Effect of organic acids on Escherichia coli O157:H7 and Staphylococcus aureus contaminated meat

Combined Effect of Citric Acid and Polyphenol-Rich Grape Seed Extract towards Bioactive Smart Food Packaging Systems

Alginate films (2% w·v^-1) were prepared with varying concentrations (5-20% w/w) of citric acid and aqueous grape seed extract (GSE) filtrate (11.66 ± 1.32 g GAE/L) using the solvent-evaporation method. Crosslinking alginate via ester bonds (FTIR analysis) with citric acid up to 10% (w/w) led to a 33% increase in tensile strength, a 34% reduction in water vapor transmission rate (WVTR), and had no impact on elongation at break. Crosslinking alginate with citric acid in the presence of GSE increased the tensile strength by 17%, decreased WVTR by 21%, and significantly improved DPPH scavenging activity. Moreover, after incubation for 24 h at 37 °C, the film-forming solutions exhibited increased antimicrobial activity, resulting in 0.5- and 2.5-log reductions for Escherichia coli and Staphylococcus aureus, respectively, compared to the values obtained without the addition of GSE. The stronger inhibitory effect observed against Gram-positive bacteria can be attributed to the unique composition and structure of their cell walls, which creates a barrier that restricts the penetration of polyphenols into the cells. The pH adjustment of the GSE film-forming solution from 2.0 to 10.0 shifted the UV/VIS absorption spectra, resulting in a colour change from yellow to red. The findings of this study have showcased the potential of combining GSE and citric acid to enhance the functionality and bioactivity of alginate films for applications in smart food packaging.

Antimicrobial activity and chemical profile of wood vinegar from eucalyptus (Eucalyptus urophylla x Eucalyptus grandis - clone I144) and bamboo (Bambusa vulgaris)

Microbial resistance to drugs is a public health problem; therefore, there is a search for alternatives to replace conventional products with natural agents. One of the potential antimicrobial agents is wood vinegar derived from the carbonization of lignocellulosic raw materials. The objectives of the present work were to evaluate the antibacterial and antifungal action of two kinds of wood vinegar (WV), one of Eucalyptus urograndis wood and another of Bambusa vulgaris biomass, and determine their chemical profile. The antimicrobial effect was assessed against Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella enteritidis, Escherichia coli, Streptococcus agalactiae, and Candida albicans. The minimum inhibitory concentration and the minimum bactericidal and fungicidal concentrations were determined. Micrographs of the microorganisms before and after exposure to both kinds of wood vinegar were obtained by scanning electron microscopy. The chemical profile of the eucalyptus and bamboo vinegar was carried out by gas chromatography and mass spectrometry (GC/MS). Both types of WV presented significant antimicrobial activity, with the bamboo one having a higher efficiency. Both studied pyroligneous extracts seem promising for developing natural antimicrobials due to their efficiency against pathogens. GC/MS analyses demonstrated that the chemical profiles of both kinds of WV were similar but with some significant differences. The major component of the eucalyptus vinegar was furfural (17.2%), while the bamboo WV was phenol (15.3%). Several compounds in both WVs have proven antimicrobial activity, such as acetic acid, furfural, phenol, cresols, guaiacol, and xylenols. Together, they are the major in the chemical composition of the organic fraction of both WVs. Bamboo vinegar had a more expressive content of organic acids. Micrographs of microorganisms taken after exposure to both kinds of wood vinegar displayed several cell modifications. The potential of both types of wood vinegar as a basis for natural antimicrobial products seems feasible due to their proven effect on inhibiting the microorganisms' growth assessed in this experiment.

Effectiveness of the Organic Acid-Based Antimicrobial Agent to Prevent Bacterial Contamination in Fish Meal

Animal feed production is an important step of the food animal production chain in a farm-to-table model. The contamination of raw ingredients with foodborne pathogens in feed production remains as an important safety issue where pathogens may spread into food animals to cause illnesses in humans when affected food animals are consumed. In the present study, we aimed to examine the quality and microbial contamination of fish meal and to investigate the effectiveness of the organic acid-based antimicrobial agent SALTEC 514^TM against Salmonella to prevent bacterial contamination in fish meal. Fish meal samples (n = 4) collected from feed mills at different locations were analyzed for protein and total volatile basic nitrogen (TVBN) content to assess their nutritional value and freshness, and its microbiological quality. The protein and TVBN content ranged from 53.2 ± 3.1 to 67.5 ± 2.3 g/100 g and 73.8 ± 4.5 to 100.4 ± 11.2 mg/100 g meal, respectively. Total plate count of the fish meal samples ranged from 2.0 ± 0.3 to 4.5 ± 0.5 log units, whereas suspected foodborne bacteria, Escherichia coli and Salmonella, were not detected in all samples. Fish meal samples were artificially contaminated (day 0) and re-challenged (day 30 and 90) with Salmonella Enteritidis (3 log CFU/g) to test for the effectiveness of SALTEC 514^TM, an organic acid-based antimicrobial formulation, in preventing Salmonella contamination and recontamination during storage. SALTEC 514^TM, when applied at three different doses, was found to reduce the number of Salmonella in monitored samples after one day of storage. A low dose of 0.5 kg/ton SALTEC 514^TM prevented Salmonella recontamination from occurring in fish meal samples stored for 37 days. In medium (1.0 kg/ton) and high doses (3.0 kg/ton), applications of SALTEC 514^TM prevented the Salmonella recontamination for a maximum storage duration of 97 days. The application of SALTEC 514^TM in fish meal and/or other feed ingredients may prove to be a safe alternative to reduce the microbial load, especially of foodborne-related microorganisms, to contribute to feed and food safety.

