A novel bacteriocin against Staphylococcus aureus from Lactobacillus paracasei isolated from Yunnan traditional fermented yogurt: Purification,antibacterial characterization,and antibiofilm activity

Staphylococcus aureus and its biofilm have emerged as a significant threat to the safety of dairy products. In recent years, lactic acid bacteria (LAB) bacteriocins have been widely acknowledged as the potential natural antibacterial substance in food biopreservation due to their excellent antibacterial effects. However, few LAB bacteriocins with antibacterial and antibiofilm activity against S. aureus have been reported in dairy products. In the present study, a novel bacteriocin LSX01 of Lactobacillus paracasei LS-6 isolated from a traditional fermented yogurt produced in Yunnan, China, was purified and characterized extensively. The LSX01 possessed a molecular weight of 967.49 Da and an AA sequence of LDQAGISYT. The minimum inhibitory concentration of LSX01 against S. aureus_45 was 16.90 μg/mL, which was close to or lower than the previously reported bacteriocins. The LSX01 exhibited an extensive antimicrobial spectrum against both gram-positive and gram-negative bacteria. Moreover, LSX01 exhibited excellent tolerance to heat and acid-base treatments, and sensitivity to the proteolytic enzymes, such as pepsin and proteinase K. Furthermore, the treatment of S. aureus_45 planktonic cells with LSX01 significantly reduced their metabolic activity and disrupted the cell membrane integrity. Scan electron microscopy results demonstrated that LSX01 induced cytoplasmic content leakage and cell deformation. Additionally, biofilm formation of S. aureus_45 was also significantly inhibited by LSX01. Overall, the results suggested that the novel LAB bacteriocin LSX01 possessed antibacterial activity and antibiofilm activity against S. aureus and, hence, could have potential for improving safety of dairy products.     

Bactericidal and antibiofilm properties of Rumex japonicus Houtt. on multidrug-resistant Staphylococcus aureus isolated from milk

Multidrug-resistant (MDR) Staphylococcus aureus and its biofilm formation have been challenging to control in milk and dairy industries. Biofilms formed by Staph. aureus may result in the failure of antibacterial agents and disinfectants to penetrate the biofilm in an attempt to control contamination. Novel natural antibacterial agents are required to combat MDR bacteria and biofilms. In this study, we evaluated the bactericidal, antibiofilm, and antimotility effects of Rumex japonicus Houtt. (RJH) extract on MDR Staph. aureus isolated from milk. The RJH extract exhibited good antibacterial activity against MDR strains with minimum inhibitory concentrations (MIC) ranging from 0.78 to 6.25 mg/mL and minimum bactericidal concentrations ranging from 3.125 to 12.5 mg/mL. The extract showed strong inhibition of biofilm formation (81.9%) at sub-MIC value and eradication of biofilm at higher concentrations. The motility of Staph. aureus was effectively blocked by the extract. Major compounds emodin, chrysophanol, and physcion were identified in RJH extract using HPLC-linear trap quadrupole (LTQ)/Orbitrap-mass spectrometry. The extract was nontoxic to human epithelial cell lines such as Caco-2 and HT-29 cell lines at concentrations ranging from 0.1 to 0.5 mg/mL, and from 0.1 to 0.75 mg/mL, respectively. These findings suggest that RJH extract could be an alternative to synthetic preservatives in milk and dairy products.     

