Mechanisms of Bacteroides fragilis resistance to metronidazole

Efficacy of metronidazole in reducing pain after hemorrhoidectomy: a meta-analysis of randomized controlled trials

OBJECTIVE

Pain is a significant issue in post-hemorrhoidectomy. Metronidazole is being explored as an adjunctive pain management option. This meta-analysis of randomized controlled trials (RCTs) assesses metronidazole's effectiveness and safety compared to a placebo post-hemorrhoidectomy, aiming to provide evidence-based pain management guidance.

METHOD

We conducted a systematic search of the Cochrane Library, Embase, PubMed, Web of Science, and ClinicalTrials.gov for RCTs comparing metronidazole to placebo after hemorrhoidectomy, covering the period from database inception to July 21, 2024. After screening per inclusion/exclusion criteria, study quality was assessed using Cochrane Handbook's risk of bias tool (version 5.1.0). The meta-analysis was conducted using RevMan 5.3 software, the quality of outcome indicators was assessed using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system, and trial sequential analysis (TSA) was employed to verify the adequacy of the sample size.

RESULTS

A total of 9 RCTs were included. The meta-analysis results showed that the pain scores on the first day post-operation [MD=-1.07, 95% CI (-1.85, -0.30), P = 0.006], the second day post-operation [MD=-1.72, 95% CI (-2.62, -0.81), P = 0.0002], the seventh day post-operation [MD=-1.73, 95% CI (-2.70, -0.76), P = 0.0005], and the fourteenth day post-operation [MD=-1.80, 95% CI (-2.67, -0.94), P < 0.0001] in the metronidazole group were lower than those in the placebo group. Additionally, the rate of additional analgesia was reduced [RR = 0.48, 95% CI (0.27, 0.84), P = 0.01]. No statistically significant differences were found between the metronidazole and placebo groups in terms of the overall incidence of complications [RR = 0.69, 95% CI (0.41, 1.16), P = 0.16] and time to return to normal activities [MD=-1.69, 95% CI (-6.58, 3.20), P = 0.50]. Sensitivity analysis indicated that the results for pain scores on the first day post-operation were unstable. High heterogeneity was observed in pain scores on the first, second, seventh, and fourteenth days post-operation, as well as in the time to return to normal activities. The TSA indicated that the sample size for the primary outcome measures had achieved the required information size (RIS), supporting the strength and dependability of the meta-analysis findings.

CONCLUSION

Metronidazole may be effective and safe in reducing postoperative pain in patients undergoing hemorrhoidectomy. However, due to the limitations of this study, further verification is needed from future large-sample, multi-center, well-designed high-quality RCTs.

CLINICAL TRIAL NUMBER

Not applicable.

Multiplex PCR-Mass Spectrometry Mini-Sequencing Technology Detected Antibiotic Resistance of Helicobacter pylori to Six Antibiotics

The abuse of antibiotics has led to widespread resistance to Helicobacter pylori (H. pylori) in the population. There is an urgent need to establish a method to detect multiple antibiotic resistance rapidly. This study aimed to construct a novel strategy for the high-throughput detection of H. pylori's resistance to varying antibiotics using multiplex PCR-mass spectrometry mini-sequencing (mPCR-MS mini-sequencing) technology. This study detected the resistance of H. pylori to six antibiotics using eight mutated sites (23S rRNA-2143; pbp1A-1667, 1684, 1240; gyrA-261, 271, 573; and 16S rRNA-928) of four resistance genes (pbp1A, gyrA, 23S rRNA, and 16S rRNA), and 525 were detected in all 528 results (99.43%). Then, the culture-based phenotypic drug susceptibility testing (DST) method was used as a reference for drug resistance detection. We found that the consistency rate between mPCR-MS mini-sequencing with the DST results of amoxicillin (AMX), moxifloxacin (MOX), levofloxacin (LEV), clarithromycin (CLA), azithromycin (AZI), and tetracycline (TET) were 95.5% (63/66), 77.3% (51/66), 68.2% (45/66), 93.9% (62/66), 92.4% (61/66), and 97.0% (64/66), respectively. This method was high-throughput and extensible, easily improving the entire detection system by adding new mutation sites. mPCR-MS mini-sequencing technology provides a new approach to mutation sites related to H. pylori's antibiotic resistance.

New functions of pirin proteins and a 2-ketoglutarate: Ferredoxin oxidoreductase ortholog in Bacteroides fragilis metabolism and their impact on antimicrobial susceptibility to metronidazole and amixicile

