The European committee on antimicrobial susceptibility testing disc diffusion susceptibility testing method for frequently isolated anaerobic bacteria

Antimicrobial susceptibility testing of Clostridioides difficile: a dual-site study of three different media and three therapeutic antimicrobials

OBJECTIVES

Increasing resistance to antimicrobials used for the treatment of Clostridioides difficile infections necessitates reproducible antimicrobial susceptibility testing. Current guidelines take a one-size-fits-all approach and/or offer limited guidance. We investigated how the choice of medium affects measured MIC values across two sites.

METHODS

We determined MIC values for the antimicrobials fidaxomicin, metronidazole, and vancomycin for a representative collection of European C. difficile strains (n = 235) using agar dilution on three different media: Brucella Blood Agar (BBA), Fastidious Anaerobe Agar supplemented with horse blood (FAA-HB), and Wilkins-Chalgren (WC) agar. The study was conducted at two sites to compare reproducibility. Usability (ease of preparation of the media as well as read-out of the assay) was assessed through a survey.

RESULTS

We found that all media result in highly consistent aggregated MIC data for all antibiotics, with MIC50 and MIC90 within two-fold of each other across sites. For fidaxomin, MIC values on WC were lower than on the other media (MIC90: WC = 0.125-0.25 mg/L; BBA and FAA-HB = 0.5 mg/L). Metronidazole showed the lowest MIC on BBA and the highest on WC (MIC90: WC = 2 mg/L; BBA = 0.5-1 mg/L; FAA-HB: 1-2 mg/L). For vancomycin, MIC values were similar across media (MIC90: all media = 1-2 mg/L). Though absolute values for individual isolates differed between sites, identified resistant isolates were similar. Results obtained on FAA-HB were most consistent between sites and results obtained on WC showed the most divergence. FAA-HB was positively evaluated in the usability survey.

DISCUSSION

This study shows medium-dependent differences in C. difficile MICs for at least two antimicrobials across two sites. We suggest the use of FAA-HB to align with general European Committee on Antimicrobial Susceptibility Testing (EUCAST) recommendations for susceptibility testing of anaerobic bacteria and deposited reference strains for standard susceptibility testing of C. difficile to increase interlaboratory reproducibility.

Diagnostic and epidemiological landscape of anaerobic bacteria in Europe, 2020-2023 (ANAEuROBE)

INTRODUCTION

Despite being implicated in a wide spectrum of community- and healthcare-acquired infections, anaerobes have not yet been incorporated into systematic surveillance programs in Europe.

METHODS

We conducted a multicentre retrospective observational study analysing all anaerobic strains isolated from blood cultures in 44 European Hospital Centres over a 4-y period (2020-2023). Diagnostic approach, epidemiology, and antimicrobial susceptibility according to EUCAST v. 15.0 were investigated.

RESULTS

Our study included 14,527 anaerobes, most of which were Gram-positive (45%) or Gram-negative (40%) bacilli. MALDI-TOF coupled to mass spectrometry was the most widely used tool for species identification (98%). Antimicrobial susceptibility testing was performed in the vast majority of centres, using mostly gradient diffusion strip (77%) and disk diffusion (45%) methods according to EUCAST guidelines. The most prevalent species were Cutibacterium acnes (18.7%), Bacteroides fragilis (16.3%), Clostridium perfringens (5.3%), Bacteroides thetaiotaomicron (4.2%), Fusobacterium nucleatum (3.5%), and Parvimonas micra (3.4%). C. acnes showed high resistance to benzylpenicillin (18%), clindamycin (39%), and imipenem (19% and 13% by MIC methods and disk diffusion, respectively). B. fragilis showed high resistance to amoxicillin/clavulanate (24%), piperacillin/tazobactam (22% and 14% by MIC methods and disk diffusion, respectively), clindamycin (22% by both MIC methods and disk diffusion), meropenem (13%), and metronidazole (10%, only by disk diffusion). A similar resistance pattern was observed in B. thetaiotaomicron, Bacteroides ovatus, and Parabacteroides distasonis. C. perfringens showed high resistance to clindamycin (69% and 45% by MIC methods and disk diffusion, respectively), while benzylpenicillin and metronidazole maintained over 90% activity. F. nucleatum showed high resistance to benzylpenicillin (11%), while Fusobacterium necrophorum showed alarming rates of resistance to clindamycin (12%), meropenem (16%) and metronidazole (11%).

CONCLUSIONS

This study presented an up-to-date analysis of the diagnostics and epidemiology of anaerobic bacteria in Europe, providing insights for future comparative analyses and the development of antimicrobial diagnostic and management strategies, as well as the optimization of current antibiotic treatments.

