Gram-negative Pathogenic Microorganisms Research Articles

SYNERGISM OF ANTIMICROBIAL ACTIVITY OF ANTIBIOTICS WITH BIOCIDES OF NATURAL ORIGIN

Currently, antibiotic therapy remains the primary method for treating infectious diseases in humans. Nevertheless, its effectiveness is rapidly decreasing due to the widespread emergence of resistant pathogens, necessitating the exploration of new treatment options. One potential approach involves the use of antibiotics in combination with other natural compounds. Aim of the review was to summarize the literature data on the synergy of the antimicrobial action of combinations of antibiotics with various biocides against Gram-positive and Gram-negative pathogenic microorganisms. The analysis of literature data has shown that promising compounds for use in combinations with antibiotics include essential oils, other plant components, antimicrobial peptides (both natural and synthetic), and microbial surfactants. In the majority of studies, the researchers calculated the fractional inhibitory concentration index, confirming the synergistic antimicrobial activity of antibiotics and the mentioned compounds. The use of natural biocides in combination with commercial antibiotics, particularly against Gram-negative (including methicillin-resistant) Staphylococcus species and Gram-positive microorganisms (Escherichia coli, Pseudomonas aureginosa, Klebsiella pneumoniae, Proteus mirabilis, Acinetobacter baumannii), enabled to consider these mixtures not only as effective antimicrobial agents but as one of the ways to reduce the effective concentration of antibiotics as well. It should be noted that in the presented studies, the researchers only observed the synergy of antimicrobial activity between a combination of antibiotics and other biocides, without emphasizing the potential mechanisms of interaction between the components of the complex. This likely depended on various factors, including the qualitative composition of natural compounds. Therefore, it was important to continue research not only on the synergy of antimicrobial activity in compound mixtures but also on the underlying mechanisms of their interaction. This would provide insights to enhance their effectiveness in combating resistant microorganisms.

The Mla system and its role in maintaining outer membrane barrier function in Stenotrophomonas maltophilia.

Stenotrophomonas maltophilia are ubiquitous Gram-negative bacteria found in both natural and clinical environments. It is a remarkably adaptable species capable of thriving in various environments, thanks to the plasticity of its genome and a diverse array of genes that encode a wide range of functions. Among these functions, one notable trait is its remarkable ability to resist various antimicrobial agents, primarily through mechanisms that regulate the diffusion across cell membranes. We have investigated the Mla ABC transport system of S. maltophilia, which in other Gram-negative bacteria is known to transport phospholipids across the periplasm and is involved in maintaining outer membrane homeostasis. First, we structurally and functionally characterized the periplasmic substrate-binding protein MlaC, which determines the specificity of this system. The predicted structure of the S. maltophilia MlaC protein revealed a hydrophobic cavity of sufficient size to accommodate the phospholipids commonly found in this species. Moreover, recombinant MlaC produced heterologously demonstrated the ability to bind phospholipids. Gene knockout experiments in S. maltophilia K279a revealed that the Mla system is involved in baseline resistance to antimicrobial and antibiofilm agents, especially those with divalent-cation chelating activity. Co-culture experiments with Pseudomonas aeruginosa also showed a significant contribution of this system to the cooperation between both species in the formation of polymicrobial biofilms. As suggested for other Gram-negative pathogenic microorganisms, this system emerges as an appealing target for potential combined antimicrobial therapies.

