Antibacterial activities of lactic acid bacteria isolated from cow faeces against potential enteric pathogens

BackgroundThe addition of sub therapeutic doses of antibiotics to cattle feed for growth promotion is a contributory factor to antibiotic resistance, thus an alternative to antibiotics is needed in animal feed additives.ObjectiveTo determine the antimicrobial activity of cow''s intestinal Lactic acid bacteria (LAB) against enteric commensals.MethodEscherichia coli, Klebsiella species (spp) and LAB were isolated from thirty different cow faecal samples and the LAB identified by partial sequencing of 16S rRNA. The antimicrobial activity of the LAB was determined against the test Escherichia coli and Klebsiella spp.ResultsFive species of LAB were isolated from thirty cow faecal samples and identified as Enterococcus hirae (8), Enterococcus durans (6), Enterococcus faecium (1), Enterococcus faecalis (1) and Weissella confusa (1). Viable cells and cell free supernatant (CFS) of the LAB were able to inhibit the growth of the test organisms with the largest zone of inhibition by the viable cells being 26mm against Escherichia coli CB6 produced by Enterococcus hirae CO6A while Weissella confusa CO29M and Enterococcus hirae CO2A produced the largest zones of inhibition (26mm) against Klebsiella CB2.ConclusionThis study shows that LAB from cow faeces possess considerable antimicrobial activity against resistant Escherichia coli from the same environment.     

Antibacterial,antibiofilm, and antiquorum sensing activities of phytosynthesized silver nanoparticles fabricated from Mespilus germanica extract against multidrug resistance of Klebsiella pneumoniae clinical strains

The aim of the present work was to investigate the antibacterial, antibiofilm, and antiquorum sensing activities of phytosynthesized silver nanoparticles (AgNPs) fabricated from Mespilus germanica extract against multidrug-resistant (MDR) Klebsiella pneumoniae strains. Fifty strains of K. pneumoniae were isolated from various clinical specimens. Biofilm-forming strains were identified using Congo red agar and polymerase chain reaction (PCR) techniques. Subsequently, the antibacterial activity of phytosynthesized AgNPs on MDR K. pneumoniae strains was investigated by broth microdilution assay and agar well-diffusion method. Finally (in the last step), the antibiofilm activity of phytosynthesized AgNPs was determined using microtiter plate assay and real-time PCR (RT-PCR) methods for the analysis of type 3 fimbriae (mrkA) and quorum-sensing system (luxS) gene expression. The results of this study showed that the phytosynthesized AgNPs had a spherical nanostructure with the mean size of 17.60 nm. The AgNPs exhibited dose-dependent antibacterial activity. The results of the microtiter plate and RT-PCR methods show that AgNPs inhibited the biofilm formation in MDR K. pneumoniae strains, and the expressions of mrkA and luxS genes were downregulated significantly in MDR strains after treatment with a subminimum inhibitory concentration of AgNPs. In conclusion, AgNPs effectively prevent the formation of biofilms and kill bacteria in established biofilms, which suggests that AgNPs might be a promising candidate for the prevention and treatment of biofilm-related infections caused by MDR K. pneumoniae strains.     

Synthesis of sericin-conjugated silver nanoparticles and their potential antimicrobial activity

Nanoparticles (NPs) are being recognized as antibacterial agents due to their rapidly increasing multidrug resistance in bacterial pathogens. Hence, there is an unmet need to identify the natural antibacterial agent. The present study aimed to evaluate the antibacterial activity of sericin-conjugated silver NPs synthesized by using sericin as a reducing and capping agent. Synthesized NPs were characterized by scanning electron microscope, nanolaser particle size analyzer (BT-90), Fourier-transform infrared analysis, and energy-dispersive X-ray. The biogenic NPs significantly inhibited the growth of Escherichia coli (12–15 mm zone of inhibition), Staphylococcus aureus (14.6–15.4 mm zone of inhibition), and Klebsiella pneumoniae (12.5–18 mm zone of inhibition). The stability of naturally synthesized NPs was examined at various temperatures (i.e., 4°C, 37°C, and 55°C) and pH (i.e., 3, 7, and 11). Temperature variability did not significantly affect the efficacy of NPs. However, NPs performed better at higher pH levels. This study suggested that the sericin-based silver NPs are not only effective against bacteria, but they also maintain the stability at different ranges of temperature and pH. We concluded that the sericin-conjugated silver NPs possess the remarkable antibacterial potential, which suggests their large-scale use as a cheap and stable antimicrobial agent in the future.     

