Introduction

Helicobacter pylori is a gram-negative bacillary bacterium that inhabits the gastric mucosa and is associated with inflammatory gastrointestinal diseases such as peptic ulcers, chronic gastritis and neoplasms such as MALT (mucosal-associated lymphoid tissue). Production of cytotoxins is associated with genes A (cagA) and the vacuolizer allele (vacA). ^1,2 H. pylori is acquired during childhood and remains asymptomatic for many years. Close contact is a risk factor. ^3,4 Studies have shown that the prevalence of H. pylori in adults in developing countries exceeds 70%, ⁵ but in developed countries it ranges from 24% to 42%. ⁶

H. pylori eradication therapy based on antibiotics associated with a proton pump inhibitor is up to 80% effective, but a percentage of therapeutic failure occurs and is mainly due to resistance to antibiotics. ⁷ An appropriate strategy for development of therapeutic guidelines based on local bacterial resistance data is the use of culturing and an antibiogram. ^7,8

The study aims to determine the prevalence of antibiotic resistance in clinical isolates of H. pylori from patients older than 18 years who have recurrent dyspepsia.

Materials and methods

Results

Of the 210 people involved in the study, 143 had some degree of gastric inflammation and two people had adenocarcinoma. A total of 89 (42.4%) strains of H. pylori were isolated. Of these, 87 were found to have gastric pathologies by histopathological testing (Table 1). Four strains could not be recovered for susceptibility testing: metronidazole, levofloxacin, amoxicillin and tetracycline. Seventy-eight isolates were studied for clarithromycin. (Figures 1 and 2).

Table 1 Results of cytological study of gastric biopsies and number of H. pylori isolates recovered 

Figure 1 Minimum Inhibitory Concentration for clarithromycin in 78 strains of H. pylori. The broken lines represent cut points according to CLSI 2017. 

Figure 2 Minimum inhibitory concentration (MIC) for amoxicillin in 83 strains of H. pylori. The dashed lines represent epidemiological cut-off points according to EUCAST 2017. 

The largest number of strains that had MICs above the reference values were for metronidazole and clarithromycin, while the antibiotic association analysis for the different therapeutic schemes showed that 32% of the isolates were resistant to the combination amoxicillin/clarithromycin and 42% to clarithromycin/metronidazole (Table 2).

Table 2 Percentage of resistance to antibiotics used in H. pylori eradication treatment. CLSI cut-off points for clarithromycin and EUCAST epidemiological cut-off points for other antibiotics. 

Discussion

H. pylori is associated with inflammatory processes in the gastrointestinal mucosa and has prevalences of around 70% to 80% worldwide, especially in developing countries. ⁵ In our study, H. pylori was isolated in 89 patients (42.4%), only 2 isolates were not associated with gastric inflammation, and prevalence was lower than those reported in other studies. Factors such as the difficulty of isolating H. pylori from cultures, difficulties with biopsy sites and quality, transportation and incubation conditions can influence results. ¹¹ In our study, the biopsies obtained from the fundus and gastric antrum were selected as recommended, ¹² while culturing was done within 2 hours to avoid loss of viability of bacterial strains.

Both primary resistance associated with the use of antibiotics for the treatment of infections caused by pathogens other than H. pylori and secondary resistance caused by previous H. pylori eradication treatment were considered. ^13,14,15 The CLSI establishes clinical cut-off points for clarithromycin, but does not do so for amoxicillin, tetracycline, metronidazole and levofloxacin. A variation among epidemiological studies has been observed regarding cut-off points. Our study used the epidemiological cut-off points given by EUCAST and used in most European countries, but we took into account both the possibility that isolates considered to be resistant can increase as well as demonstrated poor clinical efficacy. ¹⁶

Although clarithromycin continues to be recommended as the first option for H. pylori eradication treatment, ⁸ our study shows that 66% of the isolates were resistant with values well above the 12% reported for Latin America, ¹⁷ and the 9.5% in Ecuador, reported in 2003 ¹⁸. Raymont et al. have demonstrated clarithromycin resistant isolates from 68% of patients with a history of prior antibiotic therapy, ¹⁹ and a similar percentage of resistance has been demonstrated by Gao et al. ²⁰

The Maastricht IV consensus on the use of macrolides recommends that local prevalence be taken into account for empirical treatment of H. pylori, and that clarithromycin’s use should be avoided when susceptibility tests show 15% to 20% of resistant strains. ⁸ However, since these tests are complex, few laboratories perform them. Among the mechanisms of resistance described for clarithromycin are mutations in the 23S rRNA gene and the use of proton pump inhibitors. ^21,22. A deficiency of our study was that we did not investigate these mechanisms.

Our study found that 43% of the strains of amoxicillin, another first-line antibiotic in triple therapy, were resistant with MICs greater than 0.125. This is a high percentage if one takes into account that for Latin America it is between 0% and 39%, and the difference is even greater for the percentage found in Ecuador which in previous years has not exceeded 4%. ^17,18 Nishizawa et al. have demonstrated that, similar to what has happened with the use of clarithromycin, after attempts to eradicate H. pylori with amoxicillin based schemes failed, the number of resistant isolates increased from 49.5% to 72%. ²³ In our study, we did not obtain data on previous administration of antibiotics within or outside of eradication therapy. Nevertheless, patients with recurrent dyspepsia were selected and may have received previous antimicrobial therapy. A resistance of 63% to metronidazole is within the range reported for Latin America of 12.5% to 95% and not dissimilar to the report from Ecuador of 80.9%. ^17,18

More than 30% of strains present resistance simultaneously to two antibiotics used for eradication therapy, be it clarithromycin or levofloxacin.

Previous use of antibiotics is a risk factor for increasing resistance of H. pylori strains and, consequently, for therapeutic failure, either through primary or secondary resistance. ²⁴ A high prevalence of resistance to antibiotics used in eradication treatment was demonstrated in this study, unlike the results obtained in Ecuador in 2003. Risk-benefit analysis together with the performance of susceptibility tests is recommended whenever clarithromycin or amoxicillin is used as an empirical treatment in patients with recurrent dyspepsia or in those who may have already received previous treatment.