Respective Minimum Inhibitory Concentration Research Articles

The Efficacy of Apple Cider Vinegar at Different pH Values as an Antimicrobial Agent: An In Vitro Study.

This study evaluates the antimicrobial activities of commercially available 5% apple cider vinegar (ACV) against Enterococcus faecalis, Streptococcus mutans, and Lactobacillus casei. Materials and methods: Minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were conducted using the broth microdilution method. Sodium hypochlorite (NaOCl) of 5.25% was used as a positive control, and comparisons were also made with acetic acid (AA) as the main ingredient in ACV. The three test bacteria treated with the most effective ACV dilution were visualized under a transmission electron microscope (TEM) for structural changes. Minimal inhibitory concentration was determined at 0.625% of the concentration of ACV against S. mutans and E. faecalis and 1.25% of the concentration of ACV against L. casei with two-fold serial dilutions. A concentration of 5 × 10-1% with 10-fold serial dilutions was found to be the MIC value for all three bacteria. No significant differences were found when compared with the positive control (NaOCl) (p = 0.182, p = 0.171, and p = 0.234), respectively, for two-fold serial dilutions and (p = 1.000, p = 0.658, and p = 0.110), respectively for 10-fold serial dilutions. MBC was observed to be 5% ACV for both E. faecalis and S. mutans. However, positive microbial growth was observed on the agar plate when cultured with L. casei. An independent sample t-test showed no significant differences (p > 0.05) in the antimicrobial activities between 5% ACV and 5% pure AA. TEM revealed cell wall and cytoplasmic membrane disruptions on all three bacteria at MIC value. Apple cider vinegar has antimicrobial activities against Enterococcus faecalis, Streptococcus mutans, and Lactobacillus casei at their respective MIC values. Apple cider vinegar can be an alternative antimicrobial dental pulp disinfectant to sodium hypochlorite. Apple cider vinegar can be used safely, especially in children's dental pulp therapy and deep caries management, when adequate tooth isolation is not readily achievable. Thus, adverse reactions commonly associated with other frequently used chemical disinfectants can be avoided.

Efficacy Assessment of Some Commonly used Disinfectants against Multidrug Resistant Bacterial Isolates from a Tertiary Healthcare Facility in Benin City, Nigeria

The ever-rising numbers of multidrug resistant, MDR bacteria in healthcare facilities globally has correspondingly led to a rapid escalation in the use of disinfectants, antiseptics or biocides which reached unprecedented levels during the COVID-19 pandemic. This has also elicited grave apprehension about the development of resistance to disinfectants. This study was conducted to evaluate the effectiveness of some regularly used disinfectants in the study population. Five brands of disinfectants were obtained and diluted in sterile 300 ppm calcium carbonatenutrient broth to their respective minimum inhibitory concentrations, MICs to which were exposed broth cultures of MDR organisms for 2 min before sampling onto nutrient agar plates in replicates. Further samples were taken NEWPORT INTERNATIONAL JOURNAL OF SCIENTIFIC AND EXPERIMENTAL SCIENCES (NIJSES) Volume 4 Issue 1 2023 ©NIJSES Publications Open Access ONLINE ISSN: 2992-5819 PRINT ISSN: 2992-6149 Onemu et al., 2023 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited Page | 49 from the mixture at 4, 6, 8, … 30 min intervals. One set of plates were incubated at 37oC and the other at RT for 48 h and 96 h respectively and examined for growth. Sodium hypochlorite, phenol and glutaraldehyde - all proved to be effective with the fastest time kill kinetics at 2.5 min. The longest time kill kinetics were demonstrated by cetrimide and cresol against Pseudomonas aeruginosa at 16 min and 13 min respectively, thus affirming Pseudomonas aeruginosa as the most resistant organism. This study infers of a reassurance in the continued effectiveness of the disinfectants under review in the phase of the ever-soaring tide of MDR organisms in healthcare settings. Keywords: Disinfectants, usage, effectiveness, MDR-organisms

Antimicrobial activity and pathogen mutation prevention of originator and generics of cefepime, linezolid and piperacillin/tazobactam against clinical isolates of Staphylococcus aureus

