Effects of trospectomycin on serum sensitivity of Escherichia coli UC 9451.

Trospectomycin sulfate, a chemically synthesized analog of spectinomycin, exhibits a broad range of activity against both aerobes and anaerobes, including the etiological agents of sexually transmitted diseases. Its activity in vitro against Escherichia coli is considered only moderate. At subinhibitory levels, however, trospectomycin induced changes in a pathogenic strain of E. coli, UC 9451, which significantly increased its sensitivity to serum lysis. This strain of E. coli shows high-level resistance to serum in vitro, typically growing twofold within a 45-min incubation period. Following exposure to one-fifth the MIC of trospectomycin, greater than 99% of the bacteria were killed in 25% serum within 15 min. Surviving bacteria were static in this level of serum for over 3 h. Killing was due to lysis mediated by both the classical and alternative complement pathways. The bacteria exposed to trospectomycin were enlarged in both diameter and length, but they still grew at rates comparable to those of untreated bacteria. No other visible morphological changes could be directly related to the increase in serum sensitivity. The profile of outer membrane proteins obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis was identical for trospectomycin-treated or untreated bacteria. However, the relative proportion of four major outer membrane proteins varied considerably.