Bioactive Metabolites of Lactiplantibacillus plantarum K014 Against Methicillin-Resistant Staphylococcus aureus ATCC43300 and In Vitro Evaluation of Its Antibacterial, Antioxidant and Anti-inflammatory Activities

This study aims to evaluate the effects of bioactive metabolites produced by lactic acid bacteria against methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300. A total of six lactic acid bacteria (LAB) were selected to evaluate the antimicrobial activity against MRSA ATCC 43300, a skin pathogen that is highly resistant to most antibiotics. The K014 isolate from a fermented vegetable recorded the highest inhibition against MRSA ATCC 43300 at 91.93 ± 0.36%. 16S rRNA sequencing revealed the K014 isolate is closely related to L. plantarum and the sequence was subsequently deposited in the GenBank database with an accession number of MW180960, named as Lactiplantibacillus plantarum K014. The cell-free supernatant (CFS) of L. plantarum K014 had tolerance to high temperature as well as acidic pH. The bioactive metabolites, such as hydrogen peroxide, lactic acid and hyaluronic acid, were produced by L. plantarum K014. Result from ABTS assay showed higher antioxidant activity (46.28%) as compared to that obtained by DPPH assay (2.97%). The CFS had showed anti-inflammatory activity for lipoxygenase (LOX) assay at 43.66%. The bioactive metabolites of L. plantarum K014 showed very promising potential to be used topical skin pathogens.

Efficacy of Acidified Oils against Salmonella in Low-Moisture Environments

When processing low-moisture, high-fat foods such as peanut butter and nuts, water-based sanitization is unsuitable due to the immiscible nature of water and fats. Dry sanitization mainly uses flammable compounds such as isopropanol, requiring equipment cooling before application. The use of oils to deliver antimicrobials against foodborne pathogens enables the use of elevated temperatures, thus eliminating processing downtimes associated with dry sanitization. This study delivered organic acids and medium-chain fatty acids (100, 250, and 500 mM) in peanut oil against Salmonella enterica serovar Enteritidis desiccated at 75% relative humidity (RH). Acetic acid in peanut oil (AO) at 45°C was the most effective food-grade acid, causing a 4.4-log reduction in S. Enteritidis at 500 mM. AO caused cellular injury and was effective against a variety of S. Enteritidis strains. Confocal microscopy demonstrated that cells treated with 50 mM and 250 mM AO had significant membrane damage and reduced cellular respiration compared to untreated controls. Treatment efficacy increased with the increase in acid concentration, treatment duration, and treatment temperature from 20 to 45°C. Transmission electron microscopy after treatment with 100 and 250 mM AO revealed membrane ruffling and leakage in cell membranes, especially at 45°C. Reduction of the RH to 33% during desiccation of S. Enteritidis caused a decrease in AO efficacy compared to that at 75% RH, while at a higher RH of 90%, there was an increase in the efficacy of AO. Acidified oils can serve as robust, cost-effective replacements for dry-sanitation methods and improve safety of low moisture foods. IMPORTANCE Currently, dry sanitization products used during food processing often contain flammable compounds which require processing to stop and equipment to cool before application. This leads to processing downtimes and consequently, economic losses. This challenge is compounded by exposure to dryness which frequently renders Salmonella resistant to heat and different antimicrobials. Thus, the development of heat-tolerant oil-based antimicrobial compounds is a novel approach for sanitizing in low-moisture (dry) environments such as those found in peanut butter, tree nuts, and chocolate manufacturing. This study shows that acidified oils, especially acetic acid in peanut oil at elevated temperatures (45°C), was highly effective against desiccated Salmonella. Acidified oils have the potential to replace dry sanitizers, increasing the frequency of sanitization, leading to an improvement in food safety.

Antibacterial activities of indigenous yeasts isolated from pomegranate peels (Punica granatum L.)

Pomegranate peels (PGPs) are known to have the potential as antibacterial not only from their nutrient content but also the microflora. The activities might be caused by the existence of indigenous yeast that can be utilized to inhibit the growth of pathogenic bacteria. This study aims to identify antibacterial and antioxidant activity of indigenous yeast isolated from PGP. The research was conducted by experimental methods and followed by descriptive analysis. The study was done by the isolation of indigenous yeast from PGPs, which was identified using the rRNA sequence analysis of internal transcribed spacer (ITS) region with the primers of ITS1 (5'-TCCGTAGGTGAACCTGCGG-3') and ITS4 (5'-TCCTCCGCTTATTGATATGC-3') and then compared with Basic Local Alignment Search Tools (BLAST) algorithm toward the GenBank. Antibacterial activities of indigenous yeast were tested with agar plug diffusion and time kill test toward Escherichia coli and Staphylococcus aureus. The yeast identification obtained two isolates similar to Hanseniaspora uvarum CBS 314 and two isolates of Pichia kudriavzevii ATCC 6258 which have antibacterial activity against E. coli and S. aureus. P. kudriavzevii PGP D4 have best antimicrobial activities with a strong activity against E. coli (±9 mm) and medium activity against S. aureus (±3.1 mm).

