Relationships between microbial population dynamics and putrescine and cadaverine accumulation during dry fermented sausage ripening

Aims:  To evaluate the concomitant effects of three technological variables (fermentation temperature, NaCl and glucose added to the meat batter) on diamines (cadaverine, putrescine and histamine) accumulation and microbial changes during ripening of dry fermented sausages.
Methods and Results:  The variables were modulated according to an experimental design and predictive mathematical models were obtained. The models indicated that the sausages were characterized by low histamine amount independently on the applied conditions. In contrast, putrescine and cadaverine accumulation was considerable and significantly affected by the three variables. The microbial population dynamics suggest that lactic acid bacteria (LAB) and microstaphylococci are favoured by increasing glucose concentration until 0·7 g kg⁻¹, while Enterobacteriaceae are negatively influenced by NaCl concentration and, to a lesser extent, by fermentation temperature.
Conclusions:  Data obtained showed a relationship between Enterobacteriaceae growth and cadaverine and putrescine accumulation in sausages during ripening. The conditions more favourable for LAB and microstaphylococci induced a reduced growth of Enterobacteriaceae with a consequent reduced accumulation of putrescine and cadaverine.
Significance and Impact of the Study:  The use of systematic experimental designs allows to individuate the technological conditions suitable to keep the aminogenic microflora under control, thus reducing the risk of diamines production during traditional fermented food manufacture.     

Modification of azo dyes by lactic acid bacteria

Aim:  The ability of Lactobacillus casei and Lactobacillus paracasei to modify the azo dye, tartrazine, was recently documented as the result of the investigation on red coloured spoilage in acidified cucumbers. Fourteen other lactic acid bacteria (LAB) were screened for their capability to modify the food colouring tartrazine and other azo dyes of relevance for the textile industry.
Methods and Results:  Most LAB modified tartrazine under anaerobic conditions, but not under aerobic conditions in modified chemically defined media. Microbial growth was not affected by the presence of the azo dyes in the culture medium. The product of the tartrazine modification by LAB was identified as a molecule 111 daltons larger than its precursor by liquid chromatography-mass spectrometry. This product had a purple colour under aerobic conditions and was colourless under anaerobic conditions. It absorbed light at 361 and 553 nm.
Conclusion:  LAB are capable of anabolizing azo dyes only under anaerobic conditions.
Impact and Significance of the Study:  Although micro-organisms capable of reducing the azo bond on multiple dyes have been known for decades, this is the first report of anabolism of azo dyes by food related micro-organisms, such as LAB.     

Characterization and antimicrobial spectrum of bacteriocins produced by lactic acid bacteria isolated from traditional Bulgarian dairy products

Aims:  To isolate bacteriocin-producing lactic acid bacteria (LAB) with high wide spectrum antibacterial activity and to characterize their inhibitory peptides.
Method and Results:  Seven LAB strains [ Lactobacillus casei ssp. rhamnosus (PC5), Lactobacillus delbrueckii ssp. bulgaricus (BB18), Lactococcus lactis ssp. lactis (BCM5, BK15), Enterococcus faecium (MH3), Lactobacillus plantarum (BR12), Lactobacillus casei ssp. casei (BCZ2)], isolated from authentic Bulgarian dairy products were capable of producing bacteriocins, inhibiting the widest range of pathogenic bacteria. The bacteriocins were resistant to heating at 121°C for 15 min, stable at pH 2–10, sensitive to protease, insensitive to α-amylase and lipase. Two of bacteriocins produced by Lact. bulgaricus BB18 (bulgaricin BB18) and E. faecium MH3 (enterocin MH3) were purified and the molecular masses were determined. The N -terminal amino acid sequence of bulgaricin BB18 did not show strong homology to other known bacteriocins.
Conclusions:  Lactobacillus bulgaricus BB18 and E. faecium MH3 produce two novel bacteriocins highly similar to the pediocin-like nonlantibiotics.
Significance and Impact of the Study:  The two bacteriocins are potential antimicrobial agents and, in conjunction with their producers, may have use in applications to contribute a positive effect on the balance of intestinal microflora. Furthermore, bulgaricin BB18 strongly inhibits Helicobacter pylori .     