Efflux pump inhibitory activity of biologically synthesized silver nanoparticles against multidrug-resistant Acinetobacter baumannii clinical isolates

This study was carried out to investigate the possible efflux pump inhibitory activity of biologically synthesized silver nanoparticles (AgNPs) against multidrug-resistant (MDR) Acinetobacter baumannii isolates. In this study, the physicochemical characteristics of synthesized AgNPs were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared spectrophotometer (FTIR) methods. Subsequently, MDR A. baumannii isolates were recovered from clinical samples and the phenotypic cartwheel efflux assay and polymerase chain reaction (PCR) were used to elucidate the possible presence of efflux pump in MDR strains. After treatment of MDR strains with sub-minimum inhibitory concentration (MIC) concentration of AgNPs, the expression level of efflux pump genes was evaluated using a quantitative real-time PCR technique. The synthesized AgNPs had a spherical nanostructure, with mean size 38.89 nm, according to SEM and TEM data. XRD and FTIR results confirmed the synthesis of AgNPs. The results of PCR revealed that among 50 strains, 12 A. baumannii strains had efflux pump genes and the expression level of AdeA, AdeC, AdeS, AdeR, AdeI, AdeJ, and AdeK efflux pump genes was downregulated significantly after the treatment with AgNPs. In addition, the inhibitory effect of AgNPs on efflux pumps can be detected when the MIC of ethidium bromide (EtBr) with AgNPs is lower than that of EtBr alone. According to the results, the biologically synthesized AgNPs exhibit efflux pumps inhibitory activity, which may be one of the possible mechanisms of their antibacterial activity against MDR A. baumannii strains.     

具有抗菌功能的聚乳酸基纳米纤维膜的构建及生物学评价

材料表界面改性技术是实现材料性能可控制备,赋予其功能的关键.该研究采用喷纺技术制备了以聚乳酸(PLA)为基体的纳米纺丝可吸收高分子生物膜,并通过等离子体处理技术引入氨基,经过戊二醛将单宁酸接枝至纤维表面,有效提高了PLA膜的亲水性能.利用单宁酸的还原功能将纳米银原位沉积到纳米纤维膜表面,有效提高了纤维膜的抗菌性能.体外...     

Antibacterial effect of silver nanoparticles on Staphylococcus aureus

Antibacterial activity of silver nanoparticles (AgNPs) was investigated using Staphylococcus aureus PTCC1431 as a model of Gram-positive bacteria. The mechanism of antibacterial activity of AgNPs was then studied by analyzing the growth, morphology, and molecular variations in the cell wall. Experimental data showed that AgNPs at a concentration of 4 μg/ml completely inhibited bacterial growth. Transmission electron microscopy results confirmed cell wall damage produced by AgNPs as well as accumulation of AgNPs in the bacterial membrane. Meanwhile, the AgNP-treated bacteria were monitored by circular dichroism to reveal peptidoglycan variations. Some degree of variation in the α-helix position of the peptide chain was observed. Moreover, increasing the AgNP concentration to 8 μg/ml resulted in release of muramic acid (MA) into the medium, which could be attributed to cell wall distraction. A gas chromatography-tandem mass spectrometry analysis and release of MA, as a bacterial indicator, showed that glycan strands may also be decomposed as a result of AgNP treatment.     

