Evaluation of the prevalence of enterotoxigenic Bacteroides fragilis and the distribution bft gene subtypes in patients with diarrhea

Comparison of microbiological profile of enterotoxigenic Bacteroides fragilis (ETBF) isolates from subjects with colorectal cancer (CRC) or intestinal pre-cancerous lesions versus healthy individuals and evaluation of environmental factors involved in intestinal dysbiosis

OBJECTIVE

The aim of this study was to analyze enterotoxigenic Bacteroides fragilis (ETBF) isolates from colorectal biopsies of subjects with a histological analysis positive for colorectal cancer (CRC), pre-cancerous lesions (pre-CRC) or with a healthy intestinal tissue and to evaluate the environmental factors that may not only concur to CRC development but may also affect gut microbiota composition.

METHODS

ETBF isolates were typed using the ERIC-PCR method, while PCR assays were performed to investigate the bft alleles, the B. fragilis pathogenicity island (BFPAI) region and the cepA, cfiA and cfxA genes. Susceptibility to antibiotics was tested using the agar dilution method. Environmental factors that could play a role in promoting intestinal dysbiosis were evaluated throughout a questionnaire administered to the subjects enrolled.

RESULTS

Six different ERIC-PCR types were identified. The type denominated C in this study was the most prevalent, in particular among the biopsies of subjects with pre-CRC, while an isolate belonging to a different type, denominated F, was detected in a biopsy from a subject with CRC. All the ETBF isolates from pre-CRC or CRC subjects had a B. fragilis pathogenicity island (BFPAI) region pattern I, while those from healthy individuals showed also different patterns. Furthermore, 71% of isolates from subjects with pre-CRC or CRC were resistant to two or more classes of antibiotics vs 43% of isolates from healthy individuals. The B. fragilis toxin BFT1 was the most frequently detected in this study, confirming the constant circulation of this isoform strains in Italy. Interestingly, BFT1 was found in 86% of the ETBF isolates from patients with CRC or pre-CRC, while the BFT2 was prevalent among the ETBF isolates from healthy subjects. No substantial differences based on sex, age, tobacco and alcohol consumption were observed between healthy and non-healthy individuals included in this study, while most of the subjects with CRC or pre-CRC lesions were subjected to pharmacological therapy (71%) and showed a body mass index (BMI) that falls within the overweight range (86%).

CONCLUSIONS

Our data suggest that some types of ETBF seem to better adapt and colonize the human gut and that the selective pressure exerted by factors related to lifestyle, such as pharmacological therapy and weight, could facilitate their persistence in the gut and their possible involvement in CRC development.

Prevalence and antimicrobial susceptibility of enterotoxigenic extra-intestinal Bacteroides fragilis among 13-year collection of isolates in Kuwait

Background

Some strains of Bacteroides fragilis species are associated with diarrhea as a result of enterotoxin production (bft or fragilysin). Fragilysin is activated by C11 protease (fpn) and together with C10 protease (bfp) play a significant role in its invasiveness. The objectives of this study were to investigate the proportion of clinical isolates from extra-intestinal sources that are toxin producers and characterize the genes mediating toxin production. Clinical isolates submitted to our reference laboratory over the last 13 years were screened for toxin production using PCR technique. All stool isolates were excluded. The isolates were tested for their susceptibility to 8 antimicrobial agents by E test. Carbapenem resistance gene cfiA was detected by PCR.

Results

A total of 421 B. fragilis isolates were viable. Out of these, bft was detected in 210 (49.9%) isolates. Of the 210 bft-positive isolates, 171 (81.4%), 33 (15.7%) and 6 (2.8%) harbored bft-1, bft-2, and bft-3 genes, respectively. Twenty (9.5%) of the bft-positive strains originated from bloodstream infections. Twenty-five, 20 and 9 strains harbored bfp-1, bfp-2 and bfp-3 gene, respectively. Two, 3, 4 bfp isotypes were detected simultaneously in some of strains. The resistance rates against amoxicillin-clavulanic acid was 32%, clindamycin 62%, cefoxitin 26%, imipenem 11%, meropenem 17%, metronidazole 4%, piperacillin 61% and tigecycline 14%. A chromosomally located cfiA gene that encode metallo-β-lactamase was identified in only 34 isolates (16.2%).

