Browsing by Author "Gibbs, Paul A."
Now showing 1 - 10 of 20
Results Per Page
Sort Options
- Anti-listerial inhibitory lactic acid bacteria isolated from commercial cold smoked salmonPublication . Tome, Elisabetta; Teixeira, Paula; Gibbs, Paul A.The natural microflora of cold-smoked fish at the end of shelf-life are lactic acid bacteria (LAB). Some of these display a capacity to inhibit spoilage as well as several strains of pathogenic micro-organisms, e.g. Listeria monocytogenes which is isolated frequently from cold-smoked salmon (CSS). Eight batches of sliced vacuum-packed CSS from Norway, Scotland and Spain were collected at retail. Packs were stored at 5 1C and examined for chemical and microbiological characteristics, at purchase date and at expiration date. pH, water activity and salt content were similar to available data on lightly preserved fish products. There was a consistent pattern in the development of the microflora on CSS; the initial level of LAB was low on freshly produced CSS (102 cfu g 1); however, storage in vacuum packaging at refrigeration temperature was elective for LAB. At the end of the stated shelf-life these micro-organisms, represented mainly by Lactobacillus spp., attained ca.107 cfu g 1 while Enterobacteriaceae counts were consistently lower (105 cfu g 1), which indicates the ability of LAB to grow and compete with few carbohydrates available and in the presence of moderate salt concentrations. L. monocytogenes was not found in any sample. Forty-one percent of LAB strains isolated exhibited inhibitory capacity against Listeria innocua, in a plate assay. A majority of the inhibitory effects were non-bacteriocinogenic, but nevertheless were very competitive cultures which may provide an additional hurdle for improved preservation by natural means. r 2005 Elsevier Ltd. All rights reserved.
- Antimicrobial effects of a microemulsion and a nanoemulsion on enteric and other pathogens and biofilmsPublication . Teixeira, Paula C.; Leite, Gonçalo M.; Domingues, Ricardo J.; Silva, Joana; Gibbs, Paul A.; Ferreira, João PauloSome microemulsions and nanoemulsions may have antimicrobial properties and be effective anti-biofilm agents. We examined the abilities of two fine emulsions, designated BCTP and TEOP, to inactivate suspensions of vegetative cells of Salmonella spp. Escherichia coli 0157:H7 (VT-), Pseudomonas aeruginosa, Staphylococcus aureus and Listeria monocytogenes. BCTP is an O/W nanoemulsion of soybean oil and tri-n-butyl phosphate emulsified with Triton X-100, while TEOP is an O/W microemulsion of ethyl oleate with Tween 80 as emulsifier and n-pentanol as a co-emulsifier. BCTP was effective in reducing the cell numbers of L. monocytogenes, while TEOP was effective against all five organisms investigated. The abilities of these emulsions to reduce preformed biofilms of the five bacteria were also investigated. With the exception of the biofilm formed by L. monocytogenes, which surprisingly was not significantly affected by BCTP, all biofilms were inhibited by both BCTP and TEOP.
- Application of an impedimetric technique for the detection of lytic infection of salmonella spp. by specific phagesPublication . Amorim, Lara R. P.; Silva, Joana G. L.; Gibbs, Paul A.; Teixeira, Paula C.This study was performed to evaluate the adaption of the impedimetric method to detect the lytic infection by Salmonella-specific bacteriophages and to provide a higher selectivity to this rapid method in detecting Salmonella spp. by using specific agents. Three bacteriophages and twelve strains of Salmonella spp. were tested. Each of the twelve strains was used separately to inoculate TSB together with each one of the phages. The inoculumconcentration was between 106 and 107 cfu/mL, at a cell: phage ratio of 1 : 100. From the sample analysis, based on conductance (G)measurements (37◦C), the infection could be detected, by observation of both detection-time delay and distinct curve trends. The main conclusions were that kinetic detection by impedance microbiology with phage typing constitutes a method of determining whether a test microorganism is sensitive to the bacteriophage and a method to evaluate whether a lytic bacteriophage is present in a sample, by affecting bacterial growth rate/metabolic change