Metal nanoparticles and nanoparticle composites are effective against Haemophilus influenzae,Streptococcus pneumoniae,and multidrug-resistant bacteria

BackgroundTreatment for lower respiratory tract infection caused by multidrug-resistant organisms (MDRO) are often limited. This study explored the activity of different metal nanoparticles against several respiratory pathogens including MDROs.MethodsClinical isolates of carbapenem-resistant Acinetobacter baumannii (CRAB), carbapenem-resistant Klebsiella pneumoniae (CRKP), Pseudomonas aeruginosa, Haemophilus influenzae, methicillin-resistant Staphylococcus aureus (MRSA), and Streptococcus pneumoniae were tested for in vitro susceptibilities to various antibiotics and nanoparticles. Minimum inhibitory concentrations (MICs) of silver-nanoparticle (Ag-NP), selenium-nanoparticle (Se-NP), and three composites solutions ND50, NK99, and TPNT1 (contained 5 ppm Ag-NP, 60 ppm ZnO-nanoparticle, and different concentrations of gold-nanoparticle or ClO₂) were determined by broth microdilution method.ResultsFifty isolates of each bacterial species listed above were tested. Ag-NP showed lower MICs to all species than Se-NP. The MIC₅₀s of Ag-NP for CRAB, CRKP, P. aeruginosa, and H. influenzae were <3.125 ppm, 25 ppm, <3.125 ppm, and <3.125 ppm, respectively, while those for S. pneumoniae and MRSA were >50 ppm and 50 ppm. Among CRAB, CRKP and P. aeruginosa, the MIC₅₀s of ND50, NK99, and TPNT1 for CRAB were the lowest (1/8 dilution, 1/8 dilution, and 1/8 dilution, respectively), and those for CRKP (>1/2 dilution, 1/2 dilution, and 1/2 dilution, respectively) were the highest. Both MRSA and S. pneumoniae showed high MIC₅₀s to ND50, NK99, and TPNT1.ConclusionsMetal nanoparticles had good in vitro activity against Gram-negative bacteria. They might be suitable to be prepared as environmental disinfectants or inhaled agents to inhibit the growth of MDR Gram-negative colonizers in the lower respiratory tracts of patients with chronic lung diseases.     

Cationic compounds with activity against multidrug-resistant bacteria: interest of a new compound compared with two older antiseptics,hexamidine and chlorhexidine

Use of antiseptics and disinfectants is essential in infection control practices in hospital and other healthcare settings. In this study, the in vitro activity of a new promising compound, para-guanidinoethylcalix[⁴]arene (Cx1), has been evaluated in comparison with hexamidine (HX) and chlorhexidine (CHX), two older cationic antiseptics. The MICs for 69 clinical isolates comprising methicillin-resistant Staphylococcus aureus, methicillin-sensitive S. aureus, coagulase-negative staphylococci (CoNS) (with or without mecA), vancomycin-resistant enterococci, Enterobacteriaceae producing various β-lactamases and non-fermenting bacilli (Pseudomonas aeruginosa, Acinetobacter baumanii, Stenotrophomonas maltophilia) were determined. Cx1 showed similar activity against S. aureus, CoNS and Enterococcus spp., irrespective of the presence of mecA or van genes, or associated resistance genes, with very good activity against CoNS (MIC <1 mg/L). Variable activities were observed against Enterobacteriaceae; the MICs determined seemed to be dependent both on the genus (MICs of 2, 8 and 64 mg/L for Escherichia coli, Klebsiella pneumoniae and Yersinia enterocolitica, respectively) and on the resistance phenotype production of [Extended Spectrum β-Lactase (ESBLs) or other β-lactamases; overproduction of AmpC]. Poor activity was found against non-fermenting bacilli, irrespective of the resistance phenotype. CHX appeared to be the most active compound against all strains, with broad-spectrum and conserved activity against multidrug-resistant strains. HX showed a lower activity, essentially against Gram-positive strains. Consequently, the differences observed with respect to Cx1 suggest that they are certainly not the consequence of antibiotic resistance phenotypes, but rather the result of membrane composition modifications (e.g. of lipopolysaccharide), or of the presence of (activated) efflux-pumps. These results raise the possibility that Cx1 may be a potent new antibacterial agent of somewhat lower activity but significantly lower toxicity than CHX.     

纳米银的抗菌特性及其在医学中的应用

纳米银是利用现代纳米技术制造的新一代抗菌材料,因其具有优异的抗菌杀菌活性及在伤口修复方面的积极作用,在医学生物学领域获得了广泛应用.目前已有一些纳米银产品应用于临床,如纳米银抗菌凝胶、纳米银敷料、纳米银心血管支架、纳米银导管、纳米银骨水泥等.近年来的研究表明,纳米银的长效、广谱、强效的抗菌活性源于其对微生物复杂而特异的抗菌机制.尽管纳米银不会使病菌产生耐药性,是人们期望中的理想抗菌材料,但研究人员对其毒性机制依然不甚了解.本文就纳米银的合成、抗菌机制、毒性及在医学中的应用做了简要总结和展望.     

