Evaluation of the effect of Lactobacillus rhamnosus probiotic culture added to yogurt over Staphylococcus aureus, Escherichia coli O157:H7, Listeria monocytogenes and Salmonella enteritidis populations

The effect of different types of probiotics present in yogurt over known populations of Staphylococcus aureus, Escherichia coli O157:H7, Listeria monocytogenes and Salmonella enteritidis was evaluated. The three types of yogurt used were: without added probiotics, with added probiotics (Lactobacillus casei CRL_431 and L. acidophilus CRL_730 CHR HANSEN) and another one with the same probiotics mentioned above and Lactobacillus rhamnosus (LR-35) culture. About 10(9) CFU/ mL of each potentially pathogenic bacteria was added to each type of yogurt tested, and kept in refrigeration at 4 degrees C during its shelf life, about 30 days. Bacterial count was done the initial day and every four days. Results obtained show that there is a difference in the inhibition between yogurts without added probiotics and the commercial yogurt with added probiotics; there is a clear inhibitory effect of the last one over S. aureus, E. coli O157:H7 and Listeria monocytogenes. The yogurt with added probiotics and L. rhamnosus did not show any additional inhibitory effect over the bacteria tested when compared with the yogurt with added probiotics. S. enteritidis could not be evaluated because it was not detectable in any yogurt samples evaluated four days after its inoculation. This study confirms the antagonic effect of probiotic cultures over potentially pathogenic bacteria for human beings and animals that may be present in food. Nevertheless, the use of L. rhamnosus did not produce any additional inhibitory effect.     

Ozone Inactivation of Pseudomonas aeruginosa,Escherichia coli,Shigella sonnei and Salmonella typhimurium in Water.

Based on the properties of ozone as a strong germicidal agent, inactivation kinetics of Pseudomonas aeruginosa, Escherichia coli, Shigella sonnei and Salmonella typhimurium towards ozone in water were studied. The values of 90% inactivation (t₉₀) obtained varied from 0.20 minutes (2.4 mg/L, Escherichia coli ATCC 25922) to 8.33 minutes (0.39 mg/L, Pseudomonas aeruginosa wild strain). First order inactivation kinetics with respect to both the concentrations of ozone and microorganisms were found, resulting an overall second order inactivation kinetics. The ATCC strains showed to be the most sensitive toward ozone among all. Meanwhile, the environmental isolation of Pseudomonas aeruginosa was the most resistant and Escherichia coli the most sensitive wild strain. The longest time required to achieve total inactivation was 35 minutes.     

Presence of Escherichia coli O157:H7, Listeria monocytogenes and Salmonella spp. in food from animal origin in Costa Rica

The presence of Escherichia coli O157:H7, Listeria monocytogenes and Salmonella spp was analyzed in two kinds of food from animal origin in Costa Rica. 100 samples of non pasteurized milk, from the principal producing zones of the country, and 100 samples of chicken giblets, purchased in retail markets, were analyzed according to the methodology described by Food and Drug Administration, 1995. Escherichia coli O157:H7 was analyzed in both kinds of food, while L. monocytogenes was evaluated in raw milk and Salmonella spp. in chicken giblets. Five strains of E. coli O157:H7 were isolated, three of them coming from chicken giblets and the other two from raw milk. 15% positivity for Salmonella spp. was found in chicken giblet samples and 3% positivity for L. monocytogenes in raw milk samples. The results obtained show the importance of the adequate processing of food from animal origin in order to decrease the potential transmission of pathogenic agents. The introduction of Hazard Analysis Critical Control Points system (HACCP) and Good Manufacturing practices in food industry keep on being the principal control measures and inocuity warranty.     