The understanding of how central metabolism and fermentation pathways regulate antimicrobial susceptibility in the anaerobic pathogen Bacteroides fragilis is still incomplete. Our study reveals that B. fragilis encodes two iron-dependent, redox-sensitive regulatory pirin protein genes, pir1 and pir2. The mRNA expression of these genes increases when exposed to oxygen and during growth in iron-limiting conditions. These proteins, Pir1 and Pir2, influence the production of short-chain fatty acids and modify the susceptibility to metronidazole and amixicile, a new inhibitor of pyruvate: ferredoxin oxidoreductase in anaerobes. We have demonstrated that Pir1 and Pir2 interact directly with this oxidoreductase, as confirmed by two-hybrid system assays. Furthermore, structural analysis using AlphaFold2 predicts that Pir1 and Pir2 interact stably with several central metabolism enzymes, including the 2-ketoglutarate:ferredoxin oxidoreductases Kor1AB and Kor2CDAEBG. We used a series of metabolic mutants and electron transport chain inhibitors to demonstrate the extensive impact of bacterial metabolism on metronidazole and amixicile susceptibility. We also show that amixicile is an effective antimicrobial against B. fragilis in an experimental model of intra-abdominal infection. Our investigation led to the discovery that the kor2AEBG genes are essential for growth and have dual functions, including the formation of 2-ketoglutarate via the reverse TCA cycle. However, the metabolic activity that bypasses the function of Kor2AEBG following the addition of phospholipids or fatty acids remains undefined. Overall, our study provides new insights into the central metabolism of B. fragilis and its regulation by pirin proteins, which could be exploited for the development of new narrow-spectrum antimicrobials in the future.

Prolonged Bacteroides pyogenes infection in a patient with multiple lung abscesses

Bacteroides pyogenes is naturally found in the oral microbiome of cats and dogs and hence exposure, especially bites from these animals, is a major risk factor for human infections. B pyogenes is known to cause infections that persist despite antibiotic treatment and can have serious clinical outcomes. We present a novel case of complex lung abscesses associated with B pyogenes infection. A 55 year old man presents with a 3-month history of productive cough, night sweats, and 5 kg weight loss. An initial chest radiograph revealed mass-like opacities in the right upper lobe (RUL), right middle lobe (RML), and left lower lobe (LLL). Over the next 4 years the patient underwent multiple investigations and antimicrobial treatments until resolution of the abscesses. We believe that metronidazole in combination with moxifloxacin was a key component in the clinical cure of this patient.

Bacteroides and related species: The keystone taxa of the human gut microbiota

Microbial communities play a significant role in maintaining ecosystems in a healthy homeostasis. Presently, in the human gastrointestinal tract, there are certain taxonomic groups of importance, though there is no single species that plays a keystone role. Bacteroides spp. are known to be major players in the maintenance of eubiosis in the human gastrointestinal tract. Here we review the critical role that Bacteroides play in the human gut, their potential pathogenic role outside of the gut, and their various methods of adapting to the environment, with a focus on data for B. fragilis and B. thetaiotaomicron. Bacteroides are anaerobic non-sporing Gram negative organisms that are also resistant to bile acids, generally thriving in the gut and having a beneficial relationship with the host. While they are generally commensal organisms, some Bacteroides spp. can be opportunistic pathogens in scenarios of GI disease, trauma, cancer, or GI surgery, and cause infection, most commonly intra-abdominal infection. B. fragilis can develop antimicrobial resistance through multiple mechanisms in large part due to its plasticity and fluid genome. Bacteroidota (formerly, Bacteroidetes) have a very broad metabolic potential in the GI microbiota and can rapidly adapt their carbohydrate metabolism to the available nutrients. Gastrointestinal Bacteroidota species produce short-chain fatty acids such as succinate, acetate, butyrate, and occasionally propionate, as the major end-products, which have wide-ranging and many beneficial influences on the host. Bacteroidota, via bile acid metabolism, also play a role in in colonization-resistance of other organisms, including Clostridioides difficile, and maintenance of gut integrity.

Fifty years devoted to anaerobes: historical, lessons, and highlights

Renew interest and enthusiasm for anaerobes stem from both technological improvements (culture media, production of an adequate anaerobic atmosphere, identification methods) and greater awareness on the part of clinicians. Anaerobic infections were historically treated empirically, targeting the species known to be involved in each type of infection. Prevotella, fusobacteria, and Gram-positive cocci (GPAC) were considered responsible for infections above the diaphragm whereas for intra-abdominal infections, Bacteroides of the fragilis group (BFG), GPAC and clostridia were predominantly implicated. The antibiotic susceptibility of anaerobes was only taken into consideration by the clinician in the event of treatment failure or when faced with infections by multidrug-resistant bacteria (MDR). The evolution of antibiotic resistance together with clinical failures due to the absence of detection of hetero-resistant clones has resulted in a greater need for accessible antibiotic susceptibility testing (AST) and disc diffusion method. Improved isolation and identification of anaerobes, along with the availability of accessible and robust methods for performing AST, will ensure that treatment, whether empirical or guided by an antibiogram, will lead to better outcomes for anaerobic infections.

Amidinoquinoxaline N-oxides: synthesis and activity against anaerobic bacteria

We present herein an in-depth study on the activity of amidinoquinoxaline N-oxides 1 against Gram-positive and Gram-negative anaerobic bacteria. Based on 5-phenyl-2,3-dihydropyrimidoquinoxaline N-oxide 1a, the selected structural variations included in our study comprise the substituents α- to the N-oxide function, the benzofused ring, substitution and quaternization of the amidine moiety, and the amidine ring size. Compounds 1 showed good to excellent antianaerobic activity, evaluated as the corresponding CIM50 and CIM90 values, and an antimicrobial spectrum similar to metronidazole. Six out of 13 compounds 1 had CIM90 values significantly lower than the reference drug. Among them, imidazoline derivatives 1i-l were the most active structures. Such compounds were synthesized by base-promoted ring closure of the corresponding amidines. The N-oxides under study showed no significant cytotoxicity against RAW 264.7 cells, with high selectivity indexes. Their calculated ADME properties indicate that the compounds are potentially good oral drug candidates. The antianaerobic activity correlated satisfactorily with the electron affinity of the compounds, suggesting that they may undergo bioreductive activation before exerting their antibacterial activity.

