Nonspecific induction of beta-lactamase in Enterobacter cloacae

Since the introduction of the new beta-lactamase-stable beta-lactam compounds, inducible beta-lactamases have become increasingly important clinically [1]. It has recently been pointed out that most beta-lactam antibiotics appear to be affected by these derepressed enzymes either by hydrolysis or by the nonhydrolytic barrier mechanism [2]. Until now, it has generally been assumed that beta-lactamases are induced only by the beta-lactam compounds themselves. We investigated an E cloacae strain that exhibited high levels of resistance to most beta-lactam antibiotics. (MICs were greater than 32 micrograms/ml, except for N-formimidoyl thienamycin and the penem compound Sch 29482). Spontaneous production of beta-lactamase (after overnight culture in Isosensitest broth) was only marginal. However, the induction potency of Schaedler's broth even exceeded that of cefoxitin, which is known to be a good inducer [2]. We evaluated the induction potency of various cyclic compounds, such as amino acids, vitamins, purine derivatives, and steroid hormones. Only tryptophane, thiamine, folic acid, and hemine proved to be effacious inducers. Consequently, we explored the possibility that biological fluids also exhibit induction potency. The addition of inactivated serum (at a concentration of 25%) to the Isosensitest medium led to an enzyme induction comparable to that of cefoxitin. Similar results could be obtained with the addition of pleural fluid, CSF, or urine. These observations confirm the previous report that Morganella morganii strains produced considerable amounts of beta-lactamase even in a group of animals that did not receive treatment with beta-lactam compounds (granuloma pouch model) [3].(ABSTRACT TRUNCATED AT 250 WORDS)