Clarithromycin resistance in Helicobacter pylori and its molecular determinants in Northern Spain, 2013-2015

Clarithromycin resistance (CLR-R) is the main reason for failure of Helicobacter pylori infection treatment, which is frequently empirically prescribed due to the erroneous belief that culture for susceptibility testing is difficult. The aim of this study was to determine CLR-R in a region of southern Europe and to evaluate the utility of a PCR sequencing assay applied on gastroduodenal biopsies in detecting H. pylori and clarithromycin (CLR) susceptibility.

The susceptibility of all H. pylori isolates obtained by culture during 2013-2015 was determined by Etest. During 2014-2015, H. pylori detection and CLR susceptibility were also studied by PCR followed by sequencing performed on gastroduodenal biopsies. Point mutations in the 23S rRNA gene were studied in all CLR-resistant isolates in 2014.

Of 1986 H. pylori isolates obtained by culture (63 from children and 1923 from adults), 349 (17.6%) were CLR-resistant [21/63 (33.3%) in children and 328/1923 (17.1%) in adults; P<0.001], of which 31.5% were also resistant to levofloxacin. The main mutations detected were A2147G (79.8%), A2146G (17.2%) and A2146C (2%). Concordance between the PCR sequencing assay on biopsies and CLR susceptibility by Etest after culture was 89.8%.

CLR-R was high in Gipuzkoa, northern Spain. The molecular PCR method performed directly on biopsies was a good alternative to the traditional Etest susceptibility method and was an aid when culture was non-viable.