Purification,characterization, and mode of action of a novel bacteriocin BM173 from Lactobacillus crustorum MN047 and its effect on biofilm formation of Escherichia coli and Staphylococcus aureus

There is an increasing demand for dairy products, but the presence of food-spoilage bacteria seriously affects the development of the dairy industry. Bacteriocins are considered to be a potential antibacterial or antibiofilm agent that can be applied as a preservative. In this study, bacteriocin BM173 was successfully expressed in the Escherichia coli expression system and purified by a 2-step method. Furthermore, it exhibited a broad-spectrum antibacterial activity, high thermal stability (121°C, 20 min), and broad pH stability (pH 3–11). Moreover, the minimum inhibitory concentration values of BM173 against E. coli ATCC 25922 and Staphylococcus aureus ATCC 25923 were 14.8 μg/mL and 29.6 μg/mL, respectively. Growth and time-kill curves showed that BM173 exhibited antibacterial and bactericidal activity. The results of scanning electron microscopy and transmission electron microscopy demonstrated that BM173 increased membrane permeability, facilitated pore formation, and even promoted cell lysis. The disruption of cell membrane integrity was further verified by propidium iodide uptake and lactic dehydrogenase release. In addition, BM173 exhibited high efficiency in inhibiting biofilm formation. Therefore, BM173 has promising potential as a preservative used in the dairy industry.     

Study on antibacterial properties and major bioactive constituents of Chinese water chestnut (Eleocharis dulcis) peels extracts/fractions

Recently, considerable attention has been paid to the biologically active of fruit and vegetable processing wastes. In this study, antibacterial properties and major bioactive constituents of Chinese water chestnut peels (CWCP) extracts and fractions were evaluated. The data displayed that ethyl acetate fractions (EF) from CWCP showed greater antibacterial activity than n-butanol fractions, methanol extracts and water fractions against three common foodborne pathogenic bacteria (Staphylococcus aureus, Escherichia coli and Listeria monocytogenes) assessed by the inhibition zone, minimal inhibition concentration and minimal bactericidal concentration values. In accordance with disc diffusion assay, S. aureus was more susceptible to EF than the other two pathogens. Furthermore, action-mode studies indicated that EF exhibited significant bactericidal activity against S. aureus by degrading and disrupting the cell wall and cytoplasmic membrane, ultimately the leakage of cell contents led to cell death. Finally, high-performance liquid chromatography coupled with photodiode array and electrospray ionization mass spectrometry was used for characterization of bioactive constituents in EF, and ten flavonoids aglycons were identified or tentatively identified. The results suggest that the extracts and fractions from CWCP could be potentially used as a possible food supplement to improve food safety by the control or elimination of foodborne pathogenic bacteria.     

Influence of alanine uptake on Staphylococcus aureus surface charge and its susceptibility to two cationic antibacterial agents,nisin and low molecular weight chitosan

Low molecular weight chitosan (LMWC) and nisin, recognized as cationic antibacterial agents (CAAs), inhibit bacterial growth by interacting with the anionically charged cell wall. In this study, alanine uptake significantly reduced the anionic cell surface charge, as determined by the zeta potential (ZP) measurements, of Staphylococcus aureus, resulting from the incorporation of d-alanine into the cell wall. Minimum inhibitory concentration (MIC) tests and growth inhibition curves revealed that LMWC and nisin possessed inverse antibacterial activity against three strains of S. aureus, depending on the strains’ net charge. A twofold reduction in the MIC value of nisin was obtained against S. aureus, inoculated in a 1.0% d- or l-alanine-augmented trypticase soy broth medium. A flocculation test demonstrated that neutralizing the anionic surface charge using d-alanine reduced the adsorption of S. aureus onto LMWC. Furthermore, the reduced surface net charge could enhance the colonization capacity of S. aureus on glass.     

Phytochemicals of ethanolic extract and essential oil of Persicaria hydropiper and their potential as antibacterial agents for food packaging polylactic acid film

