Development of Versatile, thermally stable, flexible, UV-resistant and antibacterial polyvinyl alcohol-Nanodiamonds composite for efficient food packaging.

This research paper reports an enhancement of thermal, optical, mechanical and antibacterial activities of the Polyvinyl alcohol-Nanodiamonds (PVA-NDs) composite required for the food packaging industry. The synthesis of composites was done by the wet processing method. The large surface area of NDs facilitated the robust interaction between the hydroxyl group and macromolecular chains of PVA to enhance the hydrogen bonding of PVA with NDs rather than PVA molecules. Thus, a reduction in PVA diffraction peak intensity was reported. NDs improved the thermal stability by preventing the out-diffusion of volatile decomposition products of PVA. The results also revealed an enhancement in tensile strength (∼60 MPa) and ductility (∼180 %). PVA-NDs composite efficiently blocked the UVC (100 %), most of the part of the UVB (∼85 % above 300 nm), and UVA (∼58 %). Furthermore, enhanced antibacterial activities were reported for PVA-NDs composite against E. coli and S. aureus. NDs accumulated around the bacterial cells prevented essential cellular functions and led to death. Hence, this composite could be a promising candidate for safe, thermally stable, strong, flexible, transparent, UV- resistant antibacterial food packaging material.

Phenotypic and genotypic characterization of antimicrobial resistances reveals the effect of the production chain in reducing resistant lactic acid bacteria in an artisanal raw ewe milk PDO cheese.

Antimicrobial resistance (AMR) is a significant public health threat, with the food production chain, and, specifically, fermented products, as a potential vehicle for dissemination. However, information about dairy products, especially raw ewe milk cheeses, is limited. The present study analysed, for the first time, the occurrence of AMRs related to lactic acid bacteria (LAB) along a raw ewe milk cheese production chain for the most common antimicrobial agents used on farms (dihydrostreptomycin, benzylpenicillin, amoxicillin and polymyxin B). More than 200 LAB isolates were obtained and identified by Sanger sequencing (V1-V3 16S rRNA regions); these isolates included 8 LAB genera and 21 species. Significant differences in LAB composition were observed throughout the production chain (P ≤ 0.001), with Enterococcus (e.g., E. hirae and E. faecalis) and Bacillus (e.g., B. thuringiensis and B. cereus) predominating in ovine faeces and raw ewe milk, respectively, along with Lactococcus (L. lactis) in whey and fresh cheeses, while Lactobacillus and Lacticaseibacillus species (e.g., Lactobacillus sp. and L. paracasei) prevailed in ripened cheeses. Phenotypically, by broth microdilution, Lactococcus, Enterococcus and Bacillus species presented the greatest resistance rates (on average, 78.2 %, 56.8 % and 53.4 %, respectively), specifically against polymyxin B, and were more susceptible to dihydrostreptomycin. Conversely, Lacticaseibacillus and Lactobacillus were more susceptible to all antimicrobials tested (31.4 % and 39.1 %, respectively). Thus, resistance patterns and multidrug resistance were reduced along the production chain (P ≤ 0.05). Genotypically, through HT-qPCR, 31 antimicrobial resistance genes (ARGs) and 6 mobile genetic elements (MGEs) were detected, predominating Str, StrB and aadA-01, related to aminoglycoside resistance, and the transposons tnpA-02 and tnpA-01. In general, a significant reduction in ARGs and MGEs abundances was also observed throughout the production chain (P ≤ 0.001). The current findings indicate that LAB dynamics throughout the raw ewe milk cheese production chain facilitated a reduction in AMRs, which has not been reported to date.

Carbapenem non-susceptibility overcalling by BD phoenix NMIC-500 panel.

