Resistance of pathogenic bacteria on the surface of stainless steel depending on attachment form and efficacy of chemical sanitizers

Various bacteria including food spoilage bacteria and pathogens can form biofilms on different food processing surfaces, leading to potential food contamination or spoilage. Therefore, the survival of foodborne pathogens (Escherichia coli O157:H7, Listeria monocytogenes, Salmonella typhimurium, Staphylococcus aureus, Cronobacter sakazakii) in different forms (adhered cells, biofilm producing in TSB, biofilm producing at RH 100%) on the surface of stainless steel and stored at various relative humidities (RH 23%, 43%, 68%, 85%, and 100%) at room temperature for 5 days was investigated in this study. Additionally, the efficacy of chemical sanitizers (chlorine-based and alcohol-based commercial sanitizers) on inhibiting various types of biofilms of E. coli O157:H7 and S. aureus on the surface of stainless steel was investigated. The number of pathogens on the surface of stainless steel in TSB stored at 25 °C for 7 days or RH 100% at 25 °C for 7 days was significantly increased and resulted in the increase of 3 log₁₀ CFU/coupon after 1 day, and these levels were maintained for 7 days. When stainless steel coupons were stored at 25 °C for 5 days, the number of pathogens on the surface of stainless steel was significantly reduced after storage at RH 23%, 43%, 68%, and 85%, but not at 100%. When the bacteria formed biofilms on the surface of stainless steel in TSB after 6 days, the results were similar to those of the attached form. However, levels of S. aureus and C. sakazakii biofilms were more slowly reduced after storage at RH 23%, 43%, 68%, and 85% for 5 days than were those of the other pathogens. Formation of biofilms stored at RH 100% for 5 days displayed the highest levels of resistance to inactivation. Treatment with the alcohol sanitizer was very effective at inactivating attached pathogens or biofilms on the surface of stainless steel. Reduction levels of alcohol sanitizer treatment ranged from 1.91 to 4.77 log and from 4.35 to 5.35 log CFU/coupon in E. coli O157:H7 and S. aureus, respectively. From these results, the survival of pathogens contaminating the surfaces of food processing substrates such as stainless steel varied depending on RH and attachment form. Also, alcohol-based sanitizers can be used as a potential method to remove microbial contamination on the surfaces of utensils, cooking equipment, and other related substrates regardless of the microbial attached form.     

In vitro inactivation of Escherichia coli, Staphylococcus aureus and Salmonella spp. using slightly acidic electrolyzed water

In the current study, the effectiveness of slightly acidic electrolyzed water (SAEW) on an in vitro inactivation of Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Salmonella spp. was evaluated and compared with other sanitizers. SAEW (pH 5.6, 23 mg/l available chlorine concentration; ACC; and 940 mV oxidation reduction potential; ORP) was generated by electrolysis of dilute solution of HCl (2%) in a chamber of a non-membrane electrolytic cell. One milliliter of bacteria suspension (ca. 10–11 log₁₀CFU/ml) was mixed with 9 ml of SAEW, strong acidic electrolyzed water (StAEW; ca. 50 mg/l ACC), sodium hypochlorite solution (NaOCl; ca.120 mg/l ACC) and distilled water (DW) as control and treated for 60 s. SAEW effectively reduced the population of E. coli, S. aureus and Salmonella spp. by 5.1, 4.8, and 5.2 log₁₀CFU/ml. Although, ACC of SAEW was more than 5 times lower than that of NaOCl solution, they showed no significant bactericidal difference (p > 0.05). However, the bactericidal effect of StAEW was significantly higher (p < 0.05) than SAEW and NaOCl solution in all cases. When tested with each individual test solution, E. coli, S. aureus and Salmonella spp. reductions were not significantly different (p > 0.05). These findings indicate that SAEW with low available chlorine concentration can equally inactivate E. coli, S. aureus and Salmonella spp. as NaOCl solution and therefore SAEW shows a high potential of application in agriculture and food industry as an environmentally friendly disinfection agent.     

