Antimicrobial susceptibility testing of 230 Helicobacter pylori strains: importance of medium, inoculum, and incubation time

Abstract

No standardized method of susceptibility testing for Helicobacter pylori is currently available, so before a large agar dilution study comprising 230 H. pylori strains belonging to more than 80 genetically different groups was initiated, we performed a relatively small preliminary study to determine the influences of medium, inoculum density, and incubation time. Seven media were investigated and were primarily evaluated on the basis of their abilities to support growth both semiquantitatively and qualitatively; Iso-Sensitest agar supplemented with 10% horse blood was found to be well suited for the purpose; this was closely followed by Mueller-Hinton agar with 10% horse blood, Mueller-Hinton with 10% sheep blood, and finally, 7% lysed horse blood agar. Investigations of two inoculum densities and two incubation times resulted in recommendations for the use of 10(9) CFU/ml (10[6] CFU/spot) as the inoculum and 72 h as the incubation time. A modest inoculum effect was noted for amoxicillin and metronidazole. By the methodology derived from our preliminary study, the susceptibilities of 230 H. pylori strains to six antibiotics were subsequently determined. The results were generally in accord with those of others, and apart from metronidazole, the MIC of which for approximately 25% of the strains tested was >8 microg/ml, resistance was low in Denmark. The situation might, however, quickly change when and if the number of indications for antibiotic therapy for H. pylori infections increase. Consequently, susceptibility testing of all H. pylori strains is recommended in order to survey the development of resistance, and in our hands the described methodology was relatively easy to perform and the results were easy to read.

Purification and identification of antibacterial phenolics fromTripodanthus acutifoliusleaves

“…1997). The inoculation size in photometric assay was 20‐fold greater (because of photometric measurements) than that proposed by the National Committee for Clinical Laboratory Standards (NCCLS 1999), that is the reason why the substances were assayed at concentrations nearly 20‐fold MICs (Hartzen et al. 1997).…”

Changes in Antibiotic Susceptibility ofHelicobacter pyloriin the Course of Eight Years in the Zaanstreek Region in The Netherlands

“…Suspected colonies were Gram stained and evaluated by testing catalase, oxidase, and urease production [3]. Antibiotic susceptibility of H. pylori was determined by E -test (Biomerieux) on Columbia agar (Oxoid, Basingstoke, United Kingdom) enriched with 7% sheep blood [4]. …”

Susceptibility Profile to Common Antimicrobials Used for Eradication ofHelicobacter pyloriInfection in Mexico by Agar Dilution Method

“…The reasons for such discrepancies could be due to certain factors such as cut-off values used to determine susceptibility, the susceptibility method chosen, the type of study population, and the geographical region from where the cohort was derived. In the case of metronidazole, testing conditions, including choice of medium, age of colonies, incubation times and conditions, inoculum size, and the susceptibility method chosen have been shown to influence the test results 6,8,12,13 . It has also been shown that E-test results for metronidazole do not always correlate with those obtained using agar dilution 6,8,12 .…”