The Authentication and Grading of Edible Bird's Nest by Metabolite, Nutritional, and Mineral Profiling

Edible bird's nest (EBN) produced by Aerodramus fuciphagus has a high demand for nutritional and medicinal application throughout the world. The present study was to evaluate the authentication of a man-made house EBN, which are half cup and stripe-shaped by FTIR. Next, both samples were compared according to their metabolite, nutritional, and mineral composition. The results indicated that the FTIR spectra of both EBN samples were identical and similar to the reference, suggesting the authenticity of the EBN used. The metabolites that contribute to the possible medicinal properties of EBN were found by using GC-MS. The results of the proximate analysis, followed by the standard AOAC method, inferred that both EBN shapes to be rich in crude protein and carbohydrate contents. However, the proximate composition between the half cup and stripe-shaped EBN showed significant differences. Major mineral elements detected were calcium and sodium, and magnesium contents were significantly different between both EBN. Additionally, the half cup and stripe-shaped EBN had a low level of heavy metal content than the maximum regulatory limit as set by the Malaysian Food Act 1983. This study concludes that the nutritional composition varied between the samples and thus suggests that nutrient content should be considered as criteria for the grading requirement of commercialized EBN.

Impact of gas micro-nano-bubbles on the efficacy of commonly used antimicrobials in the food industry

AIM

To study the impact of incorporating micro-nano-bubbles (MNBs) in commonly used food antimicrobials (AMs) against Escherichia coli O157:H7 (EC) and Listeria monocytogenes (LM).

METHODS AND RESULTS

Air, carbon dioxide (CO₂ ) and nitrogen (N₂ ) were used to incorporate MNBs in city water. AM solution (with or without MNBs) of 9 ml was individually taken into sterile test tubes and mixed with 1 ml of inoculum grown in brain heart infusion (BHI) broth to get the net AM concentrations of 28·4 ppm peracetic acid (PAA), 200 ppm chlorine (Cl₂ ), 5·4% citric acid (CA) and 4·5% lactic acid (LA). After treatment time of 1·5 and 3·0 min, 1 ml of sample was neutralized using Dey-Engley neutralizing broth and plated on BHI agar. For EC, Cl₂ -CO₂ solutions resulted in significantly greater log reductions (5·2 logs) compared to that of Cl₂ solutions without MNBs (3·8 logs). For LM, PAA-CO₂ solutions resulted in significantly greater log reductions (4·4 logs) compared to that of PAA solutions without MNBs (1·7 logs).

CONCLUSIONS

This study demonstrated that the efficacy of Cl₂ and PAA AM solutions could be increased by incorporating CO₂ -MNBs against EC and LM in microbiological growth medium.

SIGNIFICANCE AND IMPACT OF THE STUDY

Incorporation of CO₂ -MNBs in AM solutions could increase the efficacy of AMs against pathogens on/in food matrices, which should be tested in future research.

Microbial Profile of the Ventriculum of Honey Bee (Apis mellifera ligustica Spinola, 1806) Fed with Veterinary Drugs, Dietary Supplements and Non-Protein Amino Acids

The effects of veterinary drugs, dietary supplements and non-protein amino acids on the European honey bee (Apis mellifera ligustica Spinola, 1806) ventriculum microbial profile were investigated. Total viable aerobic bacteria, Enterobacteriaceae, staphylococci, Escherichia coli, lactic acid bacteria, Pseudomonas spp., aerobic bacterial endospores and Enterococcus spp. were determined using a culture-based method. Two veterinary drugs (Varromed® and Api-Bioxal®), two commercial dietary supplements (ApiHerb® and ApiGo®) and two non-protein amino acids (GABA and beta-alanine) were administered for one week to honey bee foragers reared in laboratory cages. After one week, E. coli and Staphylococcus spp. were significantly affected by the veterinary drugs (p < 0.001). Furthermore, dietary supplements and non-protein amino acids induced significant changes in Staphylococcus spp., E. coli and Pseudomonas spp. (p < 0.001). In conclusion, the results of this investigation showed that the administration of the veterinary drugs, dietary supplements and non-protein amino acids tested, affected the ventriculum microbiological profile of Apis mellifera ligustica.GABA; beta-alanine; oxalic acid; diet effect; microbiota.

A Combination of Formic Acid and Monolaurin Attenuates Enterotoxigenic Escherichia coli Induced Intestinal Inflammation in Piglets by Inhibiting the NF-κB/MAPK Pathways with Modulation of Gut Microbiota

This study determined the potential of formic acid plus monolaurin (FA + ML) as an alternative to antibiotics in diet when piglets are challenged with ETEC. Piglets fed the FA + ML diet had lower fecal score and rectal temperature after the ETEC challenge. In addition, FA + ML supplementation induced lower plasma TNF-α, IL-6, and IL-1β concentration postchallenge, downregulated the mRNA expression of TNF-α, IL-1β, IL-6, and TLR4 in the ileum and TLR4 and CFTR in the jejunum. Phosphorylation levels of NF-κB p65 and MAPK p38 were reduced in the ileum of piglets fed FA + ML diet. Supplementation of FA + ML increased the relative abundance of genera Lactobacillus especially Lactobacillus amylovorus species and decreased the genus abundances of Actinobacillus, unidentified Enterobacteriaceae, Moraxella. Collectively, the combination of formic acid and monolaurin in diets have the potential to be an antibiotic alternative to mitigate inflammatory response in piglets challenged with ETEC.