Antibacterial activity of the extracts from the fruit rinds of Garcinia cowa and Garcinia pedunculata against food borne pathogens and spoilage bacteria

The crude hexane and chloroform extracts from the fruit rinds of Garcinia cowa and Garcinia pedunculata were studied for their antibacterial activity against some foodborne pathogens and spoilage bacteria such as Bacillus cereus, Bacillus coagulans, Bacillus subtilis, Staphylococcus aureus and Escherichia coli. The minimum inhibitory concentrations (MICs) of the extracts determined by the agar dilution method were ranging from 15 to 500 μg/ml and 300 to 1250 μg/ml for G. cowa and G. pedunculata, respectively. However, the hexane and chloroform extracts from the fruit rinds of G. cowa exhibited marked inhibitory effect against all the test organisms and were more effective than that of G. pedunculata extracts. The antibacterial activity of all the extracts was more pronounced against the tested Gram-positive bacteria than the tested Gram-negative bacterium. Furthermore, this study is the first report on the in vitro antibacterial activity of extracts from the fruit rinds of G. cowa and G. pedunculata.     

Efficacy of neutral electrolyzed water for sanitization of cutting boards used in the preparation of foods

The effectiveness of neutral electrolyzed water (NEW) to sanitize cutting boards used for food preparation was investigated. Cutting boards made of hardwood and bamboo were inoculated with Escherichia coli K12 and Listeria innocua, dried for 1 h, washed, rinsed and sanitized with NEW, sodium hypochlorite (NaClO) solution, or tap water (control). After each washing protocol, surviving bacterial populations were determined. Results showed that both NEW and NaClO sanitizing solutions produced similar levels of bacterial reductions. In manual washing, the population reductions by NEW and NaClO were 3.4 and 3.6 log₁₀ CFU/100 cm² for E. coli, and 4.1 and 3.9 log₁₀ CFU/100 cm² for L. innocua, respectively. In the automatic washing, the reductions by NEW and NaClO were 4.0 and 4.0 log₁₀ CFU/100 cm² for E. coli, and 4.2 and 3.6 log₁₀ CFU/100 cm² for L. innocua, respectively. No significant differences (P > 0.05) were observed in surviving bacteria counts when comparing board material types.     

Antimicrobial Activity of Thyme (Tymus vulgaris) and Oregano (Origanum vulgare) Essential Oils against Some Food-borne Microorganisms

The aim of this study was to investigate antibacterial effects of oregano and thyme essential oils (EOs) on some food-borne bacteria. GC-MS analysis of EOs was performed in order to determine their composition and phenols were predominant constituents. The investigation of the antibacterial effects of EOs was performed on Salmonella Enteritidis, Salmonella Thyphimurium, Staphylococcus aureus, methicillin resistant Staphylococcus aureus, Escherichia coli and Bacillus cereus, and MICs were determined by broth microdilution method. EOs exhibited antibacterial activity against all tested microorganisms.     

Ultraviolet light and Ultrasound as non-thermal treatments for the inactivation of microorganisms in fresh ready-to-eat foods

The effects of two non thermal disinfection processes, Ultraviolet light (UV 254 nm) and Ultrasound (US) on the inactivation of bacteria and color in two freshly cut produces (lettuce and strawberry) were investigated. The main scope of this work was to study the efficacy of UV and US on the decontamination of inoculated lettuce and strawberries with a cocktail of four bacteria, Escherichia coli, Listeria innocua, Salmonella Enteritidis and Staphylococcus aureus. Treatment of lettuce with UV reduced significantly the population of E. coli, L. innocua, S. Enteritidis and S. aureus by 1.75, 1.27, 1.39 and 1.21 log CFU/g, respectively. Furthermore, more than a 2-log CFU/g reduction of E. coli and S. Enteritidis was achieved with US. In strawberries, UV treatment reduced bacteria only by 1–1.4 log CFU/g. The maximum reductions of microorganisms, observed in strawberries after treatment with US, were 3.04, 2.41, 5.52 and 6.12 log CFU/g for E. coli, S. aureus, S. Enteritidis and L. innocua, respectively. Treatment with UV and US, for time periods (up to 45 min) did not significantly (p > 0.05) change the color of lettuce or strawberry. Treatment with UV and US reduced the numbers of selected inoculated bacteria on lettuce and strawberries, which could be good alternatives to other traditional and commonly used technologies such as chlorine and hydrogen peroxide solutions for fresh produce industry. These results suggest that UV and US might be promising, non-thermal and environmental friendly disinfection technologies for freshly cut produce.     