Synthesis and characterization of silver nanoparticles loaded with carboplatin as a potential antimicrobial and cancer therapy

In recent studies with silver nanoparticles, it has been reported that the use of nanoparticles in carrier drug systems increases tumor suppression and reduces drug-related side effects. At the same time, the combination of traditional medicine with nanotechnology provides the opportunity to develop new antimicrobial agents. The aim of this study was to determine the anticancer, antimicrobial activities and pro-apoptotic effects of silver nanoparticles (AgNPs), and carboplatin-loaded silver nanoparticles (AgNPs-Car). Characterization studies of the synthesized nanoparticles were carried out by DLS, EDX-STEM, and FTIR analysis. The antiproliferative and pro-apoptotic effects of these molecules were evaluated using XTT and Annexin V, respectively. MIC (Minimum Inhibitory Concentration) test was used to determine the antimicrobial activity. The anticancer activity of the AgNPs-Car was high in MCF-7 (human breast adenocarcinoma), A549 (human lung carcinoma), and C6 (brain glioma) cells. The cell group with the most effective selective cytotoxic activity was C6 cells. It was also shown that AgNPs-Car and AgNPs induced DNA fragmentation eventually increasing apoptosis of cells. The antimicrobial activity of AgNPs and AgNPs-Car was evaluated on Gram-positive and Gram-negative pathogenic microorganisms and yeast fungi. Among the nanomaterials that reached effective MIC values according to reference sources, AgNPs-Car achieved better results. As a result, AgNPs-Car was found to be very successful in targeting C6 glioma cells by facilitating cell entry of the drug. In addition, their anticancer activity on MCF-7 and A549 cells was high and their toxicity was low. Silver nanoparticles are preferred for creating a better drug carrier system because of their qualitative properties and effects. Therefore, it is an interesting field for research on targeting cancer cells and pathogenic microorganisms.

In Vitro Antioxidant and Antimicrobial Properties of Composite Flour Formulations Developed Using Selected Local Grain Varieties.

The aim of this study was to determine the in vitro antioxidant potential of four extruded and domestically prepared composite flour formulations developed by composting selected locally available grain varieties in Sri Lanka. The potential of the flour extracts to scavenge free radicals were evaluated by performing DPPH, ABTS, and FRAP assays. Furthermore, the antimicrobial activities of the flour formulations against selected Gram-positive and Gram-negative pathogenic microorganisms were comparatively evaluated using agar well diffusion and disk diffusion assays. Ethanol and water extracts of the samples were evaluated for their antimicrobial potential. The results showed that extruded samples possessed high antioxidant properties than samples prepared using the conventional cooking. Furthermore, the antioxidant potential of the formulations evaluated using different assays was strongly correlated. Moreover, the formulations reported positive antimicrobial potential against tested Gram-negative and Gram-positive bacteria. The ethanol extracts of flour formulations exhibited higher susceptibility to tested microbes than that of water extracts while agar well diffusion resulted significantly high inhibition against pathogenic bacteria than that of agar disk diffusion method (p < 0.05). In overall, the highest inhibition zone of 17.64 mm was depicted by F4 against Salmonella, while the lowest diameter of 6.09 mm was depicted by F1 against Listeria. In conclusion, the developed flour formulations contained natural antimicrobial agents which can combat common food spoilage and pathogenic bacteria and can be promoted as value-added products with health benefits beyond nutrition.

Antibacterial Properties of Methanolic Leaf Extracts of Melia azedarach L. against Gram-Positive and Gram-Negative Pathogenic Bacteria.

Melia azedarach L., a Meliaceae family tree, is widely used in traditional folkloric medicine for its pharmaceutical properties. In the present study, we investigated the phytochemical composition of four methanolic leaf extracts of M. azedarach of various origins (Algeria and Tunisia) using high-performance liquid chromatography (HPLC). The antibacterial efficacy and mechanisms of action against Gram-positive and Gram-negative pathogenic microorganisms were then evaluated. Our findings revealed a presence of phenolic acids and flavonoids, such as gallic acid, chlorogenic acid, caffeic acid, hyperoside, isoquercetin, quercetin, and isorhamnetin both in Algerian and Tunisian localities, with an abundance of phenolic acids compared to flavonoids. Additionally, the studied extracts exhibit a broad spectrum of antibacterial activities, with MIC values ranging from 31.25 mg/mL to 125 mg/mL. Methanolic leaf extracts of M. azedarach from Algeria exhibited more potent biofilm eradication, with a percentage of inhibition reaching 72.17% against the S. aureus strain. Furthermore, inhibitory concentrations of tested substances, particularly the extract from the Relizane area, were capable of disrupting the membrane integrity of the treated bacteria as well as producing oxidative stress through ROS generation. Likewise, our results reveal that plant extract induces lipid peroxidation by raising MDA levels in comparison to untreated cells, particularly with the plant extract of Blida. M. azedarach extracts also reduced the synthesis of antioxidant enzymes (CAT and SOD). Our findings illustrate that M. azedarach remains a plant with significant antibacterial potential and distinct mechanisms of action that are closely related to the origins of this specimen.

