Colonization Density Research Articles

Epidemiology of Streptococcus pneumoniae and Staphylococcus aureus colonization in healthy Venezuelan children

Streptococcus pneumoniae and Staphylococcus aureus cause significant morbidity and mortality worldwide. We investigated both the colonization and co-colonization characteristics for these pathogens among 250 healthy children from 2 to 5 years of age in Merida, Venezuela, in 2007. The prevalence of S. pneumoniae colonization, S. aureus colonization, and S. pneumoniae–S. aureus co-colonization was 28%, 56%, and 16%, respectively. Pneumococcal serotypes 6B (14%), 19F (12%), 23F (12%), 15 (9%), 6A (8%), 11 (8%), 23A (6%), and 34 (6%) were the most prevalent. Non-respiratory atopy was a risk factor for S. aureus colonization (p = 0.017). Vaccine serotypes were negatively associated with preceding respiratory infection (p = 0.02) and with S. aureus colonization (p = 0.03). We observed a high prevalence of pneumococcal resistance against trimethoprim–sulfamethoxazole (40%), erythromycin (38%), and penicillin (14%). Semi-quantitative measurement of pneumococcal colonization density showed that children with young siblings and low socioeconomic status were more densely colonized (p = 0.02 and p = 0.02, respectively). In contrast, trimethoprim–sulfamethoxazole- and multidrug-resistant-pneumococci colonized children sparsely (p = 0.03 and p = 0.01, respectively). Our data form an important basis to monitor the future impact of pneumococcal vaccination on bacterial colonization, as well as to recommend a rationalized and restrictive antimicrobial use in our community.

The chemokine receptor CXCR5 is pivotal for ectopic mucosa-associated lymphoid tissue neogenesis in chronic Helicobacter pylori-induced inflammation

Ectopic lymphoid follicles are a key feature of chronic inflammatory autoimmune and infectious diseases, such as rheumatoid arthritis, Sjögren's syndrome, and Helicobacter pylori-induced gastritis. Homeostatic chemokines are considered to be involved in the formation of such tertiary lymphoid tissue. High expression of CXCL13 and its receptor, CXCR5, has been associated with the formation of ectopic lymphoid follicles in chronic infectious diseases. Here, we defined the role of CXCR5 in the development of mucosal tertiary lymphoid tissue and gastric inflammation in a mouse model of chronic H. pylori infection. CXCR5-deficient mice failed to develop organized gastric lymphoid follicles despite similar bacterial colonization density as infected wild-type mice. CXCR5 deficiency altered Th17 responses but not Th1-type cellular immune responses to H. pylori infection. Furthermore, CXCR5-deficient mice exhibited lower H. pylori-specific serum IgG and IgA levels and an overall decrease in chronic gastric immune responses. In conclusion, the development of mucosal tertiary ectopic follicles during chronic H. pylori infection is strongly dependent on the CXCL13/CXCR5 signaling axis, and lack of de novo lymphoid tissue formation attenuates chronic immune responses.

Symbiotic interactions between arbuscular mycorrhizal (AM) fungi and male papaya plants: Its status, role and implications

Experiments were conducted to study the arbuscular mycorrhizal (AM) status and its role in P-uptake through assay of root phosphatases activities in four varieties of male Carica papaya L. viz. CO-1, CO-2, Honey Dew and Washington during flowering stages. In the present study, mean total root colonization of AM fungi recorded peak increase in flowering stage-II while mean root phosphatase (acid and alkaline) activities recorded peak increase in flowering stage-I. Unlike root colonization and root phosphatase activities, spore density did not exhibit any definite patterns and recorded a narrow range of fluctuation during different flowering stages of male C. papaya. The study brought out the fact that root colonization and spore density of AM fungi along with root phosphatase activities varied significantly within the four varieties of male C. papaya plants during each flowering stage. The study also recorded consistently higher acid root phosphatase activity than alkaline root phosphatase activity under P-deficient, acidic soil conditions during all flowering stages of male C. papaya plants. Studies revealed that the root colonization of AM fungi influenced root phosphatase activities (acid and alkaline) positively and significantly during all flowering stages of male C. papaya plants. A total of twelve species of AM fungi belonging to five genera viz. Acaulospora, Dentiscutata, Gigaspora, Glomus, and Racocetra were recovered from the rhizosphere of male C. papaya plants.