We aimed to assess the accuracy of BD Phoenix for determining carbapenem susceptibility because we observed a decline in carbapenem susceptibility rate from the biannual cumulative data, after we transitioned to the BD Phoenix form Vitek 2 system. Between October 2021 and May 2022, we collected 82 non-duplicated Enterobacterales showing non-susceptible to at least one of the three carbapenems by BD Phoenix. We performed the broth microdilution (BMD) and disk diffusion (DD) according to the CLSI guideline. Compared to BMD, the categorical agreements for ertapenem (ERT), imipenem (IPM) and meropenem (MEPM) was 58.8%, 56.8% and 91.5% for BD Phoenix and it was 85.4%, 89.0%, and 97.6%, respectively, for DD (p value; 0.0001 for ERT and IPM, p value; 0.17 for MEPM). The major errors/minor errors for ERT, IPM, and MEPM were 14.0%/31.7%, 2.94%/40.7%, and 2.56%/6.10%, respectively for BD Phoenix, compared to 0%/14.6%, 0%/9.8%, and 0%/2.5%, for DD. While errors in the BD Phoenix showed tendency towards resistance, those in DD displayed no tendency towards either resistance or susceptibility. With DD, 21 out of the 27 isolates showing susceptible/intermediate/susceptible pattern (ERT/IPM/MEPM) and 13 out of the 16 isolates showing intermediate/susceptible/susceptible pattern (ERT/IPM/MEPM), were correctly categorized by DD. However, for 22 isolates showing resistant/susceptible/susceptible pattern (ERT/IPM/MEPM), only 13 isolates were correctly categorized by DD. In conclusion, to mitigate the risk of overcalling carbapenem non-susceptibility with BD Phoenix, it will be helpful to perform a complementary test using DD and to provide comments on the DD results to clinicians.

2,3-Dichloronaphthoquinone derivatives: Synthesis, antimicrobial activity, molecular modelling and ADMET studies.

In the present study, an intermediate namely 2-(3-bromopropylamino)-3-chloronaphthalene-1,4-dione was initially synthesized via the nucleophilic addition-elimination reaction between 2,3-dichloro-1,4-naphthoquinone and 3-bromo-1-aminopropane. Then a coupling reaction between the intermediate and piperazine derivatives yielded a number of 1,4-naphthoquinone derivatives. Spectroscopic analysis successfully characterized the products that were obtained in good yields. In vitro antibacterial properties of the compounds were examined against different bacterial strains. In vitro antibacterial properties of the compounds were examined against the bacterial strains S. Aureus, E. Faecalis, E. Coli and P. Aeruginosa. While compound 9 was found to be effective against all bacterial strains used, compound 12 was active against three strains and compounds 10 and 11 were effective against the two. None of the compounds are effective against C. albicans strain. In silico molecular docking studies revealed that all compounds had docking scores comparable to the antibacterial drugs ciprofloxacin and gentamicin and might be considered as DNA gyrase B inhibitors. Molecular dynamics simulations were also conducted for a better understanding of the stability and the selected docked complexes. Additionally, the drug similarity of the synthesized compounds and ADMET characteristics were examined in conjunction with the antibiotic ciprofloxacin, and drug potentials were then evaluated. Compatible predictions were found with the drug similarity and ADMET parameters.

Antifungal Biofilm Inhibitory Effects of Combinations of Diclofenac and Essential Oils.

Systemic fungal infections have risen in recent decades and most of them are caused by Candida species, which are becoming increasingly resistant to conventional antifungal drugs. Biofilm production has been considered the most common growth form of Candida cells and is associated with a high level of antifungal resistance. At present, international research reports on the antifungal activity of non-traditional antimicrobial drugs and their potential use against life-threatening resistant fungal infections. Indeed, drug repurposing has led to the consideration of well-known compounds as a last-line therapy. The goal of this work is to evaluate the potential synergistic antifungal biofilm activity of new combinations between diclofenac sodium salt (DSS), a widely used non-steroidal anti-inflammatory drug (NSAID), with the essential oils (EOs) of Mentha piperita, Pelargonium graveolens, and Melaleuca alternifolia, whose antifungal activity has been well documented over the years. The in vitro antifungal activity of DSS and EOs was determined on different Candida strains. Susceptibility testing and the synergism of DSS and EOs versus biofilm cells was performed by using the broth microdilution assay and checkerboard methods. Minimum inhibitory concentrations (sMIC50) of DSS alone ranged from 1.25 to 2.05 mg/mL for all the strains considered. These values significantly decreased when the drug was used in combination with the EOs. The fractional inhibitory concentration index (FICI) was lower than 0.5 for almost all the associations, thus indicating a significant synergism, particularly for the DSS-Pelargonium graveolens combination towards the Candida strains examined. These preliminary results show that the combination of the EOs with DSS improves the antifungal activity on all the tested Candida strains, significantly lowering the concentrations of the components used and thus allowing any toxic effects to be overcome.

