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Biomedical subjects

J C Sherris

Publications and source records attributed to J C Sherris.

At least 37 records · Page 2Linked to original sources
PubMed1972

Influence of different media and bloods on results of diffusion antibiotic susceptibility tests.

As part of an International Collaborative Study, the influence of medium and certain medium components on the results of disc susceptibility testing with nine antibiotics was examined and statistically evaluated. Four basic media, Trypticase Soy Agar, Grove and Randall's formula # 9 agar, and Mueller-Hinton agar with and without 1 mg of l-tryptophan per 100 ml, were used with six bacterial strains. Significant differences in zone diameters occurred with most antibiotics. The largest consistent differences were seen with tetracycline, and appeared to result from varying degrees of chelation of the antibiotic with free cations in the media. Reproducibility studies on different batches of Mueller-Hinton agar from two manufacturers showed some statistically significant differences, which were small except with tetracycline. Reproducibility between the products of a single manufacturer was excellent. The results of experiments to determine the effect of the addition of 5% blood of different species to agar medium showed that medium containing citrated or defibrinated horse, rabbit, sheep, or human blood yielded closely similar zone diameters, except that tetracycline zones were larger with citrated blood. A single type of medium should be selected for routine susceptibility tests whenever possible, and reproducibility of performance of the products of different manufacturers should be sought.

Animals↗
PubMed1972

Reliability of the Kirby-Bauer disc diffusion method for detecting methicillin-resistant strains of Staphylococcus aureus.

The resistance of Staphylococcus aureus to methicillin and related drugs can be reliably determined by using the Kirby-Bauer method of susceptibility testing if the incubation temperature is 35 C or below, but resistance may be missed at 37 C. The 1-mug discs of oxacillin and nafcillin or the 5-mug discs of methicillin may be used for this purpose but not the 1-mug discs of cloxacillin. The latter fail to discriminate between sensitive and resistant staphylococci by zone measurement; some resistant strains of staphylococci may show larger zones of inhibition than sensitive strains. Stability of these antibiotic-containing discs was studied under conditions of temperature and humidity variation that might be encountered in a clinical laboratory refrigerator. Oxacillin discs were the most stable and are to be preferred for susceptibility testing. Nafcillin discs were less stable, and methicillin discs lose their potency rapidly unless carefully stored in a refrigerator with a desiccant.

Cloxacillin↗
PubMed1970

Stability of antibiotics and chemotherapeutics in agar plates.

The stability of chemotherapeutic agents incorporated into agar plates was studied by comparison of minimum inhibitory concentrations on fresh and stored plates and by direct bioassay of the chemotherapeutic agar plates. Plates were stored in sealed bags at 4 C. No loss of bioactivity was demonstrated after 30 days of storage in plates containing methicillin, erythromycin, cephalothin, tetracycline, chloramphenicol, kanamycin, streptomycin, polymyxin B, or nalidixic acid. Penicillin G, ampicillin, and nitrofurantoin showed statistically significant losses of activity after 4 weeks. None of the chemotherapeutics tested showed significant loss in activity after 1 week.

Agar↗
PubMed1969

Comparative study of the efficacy of seven paper-reagent strips and conventional biochemical tests in identifying gram-negative organisms.

Gram-nagative organisms were tested with commercially available reagentimpregnated strips (PATHO-TEC). Of the 291 strains, all were tested by using seven paper tests and their conventional counterparts. Excellent correlation was obtained with the oxidase, phenylalanine-deaminase, and Voges-Proskauer tests. Indole tests made on liquid medium cultures also gave complete correlation, but some false-negative results with indole-positive Proteus strains were obtained when growth from solid medium was tested by the strip method. Paper strip urease tests were positive within 2 hr with all Klebsiella and some Serratia, Herellea, and Citrobacter strains as well as with Proteus strains. Approximately 15% of citrate strip test results differed from those of the conventional tests, and reproducibility was poor on retest. The lysine decarboxylase strip test showed a number of discrepancies and posed problems of interpretation and readability. Paper reagent strip methods are simple and convenient and merit further development to increase the specificity of those which depend on pH change up to that achieved with the Voges-Proskauer, oxidase, phenylalanine, and indole methods.

Acinetobacter↗