Development of stability, antioxidant, and antimicrobial properties of biopolymeric chitosan modified starch nanocapsules containing essential oil.

Lemon essential oil (LEOs) is used as a bioactive compound with unique health properties as a medicine or dietary supplement. Nevertheless, essential oils are chemical compounds sensitive to light, oxidation, and thermal processes. Therefore, encapsulation technique can be a good way to protect them from degradation and evaporation. In current study, biopolymeric nanocapsules containing lemon essential oils (LEOs) were prepared by the emulsion method. The nanocapsules were characterized by their particle size and Encapsulation efficiency (%) ranged from 339.3 to 553.3 nm and 68.09% to 85.43%, respectively. Long-term storage (30 days) under different temperatures (4 °C, 25 °C, and 40 °C) conditions showed that nanocapsules stored at 4 °C were more stable than samples stored at higher temperatures. DPPH and ABTS free radical scavenging activity were measured to evaluate the values of antioxidant activity of LEOs and nanocapsules. The free LEO and nanocapsules were investigated for its antibacterial activity against common Gram-positive and Gram-negative pathogenic microorganisms (Staphylococcus aureus and Escherichia coli) using disk diffusion followed by the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Our results indicated that the encapsulated LEOs had a significant antioxidant and antibacterial activities, as compared to the free LEO. The LEOs nanocapsules in CS and Hicap can be suggested as an important natural alternative with suitable stability, antioxidant, and antibacterial properties to overcome the challenges associated with the direct application of these bioactive compounds in food.

Bambusa arundinacea leaves extract-derived Ag NPs: evaluation of the photocatalytic, antioxidant, antibacterial, and anticancer activities.

Bio-fabrication has become a safe approach for silver nanoparticles (Ag NPs). The plant-mediated biosynthesized Ag NPs have emerged as a potential substitute for conventional chemical formation.The biosynthesized Ag NPs were analyzed in terms of crystalline nature, morphology, chemical composition, particle size, stability, size, and shape of the particles. The XRD, FTIR, and TEM analysis indicate the presence of the bioactive secondary metabolites compounds.The bamboo-mediated Ag NPs demonstrated a notable antibacterial efficacy against Gram-positive and Gram-negative pathogenic microorganisms and showed significant antioxidant activity against DPPH free radicals. The degradation of methylene blue at various intervals under solar light irradiation was used to evaluate the photocatalytic performance of Ag NPs. Further, Ag NPs conveyed potent anticancer activity against MCF-7 cell lines with a significant value IC50. The bamboo leaves-mediated Ag NPs synthesized Ag NPs signified strong antibacterial, antioxidant, and anticancer activity; hence, it can be used in various biomedical applications and face mask coating to prevent the coronavirus after successful clinical trials in research laboratories.