Although generic medicinal products are required to have the same qualitative and quantitative composition of the active substance as their reference originator product, patients and health care professionals express concerns about their interchangeability and safety. Therefore, the present study investigated the antimicrobial activity and pathogen mutation prevention of original and generic cefepime, linezolid and piperacillin/tazobactam against Staphylococcus aureus. Two generic formulations of cefepime, linezolid and piperacillin/tazobactam were tested against their respective originator products. Susceptibility testing was performed with twenty-one clinical isolates of S. aureus and ATCC-29213 using broth microdilution. Time kill curves (TKC) were performed with ATCC-29213 at drug concentrations above and below the respective minimum inhibitory concentrations (MIC). Mutation prevention concentration was determined for each drug formulation against ATCC-29213. All experiments were performed in triplicate. Mutant colonies from mutation prevention concentration (MPC) experiments were genotypically tested by sequence analysis. MIC ratios between contiguous originator and generic drugs were similar for each isolate. No visual differences were observed in TKCs between originator and generic substances. The MPC did not differ between different formulations of the same substance. Although sequence analysis of mutant colonies revealed genomic differences compared with the original ATCC-29213, no differences in mutation frequencies were observed between clinical isolates and ATCC-29213 treated with originator or generic substances. Similar antimicrobial activity and pathogen mutation prevention was observed between contiguous substances. These results support the interchangeability of generic and originator drug formulations with the same active ingredient.

Management of potato brown rot disease using chemically synthesized CuO-NPs and MgO-NPs

BackgroundPotatoes are a crucial vegetable crop in Egypt in terms of production and consumption. However, the potato industry suffers significant annual losses due to brown rot disease. This study aimed to suppress Ralstonia solanacearum (R. solanacearum), the causative agent of brown rot disease in potatoes, using efficient and economical medications such as CuO and MgO metal oxide nanoparticles, both in vitro and in vivo, to reduce the risk of pesticide residues.ResultsCuO and MgO metal oxide nanoparticles were synthesized via a simple chemical process. The average particle size, morphology, and structure of the nanoparticles were characterized using UV-visible spectroscopy, transmission electron microscopy (TEM), zeta potential analysis, X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. The growth of R. solanacearum was strongly inhibited by CuO and MgO NPs at a concentration of 3 mg/mL, resulting in zones of inhibition (ZOI) of 19.3 mm and 17 mm, respectively. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of CuO-NPs and MgO-NPs were 0.5, 0.6, and 0.6, 0.75 mg/mL, respectively. When applied in vivo through seed dressing and tuber soaking at their respective MIC concentrations, CuO-NPs and MgO-NPs significantly reduced the incidence of brown rot disease to 71.2% and 69.4%, respectively, compared to 43.0% and 39.5% in bulk CuSO4 and bulk MgSO4 treatments, respectively. Furthermore, CuO-NPs and MgO-NPs significantly increased the yield, total chlorophyll content, and enzyme efficiency of potato plants compared with the infected control plants. TEM revealed that the bacterial cytomembrane was severely damaged by nanomechanical forces after interaction with CuO-NPs and MgO-NPs, as evidenced by lipid peroxidation and ultrastructural investigations.ConclusionThe results of this study suggest that CuO-NPs and MgO-NPs can be used as intelligent agents to manage plant pathogens in agriculture. The use of metal oxide nanoparticles could provide a risk-free alternative for treating plant diseases, which are currently one of the biggest challenges faced by the potato industry in Egypt. The significant increase in yield, photosynthetic pigments, enzymatic activity, and total phenol-promoted resistance to R. solanacearum in potato plants treated with CuO-NPs and MgO-NPs compared to infected control plants highlights the potential benefits for the potato industry in Egypt. Further investigations are needed to explore using metal oxide nanoparticles for treating other plant diseases.

The Nocardial aph(2″) Gene Confers Tobramycin and Gentamicin Resistance and Is an Effective Positive Selection Marker in Mycobacteria and Nocardia.

