Combining VITEK® 2 with colistin agar dilution screening assist timely reporting of colistin susceptibility.

OBJECTIVES: The rise in carbapenem resistance among Gram-negative bacteria has renewed interest in colistin. Recently, the EUCAST-CLSI Polymyxin Breakpoints Working Group declared that broth microdilution (BMD) is the only valid method for colistin susceptibility testing. BMD is not easily incorporated into the routine work of clinical laboratories, and usually this test is incorporated serially, resulting in delayed susceptibility reporting. We tested a strategy of combining VITEK® 2 with a 2 µg/mL colistin agar dilution (VITEK® 2/AD) screening plate to improve performance and time to reporting of colistin susceptibility. METHODS: Colistin susceptibility for 364 clinical isolates was determined by VITEK® 2/AD and compared with the reference standard BMD according to the ISO 20776-1:2007 and CLSI guidelines. The EUCAST colistin susceptibility breakpoint of ≤2 µg/mL was used. Escherichia coli NCTC 13846 served as quality control strain. Agreement, very major error (VME) and major error rates were determined using ISO 20776-2:2007. RESULTS: The VME rate for VITEK® 2 alone was 30.6% (15/49, 95% CI 18.3-45.4%), and was reduced to 10.2% (5/49, 95% CI 3.4-22.2%) using the VITEK® 2/AD combined testing. The combined testing had categorical agreement with BMD of 97% (354/364, 95% CI 95.0-98.7%), and a major error (ME) rate of 1.6% (5/315, 95% CI 0.5-3.7%). Using the combined testing, even against challenging strains, 349 (95.8%, 95% CI 93.3-97.7%) colistin susceptibility results could be reported, and only 15 isolates required further analysis by BMD. DISCUSSION: Our method is simple to apply and allows rapid reporting of colistin susceptibility.

Multicentre survey of the in-vitro activity of seven antimicrobial agents, including ertapenem, against recently isolated Gram-negative anaerobic bacteria in Greece.

The in-vitro activities of penicillin, ticarcillin-clavulanic acid, cefoxitin, imipenem, ertapenem, metronidazole and clindamycin were evaluated against 138 Gram-negative anaerobic isolates (82 Bacteroides fragilis group, 17 non-fragilis Bacteroides spp., 31 Prevotella spp., four Fusobacterium spp., two Veillonella spp., one Porphyromonas sp. and one Tissierella praeacuta) collected from six general hospitals in Athens, Greece. Overall rates of non-susceptibility (both resistant and intermediately-resistant) to penicillin and ticarcillin-clavulanic acid were 81.8% and 2.3%, respectively. The rates of non-susceptibility to cefoxitin and clindamycin were 30.3% and 31.1%, respectively, and that for metronidazole was 4.3% (four Prevotella spp. isolates, one Porphyromonas sp. isolate and one B. fragilis isolate). Only the single B. fragilis isolate was nim-positive by PCR. Only one B. fragilis isolate was resistant to both carbapenems tested, while six more Bacteroides spp. isolates were imipenem-susceptible and ertapenem-non-susceptible. The MIC range, MIC(50) and MIC(90) values were comparable for imipenem and ertapenem, although ertapenem MIC(90)s were one or two two-fold dilutions higher.

Blood culture results during the period 1995-2002 in a Greek tertiary care hospital.

Data on BacT/Alert blood cultures in a Greek hospital from 1995 to 2002 were analysed retrospectively. There was a gradual increase in the number of blood cultures (4981 in 1995 to 9054 in 2002), the true positive rate (14.4% to 16.5%) and the number of bloodstream infections/1000 hospital admissions (22.1 to 30.7). The five most common pathogens were Eschericia coli, Staphylococcus aureus, coagulase-negative staphylococci, enterococci and Klebsiella spp. The relative rates of Gram-negative and Gram-positive isolates inverted during the study period because of an increasing frequency of coagulase-negative staphylococci and enterococci.