- Characterization of anti-listeria bacteriocins isolated from shellfish: Potential antimicrobials to control non-fermented seafoodPublication . Pinto, Ana Luísa; Fernandes, Melissa; Pinto, Cristina; Albano, Helena; Castilho, Fernanda; Teixeira, Paula; Gibbs, Paul A.This work had as main objectives to characterize two bacteriocins produced by lactic acid bacteria (LAB) previously isolated from non-fermented seafood, in order to evaluate their potential as new food protective agents. The two bacteriocinogenic isolates were identified by Polymerase Chain Reaction (PCR) using genusand species-specific primers, and confirmed by 16S rDNA sequencing, as Enterococcus faecium and Pediococcus pentosaceus. The antimicrobial spectrum of each strain included several indicator microorganisms, some of them also isolated from seafood. Growth of Listeria innocua, L. monocytogenes, Staphylococcus aureus, Bacillus cereus and other LAB species were inhibited, although no inhibition of Gram-negative microorganisms was observed. Proteolytic, but not lipolytic or glycolytic enzymes, completely inactivated the antimicrobial effect of both cell-free supernatants confirming the proteinaceous nature of the inhibitors. The antimicrobial activity was maintained after treatment with NaCl, SDS, Triton X-100, Tween 20, Tween 80 and EDTA after 2 h or 5 h of exposure and both bacteriocins were stable over a wide range of pH and temperatures. Production of bacteriocin by E. faecium (bacALP7)was detected initially at exponential phase and reached a maximum activity of 25,600 AU/ml in the early stationary phase, whereas bacteriocin production by P. pentosaceus ALP57 (bacALP57) reached the maximum at exponential phase with 12,800 AU/ml. The bacteriocins did not kill L. monocytogenes ESB54 nor L. innocua 2030c however, cellular growth was reduced. The partially purified bacteriocins, bacALP7 and bacALP57, were below 6.5 kDa in size as determined by Tricine-SDS gel electrophoresis. E. faecium and P. pentosaceus contained DNA fragments corresponding in size to those recorded for enterocin B and pediocin PA-1, respectively. Sequencing of the fragments from both bacteriocins confirmed the homology. To our knowledge, for the first time two LAB producing bacteriocins similar to pediocin PA-1 and enterocin B, were isolated from non-fermented shellfish. The adaptation of the cultures to seafood matrices may be advantageous in terms of application as a biopreservation strategy for reduction of L. monocytogenes levels in seafood products.
- Characterization of bacPPK34 a bacteriocin produced by Pediococcus pentosaceus strain K34 isolated from “Alheira”Publication . Abrams, Daniel; Barbosa, Joana; Albano, Helena; Silva, Joana; Gibbs, Paul A.; Teixeira, PaulaDifferent lactic acid bacteria were isolated during different stages in the production of “Alheiras”, a traditionally fermented sausage produced in the north of Portugal, between 2005 and 2007, in a total of 484 isolates. One of 484 isolates (K34) produced a bacteriocin, designated as bacPPK34, and was identified as a strain of Pediococcus pentosaceus by 16S rRNA sequencing. The highest bacteriocin production was noted at late log/early stationary phase after 15e18 h of growth in MRS broth at 37 ºC (3200 AU/ml) against Enterococcus faecalis ATCC 29212 and 12800 AU/ml against Listeria monocytogenes (L1, L2, L3). bacPPK34 was between 2.5 kDa and 6.2 kDa in size, as determined by tricine-SDS-PAGE. Complete inactivation or significant reduction in antimicrobial activity was observed after treatment of cell-free supernatants with proteinase K, pepsin and trypsin. No change in activity was recorded when treated with catalase. The bacteriocin was resistant to treatments with lipase and detergents Triton X-100, Tween 20, SDS, NaCl, urea and EDTA. Furthermore, the bacteriocin remained active after 2 h at pH 2e12 and temperature treatments at 60, 80, 100 ºC, 1 month of storage at º20 and 4 ºC and 20 min at 121 ºC. Addition of bacPPK34 to a mid-log culture of L. monocytogenes and E. faecalis ATCC 29212 inhibited growth. The bacteriocin did not adhere to the surface of the producer cells.
- Comparison of Oxford Agar, PALCAM and Listeria monocytogenes Blood Agar for the recovery of L. monocytogenes from foods and environmental samplesPublication . Pinto, Marlene; Burria, Solange; Mena, Cristina; Almeida, Gonçalo; Carneiro, Luísa; Teixeira, Paula; Gibbs, Paul A.This work had as the main objective a comparison between Listeria monocytogenes Blood Agar (LMBA) and the conventional selective agar media, Oxford and PALCAM, relative to its efficacy in the detection of L. monocytogenes in naturally contaminated food and environmental samples. 173 environmental samples and 272 samples of foods were analysed. A higher sensitivity for detection of L. monocytogenes was verified for LMBA than for PALCAM and Oxford. In LMBA L. monocytogenes could be distinguished from other Listeria spp. by detection of hemolysis. In Oxford and PALCAM this distinction was not possible. The higher growth rate of L. innocua cf. L. monocytogenes in selective liquid media could result in a high number of false negatives (non-detection of the target organism on plates, although its presence was observed by other tests, eg. mini-VIDAS LMO). The need for specific media for the detection of L. monocytogenes in food was confirmed. LMBA could be an alternative medium to use together with PALCAM or Oxford.