A seemingly considerable increase in antimicrobial resistance in the Bacteroides fragilis group from blood cultures - the second national study in Denmark

BACKGROUND

Bacteroides fragilis group species are the most frequently encountered bacteria involved in anaerobic bacteraemia and associated with high mortality rates. In 2012, we performed the first national study of antimicrobial susceptibility in the B. fragilis group from blood cultures in Denmark.

OBJECTIVES

The purpose of the present study was to compare the antimicrobial susceptibility rates of piperacillin-tazobactam, meropenem, clindamycin and metronidazole in the B. fragilis group from blood cultures in Denmark in 2022 with susceptibility rates from 2012. In addition, we wanted to investigate whether changes to susceptibility was related to the overall use of the specified antimicrobial agents from 2012 to 2022.

METHODS

Antimicrobial susceptibility testing was performed in accordance with EUCAST guidelines using the agar dilution method and the disc diffusion method.

RESULTS

The study showed a seemingly considerable increase in resistance in the B. fragilis group (n = 234) to piperacillin-tazobactam from a reported 8.5% in 2012 to 42.7% in 2022. Resistance towards meropenem also increased from a reported 3.4% to 10.7%. Most of the increase in resistance for piperacillin-tazobactam and meropenem is caused by a recent EUCAST breakpoint change. Metronidazole still has the lowest resistance rate for the B. fragilis group (one isolate, 0.4%) in this study. The sales of piperacillin-tazobactam in the same period revealed a corresponding increase (+130%), whereas meropenem sales were stable.

CONCLUSION

The results underscore the need for timely routine antimicrobial susceptibility testing of B. fragilis group species and questions piperacillin-tazobactam monotherapy as empiric treatment for septic patients with a suspected abdominal source.

Antibiotic Use Patterns at Jimma Medical Center in Southwest Ethiopia: A Call for Local Antibiogram-Guided Prescription

Background: The discovery of antibiotics revolutionized healthcare by significantly reducing morbidity and mortality. However, excessive and inappropriate use has led to a global surge in antimicrobial resistance, particularly in low- and middle-income countries. This study aimed to evaluate antibiotic use patterns among inpatients at Jimma Medical Center (JMC) in Southwest Ethiopia. Methods: A longitudinal observational study was conducted in February and March 2019 at JMC, focusing on patients admitted for over 24 h who received antibiotics. Data on patient demographics, clinical indications, and antibiotics prescribed were systematically collected. Antibiotic consumption rates were measured as days of therapy (DOTs) per 100 patient-days, and utilization was classified according to the World Health Organization (WHO) AWaRe (Access, Watch, and Reserve) framework. Results: A total of 384 inpatients were included, with a male predominance (53.9%) and a median age of 24 years (IQR: 5-37). In total, 634 antibiotic regimens were prescribed. According to the WHO AWaRe classification, 48.3% (306/634) were "Access" and 51.7% (328/634) were "Watch" antibiotics. Patients were treated with antibiotics for a median duration of 4 days (IQR: 2-7), leading to a total of 2880 days of antibiotic therapy. Ceftriaxone was the most commonly prescribed antibiotic, with a usage rate of 44.65 DOTs per 100 patient-days. Substantial variability was observed in empirical antibiotic regimens among treating physicians and across wards. Culture and antibiotic susceptibility testing (AST) were performed for only 4.2% of patients, and none of the treatments were modified based on susceptibility data. Conclusions: The study highlights critical issues in antibiotic prescribing at JMC, including over-reliance on "Watch" antibiotics, predominantly ceftriaxone, limited use of AST results, and deviations from standard treatment guidelines. Addressing these challenges requires implementing antimicrobial stewardship programs, developing evidence-based local treatment guidelines, and strengthening and encouraging the use of microbiology services to improve rational antibiotic use.