Chemical composition and antibacterial activity of bee venom against multi-drug resistant pathogens.

Bee venom with an antimicrobial effect is a powerful natural product. One of the most important areas where new antimicrobials are needed is in the prevention and control of multi-drug resistant pathogens. Today, antibacterial products used to treat multi-drug resistant pathogen infections in hospitals and healthcare facilities are insufficient to prevent colonisation and spread, and new products are needed. The aim of the study is to investigate the antibacterial effect of the bee venom (BV), a natural substance, on the species of Methicillin resistant Staphylococcus aureus, Vancomycin resistant Enterococcus faecalis, Carbapenem resistant Escherichia coli, Carbapenem resistant Klebsiella pneumoniae and Carbapenem resistant Acinetobacter baumannii. As a result of this study, it was found that MIC90 and MBC90 values ranged from 6.25 µg/mL - 12.5 µg/mL and numbers of bacteria decreased by 4-6 logs within 1-24 h for multi-drug resistant pathogens. In particular, Vancomycin resistant Enterococcus faecalis isolate decreased 6 log cfu/mL at 50 µg/mL and 100 µg/mL concentrations in the first hour. The effective bacterial inhibition rate of bee venom suggests that it could be a potential antibacterial agent for multi-drug resistant pathogens.Contribution: The treatment options of antibiotic-resistant pathogens are a major problem in both veterinary and human medicine fields. We have detected a high antibacterial effect against these agents in this bee venom study, which is a natural product. Apitherapy is a fashionable treatment method all over the world and is used in many areas of health. Bee venom is also a product that can be used as a drug or disinfectant raw material and can fill the natural product gap that can be used against resistant bacteria.

Performance Evaluation of BD Phoenix and MicroScan WalkAway Plus for Determination of Fosfomycin Susceptibility in Enterobacterales.

BACKGROUND: Fosfomycin is an old bactericidal drug that has gained increasing interest in the last decade for its potential use in multi-drug resistant gram-negative infections. However, evidence on fosfomycin susceptibility testing reports a poor correlation between commercial methods vs. reference agar dilution (AD) for Enterobacterales (EB). The study aimed at assessing the performance of two automated systems for the determination of fosfomycin susceptibility in EB clinical isolates. METHODS: Fosfomycin susceptibility testing results of two collections of 100 non-duplicate clinical EB strains obtained using two different platforms (BD Phoenix and MicroScan WalkAway Plus) were compared with those obtained by AD. Categorical agreement (CA), major error (ME) and very major error (VME) rates were calculated. RESULTS: BD Phoenix exhibited a 6.9% rate of false-resistant results and achieved a CA of 69%, whereas MicroScan WalkAway Plus achieved 3.7% of false-resistant results and 72% of CA. Both automated systems showed poor detection of resistant isolates, with 49.1% and 56.2% of false-susceptible results for BD Phoenix and Microscan WalkAway Plus, respectively. CONCLUSIONS: Overall, agar dilution remains the most suitable method for routine laboratory antimicrobial susceptibility testing of fosfomycin on Enterobacterales strains, given the poor performance of automated systems. The application of both automated systems, in the clinical laboratories reporting of fosfomycin, should be reviewed in light of the accuracy results falling below the acceptable threshold.

Evaluation of Antimicrobial Susceptibility Testing Performance of DL 96 System for Enterobacterales.