- Could modifications of processing parameters enhance the growth and selection of lactic acid bacteria in cold-smoked salmon to improve preservation by natural meansPublication . Tomé, Elisabetta; Gibbs, Paul A.; Teixeira, Paula C.Several smoking conditions were examined with the objective of enhancing the numbers of lactic acid bacteria (LAB) by natural means in vacuum-packaged cold-smoked salmon during 21 days of storage at 5C. Three combinations of salting, drying, and smoking were used: (i) dry salting time of salting (2 or 6 h); (ii) wet salting (6 h) dry salting (6 h) with mor without sugar; and (iii) wet salting (6 h) dry salting (6 h) different times of smoking (2 or 6 h of drying and 2 or 6 h of smoking). Two batches were processed for each set of conditions. Determinations of pH and salt content in the water phase were carried out for products in each treatment. Microbiological analyses (total viable count, total LAB, Lactobacillus spp., and Enterobacteriaceae) also were conducted at the beginning of storage (t0) and after 21 days of refrigerated storage (t1). There were differential increases in total LAB and lactobacilli during the storage period according to the treatment performed. The most effective treatment to enhance LAB growth was 6 h of dry salting with sugar, 6 h of drying, and 2 h of smoking. These salting-drying-smoking conditions also selected the LAB as the dominant flora at the end of the storage period. The LAB promoted by these processing parameters seem to be potentially useful protective cultures because of their anti-Listeria activity. From the results of this research, we conclude that it is possible to enhance the growth of LAB in general and that of inhibitory strains in particular by suitable choices of processing parameters.
- Effect of stress on cells of lactobacillus delbrueckii sp. bulgaricusPublication . Silva, Joana; Carvalho, Ana Sofia; Teixeira, Paula; Gibbs, Paul A.Cultures of Lactobacillus delbrueckii sp. bulgaricus play an important role in the production of fermented foods and are frequently used as starter cultures for dairy fermentations combined with other species. It These cultures is are particularly used in the industrial production of yoghurt and cheeses. Large scale Pproduction methods of dried L. bulgaricus powders, for inoculating the production vat directly, involve treatments that stress cells in such a way that they lose some of their original activity. containing viable and active organisms which are long-term preserved during storage in the dried state, areis presented. This review covers the environmental stress responses in cells of L. bulgaricus which have been investigated. The responses of L. bulgaricus cells to heat, cold, acid, osmotic, oxygen, starvation, drying and during storage in the dried state are described. Attempts to improve the survival of L. bulgaricus during drying and subsequent storage in the dried state are also discussed in this review.
- Effect of various protecting compounds added to the growth medium upon survival of lactobacillus sakei to heating, freezing, freeze-drying and storage in the dried statePublication . Ferreira, Vânia; Soares, Vânia; Santos, Cristina; Silva, Joana; Gibbs, Paul A.; Teixeira, PaulaThe aim of the present study was to investigate if the presence of sorbitol, myoinositol, xylose, mannose and Tween 80 in the growth medium increased the survival of L. sakei during heating, freezing, freeze drying and storage of freeze dried cells. Survival during freezing was enhanced by ca. 8% when glycerol was present in the growth medium. Viability during freeze-drying and storage in the dried state was improved by the presence of xylose in the growth medium. In addition to xylose, the presence of mannose and myoinositol protected cells during storage but not during drying. Cells grown in the presence myoinositol presented the highest D value at 55?C, 1.4 folder higher than control cells. In comparison with cells grown in MRS, total amino acids concentrations were the same order of magnitude for cells grown in the presence of mannose and myoinositol but were lower for cells grown in the presence of the other compounds.
- Growth control of listeria innocua 2030c on vacuum-packaged cold-smoked salmon by lactic acid bacteriaPublication . Tomé, Elisabetta; Gibbs, Paul A.; Teixeira, Paula C.Five bacteriocin-producing lactic acid bacteria (LAB): Enterococcus faecium ET05, Lactobacillus curvatus ET06, L. curvatus ET30, L. deldrueckii ET32 and Pediococcus acidilactici ET34, selected by their capacity for growth and producing inhibition in vitro at high salt-on-water content, low temperature and anaerobic atmosphere, conditions simulating cold-smoked fish,were inoculated onto salmon fillets, in co-culturewith Listeria innocua 2030c, and cold-smoked processed (dry salted for 6h; drying for 6h; smoke for 2h).The finished product was then packed under vacuum and stored at 5 °C. Enumeration of LAB and L. innocua was performed during storage. Results showed that strain E. faecium ET05 was the best biopreservative candidate for controlling L. innocua growth in vacuum-packaged cold-smoked salmon (CSS) processed under the salting/drying/smoking parameters referred above. L. curvatus ET30 and L. delbrueckii ET32 also showed a good biopreservation potential for CSS although they were less effective than the former. L. curvatus ET06 and P. acidilactici ET34 showed a bacteriostatic mode of action against the target bacteria in vitro as well as when inoculated into the salmon fillets. This study describes a potential application of five different LAB in the biopreservation of Listeria in CSS.