Antimicrobial Activities of LL-37 Fragment Mutant-Poly (Lactic-Co-Glycolic) Acid Conjugate against Staphylococcus aureus,Escherichia coli,and Candida albicans

Various peptides and their derivatives have been reported to exhibit antimicrobial activities. Although these activities have been examined against microorganisms, novel methods have recently emerged for conjugation of the biomaterials to improve their activities. Here, we prepared CKR12-PLGA, in which CKR12 (a mutated fragment of human cathelicidin peptide, LL-37) was conjugated with poly (lactic-co-glycolic) acid (PLGA), and compared the antimicrobial and antifungal activities of the conjugated peptide with those of FK13 (a small fragment of LL-37) and CKR12 alone. The prepared CKR12-PLGA was characterized by dynamic light scattering and measurement of the zeta potential, critical micellar concentration, and antimicrobial activities of the fragments and conjugate. Although CKR12 showed higher antibacterial activities than FK13 against Staphylococcus aureus and Escherichia coli, the antifungal activity of CKR12 was lower than that of FK13. CKR12-PLGA showed higher antibacterial activities against S. aureus and E. coli and higher antifungal activity against Candida albicans compared to those of FK13. Additionally, CKR12-PLGA showed no hemolytic activity in erythrocytes, and scanning and transmission electron microscopy suggested that CKR12-PLGA killed and disrupted the surface structure of microbial cells. Conjugation of antimicrobial peptide fragment analogues was a successful approach for obtaining increased microbial activity with minimized cytotoxicity.     

Preparation,characterization, and antibacterial activity of chitosan/silicone rubber filled zeolite,silver, and copper nanocomposites against Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus

The ongoing emergence of antibiotic-resistant bacteria has become one of the biggest threats to global health and development today. Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA) are important antibiotic-resistant bacteria due to their increasing resistance to a broad array of antimicrobial agents. Herein, we developed a novel antibacterial nanocomposite based on chitosan and liquid silicone rubber filled zeolite-A, Ag, and Cu nanoparticles with remarkable antibacterial activity against P. aeruginosa and MRSA. The antibacterial activity of the nanocomposite was studied by disc diffusion and broth culture methods. Besides, the mechanical properties, wetting behavior, and chemical structure of the present nanocomposite were also investigated. The results exhibited that the inhibition zone diameter of the nanocomposite for P. aeruginosa and MRSA were 40 and 27 mm, respectively. It also took approximately 1 h to inhibit the growth of the tested bacteria. The nanocomposite sample with a thickness of around 1 mm showed an elastic elongation of nearly 49% and a contact angle of roughly 120°. Thus, the present nanocomposite was found to be useful in killing and inhibiting the growth of P. aeruginosa and MRSA, and it could also be qualified as a superior elastic and hydrophobic material.     

Evaluation of the effect of probiotic cultures added to commercial yogurt over a known population of Listeria monocytogenes and Escherichia coli O157:H7

The effect of probiotic cultures over Listeria monocytogenes and Escherichia coli O157:H7 during yogurt storage was evaluated. Two different yogurt brands, one with additional probiotic cultures (Lactobacillus casei and L. acidophilus) were inoculated with known populations (106 UFC/g) of either L. monocytogenes or E. coli O157:H7 in three different times and stored for 32 days at 5 degrees C. Every four days the count of lactic bacteria, the added pathogens and pH was evaluated, according to the methodology described in the Bacteriological Analytical Manual. The pH and lactic bacteria population were constant during the testing period. Yogurt with additional probiotic cultures reduced the population of L. monocytogenes in 8 days, the population of E. coli O157:H7 in 16; yogurt with no additional probiotics took 20 days to reduce L. monocytogenes to non-detectable levels and even after 28 days of storage, E. coli O157:H7 was cultured. In this work, the beneficial effects of additional probiotic cultures in yogurt is confirmed again.     

Insight into the Antibacterial Activity of Selected Metal Nanoparticles and Alterations within the Antioxidant Defence System in Escherichia coli,Bacillus cereus and Staphylococcus epidermidis

The antimicrobial activity of nanoparticles (NPs) is a desirable feature of various products but can become problematic when NPs are released into different ecosystems, potentially endangering living microorganisms. Although there is an abundance of advanced studies on the toxicity and biological activity of NPs on microorganisms, the information regarding their detailed interactions with microbial cells and the induction of oxidative stress remains incomplete. Therefore, this work aimed to develop accurate oxidation stress profiles of Escherichia coli, Bacillus cereus and Staphylococcus epidermidis strains treated with commercial Ag-NPs, Cu-NPs, ZnO-NPs and TiO₂-NPs. The methodology used included the following determinations: toxicological parameters, reactive oxygen species (ROS), antioxidant enzymes and dehydrogenases, reduced glutathione, oxidatively modified proteins and lipid peroxidation. The toxicological studies revealed that E. coli was most sensitive to NPs than B. cereus and S. epidermidis. Moreover, NPs induced the generation of specific ROS in bacterial cells, causing an increase in their concentration, which further resulted in alterations in the activity of the antioxidant defence system and protein oxidation. Significant changes in dehydrogenases activity and elevated lipid peroxidation indicated a negative effect of NPs on bacterial outer layers and respiratory activity. In general, NPs were characterised by very specific nano-bio effects, depending on their physicochemical properties and the species of microorganism.     