Metronidazole-Loaded Chitosan Nanoparticles with Antimicrobial Activity Against Clostridium perfringens

Background/Objectives: Even with improvements in surgical techniques and the application of appropriate antibiotic prophylaxis, wound infections are still major public health problems in low- and middle-income countries. This study proposes the design of new particulate polymeric matrices based on chitosan (CS) for the controlled release of Metronidazole (MTZ), in order for it to be used for the treatment of Clostridium perfringens infections. Methods: The nanoparticles were prepared via inverse emulsion using tannic acid (TA) and sodium tripolyphosphate (TPP) as cross-linking agents. The ratio of CS to TPP, the concentration of CS solution, and the ratio of CS to TA were varied to optimize the synthesis procedure. Nanoparticles have been characterized based on several points of view in order to correctly correlate their properties with synthesis parameters. Results: The FTIR spectra of the analyzed nanoparticles confirmed both the formation of hydrogen bonds between CS and TA and the ionic cross-linking of CS with TPP. The average diameters of the nanoparticles ranged from 70 to 170 nm, whereas the zeta potential values were around 8 mV. Their swelling degree in a weak basic environment, as well as the drug loading/release capacity was influenced, as expected, by the synthesis parameters. The obtained nanoparticles were tested in vitro to evaluate their behavior in the blood environment, the cytotoxic effect, and the antimicrobial activity of nanoparticles loaded with MTZ against Clostridium perfringens cultures. Conclusions: The in vitro obtained results demonstrate that these non-hemolytic and non-cytotoxic particles can be efficient drug delivery systems for the treatment of Clostridium perfringens in wound infections.

The EUCAST Disk Diffusion Method for Antimicrobial Susceptibility Testing of Oral Anaerobes

There is a need for standardized methods for antimicrobial susceptibility testing (AST) of anaerobic bacteria involved in oral and extra-oral infections. We tested the recently published EUCAST disk diffusion method for rapidly growing anaerobes on selected oral anaerobes. AST of 20 strains of Prevotella spp., 11 strains of Porphyromonas gingivalis, and six Fusobacterium nucleatum complex strains was performed with amoxicillin and metronidazole disks using EUCAST guidelines. Plates were incubated anaerobically, and inhibition zones were evaluated after 20 h (EUCAST recommendations) and again after 44 h. The recommended agar supported the growth of all 38 strains. Twenty-hour incubation was sufficient for the assessment of inhibition zone diameters of Fusobacterium strains. Although approved for Prevotella, an extended study of Prevotella species showed inconsistent growth within the EUCAST time limit of 20 h for some strains. All P. gingivalis strains required 44 h of incubation for the evaluation of inhibition zones. The EUCAST disk diffusion method for AST of rapidly growing anaerobes is applicable to members of the Fusobacterium nucleatum complex. P. gingivalis and several oral strains of Prevotella needed 44 h of incubation to enable reading of diffusion diameter. Further studies are necessary to validate the prolonged incubation of slow-growing anaerobes.

Advanced Platelet-Rich Fibrin (A-PRF) as Antibiotics Delivery System: In-Vitro Proof-of-Concept Study

Autologous blood centrifugation produces various forms of platelet concentrates widely used in tissue regenerative therapies due to their high concentrations of growth factors and abundance of autologous cells. Advanced Platelet-Rich Fibrin (A-PRF), introduced as a low-speed centrifugation product, contains an even higher concentration of growth factors, a greater number of cells, and a looser fibrin clot structure compared to previous Leukocyte and Platelet-Rich Fibrin (L-PRF). This study aims to assess the potential of A-PRF as a local delivery system for antibiotics. Different concentrations (0.5 mg/mL, 0.25 mg/mL, and 0.125 mg/mL) of injectable amoxicillin (AMX) and metronidazole (MTZ) were preliminarily tested for their impact on A-PRF clot formation, with 0.5 mg/mL selected for subsequent experiments. Blood samples from healthy volunteers were supplemented with antibiotics and centrifuged to form clots. Antibiotic-enriched A-PRF clots were immersed in phosphate-buffered saline (1x PBS) and analyzed at 24 h, 72 h, 7 days, and 14 days. AMX showed a consistent release (mean: 19.9 ± 4.8 ng/mL at 24 h) over 14 days, while MTZ demonstrated greater variability (mean: 12.8 ± 4.5 ng/mL at 24 h). AMX release remained constant over the 14-day period, with no significant variations among patients. In contrast, MTZ displayed a progressively lower release over time. Microbiological analysis revealed bacterial growth inhibition zones for Fusobacterium nucleatum (AMX: 23 mm, MTZ: 28 mm) and Prevotella intermedia (AMX: 34 mm, MTZ: 30 mm) at 24 h. These findings suggest that A-PRF can act as an effective local antibiotic delivery system, maintaining sustained antimicrobial activity and potentially reducing the need for systemic antibiotics.

