Gram-positive superinfections following beta-lactam chemotherapy: the significance of the enterococcus.

The recent literature was reviewed with regard to the risks of superinfection following beta-lactam chemotherapy. The summary publications for the pseudomonas-active penicillins (azlocillin, carbenicillin, mezlocillin, piperacillin and ticarcillin), cefoperazone, cefotaxime, ceftazidime, imipenem and moxalactam show marked variations. Moxalactam was most likely to produce both gram-negative (5-38%) and enterococcal (2.2-12%) superinfections. Ceftazidime or moxalactam therapy was more often associated with anaerobic superinfections, usually by Clostridium spp., than the other beta-lactams. Comparable and lower incidences of superinfections were cited for cefoperazone, ceftazidime, mezlocillin and imipenem. The most common pathogens for the above drugs were the fungi (Candida spp.), Pseudomonas spp. and some beta-lactamase-producing Enterobacteriaceae. Staphylococcal, Escherichia coli and Klebsiella spp. secondary infections were more common in patients receiving the newer penicillins. Cefotaxime had a very low incidence of superinfections (1.1%), especially caused by gram-positive organisms such as enterococci. The reasons for this favorable feature seem to be: excellent inhibitory activity and beta-lactamase stability against a wide variety of bacterial pathogens, synergistic interactions of cefotaxime and its desacetyl metabolite, enhanced anti-enterococcal activity of cefotaxime in the presence of a human serum factor and interactions of cefotaxime and desacetyl cefotaxime to suppress the development of antimicrobial resistance. The most common superinfections following cefotaxime treatment were with Pseudomonas spp., Enterobacter spp. and fungi. Cefotaxime appears to possess physical-chemical characteristics that react favorably with bacteria and the host to minimize gram-positive superinfections, especially with most enteric Streptococcus spp. (Streptococcus faecalis and Streptococcus faecium).