This study aims to determine phytochemicals and antibacterial activity of ethanolic extract and essential oil of Persicaria hydropiper, and their potential as antibacterial agents in polylactic acid (PLA) film. The yield of ethanolic extract and essential oil were 11.02 and 0.70%, respectively. Chlorogenic acid, ferulic acid, rutin, myricetin and quercetin were detected as major components in the P. hydropiper ethanolic extract, while dodecanal, caryophyllene, caryophyllene oxide, decanal, α‐caryophyllene, citronellol, heptadecanal, linalool and phytol were detected in the P. hydropiper essential oil. Based on the disc diffusion assay, both ethanolic extract and essential oil of P. hydropiper possessed antibacterial activity against bacteria Staphylococcus aureus only at different concentrations, with minimum inhibitory concentration values: 0.625 and 5 mg/ml, respectively; and minimum bactericidal concentration values: 5 and 40 mg/ml, respectively. However, they found to show antibacterial activity against three bacteria S. aureus, Escherichia coli and Salmonella Typhimurium at different concentrations and time using time‐kill kinetics assay. Incorporation of ethanolic extract and essential oil in PLA film also exhibited an antibacterial effect against S. aureus. Our findings confirmed the potential use of both P. hydropiper ethanolic extract and essential oil as antibacterial agents in biodegradable PLA film.     

Antimicrobial activity and mechanism of PLA/TP composite nanofibrous films

Electrospinning is conducted with polylactic acid (PLA) and tea polypheno (TP) to obtain PLA/TP composite nanofibrous films with high antimicrobial activity. An investigation of the composition, antimicrobial activity, and mechanism of these composite nanofibrous films was conducted by using infrared spectroscopy (FT-IR), inhibition zone method, fluorescence activated cell sorter (FACS), and transmission electron microscope (TEM). IR spectra results showed that TP and PLA composited well through valence bonds in PLA/TP composite nanofibrous films. Ranges of the inhibition zone for the growth of Escherichia coli (E. coli) and Staphylococcus (Staphylococcus aureus) were 3.67 and 3.71?cm in pure PLA nanofibrous films, but 5.17 and 5.67?cm in PLA/TP composite nanofibrous films, respectively. Results indicated that the antimicrobial activity of PLA/TP composite nanofibrous films were much higher than that of pure PLA nanofibrous films. Meanwhile, the antimicrobial activity against S. aureus was also slightly higher than E. coli. FACS results showed that the positive rate of PLA/TP composite nanofiber films was greater than that of pure PLA nanofibrous films, increasing from 1.45 and 0.78% to 9.26 and 6.47% against S. aureus and E. coli, respectively. The result of TEM indicated that PLA/TP composite nanofibrous films led to the death of bacteria by destroying the integrity of cell membrane.     

Nanoencapsulation and immobilization of cinnamaldehyde for developing antimicrobial food packaging material

Use of antimicrobial coatings on food packaging is one of the important technologies of active packaging for improving food safety. There is growing demand for natural antimicrobials because of fear of adverse health effects of synthetic preservatives. The objectives of this study were to compare antibacterial properties of free and nanoencapsulated cinnamaldehyde in solution; polylactic acid (PLA) surfaces cast with cinnamaldehyde; and glass and PLA surfaces coated with cinnamaldehyde nano-liposomes. Cinnamaldehyde was nano-encapsulated by lipid bilayers of polydiacetylene – N-hydroxysuccinimide (PDA–NHS) nano liposomes and immobilized on glass slides and PLA films. Glass surfaces immobilized with nano-encapsulated cinnamaldehyde showed significant antibacterial activity against Escherichia coli W1485 and Bacillus cereus ATCC 14579, with reductions of 2.56 log₁₀ CFU/ml and 1.59 log₁₀ CFU/ml respectively in 48 h. PLA films cast with cinnamaldehyde also showed significant antibacterial activities against E. coli W1485 (2.01 log₁₀ CFU/ml reduction) and B. cereus (4.81 log₁₀ CFU/ml reduction). However, when the liposomal encapsulated cinnamaldehyde was immobilized on PLA films, it did not show any antibacterial activity. Glass surfaces coated with nano-encapsulated cinnamaldehyde may be used as an active packaging material in preserving liquid foods; however, further study is required to improve antimicrobial activities of PLA surfaces.     

