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Results for “Antimicrobial susceptibility tests”

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At least 19 recordsLinked to original sources
PubMed1976

Short-term storage of six penicillins and cephalothin in microdilution trays for antimicrobial susceptibility tests.

To perform microdilution antimicrobial susceptibility tests efficiently, broth dilutions of the antimicrobial drugs should be prepared in large batches and stored frozen until needed. Studies were carried out to document the stability of ampicillin, benzylpenicillin, carbenicillin, methicillin, oxacillin, nafcillin, and cephalothin in microdilution trays during storage at -20 and -60 C. No significant deterioration was noted after 21 days of storage, as detected by bioassay and by replicate minimal inhibitory concentration determinations with control organisms. No significant differences were noted moreover between trays stored for three weeks at -20 C and those stored at -60 C. The microdilution technique was found to be a highly reproducible method for quantitative determination of antimicrobial susceptibility.

Biological Assay↗
PubMed1979

Rapid antimicrobial susceptibility test using tetrazolium reduction.

A rapid method of antimicrobial susceptibility testing has been developed, which uses a modified microdilution procedure and an inoculum of 10(7) bacteria per ml. Results are determined within 4 h with an indicator consisting of 2(p-iodophenyl)-3(p-nitrophenyl)-5-phenyltetrazolium chloride. The precipitation of a red formazan by bacteria uninhibited by antimicrobials is accelerated by the addition of phenazine methosulfate. Isolates are classified as resistant, indeterminate, or susceptible, based on growth in up to two antimicrobial concentrations which conform closely to concentrations which correlate with the millimeter breakpoints used in the Bauer-Kirby method. Results of testing 10 antimicrobial agents against 1,126 isolates were compared with results obtained when the Bauer-Kirby method and the agar dilution procedure were used as reference methods. Enterococci were excluded because of false resistance. Discrepancies were classified as very major (false susceptibility), major (false resistance), and minor (combinations of susceptibility or resistance with indeterminate results). The rapid method versus the agar dilution method yielded 2.3% very major, 0.7% major, and 2.9% minor discrepancies, for a total of 6.0%. Of 58 organism-antimicrobial agent combinations tested, 23 displayed 1% very major discrepancies between the rapid method and the agar dilution method. Six were not therapeutically important. The remainder involved Staphylococcus aureus, Staphylococcus epidermidis, Acinetobacter sp., and most organisms tested with chloramphenicol. It is suggested that adjustments in antibiotic concentrations and/or inoculum size may eliminate these discrepancies. The rapid method appeared economical when compared with Autobac 1 and the Bauer-Kirby procedure.

Evaluation Studies as Topic↗
PubMed1978

Evaluation of microdilution trays (sensititre) for antimicrobial susceptibility testing of Bacteroides fragilis.

Microdilution trays (Sensititre) for antimicrobial susceptibility testing of Bacteroides fragilis has been compared for accuracy with the standard agar dilution method. The microtrays were found to be reliable for all antimicrobials tested (benzylpenicillin, clindamycin, doxycycline, chloramphenicol, fusidic acid, cefoxitin, and cephalotin) but not for metronidazole.

Anti-Bacterial Agents↗
PubMed1979

Antimicrobial susceptibility testing of pneumococci: determination of Kirby-Bauer breakpoints for penicillin G, erythromycin, clindamycin, tetracycline, chloramphenicol, and rifampin.

Antimicrobial susceptibility testing of pneumococci is now essential to monitor for the presence of resistance to agents such as the penicillins, macrolides, lincomycins, chloramphenicol, and tetracycline. In this study, clinical isolates of a selection of resistant South African strains were tested for antimicrobial susceptibility by minimal inhibitory concentration (MIC) determination and by a modified Kirby-Bauer disk diffusion technique, using Mueller-Hinton medium supplemented with 5% horse blood. Disk diffusion breakpoints were determined for penicillin G, erythromycin, clindamycin, tetracycline, chloramphenicol, and rifampin. Reliable results were obtained on disk diffusion for all these agents except for penicillin G. With 6-mug penicillin G disks, zones of strains with intermediate penicillin susceptibility overlapped those of sensitive and resistant strains. With 5-mug methicillin disks, clearer separation of strains based on susceptibility to penicillin G occurred. Strains with zones of <35 mm around penicillin G disks and <25 mm around methicillin disks should have penicillin G MICs determined to confirm their resistance to penicillin G. In view of the potential for pneumococci to be resistant to the agents used in this study, antimicrobial susceptibility of all clinically significant isolates should be determined.

Chloramphenicol↗
PubMed1979

Antimicrobial susceptibility testing of Mycobacterium fortuitum complex.

A total of 24 strains of the Mycobacterium fortuitum complex were tested for susceptibility to antimicrobial agents by the disk diffusion and agar dilution techniques. By comparing zones of inhibition obtained with the disk diffusion technique with results of minimal inhibitory concentration determinations, it was shown that disk diffusion results could predict in vitro susceptibility to selected antimicrobial agents. All of 17 strains of M. fortuitum were susceptible to </=1 mug of amikacin per ml. The corresponding average zone of inhibition around a 10-mug amikacin disk was 37 mm. Seven M. chelonei strains were more resistant to amikacin, with minimal inhibitory concentrations ranging from 1 to 32 mug/ml, and the corresponding average zone size was 21 mm. Susceptibility of both M. fortuitum and M. chelonei to tetracycline was variable and none of the M. chelonei strains was inhibited by polymyxin B, whereas M. fortuitum strains consistently had zones of inhibition around the polymyxin disk. It appears that identification to species of the M. fortuitum complex may be of importance with regard to antibiotic susceptibility. Separation of M. fortuitum and M. chelonei was readily accomplished in the present study by the nitrate reduction and 3-day arylsulfatase tests.

