Analytical Variability in the Single Disk Antimicrobial Susceptibility Test

Bartlett, Raymond C.; Mazens, Mary F.

doi:10.1093/ajcp/59.3.376

Cited by 3 publications

(4 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Fay and Oldfather found 94.6% test agreements and 4.5% minor and 0.9% major discrepancies between direct and standard disk diffusion tests (7), whereas we report herein total agreement for 94.6% of all comparisons and 5.2% minor and 0.3% major discrepancies in 2,308 paired tests. Our results are well within the precision and accuracy expected within and between laboratories for the disk diffusion test (3,19). Indeed, the intralaboratory reproducibility reported for the standard single-disk test itself (91.5% agreement, and 7.1% minor and 1.2% major discrepancies) (19) is remarkably similar to our results and those of others (7).…”

Section: Discussionsupporting

confidence: 91%

“…The histograms for direct and standard zone diameters overlap almost perfectly. The mean zone diameters for all comparisons that resulted in the same interpretations were almost identical; differences between readings in the direct and standard tests averaged less than 1 mm, which is well within the precision of the disk diffusion technique (3,19). We found only 1 minor discrepancy (a shift from R by direct to I by standard testing with ampicillin) among the 15 enterococci studied.…”

Section: Resultssupporting

confidence: 69%

See 1 more Smart Citation

Comparison of direct and standard antimicrobial disk susceptibility testing for bacteria isolated from blood

Mirrett¹,

Reller²

1979

J Clin Microbiol

View full text Add to dashboard Cite

To determine the reliability of early antimicrobial susceptibility testing, we compared the results of direct and standard single-disk diffusion methods for 581 positive blood cultures processed routinely by the clinical microbiology laboratory. The direct procedure differed from the standard one only in that the 0.5 McFarland inoculum was prepared from 1 ml of turbid broth rather than five isolated colonies from a subculture plate. A major discrepancy in results was defined as a change from susceptible to resistant or vice versa according to interpretive standards for zone diameters, whereas a minor discrepancy was defined as a shift to or from the intermediate category when paired direct and standard tests were compared. The overall agreement between the two methods was 94.6% of 2,308 comparisons. There were 119 minor (5.2%) and 6 major (0.3%) discrepancies. The major discrepancies were seen with three strains of Staphylococcus epidermidis and one strain each of S. aureus, Escherichia coli, and Enterobacter sp. Direct susceptibility testing of positive blood cultures that were pure by gram-stained smear provided reliable results 24 to 36 h earlier than conventional procedures; therefore, we recommend this procedure to guide early antimicrobial therapy in patients with bacterial sepsis.

show abstract

Section: Discussionsupporting

confidence: 91%

Section: Resultssupporting

confidence: 69%

Comparison of direct and standard antimicrobial disk susceptibility testing for bacteria isolated from blood

Mirrett¹,

Reller²

1979

J Clin Microbiol

View full text Add to dashboard Cite

show abstract

“…With the PDM the range was mostly 2-4 mm and a maximum of 4 mm. These variations are within the range found by others [2], When E. coli KK was tested with Neo-Sensitabs the variations were 2-3 mm. However, when S. aureus KB was tested with the TM the variations of the zone di ameters were somewhat wider with a maxi mum range of 10 mm (streptomycin).…”

Section: Resultssupporting

confidence: 89%

Comparative Antibiotic Sensitivity Testing of Bacteria with a Paper Disc and a Tablet Method

Rollag¹,

Midtvedt²

1978

Chemotherapy

View full text Add to dashboard Cite

show abstract

“…Antimicrobial in disks of each lot was eluted in 1 ml of deionized water during 2 h of incubation at 37 C, and the pH was measured with a glass electrode potentiometer. To study the effect of pH on nitrofurantoin activity, the antimicrobial was eluted from lot I disks in 1 Rate of elution of nitrofurantoin from disks.…”

mentioning

confidence: 99%

Potential Unreliability of Nitrofurantoin Disks in Susceptibility Testing

Hoo¹,

Drew²

1974

Antimicrob Agents Chemother

View full text Add to dashboard Cite

The Kirby-Bauer disk diffusion antimicrobial susceptibility test was studied with three lots of commercial nitrofurantoin disks by using 50 strains of Proteus mirabilis. One lot of disks consistently gave zone diameters 3 to 6 mm larger than the other two and resulted in a substantial number of Proteus mirabilis strains being erroneously categorized as sensitive. Antimicrobial content in disks of the three lots did not account for these differences. The pH of eluate from the unreliable disks was higher than from disks of the other two and resulted in more rapid diffusion of the antimicrobial and consequently larger zones of inhibition.The disk diffusion method of Bauer et al. (2) is commonly used to determine the susceptibility of bacteria to antimicrobials. Many variables (1; A. W. Bauer, Proc. Third Int. Congr. Chemother., p. 466, 1964) which influence test results have been defined including inoculum size, pH, and ionic concentration of media, as well as the content of antibiotics in disks. During a circumscribed period of 1972, an inordinate number of Proteus species appeared to be susceptible to nitrofurantoin when tested in our laboratory. The present investigation was undertaken to discover the cause of these "falsely" large zones of inhibition. by overnight incubation at 37 C, and spectrophotometric absorption was measured at 400 nm with a Beckman DU spectrophotometer after nitromethane extraction and the addition of hyamine reagent (3). Complete elution of nitrofurantoin was checked by a repeat cycle of elution into fresh distilled water. The concentration of nitrofurantoin was then extrapolated from a standard plot of nitrofurantoin at various concentrations. Standards were prepared by dissolving nitrofurantoin powder in dimethyl formamide, followed by dilution in distilled water, pH 6.0. pH effect. Antimicrobial in disks of each lot was eluted in 1 ml of deionized water during 2 h of incubation at 37 C, and the pH was measured with a glass electrode potentiometer. To study the effect of pH on nitrofurantoin activity, the antimicrobial was eluted from lot I disks in 1 ml of distilled water, adjusted to pH values between 4 and 11 with either 0.01 N NaOH or 0.01 N HCl, and then reabsorbed onto the original disks by evaporation under nitrogen.

show abstract

Analytical Variability in the Single Disk Antimicrobial Susceptibility Test

Cited by 3 publications

References 0 publications

Comparison of direct and standard antimicrobial disk susceptibility testing for bacteria isolated from blood

Comparison of direct and standard antimicrobial disk susceptibility testing for bacteria isolated from blood

Comparative Antibiotic Sensitivity Testing of Bacteria with a Paper Disc and a Tablet Method

Potential Unreliability of Nitrofurantoin Disks in Susceptibility Testing

Contact Info

Product

Resources

About