The current study aimed to evaluate the feasibility of using the aminoglycoside 2″-O-phosphotransferase aph(2″) gene as a positive selection marker in N. asteroides, M. smegmatis, M. abscessus and M. tuberculosis. The aph(2″) gene, known to confer resistance to tobramycin, was PCR amplified from N. farcinica and cloned into two plasmid vectors, pMSG383 and pDB151, harboring hygromycin and zeocin selection markers, respectively. The recombinant plasmids were transformed into the target microorganisms, and selectability was assessed against varying concentrations of tobramycin and using an E-test against gentamicin. The results indicated that the aph(2″) gene is a useful selection marker in Mycobacteria and Nocardia against tobramycin, with a good selectability at 2.5-10 µg/mL for M. smegmatis mc2-155 and N. asteroides ATCC 19,247, and 60-160 µg/mL for M. abscessus ATCC 19,977 and M. tuberculosis H37Ra. The minimum inhibitory concentration (MIC) of gentamicin for recombinant N. asteroides, M. smegmatis and M. abscessus was >256 µg/mL, whereas respective MIC in wild-type strains was 0.125 µg/mL, 0.38 µg/mL and 8 µg/mL, respectively. These findings demonstrate the potential of aph(2″) as a positive selection marker for genetic manipulation processes in Mycobacteria and Nocardia, thus facilitating their research and improving the efficiency of biotechnology applications. Conclusions: the aph(2″) gene is a useful, new selection marker for genetic manipulation of Nocardia and various Mycobacteria.

Chemical composition and biological activities of volatile oil of the stem of Dombeya buettneri K. Schum. (Sterculiaceae)

Essential oil, obtained from the stem of Dombeya buettneri and characterized by high resolution GC–MS was tested for antimicrobial (using broth dilution method) and antioxidant (using spectrophotometric methods: DPPH, FRAP and ABTS) properties.Forty-three (43) essential oil components were detected which account for 96.8% of the total oil content comprising mainly: Non-terpene derivatives (31.8%), Apocarotenes (24.3%), Sesquiterpenoids (15.3%), Sesquiterpene hydrocarbons (14.4%), Monoterpenoids (10.1%) and Monoterpene hydrocarbons (0.9%). The major identified compounds in the oil were (E)-geranylacetone (14.8%), δ-cadinene (8.9%), n-hexadecane (7.8%), Tetradecanal (6.2%), β-ionone (4.9%), Borneol (4.2%), Viridiflorol (3.5%), Guaiol (3.4%), caryophyllene oxide (3.4%), Palustrol (2.5%) and Spathulenol (2.5%).The oil displayed antibacterial and antifungal activities on Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922 and Candida albicans ATCC 18804 with respective Minimum Inhibitory Concentration (MIC) of 6.25, 12.5 and 12.5%v/v. The Minimum Bactericidal/Fungicidal Concentrations on the test organisms ranged from 12.5 to 25.0%v/v. The antioxidant assay by DPPH showed a concentration dependent values of 8.0993±0.827 at 25 mg/mL, 14.7657±0.8151 and 19.449±0.6678 at 100 mg/mL with good IC50 value of 1098 µg/mL as compared with reference ascorbic acid standard with IC50 of 23.52 µg/mL. The Ferric reducing antioxidant assay (FRAP) showed activity at concentration of 0.076713±0.001227mg/FeSO4Equiv./g, while ABTS showed an activity at 0.3776±0.0025 mg AA Equiv./g with respect to the standards.The current study showed that the volatile oil of Dombeya buettneri stem possess good antioxidant and antimicrobial properties that could be utilized for cosmetic and pharmaceutical health benefits.

Reversal of Azole Resistance in Candida albicans by Human Neutrophil Peptide.

With the spread of AIDS and the increase in immunocompromised patients, multi-drug-resistant fungal infections have become a serious concern among clinicians, predominantly in the developing world. Therefore, developing novel strategies and new drugs is essential to overcome drug resistance in fungal pathogens. Antimicrobial peptides of human origin have been investigated as a potential treatment against Candida infections. In this study, human neutrophil peptide (HNP) was tested for its antifungal activity alone and in combination with fluconazole (FLC) against azole-susceptible and resistant C. albicans isolates, following CLSI guidelines. Susceptibility and combination interactions were also confirmed by MUSE cell viability assay and isobolograms for synergistic combinations, respectively. The effect of HNP on biofilm inhibition was determined spectrophotometrically and microscopically. Drug susceptibility testing showed minimum inhibitory concentrations (MICs) and minimum fungicidal concentrations (MFCs) ranging from 7.813 to 62.5 µg/mL and 15.625 to 250 µg/mL against all the tested C. albicans strains. The combination activity of FLC with HNP exhibited synergistic and additive interactions in 43% of each and indifferent interaction in 14%, and none of the combinations showed antagonistic interaction. Furthermore, HNB inhibited biofilm formation in all the tested C. albicans isolates. At the respective MICs, HNP exhibited inhibitory effects on the activity of the drug efflux pumps and their genes. These results warrant the application of HNP as a mono- or combination therapy with FLC to treat azole-resistant C. albicans.