Aminoglycosides↗
PubMed1979

A rapid (4--6-hour) urine-culture system for direct identification and direct antimicrobial susceptibility testing.

This study evaluates a new direct rapid system for urine cultures, including detection and quantitation of positive specimens by Gram stain, direct identification by 4--6-hour incubation of sediment with reagent strips, and antibiotic susceptibility testing by direct (3--4-hour) disk-elution methods. Of 987 routine urine specimens, 121 had significant (less than or equal to 10(5) colony-forming units/ml) gram-negative bacilluria, of which 89% were detected by the Gram stain. Direct rapid identification was correct in 94%. Results of direct disk-elution antimicrobial tests showed overall agreement with results of standard disk diffusion of 93% of tests, and major discrepancies in 4%. For urine specimens with gram-negative bacilluria, this system permitted detection, quantitation, identification, and antimicrobial susceptibility testing in four to six hours with reasonable, though not complete, accuracy.

Anti-Bacterial Agents↗
PubMed1977

Chemically defined antimicrobial susceptibility test medium for Pseudomonas aeruginosa.

A chemically defined growth medium containing physiological concentrations of magnesium and calcium ions was utilized in a microdilution procedure for antimicrobial drug susceptibility testing of Pseudomonas aeruginosa. Determinations of growth end points were simplified by use of sodium citrate as a sole carbon source and bromothymol blue as a pH indicator. Growth of the test organisms was detectable by a change in the indicator color from green to blue after alkalinization of the medium due to citrate utilization. Minimal inhibitory concentrations of amikacin, carbenicillin, gentamicin, and tobramycin were determined on 100 recent clinical isolates of Pseudomonas. Parallel determinations using the microdilution procedure and a conventional tube-broth dilution technique incorporating Mueller-Hinton broth with identical magnesium and calcium content generally agreed within one twofold dilution. Modal minimal inhibitory concentrations for susceptible strains using the microdilution method were: amikacin, 6 mug/ml; carbenicillin, 50 mug/ml; gentamicin, 1.5 mug/ml; tobramycin, 1.5 mug/ml. This modified microdilution technique allowed rapid, definitive minimal inhibitory concentration determinations, using growth end points defined by a color indicator change.

Amikacin↗
PubMed1978

Disc agar diffusion antimicrobial susceptibility tests with beta-lactamase producing Neisseria gonorrhoeae.

The emergence of beta-lactamase-producing strains of Neisseria gonorrhoeae has led to a reexamination of the role of the disc agar diffusion method in susceptibility testing of gonococci. Our data show that the disc agar diffusion test can be used to screen for beta-lactamase production by these organisms. The disc tests were done on GC Agar Base supplemented with 1% IsoVitaleX. An inoculum of 10(8) colony forming units/ml and either a 10-unit-penicillin or a 10-microgram-ampicillin disc were used. A zone diameter of less than or equal to 19 mm was indicative of beta-lactamase production. These results were compared with results of chemical tests for beta-lactamase and with minimal inhibitory concentrations. Recommondations were also made for a disc test with tetracycline and spectinomycin, but these methods must remain tentative because of the lack of resistant strains.

Amidohydrolases↗
PubMed1979

Storage of microtiter plates for antimicrobial susceptibility tests.

Microdilution susceptibility tests are being performed routinely and in increasing numbers in many clinical laboratories. Microtiter plates for these assays are usually prepared in large batches and stored frozen until needed. Studies were performed to investigate the stability at -20C and at -70C of ampicillin, carbenicillin, ticarcillin, gentamicin, tobramycin, amikacin, chloramphenicol, and cephalothin, using Enterobacter aerogenes, Proteus mirabilis, Proteus vulgaris, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella as test organisms. The stability at -20C and -70C of clindamycin, vancomycin, cephalothin, cefazolin, oxacillin, methicillin, nafcillin, and penicillin was analyzed using Staphylococcus eureus, Staphylococcus epidermidis, Enterococcus, and alpha Streptococcus as the test organisms. No significant deterioration of any of the antibiotics was noted after ten weeks of storage at -70C, as detected by minimum inhibitory concentration determinations. No significant differences were noted at -20C for clindamycin, chloramphenicol, vancomycin, cefazolin, cephalothin, gentamicin, tobramycin, and amikacin. By ten weeks' storage at -20C, significant deterioration of carbenicillin, ticarcillin, ampicillin, penicillin, methicillin, oxacillin, and nafcillin was observed.

Anti-Bacterial Agents↗
PubMedDate not supplied

Automation of antimicrobial susceptibility testing.

Laboratory services lag significantly behind the time demands of the clinician in determining the appropriate antimicrobic drug to treat a bacterial infection. The authors discuss several new automated optical systems that promise to shorten the time lag for results, as well as lead to improved precision and standardization. The advantages of expressing antimicrobic susceptibility results as Minimum Inhibitory Concentration (MIC) over the three classifications of sensitive, intermediate, or resistant commonly determined by the Kirby-Bauer disc diffusion method are discussed. Computerization is a central feature of emerging instrumentation for antimicrobic susceptibility testin, and it will be potentially useful in providing interpretive data relating the MIC to specific dose-site combinations. The paper is concluded by short descriptions of nonoptical techniques that investigators have used to measure bacterial growth.

Calorimetry↗