Metronidazole resistance and nim genes in anaerobes: A review

Anaerobic resistance: should we be worried?

PURPOSE OF REVIEW

Anaerobic bacteria are implicated in a broad range of infections and can cause significant morbidity and mortality. As such, development of antimicrobial resistance (AMR) increases the risk of worse clinical outcomes and death.

RECENT FINDINGS

Anaerobe AMR is highly variable according to region and species included in the survey. The overall trend is to increasing resistance, particularly in Europe and Asia, and in the Bacteroides fragilis group and Clostridium sp. Conversely, with the decline in RT027, resistance in Clostridiodes difficile is decreasing. Resistance to moxifloxacin and clindamycin has reached 30-50%, whereas prevalence of metronidazole and carbapenem resistance is generally low. Infections due to multidrug anaerobes have been increasingly reported, with clinical studies demonstrating adverse clinical outcomes, including higher mortality, with anaerobic resistance or inappropriate therapy. The role of antimicrobial stewardship in the setting of increasing anaerobe resistance is yet to be fully elucidated.

SUMMARY

These findings highlight the importance of continuous surveillance in monitoring emerging trends in anaerobe AMR. Mean inhibitory concentrations should be reported due to variable susceptibility breakpoints and for detection of isolates with reduced susceptibility. At a local level, the clinical microbiology laboratory has a key role in identifying and undertaking susceptibility testing to inform individual patient management, develop local antibiograms and liaise with antimicrobial stewardship teams. A greater understanding of the clinical impact of anaerobic resistance and the role of antimicrobial stewardship in preventing resistance is required.

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.

Clinical Findings and Antimicrobial Susceptibility of Anaerobic Bacteria Isolated in Bloodstream Infections

The objectives of this study were to report on the antimicrobial susceptibility of 141 clinically significant anaerobic bacteria isolated from bloodstream infections between January 2016 and April 2020 in a tertiary-care hospital in Granada (Spain) and to describe the main clinical features of the patients. Species identification was performed by MALDI-TOF MS (Bruker Daltonics, Billerica, MA, USA). Antimicrobial susceptibility tests were performed against penicillin, amoxicillin-clavulanic acid, imipenem, moxifloxacin, clindamycin, metronidazole, and piperacillin-tazobactam using the gradient diffusion technique and EUCAST breakpoints, except for moxifloxacin (CLSI breakpoints). The most frequent anaerobes were Bacteroides (43.9%, n = 62), Clostridium (24.1%, n = 34) and Gram-positive anaerobic cocci (GPACs) (15.6%, n = 22). Almost all tested anaerobes were susceptible to imipenem and amoxicillin-clavulanic acid, except for Bacteroides. High overall resistance rates to clindamycin were observed, especially for Gram-positive anaerobic cocci (GPACs) (54.5%) and for Bacteroides spp. (45.1%). Overall, low resistance rates to almost all antibiotics were observed for Clostridium. High resistance rates to penicillin were also observed for Gram-positive anaerobic bacilli (GPABs) (44.4%), as well as to metronidazole (22.2%), although only nine isolates were included. Antimicrobial susceptibility testing for anaerobes should always be performed in severe infections, such as those localized in the bloodstream. The information obtained contributes to selecting empirical treatments according with local data on resistance.

Spontaneous closure of an extensive postdebridement perineal wound in a newly diagnosed diabetic patient presenting with necrotizing fasciitis

Diabetes mellitus may present for the first time with necrotizing fasciitis. Early treatment of septic shock and immediate surgical debridement reduces mortality. A diverting loop colostomy prevents soiling of extensive postdebridement wound. Local wound care together with good glycemic and infection control leads to spontaneous wound closure.

Trends and Impact in Antimicrobial Resistance Among Bacteroides and Parabacteroides Species in 2007-2012 Compared to 2013-2017

Purpose: The aim of this study was to analyze the susceptibility of Bacteroides and Parabacteroides spp. strains, isolated from patients hospitalized in the clinical hospital in Poland to penicillin, amoxicillin with clavulanic acid, imipenem, clindamycin, and metronidazole. Methods: We analyzed susceptibility of 476 isolates to routinely use for the treatment of anaerobic bacterial infections antibiotics. E test method was used to determining the minimal inhibitory concentration values. To show the trend of drug resistance, we compared data from two periods within the years 2003-2017. Results: Research results indicate that the problem of resistance is mainly related to strains belonging to non-fragilis Bacteroides. In the analyzed periods, there was an increase in the percentage of clindamycin-resistant isolates (35.21% vs. 53.33%), amoxicillin/clavulanic acid (2.83% vs. 8.15%), and imipenem (1.41% vs. 3.7%). In isolates belonging to Parabacteroides distasonis, we observed a constant high (∼50%) percentage of clindamycin-resistant strains. The overwhelming majority of B. fragilis strains were resistant to penicillin (>95%) and about 20% of the isolates were not susceptible to clindamycin. Conclusions: Clindamycin, due to the high and increasing percentage of resistant strains, may not be a good choice in the empirical therapy of infections caused by Bacteroides and P. distasonis. Our study highlighted the importance of a routine or at least periodic monitoring of antimicrobial susceptibility of anaerobic Gram-negative bacilli, providing important information for appropriate therapy. The study shows that infection caused (or suspected of being caused) by Bacteroides and Parabacteroides spp. can be empirically treated with metronidazole or imipenem.