Collateral sensitivity: An evolutionary trade-off between antibiotic resistance mechanisms, attractive for dealing with drug-resistance crisis

Background

The discovery and development of antimicrobial drugs were one of the most significant advances in medicine, but the evolution of microbial resistance limited the efficiency of these drugs.

Aim

This paper reviews the collateral sensitivity in bacteria and its potential and limitation as a new target for treating infections.

Results and Discussion

Knowledge mechanisms of resistance to antimicrobial agents are useful to trace a practical approach to treat and control of resistant pathogens. The effect of a resistance mechanism to certain antibiotics on the susceptibility or resistance to other drugs is a key point that may be helpful for applying a strategy to control resistance challenges. In an evolutionary trade-off known as collateral sensitivity, the resistance mechanism to a certain drug may be mediated by the hypersensitivity to other drugs. Collateral sensitivity has been described for different drugs in various bacteria, but the molecular mechanisms affecting susceptibility are not well demonstrated. Collateral sensitivity could be studied to detect its potential in the battle against resistance crisis as well as in the treatment of pathogens adapting to antibiotics. Collateral sensitivity-based antimicrobial therapy may have the potential to limit the emergence of antibiotic resistance.

Antibiotic resistance characteristics and risk factors analysis of Helicobacter pylori strains isolated from patients in Liaoning Province, an area in North China

Background

The prevalence of Helicobacter pylori (H. pylori) keeps rising while the eradication rate continues to decline due to the increasing antibiotic resistance. Regional variations of antimicrobial resistance to H. pylori have been recommended by guidelines in recent years. This study aims to investigate the antibiotic resistance rate of H. pylori and its association with infected subjects' characteristics in Liaoning Province, an area in north China.

Methods

Gastric tissues from 178 H. pylori positive participants without previous antibiotic use within four weeks were collected for H. pylori culture. Antibiotic susceptibility to furazolidone (AOZ), tetracycline (TC), levofloxacin (LFX), metronidazole (MET), clarithromycin (CLA), and amoxicillin (AMX) were examined with the agar dilution method. Associations between H. pylori resistance and patient characteristics were further analysed.

Results

No resistance was observed in AOZ or TC. For LFX, MET, CLA, and AMX, the overall resistance rates were 41.10%, 79.14%, 71.78%, and 22.09% respectively. There were significant differences between resistance to CLA and MALToma (P = 0.021), and between resistance to MET and age (P < 0.001).

Conclusions

The primary resistant rates of LEX, MET, CLA, and AMX were relatively high in Liaoning. Treatment effectiveness improvement could be achieved by prior antimicrobial susceptibility tests before antibiotic prescription.

Phenotypic and Genotypic Correlation of Antimicrobial Susceptibility of Bacteroides fragilis: Lessons Learnt

Background Bacteroides fragilis is an opportunistic pathogen causing severe infections, including bacteremia. There have been increased reports of antimicrobial resistance in B. fragilis. However, phenotypic testing of susceptibility is time consuming and not cost effective for anaerobes. The present study investigates the correlation of phenotypic susceptibility with genotypic markers; to determine if these could be considered for deciding empirical therapy for B. fragilis. Material and methods Bacteroides fragilis isolates from various clinical samples including exudates, tissue, and body fluids were collected between November 2018 and January 2020 in the Department of Clinical Microbiology, Christian Medical College (CMC) Vellore. Species identification was done by Matrix Assisted Laser Desorption Ionization time of flight mass spectrometry (MALDI TOF) according to the manufacturer's instructions. A total number of 51 B. fragilis isolates were tested against metronidazole, clindamycin, piperacillin/tazobactam, and meropenem phenotypically by agar dilution method using Clinical & Laboratory Standards Institute (CLSI) 2019 guidelines and minimum inhibitory concentrations (MIC) were interpretated. The genotypic markers for antimicrobial resistance genes (nim, emrF, and cfiA) were studied by polymerase chain reaction (PCR) assay as per the standard protocol on all isolates to detect resistance genes. Results B. fragilis isolates in this study expressed 45%, 41%, and 16% phenotypic resistance to clindamycin, metronidazole, and meropenem, respectively, with least resistance to piperacillin/tazobactam (6%). Among the metronidazole resistant isolates, 52% harbored nim gene. Nim gene was also present in 76% (23/30) of the metronidazole susceptible isolates. Similarly, cfiA was present in all eight meropenem resistant isolates in addition to 22% (9/41) of the susceptible isolates. All cfiA negative isolates were phenotypically susceptible. Interestingly, 74% (17/23) of the clindamycin resistant isolates were positive for ermF. Conclusions Detection of a limited set of genes does not always correlate with phenotypic resistance to metronidazole and clindamycin due to the reported influence of insertion sequence (IS) elements, efflux, and other genetic determinants. Certainly, the absence of the cfiA gene can be employed to rule out meropenem resistance. However, redundant use of antibiotics such as meropenem along with metronidazole could be avoided for B. fragilis, which might otherwise elevate meropenem resistance. Recommendation of metronidazole requires prior phenotypic testing due to the reported 41% resistance.

