The Inhibition in Beef of Chlortetracycline-Resistant Bacteria by Sub-Bacteriostatic Concentrations of the Antibiotic12

Abstract

Previous work has shown that chlortetracycline is effective against resistant strains of Proteus and Pseudomonas in beef whereas the antibiotic is ineffective at the same concentration against these same organisms in complete nutrient media (Jay et al., 1956). The inhibition of these organisms by this antibiotic has also been demonstrated in 0.5 per cent proteose-peptone broth incubated at 30 C (Jay et al., 1957a). In addition to chlortetracycline, oxytetracycline and tetracycline have been shown to act in a similar manner whereas chloramphenicol, penicillin G, and streptomycin lacked this property (Jay et al., 1957b). In explanation of this phenomenon, the hypothesis was advanced that the tetracycline antibiotics were able to compete with the organisms for essential ions or other nutrients in beef and in the proteose-peptone medium, since it has been shown that the tetracyclines can act as chelating agents and disturb the ionic balance (Albert, 1953; Weinberg, 1957). This hypothesis is supported by the observations that the inhibition of a resistant strain of Proteus vulgaris in beef was reversed by the addition of Mn++ (Jay et al., 1956), W03=, MoO4=, Mg++, Ca++, borate, silicate, Sr++, and Ba++ (Jay et al., 1957a). This report deals with further studies on this phenomenon. The effectiveness of chlortetracycline in cooked beef and in water extracts of beef was investigated. A comparison has been made between its effectiveness and that of certain other antibiotics against antibiotic-resistant Proteus in beef extracts.