Survey of antibiotic resistance in an integrated marine aquaculture system under oxolinic acid treatment.

The consequences of antibiotic use in aquatic integrated systems, which are based on trophic interactions between different cultured organisms and physical continuity through water, need to be examined. In this study, fish reared in a prototype marine integrated system were given an oxolinic acid treatment, during and after which the level of resistance to this quinolone antibiotic was monitored among vibrio populations from the digestive tracts of treated fish, co-cultured bivalves and sediments that were isolated on thiosulfate-citrate-bile-sucrose. Oxolinic acid minimum inhibitory concentration distributions obtained from replica plating of thiosulfate-citrate-bile-sucrose plates indicated that a selection towards oxolinic acid resistance had occurred in the intestines of fish under treatment. In contrast, and despite oxolinic acid concentrations higher than minimum inhibitory concentrations of susceptible bacteria, no clear evolution of resistance levels was detected either in bivalves or in sediments.

The efficacy of a single intraperitoneal injection of oxolinic acid in the treatment of bacterial infections in goldsinny wrasse (Ctenolabrus rupestris) and corkwing wrasse (Symphodus melops) studied under field and laboratory conditions.

The efficacy of a single intraperitoneal injection of oxolinic acid to control an outbreak of atypical Aeromonas salmonicida infection in goldsinny wrasse (Ctenolabrus rupestris) and in the treatment of systemic vibriosis in corkwing wrasse (Symphodus melops) was examined. In addition a field study was performed to examine the effect of medication on the survival rate of goldsinny wrasse in Atlantic salmon cages. Four groups of wild caught goldsinny wrasse, each of 50 fish, were treated with an intraperitoneal injection of propylene glycol:saline (50:50) (control) or 50 mg/kg oxolinic acid at a concentration of 50 mg/mL. Three days after medication the fish in all groups were treated by an intraperitoneal injection of prednisolone acetate and an increase in seawater temperature from 9.0 to 11.5 degrees C. Cumulative mortalities were 18% in the two groups treated with oxolinic acid and 94 and 100% in the unmedicated control groups, giving a 'relative percentage survival' (RPS) value of 82%. A laboratory maintained population of originally wild caught corkwing wrasse experiencing high daily mortality was treated with oxolinic acid (50 mg/kg) or propylene glycol:saline (control). Cumulative mortalities were 84% (control) and 42% (oxolinic acid medicated group) giving an RPS value of 50%. In a field investigation using goldsinny wrasse approximately 30% were medicated with oxolinic acid (50 mg/kg) prior to stocking in cages with Atlantic salmon. In two of three cages the cumulative mortality was significantly lower (P = 0.025 and P < 0.001) in the medicated groups.

Comparisons of nonspecific and specific immunomodulation by oxolinic acid, oxytetracycline and levamisole in salmonids.

Oxolinic acid, a promising drug for the treatment of bacterial fish disease agents, was tested for possible immunomodulatory effects on fish. Another antibiotic oxytetracycline, known to be immunosuppressive at higher treatment doses, and levamisole, a known immunostimulator for higher vertebrates, were also compared for causing changes in the nonspecific defense compartment and the specific immune system in rainbow trout. Groups of fish were immunized with Yersinia ruckeri O-antigen bacterin in combination with selected doses of the drugs. The nonspecific defense activity was measured by demonstrating neutrophil metabolic activity by the nitroblue tetrazolium assay, by counting engulfed bacterial cells for a phagocytic index and by counting leukocytes with adherent bacterial cells for the adherence index. The specific immune response was monitored by the passive hemolytic plaque assay demonstrating the numbers of antibody-producing cells. The results showed that oxolinic acid, used at recommended doses for the treatment of bacterial diseases, did not cause immunosuppression in either the nonspecific defense or specific immune system compartments, whereas tetracycline at 10 mg/kg caused reduced activity in both. Fish given levamisole injections before the antigen injection showed a stimulated nonspecific defense but a much reduced specific immune response.

Effects of DNA gyrase inhibitors in a polyamine-auxotrophic strain of Escherichia coli.

The polyamine content of the Escherichia coli polyamine-auxotrophic strain BGA 8 seemed to influence the effects of nalidixic acid, an antibiotic acting on subunit A of DNA gyrase. The growth rate was more affected under conditions of putrescine depletion and the inhibition could be partially relieved if the polycation was added back to the culture. DNA synthesis was likewise more sensitive to nalidixic acid in cultures grown without polyamine. The expression of some proteins characteristic of the heat-shock response, evoked by the antibiotic, showed a different persistence according to the presence or absence of polyamines. Novobiocin, acting on subunit B of gyrase, also promoted a differential effect depending on the polyamine content, but in this case putrescine-supplemented cells were more sensitive. The described findings suggest a role of polyamines in all the reactions carried out by gyrase, perhaps due to the influence of the polycations on the state of DNA aggregation.

[Evaluation of the in vitro activity of enoxacin on bacterial strains recently isolated in a hospital milieu]. / Valutazione dell'attività in vitro dell'enoxacin su ceppi batterici di recente isolamento ospedaliero.

The in vitro activity of enoxacin, a new quinolone derivative, was tested against 2180 bacterial strains, recently clinically isolated, by measuring the minimum inhibitory concentrations. Comparisons were made with other drugs (flumequine, oxolinic acid, pipemidic acid) widely utilized for the treatment of urinary tract infections. Enoxacin showed the highest activity against all the tested strains, with a geometrical mean of MICs (MG) of 0.39 micrograms/ml and a MIC 50 and MIC 90 of 0.25 and 4 micrograms/ml, respectively.

Enhancement of ribosomal ribonucleic acid synthesis by deoxyribonucleic acid gyrase activity in Escherichia coli.

The effect of the deoxyribonucleic acid (DNA) gyrase inhibitors coumermycin A1, novobiocin, and oxolinic acid on ribonucleic acid (RNA) synthesis in Escherichia coli was studied in vivo and in vitro. Preferential inhibition of ribosomal RNA (rRNA) synthesis was observed. No effect of oxolinic acid and coumermycin on rRNA synthesis was seen in mutants having a DNA gyrase which is resistant to these inhibitors. In a temperature-sensitive DNA gyrase mutant rRNA synthesis was decreased at nonpermissive temperatures. Thus, a functional DNA gyrase is required for rRNA synthesis. Purified DNA gyrase had no effect on rRNA synthesis in a purified system. However, DNA gyrase does show preferential stimulation of rRNA synthesis in a system supplemented with other proteins. Apparently, DNA gyrase stimulation of rRNA synthesis requires another protein.