Conclusions

The prevalence of enterotoxin-producing B. fragilis was high among the extra-intestinal isolates. Metronidazole was the most active agent against all isolates. There was no statistically significance difference between resistance rates among bft-positive and bft-negative isolates except for clindamycin.

The presence of antibiotic resistance genes and bft genes as well as antibiotic susceptibility testing of Bacteroides fragilis strains isolated from inpatients of the Infant Jesus Teaching Hospital, Warsaw during 2007-2012

The purpose of this study was to assess drug susceptibility of clinical B. fragilis strains and to determine any correlation between drug resistance and the presence of specific genes. Antimicrobial susceptibility was assessed using E-tests. All isolates were analyzed with the PCR technique for the presence of antibiotic resistance genes (cepA, cfxA, cfiA, ermF, ermB, ermG, nim), insertion sequences elements (IS1186, IS1187, IS1188, IS942), and enterotoxin-encoding genes (bft). Susceptibility tests yielded the following rates of resistance to the evaluated antibiotics: penicillin G (100%), clindamycin (22.5%), cefoxitin (6.3%), amoxicillin/clavulanic acid (1.8%). All strain were susceptible to imipenem, and metronidazole. The following antibiotic resistance genes were detected in the evaluated isolates: cepA (in 96.4% of isolates), cfxA (in 12.6%), cfiA (in 1.8%), and ermF (in 25.2%). Genes ermB, ermG, and nim were not found. The presence of the cepA gene showed no correlation with the penicillin G MIC. However, we observed a high correlation between cefoxitin MIC values and the presence of gene cfxA as well as a nearly complete correlation between clindamycin MIC values and the presence of gene ermF. The presence of a bft gene was detected in 14.4% of the analyzed B. fragilis isolates; with the bft-1 allele found in 75%, bft-2 in 25%, and bft-3 in none of the isolates. Antibiotic susceptibility profiles of enterotoxin gene-positive isolates in our study did not differ from those of enterotoxin gene-negative isolates.

The Bacteroides fragilis toxin gene is prevalent in the colon mucosa of colorectal cancer patients

BACKGROUND

Enterotoxigenic Bacteroides fragilis (ETBF) produces the Bacteroides fragilis toxin, which has been associated with acute diarrheal disease, inflammatory bowel disease, and colorectal cancer (CRC). ETBF induces colon carcinogenesis in experimental models. Previous human studies have demonstrated frequent asymptomatic fecal colonization with ETBF, but no study has investigated mucosal colonization that is expected to impact colon carcinogenesis.

METHODS

We compared the presence of the bft gene in mucosal samples from colorectal neoplasia patients (cases, n = 49) to a control group undergoing outpatient colonoscopy for CRC screening or diagnostic workup (controls, n = 49). Single bacterial colonies isolated anaerobically from mucosal colon tissue were tested for the bft gene with touch-down polymerase chain reaction.

RESULTS

The mucosa of cases was significantly more often bft-positive on left (85.7%) and right (91.7%) tumor and/or paired normal tissues compared with left and right control biopsies (53.1%; P = .033 and 55.5%; P = .04, respectively). Detection of bft was concordant in most paired mucosal samples from individual cases or controls (75% cases; 67% controls). There was a trend toward increased bft positivity in mucosa from late- vs early-stage CRC patients (100% vs 72.7%, respectively; P = .093). In contrast to ETBF diarrheal disease where bft-1 detection dominates, bft-2 was the most frequent toxin isotype identified in both cases and controls, whereas multiple bft isotypes were detected more frequently in cases (P ≤ .02).