Intestinal Clostridium species lower host susceptibility to enterohemorrhagic Escherichia coli O157:H7 infection

Susceptibility to enterohemorrhagic Escherichia coli (EHEC) infection varies among humans. The intestinal microbiota seems to play an essential role in host defense against EHEC; thus, we hypothesized that indigenous bacteria, such as Clostridium ramosum and Clostridium perfringens, could influence the susceptibility to EHEC infection. To evaluate the effect of indigenous bacteria on EHEC infection, germ-free mice were precolonized with each indigenous bacterium, and then infected with EHEC O157:H7. Precolonization with C. ramosum or C. perfringens completely prevented death from EHEC infection througout a test period. Precolonization with C. ramosum also reduced the level of secreted Shiga toxin (Stx) 2 and prevented histopathological changes in the kidneys in a similar way to precolonization with Bifidobacterium longum, which is used as a model for preventing EHEC infection. In contrast, the mice precolonized with C. perfringens showed mild renal injuries. When evaluated using an in vitro co-culturing system, again C. ramosum inhibited the growth and Stx production of EHEC more potently than C. perfringens. These results indicate that C. ramosum and C. perfringens suppressed EHEC infection; however, the extent of their preventive effects differed. Therefore, the susceptibility to EHEC infection and its severity can depend on the functional bacteria present in the intestinal microbiota of individuals.

In Vitro Antimicrobial Activities of Organic Acids and Their Derivatives on Several Species of Gram-Negative and Gram-Positive Bacteria

The objective of this study was to determine the in vitro antimicrobial activity of several organic acids and their derivatives against Gram-positive (G+) and Gram-negative (G-) bacteria. Butyric acid, valeric acid, monopropionin, monobutyrin, monovalerin, monolaurin, sodium formate, and ProPhorce-a mixture of sodium formate and formic acid (40:60 w/v)-were tested at 8 to 16 concentrations from 10 to 50,000 mg/L. The tested bacteria included G- bacteria (Escherichia coli, Salmonella enterica Typhimurium, and Campylobacter jejuni) and G+ bacteria (Enterococcus faecalis, Clostridium perfringens, Streptococcus pneumoniae, and Streptococcus suis). Antimicrobial activity was expressed as minimum inhibitory concentration (MIC) of tested compounds that prevented growth of tested bacteria in treated culture broth. The MICs of butyric acid, valeric acid, and ProPhorce varied among bacterial strains with the lowest MIC of 500-1000 mg/L on two strains of Campylobacter. Sodium formate at highest tested concentrations (20,000 mg/L) did not inhibit the growth of Escherichia coli, Salmonella Typhimurium, and Enterococcus faecalis, but sodium formate inhibited the growth of other tested bacteria with MIC values from 2000 to 18,800 mg/L. The MIC values of monovalerin, monolaurin, and monobutyrin ranged from 2500 to 15,000 mg/L in the majority of bacterial strains. Monopropionin did not inhibit the growth of all tested bacteria, with the exception that the MIC of monopropionin was 11,300 mg/L on Clostridia perfringens. Monolaurin strongly inhibited G+ bacteria, with the MIC value of 10 mg/L against Streptococcus pneumoniae. The MIC tests indicated that organic acids and their derivatives exhibit promising antimicrobial effects in vitro against G- and G+ bacteria that are resistant to antimicrobial drugs. The acid forms had stronger in vitro antimicrobial activities than ester forms, except that the medium chain fatty acid ester monolaurin exhibited strong inhibitory effects on G+ bacteria.

Prevalence of antibiotic-resistant E. coli in broilers challenged with a multi-resistant E. coli strain and received ampicillin, an organic acid-based feed additive or a synbiotic preparation

The aim of this study was to evaluate the effect of ampicillin, an organic acid-based feed additive and a synbiotic preparation on the prevalence of antibiotic-resistant E. coli in the ceca of broilers. A total of 2000 broiler chickens (Ross 708) were randomly assigned to 5 groups with 8 replicates. The negative control group was the only group that was not subjected to avian pathogenic E. coli challenge, while all the other 4 groups received a multi-resistant E. coli strain that was resistant to ampicillin, cephalexin, and nalidixic acid as an oral challenge. The second group served as a challenge control, and the third group received the antibiotic ampicillin via water for 5 d. The fourth group received a feed additive based on organic acids and cinnamaldehyde, and the fifth group received a synbiotic preparation via feed and water. On day 17 and 38 of the trial, cecal samples from 3 birds from each of the 40 pens were obtained, and the E. coli counts and abundances of antibiotic-resistant E. coli were determined. Oral challenge with an avian pathogenic E. coli strain did not influence the performance, and there was no significant difference in growth performance between groups. The total E. coli count was lower (P < 0.05) in the group supplemented with the synbiotic than in the challenge control group on day 38 of the trial. Administration of an antibiotic for 5 d led to a significant increase in the abundance of E. coli strains resistant to ampicillin, amoxicillin-clavulanic acid, cefoxitin, and ceftriaxone. There was no increase in the abundance of antibiotic-resistant E. coli observed in the groups that received feed supplemented with an organic acid/cinnamaldehyde-based feed additive or a synbiotic. Moreover, the effects of the tested feed additives on the prevalence of resistant E. coli are demonstrated by the lower ceftriaxone minimal inhibitory concentration values for this group than for the antibiotic group. Additionally, the synbiotic group exhibited lower ceftriaxone minimal inhibitory concentration values than the antibiotic group.