Characterizing and Developing the Antioxidant and Antimicrobial Properties of the Nano-Encapsulated Bioactive Compounds of Spirulina platensis in Liposome

ABSTRACT This study was done to prepare a nanoliposomal system incorporated with bioactive compounds extracted from microalgae (Spirulina platensis) with chitosan coating (0.5%, 1%, and 1.5% w/v) and to characterize the physicochemical and antimicrobial properties of nanoliposomes. The results show that the mean particle size was in the range of 350.1–702.5 nm with a zeta potential from −64.3 to +30.4 and a polydispersity index (PDI) of 0.22–0.55 in nanoliposomes. The encapsulation efficiency (EE%) values were significantly influenced by chitosan concentration in liposomes. The antioxidant activity of free and nanoliposomal samples was estimated using DPPH, ABTS, and FRAP assay. The antibacterial activity of free extract and nanoliposomes against common Gram-positive and Gram-negative pathogenic microorganisms (Staphylococcus aureus and Escherichia coli) was indicated by MIC and MBC. The results showed that antioxidant and antibacterial activities were significantly increased after encapsulation compared to the free algal extract. Hence, the spirulina extract encapsulated in nanoliposomes can be used as a unique delivery system for natural antioxidant and antimicrobial compounds for direct application in food.

Antimicrobial Activity of Benzimidazoles Derivatives

The anti-microbial action of benzimidazole of ampicillin, was examined in Vitro beneath a specific conditions, utilizing the disc diffusion method, against different gram-positive and gram-negative pathogenic microorganisms such as Bacillus cereus, Staphylococcus aureus Pseudomonas aeruginosa and Escherichia Coli. An arrangement of these compounds were arranged and have appeared to hinder phthogenic development, the range of the zone of restraint. The zone of Obstacles of compounds founds from 7 mm2 to 46 mm2 Among the synthesized compounds in common. 6-Methoxy-N-phenyl- 1H-benzo [d]imidazol-2-amine(1c, zone of inhibition 9 mm2 at 40 µg/ml against Escherichia coli ) and 6-Chloro-N-phenyl-1H-benzo [d]imidazol-2-amine (1d, zone of inhibition 18 mm2 at 40 µg/ml against Bacillus cereus) have appeared great movement. While 1j, zone of inhibition 20 mm2 at 40 µg/ml), and (1i, zone of inhibition 20 mm2 at 40 µg/ml) were found to be displayed directly to great action against Bacillus cereus and Escherichia coli. 1p did not appear any movement against Staphylococcus aureus .1e did not appear any movement against Escherichia Coli and Staphylococcus aureus.The results have shown clearly that the contribution of el ectron -donation and electron- withdrawal to the aromatic ring i ncreases antibacterial activity. Target benzimidazolessamples sho wed antibacterial &amp; reference antibiotic ampicillin in vitro.

Development of an Ionic Liquid@Metal-Based Nanocomposite-Loaded Hierarchical Hydrophobic Surface to the Aluminum Substrate for Antibacterial Properties.

Designing biomaterials and substrates possessing antibacterial properties is a growing field nowadays. In this context, we have developed benzimidazolium ionic liquids ILs-1(a-d)-based metal hybrid nanocomposites using various metals such as silver (Ag), gold (Au), and copper (Cu), which were fully characterized by various techniques. Their morphology, elemental composition, crystallinity, and size were studied by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, powder X-ray diffraction, and dynamic light scattering, respectively. Further, the prepared ionic liquids ILs-1(a-d) and ionic liquid@metal composites were screened for their antibacterial potential against Gram-positive and Gram-negative pathogenic microorganisms via the colony forming unit assay, and their minimum inhibitory concentrations (MICs) were also evaluated. The results obtained from preliminary antibacterial screening demonstrated that these ionic liquid@metal nanocomposites IL-1d@M (M = Ag, Cu, and Au) exhibited potent antibacterial activity in comparison to the ionic liquids ILs-1(a-d). In particular, the ionic liquid@silver nanocomposites (IL-1d@Ag) showed the most potent activity against both E. coli and S. aureus bacterial strains with MIC = 12 ± 2 and 08 ± 2 μg/mL, respectively. The mechanism of action for antibacterial activity of IL-1d@Ag nanocomposites was investigated through generation of 1O2 (ROS), whereas the morphology of treated pathogenic bacteria was examined through atomic force microscopy and SEM. Furthermore, to utilize this developed material IL-1d@Ag in biomedical applications, the prepared ionic liquid material was fabricated onto a microstructured aluminum (Al) substrate with hierarchically arranged functionalities, and the modified surface was characterized and also evaluated for antibacterial activity. Moreover, the hydrophobicity of the material coated onto the Al substrate was also measured by static water contact angle measurement, which reveals its improved hydrophobic character. Thus, the developed hierarchical hydrophobic coating material possessing long-term antibacterial activity on an Al substrate may minimize the wetting by biological secretions and also prevent the substrate from corrosion.

