Failure of Padac test strips to detect staphylococcal beta-lactamase

Structural correlates of antibacterial and membrane-permeabilizing activities in acylpolyamines

A homologous series of mono- and bis-acyl polyamines with varying acyl chain lengths originally synthesized for the purpose of sequestering lipopolysaccharide were evaluated for antimicrobial activity to test the hypothesis that these bis-cationic amphipathic compounds may also bind to and permeabilize intact gram-negative bacterial membranes. Some compounds were found to possess significant antimicrobial activity, mediated via permeabilization of bacterial membranes. Structure-activity relationship studies revealed a strong dependence of the acyl chain length on antimicrobial potency and permeabilization activity. Homologated spermine, bis-acylated with C8 or C9 chains, was found to profoundly sensitize Escherichia coli to hydrophobic antibiotics such as rifampin. Nonspecific cytotoxicity is a potential drawback of these membranophilic compounds. However, the surface activity of these cationic amphipaths is strongly attenuated under physiological conditions via binding to serum albumin. Significant antibacterial activity is still retained in the presence of physiological concentrations of human serum albumin, suggesting that these compounds may serve as leads in the development of novel adjuncts to conventional antimicrobial chemotherapy.

Multicenter clinical laboratory evaluation of a beta-lactamase disk assay employing a novel chromogenic cephalosporin, S1

S1, a new chromogenic cephalosporin (International BioClinical, Inc., Portland, Oreg.), was used to detect beta-lactamase production among a variety of commonly encountered bacteria in a four-center collaborative study. Results of an S1 disk assay were compared with those obtained by a nitrocefin-based disk procedure (Cefinase; Becton-Dickinson Microbiology Systems, Cockeysville, Md.), with repetitive testing of five quality control organisms and with individual tests of recent clinical isolates of Neisseria gonorrhoeae (162 strains), Haemophilus influenzae (162 strains), Moraxella catarrhalis (155 strains), Staphylococcus aureus (161 strains), and Bacteroides fragilis (164 strains). The performances of the two beta-lactamase disk assays were comparable for the first three species cited above. However, the S1 assay appeared to be a more sensitive procedure than the Cefinase assay when applied to S. aureus and B. fragilis, with respect to both total numbers of positive results and length of time to a definitive positive endpoint.

Rapid, inexpensive method for specific detection of microbial beta-lactamases by detection of fluorescent end products

A rapid method was developed for specific detection of microbial beta-lactamases which uses ampicillin and cephalexin as substrates. The end products (open beta-lactam ring forms) generated after separately incubating either substrate with beta-lactamase-producing organisms initially were separated from the unhydrolyzed substrates by high-voltage electrophoresis at pH 2.1. The end products of both antibiotics were highly fluorescent and could be analyzed visually and semiquantitatively under a long-wave UV lamp. Application of 5 microliters of the same incubation mixture onto filter paper without subsequent electrophoretic separation also resulted in development of fluorescence after brief heating at 120 degrees C for 5 min. This spot test differentiates penicillinase activity from cephalosporinase activity and distinguishes between beta-lactamase and acylase activities, since the end products of acylase [the common side chain, D(-)-alpha-aminophenylacetic acid, and the intact beta-lactam nuclei, 6-aminopenicillanic acid and 7-aminodeacetoxycephalosporanic acid] are not fluorescent. This method was relatively rapid, inexpensive, and more sensitive than the chromogenic cephalosporin (nitrocefin) method when 21 strains of 7 gram-positive species and 77 strains of 29 gram-negative species of bacteria were tested.

Pyridinium 2-azo-p-dimethylaniline chromophore, a chromogenic reagent for beta-lactamase testing compared to nitrocefin

Pyridinium-2-azo-p-dimethylaniline chromophore was evaluated as a test tube, filter paper and spectrophotometric assay for detection of beta-lactamases from gram-positive and gram-negative organisms. Although useful for detection of TEM beta-lactamases in Haemophilus influenzae and Neisseria gonorrhoeae, it was a poor agent for detecting TEM, OXA and PSE enzymes in Enterobacteriaceae. It also proved poor for detecting cephalosporinases in Pseudomonas aeruginosa and Enterobacteriaceae, and penicillinases in Staphylococcus aureus when compared to nitrocefin. As a spectrophotometric substrate it was equivalent to nitrocefin and cephaloridine with various beta-lactamases.

Rapid detection of beta-lactamase by PADAC test strip

A total of 967 isolates of Gram-positive and Gram-negative bacteria were tested for the production of beta-lactamase by the PADAC test strip, and the results were compared with acidometric, disk diffusion and antibiotic dilution procedures. All the penicillinase producting strains of gonococci (23) and Haemophilus influenzae (36) gave positive results with PADAC, but the 361 isolates of Staphylococcus aureus and S. epidermidis remained negative. All of the 547 strains of penicillin sensitive strains of gonococci, Haemophilus and staphylococci were negative with PADAC test.