Disruption of Staphylococcus aureus biofilms using rhamnolipid biosurfactants

Staphylococcus aureus is an important pathogen that has shown ability to establish biofilm communities that can represent a source of contamination and resistance in food processing. Rhamnolipids (RL) have attracted attention as candidates to replace synthetic surfactants, exhibiting high surface activity combined with its microbial origin, biodegradability, and low toxicity. In this work, an RL biosurfactant was evaluated regarding its ability to disrupt or remove S. aureus biofilms established on polystyrene plates using nutrient broth and skim milk as the growth media. Rhamnolipid treatment was performed at different surfactant concentrations and temperatures. Rhamnolipid removes up to 88.9% of milk-based biofilms, whereas for nutrient medium 35% removal was attained. The RL concentration affects the disruption of nutrient medium-based biofilms. High carbohydrate content of milk-based biofilms favors disruption by RL and the organization of RL molecules in solution showed a predominance of aggregates from 1 to 10 and 100 to 1,000 nm in all conditions studied. Biofilm disruption activity of RL is nutrient-specific and dependent on biofilm matrix composition. Staphylococcus aureus biofilms established in milk were significantly reduced using RL at low concentrations and temperatures. These findings suggest potential application of RL in milk (dairy) processing industries where low temperatures are applied.     

Comparison of the antimicrobial and antioxidant activities of selected wheat varieties

Antibacterial and antioxidant activities of wheat seed ethyl acetate extracts for Jokyoung (JK), Dark northern spring (DNS), Keumkang (KK), Woori (WR), and Winter wheat (WW) were investigated. Antibacterial activities were evaluated in vitro against the common food and cosmetic industry contaminants Escherichia coli, Salmonella typhimurium, and Staphylococcus aureus using well diffusion assays. WW had the highest inhibitory activity against all tested strains, with S. aureus being the most sensitive strain. The minimum inhibitory concentration (MIC) values of WW and WR against S. aureus were 0.50 and 1.25 mg/mL, respectively. The 2,6-dimethoxy-1,4- benzoquinone (DMBQ) content was measured using HPLC. The antibacterial activities of wheat seed extracts were correlated with the total phenolic contents (Pearson’s correlation coefficient=0.994), with the ABTS radical scavenging activity (0.978), and with the DMBQ content (0.968). WW and WR have potential for use as natural antimicrobials for prevention of food and cosmetics spoilage.     

Molecular characterisation and biofilm production in Staphylococcusaureus isolates from the dairy production chain in Northern Italy

Staphylococcus aureus is able to produce enterotoxins causing staphylococcal food poisoning, and is frequently harboured by dairy products. Also, S. aureus is able to form biofilm in the production environment, enhancing the risk of food contamination. The ability of 49 S. aureus isolates from the dairy production chain to form biofilm aim was tested, and their genetic diversity in terms of population structure and presence of genes involved in biofilm formation or enterotoxins production was explored. The majority of the genotypes found were generally bovine associated; however, some have been also reported frequently in human clinical cases. Two isolates were methicillin-resistant. In total, 38.7% of the isolates were biofilm producers, and among them 47.3%, 42.1% and 10.5% exhibited weak, moderate, or strong biofilm-forming ability, respectively. In total 68% of the biofilm producing isolates were also positive for enterotoxins genes, raising concerns for consumer safety.     

Biofilm-producing ability of Staphylococcus aureus isolates from Brazilian dairy farms

