Effect of low concentrations of quinolone antibiotics on bacterial virulence mechanisms.

Recent studies have shown that exposure to quinolone antibiotics at or below the minimal inhibitory concentration (MIC) results in reduction in the level of production or total elimination of certain factors that contribute to the virulence of bacteria. This study was designed to determine whether low concentrations of enoxacin, lomefloxacin, and ciprofloxacin altered the morphology or affected the production of various virulence factors in several different genera of bacteria. The factors studied were nuclease and a toxin production in Staphylococcus aureus, cell size, pili and fimbriae production, and adherence of Salmonella typhimurium, Escherichia coli, and Pseudomonas aeruginosa to urinary epithelial cells and dog bladder cells, and the major virulence factor in Yersinia pseudotuberculosis. In addition, the effect of growth in low levels of enoxacin on phagocytosis of S. aureus by human polymorphonuclear leukocytes (PMNs) was studied. Following exposure to subinhibitory levels of quinolones tested, significant reduction in activity or complete elimination was seen in all of those factors measured. Minor differences were noted in the efficiency of elimination among the three quinolones tested. At as low as 1/8 MIC there is significant enhancement of phagocytic activity by human PMNs. These data suggest that exposure to quinolones at concentrations below the MIC disrupts the regulatory mechanisms that control cell morphology, adherence as well as exocellular enzyme production and plasmid maintenance. This may mean that certain virulent organisms that survive exposure to quinolone antibiotics may be less likely to produce or maintain the disease state in susceptible hosts.

In vitro activity of lomefloxacin (SC 47111 or NY-198), a new quinolone antimicrobial, against clinical isolates of common pathogens.

The lomefloxacin antibacterial activity was assessed against 442 clinical isolates of common bacterial pathogens and compared to the previously studied activity of ciprofloxacin, imipenem, norfloxacin, and other commonly used antibacterials. Lomefloxacin showed activity against the species of Enterobacteriaceae tested at a concentration equal to or below that of the most commonly used agents. Activity was lower against Pseudomonas species as well as most Gram-positive isolates tested with the exception of Staphylococcus aureus. Streptococcal strains were least susceptible. The results of this study support previous reports of excellent antimicrobial activity for lomefloxacin, especially against Gram-negative organisms.

Alteration of bacterial DNA structure, gene expression, and plasmid encoded antibiotic resistance following exposure to enoxacin.

Enoxacin inhibits growth of Escherichia coli K12 strains primarily by binding to the GyrA subunit of DNA gyrase (topoisomerase II); strains with gyrA, but not gyrB, mutations are less susceptible to the bactericidal effects of this agent. In sensitive strains, enoxacin completely inhibits DNA synthesis within 5 min and produces drug-gyrase-DNA complexes at numerous sites throughout the E. coli chromosome, as shown by the formation of linear DNA molecules after detergent treatment. Enoxacin, even at subminimal inhibitory concentrations, induces the bacterial SOS system, even in partially resistant gyrA strains. This drug also inhibits the induced expression of the lacZ encoded beta-galactosidase, regardless of whether this gene is located on the chromosome, a low copy number F' plasmid or high copy number Col E1 related plasmids. This inhibition of gene expression at subminimal inhibitory concentrations is likely to be a factor, in addition to gyrase inhibition, in the elimination of Col E1 plasmids and to the reduction in R plasmid conjugal transfer. Enoxacin enhances the bactericidal effects of kanamycin in both in-vitro and in-vivo models, suggesting that this quinolone may be effective in the treatment of infections due to strains resistant to antibacterials as a consequence of plasmid encoded resistance determinants.

Nature of the elimination of the penicillinase plasmid from Staphylococcus aureus by surface-active agents.

Growth of Stapylococcus aureus in various ionic surface-active agents resulted in loss of the ability to produce penicillinase, whereas growth in nonionic surface-active agents had no effect on penicillinase production. The curing effect of various alkyl sulfates was found to be dependent upon the chain length. Curing by surface-active agents could be inhibited by magnesium. Reciprocal transduction experiments showed that curing by a surface-active agent was a property of the plasmid, not of the bacterial strain in which the plasmic resides.

Loss of the penicillinase plasmid after treatment of Staphylococcus aureus with sodium dodecyl sulfate.

Two strains of Staphylococcus aureus (PC1 and 196E), when grown in medium containing 0.002% sodium dodecyl sulfate (SDS), showed from 96.1 to 100% loss of the ability to produce penicillinase. Resistance to cadmium and zinc was lost concomitantly with the ability to produce penicillinase. A comparison of the rate of curing by SDS with the curing effects exerted by elevated temperature and ethidium bromide suggested that SDS is a more effective plasmid curing agent for susceptible strains of S. aureus than methods in use at present.

Staphylococcal bacteriophage-associated lysin: a lytic agent active against Staphylococcus aureus.

A lytic enzyme active against viable, intact staphylococci is released into culture fluids upon lysis of bacteriophage-infected Staphylococcus aureus PS53 cells. This enzyme, staphylococcal phage-associated lysin (PAL), was partially purified by ammonium sulfate precipitation and gel filtration through Sephadex G-200. PAL is optimally active at pH 6.5 and 30 C, and lytic activity is greatly enhanced by the addition of reducing agents. Lytic activity was observed against all strains of staphylococci tested and against purified staphylococcal cell walls, but no activity was noted against other bacterial species. PAL possesses peptidase activity and results in the production of spheroplasts which can be osmotically stabilized for extended periods by the addition of 7.5% polyethylene glycol 4000.