Heterogeneity in resistant fecal Bacteroides fragilis group collected from healthy people

Comparison of Phenotypic and Genotypic Patterns of Antimicrobial-Resistant Bacteroides fragilis Group Isolated from Healthy Individuals in Vietnam and Japan

Purpose

Normal non-pathogenic flora can harm the host by acting as a reservoir of resistance determinants that are potentially transferable to human pathogens. This study aimed to assess the phenotypic and genotypic antimicrobial susceptibility patterns of the Bacteroides fragilis group (BFG) isolated from healthy individuals in Vietnam and Japan in order to elucidate the prevalence of antimicrobial resistance in human flora in the two economically and geographically different countries.

Materials and Methods

BFG was isolated from fecal samples of 80 healthy individuals in Vietnam (n=51) and Japan (n=29). Isolated strains were identified using MALDI-TOF MS, and the minimum inhibitory concentration (MIC) of 18 antibiotics was determined using the agar dilution method. Additionally, 20 antimicrobial resistance genes were detected using standard PCR.

Results

A total of 139 BFG strains belonging to 11 BFG species were isolated from the two countries, with diversity in the prevalence of each species. B. fragilis was not the predominant species. Isolations from Vietnam and Japan showed some similarities in terms of MIC₅₀ values, MIC₉₀ values, and the percentage of resistant strains. However, isolations from Vietnam showed significantly higher resistance to piperacillin, cefmetazole, clindamycin, tetracycline, and minocycline. ErmB, tet36, tetM, nim, catA, and qnrA were not found in either country. CepA was more common in B. fragilis than in non-fragilis Bacteroides. In contrast, cfiA, ermG, mefA, msrSA, tetX, tetX1, bexA, qnrB, and qnrS were found only in non-fragilis Bacteroides. There were differences in the prevalence of ermG, linA, mefA, msrSA, and qnrS between isolates from Vietnam and Japan.

Conclusion

This study is the first report on the antimicrobial susceptibility patterns in the BFG isolated from healthy individuals in Vietnam and Japan. Compared to isolations from Japan, isolations from Vietnam showed significantly higher resistance to antimicrobial agents. The distribution of various antibiotic resistance genes also differed between the two countries.

Antibiotic resistance pattern of Bacteroides fragilis isolated from clinical and colorectal specimens

BACKGROUND

Bacteroides fragilis is a part of the normal gastrointestinal flora, but it is also the most common anaerobic bacteria causing the infection. It is highly resistant to antibiotics and contains abundant antibiotic resistance mechanisms.

METHODS

The antibiotic resistance pattern of 78 isolates of B. fragilis (22 strains from clinical samples and 56 strains from the colorectal tissue) was investigated using agar dilution method. The gene encoding Bacteroides fargilis toxin bft, and antibiotic resistance genes were targeted by PCR assay.

RESULTS

The highest rate of resistance was observed for penicillin G (100%) followed by tetracycline (74.4%), clindamycin (41%) and cefoxitin (38.5%). Only a single isolate showed resistance to imipenem which contained cfiA and IS1186 genes. All isolates were susceptible to metronidazole. Accordingly, tetQ (87.2%), cepA (73.1%) and ermF (64.1%) were the most abundant antibiotic-resistant genes identified in this study. MIC values for penicillin, cefoxitin and clindamycin were significantly different among isolates with the cepA, cfxA and ermF in compare with those lacking such genes. In addition, 22.7 and 17.8% of clinical and GIT isolates had the bft gene, respectively.

CONCLUSIONS

The finding of this study shows that metronidazole is highly in vitro active agent against all of B. fragilis isolates and remain the first-line antimicrobial for empirical therapy.

In vitro sensitivity of 30 anaerobic bacterial strains of the human intestinal core microbiota to antibiotics: Culture and LC-MS/MS approaches

We have a vast knowledge on human intestinal microbiota but it can still be regarded incomplete. One of the objectives of scientists using so-called "omics" techniques is to be interested in the consequences that drugs can have on the composition of the intestinal microbiota and inversely. To date, few publications have reported the effects of drugs on the growth of bacteria composing this microbiota using a "culturomics" approach. We focused on antibiotics commonly prescribed for which the only published are the susceptibility of the pathogenic strains and not that of the commensal strains. The aim of our study was to determine the sensitivity of 30 strains considered to represent the intestinal core microbiota to 8 antibiotics and to study the possible modification of these molecules by bacteria. The 30 bacterial strains were cultured under anaerobic conditions in order to determine their sensitivity to the antibiotics. After 48 h of culture, the supernatants were also analyzed via UHPLC-MS/MS in order to determine if the antibiotics have been chemically modified. Under the current experimental conditions, cefpodoxime, metronidazole, erythromycin, sulfamethozaxole, trimethoprim and the trimethoprim/sulfamethozaxole combination have little impact on the core microbiota strain growth. On the contrary, moxifloxacin and amoxicillin inhibit the growth of numerous strains of our panel. Using UHPLC-MS/MS analyses, we have shown that some antibiotics can be modifed by the bacteria composing the intestinal core microbiome. The bacteria that make up the intestinal microbiota core are impacted by the antibiotics most commonly prescribed in clinics today and inversely.