This study aimed to investigate the in silico biofilm production ability of Staphylococcus aureus strains isolated from milking parlor environments on dairy farms from São Paulo, Brazil. The Staph. aureus isolates were obtained from 849 samples collected on dairy farms, as follows: milk from individual cows with subclinical mastitis or history of the disease (n = 220); milk from bulk tank (n = 120); surfaces of milking machines and utensils (n = 389); and milk handlers (n = 120). Thirty-one Staph. aureus isolates were obtained and categorized as pulsotypes by pulsed-field gel electrophoresis and submitted to assays for biofilm formation on polystyrene, stainless steel, rubber, and silicone surfaces. Fourteen (45.2%) pulsotypes were considered producers of biofilm on the polystyrene microplate assay, whereas 13 (41.9%) and 12 (38.7%) pulsotypes were biofilm producers on stainless steel and rubber, respectively. None of the pulsotypes evaluated produced biofilms on silicone. Approximately 45% of Staph. aureus pulsotypes isolated from different sources on dairy farms showed the ability to produce biofilms in at least one assay, indicating possible persistence of this pathogen in the milking environment. The potential involvement of Staph. aureus in subclinical mastitis cases and its occurrence in milk for human consumption emphasize the need to improve hygiene practices to prevent biofilm formation on the farms studied.     

Antibacterial activity and mechanism of a novel bacteriocin produced by Lactiplantibacillus plantarum against Escherichia coli and Staphylococcus aureus

The purpose of the study was to explore the antibacterial effect and mechanism of a novel bacteriocin of Lactiplantibacillus plantarum (L. plantarum) against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The antibacterial activity was determined by the Oxford cup method, and the dynamic growth curves were conducted with continuous shaking incubation. The result showed that the bacteriocin was a protein or protein-like antibacterial substance susceptible to pepsin and trypsin. And it had good antibacterial activity, pH stability, thermostability and enzyme treatment stability against E. coli and S. aureus. The SEM, flow cytometry and nucleic acid leakage showed that the bacteriocin disrupted the cell structures of the two bacteria by damaging cell walls and cell membranes. An agarose gel electrophoresis and SDS-PAGE analysis showed that the bacteriocin inhibited DNA replication and interfered with the protein formation, which resulted in the inhibition of the two bacteria's growth. Therefore, the use of the L. plantarum bacteriocin might be a promising biocontrol strategy to inhibit the pollution of E. coli and S. aureus simultaneously in foods.     

Isolation and identification of pentagalloylglucose with broad-spectrum antibacterial activity from Rhus trichocarpa Miquel

Rhus trichocarpa Miquel has been utilised both as a food and for medicinal purposes. In this study, we determined that the methanol extracts of the stem and leaf portions of R. trichocarpa inhibited the growth of both Gram-negative and Gram-positive bacteria. The active constituent was isolated, and identified via mass spectrometry and NMR as 1,2,3,4,6-penta-O-galloyl-β-d-glucose. The compound also evidenced a broad spectrum of antibacterial activity against both Gram-negative and Gram-positive bacteria including Staphylococcus aureus (both methicillin-resistant S. aureus and quinolone-resistant S. aureus), Bacillus subtilis, Streptococcus mutans, Escherichia coli, Salmonella typhimurium, and Pseudomonas aeruginosa with MRC values of 16–32 μg/ml, whereas gallate failed to inhibit the growth of Gram-negative bacteria, even at a concentration of 128 μg/ml. The antibacterial activity of penta-O-galloylglucose was restored by the addition of Fe²⁺, whereas gallate was not, thereby indicating that its antibacterial activity could be attributable to the chelation of iron. The results of the time-kill study against S. aureus and E. coli revealed that penta-O-galloylglucose exhibited bacteriostatic activity. These findings indicate that the extracts of R. trichocarpa as well as its active component, penta-O-galloylglucose, may have profound potential for the control of both Gram-positive and negative pathogens.     

Enhancement Antimicrobial Activity of Hyphothiocyanite Using Carrot Against Staphylococcus Aureus and Escherichia Coli

Hypothiocyanite has been known as antimicrobial agent that was generated from lactoperoxidase system (LPOS) but its antimicrobial activity was low against pathogenic bacteria in milk. This research has been done to enhance the antimicrobial activity of hypothiocyanite against pathogenic bacteria commonly found in milk: Staphylococcus aureus and Escherichia coli by addition of carrot extract. The result showed that carrot extract was able to enhance the antimicrobial activity of hypothiocyanite strongly against E. coli, however less enhancement has been found in the antibacterial activity of hypothiocyanite against S. aureus.     