Biosynthesis of silver nanoparticles by Nocardiopsis sp.-MW279108 and its antimicrobial activity

The utilization of microorganisms like bacteria in the biological synthesis of silver nanoparticles (AgNPs) has attracted widespread attention due to their ability to synthesize different shape sizes, states, and morphology nanoparticles. In the current study, the green synthesis of AgNPs by Nocardiopsis sp. 16S ribosomal RNA analysis was used to characterize the Nocardiopsis sp. The synthesized AgNPs were characterized through multi-instrument platforms such as transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), UV–Vis spectroscopy, scanning electron microscope (SEM), and X-ray diffraction analysis (XRD). The antimicrobial activity of the synthesized AgNPs was determined by the agar plate diffusion method. The UV-Vis absorbance analysis of the synthesized AgNPs has a significant absorbance at 384 nm, confirming the AgNPs' surface plasmon resonance. The SEM and TEM characterizations indicate that the particle size ranges from 2 to 10 nm and is spherical. Additionally, the FTIR spectra revealed bands from 476 to 3819cm⁻¹, respectively. The XRD planes study pronounced strong bands ranging are between 111 and 311 corresponding to cubic face-center of the silver. Also, the antimicrobial activity of AgNPs indicated the biogenic AgNPs could control the growth of the clinical isolates. The AgNPs produced by Nocardiopsis sp. supernatant could be used in different nanomedicinal applications.     

纳米载银抗菌剂与四针状氧化锌抗白色念珠菌的性能

背景：口腔修复材料室温固化甲基丙烯酸甲酯的表面结构疏松多孔,极易附着各种细菌、微生物导致患者义齿性口炎的发生,所以在甲基丙烯酸甲酯中加入抗菌剂成为国内外学者研究的热点。 目的：比较加入纳米载银抗菌剂与四针状氧化锌抗菌剂后,室温固化甲基丙烯酸甲酯对白色念珠菌的抗菌活性。 方法：采用对倍稀释法测定纳米载银抗菌剂与四针状氧化锌抗菌剂对白色念珠菌的最小杀菌浓度。将纳米磷酸锆载银抗菌粉体与四针状氧化锌抗菌剂分别以0%,1%,2%,3%的质量比加入到室温固化甲基丙烯酸甲酯粉剂中,检测各组试件对白色念珠菌的抗菌率。 结果与结论：纳米载银抗菌剂对白色念珠菌的最小杀菌浓度为 40 g/L,四针状氧化锌抗菌剂对白色念珠菌的最小杀菌浓度为25 g/L。未加入纳米载银抗菌剂或四针状氧化锌抗菌剂的甲基丙烯酸甲酯几乎无抗菌活性,加入两种抗菌剂后其抗菌活性明显增加,随着加入抗菌剂质量比的增加,抗菌活性逐渐增强;当抗菌剂质量比增加到3%时,加入纳米载银抗菌剂的甲基丙烯酸甲酯抗菌率为92.23%,加入四针状氧化锌抗菌剂的甲基丙烯酸甲酯抗菌率为98.23%。表明纳米载银抗菌剂与四针状氧化锌抗菌剂对白色念珠菌均有抗菌效果,且四针状氧化锌抗菌剂比纳米载银系抗菌剂抗菌效果好。     

Synthesis,characterization, and biological activity of cross-linked chitosan biguanidine loaded with silver nanoparticles