Molecular study on metronidazole resistance in Bacteroides fragilis group isolates from a South Indian tertiary care center

OBJECTIVE

Bacteroides species are an important part of human intestinal microbiota. They can cause infections of significant mortality and morbidity when moved out of their niche in the gut. The cornerstone drug for prophylaxis and therapy, metronidazole, is exhibiting signs of resistance, which are frequently attributed to nitroimidazole (nim) resistance genes. The aim of this study was to use Epsilometer test (E-test) to assess the metronidazole susceptibility and conventional PCR methodology to map the distribution of nim genes in Bacteroides fragilis group (BFG) isolates.

METHODS

MALDI-TOF MS was used to identify BFG isolates. Using the E-test methodology, metronidazole minimum inhibitory concentrations (MICs) were determined. The presence of nim genes in these isolates were checked by conventional PCR methodology. Sequencing was done on selected amplicons for determining the nim gene types.

RESULTS

Bacteroides fragilis accounted for 55.3% of the total 273 BFG members identified. Of these, 196 (71.8%) were susceptible, 43 (15.8%) intermediate and 34 (12.5%) resistant to metronidazole as determined by the E-test. nim gene was present in 101 (37%) of the total 273 isolates. Out of the 34 phenotypically resistant isolates (MIC ≥32 μg/ml), 29 harboured nim gene (Chi-square test, p < 0.0000001) but nim gene was absent in 5 (14.7%) isolates. Also, nim gene was detected in 72 (30.1%) of the 239 isolates with susceptible and intermediate metronidazole MIC. Sequencing of 20 amplicons gave a nimE gene type.

CONCLUSIONS

In view of the rising metronidazole resistance among BFG and its close association with nim genes, there is a need for implementing routine metronidazole susceptibility testing and more researches are needed to find the molecular basis of these nim genes.

Fluoroquinolones Hybrid Molecules as Promising Antibacterial Agents in the Fight against Antibacterial Resistance

The emergence of bacterial resistance has motivated researchers to discover new antibacterial agents. Nowadays, fluoroquinolones keep their status as one of the essential classes of antibacterial agents. The new generations of fluoroquinolones are valuable therapeutic tools with a spectrum of activity, including Gram-positive, Gram-negative, and atypical bacteria. This review article surveys the design of fluoroquinolone hybrids with other antibacterial agents or active compounds and underlines the new hybrids' antibacterial properties. Antibiotic fluoroquinolone hybrids have several advantages over combined antibiotic therapy. Thus, some challenges related to joining two different molecules are under study. Structurally, the obtained hybrids may contain a cleavable or non-cleavable linker, an essential element for their pharmacokinetic properties and mechanism of action. The design of hybrids seems to provide promising antibacterial agents helpful in the fight against more virulent and resistant strains. These hybrid structures have proven superior antibacterial activity and less susceptibility to bacterial resistance than the component molecules. In addition, fluoroquinolone hybrids have demonstrated other biological effects such as anti-HIV, antifungal, antiplasmodic/antimalarial, and antitumor activity. Many fluoroquinolone hybrids are in various phases of clinical trials, raising hopes that new antibacterial agents will be approved shortly.

Antibiotic Resistance and Mechanisms of Pathogenic Bacteria in Tubo-Ovarian Abscess

A tubo-ovarian abscess (TOA) is a common type of inflammatory lump in clinical practice. TOA is an important, life-threatening disease, and it has become more common in recent years, posing a major health risk to women. Broad-spectrum antimicrobial agents are necessary to cover the most likely pathogens because the pathogens that cause TOA are polymicrobial. However, the response rate of antibiotic treatment is about 70%, whereas one-third of patients have poor clinical consequences and they require drainage or surgery. Rising antimicrobial resistance serves as a significant reason for the unsatisfactory medical outcomes. It is important to study the antibiotic resistance mechanism of TOA pathogens in solving the problems of multi-drug resistant strains. This paper focuses on the most common pathogenic bacteria isolated from TOA specimens and discusses the emerging trends and epidemiology of resistant Escherichia coli, Bacteroides fragilis, and gram-positive anaerobic cocci. Besides that, new methods that aim to solve the antibiotic resistance of related pathogens are discussed, such as CRISPR, nanoparticles, bacteriophages, antimicrobial peptides, and pathogen-specific monoclonal antibodies. Through this review, we hope to reveal the current situation of antibiotic resistance of common TOA pathogens, relevant mechanisms, and possible antibacterial strategies, providing references for the clinical treatment of drug-resistant pathogens.

Haemin deprivation renders Bacteroides fragilis hypersusceptible to metronidazole and cancels high-level metronidazole resistance

BACKGROUND

Infections with Bacteroides fragilis are routinely treated with metronidazole, a 5-nitroimidazole antibiotic that is active against most anaerobic microorganisms. Metronidazole has remained a reliable treatment option, but resistance does occur, including in B. fragilis.