Nutritional biotransformation in traditional fermented tea (Miang) from north Thailand and its impact on antioxidant and antimicrobial activities

Miang is a traditional fermented tea made from fermentation of Assam tea leaves with mixed microbial culture involving lactic acid bacteria and yeast. Miang has important bioactive benefits such as antioxidant and antimicrobial activity with relevance to health benefits. Miang is categorized into two processes; filamentous fungi growth-based (FFP) and non-filamentous fungi-based (NFP) process, depending on area of production. Further, Miang is also divided into 2 types; astringent Miang and sour Miang, depending on fermentation time. The aim of this research was to determine the important macronutrient biotransformation of Miang diversity under above processes and types and explore the impact on bioactive compounds relevant to antioxidant and antimicrobial activities. During fermentation, pH, total acid, nutritional components, total polyphenols (TP), total tannins (TT), total flavonoids (TF), total catechins (TC), antioxidant activity and antimicrobial activity were evaluated. Miang when fermented for longer sour Miang process compared to shorter time astringent Miang increased crude protein, fiber, and ash contents whereas soluble carbohydrates decreased. Even though TP, TT, TF and TC of sour Miang was lower, the overall antioxidant activity was higher than astringent Miang. This suggests that in addition to the phenolic compounds, other specific phenolics and substances such as biotransformed protein and fat could contribute to antioxidant properties. Additionally, Miang also contains antimicrobial activities against dental caries pathogenic bacteria Streptococcus mutans, gastrointestinal disease causing Vibrio cholerae and Salmonella enterica serovar Typhimurium through likely effects of organic acids and phenolic compounds.

Antiseptic effect of natural teat dip containing lactic acid against mastitis-causing Escherichia coli

Aim:

This study aimed to estimate the enumeration of total bacteria and coliform on teat skin from dairy cows and evaluate the efficacy of the natural rice gel containing 5% v/v lactic acid (NGL) against Escherichia coli standard and field strains isolated from bovine teat skin.

Materials and Methods:

A total of 100 bacterial teat skin samples (25 cows) were collected from dairy cows in smallholder farm. The cows were housed in freestall barns. The colonization of total bacteria and E. coli on teat skin was measured by 3M Petrifilm method. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of lactic acid were evaluated for reference strain of E. coli ATCC 25922 and two field strains of E. coli. The natural teat sanitizer was formulated using 5% NGL with modified rice gel. In vitro antiseptic efficacy of 5% NGL was determined by time-kill kinetic assay. E. coli morphology after exposure with 5% NGL was examined under a scanning electron microscope (SEM).

Results:

The total bacteria and coliform counts from bovine teat skin were 2.11×10⁴ and 1.54×10¹ colony-forming units/ml, respectively. The MIC and MBC of lactic acid on the tested bacteria were 0.5% v/v. The natural teat dip was successfully prepared with minimum change in consistency after 1 year of storage at 4°C. The reduction rate of 5% NGL on E. coli ATCC 25922 and field strain showed 32.77% and 27.58%, respectively. An appearance under SEM of non-viable E. coli after being incubated with 5% NGL clearly showed atypical form and rough surface cell membrane.

Conclusion:

The rice gel containing 5% v/v lactic acid is a promising preparation as a natural teat antiseptic for reducing bacteria on teat skin. It was shown to be effective against E. coli causing bovine mastitis in dairy cows.

Interactions of organic acids with Campylobacter coli from swine

Campylobacter coli is a bacterial species that is a major cause of diarrheal disease worldwide, and Campylobacter spp. are among the top 5 foodborne pathogens in the United States. During food production organic acids (OAs) are often used to remove bacteria from animal carcasses. The interactions of six OAs with 111 C. coli strains obtained from swine and retail pork chops were studied by determining the molar minimum inhibitory concentrations (MICMs) of the C. coli strains, and the pH at the MICMs. The Henderson-Hasselbalch equation was used to calculate the concentrations of the undissociated and dissociated OAs at the MICMs of the C. coli strains. The results for the 111 different C. coli strains obtained from different locations were treated as a single group for each OA since many of the C. coli strains behaved similarly to each different OA. Inhibition of C. coli was not dependent on pH or on the undissociated OA species, but C. coli inhibition correlated with the dissociated OA species. Therefore, if the concentration of the dissociated OAs decreases from optimum, one may then expect that C. coli bacteria would escape disinfection. The concentration of the dissociated OA should be carefully controlled in a carcass wash. We suggest maintaining a concentration of the dissociated acetic, butyric, citric, formic, lactic and propionic acids at 29, 23, 11, 35, 22 and 25 mM, respectively, when using a carcass wash with these OAs to remove C. coli bacteria. However, due to C. coli utilization of acetate, formate, lactate and propionate, these four OAs may not be the best choice to use for a carcass wash to remove C. coli contamination. Of the six OAs, citric acid was the most efficient at inhibiting C. coli.