Antimicrobial activity of essential oil of Lindera umbellate var. Membrancea

Lindera umbellate var. Membrancea is endemic throughout Japan and has long been used as a fragrant wood and for crafting. Examination of its chemical composition identified linalool as the most abundant constituent. In activity testing by micro-broth dilution method, the minimum inhibitory concentration (MIC) of essential oil of L. umbellate against Staphylococcus aureus FDA209P and Escherichia coli NIHJ JC2 was 50 and 800 mg/ml, respectively. With essential oil at the respective MICs at broth dilution with shaking method, the growth of S. aureus was not observed for 15 h and the growth of E. coli was delayed for 23.4 h. We showed that essential oil of L. umbellate effectively inhibited the growth of bacteria.

Anti-MRSA and clot lysis activities of Pestalotiopsis microspora isolated from Dillenia pentagyna Roxb.

There is an urgent call to search for novel natural compounds against developing multidrug-resistant microorganisms. The present work focuses on the characterization of a plant-associated fungus having bioactivity against methicillin-resistant Staphylococcus aureus (MRSA) strains. A fungal strain P31 was isolated from bark of Dillenia pentagyna and identified as Pestalotiopsis microspora. The maximum anti-MRSA activity was observed from extract of P31 grown in sabouraud dextrose broth. The minimum inhibitory concentrations(MIC) values of P31 extract were 14 μg/ml for methicillin-sensitive S. aureus (MSSA) and 32 μg/ml for MRSA strain, respectively. A crude P31 extract showed strong bactericidal activity by killing all treated MRSA cells within 24 h of treatment at their respective MIC value. A scanning electron microscopic study visualized morphological damage of MRSA cells. The membrane permeability of P31 extract-treated MRSA cells gradually increased which caused release of internal cytoplasmic nucleic acids, proteins and potassium ions (K+ ) from cells suggesting cell lysis or leakage from cells. A very low concentration of P31 extract was able to inhibit biofilm formed by MRSA cells. Thin layer chromatographic separation followed by gas chromatography-mass spectrometry analysis of the P31 extract revealed a number of antimicrobial compounds along with an anti-MRSA compound 2,4-di-tert-butylphenol. In addition, the P31 extract also showed in-vitro human blood clot lysis activity at various concentrations. The clot lysis activity of P31 extract was found maximum at 500 µg/ml. These findings suggest that fungal isolate P31 has potential as a source of anti-MRSA compounds useful in staph infections.

Resistance profiles of Neisseria gonorrhoeae isolates in Vienna, Austria: a phenotypic and genetic characterization from 2013 to 2020

International surveillance data show a constant rise in the number of Neisseria gonorrhoeae infections and an increase in drug resistance of N. gonorrhoeae. As recent N. gonorrhoeae surveillance data in Austria are scarce, this study investigated phenotypic and genotypic antimicrobial resistance in N. gonorrhoeae isolates. In total, 440 N. gonorrhoeae samples were collected at the Medical University of Vienna, and the minimal inhibitory concentrations (MICs) for a range of different antibiotics were determined. Sampling sites and treatments were recorded, and whole-genome sequencing of N. gonorrhoeae isolates was performed using allele libraries to determine genotypic resistance. The median MICs for ceftriaxone, cefixime, azithromycin, ciprofloxacin, tetracycline and penicillin were <0.002 µg/mL, <0.016 µg/mL, 0.25 µg/mL, 2.0 µg/mL, 1.5 µg/mL and 0.25 µg/mL, respectively. Annual comparison showed that MICs were generally stable for all antimicrobial agents except azithromycin, for which an increase in median MIC was observed from 2017 (0.25 µg/mL). There was no genetic resistance to ceftriaxone; 8% of samples displayed resistance mutations against cefixime, primarily located in the penA gene. Resistance to azithromycin increased from 2% in 2013 to 12% in 2020. MtrD mosaic had the highest impact on azithromycin susceptibility; 47% of the resistant isolates showed this mutation. The majority of cases of gonorrhoea were treated successfully with either ceftriaxone or a ceftriaxone/azithromycin regime. Two treatment failures occurred under monotherapy with doxycycline. Overall, genotypic resistance corresponded significantly to all respective MICs. The resistance rate of N. gonorrhoeae to antibiotics has remained stable in Vienna over the last decade, except for azithromycin. The strong correlation found between genetic and phenotypic patterns in this study holds promise for future diagnostics of N. gonorrhoeae resistance based on genotypes.