OBJECTIVES

In this study we tested whether haemin, a growth supplement for B. fragilis in vivo and in vitro, had an influence on the susceptibility of resistant B. fragilis strains to metronidazole. We further tested whether haemin-deprived B. fragilis would be more susceptible to oxygen and oxidative stress. Metronidazole has been described to cause oxidative stress, which we argued would be exacerbated in haemin-deprived B. fragilis because the bacteria harness haemin, and the iron released from it, in antioxidant enzymes such as catalase and superoxide dismutase.

METHODS

Haemin was omitted from growth media and the effect on metronidazole susceptibility was monitored in susceptible and resistant B. fragilis strains. Further, haemin-deprived B. fragilis were tested for resistance to aeration and hydrogen peroxide and the capacity for the removal of oxygen.

RESULTS

Omission of haemin from the growth medium rendered metronidazole-resistant B. fragilis strains, including an MDR isolate from the UK, highly susceptible to metronidazole. Haemin deprivation further rendered B. fragilis highly susceptible to oxygen, which was further exacerbated in resistant strains. B. fragilis was incapable of scavenging oxygen when haemin was omitted.

CONCLUSIONS

We propose that haemin deprivation overrules resistance mechanisms by rendering B. fragilis hypersusceptible to metronidazole due to a compromised antioxidant defence. Monitoring of haemin concentrations is imperative when conducting metronidazole susceptibility testing in B. fragilis.

Characterization of polysaccharide from Pleurotus eryngii during simulated gastrointestinal digestion and fermentation

Pleurotus eryngii is a valuable new edible mushroom variety cultivated on a large scale in China. The polysaccharides found in this mushroom are strong bioactive. This study used simulated digestion and fermentation model to study the digestion and fermentation characteristics of Pleurotus eryngii polysaccharide (PEP) and its effect on gut microbiota. The results showed that the molecular weight of PEP remained unchanged after simulated digestion, and the overall structure of PEP was not destroyed, indicating that PEP was not decomposed during digestion. However, during fermentation, PEP was degraded and utilized by intestinal flora to produce a variety of short-chain fatty acids (SCFAs), which reduced the pH value in fecal cultures. Meanwhile, PEP regulated the composition of intestinal flora, and the relative abundance of Firmicutes increased significantly. These suggests that PEP can be used as a functional food to promote intestinal health and prevent disease.

The Application of Transposon Insertion Sequencing in Identifying Essential Genes in B. fragilis

Essential genes are those that are indispensable for the survival of organism under specific growth conditions. Investigating essential genes in pathogenic bacteria not only helps to understand vital biological networks but also provides novel targets for drug development. Availability of genetic engineering tools and high-throughput sequencing methods has enabled essential genes identification in many pathogenic gram-positive and gram-negative bacteria. Bacteroides fragilis is one of the major bacteria specific of human gastrointestinal microbiota. When B. fragilis moves out of its niche, it turns into deadly pathogen. Here, we describe detailed method for the essential gene identification in B. fragilis. Generated transposon mutant pool can be used for other applications such as identification of genes responsible for drug resistance in B. fragilis.

Combination of metronidazole and pearl powders for the treatment of stage 2 pressure injury wounds: Case report and literature review

Pressure injury (PI) is a worldwide health problem that has attracted widespread attention from scientific and clinical research communities. PI incidence correlates with the increase of the aging population. In this situation, it is crucial to select effective and affordable drugs for patients and healthcare systems. Herein, we report a case of a 94-year-old female with a stage 2 PI wound, which was treated topically using a novel combination of mixed powders: metronidazole and nano pearl powders. Metronidazole is the preferred option to treat infected wounds due to its excellent antibacterial ability. However, some drawbacks have limited the use of metronidazole in PI wound management, such as its poor capacity to accelerate wound closure. Pearl powder has a strong capacity to promote wound healing and closure but has not been effective at resisting wound infection. To take advantage of powdered drugs' wound treatment properties and accelerate PI wound healing, we prepared powdered mixtures for wound application. Both drugs are cost-effective and were beneficial to wound healing. Therefore, the combination of metronidazole and pearl powders offer a promising choice to patients with PI wounds.

Diversity of antimicrobial resistance genes in Bacteroides and Parabacteroides strains isolated in Germany

OBJECTIVES

Bacteroides spp. are normal constituents of the human intestinal microflora, but they are also able to cause severe diseases. The aim of this study was to determine the diversity of antibiotic resistance genes found in phenotypically resistant Bacteroides and Parabacteroides strains.

METHODS

A total of 71 phenotypically resistant Bacteroides spp. from human clinical specimens were screened for the antibiotic resistance genes cfiA, tetQ, tetM, tet36, cepA, cfxA, nim, ermG, ermF, bexA, bla_VIM, bla_NDM, bla_KPC, bla_OXA-48 and bla_GES. The presence of these genes was compared with phenotypic resistance to ampicillin/sulbactam, cefoxitin, ceftolozane/tazobactam, piperacillin/tazobactam, imipenem, meropenem, meropenem/vaborbactam, clindamycin, moxifloxacin, tigecycline, eravacycline and metronidazole.