DL96 Microbial Identification/Antimicrobial Susceptibility Testing (ID/AST) System (Zhuhai DL, Guangdong, China) is one of the most commonly used commercial ID/AST System in China. This study aims to evaluate the performance of DL 96E for Antimicrobial Susceptibility Testing (AST) of 270 Enterobacterales isolates from Hainan general hospital using the broth microdilution method (BMD) as reference method. CLSI M52 criteria was followed when analyzing the evaluation results. Twenty antimicrobial agents were evaluated, and categorical agreement (CA) ranged from 62.8% to 96.5%. Imipenem had the lowest CA (63.9%) and highest very major errors (VME) (52.8%). A total of 103 carbapenem-resistant Enterobacterales were evaluated; DL 96E miss identified 22 isolates, including six carbapenemase-producing Enterobacteriaceae. DL 96E must adjust the Minimum Inhibitory Concentration (MIC) ranges of ciprofloxacin, levofloxacin, and piperacillin-tazobactam to cover Clinical and Laboratory Standards Institute (CLSI) breakpoints, adjust the formulation of some antimicrobial, such as imipenem, and increase the MIC detection range to cover the Quality control (QC) strains' MIC range.

Antiproliferative assay of suma or Brazilian ginseng (Hebanthe eriantha) methanolic extract on HCT116 and 4T1 cancer cell lines, in vitro toxicity on Artemia salina larvae, and antibacterial activity.

Hebanthe eriantha is a medicinal plant used in folk medicine and a subject of commercial interest. The cytotoxicity effects from H. eriantha root extracts on cancerous and normal cells were assessed by the MTT method, and in vitro toxicity was evaluated on Artemia salina. The inhibition of the proliferation of bacteria and MIC values were examined by the disc diffusion and the broth microdilution method, respectively. Human colon cancer HCT116 and mouse breast tumour model 4T1 cells treated with methanolic extract showed a significant decrease in viability of cells with IC50: 272.6 and 88.5 µg/mL at 72h, respectively. The methanolic extract of H. eriantha showed moderate toxicity against A. salina (LC50: 589.4 µg/mL). In antimicrobial activity, the methanolic extract showed the highest inhibitory function against S. aureus and P. vulgaris (17.5 and 16 mm) with MICs of 500 µg/mL. The results confirmed the potential of plant roots as cytotoxic agents.

Synergistic Action of Cinnamomum verum Essential Oil with Sertraline.

Cinnamomum verum L. essential oil (CEO), commonly known as Ceylon cinnamon or cinnamon tree, is regarded as one of the most employed essential oils in the field of aromatherapy. It is usually applied externally as astringent, antipruritic, rubefacient, and anti-septic agent. Furthermore, both in vitro and in vivo research have demonstrated its numerous pharmacological effects, including the potentiality for treating neuralgia, myalgia, headache, and migraine. Several pieces of research also corroborated its significant antiviral and antimicrobial properties. Cinnamaldehyde, eugenol, caryophyllene, cinnamyl acetate, and cinnamic acid are the most representative compounds that are generally found in greater quantities in CEO and play a pivotal role in determining its pharmacological activities. Due to the global antibiotic resistance scenario and the dwindling amount of funding dedicated to developing new antibiotics, in recent years research has concentrated on exploring specific economic approaches against microbial infections. In this context, the purpose of this study was the investigation of the synergistic antibacterial activities of commercially available and chemically characterized CEO in combination with sertraline, a selective serotonin reuptake inhibitor (SSRI), whose repositioning as a non-antibiotic drug has been explored over the years with encouraging results. In vitro effects of the titled combination were assessed toward a wide panel of both Gram-positive and Gram-negative bacteria. The antimicrobial efficacy was investigated by using the checkerboard microdilution method. The interesting preliminary results obtained suggested a synergistic effect (fractional inhibitory index, FICI < 0.5) of sertraline in combination with CEO, leading to severe growth inhibition for all bacterial species under investigation.

Susceptibility of Meropenem-Resistant and/or Carbapenemase-Producing Clinical Isolates of Enterobacterales (Enterobacteriaceae) and Pseudomonas aeruginosa to Ceftazidime-Avibactam and Ceftolozane-Tazobactam as Assessed by In Vitro Testing Methods.