CONCLUSIONS

The bft gene is associated with colorectal neoplasia, especially in late-stage CRC. Our results suggest that mucosal bft exposure is common and may be a risk factor for developing CRC.

[Anaerobic bacteria 150 years after their discovery by Pasteur]

In 2011 we celebrated the 150th anniversary of the discovery of anaerobic bacteria by Louis Pasteur. The interest of the biomedical community on such bacteria is still maintained, and is particularly focused on Clostridium difficile. In the past few years important advances in taxonomy have been made due to the genetic, technological and computing developments. Thus, a significant number of new species related to human infections have been characterised, and some already known have been reclassified. At pathogenic level some specimens of anaerobic microflora, that had not been isolated from human infections, have been now isolated in some clinical conditions. There was emergence (or re-emergence) of some species and clinical conditions. Certain anaerobic bacteria have been associated with established infectious syndromes. The virulence of certain strains has increased, and some hypotheses on their participation in certain diseases have been given. In terms of diagnosis, the routine use of MALDI-TOF has led to a shortening of time and a cost reduction in the identification, with an improvement directly related to the improvement of data bases. The application of real-time PCR has been another major progress, and the sequencing of 16srRNA gene and others is currently a reality for several laboratories. Anaerobes have increased their resistance to antimicrobial agents, and the emergence of resistance to carbapenems and metronidazole, and multi-resistance is a current reality. In this situation, linezolid could be an effective alternative for Bacteroides. Fidaxomicin is the only anti-anaerobic agent introduced in the recent years, specifically for the diarrhoea caused by C.difficile. Moreover, some mathematical models have also been proposed in relation with this species.

Case-control study on the role of enterotoxigenic Bacteroides fragilis as a cause of diarrhea among children in Kolkata, India

A total of 874 fecal specimens (446 diarrheal cases and 428 controls) from diarrheal children admitted in the Infectious Diseases Hospital, Kolkata and age and sex matched asymptomatic subjects from an urban community were assessed for the prevalence of enterotoxigenic Bacteroides fragilis (ETBF). Isolates of B. fragilis were tested for the presence of enterotoxin gene (bft) by PCR. The detection rate of ETBF was 7.2% (63 of 874 specimens) that prevailed equally in diarrheal cases and controls (7.2% each; 32 of 446 cases and 31 of 428 controls). Male children up to one year age group was significantly (p<0.05) associated with ETBF infection as compared to children > 2 years of age in cases and controls. In 25 ETBF isolates, the bft gene was genotyped using PCR-RFLP and only two alleles were identified with prevalence rate of 40% and 60% for bft-1 and bft-3, respectively. All the ETBF isolates were susceptible for chloramphenicol and imipenem but resistant to clindamycin (48%), moxifloxacin (44%) and metronidazole (32%). Resistance of ETBF to moxifloxacin (44%) and metronidazole is an emerging trend. Pulsed-field gel electrophoresis (PFGE) revealed that majority of the ETBF isolates are genetically diverse. In the dendrogram analysis, two clusters were identified, one with ETBF resistant to 5–8 antimicrobials and the other cluster with metronidazole and moxifloxacin susceptible isolates from diarrheal cases. To our knowledge, this is the first detailed report on ETBF from India indicating its clinical importance and molecular characteristics.

Comparative evaluation of conventional and real-time PCR assays for detecting Bacteroides fragilis in clinical samples

A conventional PCR and a real-time PCR for detecting Bacteroides fragilis were evaluated against clinical specimens. Analytical sensitivities were 100 and 40 fg of DNA, respectively. Detection limits were 100 and 10 CFU/ml, respectively. A total of six culture-negative specimens were positive by PCR. Altering the gold standard from "positive culture" to "positive culture or both PCR assays positive" resulted in sensitivities of 91.7% and 100%, respectively, and in specificities of 100% and 98.6%, respectively.