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Significance of Anaerobic Preincubation of Helicobacter pylori tor Measuring Metronidazole Susceptibility by the Etest
Author(s) -
ChidaSakata Noriko,
Baba Masaru,
Inagawa Hiroko,
Wada Akihito,
Tanaka Tatsuro,
Hoshihara Yoshio,
Takemoto Tadayoshi
Publication year - 1999
Publication title -
microbiology and immunology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.664
H-Index - 70
eISSN - 1348-0421
pISSN - 0385-5600
DOI - 10.1111/j.1348-0421.1999.tb02422.x
Subject(s) - etest , agar dilution , metronidazole , microbiology and biotechnology , agar , helicobacter pylori , microaerophile , biology , anaerobic exercise , minimum inhibitory concentration , anaerobic bacteria , bacteria , antibiotics , physiology , genetics
The Etest is widely used for measuring the susceptibility of Helicobacter pylori to metronidazole. By using 55 H. pylori isolates from 55 patients and a standard H. pylori strain, NCTC11637, we compared metronidazole susceptibility results obtained from the Etest with or without anaerobic preincubation to those obtained from the agar dilution method. Mueller Hinton agar plates supplemented with 5% horse blood were used for both methods. For the Etest, plates were incubated for 72 hr at 35 C under microaerophilic conditions after 0‐, 4‐ or 24‐hr periods of anaerobic preincubation. For the agar dilution method, the plates were incubated at the same microaerophilic conditions as those for the Etest. Without anaerobic preincubation for the Etest, 39 of the 56 (70%) H. pylori isolates were categorized as resistant to metronidazole (minimal inhibitory concentration >8 mg/liter), whereas only one of the 56 (1.8%) isolates was resistant according to the agar dilution method. The resistant and susceptible agreement rate was 32%. Four‐hour anaerobic preincubation did not alter the readings of the Etest significantly. However, when the Etest was performed with 24‐hr anaerobic preincubation, the number of isolates categorized as resistant was reduced to six (11%), improving the agreement rate to 91%. For measuring the metronidazole susceptibility of H. pylori by the Etest, 24‐hr anaerobic preincubation is necessary to agree with the results obtained by the agar dilution test.