Antibacterial activity of Thai edible plants against gastrointestinal pathogenic bacteria and isolation of a new broad spectrum antibacterial polyisoprenylated benzophenone,chamuangone

Twenty-two edible plant extracts were subjected to evaluation of their antibacterial activity against some gastrointestinal pathogenic bacteria, including Escherichiacoli, Salmonella typhimurium, Salmonella typhi, Shigella sonnei and Helicobacter pylori using the disc diffusion and broth microdilution methods. Sixteen of the plant extracts exhibited antibacterial activity against one or more tested bacteria. Only Garcinia cowa leaf extracts exhibited antibacterial activity against all tested bacteria. Purification of the ethyl acetate extract of G. cowa leaves using an antimicrobial assay-guided isolation afforded a new polyprenylated benzophenone, chamuangone, that exhibited satisfactory antibacterial activity against Streptococcus pyogenes (minimum inhibitory concentration (MIC) 7.8 μg/ml), Streptococcus viridans and H. pylori (MICs 15.6 μg/ml), and Staphylococcus aureus, Bacillus subtilis and Enterococcus sp. (MICs 31.2 μg/ml).     

Inhibitory parameters of the essential oil and various extracts of Metasequoia glyptostroboides Miki ex Hu to reduce food spoilage and food-borne pathogens

The aim of this work was to examine the chemical composition of the essential oil and various solvent extracts isolated from the floral cone of Metasequoia glyptostroboides Miki ex Hu and to test their efficacy against a diverse range of organisms comprising food spoilage and food-borne pathogenic bacteria. The chemical composition of essential oil isolated by hydrodistillation was analysed by GC-MS. It was determined that 59 compounds, which represented 97.06% of total oil, were present in the oil. The oil contains mainly α-pinene (29.54%), totarol (9.37%), α-thujene (8.63%), bornylene (8.63%), β-caryophyllene (4.40%), totarol acetate (3.98%), δ-3-carene (3.19%) and 2-β-pinene (2.25%). The oil was found containing mainly the oxygenated mono- and sesquiterpenes and their respective hydrocarbons. Antibacterial activity of essential oil, methanol extract and various organic sub-fractions of methanol extract of M. glyptostroboides was determined in vitro using agar diffusion method and MIC determination test against eleven (four Gram-positive, seven Gram-negative) bacterial strains including food spoilage and food-borne pathogens. The essential oil (5 μl/ml, corresponding to 1000 ppm/disc), methanol extract and various organic sub-fractions (7.5 μl/ml, corresponding to 1500 ppm/disc) of M. glyptostroboides exhibited great potential of antibacterial activity against four Gram-positive bacteria such as Bacillus subtilis (ATCC 6633), Listeria monocytogenes (ATCC 19166), Staphylococcus aureus (KCTC 1916), S. aureus (ATCC 6538) and one Gram-negative bacterium, Pseudomonas aeruginosa (KCTC 2004). The zones of inhibition of different concentrations of essential oil, methanol extract and its derived various organic sub-fractions against the tested bacteria were found in the range of 10 ∼ 20 mm and the MIC values were recorded between 125 and 1000 μg/ml. This study shows that M. glyptostroboides mediated essential oil and extracts can be applied in food industries as a natural preservatives or flavoring additives to control food spoilage and food-borne pathogenic bacteria causing severe destruction in food.     

