Antibacterial activity of the monobactam SQ 26,776 against antibiotic resistant enterobacteria, including Serratia spp.

Abstract

The activity <it>in vitro</it> of the new monobactam SQ 26,776 (SQ) was determined against 493 clinical bacterial isolates by an agar dilution technique. Ampicillin, cefazolin, cefotaxime, cefoperazone, ceftazidime, gentamicin, mezlocillin, moxalactam, netilmicin and piperacillin were used as comparator agents. The activity of SQ and other agents against a control strain of <it>Escherichia coli</it> and its R-plasmid-bearing transconjugants was also determined. SQ showed no useful activity against Gram-positive species and <it>Bacteroides fragills</it>, but was highly active against Gram-negative aerobes with an MIC<inf>50</inf>, lower than 1 mg/l for all species tested, excepting <it>Actinetobacter</it> species and <it>Pseudomonas aeruginosa</it>, even at an inoculum of 106 cfu. The MIC<inf>90</inf>, was generally within one or two dilutions of the MIC<inf>50</inf>. The activity of SQ against <it>E. coli</it>, <it>Citrobacter</it> spp, <it>Salmonella</it> spp, and <it>Proteus mirabilis</it> was very high (MIC<inf>50</inf>, 0.06 mg/l) and exceeded that of the so-called third generation cephalosponns tested. SQ was generally active against enterobacteria resistant to older antimicrobials, including <it>Serratia</it> species, inhibiting all strains tested of that genus at 8 mg/l with MIC<inf>50</inf> and 90 and 0.12 and 4mg/l, respectively. The MIC<inf>90</inf>, for <it>Ps aeruginosa</it> was 8 mg/l. Activity against Haemophilus influenzae was very high. The above results implied a high degree of stability to <it>β</it>-lactamases, and this was borne out by the similar MICs to control strain of <it>E. coli</it> transconjugants with plasmids coding for TEM-1, TEM-2, OXA-1, OXA-2, and SMV-1 <it>β</it>-lactamases. We concluded that SQ was a highly active agent deserving clinical investigation in infections caused by enterobacteria and <it>Ps. aeruginosa</it>, particularly in situations where strains resistant to other agents are a problem.