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Comparison of the Etest and the Neo-Sensitabs method for antimicrobial susceptibility testing of Helicobacter pylori

Abstract number: P1179

Rasmussen L., Jonaitis L., Kupcinskas L., Andersen L.

Objectives: To assess the reliability of the E-test (AB BIODISK) compared with the Neo-Sensitabs (Rosco) method for antimicrobial susceptibility testing of Helicobacter pylori.

Methods:H. pylori strains were susceptibility tested by both the E-test and the Neo-Sensitabs method for ampicilin, metronidazole, ciprofloxacin, tetracycline and clarithromycin.

50 clinically isolated H. pylori strains were grown on chocolate agar plates and incubated at 37°C in a microaerobic gas chamber. The bacteria were harvested after 72 hours, suspended in API suspension medium (bioMérieux) and adjusted to a McFarland turbidity standard of 4 (109 CFU/ml). Inoculation was performed by applying 100 ml of the bacteria suspension to each plate (plates were room tempered before inoculation) and spread by drigalski loop. Before applying the E-test strips and the Neo-Sensitabs plates were left to dry for 15 minutes. The strips/tablets were applied using sterile forceps and only one strip/tablet per plate was applied. Incubation was conducted at 37°C in a microaerobic gas chamber and reading after 72 hours.

In order to allow a direct comparison of E-test and tablet results, MIC (Minimal inhibitory concentration) values were first log2 transformed and then converted to scores ranging from 1 to 15 [1]. Correlations between scored MIC and zonesize were tested using Pearson's regression.

Figure 1. Correlation between metronidazole MIC values and zonesizes with 50 H. pylori isolates.

Results: Zonesize is plotted as a function of scored MIC of ampicilin, metronidazole, ciprofloxacin, tetracycline and clarithromycin and correlations calculated. The corresponding correlation coefficients are -0.49, -0.97, -0.89. -0.49 and -0.67 respectively. As an example Figure 1 shows the results of metronidazole.

Conclusion: Excellent correlation was demonstrated by statistical analysis between MIC score and zonesize values for metronidazole and ciprofloxacin while the correlation was acceptable for ampicilin, tetracycline and clarithromycin.

References

1. Glupczynski et al, 2002. Comparison of the E Test and Agar Dilution Method for Antimicrobial Susceptibility Testing of Helicobacter pylori.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Barcelona, Spain
Presentation type:
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