Influence of ionizing radiation on the antimicrobial activity of the antibiotics sulfamethoxazole and trimethoprim

The response of the antimicrobial compounds sulfamethoxazole (SMX) and trimethoprim (TMP) - individually and in mixtures - to ionizing radiation was investigated using laboratory prepared mixtures and a commercial pharmaceutical formulation. The residual antibacterial activity of the solutions was monitored using Staphylococcus aureus and Escherichia coli test strains. Based on antibacterial activity, SMX was more susceptible to ionizing radiation as compared to TMP. The antibacterial activity of SMX and TMP was completely eliminated at 0.2 kGy and 0.8 kGy, respectively. However, when SMX and TMP were in a mixture, the dose required to eliminate the antibacterial activity was 10 kGy, implying a synergistic antibacterial activity when these are present in mixtures. Only when the antibiotic concentration was below the Minimum Inhibitory Concentration of TMP (i.e., 2 µmol dm^-3) did the antibacterial activity of the SMX and TMP mixture disappear. These results imply that the synergistic antimicrobial activity of antimicrobial compounds in pharmaceutical waste streams is a strong possibility. Therefore, antimicrobial activity assays should be included when evaluating the use of ionizing radiation technology for the remediation of pharmaceutical or municipal waste streams.

Effect of an organic acids based feed additive and enrofloxacin on the prevalence of antibiotic-resistant E. coli in cecum of broilers

Increasing antibiotic resistance is a major public health concern. Fluoroquinolones are used to treat and prevent poultry diseases worldwide. Fluoroquinolone resistance rates are high in their countries of use. The aim of this study was to evaluate the effect of an acids-based feed additive, as well as fluoroquinolone antibiotics, on the prevalence of antibiotic-resistant E. coli. A total of 480 broiler chickens (Ross 308) were randomly assigned to 3 treatments: a control group receiving a basal diet; a group receiving a feed additive (FA) based on formic acid, acetic acid and propionic acid; and an antibiotic enrofloxacin (AB) group given the same diet, but supplemented with enrofloxacin in water. A pooled fecal sample of one-day-old chicks was collected upon arrival at the experimental farm. On d 17 and d 38 of the trial, cecal samples from each of the 8 pens were taken, and the count of E. coli and antibiotic-resistant E. coli was determined.The results of the present study show a high prevalence of antibiotic-resistant E. coli in one-day-old chicks. Supplementation of the diet with FA and treatment of broilers with AB did not have a significant influence on the total number of E. coli in the cecal content on d 17 and d 38 of the trial. Supplementation with FA contributed to better growth performance and to a significant decrease (P ≤ 0.05) in E. coli resistant to ampicillin and tetracycline compared to the control and AB groups, as well as to a decrease (P ≤ 0.05) in sulfamethoxazole and ciprofloxacin-resistant E. coli compared to the AB group. Treatment with AB increased (P ≤ 0.05) the average daily weight compared to the control group and increased (P ≤ 0.05) the number of E. coli resistant to ciprofloxacin, streptomycin, sulfamethoxazole and tetracycline; it also decreased (P ≤ 0.05) the number of E. coli resistant to cefotaxime and extended spectrum beta-lactamase- (ESBL-) producing E. coli in the ceca of broilers.

Effect of organic acids on biofilm formation and quorum signaling of pathogens from fresh fruits and vegetables

Organic acids are known to be used as food preservatives due to their antimicrobial potential. This study evaluated the ability of three organic acids, namely, acetic acid, citric acid and lactic acid to manage E. coli and Salmonella sp. from fresh fruits and vegetables. Effect of these organic acids on biofilm forming ability and anti-quorum potential was also investigated. The effect of organic acids on inactivation of E. coli and Salmonella sp. on the surface of a selected vegetable (cucumber) was determined. The minimum inhibitory concentration of the organic acids were found to be 1.5, 2 and 0.2% in E. coli while it was observed to be 1, 1.5 and 1% in Salmonella sp. for acetic, citric and lactic acids respectively. Maximum inhibition of biofilm formation was recorded at 39.13% with lactic acid in E. coli and a minimum of 22.53% with citric acid in Salmonella sp. EPS production was affected in E. coli with lactic acid showing reduction by 13.42% while citric acid and acetic acid exhibited only 6.25% and 10.89% respectively. Swimming and swarming patterns in E. coli was notably affected by both acetic and lactic acids. Lactic and acetic acids showed higher anti-quorum sensing (QS) potential when compared to citric acid. 2% lactic acid showed a maximum inhibition of violacein production by 37.7%. Organic acids can therefore be used as potential quorum quenching agents in food industry. 2% lactic acid treatment on cucumber demonstrated that it was effective in inactivating E. coli and Salmonella sp. There was 1 log reduction in microbial count over a period of 6 days after the lactic acid treatment. Thus, organic acids can act as effective potential sanitizers in reducing the microbial load associated with fresh fruits and vegetables.