Chitosan biguanidine hydrochloride (ChG) and glutaraldehyde cross-linked chitosan biguanidine (CChG) were synthesized and characterized by Fourier transform infrared spectroscopy, ¹H NMR and ¹³C NMR, X-ray diffraction, scanning electron microscopy (SEM) and thermal analyses (TGA and DTA). The results showed that ChG and CChG had a more amorphous structure than that of chitosan, and their thermal stability were slightly lower than that of chitosan. Colloidal silver nanoparticles (AgNPs) were prepared using borohydride reduction method and then investigated as fillers in partially cross-linked chitosan biguanidine. The obtained nanoparticles were uniform and spherical with average size of 9.6 ± 0.5 nm. The prepared CChG/AgNPs composites were characterized for their morphology, thermal properties, cytotoxicity and antimicrobial activity. The SEM images showed that the AgNPs are well imbedded in the CChG matrix. The thermal stability of CChG was improved with incorporation of AgNPs. The CChG and CChG/AgNPs showed less cytotoxicity to breast cancer cells (MCF-7). Compared with chitosan and CChG, the ChG and CChG/AgNPs showed better antimicrobial activity against Streptococcus pneumoniae and Bacillus subtilis as Gram-positive bacteria, Escherichia coli as Gram-negative bacteria and Aspergillus fumigatus, Geotricum candidum and Syncephalastrum recemosum as fungi.     

Immunotoxic effects of gold and silver nanoparticles: Inhibition of mitogen-induced proliferative responses and viability of human and murine lymphocytes in vitro

Understanding the effects of nanoparticles (NP) on immune cell functions is essential in designing safe and effective NP-based in vivo drug delivery systems. The immunomodulatory potential of gold nanoparticles (GNP) and silver nanoparticles (SNP) was investigated in vitro using murine splenic and human peripheral blood lymphocytes (PBL) in terms of effects on viability and mitogen-induced proliferation. Hydrodynamic size and number of NP were characterized using NP tracking analysis (NTA); modal diameters of GNP and SNP were 28 (±1.5) and 66 (±?2.7) nm, respectively, with a unimodal distribution. Lymphocytes were incubated with GNP or SNP in the presence/absence of B- or T-cell mitogens and proliferative responses then determined using [³H]-thymidine incorporation. Concanavalin A (T-cell-specific) and lipopolysaccharide- (B-cell-specific) stimulated responses of murine splenic lymphocytes, as well as phytohemagglutinin (T-cell-specific) and pokeweed mitogen- (B-and T-cell specific) induced responses of human lymphocytes, were significantly inhibited by GNP (25–200?μg/ml) and SNP (12.5–50?μg/ml). However, [³H]-thymidine incorporation by unstimulated lymphocytes was unaffected in the presence of GNP or SNP. Viability of lymphocytes was determined using trypan blue dye exclusion and was significantly inhibited only at 200 μg GNP/ml and 25 or 50?μg SNP/ml. As mitogen responses are most useful to provide supportive mechanistic information on primary immunotoxicologic functional observations, and so far more comprehensive data (in vivo and in vitro) is still needed, the results nevertheless suggest to us that GNP and SNP might potentially be able to modulate immune responses by impacting on lymphocyte activation.     

局部应用唑来膦酸与纳米银对即刻种植骨结合影响的比较

背景:有研究表明局部应用唑来膦酸和局部应用纳米银都可促进骨形成,但两者效果的差异尚未见研究报道。目的:观察局部应用唑来膦酸和局部应用纳米银对兔拔牙窝即刻种植钛螺纹钉骨结合的影响差异。方法:将24只新西兰大白兔随机分为唑来膦酸和纳米银组,每组12只,在拔除兔上下颌4个切牙后,分别在2组的拔牙窝内填唑来膦酸-纳米羟基磷灰石复合物和纳米银-纳米羟基磷灰石混合物,并均同期植入钛螺纹钉。术后4,8,12周取兔上、下颌骨离体标本,通过一般形态观察、扭矩测试、骨密度检测及组织形态学观察。实验于2015年12月经河北医科大学第三医院医学伦理委员会批准(批准号:Z2015-021-1)。结果与结论:①扭矩力学实验测试结果显示,两组钛钉扭矩峰值的平均值随着时间延长而增加(扭矩峰值平均值数值),均在12周时达到最大(扭矩峰值平均值数值),术后4,8,12周,唑来膦酸组钛螺纹钉扭矩峰值平均值均略高于同期纳米银组,唑来膦酸组钛螺纹钉稳定性略优于纳米银组,但差异无显著性意义(P>0.05);②一般形态和组织学观察发现,术后4,8,12周唑来膦酸组种植体周围骨硬度和结构均明显优于同期纳米银组;③骨密度分析结果显示,术后4,8,12周,唑来膦酸组钛螺纹钉周围骨组织灰度值略高于同期纳米银组,但差异无显著性意义(P>0.05);④结果证实,从植入材料对影响种植体周围骨替代材料成骨的效果来看,用唑来膦酸纳米羟基磷灰石复合物进行即刻种植骨结合的效果略优于纳米银与纳米羟基磷灰石混合植骨。     