The dark side of the mycorrhiza

Plant association with arbuscular mycorrhizal (AM) fungi is usually regarded as mutualistic. However, this positive effect could disappear if the benefit of the fungal-plant association changes with colonization density. In order to test the conditionality of this interaction, we evaluated plant performance and tolerance to defoliation across five levels of commercial AM fungal inoculum concentrations. Additionally, we evaluated if plant performance and tolerance were similarly affected by a whole soil community collected under a native congener. Along the gradient of inoculation, plant performance exhibited a peak at intermediate inoculum concentration, indicating the presence of an optimum level of AM fungal concentration that maximized AM fungal benefit. Root colonization by fungal hyphae increased linearly across the experimental inoculation gradient. Paralleling root colonization, plant tolerance to defoliation decreased linearly along the inoculum gradient. Plant performance was similar under the whole soil and commercial treatments. Our results show a negative correlation between tolerance to defoliation and AM fungal inoculum concentration, indicating that AM fungi colonization could constrain the evolution of plant tolerance to herbivory.

Multiple Colonization with S. pneumoniae before and after Introduction of the Seven-Valent Conjugated Pneumococcal Polysaccharide Vaccine

BackgroundSimultaneous carriage of more than one strain of Streptococcus pneumoniae promotes horizontal gene transfer events and may lead to capsule switch and acquisition of antibiotic resistance. We studied the epidemiology of cocolonization with S. pneumoniae before and after introduction of the seven-valent conjugated pneumococcal vaccine (PCV7).MethodologyNasopharyngeal swabs (n 1120) were collected from outpatients between 2004 and 2009 within an ongoing nationwide surveillance program. Cocolonization was detected directly from swabs by restriction fragment length polymorphism (RFLP) analysis. Serotypes were identified by agglutination, multiplex PCR and microarray.Principal FindingsRate of multiple colonization remained stable up to three years after PCV7 introduction. Cocolonization was associated with serotypes of low carriage prevalence in the prevaccine era. Pneumococcal colonization density was higher in cocolonized samples and cocolonizing strains were present in a balanced ratio (median 1.38). Other characteristics of cocolonization were a higher frequency at young age, but no association with recurrent acute otitis media, recent antibiotic exposure, day care usage and PCV7 vaccination status.ConclusionsPneumococcal cocolonization is dominated by serotypes of low carriage prevalence in the prevaccine era, which coexist in the nasopharynx. Emergence of such previously rare serotypes under vaccine selection pressure may promote cocolonization in the future.

Colonisation by extended-spectrum β-lactamase-producing Klebsiella spp. in a paediatric intensive care unit

A prospective cohort study was performed in order to study the incidence and risk factors for bacterial colonisation with extended-spectrum producing beta-lactamase (ESBL) Klebsiella spp. in children. The study took place in a paediatric intensive care unit (PICU) in Recife, Brazil over a five-month period in 2008. Rectal swabs were collected during the first 24h of admission and on the 2nd, 5th, 7th and 14th days of PICU stay. ESBL-producing strains of Klebsiella spp. were detected by Kirby-Bauer disc diffusion and confirmed by double disc synergy testing. A total of 186 children were enrolled with a median age of three years. The overall colonisation rate with ESBL-producing Klebsiella spp. was 14%, but 13 (7%) children were already colonised upon admission. The incidence density of colonisation during PICU admission was 14.2 per 1000 patient-days. On multivariable analysis, the use of third generation cephalosporins (P=0.008) was a risk factor for colonisation. Survival analysis revealed an increase in the accumulated risk of colonisation with an increase in length of stay in the PICU. The present study provides baseline information to guide improved practices in similar settings and direct future studies in relation to the magnitude of cross-infection and effectiveness of infection control interventions.

Substance P and vasoactive intestinal peptide are reduced in right transverse colon in pediatric slow‐transit constipation

