Influence of 2,4,5-trichlorophenoxyacetic Acid on Staphylococcal Penicillinase.

Phytohormones, of which indole-3-acetic acid (IAA) is most widely recognized, are naturally occurring compounds which regulate plant growth activities. Other plant growth-regulating compounds, such as 2,4,5-trichlorophenoxyacetic acid (2,4, 5-T), differ in that they are chemically synthesized. There are indications that both natural and synthetic plant growth regulators have significant activity beyond their accepted role in plants. McQuarrie et al. (Arch. Biochem. 5:307, 1944) reported that IAA inactivated bacterial penicillinase up to 50%. Recently, it was shown that IAA in combination with penicillin G increased the susceptibility of a penicillin G-resistant staphylococcus to the antibiotic, and this apparent activity of IAA was directed toward the decrease of penicillinase production (Kucera et al., Antimicrobial Agents and Chemotherapy1963, p. 489, 1964). The present investigation was carried out to examine this phenomenon with a representative synthetic plant growth regulator. The test organism, Staphylococcus aureus 5565, was resistant to > 500 ,ug/ml of penicillin G (Chas. Pfizer & Co., Inc., New York, N. Y.) by virtue of penicillinase production initially observed by the Haight and Finland (Am. J. Clin. Pathol. 22:806, 1952) test. A stock solution of 2,4, 5-T (Nutritional Biochemicals Corp., Cleveland, Ohio) was prepared in absolute ethyl alcohol and diluted in distilled water. Quantitative growth tests, penicillinase induction experiments, and assay of penicillinase activity were performed as previously described by Kucera et al. Preformed staphylococcal penicillinase with an activity of 58 units per ml of culture was prepared from oxacillin (5-methyl-3-phenyl4-isoxazolyl penicillin, Bristol Laboratories, Inc., Syracuse, N. Y.)-induced cells of strain