This study aimed to assess the comparability of in vitro susceptibility testing methods to ceftazidime-avibactam (CZA) and ceftolozane-tazobactam (C/T). Meropenem-resistant and/or carbapenemase-producing clinical isolates of Enterobacterales (Enterobacteriaceae) and Pseudomonas aeruginosa were tested by both bioMérieux ETEST and VITEK-2 AST-N397 card and compared with a Micronaut AST-system broth microdilution (BMD) method. CZA and C/T MICs were interpreted using EUCAST breakpoints. Of the 153 Enterobacteriaceae isolates, 55.6% and 0.0% (VITEK 2) and 56.9% and 0.0% (ETEST and BMD) were susceptible to CZA and C/T, respectively. Of 52 P. aeruginosa isolates, 50.0% and 40.4% (VITEK 2, ETEST, and BMD) were susceptible to CZA and C/T, respectively. The essential agreement (EA) was 96.1% (197/205; VITEK 2 versus BMD) and 95.6% (196/205; ETEST versus BMD) for CZA testing, whereas EA was 98.0% (201/205; VITEK 2 versus BMD) and 96.6% (198/205; ETEST versus BMD) for C/T testing. The categorical agreement (CA) was 98.0% (201/205; VITEK 2 versus BMD) and 100% (ETEST versus BMD) for CZA testing, whereas CA was 100% (VITEK 2 versus BMD) and 100% (ETEST versus BMD) for C/T testing. Categorical errors regarded four Enterobacteriaceae isolates. VITEK 2 and ETEST yielded equivalent CZA and C/T susceptibility testing results, compared to the BMD method, in such a clinical context.

In Vitro Growth-Inhibitory Synergistic Effect of Zinc Pyrithione in Combination with Gentamicin against Bacterial Skin Pathogens of Livestock.

Bacterial skin diseases of livestock could be a serious global threat, especially in association with overcoming bacterial resistance. Combinatory action of antimicrobial agents proves to be an effective strategy to overcome the problem of increasing antibiotic resistance of microorganisms. In this study, the in vitro combined effect of zinc pyrithione with gentamicin against bacterial skin pathogens of livestock (Staphylococcus aureus, Streptococcus agalactiae, and Streptococcus dysgalactiae) was evaluated according to the sum of fractional inhibitory concentration indices (FICI) obtained by checkerboard method. The results showed that a combination of zinc pyrithione with gentamicin produced a strong synergistic effect (p < 0.001) against all tested streptococcal strains (with FICI values ranging from 0.20 to 0.42). Compared to that, only three out of eight S. aureus strains were highly susceptible to the combination of antimicrobial agents at single concentration (0.25 µg/mL) of zinc pyrithione with range of FICI 0.35−0.43. These findings suggest that interference between agents tested in this study can be used for the development of future veterinary pharmaceutical preparations for the treatment of bacterial skin infections of livestock.

The Synthesis of Triazolium Salts as Antifungal Agents: A Biological and In Silico Evaluation.

The control of fungal pathogens is increasingly difficult due to the limited number of effective drugs available for antifungal therapy. In addition, both humans and fungi are eukaryotic organisms; antifungal drugs may have significant toxicity due to the inhibition of related human targets. Furthermore, another problem is increased incidents of fungal resistance to azoles, such as fluconazole, ketoconazole, voriconazole, etc. Thus, the interest in developing new azoles with an extended spectrum of activity still attracts the interest of the scientific community. Herein, we report the synthesis of a series of triazolium salts, an evaluation of their antifungal activity, and docking studies. Ketoconazole and bifonazole were used as reference drugs. All compounds showed good antifungal activity with MIC/MFC in the range of 0.0003 to 0.2/0.0006-0.4 mg/mL. Compound 19 exhibited the best activity among all tested with MIC/MFC in the range of 0.009 to 0.037 mg/mL and 0.0125-0.05 mg/mL, respectively. All compounds appeared to be more potent than both reference drugs. The docking studies are in accordance with experimental results.

Thiazolidin-4-Ones as Potential Antimicrobial Agents: Experimental and In Silico Evaluation.