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.

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.

Microbiological and Clinical Aspects of Cervicofacial Actinomyces Infections: An Overview

Similarly to other non-spore-forming Gram-positive anaerobes, members of the Actinomyces genus are important saprophytic constituents of the normal microbiota of humans. Actinomyces infections are considered to be rare, with cervicofacial infections (also known as ‘lumpy jaw syndrome’) being the most prevalent type in the clinical practice. Actinomycoses are characterized by a slowly progressing (indolent) infection, with non-specific symptoms, and additionally, the clinical presentation of the signs/symptoms can mimic other pathologies, such as solid tumors, active Mycobacterium tuberculosis infections, nocardiosis, fungal infections, infarctions, and so on. The clinical diagnosis of actinomycosis may be difficult due to its non-specific symptoms and the fastidious, slow-growing nature of the pathogens, requiring an anaerobic atmosphere for primary isolation. Based on 111 references, the aim of this review is to summarize current advances regarding the clinical features, diagnostics, and therapy of cervicofacial Actinomyces infections and act as a paper for dentistry specialists, other physicians, and clinical microbiologists.

Multidrug resistance in anaerobes

Multidrug resistance (MDR) in anaerobes is not a well-known topic. Bacteroides fragilis group isolates have numerous resistance determinants such as multidrug efflux pumps, cfiA and nimB genes and activating insertion sequences, and some isolates exhibited extensive drug-resistant patterns. MDR rates in B. fragilis group were from 1.5 to >18% and up to >71% in cfiA and nimB positive isolates carrying insertion sequences. MDR was present in >1/2 of Clostridioides difficile isolates, most often in epidemic/hypervirulent strains and unusually high metronidazole or vancomycin resistance has been reported in single studies. MDR was found in Prevotella spp. (in ≤10% of isolates), Finegoldia magna, Veillonella spp. and Cutibacterium acnes. Resistance in the anaerobes tends to be less predictable and anaerobic microbiology is required in more laboratories. New hopes may be new antibiotics such as eravacycline, cadazolid, surotomycin, ridinilazol or C. difficile toxoid vaccines; however, more efforts are needed to track the MDR in anaerobes.

Antimicrobial susceptibility and clinical findings of significant anaerobic bacteria in southern Spain

The objectives of this study were to report on the antimicrobial susceptibility of 276 clinically significant anaerobic bacteria belonging to the major genera isolated between May 2017 and November 2018 in a tertiary hospital in Granada (Spain) and to describe key clinical features of the patients. Species identification was performed by MALDI-TOF MS. Antimicrobial susceptibility tests were performed against penicillin, amoxicillin-clavulanic, imipenem, meropenem, moxifloxacin, clindamycin, metronidazole, vancomycin, and piperacillin-tazobactam using the gradient diffusion technique and EUCAST breakpoints (except for moxifloxacin). The most frequent anaerobes were Bacteroides (29.7%; n = 82), Clostridioides difficile (15.9%, n = 44), Prevotella (10.8%, n = 30), and Propionibacterium (10.7%, n = 25). Metronidazole was not universally active against all genera tested, and some isolates showed resistance to this drug. Almost all tested anaerobes were susceptible to carbapenems and amoxicillin-clavulanate except for Clostridioides difficile (resistance rate of 94%) and Bacteroides (19%), respectively. High overall resistance rates to clindamycin were observed, especially for genera Finegoldia (54%), Bacteroides (49%), and Prevotella (40%). Resistance rates to carbapenems and amoxicillin-clavulanate were very low for the majority of tested genera but were high for Clostridioides difficile and Bacteroides spp., respectively. Resistance to clindamycin was very high, especially for Bacteroides, Finegoldia magna, Prevotella and Peptoniphilus. Routine antimicrobial susceptibility testing for anaerobes contributes information on the global situation and allows empirical therapies to be selected in accordance with local data on resistant strains.

Antibiotic Discovery: Where Have We Come from, Where Do We Go?

Given the increase in antibiotic-resistant bacteria, alongside the alarmingly low rate of newly approved antibiotics for clinical usage, we are on the verge of not having effective treatments for many common infectious diseases. Historically, antibiotic discovery has been crucial in outpacing resistance and success is closely related to systematic procedures—platforms—that have catalyzed the antibiotic golden age, namely the Waksman platform, followed by the platforms of semi-synthesis and fully synthetic antibiotics. Said platforms resulted in the major antibiotic classes: aminoglycosides, amphenicols, ansamycins, beta-lactams, lipopeptides, diaminopyrimidines, fosfomycins, imidazoles, macrolides, oxazolidinones, streptogramins, polymyxins, sulphonamides, glycopeptides, quinolones and tetracyclines. During the genomics era came the target-based platform, mostly considered a failure due to limitations in translating drugs to the clinic. Therefore, cell-based platforms were re-instituted, and are still of the utmost importance in the fight against infectious diseases. Although the antibiotic pipeline is still lackluster, especially of new classes and novel mechanisms of action, in the post-genomic era, there is an increasingly large set of information available on microbial metabolism. The translation of such knowledge into novel platforms will hopefully result in the discovery of new and better therapeutics, which can sway the war on infectious diseases back in our favor.