Derivatografic study of the ointment with piroctone olamine for therapy and prevention of seborrheic dermatitis

Пироктон оламин (октопирокс) вместе с выраженным антимикотическим действием обладает широким спектром антибактериальной активности в отношении грам-положительных и грам-отрицательных патогенных микроорганизмов. Октопирокс характеризуется хорошей переносимостью и безвредностью при наружном применении, а также наличием дезодорирующего эффекта. Также перспективным представляется сочетание в рецептуре мази для наружного применения пироктон оламина с нафталаном обессмоленным. Нафталан обессмоленный – натуральное вещество минерального происхождения, обладает десенсибилизирующими, противовоспалительными, обезболивающими, рассасывающими, противозудными, согревающими и антибактериальными свойствами. Сотрудники кафедры технологии лекарств Запорожского государственного медицинского университета на основании комплексных исследований предложили композиционный состав мази с пироктон оламином и нафталаном обессмоленным для топической терапии больных себорейным дерматитом с поражением волосистой части головы. Прогнозируется, что применение разработанного фармакотерапевтического средства будет способствовать нормализации липидной мантии, кератинизации, десквамации, устранению зуда и воспаления пораженных кожных покровов. Цель работы – изучение последствий термообработки комбинационной трихологической мази на гидрофильной основе в интервале температур, сопровождающих технологический процесс производства этой лекарственной формы. Материалы и методы. В качестве объектов дериватографических исследований использовали экспериментальную мазь для местного применения, а также действующие (пироктон оламин, нафталан обессмоленный) и вспомогательные (натрий карбоксиметилцеллюлоза, глицерин, твин 80, пропиленгликоль) вещества этой лекарственной формы. Термогравиметрический анализ проводили с использованием дериватографа «Shimadzu DTG-60» (Япония), снабженного платиново-платинородиевой термопарой. Результаты. Полученные данные термического анализа убедительно свидетельствуют о термической стойкости активных фармацевтических ингредиентов и вспомогательных веществ исследуемой лекарственной формы. На дериватограмах мази с пироктон оламином и ее гидрофильного носителя-плацебо наблюдают совпадение тепловых эффектов с таковыми активно действующего компонента и вспомогательных веществ. Это указывает на отсутствие химического взаимодействия между ними. Выводы. Установлено, что ингредиенты разработанной мягкой лекарственной формы для топической терапии себорейного дерматита с пироктон оламином на гидрофильной основе не взаимодействуют, и потому эта композиция является механической смесью действующих и вспомогательных веществ. Учитывая результаты анализа тепловых эффектов ингредиентов разработанной мази для внешнего применения, целесообразно проведение технологического процесса ее изготовления при температурах, не превышающих 90°С.