Antibacterial and Antibiofilm Potency of Menadione Against Multidrug-Resistant S. aureus.

Menadione is an analogue of 1,4-naphthoquinone (1,4-NQ) that possesses enormous pharmaceutical potential. The minimum inhibitory concentration (MIC) of menadione was determined against eighteen pathogens of the ESKAPE category, including thirteen multidrug-resistant (MDR) and five standard strains. From a total of eighteen pathogens, five strains of S. aureus (four: MDR and one: Standard strain) were considered further for detailed studies. This study included the determination of minimum bactericidal concentration (MBC), time-kill assay, scanning electron microscopic technique (SEM), and detection of reactive oxygen species (ROS). Additionally, the effect of menadione on biofilms of three strains of S. aureus was performed through crystal violet assay, SEM, and confocal laser scanning microscopy (CLSM). Menadione exerted substantial antibacterial activity against S. aureus (S8, S9, NCIM 5021) at a lower MIC (64µg/mL). Whereas, the MIC of 256µg/mL was displayed against J2 and J4 (MDR and biofilm-forming strains). The time-killing effect of menadione against S. aureus strains was observed after 9h at MBCs of 64µg/mL (NCIM 5021), 128µg/mL (S8, S9), and 512µg/mL (J2, J4). Enhanced levels of ROS in all five S. aureus were observed in presence of menadione (MICs and MBCs). The relation of enhanced ROS due to menadione activity invigorated us to explore its effect on S. aureus biofilms. We report menadione-mediated inhibition (> 90%) of biofilm formation (at respective MICs) and effect on preformed biofilms (> 85%) at 1024µg/mL. Menadione possessing antibacterial and antibiofilm potentials are imperative in the era of multidrug resistance developed by bacterial pathogens.

Wastewater Treatment Works: A Last Line of Defense for Preventing Antibiotic Resistance Entry Into the Environment

With their large, diverse microbial communities chronically exposed to sub-inhibitory antibiotic concentrations, wastewater treatment works (WWTW) have been deemed hotspots for the emergence and dissemination of antimicrobial resistance, with growing concern about the transmission of antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) into receiving surface waters. This study explored (1) the prevalence of ARG and ARB in local WWTW, (2) the effect of sub-inhibitory antimicrobial exposure on ARG copy numbers in pure cultures from WWTW, and (3) two WWTW with different treatment configurations. For each WWTW, qPCR determined the prevalence ofmcr3, sul1, sul2, andblaKPCduring the treatment process, and culture methods were used to enumerate and identify ARB. Bacterial colonies isolated from effluent samples were identified by 16S rDNA sequencing and their respective minimum inhibitory concentrations (MIC) were determined. These were compared to the MICs of whole community samples from the influent, return activated sludge, and effluent of each WWTW. Resistance genes were quantified in 11 isolated cultures before and after exposure to sub-MIC concentrations of target antibiotics. The numbers of ARG and ARB in both WWTW effluents were notably reduced compared to the influent.Sul1andsul2gene copies increased in cultures enriched in sub-MIC concentrations of sulfamethoxazole, whileblaKPCdecreased after exposure to amoxicillin. It was concluded, within the parameters of this study, that WWTW assist in reducing ARG and ARB, but that sub-inhibitory exposure to antimicrobials has a varied effect on ARG copy number in pure cultures.