RESULTS

tetQ was the most frequently detected gene, followed by cfiA, ermF, cfxA, ermG, cepA, nim and bexA. None of the strains were positive for tetM, tet36, bla_VIM, bla_NDM, bla_KPC, bla_OXA-48 or bla_GES. Resistance to the tested β-lactams was mainly linked to the presence of the cfiA gene. Clindamycin resistance correlated with the presence of the genes ermG and ermF. The bexA gene was found in six strains, but only two of them were resistant to moxifloxacin. Tigecycline and eravacycline showed good activities despite the frequent occurrence of tetQ. The nim gene was detected in six isolates, five of which were resistant to metronidazole.

CONCLUSION

The findings of our study support the general belief that antimicrobial resistance within Bacteroides should be taken into consideration. This underlines the necessity of reliable routine antimicrobial susceptibility test methods for anaerobic bacteria and the implementation of antimicrobial surveillance programmes worldwide.

Tightly controlled response to oxidative stress; an important factor in the tolerance of Bacteroides fragilis

The exposure of Bacteroides fragilis to highly oxygenated tissues induces an oxidative stress due to a shift from the reduced condition of the gastrointestinal tract to an aerobic environment of host tissues. The potent and effective responses to reactive oxygen species (ROS) make the B. fragilis tolerant to atmospheric oxygen for several days. The response to oxidative stress in B. fragilis is a complicated event that is induced and regulated by different agents. In this review, we will focus on the B. fragilis response to oxidative stress and present an overview of the regulators of responses to oxidative stress in this bacterium.

Genotyping of multi drug resistant Bacteroides fragilis group of clinical isolates from mangalore, south India

INTRODUCTION

Bacteroides fragilis group, the most encountered anaerobic bacterium is emerging with resistance to antibiotics. This study explores the antibiogram and occurrence of resistance genes in isolates of B fragilis group from clinical samples.

METHOD

In this study the antimicrobial susceptibility test was done using commercially available E strip test and the results were recorded according to CLSI guidelines. Genotypic investigations were performed by conventional PCR to detect the target resistant genes.

RESULTS

Ceftriaxone, cefoxitin, clindamycin and imipenem were found to be the most resistant antimicrobials in E test method. Metronidazole has shown resistance in 7 strains in vitro while resistance nim genes were detected in 12 strains from 62 randomly selected isolates. Other resistance genes (cfiA, ermF and cepA) were expressed at 58%, 62.9% and 48.3% respectively, among these strains.

CONCLUSION

B fragilis group harbouring the resistant genes may not be fully expressed phenotypically. Hence, detection of these genes by PCR might be necessary for a pertinent conclusion.

The central role of the SOS DNA repair system in antibiotics resistance: A new target for a new infectious treatment strategy

Bacteria have a considerable ability and potential to acquire resistance against antimicrobial agents by acting diverse mechanisms such as target modification or overexpression, multidrug transporter systems, and acquisition of drug hydrolyzing enzymes. Studying the mechanisms of bacterial cell physiology is mandatory for the development of novel strategies to control the antimicrobial resistance phenomenon, as well as for the control of infections in clinics. The SOS response is a cellular DNA repair mechanism that has an essential role in the bacterial biologic process involved in resistance to antibiotics. The activation of the SOS network increases the resistance and tolerance of bacteria to stress and, as a consequence, to antimicrobial agents. Therefore, SOS can be an applicable target for the discovery of new antimicrobial drugs. In the present review, we focus on the central role of SOS response in bacterial resistance mechanisms and its potential as a new target for control of resistant pathogens.

To resist and persist: Important factors in the pathogenesis of Bacteroides fragilis

Bacteroides fragilis is a most frequent anaerobic pathogen isolated from human infections, particularly found in the abdominal cavity. Different factors contribute to the pathogenesis and persistence of B. fragilis at infection sites. The knowledge of the virulence factors can provide applicable information for finding alternative options for the antibiotic therapy and treatment of B. fragilis caused infections. Herein, a comprehensive review of the important B. fragilis virulence factors was prepared. In addition to B. fragilis toxin (BFT) and its potential role in the diarrhea and cancer development, some other important virulence factors and characteristics of B. fragilis are described including capsular polysaccharides, iron acquisition, resistance to antimicrobial agents, and survival during the prolonged oxidative stress, quorum sensing, and secretion systems.

Antimicrobial Susceptibility and Clonality of Vaginally Derived Multidrug-Resistant Mobiluncus Isolates in China

Here, the antimicrobial susceptibility, resistance mechanisms, and clonality of Mobiluncus sp. isolates recovered from gynecological outpatients in China were investigated. Compared to M. mulieris, M. curtisii exhibited higher antimicrobial resistance to metronidazole, clindamycin, and tetracycline. Whole-genome sequencing indicated that the clindamycin resistance gene erm(X) was located on a transposable element, Tn5432, which was composed of two IS1249 sequences. Phylogenetic analysis indicated that Mobiluncus spp. had high diversity, with isolates being grouped into several sporadic clades.

Metronidazole in the Management of Post-Open Haemorrhoidectomy Pain: Systematic Review

Purpose

Open haemorrhoidectomy is associated with significant postoperative pain. Metronidazole is commonly prescribed in the postoperative period as an adjunct to analgesia in pain management.