Antimicrobial activity of quinine derivatives against human pathogenic bacteria

Nowadays, the antimicrobial resistance is considered as one of the greatest concern facing human health, as many of bacterial strains had become resistant to available antibiotics. The misuse of antibiotics has potentially reduced the efficacy of drugs, concurrent with the increase of bacterial resistance to commercially available drugs. Therefore, the discovery of effective antimicrobial agents are desperately needed to overcome this epidemic, especially from traditional medical plants and their derivatives. Quinine is a natural alkaloid from the bark of the cinchona tree that has been used for years as an antimalarial drug. Various literatures also regarded an antibacterial effect of quinine against both Gram-positive and Gram-negative pathogenic microorganisms. With this vision, a series of some novel quinine derivatives were synthesized and their biological activities against pathogenic bacteria were assessed. This present study therefore attempted to examine the antimicrobial properties of quinine-derived compounds and their Minimal Inhibitory of Concentration (MIC) against common pathogenic bacteria strains, e.g. Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus substillis. Disk diffusion test was performed for screening of antimicrobial activity of quinine derivatives. The results were evaluated and compared with references drug streptomycin. It was found that quinine derivatives showed moderate antimicrobial activity as compared with quinine itself on tested pathogenic bacterial strains. Ester quinine propionate was found to give the highest antibacterial activity among other derivatives, with a range inhibition zone from 9 to 23.5 mm to bacteria strains, compared to streptomycin with a range of inhibition zone from 8 to 12 mm. Further studies are needed to assess the bactericidal mechanisms of those derivative compounds.

INCREASING PERMEABILITY OF OUTER MEMBRANE OF E.COLI UNDER ULTRA-LOW FREQUENCY ALTERNATING MAGNETIC FIELD IN THE PRESENCE OF MAGNETIC NANOPARTICLES

Currently, the bacterial etiology infectious diseases still remain a global health problem. Most of them are caused by gram-negative pathogenic microorganisms. The traditional method of infectious diseases treatment is based on the use of antibiotics. However, the rapid development of the resistance of pathogenic microorganisms to existing antibiotics forces to seek alternatives to traditional therapy. One of such alternatives is the therapy with bacteriophage endolysins - bacteriolytic enzymes capable of destroying the bacterial cell wall by hydrolyzing the peptidoglycan. Endolysins are highly specific for certain pathogens. The main limitation of their use towards gram- negative bacteria is the presence of an outer membrane in the latter preventing the penetration of lytic enzyme to its substrate. The effectiveness of endolysin penetration can be increased by destabilizing the outer membrane of gram-negative bacteria

Antimicrobial Activity of Supernatant of Lactobacillus plantarum against Pathogenic Microorganisms.

We studied ntimicrobial activity of L. plantarum strain against different pathogens: Escherichia coli, Pseudomonas aeruginosa, Streptococcus pyogenes, Staphylococcus aureus. It was shown that supernatant of 48-h L. plantarum culture in liquid nutrient medium exhibits inhibitory activity against gram-positive and gram-negative pathogenic microorganisms. Supernatant of 24-h culture exhibited lower activity, while supernatant of 72-h culture produced no inhibitory effect. Boiling and proteinase K treatment did not affect activity of the preparation, i.e. antimicrobial activity of the supernatant was not associated with protein or peptide component. These data were confirmed by the results observed after ultrafiltration of the preparation: the growth of E. coli, P. aeruginosa, and S. aureus was inhibited by the low-molecular-weight fraction, but not high-molecular-weight fraction of the supernatant. On the other hand, the high-molecular-weight fraction suppressed the growth of streptococcus by 3 times. We hypothesized that L. plantarum supernatant obtained in our experiments contained at least two antimicrobial components with different molecular weights.

Genotypic Characterization of Arcobacter spp. Isolated from Chicken Meat in Brazil.

Arcobacter butzleri, Arcobacter cryaerophilus, and Arcobacter skirrowii are Gram-negative pathogenic microorganisms that cause watery diarrhea and septicemia in humans. The aims of this study were to detect the presence of Arcobacter spp. in chicken meat from butcher shops in São Paulo (Brazil) and to verify their virulence genes and genotypic profiles. A total of 300 chicken cuts were analyzed. The results show the presence of Arcobacter spp. in 18.3% of samples, which were identified as A. butzleri (63.6%) and A. cryaerophilus (36.3%). All strains were positive for the virulence genes ciaB and mviN, followed by cj1349 (98%), pldA (94.4%), cadF (72.7%), tlyA (92.7%), hecA (49%), irgA (47.2%), and hecB (34.5%). These strains were subjected to single-enzyme amplified fragment length polymorphism. Nineteen genotypic profiles were obtained for A. butzleri, and 17 for A. cryaerophilus. These results confirm the presence of virulent strains of A. butzleri and A. cryaerophilus in the chicken meat in Brazil. The presence of potentially virulent strains of Arcobacter highlights a possible public health risk, particularly with respect to ingestion of undercooked foods and cross-contamination from uncooked foods during food preparation and contaminated utensils.

