Agar Incorporation Research Articles

The influence of anaerobiosis on the activity of fosfomycin trometamol.

MICs of fosfomycin trometamol were estimated for 40 strains of bacteria (20 gram-positive cocci, 20 gram-negative bacilli) by the agar incorporation method (Iso-Sensitest agar) in the presence of the potentiating agent, glucose-6-phosphate (25 mg/l). Titrations were carried out in duplicate under aerobic and anaerobic conditions. For 22 strains (12 gram-negative bacilli), a fourfold or greater reduction in MIC was observed in tests conducted under anaerobic conditions. The effect was particularly marked with Klebsiella spp., four of five strains of which showed a 16- to 32-fold reduction in MIC in anaerobic conditions. To investigate the reasons for the effect of anaerobiosis, selected strains were examined in an opacity monitoring device in which cultures can be grown in aerobic or anaerobic atmosphere. Surprisingly, the effect of anaerobiosis observed by continuous turbidimetric monitoring was much less than that seen in agar incorporation MIC titrations: under anaerobic conditions, there was little or no reduction in the concentration of fosfomycin trometamol required to cause a lytic effect on dense bacterial cultures, and a small, but variable effect on the emergence of resistant variants.

In vitro activity of lomefloxacin and other antimicrobials against bacterial enteritis pathogens

Lomefloxacin is a new, difluoroquinolone. In this study, the in vitro activity of lomefloxacin against clinical isolates of a variety of bacterial species associated with acute diarrheal disease was determined and compared with that of ciprofloxacin, ofloxacin, amoxicillin, sulphamethoxazole, trimethoprim, tetracycline, and chloramphenicol. Bacterial isolates were obtained from different geographical areas, including Western Europe and the United Kingdom, Southern Europe, Africa, the Middle East, South and Southeast Asia, and South America, and were included to reflect the range of susceptibility seen throughout the world. Minimum inhibitory concentrations (MICs) were determined using an agar incorporation technique in Mueller-Hinton medium supplemented when necessary with saponin-lysed horse blood at a final concentration of 10% vol/vol. Lomefloxacin was highly active against all the species examined which included Salmonella spp., Shigella spp., Escherichia coli enterotoxigenic [(ETEC), enteroinvasive (EIEC), and enteropathogenic (EPEC) strains], Yersinia enterocolitica, Campylobacter jejuni, Vibrio spp., and Aeromonas hydrophila, with all isolates inhibited by 1 mg/L or less. This activity was similar to ofloxacin and slightly less than that of ciprofloxacin. By contrast, many of the isolates were resistant to one or more of the other, unrelated animicrobials. No cross-resistance between lomefloxacin and any of the nonfluoroquinolone antimicrobials examined in the study was observed.

In vitro effects of titanium powder on oral bacteria

Biomaterial research has been mostly concerned with biocompatibility i.e. tissue response, of materials for dental or orthopaedic implantation. In this study, the effects of titanium powder on seven bacterial species commonly found in dental plaque or gingival sulcus, were determined by agar incorporation and by liquid medium culture. In neither culture system could any inhibitory or stimulatory activity be detected.

A Culture Technique for the Detection of Bacillus Larvae in Honeybees

SummaryA culture procedure involving heat treatment and employing sheep blood agar was used for the isolation of Bacillus larvae from bees. B. larvae was cultured from all 18 samples collected from hives affected with American foulbrood (AFB) disease and from 2 (3·8%) samples taken from 56 apparently normal hives with no previous history of AFB. B. larvae was also isolated from 12 (26·1%) of 46 apparently normal hives from apiaries with AFB-diseased hives or from apiaries with recent histories of AFB.Bacillus alvei was found to be a common inhabitant of bees being isolated from 55 (45·8%) of the 120 samples examined. The incorporation of agar at a concentration of 7% in the culture plates prevented the characteristic swarming of this organism and enabled the isolation of B. larvae from bee extracts containing B. alvei.

The in-vitro activity of doxycycline and minocycline against anaerobic bacteria.