Methods

In our systematic review, studies were identified using PubMed/MEDLINE, Embase/Ovid and Cochrane Register of Controlled Trials databases. Studies were included if they were randomised controlled trials (RCTs) involving interventions with oral metronidazole at any dose over any time period. The primary outcome was pain score (visual analogue scale, VAS) after open haemorrhoidectomy. Secondary outcomes included time to return to normal daily activities, additional analgesia usage, and postoperative complications.

Results

Of 14 RCTs reviewed, 4 met inclusion criteria and were selected. The studies comprised 336 study subjects and 169 subjects were randomised to metronidazole while 167 were in the control group. There was a significant reduction in VAS across all time points, with maximal reduction seen on day 5 posthaemorrhoidectomy (mean difference, -2.28; 95% confidence interval, -2.49 to -2.08; P < 0.001). There was no difference in incidence of complications (P = 0.13). The Cochrane Risk of Bias Tool showed 3 of 4 of the studies had a risk of bias.

Conclusion

Metronidazole may be associated with decreased pain but there is insufficient evidence from RCTs to provide a strong grade of recommendation. Further RCTs are required.

Application of Antibiotics/Antimicrobial Agents on Dental Caries

Dental caries is the most common oral disease. The bacteriological aetiology of dental caries promotes the use of antibiotics or antimicrobial agents to prevent this type of oral infectious disease. Antibiotics have been developed for more than 80 years since Fleming discovered penicillin in 1928, and systemic antibiotics have been used to treat dental caries for a long time. However, new types of antimicrobial agents have been developed to fight against dental caries. The purpose of this review is to focus on the application of systemic antibiotics and other antimicrobial agents with respect to their clinical use to date, including the history of their development, and their side effects, uses, structure types, and molecular mechanisms to promote a better understanding of the importance of microbial interactions in dental plaque and combinational treatments.

Draft Genome Sequence of a Metronidazole-Resistant Bacteroides fragilis Strain Isolated in Ecuador

Here, we report the draft genome sequence of Bacteroides fragilis strain Z&Z143, a metronidazole-resistant bacterium isolated from a blood culture from an Ecuadorian patient hospitalized in a medical institution in Quito, Ecuador. We describe a new variant of the nim genes, which is associated with metronidazole resistance.

Here, we report the draft genome sequence of Bacteroides fragilis strain Z&Z143, a metronidazole-resistant bacterium isolated from a blood culture from an Ecuadorian patient hospitalized in a medical institution in Quito, Ecuador. We describe a new variant of the nim genes, which is associated with metronidazole resistance.

Wnt/β-Catenin Signaling as a Molecular Target by Pathogenic Bacteria

The Wnt/β-catenin signaling pathway is crucial to regulate cell proliferation and polarity, cell determination, and tissue homeostasis. The activation of Wnt/β-catenin signaling is based on the interaction between Wnt glycoproteins and seven transmembrane receptors-Frizzled (Fzd). This binding promotes recruitment of the scaffolding protein Disheveled (Dvl), which results in the phosphorylation of the co-receptor LRP5/6. The resultant molecular complex Wnt-Fzd-LRP5/6-Dvl forms a structural region for Axin interaction that disrupts Axin-mediated phosphorylation/degradation of the transcriptional co-activator β-catenin, thereby allowing it to stabilize and accumulate in the nucleus where it activates the expression of Wnt-dependent genes. Due to the prominent physiological function, the Wnt/β-catenin signaling must be strictly controlled because its dysregulation, which is caused by different stimuli, may lead to alterations in cell proliferation, apoptosis, and inflammation-associated cancer. The virulence factors from pathogenic bacteria such as Salmonella enterica sv Typhimurium, Helicobacter pylori, Mycobacterium tuberculosis, Pseudomonas aeruginosa, Citrobacter rodentium, Clostridium difficile, Bacteroides fragilis, Escherichia coli, Haemophilus parasuis, Lawsonia intracellularis, Shigella dysenteriae, and Staphylococcus epidermidis employ a variety of molecular strategies to alter the appropriate functioning of diverse signaling pathways. Among these, Wnt/β-catenin has recently emerged as an important target of several virulence factors produced by bacteria. The mechanisms used by these factors to interfere with the activity of Wnt/β-catenin is diverse and include the repression of Wnt inhibitors' expression by the epigenetic modification of histones, blocking Wnt-Fzd ligand binding, activation or inhibition of β-catenin nuclear translocation, down- or up-regulation of Wnt family members, and inhibition of Axin-1 expression that promotes β-catenin activity. Such a variety of mechanisms illustrate an evolutionary co-adaptation of eukaryotic molecular signaling to a battery of soluble or structural components synthesized by pathogenic bacteria. This review gathers the recent efforts to elucidate the mechanistic details through which bacterial virulence factors modulate Wnt/β-catenin signaling and its physiological consequences concerning the inflammatory response and cancer.