Evaluation of the Effects of Ag,Cu, ZnO and TiO2 Nanoparticles on the Expression Level of Oxidative Stress-Related Genes and the Activity of Antioxidant Enzymes in Escherichia coli,Bacillus cereus and Staphylococcus epidermidis

Although the molecular response of bacteria exposed to metal nanoparticles (NPs) is intensively studied, many phenomena related to their survival, metal uptake, gene expression and protein production are not fully understood. Therefore, this work aimed to study Ag-NPs, Cu-NPs, ZnO-NPs and TiO₂-NPs-induced alterations in the expression level of selected oxidative stress-related genes in connection with the activity of antioxidant enzymes: catalase (CAT), peroxidase (PER) and superoxide dismutase (SOD) in Escherichia coli, Bacillus cereus and Staphylococcus epidermidis. The methodology used included: the extraction of total RNA and cDNA synthesis, the preparation of primers for selected housekeeping and oxidative stress genes, RT-qPCR reaction and the measurements of CAT, PER and SOD activities. It was established that the treatment of E. coli and S. epidermidis with NPs resulted mainly in the down-regulation of targeted genes, whilst the up-regulation of genes was confirmed in B. cereus. The greatest differences in the relative expression levels of tested genes occurred in B. cereus and S. epidermidis treated with TiO₂-NPs, while in E. coli, they were observed under ZnO-NPs exposure. The changes found were mostly related to the expression of genes encoding proteins with PER and CAT-like activity. Among NPs, ZnO-NPs and Cu-NPs increased the activity of antioxidants in E. coli and B. cereus. In turn, TiO₂-NPs had a major effect on enzymes activity in S. epidermidis. Considering all of the collected results for tested bacteria, it can be emphasised that the impact of NPs on the antioxidant system functioning was dependent on their type and concentration.     

Interest of Homodialkyl Neamine Derivatives against Resistant P. aeruginosa,E. coli,and β-Lactamases-Producing Bacteria—Effect of Alkyl Chain Length on the Interaction with LPS

Development of novel therapeutics to treat antibiotic-resistant infections, especially those caused by ESKAPE pathogens, is urgent. One of the most critical pathogens is P. aeruginosa, which is able to develop a large number of factors associated with antibiotic resistance, including high level of impermeability. Gram-negative bacteria are protected from the environment by an asymmetric Outer Membrane primarily composed of lipopolysaccharides (LPS) at the outer leaflet and phospholipids in the inner leaflet. Based on a large hemi-synthesis program focusing on amphiphilic aminoglycoside derivatives, we extend the antimicrobial activity of 3′,6-dinonyl neamine and its branched isomer, 3′,6-di(dimethyloctyl) neamine on clinical P. aeruginosa, ESBL, and carbapenemase strains. We also investigated the capacity of 3′,6-homodialkyl neamine derivatives carrying different alkyl chains (C7–C11) to interact with LPS and alter membrane permeability. 3′,6-Dinonyl neamine and its branched isomer, 3′,6-di(dimethyloctyl) neamine showed low MICs on clinical P. aeruginosa, ESBL, and carbapenemase strains with no MIC increase for long-duration incubation. In contrast from what was observed for membrane permeability, length of alkyl chains was critical for the capacity of 3′,6-homodialkyl neamine derivatives to bind to LPS. We demonstrated the high antibacterial potential of the amphiphilic neamine derivatives in the fight against ESKAPE pathogens and pointed out some particular characteristics making the 3′,6-dinonyl- and 3′,6-di(dimethyloctyl)-neamine derivatives the best candidates for further development.