Biosynthesis of silver nanoparticles using actinomycetes,phytotoxicity on rice seeds,and potential application in the biocontrol of phytopathogens

To find effective silver nanoparticles (AgNPs) for control of phytopathogens, in this study, two strains of actinomycetes isolated from the soil of the Brazilian biome Caatinga (Caat5–35) and from mangrove sediment (Canv1–58) were utilized. The strains were identified by using the 16S rRNA gene sequencing as Streptomyces sp., related to Streptomyces mimosus species. The obtained AgNPs were coded as AgNPs ₃₅ and AgNPs₅₈ and characterized by size and morphology using dynamic light scattering, zeta potential, transmission electron microscopy, and Fourier transformed infrared (FTIR). The antifungal activity of the AgNPs₃₅ and AgNPs₅₈ was evaluated in vitro by the minimal inhibitory concentration (MIC) assay on the phytopathogens, Alternaria solani, Alternaria alternata, and Colletotrichum gloeosporioides. The phytotoxic effect was evaluated by the germination rate and seedling growth of rice (Oryza sativa). AgNPs₃₅ and AgNPs₅₈ showed surface plasmon resonance and average sizes of 30 and 60 nm, respectively. Both AgNPs presented spherical shape and the FTIR analysis confirmed the presence of functional groups such as free amines and hydroxyls of biomolecules bounded to the external layer of the nanoparticles. Both AgNPs inhibited the growth of the three phytopathogens tested, and A. alternate was the most sensible (MIC ≤ 4 µM). Moreover, the AgNPs₃₅ and AgNPs₅₈ did not induce phytotoxic effects on the germination and development of rice seedlings. In conclusion, these AgNPs are promising candidates to biocontrol of these phytopathogens without endangering rice plants.     

The effects of titania nanotubes with embedded silver oxide nanoparticles on bacteria and osteoblasts

A versatile strategy to endow biomaterials with long-term antibacterial ability without compromising the cytocompatibility is highly desirable to combat biomaterial related infection. TiO₂ nanotube (NT) arrays can significantly enhance the functions of many cell types including osteoblasts thus having promising applications in orthopedics, orthodontics, as well as other biomedical fields. In this study, TiO₂ NT arrays with Ag₂O nanoparticle embedded in the nanotube wall (NT-Ag₂O arrays) are prepared on titanium (Ti) by TiAg magnetron sputtering and anodization. Well-defined NT arrays containing Ag concentrations in a wide range from 0 to 15 at % are formed. Ag incorporation has little influence on the NT diameter, but significantly decreases the tube length. Crystallized Ag₂O nanoparticles with diameters ranging from 5 nm to 20 nm are embedded in the amorphous TiO₂ nanotube wall and this unique structure leads to controlled release of Ag⁺ that generates adequate antibacterial activity without showing cytotoxicity. The NT-Ag₂O arrays can effectively kill Escherichia coli and Staphylococcus aureus even after immersion for 28 days, demonstrating the long lasting antibacterial ability. Furthermore, the NT-Ag₂O arrays have no appreciable influence on the osteoblast viability, proliferation, and differentiation compared to the Ag free TiO₂ NT arrays. Ag incorporation even shows some favorable effects on promoting cell spreading. The technique reported here is a versatile approach to develop biomedical coatings with different functions.     