Evaluation of the genetic relatedness of Bacteroides fragilis isolates by TRs analysis

OBJECTIVES

Human gastrointestinal tract harbors a variety of bacteria with vital roles in human health. Bacteroides fragilis is considered one of the dominant constituents of gut microflora which can act as an opportunistic pathogen leading to various diseases, including colon cancer, diarrhea, uterine and intrathecal abscesses, septicemia, and pelvic inflammation. In this study, multiple locus variable number of tandem repeats analysis (MLVA) was performed to genetically differentiate 50 B. fragilis isolates.

MATERIALS AND METHODS

Eight suitable tandem repeats (TRs) were selected by bioinformatics tools and were then subjected to PCR amplification using specific primers. Finally, MLVA profiles were clustered using BioNumerics 7.6 software package.

RESULTS

All VNTR loci were detected in all isolates using the PCR method. Overall, B. fragilis isolates were differentiated into 27 distinct MLVA types. The highest diversity index was allocated to TR1, TR2, TR5, TR6, and TR8; with this taken into account, strain type 14 was the most prevalent with 12 strains belonging to this type. Clustering revealed three major clusters of A, B, and C. With regards to the pathogenicity of B. fragilis and the outcomes of infections related to this microorganism, it is imperative to study this microorganism isolated from both patients and healthy individuals.

CONCLUSION

This study aimed at evaluating the efficiency of MLVA for the genetic differentiation of B. fragilis. The results of this study indicate the promising efficiency of MLVA typing for cluster detection of this bacterium.

A Europe-wide assessment of antibiotic resistance rates in Bacteroides and Parabacteroides isolates from intestinal microbiota of healthy subjects

Here, we sought to assess the levels of antibiotic resistance among intestinal Bacteroides and Parabacteroides strains collected between 2014 and 2016 in Europe and also attempted to compare resistance levels between clinical and commensal isolates. Bacteroides and Parabacteroides isolates were recovered from faecal samples via the novel Bacteroides Chromogenic Agar (BCA) method. Antibiotic susceptibilities were determined by agar dilution for ten antibiotics. The values obtained were then statistically evaluated. Altogether 202 Bacteroides/Parabacteroides isolates (of which 24, 11.9%, were B. fragilis) were isolated from the faecal specimens of individuals taken from five European countries. The percentage values of isolates resistant to ampicillin, amoxicillin/clavulanate, cefoxitin, imipenem, clindamycin, moxifloxacin, metronidazole, tetracycline, tigecycline and chloramphenicol were 96.6, 4.5, 14.9, 2.0, 47.3, 11.4, 0, 66.2, 1.5 and 0%, respectively. These values are close to those reported in the previous European clinical Bacteroides antibiotic susceptibility survey except for amoxicillin/clavulanate and clindamycin, where the former was lower and the latter was higher in normal microbiota isolates. To account for these latter findings and to assess temporal effects we compared the data specific for Hungary for the same period (2014-2016), and we found differences in the resistance rates for cefoxitin, moxifloxacin and tetracycline.

Antimicrobial resistance in the Bacteroides fragilis group in faecal samples from patients receiving broad-spectrum antibiotics

Members of the Bacteroides fragilis group are opportunistic pathogens and cause severe infections including bacteraemia. As increased levels of antimicrobial resistance in B. fragilis group bacteria can be detected years after administration of specific antibiotics, monitoring antimicrobial susceptibility in the gut microbiota could be important. The objectives of this study were to 1) investigate the distribution of species and the occurrence of reduced antimicrobial susceptibility in the B. fragilis group from patients treated at departments with a high level of antibiotic use, 2) to determine the prevalence of the carbapenem resistance gene cfiA in B. fragilis in this patient group, and 3) to determine the association between previous antibiotic treatment and reduced susceptibility to clindamycin, meropenem, metronidazole, and piperacillin-tazobactam. Consecutive faecal samples (n = 197) were collected from patients at the departments of haematology, oncology, and infectious diseases at Odense University Hospital, Denmark. Three colonies from each sample were identified by Matrix Assisted Lazer Desorption Ionization Time of Flight Mass Spectrometry and isolates were screened for resistance to clindamycin, meropenem, metronidazole, and piperacillin-tazobactam. B. fragilis isolates were tested for the cfiA metallo-beta-lactamase gene. Fisher's Exact test was used to test for correlation between antimicrobial exposure and reduced susceptibility. A total of 359 isolates were tested for reduced susceptibility. Of these 28%, 5%, <1%, and 11% were intermediate susceptible or resistant to clindamycin, meropenem, metronidazole, and piperacillin-tazobactam respectively. Three metronidazole resistant Bacteroides spp. were isolated. The proportion of B. fragilis belonging to division II (cfiA+) was 5.3%. Previous exposure to meropenem was associated with reduced susceptibility to meropenem (p= 0.001). In conclusion, antimicrobial resistance is prevalent and the distribution of species appears to be affected in the B. fragilis group from patients receiving broad-spectrum antibiotics, with meropenem exposure being associated with meropenem resistance.