In Vitro Characterization of Lactobacillus plantarum Strains with Inhibitory Activity on Enteropathogens for Use as Potential Animal Probiotics

The present study evaluates the probiotic properties of three Lactobacillus plantarum strains MJM60319, MJM60298, and MJM60399 possessing antimicrobial activity against animal enteric pathogens. The three strains did not show bioamine production, mucinolytic and hemolytic activity and were susceptible to common antibiotics. The L. plantarum strains survived well in the simulated orogastrointestinal transit condition and showed adherence to Caco-2 cells in vitro. The L. plantarum strains showed strong antimicrobial activity against enterotoxigenic Escherichia coli, Shiga toxin-producing E. coli, Salmonella enterica subsp. enterica serovar Typhimurium, Choleraesuis and Gallinarum compared to the commercial probiotic strain Lactobacillus rhamnosus GG. The mechanism of antimicrobial activity of the L. plantarum strains appeared to be by the production of lactic acid. Furthermore, the L. plantarum strains tolerated freeze-drying and maintained higher viability in the presence of cryoprotectants than without cryoprotectants. Finally, the three L. plantarum strains tolerated NaCl up to 8% and maintained >60% growth. These characteristics of the three L. plantarum strains indicate that they could be applied as animal probiotic after appropriate in vivo studies.

Effect of different marinating conditions on the evolution of spoilage microbiota and metabolomic profile of chicken breast fillets

Five different marinades were prepared containing lemon juice, apple cider vinegar, pomegranate juice and combinations of them. Three different temperatures (4, 10, and 20 °C) and five marinating time intervals (1, 3, 6, and 9 h) were tested. Microbial, physicochemical as well as sensory analyses were performed to assess marination. Noticeable microbial reductions and satisfactory sensory results were observed only in samples treated for short time (1 and 3 h). The marinade in which pomegranate and lemon juices were combined caused a decrease in microbial counts and led to desirable sensory attributes. Each of the marinades was characterized by a distinguishable organic acid profile, while the discrimination of the samples, based on organic acid concentration, between low (1 and 3) and high (6 and 9) marinating time was feasible. It can be concluded that marinating time affected the indigenous microbiota and the sensory characteristics of chicken meat while pomegranate could be a promising marinating ingredient from a microbiological and physicochemical perspective.

Antimicrobial activity of the pygidial gland secretion of the troglophilic ground beetle Laemostenus (Pristonychus) punctatus (Dejean, 1828) (Insecta: Coleoptera: Carabidae)

The antimicrobial activity of the pygidial gland secretion released by adult individuals of the troglophilic ground beetle Laemostenus (Pristonychus) punctatus (Dejean, 1828), applying microdilution method with the aim to detect minimal inhibitory concentration, minimal bactericidal concentration and minimal fungicidal concentration, has been investigated. In addition, morphology of the pygidial glands is observed. We have tested 16 laboratory and clinical strains of human pathogens - eight bacterial both gram-positive and gram-negative species and eight fungal species. The pygidial secretion samples have showed antimicrobial properties against all strains of treated bacteria and fungi. Micrococcus flavus proved to be more resistant compared with other bacterial strains. More significant antimicrobial properties of the secretion are observed against Escherichia coli, which proved to be the most sensitive bacteria. Aspergillus fumigatus proved to be the most resistant, while Penicillium ochrochloron and Penicillium verrucosum var. cyclopium the most sensitive micromycetes. Commercial antibiotics Streptomycin and Ampicillin and antimycotics Ketoconazole and Bifonazole, applied as positive controls, showed higher antibacterial properties for all bacterial and fungal strains, except for P. ochrochloron, which proved to be more resistant on Ketoconazole compared with the pygidial gland secretion of L. (P.) punctatus. Apart from the role in ecological aspects, the antimicrobial properties of the tested secretion possibly might have medical significance in the future.

Formic acid and acetic acid induce a programmed cell death in pathogenic Candida species

Cutaneous fungal infections are common and widespread. Antifungal agents used for the treatment of these infections often have undesirable side effects. Furthermore, increased resistance of the microorganisms to the antifungal drugs becomes the growing problem. Accordingly, the search for natural antifungal compounds continues to receive attention. Apoptosis is highly regulated programmed cell death. During yeast cell apoptosis, amino acids and peptides are released and can stimulate regeneration of human epithelium cells. Thus, detection of chemical compounds inducing apoptosis in yeast and nontoxic for humans is of great medical relevance. The aim of this study was to detect chemical compound inducing apoptosis in pathogenic Candida species with the lowest toxicity to the mammalian cells. Five chemical compounds--acetic acid, sodium bicarbonate, potassium carbonate, lithium acetate, and formic acid--were tested for evaluation of antifungal activity on C. albicans, C. guilliermondii, and C. lusitaniae. The results showed that acetic acid and formic acid at the lowest concentrations induced yeast cells death. Apoptosis analysis revealed that cells death was accompanied by activation of caspase. Minimal inhibitory concentrations of potassium carbonate and sodium bicarbonate induced Candida cells necrosis. Toxicity test with mammalian cell cultures showed that formic acid has the lowest effect on the growth of Jurkat and NIH 3T3 cells. In conclusion, our results show that a low concentration of formic acid induces apoptosis-like programmed cell death in the Candida yeast and has a minimal effect on the survivability of mammalian cells, suggesting potential applications in the treatment of these infections.

