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Oxytetracycline Inhibition of Arginine Metabolism by Streptococcus Lactis^{1, 2,}

Department of Dairy Technology, The Ohio State University, Columbus

ABSTRACT

Arginine breakdown by Streptococcus faecalis has been shown by Oginsky and Gehrig (3, 4) to be catalyzed by the enzyme, arginine desimidase. A recent report (2) has revealed that a twofold reduction in arginine desimidase activity by resting cell preparations occurs upon the development of oxytetracycline resistance by a strain of Streptococcus lactis. A simple colorimetric procedure for measuring arginine breakdown by actively growing cells with the use of a decarboxylase base medium (Difco, 0872) fortified with 0.5% L-arginine has been described by Mikolajcik (1). This involves a color change from yellow (acid production) to purple (arginine breakdown). This procedure was utilized in this study to ascertain the oxytetracycline level necessary to inhibit oxytetracycline-susceptible and -resistant strains of S. lactis from degrading arginine. The resistant strain in broth containing 100 µg oxytetracycline/milliliter did not decompose arginine and from 15–18 transfers in antibiotic-free broth were required before this activity could be observed consistently.

¹ Article 19:64. Department of Dairy Technology, The Ohio State University. This investigation was supported by Public Health Services Research Grant No. EF 00101-10 from the Division of Environmental Engineering and Food Protection (National Institutes of Health).

² The trademark of Chas. Pfizer & Co., Inc. for oxytetracycline is Terramycin.