BL-S640, a new oral cephalosporin analogue, was evaluated in vitro against 102 gram-negative and 80 gram-positive bacteria. The antimicrobial spectrum was similar to that of previous cephalosporin analogues. Good antimicrobial activity against strains of Escherichia coli, Klebsiella , staphylococci, and streptococci was demonstrated. Relatively poor activity and/or resistance was noted among most strains of Proteus, Providencia, Pseudomonas , and Serratia . In comparative studies BL-S640 had better activity against strains of Hemophilus influenzae, Staphylococcus aureus , and Enterobacteriaceae than many cephalosporin analogues. Variation of susceptibility results was dependent upon the type of media and inoculum size. Cross-resistance between BL-S640 cephalexin, cephalothin, and cefazolin was demonstrated. Among strains of Klebsiella the more rapid selection of resistance ot other cephalosporins was in contrast to BL-S640. Experience in vitro with BL-S640 has documented its antimicrobial activity,and further studies of pharmacokinetics and therapeutic efficacy are indicated.
The emergence of a strain of Providencia stuartii resistant to multiple antibiotics with the exception of amikacin provided a test organism for a microbiological assay for this new semisynthetic aminoglycosidic aminocyclitol. Results can be read at 4 h and are specific for amikacin. The resistance of P. stuartii to all currently used antibiotics allows the utilization of this technique in the presence of other concurrently administered antibiotics and therefore eliminates the need for their inactivation in the assay procedure. The rapidity, specificity, and simplicity of this microbiological assay may provide a technique for routine clinical monitoring of patients on therapeutic regimens and could be utilized by institutions unable to perform the radioimmunoassay or radioassay techniques.
The isolation of Providencia stuartii resistant to multiple aminoglycoside antibiotics prompted an investigation into the mechanism of their resistance. Crude enzyme extracts of a strain of P. stuartii inactivated kanamycin, lividomycin A, and butirosin B in the presence of adenosine 5′-triphosphate (ATP), as measured by a microbiological assay. The occurrence of inhibitory concentrations of 500 μg or greater per ml against kanamycin, lividomycin A, and butirosin B, coupled with the inactivation of these antibiotics in the presence of ATP, suggested enzymatic phosphorylation. This was documented by the transfer of the γ-phosphate of [γ- 32 P]ATP. In contrast, the inability to inactivate gentamicin or tobramycin by the crude enzyme extracts in the presence of ATP suggests another enzymatic mechanism of resistance for these antibiotics, such as adenylation or acetylation. Of importance is the fact that amikacin, a semisynthetic analogue of kanamycin A which is resistant to inactivation by most resistance transfer factor enzymes, was found to inhibit the growth of P. stuartii at low concentrations.
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