Eucalyptus citriodora leaf extract‐mediated biosynthesis of silver nanoparticles: broad antimicrobial spectrum and mechanisms of action against hospital‐acquired pathogens

Pathogen resistance to conventional antibiotics has become a serious clinical and public health problem, making the development of an alternative mean a very urgent issue. Recently, biosynthesis of silver nanoparticles (AgNPs) was successfully accomplished in the presence of Eucalyptus citriodora leaf extract as a reducing agent. In this study, the antimicrobial mechanisms of AgNPs against important hospital‐acquired pathogens, including Gram‐positive, Gram‐negative bacteria, and fungi were further assessed. The results indicated that AgNPs could enhance a broad antimicrobial spectrum against drug‐resistant organisms, with a range of minimum inhibitory concentration from 0.02 to 0.36 μg/mL. Time‐kill assay showed that AgNPs produced bactericidal effects on the microorganisms. AgNPs could significantly reduce biofilm production in pathogens without affecting growth of the pathogens (p < 0.05). AgNPs inhibited cell viability and biofilm formation in a dose‐dependent manner. Cell membrane damage in microorganisms resulting from effects of AgNPs was observed. A significant increase in per cent uptake of crystal violet was observed in all isolates treated with AgNPs when compared with the control (p < 0.05). Upon treatment with AgNPs, the surface charge of the reference strains and clinical isolates of pathogens moved towards neutral. The alteration of surface potential after exposure to AgNPs could contribute to membrane disruption and cell viability. Scanning electron microscopy further confirmed morphological cell changes and disrupted the cell membrane. Increasing resistance to AgNPs was not induced by stepwise isolation of the bacteria after 45 passages on Luria‐Bertani agar supplemented with AgNPs. Furthermore, AgNPs was not toxic to red blood cells.     

Study of some of the mechanisms involved in the prevention against Salmonella enteritidis serovar Typhimurium infection by lactic acid bacteria

The possible mechanism exerted by different lactic acid bacteria (LAB) in the protection against Salmonella enteritidis serovar Typhimurium (S. typhimurium) infection was determined. LAB was administered to BALB/c mice, and the animals were subsequently challenged with S. typhimurium. The inhibition of the translocation of S. typhimurium in the liver was correlated with a decrease in cellular apoptosis determined in slices from the small intestine of mice. The microbiocidal activity of peritoneal macrophages was increased by Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, but not for the probiotic strain L. casei CRL 431. The levels of IFNγ and Bcl-2 positive cells in the small intestine of mice fed with the LAB were also determined by immunofluorescence. Using in vivo studies, we demonstrated that the biological and immune mechanisms induced by the LAB studied were different for each bacterium and were mediated by anti-S. typhimurium S-IgA microbiocidal activity and/or cellular apoptosis inhibition of infected immune cells.     

Protective ability of certain lactic acid bacteria against an infection with Candida albicans in a mouse immunosuppression model by corticoid

The protective effect of Lactobacillus casei, L. acidophilus, L. delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus administered orally against an infection with Candida albicans in a corticoid immunosuppression model was studied. Balb/c mice were infected intraperitoneally with C. albicans (5 × 10⁷ cells/mouse) on the third day post‐corticoid inoculation. At 24 h after infection, 1.2 × 10⁹ cells/day/mouse of the bacteria under study were administered orally to the test animals for 2 days. The number of C. albicans colony‐forming units in liver, spleen and kidney was determined at 4–5 day intervals for 17 days. During the same period, the influence of the oral administration of the above bacteria on the immune response of non‐infected corticoid‐treated mice was also studied. The phagocytic capacity of peritoneal macrophages was determined by in vitro assays, the humoral immune response by the number of plaque‐forming cells and T‐lymphocyte activity by the delayed hypersensitivity response for sheep red blood cell antigen. Oral administration of L. casei and L. bulgaricus in corticoid‐immunosuppressed animals was demonstrated to give protection against C. albicans infection. This was due to a significant increase in the specific and non‐specific immune response, which reached higher values than the non‐immunosuppressed controls. L. acidophilus proved to be less effective at protection, although it reverts corticoid immunosuppression, reaching values similar to those of the normal controls. S. thermophilus was ineffective for protection, and it did not favour enhancement of the immune response, which was only slightly higher than that of the suppression controls. The authors believe that the oral administration of certain lactic acid bacteria may be extremely useful as support therapy for the control of infections produced by opportunistic microorganisms. It could affect the immunosuppression that occurs in tumour processes or other immunodeficiencies but never in autoimmune pathological events.