Efficiency of high hydrostatic pressure at 600 MPa against food-borne microorganisms by challenge tests on convenience meat products

The food-borne pathogens Listeria monocytogenes, Salmonella enterica, Staphylococcus aureus, Yersinia enterocolitica and Campylobacter jejuni, and the spoilage lactic acid bacteria (LAB), Escherichia coli and the yeast Debaryomyces hansenii were inoculated on slices of cooked ham, dry cured ham and marinated beef loin. During storage at 4 °C, L. monocytogenes and LAB increased up to 3.5 log units while the other species, unable to grow under refrigeration, continued at the spiking level. The application of a 600 MPa treatment effectively inactivated most of the microorganisms, the counts of which, except for LAB that increased in cooked ham and in beef loin, progressively decreased or maintained below the detection limit during the whole storage (120 days at 4 °C).     

Combined effect of enterocin AS-48 and high hydrostatic pressure to control food-borne pathogens inoculated in low acid fermented sausages

The single and combined effects of enterocin AS-48 and high hydrostatic pressure (HHP) on Listeria monocytogenes, Salmonellaenterica, and Staphylococcus aureus was investigated in fuet (a low acid fermented sausage) during ripening and storage at 7 °C or at room temperature. AS-48 (148 AU g⁻¹) caused a drastic 5.5 log cfu g⁻¹ decrease in L. monocytogenes (P < 0.001) and a significant (P < 0.01) inhibition (1.79 logs) for Salmonella at the end of ripening (10 d). After pressurization (400 MPa) and storage Listeria counts remained below 5 cfu g⁻¹ in all fuets containing AS-48 (pressurized or not). HHP alone had no anti-Listeria effect. HHP treatment significantly reduced Salmonella counts, with lowest levels in pressurized fuets with AS-48. S. aureus showed similar growth for all treatments and storage conditions. These results indicate that AS-48 can be applied alone to control L. monocytogenes and combined with HHP treatment to control Salmonella in fuets.     

Evaluation of the effects of ultraviolet light on bacterial contaminants inoculated into whole milk and colostrum,and on colostrum immunoglobulin G

Raw milk and colostrum can harbor dangerous microorganisms that can pose serious health risks for animals and humans. According to the USDA, more than 58% of calves in the United States are fed unpasteurized milk. The aim of this study was to evaluate the effect of UV light on reduction of bacteria in milk and colostrum, and on colostrum IgG. A pilot-scale UV light continuous (UVC) flow-through unit (45 J/cm²) was used to treat milk and colostrum. Colostrum and sterile whole milk were inoculated with Listeria innocua, Mycobacterium smegmatis, Salmonella serovar Typhimurium, Escherichia coli, Staphylococcus aureus, Streptococcus agalactiae, and Acinetobacter baumannii before being treated with UVC. During UVC treatment, samples were collected at 5 time points and bacteria were enumerated using selective media. The effect of UVC on IgG was evaluated using raw colostrum from a nearby dairy farm without the addition of bacteria. For each colostrum batch, samples were collected at several different time points and IgG was measured using ELISA. The UVC treatment of milk resulted in a significant final count (log cfu/mL) reduction of Listeria monocytogenes (3.2 ± 0.3 log cfu/mL reduction), Salmonella spp. (3.7 ± 0.2 log cfu/mL reduction), Escherichia coli (2.8 ± 0.2 log cfu/mL reduction), Staph. aureus (3.4 ± 0.3 log cfu/mL reduction), Streptococcus spp. (3.4 ± 0.4 log cfu/mL reduction), and A. baumannii (2.8 ± 0.2 log cfu/mL reduction). The UVC treatment of milk did not result in a significant final count (log cfu/mL) reduction for M. smegmatis (1.8 ± 0.5 log cfu/mL reduction). The UVC treatment of colostrum was significantly associated with a final reduction of bacterial count (log cfu/mL) of Listeria spp. (1.4 ± 0.3 log cfu/mL reduction), Salmonella spp. (1.0 ± 0.2 log cfu/mL reduction), and Acinetobacter spp. (1.1 ± 0.3 log cfu/mL reduction), but not of E. coli (0.5 ± 0.3 log cfu/mL reduction), Strep. agalactiae (0.8 ± 0.2 log cfu/mL reduction), and Staph. aureus (0.4 ± 0.2 log cfu/mL reduction). The UVC treatment of colostrum significantly decreased the IgG concentration, with an observed final mean IgG reduction of approximately 50%. Development of new methods to reduce bacterial contaminants in colostrum must take into consideration the barriers imposed by its opacity and organic components, and account for the incidental damage to IgG caused by manipulating colostrum.     