The likelihood of bacterial resistance now prevents the use of oxytetracycline in the empirical therapy of anaerobic infections. This study investigates the in-vitro activity of two semi-synthetic derivatives, doxycycline and minocycline, against a range of anaerobic bacteria. MICs for each antibiotic were determined by an agar incorporation technique. Doxycycline and minocycline were four to eight times more active against the majority of strains than oxytetracycline. With the exception of Bacteroides bivius, almost 90% of strains were inhibited by 4 mg/l of doxycycline or minocycline, but resistance to the same concentration of oxytetracycline was present in 60% of the B. fragilis group, 30% of Peptostreptococcus spp. and 24% of Clostridium perfringens. Doxycycline and minocycline represent an alternative therapy for anaerobic infections where bacterial sensitivities are known.

Testing sensitivity of Neisseria gonorrhoeae to spectinomycin.

A concentration of 16 mg/l spectinomycin incorporated in agar gave the best discrimination between Neisseria gonorrhoeae sensitive and resistant to spectinomycin. This method was compared with spectinomycin sensitivity testing with 25 micrograms or 100 micrograms discs. Both methods agreed fully for 197 spectinomycin sensitive and three spectinomycin resistant gonococci. The agar incorporation "breakpoint" concentration technique failed to detect a small spectinomycin resistant population in a fourth isolate, which was detected by disc testing. It may be possible to predict the emergence of spectinomycin resistance among strains of N gonorrhoeae.

Improvement of two toluidine blue O-mediated techniques for DNase detection.

Two DNase detection techniques in which the metachromatic dye toluidine blue O (TBO) is used have been improved, and a potential source of difficulty for personnel attempting to use TBO-related methods has been identified. Reducing the concentration of TBO in the Streitfeld plate-flooding method from 0.1 to 0.05% resulted in easier control of staining intensity, less masking of DNase-positive reactions due to overstaining, sharper delineation of zones of DNase activity, and more sensitive detection of weak DNase reactions. Incorporation of 0.005% TBO in DNase agar, rather than the recommended 0.01%, allowed growth and expression of DNase activity by gram-positive as well as gram-negative bacteria. The reduced dye content in the agar also enhanced expression of DNase activity by some organisms and provided sharper delineation of DNase-positive reactions. Because optimum expression of DNase activity depends upon exact TBO concentrations in both the flooding and agar incorporation techniques, strict attention must be paid to the dye content of commercially available TBO dye powders. TBO concentrations must reflect actual dye content; therefore, calculations must include a conversion factor that accounts for the true dye content of the commercial preparation. The conversion factor that we developed is determined by dividing 100 by the percentage of dye in the commercial powder. The grams of commercial dye powder required per 100 ml of dye mixture is calculated by multiplying the percentage of dye required in the dye mixture by the conversion factor.

In-vitro resistance to imidazole antifungals in Candida albicans

Three strains of Candida albicans from patients with chronic mucocutaneous candidosis (CMC) who relapsed during prolonged treatment with ketoconazole were compared with three other Can. albicans strains by means of an agar incorporation MIC method, a broth microdilution method for IC30 determination, and a hyphal elongation assessment method. The MICs of ketoconazole, tioconazole and miconazole were difficult to interpret, but were much higher for the three CMC strains if low inoculum concentrations and short incubation times were used. The IC30S of the three imidazoles were much higher for the CMC strains than for the others. The imidazoles all caused minimal inhibition of hyphal elongation by the three CMC strains at concentrations up to 50 mg/l. Concentrations of 0.5 mg/l caused marked inhibition of the other strains.

Study of the enhancement of beta-lactam activity by amdinocillin in a model of the human urinary bladder

Synergy between a 2:1 combination of ampicillin and amdinocillin was studied with 10 urinary isolates of Enterobacteriaceae. Synergy was observed with six organisms in a bladder model that reproduced many features of the milieu of the human bladder. Antibiotic susceptibility of these organisms was also determined by the agar incorporation plate method, by tube dilution (urine and broth), microtiter method (urine and broth) and disk susceptibility test. Minimal inhibitory concentrations of individual antibiotics were of no value in predicting the synergistic response and were sometimes misleading. None of the laboratory tests could predict synergy in the bladder model. Evidence is available that the bladder model may be superior to other in vitro tests for synergy studies.

The effect of culture conditions and toxicity on the Ames Salmonella/microsome agar incorporation mutagenicity assay.

Various methods were used to reconstruct an environment similar to a chemically bactericidal or bacteriostatic effect in the Ames mutagenicity assay in order to determine whether a false-positive result could occur. Neither population reduction, sonication, nor increased histidine produced an increase of spurious revertant colonies.