Effect of structure on the interactions between five natural antimicrobial compounds and phospholipids of bacterial cell membrane on model monolayers.

Monolayers composed of bacterial phospholipids were used as model membranes to study interactions of the naturally occurring phenolic compounds 2,5-dihydroxybenzaldehyde and 2-hydroxy-5-methoxybenzaldehyde, and the plant essential oil compounds carvacrol, cinnamaldehyde, and geraniol, previously found to be active against both Gram-positive and Gram-negative pathogenic microorganisms. The lipid monolayers consist of 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DPPE), 1,2-dihexa- decanoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG), and 1,1',2,2'-tetratetradecanoyl cardiolipin (cardiolipin). Surface pressure–area (π-A) and surface potential–area (Δψ-A) isotherms were measured to monitor changes in the thermodynamic and physical properties of the lipid monolayers. Results of the study indicated that the five compounds modified the three lipid monolayer structures by integrating into the monolayer, forming aggregates of antimicrobial –lipid complexes, reducing the packing effectiveness of the lipids, increasing the membrane fluidity, and altering the total dipole moment in the monolayer membrane model. The interactions of the five antimicrobial compounds with bacterial phospholipids depended on both the structure of the antimicrobials and the composition of the monolayers. The observed experimental results provide insight into the mechanism of the molecular interactions between naturally-occurring antimicrobial compounds and phospholipids of the bacterial cell membrane that govern activities.

Effect of temperature, pH and presence of nisin on inactivation of Salmonella Typhimurium and Escherichia coli O157:H7 by pulsed electric fields

The aim of this investigation is to evaluate the concurrent influence of temperature (4–50°C), pH (3.5–7.0), and the presence of nisin (up to 200μg/mL) on the inactivation of two PEF-resistant Gram-negative, pathogenic bacteria, Salmonella Typhimurium STCC 878 and Escherichia coli O157:H7, using a PEF treatment of 30kV/cm and 99μs. A response surface model using a central composite design was developed for the purpose of understanding the individual effects and interactions of these factors.The models showed that temperature was the factor with the greatest influence on the PEF inactivation in the two strains investigated. Increasing the treatment temperature from 4 to 50°C increased the lethality of PEF up to at least 4 Log10 reductions for both microorganisms at all pH levels investigated. PEF lethality varied with the square of the pH observing the highest microbial PEF sensitivity at pH 5.25 at all temperatures. The addition of nisin to the treatment medium did not influence the PEF lethality independently of the temperature.PEF induced 1.0–1.5 Log10 cycles of damaged cells at pH 3.5 for Salmonella Typhimurium STCC 878 and at pH 5.25 for E. coli O157:H7, independently of the temperature or the presence of nisin in the treatment medium.The application of PEF at 50°C permitted the achievement of 5 Log10 reductions of Salmonella Typhimurium STCC 878 and E. coli O157:H7 in a range of pH from 4.2 to 6.7 and from 4.5 to 6.0, respectively. Therefore, the application of PEF at moderate temperatures has great potential for achieving effective control of Gram-negative pathogenic microorganisms in the range of pH found in most foods.