Antimicrobial activity of soy edible films incorporated with thyme and oregano essential oils on fresh ground beef patties

Antibacterial activity of soy protein edible films (SPEF) incorporated with 1, 2, 3, 4 and 5% oregano (OR) or thyme (TH) essential oils was evaluated against Escherichia coli, E. coli O157:H7, Staphylococcus aureus, Pseudomonas aeruginosa and Lactobacillus plantarum by the inhibition zone test. Effects of SPEF containing 5% OR and TH or a mixture of OR + TH (ORT) were also tested on fresh ground beef during refrigerated storage (at 4 °C). OR and TH incorporated SPEF exhibited similar antibacterial activity against all bacteria in inhibition zone test. While E. coli, E. coli O157:H7 and S. aureus were significantly inhibited by antimicrobial films, L. plantarum and P. aeruginosa appeared to be the more resistant bacteria. SPEF with OR, ORT, and TH did not have significant effects on total viable counts, lactic acid bacteria and Staphylococcus spp. when applied on ground beef patties whereas reductions (p < 0.05) in coliform and Pseudomonas spp. counts were observed.     

Assessment of antimicrobial activity of coffee brewed in three different ways from different origins

The antimicrobial effect against pathogens such as Staphylococcus aureus, Enterecoccus faecalis, Listeria monocytogenes, Pseudomonas aeruginosa, Escherichia coli and Salmonella choleraesius was determined in four types of coffee (Coffea arabica L. cv. Colombia, decaffeinated cv. Colombia, cv. Ethiopia and cv. Kenya). Coffee was seen to have significant activity against the growth of food spoilage bacteria. Among the Gram-positive bacteria, coffee was strongly active against S. aureus, moderately active against L. monocytogenes and had a slightly inhibitory effect against E. faecalis. However, coffee samples were found to be less active against Gram-negative bacteria. The results show that espresso Colombia coffee has better antimicrobial activity than filter and Italian coffee with significant differences (p?<?0.05). Taking into account the origin, there were significant differences (p?<?0.05) between Kenya and decaffeinated Colombia, on the one hand, and Ethiopia and Colombia coffee, on the other, the two last showing the highest antimicrobial activity. The antimicrobial activity of the coffee from different origins studied in this paper increased with concentration. Typical coffee compounds were also analysed, and only caffeic and chlorogenic acids showed any inhibitory effect against the growth of all the analysed bacteria. The antibacterial properties of coffee means that it has a promising potential as natural food ingredient to extend the shelf life of foods such as cake, cookies or biscuits, coffee flavoured with shakes, yoghurt.     

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.     

Pulsed Ligh inactivation of Listeria innocua on food packaging materials of different surface roughness and reflectivity

Inactivation of Listeria innocua on food packaging materials by Pulsed Light (PL) treatment was investigated. Coupons of low density polyethylene (LDPE), high density polyethylene (HDPE), polyethylene-laminated ultra-metalized polyethylene terephthalate (MET), polyethylene-coated paperboard (TR), and polyethylene-coated aluminum foil paperboard laminate (EP) were inoculated with L. innocua cells in stationary growth phase. Inoculated coupons (∼8 CFU/coupon) were treated with Pulsed Light fluence of up to 8.0 J/cm², and survivors were determined. Reductions up to 7.2 ± 0.29, 7.1 ± 0.06, 4.4 ± 0.85, 4.5 ± 1.32, and 3.5 ± 0.82 log CFU/coupon were obtained on LDPE, HDPE, MET, TR, and EP, respectively. Inactivation data were used to determine Weibull kinetic parameters and predict inactivation in a wide range of fluence. Increasing surface reflectivity and surface roughness appeared to induce lower inactivation. Minimal surface heating was observed for all materials except MET, on which significant heating occurred. These results demonstrate the potential of Pulsed Light as an effective method for decontaminating food packaging materials.     