Herein, we report computational and experimental evaluations of the antimicrobial activity of twenty one 2,3-diaryl-thiazolidin-4-ones. All synthesized compounds exhibited an antibacterial activity against six Gram-positive and Gram-negative bacteria to different extents. Thus, the MIC was in the range of 0.008-0.24 mg/mL, while the MBC was 0.0016-0.48 mg/mL. The most sensitive bacterium was S. Typhimurium, whereas S. aureus was the most resistant. The best antibacterial activity was observed for compound 5 (MIC at 0.008-0.06 mg/mL). The three most active compounds 5, 8, and 15, as well as compound 6, which were evaluated against three resistant strains, MRSA, P. aeruginosa, and E. coli, were more potent against all bacterial strains used than ampicillin. The antifungal activity of some compounds exceeded or were equipotent with those of the reference antifungal agents bifonazole and ketoconazole. The best activity was expressed by compound 5. All compounds exhibited moderate to good drug-likeness scores ranging from -0.39 to 0.39. The docking studies indicated a probable involvement of E. coli Mur B inhibition in the antibacterial action, while CYP51 inhibition is likely responsible for the antifungal activity of the tested compounds. Finally, the assessment of cellular cytotoxicity of the compounds in normal human MRC-5 cells revealed that the compounds were not toxic.

The Influence of Liquid Medium Choice in Determination of Minimum Inhibitory Concentration of Essential Oils against Pathogenic Bacteria.

So far there is no internationally accepted, standardized method for MIC determination of natural substances such as essential oils (EOs). The aim of this study was to elucidate how much the MIC values obtained from various studies using different culture media are comparable. The median MICs for cinnamon essential oil (EO) obtained by broth dilution were 517, 465 and 517 µg/mL for Mueller-Hinton Broth (MHB), Tryptone Soya Broth (TSB) and Brain Heart Infusion (BHI), respectively. The MIC values for oregano EO were significantly (p < 0.001) lower in MHB than in highly nutritious media; the median MICs were 616 µg/mL for MHB and 474 µg/mL for TSB and BHI. This statistically significant difference was noted for all the pathogens studied (Salmonella Enteritidis, Escherichia coli O157, Listeria monocytogenes, Staphylococcus aureus). In the presence of oregano EO lag phase was also much less prolonged in MHB (by 6-17%) than in the other media (by 92-189%). Some components of EOs may bind to starch in MHB; since the phenomenon seems to be selective and EO dependent, the use of MHB for comparison of antimicrobial properties of various EOs thus cannot be recommended.

Synthesis, Biological Evaluation and Molecular Docking Studies of 5-Indolylmethylen-4-oxo-2-thioxothiazolidine Derivatives.

BACKGROUND: Infectious diseases represent a significant global strain on public health security and impact on socio-economic stability all over the world. The increasing resistance to the current antimicrobial treatment has resulted in the crucial need for the discovery and development of novel entities for the infectious treatment with different modes of action that could target both sensitive and resistant strains. METHODS: Compounds were synthesized using the classical organic chemistry methods. Prediction of biological activity spectra was carried out using PASS and PASS-based web applications. Pharmacophore modeling in LigandScout software was used for quantitative modeling of the antibacterial activity. Antimicrobial activity was evaluated using the microdilution method. AutoDock 4.2® software was used to elucidate probable bacterial and fungal molecular targets of the studied compounds. RESULTS: All compounds exhibited better antibacterial potency than ampicillin against all bacteria tested. Three compounds were tested against resistant strains MRSA, P. aeruginosa and E. coli and were found to be more potent than MRSA than reference drugs. All compounds demonstrated a higher degree of antifungal activity than the reference drugs bifonazole (6-17-fold) and ketoconazole (13-52-fold). Three of the most active compounds could be considered for further development of the new, more potent antimicrobial agents. CONCLUSION: Compounds 5b (Z)-3-(3-hydroxyphenyl)-5-((1-methyl-1H-indol-3-yl)methylene)-2-thioxothiazolidin-4-one and 5g (Z)-3-[5-(1H-Indol-3-ylmethylene)-4-oxo-2-thioxo-thiazolidin-3-yl]-benzoic acid as well as 5h (Z)-3-(5-((5-methoxy-1H-indol-3-yl)methylene)-4-oxo-2-thioxothiazolidin-3-yl)benzoic acid can be considered as lead compounds for further development of more potent and safe antibacterial and antifungal agents.