RmtC introduces G1405 methylation in 16S rRNA and confers high-level aminoglycoside resistance on Gram-positive microorganisms

Seven plasmid-mediated 16S rRNA methyltransferases (MTases), RmtA, RmtB, RmtC, RmtD, RmtE, ArmA, and NpmA, conferring aminoglycoside resistance have so far been found in Gram-negative pathogenic microorganisms. In the present study, by performing an RNase protection assay, primer extension, and HPLC, we confirmed that RmtC indeed methylates at the N7 position of nucleotide G1405 in 16S rRNA as found in ArmA and RmtB. RmtC has an MTase activity specific for the bacterial 30S ribosomal subunit consisting of 16S rRNA and several ribosomal proteins, but not for the naked 16S rRNA, as seen in ArmA, RmtB, and NpmA. All seven 16S rRNA MTases have been found exclusively in Gram-negative bacilli to date, and no plasmid-mediated 16S rRNA MTase has been reported in Gram-positive pathogenic microorganisms. Thus, we checked whether or not the RmtC could function in Gram-positive bacilli, and found that RmtC could indeed confer high-level resistance to gentamicin and kanamycin in Bacillus subtilis and Staphylococcus aureus. 16S rRNA MTases seemed to be functional to some extent in any bacterial species, regardless of the provenance of the 16S rRNA MTase gene responsible for aminoglycoside resistance.

Host-Mediated Inflammation Disrupts the Intestinal Microbiota and Promotes the Overgrowth of Enterobacteriaceae

While the normal microbiota has been implicated as a critical defense against invading pathogens, the impact of enteropathogenic infection and host inflammation on intestinal microbial communities has not been elucidated. Using mouse models of Citrobacter rodentium, which closely mimics human diarrheal pathogens inducing host intestinal inflammation, and Campylobacter jejuni infection, as well as chemically and genetically induced models of intestinal inflammation, we demonstrate that host-mediated inflammation in response to an infecting agent, a chemical trigger, or genetic predisposition markedly alters the colonic microbial community. While eliminating a subset of indigenous microbiota, host-mediated inflammation supported the growth of either the resident or introduced aerobic bacteria, particularly of the Enterobacteriaceae family. Further, assault by an enteropathogen and host-mediated inflammation combined to significantly reduce the total numbers of resident colonic bacteria. These findings underscore the importance of intestinal microbial ecosystems in infectious colitis and noninfectious intestinal inflammatory conditions, such as inflammatory bowel disease.

Evaluation of use of a new chromogenic agar in detection of urinary tract pathogens.

CHROMagar Orientation, a new chromogenic medium, was evaluated for the detection and differentiation of gram-positive and gram-negative pathogenic microorganisms in 900 urine samples from hospitalized patients. Performance characteristics of the medium were evaluated in comparison to those of 5% sheep blood and MacConkey agars by direct inoculation of the urine samples on the three media. Four gram-negative and two gram-positive strains as well as one yeast control strain from the American Type Culture Collection were used to ensure quality control. CHROMagar Orientation succeeded in detecting all the urine pathogens that were detected by the reference media, including gram-negative bacilli, staphylococci, streptococci, and yeasts. Colony color and morphology on CHROMagar Orientation accurately differentiated Escherichia coli, Proteus mirabilis, Proteus vulgaris, Pseudomonas aeruginosa, and Acinetobacter spp. Owing to the similarity in the pigmentation produced by Klebsiella, Enterobacter, and Citrobacter isolates, the medium failed to distinguish among them; however, these isolates were easily recognized as coliforms because of their metallic blue coloration. Staphylococci were clearly perceptible: S. aureus and S. epidermidis grow in regular-size colonies that range from opaque white to yellowish, and S. saprophyticus produces opaque pink colonies. All streptococcus strains, including those from groups B and C, were detected. They grow as undifferentiated flat dry diffused colonies, and additional tests were required for identification. Enterococci were easily discriminated by their strong turquoise pigmentation and their typical growth on the agar's surface. Yeast grow in typical creamy wet convex colonies. The accuracy of antibiotic susceptibility determinations according to standard methods was also tested by picking isolates directly from CHROMagar Orientation. The results showed excellent correlation with those obtained with microorganisms picked from reference media. Owing to the ease in differentiating mixed flora on CHROMagar Orientation, antimicrobic susceptibility tests were performed directly from primary isolates in all cases without the need for subcultures.