Synthesis, Characterization and in vitro Antifungal Action of Gum Ghatti Capped Copper Oxide Nanoparticles

Copper oxide nanoparticles gained significance in agriculture for their antifungal action on various fungal plant pathogens. In this context, gum ghatti capped copper oxide nanoparticles (CuO NP) were generated by optimizing metal precursor conc. Synthesized NP were analyzed with different instrumental techniques such as UV-vis spectroscopy (UV-vis), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering, and transmission electron microscopy. NP showed characteristic absorption at 280 nm in UV-vis spectra and indicated monoclinic crystal structure. FTIR spectra confirmed the capping of NP by functional groups of the gum. Produced NP were spherical and showed a mean particle size of 4.5 ± 1 nm. The in vitro antifungal action of the gum-capped NP (25-100 µg/mL) was determined using resazurin broth assay against mycelia and sclerotia of Rhizoctonia solani, a soil and seed-borne fungal plant pathogen. Minimum inhibitory concentration (MIC) values ranged from 50-75 and 75-100 µg/mL, respectively, for mycelia and sclerotia of R. solani strains. NP inhibited the mycelial growth and sclerotial germination by 41.4-59% and 46.8-69.3% at respective MIC values. Therefore, the present report paves the way for the production of CuO NP-based fungicidal formulations towards the control and management of different fungal diseases in a broad range of crops.

Prediction of antimicrobial minimal inhibitory concentrations for Neisseria gonorrhoeae using machine learning models

The lowest concentration of an antimicrobial agent that can inhibit the visible growth of a microorganism after overnight incubation is called as minimum inhibitory concentration (MIC) and the drug prescriptions are made on the basis of MIC data to ensure successful treatment outcomes. Therefore, reliable antimicrobial susceptibility data is crucial, and it will help clinicians about which drug to prescribe. Although few prediction studies based on strategies have been conducted, however, no single machine learning (ML) modelling has been carried out to predict MICs in N. gonorrhoeae. In this study, we propose a ML based approach that can predict MICs of a specific antibiotic using unitigs sequences data. We retrieved N. gonorrhoeae genomes from European Nucleotide Archive and NCBI and analysed them combined with their respective MIC data for cefixime, ciprofloxacin, and azithromycin and then we constructed unitigs by using de Brujin graphs. We built and compared 35 different ML regression models to predict MICs. Our results demonstrate that RandomForest and CATBoost models showed best performance in predicting MICs of the three antibiotics. The coefficient of determination, R2, (a statistical measure of how well the regression predictions approximate the real data points) for cefixime, ciprofloxacin, and azithromycin was 0.75787, 0.77241, and 0.79009 respectively using RandomForest. For CATBoost model, the R2 value was 0.74570, 0.77393, and 0.79317 for cefixime, ciprofloxacin, and azithromycin respectively. Lastly, using feature importance, we explore the important genomic regions identified by the models for predicting MICs. The major mutations which are responsible for resistance against these three antibiotics were chosen by ML models as a top feature in case of each antibiotics. CATBoost, DecisionTree, GradientBoosting, and RandomForest regression models chose the same unitigs which are responsible for resistance. This unitigs-based strategy for developing models for MIC prediction, clinical diagnostics, and surveillance can be applicable for other critical bacterial pathogens.

Single‐cell Raman microspectroscopy‐based assessment of three intracanal disinfectants' effect on Enterococcus faecalis

AbstractEnterococcus faecalis (E. faecalis) is frequently encountered in asymptomatic, persistent endodontic infections; thus, its control and eradication via disinfectants are important. To explore a disinfectant formulation that is effective yet with minimal side effects, here, we evaluated the susceptibility of E. faecalis to three intracanal disinfectants. We quantitatively assessed and compared the growth‐ or metabolism‐inhibiting effects of intracanal disinfectants via minimum inhibitory concentration (MIC) and minimum inhibitory concentration based on metabolic activity (MIC‐MA), based on the broth dilution test and D2O‐probed single‐cell Raman spectra (SCRS), respectively. For sodium hypochlorite (NaClO), hydrogen peroxide (H2O2), and chlorhexidine gluconate (CHX), the corresponding MIC was 0.45 g/L, 110 mg/L, and 6 mg/L, respectively. Under their respective MIC doses, metabolic activity of bacterial cells was reduced to 2%, 4%, and 2% remained at 8 h, yet recovered to a retention level of 90%, 97%, and 2% at 24 h. Despite the halting of growth, the remained metabolic activity suggests a “nongrowing but metabolically active” (NGMA) state that may lead to potential recurring infections. In contrast, at their respective MIC‐MA doses of 0.9 g/L, 220 mg/L, and 12 mg/L, metabolic activities of all cells were completely inhibited throughout 24‐h exposure. Furthermore, lower combined concentration of above three intracanal disinfectants can elicit equivalent metabolism‐inhibiting effect with that of solo use of each one at the MIC‐MA dose. Thus, binary combined use of disinfectants can outperform their solo use in controlling infection of E. faecalis and reducing side effects. In conclusion, the MIC‐MA derived from D2O‐probed single‐cell Raman microspectroscopy is a promising approach in quantitatively assessing disinfectants' antimicrobial efficacy via metabolic activity.

