Agents which had previously been shown to act as permeabilizers against Pseudomonas aeruginosa or other Gram‐negative bacteria were tested to determine whether susceptibility to various antibiotics could be increased. In the absence of a permeabilizer, Ps. aeruginosa was resistant to several hydrophobic antibiotics and vancomycin, but not to gentamicin. Tartaric and gluconic acids had weak potentiating activity, whereas ethylenediamine tetraacetic acid and citric acid were more effective permeabilizers. However, sodium polyphosphate enhanced the activity of erythromycin, fucidin, novobiocin, rifampicin and methicillin ; vancomycin was unaffected and the activity of gentamicin was reduced considerably.

A rapid (< 30 min) spectrophotometric method has been used to assess the ability of chemical agents to permeabilize the outer membrane of Pseudomonas aeruginosa. When permeabilized, the cells are rendered readily sensitive to lysozyme, an enzyme that is normally excluded from the peptidoglycan of this organism. In addition to ethylenediamine tetraacetic acid, substances showing permeabilizing activity were citric, isocitric, malic and gluconic acids (but not gluconic acid lactone) and sodium polyphosphate.

US SE L L. 1998. The presence of divalent (Mg 2+ ) ions greatly reduced the lysis of Pseudomonas aeruginosa strain G48 in a system at pH 7·8 or 9·0 consisting of ethylenediamine tetraacetic acid (EDTA), lysozyme and tris. Similar reductions in lysis occurred when EDTA was replaced by nitrilotriacetic acid, sodium citrate or sodium polyphosphate. The effect depended on the cation concentration. Mg 2+ may replace cations removed from the outer membrane, or may effectively remove the permeabilizer from the system. The results suggest that the permeabilizing activity associated with these agents against this organism has a common basis in affecting the outer membrane.

A simple Pseudomonas aeruginosa G48 biofilm on stainless steel discs provided a useful primary screen of the potentiating effects of various permeabilizing agents on antibacterial agents. Experiments with Ps. aeruginosa suspensions could not be used to predict the effects of biocides and permeabilizers on biofilms. Although antibacterial activity against biofilms was less than demonstrated in suspension tests, potentiation by some permeabilizers was still observed.

The lytA gene encoding the autolysin of Streptococcus pneumoniae may be a virulence determinant. Singlestrand conformational polymorphism analysis demonstrated heterogenicity throughout the gene in clinical isolates and strains from the clonal serotypes 7 and 14. Sequence analysis of part of the choline-binding domain showed that in two isolates four amino acid substitutions occurred.