citrobacter, Klebsiella, Proteus, and Enterobacter spp. Enterobacter aerogenes was not isolated. Most of the isolates (84.3%) were recovered from rear quarters. Most microorganisms (71.4%) were isolated during lactation.