Comparative evaluation of agar dilution and broth microdilution by commercial and in-house plates for Bacteroides fragilis group: An economical and expeditious approach for resource-limited settings.

OBJECTIVE: To compare the performance of agar dilution and broth microdilution by commercial and in-house prepared plates for the Bacteroides fragilis group. The cost analysis was performed to demonstrate that in-house prepared BMD plates were a suitable alternative to agar dilution given the high cost and low feasibility of incorporating commercial BMD plates in routine, particularly in the tertiary care institutes of many low- and middle-income countries. METHODS: Thirty B. fragilis group isolates were tested against six antibiotics, frequently used as empirical therapy for anaerobic infections including metronidazole, clindamycin, imipenem, piperacillin-tazobactam, cefoxitin, and chloramphenicol. The running consumable expenditure for all methodologies was calculated. RESULTS: The results demonstrated essential and categorical agreement of >90% for all antibiotics except cefoxitin, which showed <90% categorical agreement. No major or very major errors were observed. We observed a high agreement and strong concordance for MIC values between both methods and inter-rate reliability of >0.9 by Cohen's kappa analysis, indicating almost perfect agreement between both methods using either of the plates. In contrast to agar dilution, a 20.5 fold cost reduction was seen in BMD using in-house plates and a 5.8 fold reduction using commercial plates to test a single isolate. However, when testing 30 isolates concurrently the cost significantly increased for commercial BMD plates by 8.4 folds, and only 1.03 fold cost reduction was seen with in-house BMD plates. CONCLUSION: BMD gives comparable results to agar dilution and can be considered a method of choice to test a small number of samples. The technique is an economical option when plates are standardized in-house and could be employed for susceptibility testing of the B. fragilis group.

Comparative study of in vitro activities of polymyxin B commercial products on Pseudomonas aeruginosa isolated from hospitalized patients / Estudio comparativo de las actividades in vitro de productos comerciales de polimixina B sobre Pseudomonas aeruginosa aislada de pacientes hospitalizados

Introducción: La polimixina B se ha aplicado como uno de los antibióticos de último recurso para el tratamiento de la multirresistencia entre las infecciones bacterianas Gram negativas. Debido a efectos secundarios como toxicidad renal, el uso de polimixina se asocia con limitaciones. El presente estudio evalúa la actividad antibacteriana in vitro de varios productos comerciales de polimixina B contra Pseudomonas aeruginosa. Métodos: Este estudio incluyó 63 aislados de P. aeruginosa no duplicados que se examinaron para la prueba de susceptibilidad in vitro a la polimixina B utilizando los siguientes discos de polvo: sulfato de polimixina B, otosporina, Poly-Mxb y Myxacort. También se han identificado las MIC50 y MIC90 para los antibióticos de polimixina B. Resultados: Myxacort tuvo una actividad funcional contra la mayoría de los aislados de P. aeruginosa, y sólo siete aislados tuvieron una CIM relativamente alta. Las actividades de Poly-MXb y Myxacort fueron las mismas que las de otosporina. Conclusiones: Nuestros resultados revelaron que el producto genérico nacional de polimixina B (Myxacort), y dos productos externos (Otosporin, Poly-MXb) son similares en términos de actividad microbiológica. (AU)

Introduction: Polymyxin B has been applied as one of the last-resort antibiotics for the treatment of multidrug resistance among Gram-negative bacterial infections. Due to side effects such as renal toxicity, the use of polymyxin is associated with limitations. The present study evaluates in vitro antibacterial activity of a number of polymyxin B commercial products against Pseudomonas aeruginosa. Methods: This study included 63 non-duplicated P. aeruginosa isolates examined for in vitro polymyxin B suscepti-bility testing using the following powder disks: polymyxin B sulfate, otosporin, Poly-Mxb, and Myxacort. MIC50 and MIC90 have also been identified for polymyxin B antibiotics. Results: Myxacort had functional activity against most P. aeruginosa isolates, and only seven isolates had a relative-ly high MIC. The activities of Poly-MXb and Myxacort were the same as otosporin. Conclusions: Our findings revealed that the national generic polymyxin B product (Myxacort), and two external products (Otosporin, Poly-MXb) are similar in terms of microbiological activity. (AU)