Rapid detection of antimicrobial susceptibility of the Bacteroides fragilis group by flow cytometry: A preliminary study

A total of nine Bacteroides fragilis group strains and B. fragilis ATCC 25285 were studied. Six antibiotics were used in the study. Broth dilution method was used for flow cytometry (FCM) analysis. Cell suspensions with antibiotics and antibiotic-free were stained with thiazole orange and propidium iodide (PI) to differentiate dead/live cells. The percentage of dead and live cells was calculated using FCM device. Cut-off values for antibiotics (26,7 %, 35,5 % and 30,2 % for meropenem, AMC and clindamycin, respectively) were calculated for dead/live cell differentiation. A common cut-off value was calculated for bactericidal and bacteriostatic (31,8 % and 25,7 % respectively). The PI staining ratios of the B. fragilis ATCC 25285 calculated in the MIC ranges for each antibiotic were under the cut-off values calculated with clinical isolates. The cut-off values we calculated are compatible with MBC rather than MIC values. The FCM method is one of the candidate methods for antimicrobial susceptibility testing.

Prevalence of antibiotic-resistant Cutibacterium acnes (formerly Propionibacterium acnes) isolates, a systematic review and meta-analysis

OBJECTIVE

This study aimed to assess the overall antibiotic susceptibility of Cutibacterium acnes (C. acnes), a bacterium implicated in acne vulgaris, with a particular focus on clindamycin and fluoroquinolones, which are commonly used in inflammatory acne treatment.

METHODS

A systematic search of Scopus, PubMed, Web of Science and EMBASE databases was conducted to identify relevant studies. Pooled prevalence estimates were calculated using a random-effects model, and additional analyses included quality assessment, evaluation of publication bias, meta-regression and subgroup analyses based on antimicrobial susceptibility methods and year of publication.

RESULTS

The analysis incorporated a total of 39 studies. The random-effects model revealed that the proportion of clindamycin-resistant isolates was 0.031 (95% CI: 0.014-0.071). Additionally, macrolides, including erythromycin (0.366; 95% CI: 0.302-0.434) and azithromycin (0.149; 95% CI: 0.061-0.322), exhibited distinct prevalence rates. Tetracyclines, including doxycycline (0.079; 95% CI: 0.014-0.071), tetracycline (0.062; 95% CI: 0.036-0.107) and minocycline (0.025; 95% CI: 0.012-0.051), displayed varying prevalence estimates. Fluoroquinolones, including ciprofloxacin (0.050; 95% CI: 0.017-0.140) and levofloxacin (0.061; 95% CI: 0.015-0.217), demonstrated unique prevalence rates. Additionally, the prevalence of the combination antibiotic trimethoprim/sulfamethoxazole (SXT) was estimated to be 0.087 (95% CI: 0.033-0.208).

CONCLUSION

The study findings highlight a concerning increase in antimicrobial-resistant C. acnes with the use of antibiotics in acne treatment. The strategic utilization of appropriate antimicrobials has emerged as a crucial measure to mitigate the emergence of antimicrobial-resistant skin bacteria in acne management.

A subanalysis of Clostridium perfringens bloodstream infections from a 5-year retrospective nationwide survey (ITANAEROBY)

Clostridium perfingens bloodstream infections (BSIs) can be associated with high mortality rates. We performed a subanalysis of all C. perfringens BSIs enrolled during a multicentric retrospective observational study (ITANAEROBY). Data were collected from January 2016 to December 2020. C. perfringens BSIs were 134 (134/1960, 6.8 %). The highest resistance rate was observed for clindamycin (26/120, 21.6 %), penicillin (11/71, 15.4 %) and metronidazole (14/131, 10.7 %). In conclusion, C. perfringens reduced susceptibility phenotype to first-line therapy.

Recent development and fighting strategies for lincosamide antibiotic resistance

SUMMARYLincosamides constitute an important class of antibiotics used against a wide range of pathogens, including methicillin-resistant Staphylococcus aureus. However, due to the misuse of lincosamide and co-selection pressure, the resistance to lincosamide has become a serious concern. It is urgently needed to carefully understand the phenomenon and mechanism of lincosamide resistance to effectively prevent and control lincosamide resistance. To date, six mobile lincosamide resistance classes, including lnu, cfr, erm, vga, lsa, and sal, have been identified. These lincosamide resistance genes are frequently found on mobile genetic elements (MGEs), such as plasmids, transposons, integrative and conjugative elements, genomic islands, and prophages. Additionally, MGEs harbor the genes that confer resistance not only to antimicrobial agents of other classes but also to metals and biocides. The ultimate purpose of discovering and summarizing bacterial resistance is to prevent, control, and combat resistance effectively. This review highlights four promising strategies, including chemical modification of antibiotics, the development of antimicrobial peptides, the initiation of bacterial self-destruct program, and antimicrobial stewardship, to fight against resistance and safeguard global health.