Antibacterial activity produced by Enterococcus spp. isolated from an artisanal Mexican dairy product,Cotija cheese

Several Enterococci were isolated from Cotija cheese, which is a Mexican farmhouse-made product prepared from whole raw milk. No thermal step, neither starter cultures, are used in its manufacturing process. From the isolated strains two were outstanding for their extracellular lytic activity against Staphylococcus aureus, and were identified by 16S rDNA sequencing as Enterococcus faecalis and Enterococcus faecium, respectively. They also showed bacteriolytic activity against other pathogenic bacteria, such as Yersinia enterocolitica, Salmonella enterica Typhimurium and Pseudomonas aeruginosa, as demonstrated by agar diffusion tests. By zymography it was shown that they produced proteins with bacteriolytic activity with molecular masses of 95 and 81 kDa, respectively. Protein identification by LC/ESI–MS/MS showed that they correspond to different enzymes with peptidoglycan hydrolase (PGH) activity of N-acetylglucosaminidase. Two of them were considered as putative enzymes and had not been studied before. Concentrated protein preparations from both strains showed lytic activity on S. aureus growth in liquid culture, as well. Considering that the PGHs studied are produced by lactic bacteria isolated from a dairy product and their spectrum of bacterial inhibition, these enzymes have a potential use in food preservation.     

Species,roasting degree and decaffeination influence the antibacterial activity of coffee against Streptococcus mutans

Coffee beverage has been associated with antibacterial activity against Streptococcus mutans, a cariogenic bacterium. This study aimed at identifying natural compounds in coffee that contribute to such activity and investigate the influence of species, roasting and decaffeination on it. Coffee chemical compounds and aqueous extracts of green and roasted regular and decaffeinated Coffea arabica and Coffea canephora beans were tested. MIC, biofilm inhibition and biofilm reduction results were correlated with the concentration of coffee compounds in the extracts. 5-Caffeoylquinic acid, trigonelline and caffeic acid solutions showed bacteriostatic activity (MIC = 0.8 mg/mL). Lighter and regular extracts showed higher inhibitory activity than darker and decaffeinated extracts, with an inverse correlation between bacterial colony-forming units and roasting degree. Only regular C. canephora extracts showed biofilm formation inhibition. The joint effect of chlorogenic acids, trigonelline and caffeine or other compounds removed by decaffeination seems to be one of the causes for coffee antibacterial activity against S. mutans.     

Antimicrobial activity of bovine β-lactoglobulin against mastitis-causing bacteria

Bovine mastitis is one of the most economically deleterious diseases affecting dairy herds and results from an infection of the udder by pathogenic microorganisms such as Staphylococcus aureus, Streptococcus uberis, and Escherichia coli. The mammary gland is capable of preventing and combating bacterial infection by means of a complex network of innate and adaptive immune mechanisms. Lactoferrin is an 86-kDa protein with antibacterial activity that plays a role in the mammary gland's defense against infection. β-Lactoglobulin (β-LG) is an 18-kDa protein that is present in most mammals but is notably absent in humans, rodents, and lagomorphs. Different genetic variants of this protein exist, with β-LG A and β-LG B being the most common. In spite of being well studied, the biological function of β-LG is not thoroughly understood, and most noticeably, no reports exist on the effects of the native protein on bacterial growth. Hence, the objective of this study was to assess the potential antibacterial activity of β-LG against mastitis agents. To do this, we purified β-LG from normal bovine milk using a mild, nondenaturing method and performed in vitro growth inhibition assays with Staph. aureus, E. coli, and Strep. uberis. β-Lactoglobulin inhibited the growth of Staph. aureus and Strep. uberis but had no effect on E. coli. The antimicrobial activity against Staph. aureus and Strep. uberis was concentration dependent and was elicited by the intact protein because Tricine-sodium dodecyl sulfate-PAGE and analytical gel filtration chromatography did not reveal the presence of short degradation peptides. Analysis of the genetic variants of β-LG showed that β-LG A has higher inhibitory activity against Staph. aureus and Strep. uberis than β-LG B. Coincubation of β-LG and lactoferrin resulted in an augmented antibacterial activity against Staph. aureus, suggesting an additive effect of the proteins. This result, along with the proteins’ complementary spectrum of action, suggests that β-LG and lactoferrin may complement each other in the mammary gland's defenses against bacterial infection.     