Effect of starter culture inoculation on feed hygiene and microbial population development in fermented pig feed composed of a cereal grain mix with wet wheat distillers' grain

Aims:  Investigating the influence of an added starter culture on the properties of fermented liquid pig feed.
Methods and Results:  Diets of cereal grain blended with wet wheat distillers' grain that were either not inoculated (WWDG), inoculated with a silage starter culture at start (WWDGsc1) or at start and at each backslopping (replacement of 80% the content with fresh mixture, simulating feed outtake, WWDGsc5) were fermented for 5 days, followed by 5 days of daily backslopping. Numbers of undesirable micro-organisms (enterobacteria, moulds) were reduced in all fermentations; particularly enterobacteria in the starter culture inoculated diets. Lactobacillus plantarum present in the starter culture became dominant in diets WWDGsc1 and WWDGsc5. However, Lactobacillus panis that was dominating WWDG was also abundant in WWDGsc1 and WWDGsc5. Yeast populations were not influenced by the starter culture, with Pichia fermentans dominating all fermentations. All diets had similar chemical characteristics with the exception of a significant increase of all tested organic acids in WWDGsc5.
Conclusions:  The addition of a starter culture influences the bacterial population in fermented liquid feed, but there is also a strong impact of the flora already present in the feed ingredients. The yeast population is not influenced by adding a lactic acid bacteria (LAB) starter culture. A consortium of LAB and yeast strains adapted to the fermentation should be used as starter culture.
Significance and Impact of the Study:  The results suggest that it is possible to influence the current unpredictable and spontaneous process of feed fermentation when appropriate starter cultures are used. For this purpose, LAB and yeasts with desirable characteristics should be isolated.     

Monitoring the bacterial community during fermentation of sunki, an unsalted, fermented vegetable traditional to the Kiso area of Japan

Aims:  To investigate the microbial community in sunki , an indigenous, unsalted, fermented vegetable, made from the leaves of red beet.
Methods and Results:  Fermenting samples were collected at 1- to 2-day intervals from four houses and investigated by culture-dependent and culture-independent techniques. PCR-Denaturing-Gradient-Gel-Electrophoresis profiles indicated that the bacterial community was stable and Lactobacillus delbrueckii , Lact. fermentum and Lact. plantarum were dominant during the fermentation. This result agreed well with that obtained by the culturing technique. Moulds, yeasts or bacteria other than lactic acid bacteria (LAB) were not detected.
Conclusions:  The bacterial community was stable throughout the fermentation, and Lact. delbrueckii , Lact. fermentum and Lact. plantarum were dominant. The acidic pH and lactic acid produced by LAB probably preserve the sunki from spoilage.
Significance and Impact of the Study:  This is the first report on the use of both culture-dependent and culture-independent techniques to study the bacterial community in sunki . A combination of culture-dependent and culture-independent techniques is necessary for the analysis of complex microbial communities.     

Isolation and characteristics of lactic acid bacteria from koshu vineyards in Japan

Aims:  To isolate, characterize and identify lactic acid bacteria (LAB) in the vineyards where koshu grapes, a primary wine grape cultivar in Japan, are grown.
Methods and Results:  Sixty samples, including leaves, undamaged grape berries and soil under damaged berries, were collected at four koshu vineyards in Yamanashi Prefecture, Japan. One hundred and 15 acid-producing cultures were isolated from these samples, and the isolates were divided into classes by phenotype and then into groups by restriction fragment length polymorphism analysis and sequencing of 16S ribosomal DNA (rDNA). Phenotypic and biochemical characteristics identified seven different bacterial groups (A to G). Lactococcus lactis ssp. lactis was the most abundant type of LAB distributed in three koshu vineyards, and Leuconostoc pseudomesenteroides was the most abundant LAB found in the remaining vineyard. Forty-six isolates produced bacteriocin-like inhibitory substances (BLIS) against the indicator strain Lactobacillus sakei JCM 1157^T.
Conclusions:  These results suggest that various LAB are distributed in koshu vineyards, of which a large number produce BLIS.
Significance and Impact of the Study:  This is the first report describing the distribution and varieties of LAB that exist in koshu vineyards.     