Efficacy of Neutral Electrolyzed Water,Quaternary Ammonium and Lactic Acid‐Based Solutions in Controlling Microbial Contamination of Food Cutting Boards Using a Manual Spraying Technique

Bactericidal activity of neutral electrolyzed water (NEW), quaternary ammonium (QUAT), and lactic acid‐based solutions was investigated using a manual spraying technique against Salmonella Typhimurium, Escherichia coli O157:H7, Campylobacter jejuni, Listeria monocytogenes and Staphylococcus aureus that were inoculated onto the surface of scarred polypropylene and wooden food cutting boards. Antimicrobial activity was also examined when using cutting boards in preparation of raw chopped beef, chicken tenders or salmon fillets. Viable counts of survivors were determined as log₁₀ CFU/100 cm² within 0 (untreated control), 1, 3, and 5 min of treatment at ambient temperature. Within the first minute of treatment, NEW and QUAT solutions caused more than 3 log₁₀ bacterial reductions on polypropylene surfaces whereas less than 3 log₁₀ reductions were achieved on wooden surfaces. After 5 min of treatment, more than 5 log₁₀ reductions were achieved for all bacterial strains inoculated onto polypropylene surfaces. Using NEW and QUAT solutions within 5 min reduced Gram‐negative bacteria by 4.58 to 4.85 log₁₀ compared to more than 5 log₁₀ reductions in Gram‐positive bacteria inoculated onto wooden surfaces. Lactic acid treatment was significantly less effective (P < 0.05) compared to NEW and QUAT treatments. A decline in antimicrobial effectiveness was observed (0.5 to <2 log₁₀ reductions were achieved within the first minute) when both cutting board types were used to prepare raw chopped beef, chicken tenders or salmon fillets.     

Inactivation of Escherichia coli O157:H7 on stainless steel upon exposure to Paenibacillus polymyxa biofilms

We investigated the potential use of biofilm formed by a competitive-exclusion (CE) microorganism to inactivate Escherichia coli O157:H7 on a stainless steel surface. Five microorganisms showing inhibitory activities against E. coli O157:H7 were isolated from vegetable seeds and sprouts. The microorganism with the greatest antimicrobial activity was identified as Paenibacillus polymyxa (strain T5). In tryptic soy broth (TSB), strain T5 reached a higher population at 25 °C than at 12 or 37 °C without losing inhibitory activity against E. coli O157:H7. When P. polymyxa (6 log CFU/mL) was co-cultured with E. coli O157:H7 (2, 3, 4, or 5 log CFU/mL) in TSB at 25 °C, the number of E. coli O157:H7 decreased significantly within 24 h. P. polymyxa formed a biofilm on stainless steel coupons (SSCs) in TSB at 25 °C within 24 h, and cells in biofilms, compared to attached cells without biofilm formation, showed significantly increased resistance to a dry environment (43% relative humidity [RH]). With the exception of an inoculum of 4 log CFU/coupon at 100% RH, upon exposure to biofilm formed by P. polymyxa on SSCs, populations of E. coli O157:H7 (2, 4, or 6 log CFU/coupon) were significantly reduced within 48 h. Most notably, when E. coli O157:H7 at 2 log CFU/coupon was applied to SSCs on which P. polymyxa biofilm had formed, it was inactivated within 1 h, regardless of RH. These results will be useful when developing strategies using biofilms produced by competitive exclusion microorganisms to inactivate foodborne pathogens in food processing environments.     