The effects of methanolic extract of Uncaria gambir against microflora of dental caries

The antibacterial effects of Uncaria gambir extract have the potential to be expanded in dentistry, mainly in the management of dental caries and its sequelae. This preliminary study was conducted to investigate the in vitro antibacterial activity of methanolic extract of U. gambir against dental caries-related microflora: Streptococcus mutans, Streptococcus sobrinus, Lactobacillus casei and Enterococcus faecalis. The methanolic extract of U. gambir in powder form was dissolved and serially diluted in 1% dimethyl sulfoxide. The antibacterial effects of the extract were determined using the broth microdilution technique. A transmission electron microscope (TEM) was used to assess the effects of the extract on the morphology of the bacteria. A 0.12% chlorhexidine (CHX) and Man-Rogosa-Sharpe/brain heart infusion broth were used as positive and negative control respectively. Greatest antibacterial effects were seen on both Streptococci species with the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values of 1.25 and 5 mg/mL respectively, followed by Enterococcus faecalis (MIC=2.5 mg/mL, MBC=10 mg/mL) and Lactobacillus casei (MIC=7.5 mg/mL, MBC=30 mg/mL) in ascending order. Cell wall damage of all bacteria at their respective MIC value was observed through the TEM analysis. Tukey’s posthoc test showed no statistically significant difference in the antibacterial activity exerted by U. gambir extract and 0.12% CHX, with P> 0.05. Conclusively, U. gambir extract exhibits a good antibacterial effect against the microflora of dental caries and carries great potential for future development.

Candida glabrata MSH2 deletion increases antifungal tolerance in vitro and during intra-abdominal candidiasis (IAC), it does not impact pathogenesis of peritonitis or intra-abdominal abscesses

Background: IAC is the second most common type of invasive Candidiasis, but its pathogenesis is poorly understood. We have shown that Candida albicans DNA damage response genes are strongly induced within intra-abdominal abscesses. Deletion of C. glabrata MSH2, A DNA mismatch repair (MMR) gene, results in a mutator phenotype that facilitates multidrug resistance in vitro and in mouse gastrointestinal tracts. Our goal was to determine if CGMSH2 Contributed to pathogenesis or resistance to the new antifungal rezafungin during IAC. Methods: We createdΔMSH2 in BG2 using SAT-Flipper, and tested virulence and rezafungin responses in a mouse model of IAC. Results: ΔMSH2 displayed no growth defects at 30°C in liquid (YPD, Ypglycerol) or solid media (YPD+0.02% MMS, 1MM H2O2, 1M NACL, 20 UG/ML CW, 250 UG/ML OR 0.02% SDS). ΔMSH2 longevity in YPD was comparable to BG2. Caspofungin-, Rezafungin- and Fluconazole-resistant mutants arose 24-, 16- and 3-fold more often, respectively, for ΔMSH2 than BG2 (108-106 CFU overnight in YPD, selected on 8XMIC-Containing plates). However, respective minimum inhibitory concentrations (MICS) were not different, nor were rezafungin time-kills.ΔMSH2 was comparable to BG2 in peritonitis and abscess burdens in mouse IAC.ΔMSH2 demonstrated significantly greater caspofungin- and fluconazole-tolerance than BG2 in abscesses. Rezafungin reduced peritonitis and abscess burdens ofΔMSH2,BG2 ANDFKS mutant strains to similar extents. Conclusions: CgMSH2 deletionincreased the frequency of spontaneously-arising echinocandin- and fluconazole-resistant colonies in vitro and tolerance in intra-abdominal abscesses, but it did not attenuate virulence or rezafungin responses during IAC.