Isolation of bovine intestinal Lactobacillus plantarum and Pediococcus acidilactici with inhibitory activity against Escherichia coli O157 and F5

Aims:  The growth rate of bovine lactic acid bacteria (LAB) in five different culture conditions, and their inhibitory activity against Escherichia coli O157 and F5 in two assays was assessed to identify LAB for potential prophylactic use in cattle.
Methods and Results:  106 bovine-derived faecal/intestinal LAB were tested in vitro for tolerance to pH 2·0, pH 4·0, 0·15% and 0·3% bile, aerobic incubation, and for inhibitory activity against E. coli O157 ( n  = 3) and F5 ( n  = 1). While no LAB grew at pH 2·0, LAB survivability varied between 35% and 100% on the other tests. Exactly 7·6% (8/106) of LAB supernatants inhibited the growth of E. coli in two assays, whereas 6·6% (7/106) of isolates enhanced the growth of all E. coli strains. Partial 16s rRNA gene sequencing of six best isolates (95th percentile) revealed that five were Lactobacillus plantarum and one Pediococcus acidilactici.
Conclusion:  Lactobacillus plantarum with acid/bile and aerobic resistance and inhibitory activity against E. coli O157 and F5 inhabit the intestinal tract of healthy cattle. Some LAB may enhance E. coli growth.
Significance and Impact of the Study:  Lactobacillus plantarum and P. acidilactici are natural plant micro-organisms and studied silage inoculants. Their identification from gastrointestinal samples of healthy cattle is prophylactically promising.     

Lactic acid bacteria as live vaccines

Mucosal routes for vaccine delivery offer several advantages over systemic inoculation from both immunological and practical points of view. The development of efficient mucosal vaccines therefore represents a top prority in modern vaccinology. One way to deliver protective antigens at the mucosal surfaces is to use live bacterial vectors. Until recently most of these were derived from attenuated pathogenic microorganisms. As an alternative to this strategy, non-pathogenic food grade bacteria such as lactic acid bacteria (LAB) are being tested for their efficacy as live antigen carriers. The LABVAC european research network is presently comparing the vaccine potential of Lactococcus lactis, Streptococcus gordonii and Lactobacillus spp. To date, it has been shown that systemic and mucosal antigen-specific immune responses can be elicited in mice through the nasal route using the three LAB systems under study. Data on successful oral and vaginal immunisations are also accumulating for L. lactis and S. gordonii, respectively. Moreover, the immune responses can be potentiated by co-expression of interleukins. Future areas of research include improvement of local immunisation efficiency, analysis of in vivo antigen production, unravelling of the Lactobacillus colonisation mechanisms and construction of biologically contained strains.     

Microbial characterisation of fermented meat products from the Sicilian swine breed “Suino Nero Dei Nebrodi”

Two traditional sausage products (“salsiccia” and “salame”) processed from the raw meat of the Black Sicilian swine “Suino Nero dei Nebrodi” were microbiologically investigated during the manufacturing and ripening stages. Both products were dominated by lactic acid bacteria (LAB), especially rod-shaped types. The concentration of enterococci was consistent in salame. Coagulase-negative cocci increased slower than LAB. Yeasts showed an increasing trend during the ripening of both products. Enterobacteriaceae were counted at a constant level of about 10⁵ CFU/g in both products, while pseudomonads diminished during ripening. Coagulase-positive staphylococci, Listeria monocytogenes and Salmonella spp. were not detected at the end of the ripening process. Characterisation of LAB at the strain and species level revealed that Lactococcus lactis was found only in the meat mixture, while Lactobacillus sakei and various enterococci persisted during the monitoring period. Some LAB strains isolated from sausages were also identified on the surface of the factory equipment. Two strains (Lactobacillus sakei SS106A and Enterococcus faecalis SS91) were characterised by their anti-Listeria properties due to bacteriocin-like inhibitory substance production. A multiple strain starter composed of Lactobacillus sakei and enterococci has been proposed to maintain the typical characteristics of the two fermented meat products microbiologically investigated in this study.     