Lipid components and water soluble metabolites in salted and dried tuna (Thunnus thynnus L.) roes

The salted and dried product of tuna roe (bottarga) is a seafood characteristic of the Mediterranean area and exported all over the world. Samples of bottarga from bluefin tunas (Thunnus thynnus, L.) caught in the southwest Mediterranean sea were analysed. The samples were characterised by high content of marine wax esters (55–67 mol% of lipid classes), of docosahexaenoic (22:6 n-3, 25 w%) and oleic (18:1 n-9, 19 w%) fatty acids. Cholesterol was detected as 7–9 w% of lipids. Free fatty acids, index of lipid hydrolysis, represented 32–39 mol% over total fatty acids. Among metabolites, nutrients as taurine, nicotinamide and β-alanine, were found. The microflora comprised staphylococci, enterococci (2.2 log₁₀ CFU/g) and lactic acid bacteria (3 log₁₀ CFU/g). The food-borne pathogens Staphylococcus aureus, Listeria monocytogenes and Salmonella spp. were not detected. These findings indicate tuna bottarga as valuable source of nutrients.     

Antibacterial activity of eicosapentaenoic acid (EPA) against foodborne and food spoilage microorganisms

Eicosapentaenoic acid (EPA), a long-chain polyunsaturated fatty acid of ω-3 type was evaluated for its antimicrobial action against the range of foodborne and food spoilage pathogens, using agar disc diffusion assay in Luria broth (LB) media. The EPA exhibited antimicrobial activity against Bacillus subtilis ATCC 6633, Listeria monocytogenes ATCC 19166, Staphylococcus aureus ATCC 6538, S. aureus KCTC 1916 and Pseudomonas aeruginosa KCTC 2004. The minimum inhibitory concentrations (MICs) of the EPA against the tested bacterial strains were found in the range of 500-1350 μg/ml using broth dilution method. EPA reduced the viability of S. aureus at 250, 125 and 62.5 μg/ml after 15 min exposure and a steep decline in colony forming units (CFUs) was observed at 125 μg/ml after 30 min exposure, while similar reduction in CFU rate was exhibited by EPA when treated with 62.5 μg/ml after 180 min. EPA also reduced the CFU numbers of P. aeruginosa at all the concentrations used in this study after 15 min exposure. On the other hand, scanning electron microscopy (SEM) study of bacterial cells clearly exhibited the antibacterial effect of EPA as evidenced by the damages found in the outer membrane of the cells when treated with EPA. The results demonstrated that EPA exerted significant bactericidal and bacteriostatic effects against both P. aeruginosa and S. aureus.     

Evaluation of the antibacterial effect of a triclosan-containing floor used in the food industry

Antibacterial surfaces are increasingly used in the food industry. In the present study, the antibacterial effect of a triclosan-containing industrial floor was assessed. A poultry processing plant, which had a floor that contained triclosan, was visited, and the floor was sampled for bacteria. A high bacterial diversity was found on the floor. Testing showed that bacteria isolated from the floor showed a sensitivity to triclosan that covered a range of MICs from 0.07 to >40 ppm. Staphylococci were the most sensitive, and Pseudomonas fluorescens and Serratia marcescens were the most tolerant. The MICs of triclosan for the strains isolated from the floor were similar to the control strains from the corresponding genera or species of other origin. Thus, the floor seemed not to select for strains that were tolerant to triclosan or that led to the development of resistance to triclosan. Laboratory studies showed that the ability of bacteria to survive under dry conditions on coupons of the floor was similar to that for stainless steel and that the survival of the bacteria on the floor was not linked to their tolerance of triclosan, as determined by the MICs of triclosan. Adherence studies showed that bacteria were able to adhere to coupons of the floor; however, no thick biofilm developed after 3 days of incubation. In an agar plate assay, the floor produced inhibition zones against staphylococci, which are known to be very sensitive to triclosan, whereas no inhibition zones were observed for other bacteria tested. In conclusion, the antibacterial effect of the floor seemed to be very low. Because the concentration of triclosan in the floor was low compared to what has been reported for other triclosan-incorporated surfaces, sufficient amounts of triclosan may not have been available on the surface of the floor to kill the bacteria.