Assessment of the antibacterial activity of a triclosan-containing cutting board

Several studies have shown that consumers may not clean cutting boards properly between preparation of raw and cooked meat. Cutting boards may therefore act as sources for contamination of cooked meat or other ready-to-eat foods with pathogenic and spoilage bacteria. The aim of the work was to investigate if cutting boards containing the antimicrobial compound triclosan can reduce the viability of bacteria, thus acting as a hygiene barrier. Survival and growth of food pathogens and spoilage bacteria on two cutting boards without antimicrobials and a commercial cutting board containing triclosan were tested. No difference in bacterial counts on cutting boards without and with triclosan was found after exposure to naturally contaminated chicken filets for one hour. Pathogenic and spoilage bacteria were inoculated on coupons (6.7-7 log per coupon) of cutting boards and incubated at 25 °C at controlled relative humidity for 24 and 72 h. At a relative humidity of 100%, growth of Escherichia coli, Salmonella, Staphylococcus aureus, coagulase-negative staphylococci (CNS) and Serrratia spp. was observed and no antibacterial effect of the triclosan-containing board was found except for against Listeria monocytogenes. At lower humidity (70% RH) less growth was found on the triclosan-containing cutting board than untreated boards after 24 h. After 72 h of incubation, cell counts were reduced on triclosan-containing boards, with the most pronounced antibacterial effects observed against Salmonella, S. aureus and CNS. For S. aureus and Salmonella it was found that when a lower initial cell count was applied (3.5 log per coupon), the triclosan-containing board had an antibacterial effect under humid conditions, as well as a more pronounced antibacterial effect under dry conditions.An agar overlay assay showed that triclosan migrated out of the coupons. Repeated washing of the triclosan-containing cutting boards reduced the antibacterial effect, thus the amount of triclosan available on the surface seemed to be limited. In conclusion, using triclosan-containing cutting boards as a hygienic barrier may only work under certain conditions (low humidity, long exposure time, and clean conditions) and not against all genera of bacteria.     

Factors affecting the susceptibility of Staphylococcus aureus CCRC 12657 to water soluble lactose chitosan derivative

In this study, the susceptibility of Staphylococcus aureus CCRC 12657 to water-soluble lactose chitosan derivative as influenced by pH, temperature and cell age were investigated. Besides, the effect of this chitosan derivative on enterotoxin production and cell leakage of S. aureus CCRC 12657 was also examined.It was found that the susceptibility of S. aureus CCRC 12657 to lactose chitosan derivative varied with incubation temperature, pH and cell age. The lactose chitosan derivative exerted a higher antibacterial activity against S. aureus CCRC 12657 at 37°C than at 22 and 5°C. At pH 6.5–7.0, S. aureus CCRC 12657 was more susceptible to the chitosan derivative than at pH 6.0 or 7.5. Besides, cells of S. aureus CCRC 12657 in the late-exponential phase (12 h) were most susceptible to the chitosan derivative followed by cells in the stationary phase (24 h) and mid-exponential phase (6 h). Supernatant of cell suspension showed a marked increase in absorbance at 280 nm after the cells of the test organism were exposed to deionized water-containing lactose chitosan derivative. Furthermore, it was also noted that the lactose chitosan derivative not only caused the death of S. aureus CCRC 12657 but also inhibited enterotoxin production in Brain–Heart infusion broth.