Staphylococcal biofilm formation as affected by type acidulant

Staphylococcal growth and biofilm formation in culture medium where pH was lowered with weak organic (acetic and lactic) or strong inorganic (hydrochloric) acids were studied. The effects were evaluated by biomass measurements, cell-surface hydrophobicity, scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM). The results demonstrated that the inhibition was related to type of acidulant and pH value. At pH 5.0, the antibacterial effect was more pronounced in the presence of acetic acid (58-60% growth reduction) compared with that in the presence of lactic (7-16% growth reduction) and hydrochloric acids (23-24% reduction). The biofilm biomass of Staphylococcus aureus and Staphylococcus epidermidis was reduced by 92, 85, 63, and 93, 87, 81% after exposition to acetic, lactic, and hydrochloric acids, respectively. Increasing the pH from 5.0 to 6.0 resulted in a noticeable reduction in the effectiveness of acids. A minor cells hydrophobic character was also documented. The SEM and CLSM revealed a poorly structured and thinner biofilm compared with the dense and multilayered control. Acidic environment could have important implications for food-processing system to prevent bacterial colonization and control biofilm formation. The findings of this study lead to consider the rational use of the type of acid to achieve acidic environments.

Inhibition of Listeria monocytogenes by propionic acid-based ingredients in cured deli-style Turkey

Listeria monocytogenes growth can be controlled on ready-to-eat meats through the incorporation of antimicrobial ingredients into the formulation or by postlethality kill steps. However, alternate approaches are needed to provide options that reduce sodium content but maintain protection against pathogen growth in meats after slicing. The objective of this study was to determine the inhibition of L. monocytogenes by propionic acid-based ingredients in high-moisture, cured turkey stored at 4 or 7°C. Six formulations of sliced, cured (120 ppm of NaNO2 ), deli-style turkey were tested, including control without antimicrobials, 3.2% lactate-diacetate blend (LD), 0.4% of a liquid propionate-benzoate-containing ingredient, or 0.3, 0.4, and 0.5% of a liquid propionate-containing ingredient. Products were inoculated with 5 log CFU L. monocytogenes per 100-g package (3 log CFU/ml rinsate), vacuum-sealed, and stored at 4 or 7°C for up to 12 weeks; and populations were enumerated by plating on modified Oxford agar. As expected, the control without antimicrobials supported rapid growth, with >2 log average per ml rinsate increase within 4 weeks of storage at 4°C, whereas growth was observed at 6 weeks for the LD treatment. For both replicate trials, all treatments that contained liquid propionate or propionate-benzoate limited L. monocytogenes growth to an increase of <1 log through 9 weeks storage at 4°C. Sporadic growth (>1-log increase) was observed in individual samples for all propionate-containing treatments at weeks 10, 11, and 12. As expected, L. monocytogenes grew more rapidly when products were stored at 7°C, but trends in relative inhibition were similar to those observed at 4°C. These results verify that propionate-based ingredients inhibit growth of L. monocytogenes on sliced, high-moisture, cured turkey and can be considered as an alternative to reduce sodium-based salts while maintaining food safety.

Fermentation of Propionibacterium acnes, a commensal bacterium in the human skin microbiome, as skin probiotics against methicillin-resistant Staphylococcus aureus

Bacterial interference creates an ecological competition between commensal and pathogenic bacteria. Through fermentation of milk with gut-friendly bacteria, yogurt is an excellent aid to balance the bacteriological ecosystem in the human intestine. Here, we demonstrate that fermentation of glycerol with Propionibacterium acnes (P. acnes), a skin commensal bacterium, can function as a skin probiotic for in vitro and in vivo growth suppression of USA300, the most prevalent community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). We also promote the notion that inappropriate use of antibiotics may eliminate the skin commensals, making it more difficult to fight pathogen infection. This study warrants further investigation to better understand the role of fermentation of skin commensals in infectious disease and the importance of the human skin microbiome in skin health.

Regulation of cell division, biofilm formation, and virulence by FlhC in Escherichia coli O157:H7 grown on meat

To understand the continuous problems that Escherichia coli O157:H7 causes as food pathogen, this study assessed global gene regulation in bacteria growing on meat. Since FlhD/FlhC of E. coli K-12 laboratory strains was previously established as a major control point in transducing signals from the environment to several cellular processes, this study compared the expression pattern of an E. coli O157:H7 parent strain to that of its isogenic flhC mutant. This was done with bacteria that had been grown on meat. Microarray experiments revealed 287 putative targets of FlhC. Real-time PCR was performed as an alternative estimate of transcription and confirmed microarray data for 13 out of 15 genes tested (87%). The confirmed genes are representative of cellular functions, such as central metabolism, cell division, biofilm formation, and pathogenicity. An additional 13 genes from the same cellular functions that had not been hypothesized as being regulated by FlhC by the microarray experiment were tested with real-time PCR and also exhibited higher expression levels in the flhC mutant than in the parent strain. Physiological experiments were performed and confirmed that FlhC reduced the cell division rate, the amount of biofilm biomass, and pathogenicity in a chicken embryo lethality model. Altogether, this study provides valuable insight into the complex regulatory network of the pathogen that enables its survival under various environmental conditions. This information may be used to develop strategies that could be used to reduce the number of cells or pathogenicity of E. coli O157:H7 on meat by interfering with the signal transduction pathways.