A potential species of next-generation probiotics? The dark and light sides of Bacteroides fragilis in health

Bacteroides fragilis (B. fragilis) is a commensal Gram-negative obligate anaerobe that resides in the mammalian lower gut and can profoundly affect the susceptibility of the host to inflammatory diseases. Previous studies have identified B. fragilis as a common opportunistic pathogen in clinical infections and suggested that it may be responsible for a range of diseases involving a permeable intestinal barrier. However, recent studies of the relationship between nontoxigenic B. fragilis and the immune system have indicated that several B. fragilis strains may be potential probiotic. In the present review, we summarize the factors influencing the intestinal abundance of B. fragilis and discuss the biological interactions between this microbe and the host. Immune system development, age, individual dietary habits, physical condition, drug intake and personal lifestyle habits can all affect the abundance of B. fragilis in the human intestine. Polysaccharide A or outer membrane vesicles from nontoxigenic B. fragilis may mediate beneficial interactions with the host, whereas enterotoxigenic B. fragilis toxin or lipopolysaccharide may stimulate colitis or even systemic inflammation. Generally, this review summarizes the biological characteristics of B. fragilis and describes future application of probiotics.

Empirical metronidazole for patients with severe bacterial infection: A systematic review with meta-analysis and trial sequential analysis

BACKGROUND

Metronidazole is the preferred empirical anti-anaerobic agent for patients with suspected anaerobic infection. The balance between benefits and harms of empirical metronidazole is unclear. We aimed to assess patient-important benefits and harms of empirical metronidazole vs placebo/no treatment in adult patients with severe bacterial infection of any origin.

METHODS

We conducted a systematic review with meta-analysis and trial sequential analysis of randomized clinical trials assessing empirical metronidazole vs placebo/no treatment in adult hospitalized patients with severe bacterial infection. The review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement, the Cochrane Handbook and the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) methodology. A protocol and statistical analysis plan was published prior to conducting the review.

RESULTS

We included a total of nine trials (n = 1753 patients), all of which were adjudicated as having high risk of bias. We found no difference in the primary outcome mortality within 90 days (relative risk 1.56, 95% confidence interval 0.39-6.25). Fewer patients receiving metronidazole had secondary infections (relative risk 0.43, 95% CI: 0.27-0.68). Trial sequential analysis indicated high risk of random errors due to lack of data, and the quality of evidence was very low for all outcomes.

CONCLUSIONS

There is low quantity and quality of evidence supporting the use of empirical metronidazole in adult patients with severe bacterial infections of any origin, and no firm evidence for benefit or harm.

Evaluation of VITEK MS, Clin-ToF-II MS, Autof MS 1000 and VITEK 2 ANC card for identification of Bacteroides fragilis group isolates and antimicrobial susceptibilities of these isolates in a Chinese university hospital

BACKGROUND AND PURPOSE

Bacteroides fragilis group isolates are most frequently isolated anaerobic pathogens. This study aimed to evaluate the accuracy of VITEK MS, Clin-ToF-II MS, Autof MS 1000 and VITEK 2 ANC card on the identification of clinical B. fragilis group isolates, as well as to determine their antimicrobial susceptibilities.

METHODS

A total of 138 isolates of B. fragilis group isolates were identified with the three MALDI-TOF MS systems and VITEK 2 ANC cards. 16S rRNA gene sequencing was used as the reference identification method for comparison. Antimicrobial susceptibilities were determined by agar dilution method to 19 antimicrobial agents recommended by Clinical and Laboratory Standards Institute (CLSI).

RESULTS

Hundred thirty three isolates of Bacteroides spp. and 5 isolates of Parabacteroides spp. were identified by 16S rRNA sequencing. The rates of accurate identification at species level of VITEK MS, Clin-ToF-II MS, Autof MS 1000 and VITEK 2 ANC card were 94.2%, 94.2%, 98.6% and 94.9%, respectively, while that at genus level were 99.3%, 100%, 100% and 97.8%, respectively. Metronidazole and chloramphenicol were the most susceptible agents (99.3% and 92.8%, respectively), followed by meropenem, ertapenem, imipenem and piperacillin/tazobactam to which the susceptible rates ranged from 76.8% to 79.0%. The susceptible rates to carbapenems decreased 12.4-15.3% from 2010-2013 to 2014-2017.

CONCLUSION

All the four systems provided high accurate rate on the identification of B. fragilis group isolates. Metronidazole showed highest activity against these isolates. Attention should be paid to the higher resistant rates to carbapenems, clindamycin, moxifloxacin and tigecycline than the other countries.

Hyperbaric oxygen therapy: Antimicrobial mechanisms and clinical application for infections

Hyperbaric oxygen therapy (HBOT) is a treatment procedure that involves breathing 100% O₂ for a certain time and under a certain pressure. HBOT is commonly administrated as a primary or alternative therapy for different diseases such as infections. In this paper, we reviewed the general aspect of HBOT procedures, the mechanisms of antimicrobial effects and the application in the treatment of infections. Parts of the antimicrobial effects of HBOT are believed to result of reactive from the formation of reactive oxygen species (ROS). It is also said that HBOT enhances the antimicrobial effects of the immune system and has an additive or synergistic effect with certain antimicrobial agents. HBOT has been described as a useful procedure for different infections, particularly in deep and chronic infections such as necrotizing fasciitis, osteomyelitis, chronic soft tissue infections, and infective endocarditis. The anti-inflammation property of HBOT has demonstrated that it may play a significant role in decreasing tissue damage and infection expansion. Patients treated by HBOT need carful pre-examination and monitoring. If safety standards are strictly tracked, HBOT can be considered a suitable procedure with an apt rate of complication.