Evaluation of the double-disk synergy test for New Delhi metallo-ß-lactamase-1 and other metallo-ß-lactamase producing gram-negative bacteria by using metal-ethylenediaminetetraacetic acid complexes.

New Delhi metallo-ß-lactamase-1 (NDM-1), one of the metallo-ß-lactamases (MBLs), has been identified from clinical isolates worldwide. Rapid detection of NDM-1 producers is necessary to prevent their dissemination. Seven types of EDTA complexes were evaluated as MBL inhibitors in double-disk synergy tests (DDSTs), resulting in detection of the first isolate of NDM-1-producing Escherichia coli (NDM-1 Dok01) in Japan. NDM-1 Dok01 was detected when EDTA magnesium disodium salt tetrahydrate (Mg-EDTA), EDTA calcium disodium salt dihydrate, EDTA cobalt disodium salt tetrahydrate and EDTA copper disodium salt tetrahydrate were used as MBL inhibitors. The sensitivity and specificity of DDSTs using Mg-EDTA for 75 MBL producers and 25 non-MBL producers were 96.0% and 100%, respectively. These findings indicate that the DDST method using Mg-EDTA can detect MBL-producing strains, including NDM-1 producers.

Development of interpretive criteria for tebipenem disk diffusion susceptibility testing with Staphylococcus spp. and Haemophilus influenzae.

Disk diffusion susceptibility interpretive criteria for tebipenem against Staphylococcus spp. and Haemophilus influenzae were developed using the Clinical and Laboratory Standards Institute (CLSI) guidelines. Tebipenem was tested by disk diffusion and broth microdilution methods against 119 clinical isolates of Staphylococcus spp. and 102 clinical isolates of H. influenzae. The zone diameters of 5-, 10-, and 30-µg disks were compared with broth microdilution minimum inhibitory concentration (MIC) results by scattergram and regression analysis. When the MIC breakpoint of 1 µg/ml was applied to the scattergrams, the 10-µg disk showed good correlation between the zone diameters and the MIC values. The corresponding disk diffusion zone diameter breakpoints with the 10-µg disk for Staphylococcus spp. were ≧22 mm (MIC ≦1 µg/ml) for susceptible, 20-21 mm (MIC = 2 µg/ml) for intermediate, and ≦19 mm (MIC ≧4 µg/ml) for resistant. We also proposed the breakpoint zone diameter of H. influenzae: ≧22 mm (MIC ≦1 µg/ml) for susceptible. These criteria demonstrated that the categorical agreements between disk diffusion and broth microdilution methods for Staphylococcus spp. and H. influenzae were 95.0% and 99.0%, respectively. The discrepancy rates of these criteria were acceptable to the CLSI guidelines.

[Evaluation of the diagnostic reagents which detect group A Streptococcus with the immunochromatographical method].

Dipstick 'Eiken' Strep A was evaluated for this sensitivity and specificity. Dipstick 'Eiken' Strep A had a capacity to detect Group A Streptococcus in 1.5x10(5) cfu/swab. The sensitivity of Dipstick 'Eiken' Strep A was 4 times higher than the sensitivity of the latex agglutination test (Serodirect 'Eiken' Strep A) and was almost the same as the immunochromatography test (TESTPACK Plus STREP A, CLEARVIEW STREP A and ImmunoCard STAT! STREP A TEST). No cross reaction was observed among 27 strains of 25 species microorganisms with Dipstick 'Eiken' Strep A. Dipstick 'Eiken' Strep A was compared with TESTPACK Plus STREP A among throat swabs from 50 patients with pharyngitis. Dipstick 'Eiken' Strep A had a sensitivity of 92.9%, a specificity of 90.5% and an agreement of 91.8%. Dipstick 'Eiken' Strep A is found to be useful diagnostic assay in the clinical laboratories.