Novel amino acid‐stilbene quaternary ammonium salt fluorescent whitening agents: synthesis, optical properties, acid resistance and anti‐bacterial activity

AbstractWith 4,4'‐diaminostilbene‐2,2'‐disulfphonic acid, 2,4,6‐trichloro‐1,3,5‐triazine and N,N‐dimethyldodecylamine as main raw materials, a stilbene quaternary ammonium salt intermediate was synthesised by condensation and quaternisation reaction under the catalysis of sodium hydroxide, and then reacted with two different amino acids to prepare novel amino acid‐stilbene quaternary ammonium salt fluorescent whitening agents. The structures of target compounds were characterized by Fourier Transform–infrared and proton nuclear magnetic resonance spectroscopy. Their photophysical properties, whitening performance and firmness in aqueous solution were assessed by means of ultraviolet absorption spectra, fluorescence emission spectra and a cotton fibre application test. The results showed that the two amino acid‐stilbene quaternary ammonium salt fluorescent whitening agents had a good whitening effect on cotton fibres and displayed strong acid resistance. Compared with the traditional fluorescent whitening agent C186, their firmness was greatly improved. The anti‐bacterial activities against three strains were evaluated in vitro. The results showed that they exhibited significant anti‐bacterial activity against the selected strains, and the respective minimum inhibitory concentration values against Candida albicans and Escherichia coli were 16.8 and 8.16 μg/ml.

Antibiotic resistance and biofilm formation of Acinetobacter baumannii isolated from high-risk effluent water in tertiary hospitals in South Africa

Discharge of drug-resistant, biofilm-forming pathogens from hospital effluent water into municipal wastewater treatment plants poses a public health concern. This study examined the relationship between antibiotic resistance levels and biofilm formation of Acinetobacter baumannii strains isolated from hospital effluents. Antibiotic susceptibility of 71 A. baumannii isolates was evaluated by the Kirby-Bauer disk diffusion method. Minimum inhibitory concentrations (MICs) were determined by the agar dilution method, while the minimum biofilm eradication concentration (MBEC) was determined by the broth dilution method. Genotyping was performed for plasmid DNA. Biofilm formation was evaluated by the microtitre plate method and was quantified using crystal violet. A P-value of <0.05 was regarded as statistically significant in all tests. Extensively drug-resistant (XDR) strains made up 58% of the isolates, while multidrug-resistant (MDR) and pandrug-resistant (PDR) strains made up 50% of the isolates from final effluent. The MBEC of ciprofloxacin increased by 255-fold, while that of ceftazidime was as high as 63-1310-fold compared with their respective MICs. Isolates were classified into four plasmid pattern groups with no association between biofilm formation and plasmid type (P=0.0921). The degree of biofilm formation was independent of the level of antibiotic resistance, although MDR, XDR and PDR isolates produced significant biofilm biomass (P=0.2580). These results suggest that hospital effluent is a potential source of MDR biofilm-forming A. baumannii strains. Appropriate treatment and disposal of effluents are essential to prevent the presence of drug-resistant pathogens in wastewater.

Development of a low-temperature extrusion process for production of GRAS bioactive-polymer loaded compounds for targeting antimicrobial-resistant (AMR) bacteria

Antimicrobial resistance (AMR) is recognised globally as one of the greatest threats to human and animal health; thus, discovery of alternative antibacterial agents to address AMR is a priority challenge. This study constitutes the first report of a low-melting temperature, polymer- extrusion process for the smart delivery of thermally-sensitive antimicrobial bioactives, including generally-regarded-as-safe (GRAS) bioactives derived from various sources. Bioactives were assessed before and after extrusion by determining their respective minimum inhibitory concentrations (MIC). WHO-priority AMR-bacterial isolates causing zoonotic infections were evaluated along with use of standard ATCC strains. Findings revealed that this copolymer method was capable of delivering thermally-sensitive bioactives with varying degrees of growth inhibition against the AMR-bacterial strains. The extrusion process was found to increase the effect of nisin against MRSA (4-fold increase) and L. monocytogenes (6.4-fold increase), silver nitrate (AgNO3) against E. coli (3.6-fold increase) and S. epidermidis (1.25-fold increase), and chitosan against S. aureus (1.25-fold). Findings show the potential applicability of this polymer extrusion process for developing future bioactive-loaded polymer compounds; thus, highlighting the potential of converging bio-based industry with novel materials for enabling ‘One-Health’ solutions.