Inactivation of some semisynthetic penicillins by gram-negative bacilli.

Sabath, Leon (Boston City Hospital, Boston, Mass.) and Maxwell Finland. Inactivation of some semisynthetic penicillins by gram-negative bacilli. J. Bacteriol. 85:314-321. 1963.-An agar diffusion method was used to test 55 strains of gram-negative bacilli for their ability to inactivate penicillin G, methicillin, biphenylpenicillin, oxacillin, and ampicillin; 26 strains inactivated one or more of them. All strains of Klebsiella-Aerobacter, nearly all of Escherichia coli, and some of Pseudomonas aeruginosa, but not those of Proteus or Salmonella, were active by this method. Penicillin G was inactivated by the largest number of strains, biphenylpenicillin and ampicillin by somewhat fewer, and oxacillin and methicillin by about half as many. When the five penicillins were incubated with four strains of different bacteria in broth at 37 C, all were inactivated to a considerable extent by all the strains, each penicillin to a different degree, but to about the same extent by all the strains. Adsorption alone did not account for the loss of activity. The results suggest that there are qualitative, as well as quantitative, differences among species or even strains of gram-negative bacilli in their ability to inactivate the various penicillins.