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To study the role of cytotoxin‐associated protein (cagA) and vacuolating cytotoxin (vacA) in Helicobacter pyloriinfection in an experimental murine model, mice were infected with seven strains with different cagA and vacA status. Groups of 10 NMRI mice were challenged and were killed 5 weeks later. In a second study, 20 mice were challenged with a mixture of the same seven strains and killed 1, 3, 15 and 17 weeks post‐inoculation. All seven strains were found to colonize the mice for the 5‐week experimental period. Animals infected with vacA‐positive strains, regardless of cagA status, showed an elevation of antibody titers. Two cagA‐negative and vacA‐positive strains and one cagA‐ and vacA‐positive strain were found to ‘take over’ in the mixed infection as analyzed by the randomly amplified polymorphic DNA‐polymerase chain reaction technique and in one mouse stomach we found coexistence of two of the strains. We found no evidence of the different strains colonizing different parts of the stomach.

Eighteen Dunkin–Hartley guinea pigs and 50 NMRI mice were inoculated with Helicobacter pyloriand the infection followed by culture, histopathology, antibody response, and plasma levels of the acute‐phase proteins albumin, C3, and transferrin for up to 7 weeks. The immune response to H. pylorisurface proteins was studied by an enzyme immunoassay (EIA) and Western immunoblot and the plasma levels of albumin, C3, and transferrin were analyzed by single radial immunodiffusion. Guinea pigs had a more severe gastritis and a higher EIA immune response than NMRI mice. Serum C3 levels were elevated in infected guinea pigs after 3 and 7 weeks indicating a systemic inflammatory response and a possible link between H. pyloriinfection and extragastric manifestations such as vasculitis associated with atherosclerosis. Serum cholesterol levels were analyzed in guinea pigs at 7 weeks and indicated a higher level in H. pylori‐infected than in control animals, but this difference was not statistically significant.

The influence of lipopolysaccharide (LPS) O‐polysaccharide chain production on the colonisation ability of Helicobacter pyloriin four mouse models (NMRI, C57BL/6, CBA/Ca, and BALB/cA mice) was studied. H. pyloristrains that produced smooth‐form LPS (S‐LPS) detectable in silver‐stained electrophoretic gels colonised mice. In contrast, a laboratory‐passaged strain G50 and the culture collection strain CCUG 17874 did not colonise mice; the former strain produced low amounts of O‐chains only detectable in immunoblotting but not in silver‐stained gels, whereas the latter produced rough‐form LPS (R‐LPS) without O‐chains. Furthermore, a galEisogenic mutant, which produced R‐LPS, did not colonise mice. However, after repeated broth culture, strains G50 and CCUG 17874 produced S‐LPS detectable in silver‐stained gels and were capable of colonising mice. Consistent with the production of O‐chains, all colonising strains produced Lewis (Le) antigens, Lexand/or Ley. Except for low expression of Leyby non‐colonising G50, reflecting low production of O‐chains, all other non‐colonising strains and the galEmutant lacked expression of Le antigens consistent with their production of R‐LPS. Lectin typing of strains supported these findings, and also showed that lectin types did not differ before and after colonisation. The low level of O‐chain production and Le antigen expression by the non‐colonising G50 may not be sufficient to aid colonisation. Examination of protein profiles of H. pyloristrains before inoculation showed that protein expression was not significantly different between colonising and non‐colonising strains. These results show that S‐LPS production with O‐chain expression is required by H. pylorifor colonisation in a number of mouse models and that care should be taken with inoculating H. pyloristrains that loss of O‐chains does not occur during subculturing.

ABSTRACTRapid and accurate drug susceptibility testing (DST) is essential for the treatment of multi- and extensively drug-resistant tuberculosis (M/XDR-TB). We compared the utility of genotypic DST assays with phenotypic DST (pDST) using Bactec 960 MGIT or Löwenstein-Jensen to construct M/XDR-TB treatment regimens for a cohort of 25 consecutive M/XDR-TB patients and 15 possible anti-TB drugs. Genotypic DST results from Cepheid GeneXpert MTB/RIF (Xpert) and line probe assays (LPAs; Hain GenoType MTBDRplus2.0 and MTBDRsl2.0) and whole-genome sequencing (WGS) were translated into individual algorithm-derived treatment regimens for each patient. We further analyzed if discrepancies between the various methods were due to flaws in the genotypic or phenotypic test using MIC results. Compared with pDST, the average agreement in the number of drugs prescribed in genotypic regimens ranged from just 49% (95% confidence interval [CI], 39 to 59%) for Xpert and 63% (95% CI, 56 to 70%) for LPAs to 93% (95% CI, 88 to 98%) for WGS. Only the WGS regimens did not contain any drugs to which pDST showed resistance. Importantly, MIC testing revealed that pDST likely underestimated the true rate of resistance for key drugs (rifampin, levofloxacin, moxifloxacin, and kanamycin) because critical concentrations (CCs) were too high. WGS can be used to rule in resistance even in M/XDR strains with complex resistance patterns, but pDST for some drugs is still needed to confirm susceptibility and construct the final regimens. Some CCs for pDST need to be reexamined to avoid systematic false-susceptible results in low-level resistant isolates.