Slow-transit constipation (STC) is recognized in children but the etiology is unknown. Abnormalities in substance P (SP), vasoactive intestinal peptide (VIP) and nitric oxide (NO) have been implicated. The density of nerve fibers in circular muscle containing these transmitters was examined in colon from children with STC and compared to other pediatric and adult samples. Fluorescence immunohistochemistry using antibodies to NO synthase (NOS), VIP and SP was performed on colonic biopsies (transverse and sigmoid colon) from 33 adults with colorectal cancer, 11 children with normal colonic transit and anorectal retention (NAR) and 51 with chronic constipation and slow motility in the proximal colon (STC). The percentage area of nerve fibers in circular muscle containing each transmitter was quantified in confocal images. In colon circular muscle, the percentage area of nerve fibers containing NOS > VIP > SP (6 : 2 : 1). Pediatric groups had a higher density of nerve fibers than adults. In pediatric samples, there were no regional differences in NOS and VIP, while SP nerve fiber density was higher in sigmoid than proximal colon. STC children had lower SP and VIP nerve fiber density in the proximal colon than NAR children. Twenty-three percent of STC children had low SP nerve fiber density. There are age-related reductions in nerve fiber density in human colon circular muscle. NOS and VIP do not show regional variations, while SP nerve fiber density is higher in distal colon. 1/3 of pediatric STC patients have low SP or VIP nerve fiber density in proximal colon.

Chromogranin A as a possible tool in the diagnosis of irritable bowel syndrome

Objective. Serum chromogranin A (CgA) levels have been reported to be normal, reduced or elevated in irritable bowel syndrome (IBS) patients. The aim of the present study was to establish a possible abnormality in CgA plasma level and in intestinal CgA cell density in IBS patients and to evaluate the outcome for the diagnosis of IBS. Material and methods. Forty-one patients with irritable bowel syndrome according to Rome Criteria III (39 females and 2 males; average age 35 years) and 59 healthy controls (37 females and 22 males; average age 45.5 years) were included in the study. Duodenal and colonic biopsies were obtained from all IBS patients. Forty-two of these healthy subjects underwent gastroscopy with duodenal biopsies. The remaining 17 subjects underwent colonoscopy with biopsies. The biopsies were immunostained with avidin–biotin-complex method for CgA cells. The cell densities were quantified by computerized image analysis. CgA plasma level was determined with ELISA technique. Results. The density of CgA cells in both the duodenum and colon was reduced in patients with IBS. CgA cell density in the left colon was, however, unaffected in patients with IBS-constipation. There was no difference in the plasma level of CgA between patients with IBS and controls. Conclusion. The reduced density of intestinal CgA cells should be considered as a reduction in the total amount of intestinal endocrine cells. Which endocrine cell type is affected remains to investigate. This reduction may offer a histopathological test for the diagnosis of IBS. It is doubtful that the blood level of CgA has any clinical impact in IBS.

Breeding performance of the second generation in some bivoltine populations of Ips typographus (Coleoptera Curculionidae) in the south-eastern Alps

The spruce bark beetle, Ips typographus, is one of the most extensively studied European forest pests. Gaps exist in the knowledge about second generation breeding performance in bivoltine populations. In this study, the breeding performance of the second generation was eval- uated in three bivoltine populations of I. typographus in the SE Alps. Length of the maternal galleries (from 40.5 to 44.8 mm), population growth rate (PGR; from 0.7 to 3.6), and emerged adults per m 2 (from 669 to 1,570 insects/m 2 ) varied among populations and were negatively correlated with bark colonisation density. Pheromone traps set up in the three investigated forests differed in the number of trapped beetles, with mean captures ranging between 5,310 and 19,850 insects per trap. The populations giving the highest captures in the traps showed the lowest bark col- onisation density (248 vs. 489 maternal galleries per m 2 ) and the best breeding performance. The populations of parasitoids and predators corresponded to just 1-9 and 2-10% of the emerging I. typographus adults, respectively, and phloem temperature never reached thresholds lethal to I. typographus. Interspecific competition was negligible, whereas intraspecific competition was found to be the main factor affecting the breeding performance of the second generation, although with different intensity according to the colonisation density. It is hypothesised that competition with the first generation and spring precipitation influence the number of suitable hosts available to the second generation.

Probiotics and Intestinal Colonization by Vancomycin-Resistant Enterococci in Mice and Humans

We investigated the impact of probiotics on the intestinal carriage of vancomycin-resistant enterococci (VRE). Administration of Lactobacillus rhamnosus Lcr35 but not Escherichia coli Nissle reduced, although not significantly, the density of VRE colonization in a murine model. No effect of Lcr35 was observed in a double-blind placebo randomized study, involving nine patients.