Antimicrobial, Antioxidant and Cytotoxic Effects of Essential Oil, Fatty Acids and Bioactive Compounds of Beta vulgaris var. crassa (Fodder Beet)

Beta vulgaris var. crassa is undoubtedly a very important plant that is not used enough in the world. In this study, it was aimed to determine the cytotoxic activities of the components (essential oils, fatty acids, total phenol and flavonoid) found in the leaf parts of Beta vulgaris var. crassa against PC-3, MCF-7 and HeLa cancer cell lines. In addition, the effectiveness of these ingredients against bacteria and fungi that can cause serious health problems in humans was tested. In experiments, three tumor cell lines were exposed to various plant extract concentrations (31.25, 62.5, 125, 250, 500 and 1000 µg/mL) for 72 h. It was found that plant extracts showed high (SI: 2.14 > 2) cytotoxicity to PC-3 cells, moderate (SI: 1.62 < 2) to HeLa cells, and low (SI: 0.93 < 2) cytotoxicity to MCF-7 cells. Also, different plant extract concentrations were found to cause an inhibition rate of 16.3-22.3% in Staphylococcus aureus, 16.8-23.5% in Streptococcus pyogenes and 12-16.2% in Cutibacterium acnes. Similarly, inhibition rates were determined between 9.5-20.7% for Candida albicans, 3.5-7.7% for Candida auris, and 5.5-15.1% for Candida glabrata. The results showed that the plant extract exhibited a concentration-dependent cytotoxic and antimicrobial effect against both cancer cell lines and microbial pathogens.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-024-01269-8.

Effects of UV/H2O2 Degradation on the Physicochemical and Antibacterial Properties of Fucoidan

The applications of fucoidan in the food industry were limited due to its high molecular weight and low solubility. Moderate degradation was required to depolymerize fucoidan. A few studies have reported that fucoidan has potential antibacterial activity, but its antibacterial mechanism needs further investigation. In this study, the degraded fucoidans were obtained after ultraviolet/hydrogen peroxide treatment (UV/H2O2) at different times. Their physicochemical properties and antibacterial activities against Staphylococcus aureus and Escherichia coli were investigated. The results showed that the average molecular weights of degraded fucoidans were significantly decreased (up to 22.04 times). They were mainly composed of fucose, galactose, and some glucuronic acid. Fucoidan degraded for 90 min (DFuc-90) showed the strongest antibacterial activities against Staphylococcus aureus and Escherichia coli, with inhibition zones of 27.70 + 0.84 mm and 9.25 + 0.61 mm, respectively. The minimum inhibitory concentrations (MIC) were 8 mg/mL and 4 mg/mL, respectively. DFuc-90 could inhibit the bacteria by damaging the cell wall, accumulating intracellular reactive oxygen species, reducing adenosine triphosphate synthesis, and inhibiting bacterial metabolic activity. Therefore, UV/H2O2 treatment could effectively degrade fucoidan and enhance its antibacterial activity.

Exploring Sorbus torminalis Leaves: Unveiling a Promising Natural Resource for Diverse Chemical and Biological Applications

Sorbus torminalis (L.) Crantz has a rich history of versatile applications spanning the fields of medicine and nutrition. It is noteworthy that the decoction obtained from S. torminalis leaves is a traditional treatment method against both diabetes and stomach disorders. Phytochemical profiling determined by HPLC/MS-MS. The effects of the extracts on cell viability were investigated using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) method against MDA-MB-231 cell line (human breast adenocarcinoma).The ethanol/water extract contained more concentration of total phenolic (91.41 mg gallic acid (GAE) equivalent /gr) and flavanoid (29.10 mg rutin (RE) equivalent/gr) in the tested extract (p<0.05). Resulting of HPLC analysis, the chemical constituents varied depending on the solvents and chlorogenic acid, hyperoside, isoquercetin, delphindin-3,5-diglucoside, procyanidin B2, epicatechin, neochlorogenic acid, 3,5-dicaffeoylquinic acid were identified in all extracts. Overall, ethanol, n-hexane and ethyl acetate extracts showed the highest inhibition for the tyrosinase enzyme. The effect of leaf extracts of S. torminalis on antimicrobial, biofilm inhibitory, and anticancer activities was examined. Based on outcomes of our study recognize this plant as a critical source of medically active chemicals for feasible phytopharmaceutical and nutraceutical applications, providing the first scientific insight into the detailed biological and chemical profiles of S. torminalis.