Comparison of Etest and broth microdilution for evaluating the susceptibility of Staphylococcus aureus and Streptococcus pneumoniae to ceftaroline and of carbapenem-resistant Enterobacterales and Pseudomonas aeruginosa to ceftazidime/avibactam.

OBJECTIVES: Decreased susceptibility to ceftazidime/avibactam (CZA) and ceftaroline (CPT) has been reported during antimicrobial resistance surveillance and therapy. Conventional laboratories are unable to provide timely susceptibility testing for CZA and CPT because these antimicrobial agents are not incorporated in automated susceptibility testing systems. METHODS: We evaluated Etest and the Sensititre broth microdilution (BMD) method for testing CZA against carbapenem-resistant Gram-negative bacilli and CPT against important Gram-positive cocci bloodstream isolates. Genotypes of carbapenemases in Enterobacterales were also determined using the Xpert® Carba-R assay. RESULTS: Etest showed ≥90% agreement with Sensititre BMD for carbapenem-resistant Klebsiella pneumoniae (CRKP) (n = 187), carbapenem-resistant Escherichia coli (CREC) (n = 28) and Streptococcus pneumoniae (n = 35); however, the very major error rate exceeded 3%. Agreement between Etest and Sensititre BMD was <90% for carbapenem-resistant Pseudomonas aeruginosa (CRPA) (n = 81), methicillin-susceptible Staphylococcus aureus (MSSA) (n = 92) and methicillin-resistant S. aureus (MRSA) (n = 170). Both agents remained potent with a high susceptibility rate by Sensititre BMD as follows: CZA against CRKP (95.0%), CREC (89.3%) and CRPA (84.5%); and CPT against MSSA (100.0%), MRSA (95.3%) and S. pneumoniae (94.3%). CZA was active against blaKPC-carrying CRKP (98.5% susceptible), and resistance in the majority of CZA-resistant Enterobacterales isolates (6 of 10 CRKP and 2 of 3 CREC) was due to the presence of a metallo-ß-lactamase gene. CONCLUSION: Our results suggest that interpretation of susceptibility results obtained by Etest for both agents should be undertaken cautiously and remains challenging.

Colistin Susceptibility Testing by Rapid Colistin Disk Elution Test Among Enterobacteriaceae in Low-Resource Setting.

We modified rapid polymyxin Nordmann-Poirel (RPNP) test, called rapid colistin disk elution (RCDE) test, for detecting colistin resistance in Gram-negative bacilli and evaluated its performance compared with colistin broth disk elution (CBDE) test recommended by Clinical and Laboratory Standards Institute (CLSI). The RCDE test was performed by using a 10-µg colistin disk in 2.7 mL volume (final colistin concentration of 3.7 µg/mL) of either cation-adjusted Mueller-Hinton broth or phenol red broth base media with bacterial inoculum of 1-µL loop, and 1-4 and 16-20 hr incubation for Enterobacteriaceae and Acinetobacter baumannii isolates, respectively. Both tests were evaluated in 236 Enterobacteriaceae and 49 A. baumannii isolates using broth microdilution as reference method. Among the Enterobacteriaceae isolates, categorical agreement and very major error (VME or false intermediate susceptibility) rate were 98.3% and 5.4%, respectively, for the RCDE test, compared with 97.9% and 7.1%, respectively, for the CBDE test. Both tests had major error (ME or false resistance) rate of 0.6%. For the A. baumannii isolates, the RCDE and CBDE tests gave high VME rates of 8.3% and 16.7%, respectively. The RCDE test showed good performance comparable with the CBDE test but is cheaper and more rapid (3 hr) and convenient, thus suggesting as an alternative for detecting colistin resistance among Enterobacteriaceae in low-income countries.