Biomedical subjects
Publications and source records attributed to B F Woolfrey.
Explore the source record for details and available documents.
A total of 1,013 isolates of Enterobacteriaceae were identified in parallel by the Repliscan (Cathra International, Ontario, Canada) and API 20E (Analytab Products, Plainview, N.Y.) systems. There was a 62% agreement at the genus level between the two systems. Of the 38% discrepant results, Repliscan classified 22% as "biochemical pattern not on file," 8% as a multiple-genus group which included the API 20E identification, and 8% as a genus other than that designated by API 20E. Relative to the various genera, Repliscan agreed with API 20E as follows: Escherichia coli, 80%; Klebsiella spp., 76%; Citrobacter spp., 75%; Proteus spp., 69%; Providencia spp., 54%; Serratia spp., 49%; Enterobacter spp., 25%; Shigella spp., 4%; and Salmonella spp., 0%. Repliscan identified 35% of Enterobacter spp. isolates as Citrobacter spp., 91% of Shigella spp. isolates as a multiple-choice-genus group, and 67% of Salmonella spp. isolates as "biochemical pattern not on file." Repliscan agreed with API 20E at the species level as follows: E. coli, 80%; Klebsiella spp., 56%; Citrobacter spp., 66%; Proteus spp., 55%; Providencia spp., 46%; Serratia spp., 39%; Enterobacter spp., 18%; Shigella spp., 4%; and Salmonella spp., 0%. These findings indicate that the Repliscan system in its present stage of development does not reliably identify the Enterobacteriaceae.
In a precious report (Woolfrey et al., J Clin. Microbiol. 13:58-61, 1981), we indicated that the Repliscan system did not reliably identify Enterobacteriaceae. Recent improvements in the system prompted us to evaluate Repliscan II (Cathra International, Inc., St. Paul, Minn.) by using representative isolates of the population sample previously used to test the system. Isolates (692) representing eight genera were identified in parallel by the Repliscan II and API 20E (Analytab Products, Plainview, N.Y.) systems. Isolates given different identifications by the two systems were assigned reference identifications by using classical microbiological methods. Repliscan II identified 95.2% correctly, 4.0% incorrectly, and 0.7% as unknown. API 20E identified 99.4% correctly, 0.6% incorrectly, and none as unknown. Repliscan II correctly identified Salmonella and Shigella spp. to the genus level and isolates of six other genera to the species level as follows: Salmonella spp., 100%; Shigella spp., 97.7%; Escherichia spp., 95.2%; Citrobacter spp., 82.1%; Enterobacter spp., 85.2%; Klebsiella spp., 98.6%; Proteus spp., 97.2%; and Serratia spp., 97.9%. These findings indicate that Repliscan II is a significantly improved system and provides acceptable identification of Enterobacteriaceae.
This study investigates the dispensing and inoculating characteristics of the MIC-2000 micro-broth dilution system and compares its ability to determine minimum inhibitory concentrations with that of the reference macro-broth dilution method. Micro-well filling showed a coefficient of variation of 6.8%, and micro-well inoculating showed a coefficient of variation of 6.1%. The reference macro-broth dilution method showed a coefficient of variation of 2.9% for dispensing and a coefficient of variation of 2.9% for inoculating. Ninety-three and eight tenths per cent of macro-broth minimum inhibitory concentrations duplicated the macro-broth modal value, with 100% falling within +/-1 double-dilution step. Eighty-five per cent of micro-broth minimum inhibitory concentrations duplicated the micro-broth modal value, with 99.8% falling within +/-1 double-dilution step. When the micro-broth results were evaluated using the macro-broth modal minimum inhibitory concentration value as a reference point, 55.8% duplicated the macro-broth modal value, with 4.7% falling above it and the remainder being skewed below it, with 6.2% at -2 double-dilution steps. These findings indicate that minimum inhibitory concentrations measured by the MIC-2000 system are somewhat lower than those of the reference macro-broth method. As a result, the micro-broth minimum inhibitory concentrations show a wider dispersion when referenced to the macro-broth modal minimum inhibitory concentration than when referenced to their own modal value.
Concave deformaties of the bottom of Petri dishes are a potential source of error for disk agar diffusion antibiotic assay and susceptibility procedures. This is due to differences in agar depth between the central and peripheral areas of the Petri dishes. We have observed significant concave deformities in both empty and commercially filled 150-mm plastic Petri dishes. For this reason we recommend that inspections for Petri dish deformity be incorporated into microbiology laboratory quality control programs.
The usefulness of the moving intermediate zone concept for improving the performance of the standardized disk agar-diffusion test in measuring susceptibility of the fluorescent group of pseudomonads to gentamicin was studied. For this purpose, a 3-mm moving intermediate zone lying --3 mm and --6 mm below that measured for the quality control microorganism Pseudomonas aeruginosa, ATCC 27853, and a wider moving intermediate zone lying --2 mm and --7 mm below that for the quality control microorganism were investigated. Data from the authors' previous study of the usefulness of using fixed breakpoints and fixed zones for assessing susceptibility of the fluorescent pseudomonads to gentamicin were used for this analysis. The results indicate that both the 3-mm moving intermediate zone and the wider 5-mm moving intermediate zone produced unacceptably high rates of error for testing the susceptibility of the fluorescent group of pseudomonads to gentamicin by the standardized disk agar-diffusion test.
Four hundred thirteen clinical isolates of fluorescent pseudomonads consisting of 286 Pseudomonas aeruginosa and 127 organisms of the Pseudomonas fluorescent group were tested for susceptibilities to gentamicin by the broth-dilution method and by the standardized disk agar-diffusion test, using Mueller-Hinton agar from three sources. Different regression lines and significantly different mean inhibition zone diameters were found for the three Mueller-Hinton agars. Single zone-diameter breakpoints of either 13 or 16 mm for the standardized disk agar-diffusion test produced unacceptable rates of false-sensitive and false-resistant interpretations. When error rates were limited by using zone-diameter breakpoints determined by the method of error rate-bound analysis, the percentage of indeterminate interpretations became so large as to make the standardized disk agar-diffusion test impractical. It is concluded that the standardized disk agar-diffusion test should not be used for testing susceptibility of the fluorescent pseudomonads to gentamicin, and presumably other aminoglycosides.
Explore the source record for details and available documents.