Stat3 and Th17-mediated colitis promotes regional tumorigenesis in response to a common commensal bacterium: role of Foxp3+ Treg/Th17 balance (90.17)

Abstract Enterotoxigenic Bacteroides fragilis (ETBF) is an inducer of inflammatory diarrheal disease with acute colitis, and may even be linked to chronic colitis and colorectal cancer in humans. The pathogenesis of ETBF can largely be attributed to the secretion of a toxin, BFT (B. fragilis toxin), which has a profound effect on the colonic microenvironment. BFT promotes cleavage of E-cadherin, activates NF-kB and Wnt/b-catenin signaling, and stimulates the secretion of pro-inflammatory cytokines, such as IL-6, IL-8, and TNF-a. The inflammation associated with ETBF is characterized by widespread colonic Stat3 activation and IL-17 cytokine secretion. In Min mice, the Th17-mediated inflammation promotes the formation of distal colon tumors, as demonstrated by reduced tumorigenesis in response to IL-17 blockade. Our research has been focused on elucidating the immunologic differences between the distal and proximal colon in an attempt to determine why tumorigenesis is so regional. We have found that the proximal colon has a greater density of Foxp3+ Tregs than the distal colon. Furthermore, preliminary data suggests that the Th17 cytokines are differentially expressed in the two regions. We propose that increased Treg density in the proximal colon restrains Th17-mediated inflammation relative to the distal colon. We are currently studying the relationship between the Treg cells and infiltrating effector cells and how that affects tumorigenesis in response to ETBF.

Evaluation of the potential of trap plants to detect arbuscular mycorrhizal fungi using polymerase chain reaction-denaturing gradient gel electrophoresis analysis

To isolate arbuscular mycorrhizal (AM) fungi from environments, the choice of appropriate trap plants is critical. The spore morphology based technique is inevitably biased because of the preference of AM fungi. In the present study, we developed a novel, polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) based technique to evaluate the trapping potential of trap plants. A lateritic red soil (pH 4.5) from a citrus orchard was used for the trap culture. Clover (Trifolium repens), sorghum (Sorghum bicolor) and maize (Zea mays) were grown alone or in combination as trap plants. At harvest, AM fungal colonization, extraradical hyphal density and sporulation were measured. DNA was extracted from the roots and substrate and the 18S rDNA fragment of AM fungi was amplified, followed by DGGE analysis. Diversity and species richness were analyzed based on the DGGE profile. Sorenson’s pairwise similarity (Cs) was calculated for evaluation. Maize exhibited the lowest AM fungal colonization and extraradical hyphae density, but the highest spore number, diversity and species richness. The AM fungal diversity and species richness were higher in the substrate than in the roots. A clustering analysis based on the Cs values revealed that a combination of the three plant species detected the most AM fungi; maize was the best if grown alone. Our results suggest that this DGGE-based technique is a reliable way to select appropriate trap plants, and a combination of plant species is superior to a single species.

Nasopharyngeal bacterial colonisation is not necessarily asymptomatic

Nasal colonisation with bacteria including pneumococcus (Pnc), <i>Haemophilus influenzae</i> (<i>H flu</i>) and <i>Staphylococcus aureus</i> is generally assumed to be asymptomatic. The authors hypothesised that it is associated with upper respiratory symptoms. 439 children (4–75 months, 233 males) attending six nurseries each had alginate nasal swabs taken in February 2009 and stored in STGG broth. At sampling, nurses obtained a single symptom score for nasal discharge, nasal blockage and sneezing from parents as follows: 0, none; 1, mild–slight; 2, moderate–definite; 3, severe–bad. Swabs were cultured and bacteria identified using standard methods. For pneumococcus, density was scored as 1–5(1), -20(2), -50(3), -100(4), &gt;100(5) colonies/50 μl broth. 231 (52.6%), 134 (30.5%) and 62 (14.1%) swabs were positive for Pnc, <i>H flu</i> and <i>S aureus</i>, respectively. Among 428 children for whom scores were available, the proportion of children colonised with Pnc and <i>H flu</i> rose progressively with rising symptom scores (<i>χ</i>² for trend p=0.00023, 0.00001) but appeared to fall for <i>S aureus</i> (table 1, ns). Symptom scores and Pnc colonisation density were strongly correlated (figure 1) (p=0.00021). These results show that uncomplicated nasopharyngeal colonisation with Pnc and <i>H flu</i> but not <i>S aureus</i> in healthy children is strongly associated with nasal symptoms which are correlated to carriage density at least for Pnc. This could be because Pnc and <i>H flu</i> induce these symptoms and <i>S aureus</i> does not. This would be consistent with known proinflammatory effects of Pnc on respiratory epithelium. Such symptoms may promote transmission but also elimination. <i>S aureus</i>, which commonly colonises the skin, may utilise other mechanisms. Alternatively respiratory viral infections, commonly associated with rhinitis, may cause symptoms and thus promote either acquisition or proliferation of Pnc and <i>H flu</i> but not <i>S aureus</i>. Further studies to detect common viruses in these samples may therefore help further elucidate these cause and effect relationships.

Protection against nasal colonization with Streptococcus pneumoniae by parenteral immunization with a DNA vaccine encoding PspA (Pneumococcal surface protein A)

Pneumococcal surface protein A (PspA) is an important candidate for a cost-effective vaccine with broad coverage against Streptococcus pneumoniae. We have previously shown that intramuscular immunization with PspA as a DNA vaccine induces an immune response characterized by the induction of a balanced IgG1/IgG2a antibody response in BALB/c mice, which was able to efficiently mediate complement deposition onto intact bacteria and to induce protection against an intraperitoneal challenge. We now confirm the results in C57BL/6 mice and further show that the response induced by the DNA vaccine expressing PspA is able to mediate protection against colonization of the nasopharyngeal mucosa even though immunization was given parenterally. Moreover, a positive correlation was observed between IgG1 and the numbers of CFU recovered, whereas an inverse correlation was observed between nasal CFU levels and IgG2a. A positive correlation was also found for IgG1/IgG2a antibody ratios with CFU recovered from the nasopharynx. Therefore, reduction of nasal colonization was strongly associated with increased levels of serum IgG2a complement fixing antibody and low levels of IgG1 antibody which has much less complement fixing activity. Passive transfer of serum from animals immunized with the DNA vaccine expressing PspA was also able to reduce the fraction of mice with high density of colonization of the nasopharynx. Secretion of IFN-γ, but not IL-17, was observed in splenocytes from mice immunized with the DNA vaccine.

Arbuscular mycorrhizal fungal diversity in some commonly occurring medicinal plants of Western Ghats, Goa region

Thirty-six medicinal plant species belonging to 25 families were surveyed to study Arbuscular mycorrhizal (AM) fungal diversity from different localities of North and South Goa of Western Ghats, Goa region, India. A total of 30 medicinal plant species were found to be mycorrhizal and six plant species showed absence of AM fungal colonization. Forty two AM fungal species belonging to five genera viz., Glomus, Acaulospora, Scutellospora, Gigaspora and Ambispora were recovered from the rhizosphere soil. Glomus was found to be the most dominant genera in the study sites, and Glomus fasciculatum the most dominant AM fungal species. Negative significant correlation was observed between percent colonization and spore density. Simpson’s and Shannon Weiner diversity index studies carried out in North and South Goa exhibited less variation in both the sites, indicating a stable and a diverse plant community.

Arbuscular Mycorrhizal Technology in Reclamation and Revegetation of Coal Mine Spoils under Various Revegetation Models

Reclamation and revegetation of a coal mine spoils with various revegetation models utilizing the mycorrhizal technology were studied. The models with different combination of plant species were designed to test the hypothesis of speedy revegetation. Root colonization and spore density of arbuscular mycorrhizae (AM) were lowest in plants seeded directly on slopes of the overburden (coal mine dump). At flat surfaces, the mycorrhizal colonization in plant species was higher than that observed at slopes. In other revegetation models, i.e., tree monoculture, tree monoculture + crop species (agroforestry), and two strata plantations (combination of different plant species), maximum AM colonization was recorded for tree species grown along with crop species. This was followed by two strata plantations and tree monoculture. In two strata plantations three categories of AM associations were recognized: 1) every plant in the combination, possessed high mycorrhizal association, 2) only one plant in the combination possessed high mycorrhizal association, and 3) none of the plants in the combination possessed high mycorrhizal association. Azadirachta indica, Pongamia pinnata, Leucaena leucocephala and Acacia catechu were most effective in catching mycorrhizae, and can be used as the effective tool in rehabilitation of the degraded ecosystems.

Arbuscular Mycorrhizal Technology in Reclamation and Revegetation of Coal Mine Spoils under Various Revegetation Models

Reclamation and revegetation of a coal mine spoils with various revegetation models utilizing the mycorrhizal technology were studied. The models with different combination of plant species were designed to test the hypothesis of speedy revegetation. Root colonization and spore density of arbuscular mycorrhizae (AM) were lowest in plants seeded directly on slopes of the overburden (coal mine dump). At flat surfaces, the mycorrhizal colonization in plant species was higher than that observed at slopes. In other revegetation models, i.e., tree monoculture, tree monoculture + crop species (agroforestry), and two strata plantations (combination of different plant species), maximum AM colonization was recorded for tree species grown along with crop species. This was followed by two strata plantations and tree monoculture. In two strata plantations three categories of AM associations were recognized: 1) every plant in the combination, possessed high mycorrhizal association, 2) only one plant in the combination possessed high mycorrhizal association, and 3) none of the plants in the combination possessed high mycorrhizal association. Azadirachta indica, Pongamia pinnata, Leucaena leucocephala and Acacia catechu were most effective in catching mycorrhizae, and can be used as the effective tool in rehabilitation of the degraded ecosystems.

Arbuscular mycorrhizal status and root phosphatase activities in vegetative Carica papaya L. varieties

The arbuscular mycorrhizal (AM) status and root phosphatase activities were studied in four vegetative Carica papaya L. varieties viz., CO-1, CO-2, Honey Dew and Washington. Standard techniques were used to ascertain information on spore density and species diversity of AM fungi. Although in case of estimation of root colonization and root phosphatase activities, the existing methods were slightly modified. Root colonization and spore density of AM fungi along with root phosphatase (acid and alkaline) activities varied significantly in four papaya varieties. The present study recorded higher acid root phosphatase activity when compared with alkaline root phosphatase activity under P-deficient, acidic soil conditions. The present study revealed that the root colonization of AM fungi influenced acid root phosphatase activity positively and significantly under P-deficient, acidic soil conditions. A total of 11 species of AM fungi belonging to five genera viz., Acaulospora, Dentiscutata, Gigaspora, Glomus and Racocetra were recovered from the rhizosphere of four papaya varieties.

Variation in arbuscular mycorrhizal fungi colonization modifies the expression of tolerance to above‐ground defoliation

Summary 1. Plant association with arbuscular mycorrhizal fungi (AMF) has been considered a factor increasing plant tolerance to herbivory. However, this positive effect could decrease with colonization density if the benefit : cost ratio of the AMF–plant association changes. We measured plant performance and tolerance to defoliation across a gradient of commercial AMF (Glomus sp.) inoculum concentration. 2. Six genetic families of Datura stramonium were grown under greenhouse conditions and subjected to five increasing levels of AMF inoculum concentration and to defoliation treatments, i.e. the presence/absence of 50% artificial damage, following a full‐factorial design. 3. AMF colonization increased linearly with inoculum concentration while foliar area, root mass, flowering phenology and seed production expressed nonlinear functions. Plant genetic variation in the benefit function of AMF colonization was also detected. We show a negative interaction between AMF concentration and plant tolerance to defoliation. 4. Synthesis. The negative correlation between plant tolerance and AMF concentration suggests that defoliation can reduce AMF benefits and that natural variations in AMF can limit the evolution of optimum levels of tolerance. Moreover, genetic variation in the shape of the reaction norms to AMF in the presence/absence of defoliation suggests that plants may evolve in response to variation in densities of AMF and herbivores.

Sensitivity is not an intrinsic property of a diagnostic test: empirical evidence from histological diagnosis of Helicobacter pylori infection

BackgroundWe aimed to provide empirical evidence of how spectrum effects can affect the sensitivity of histological assessment of Helicobacter pylori infection, which may contribute to explain the heterogeneity in prevalence estimates across populations with expectedly similar prevalence.MethodsCross-sectional evaluation of dyspeptic subjects undergoing upper digestive endoscopy, including collection of biopsy specimens from the greater curvature of the antrum for assessment of H. pylori infection by histopathological study and polymerase chain reaction (PCR), from Portugal (n = 106) and Mozambique (n = 102) following the same standardized protocol.ResultsIn the Portuguese sample the prevalence of infection was 95.3% by histological assessment and 98.1% by PCR. In the Mozambican sample the prevalence was 63.7% and 93.1%, respectively. Among those classified as infected by PCR, the sensitivity of histological assessment was 96.2% among the Portuguese and 66.3% among the Mozambican. Among those testing positive by both methods, 5.0% of the Portuguese and 20.6% of the Mozambican had mild density of colonization.ConclusionsThis study shows a lower sensitivity of histological assessment of H. pylori infection in Mozambican dyspeptic patients compared to the Portuguese, which may be explained by differences in the density of colonization, and may contribute to explain the heterogeneity in prevalence estimates across African settings.