Characterization of some bacteriocins produced by lactic acid bacteria isolated from fermented foods

Lactic acid bacteria (LAB) isolated from different sources (dairy products, fruits, fresh and fermented vegetables, fermented cereals) were screened for antimicrobial activity against other bacteria, including potential pathogens and food spoiling bacteria. Six strains have been shown to produce bacteriocins: Lactococcus lactis 19.3, Lactobacillus plantarum 26.1, Enterococcus durans 41.2, isolated from dairy products and Lactobacillus amylolyticus P40 and P50, and Lactobacillus oris P49, isolated from bors. Among the six bacteriocins, there were both heat stable, low molecular mass polypeptides, with a broad inhibitory spectrum, probably belonging to class II bacteriocins, and heat labile, high molecular mass proteins, with a very narrow inhibitory spectrum, most probably belonging to class III bacteriocins. A synergistic effect of some bacteriocins mixtures was observed. We can conclude that fermented foods are still important sources of new functional LAB. Among the six characterized bacteriocins, there might be some novel compounds with interesting features. Moreover, the bacteriocin-producing strains isolated in our study may find applications as protective cultures.     

Preliminary characterization of lactic acid bacteria isolated from Zlatar cheese

AIMS: Isolation, characterization and identification of lactic acid bacteria (LAB) from artisanal Zlatar cheese during the ripening process and selection of strains with good technological characteristics. METHODS AND RESULTS: Characterization of LAB was performed based on morphological, physiological and biochemical assays, as well as, by determining proteolytic activity and plasmid profile. rep-polymerase chain reaction (PCR) analysis and 16S rDNA sequencing were used for the identification of LAB. PCR analysis was performed with specific primers for detection of the gene encoding nisin production. Strains Lactobacillus paracasei subsp. paracasei, Lactobacillus plantarum, Lactobacillus brevis, Lactococcus lactis subsp. lactis, Enterococcus faecium and Enterococcus faecalis were the main groups present in the Zlatar cheese during ripening. CONCLUSIONS: Temporal changes in the species were observed during the Zlatar cheese ripening. Mesophilic lactobacilli are predominant microflora in Zlatar cheese. SIGNIFICANCE AND IMPACT OF THE STUDY: In this study we determined that Zlatar cheese up to 30 days old could be used as a source of strains for the preparation of potential starter cultures in the process of industrial cheese production. As the Serbian food market is adjusting to European Union regulations, the standardization of Zlatar cheese production by using starter culture(s) based on autochtonous well-characterized LAB will enable the industrial production of this popular cheese in the future.     

Volatile sulfur compounds produced by probiotic bacteria in the presence of cysteine or methionine

Aims:  To investigate the abilities of various probiotic bacteria to produce volatile sulfur compounds (VSCs) relevant to food flavour and aroma.
Methods and Results:  Probiotic strains ( Lactobacillus acidophilus NCFM, Lactobacillus plantarum 299v, Lactobacillus rhamnosus GG, Lactobacillus reuteri ATCC55730 and L. reuteri BR11), Lactobacillus delbrueckii ATCC4797, L. plantarum ATCC14917 and Lactococcus lactis MG1363 were incubated with either cysteine or methionine. Volatile compounds were captured, identified and quantified using a sensitive solid-phase microextraction (SPME) technique combined with gas chromatography coupled to a pulsed flame photometric detector (SPME/GC/PFPD). Several VSCs were identified including H₂S, methanethiol, dimethyldisulfide and dimethyltrisulfide. The VSC profiles varied substantially for different strains of L. plantarum and L. reuteri and it was found that L. reuteri ATCC55730 and L. lactis MG1363 produced the lowest levels of VSCs ( P  < 0·05). Levels of VSCs generated by bacteria were found to be equivalent to, or higher than, that found in commercial cheeses.
Conclusions:  Several probiotic strains are able to generate considerable levels of VSCs and substantial variations in VSC generating potential exists between different strains from the same species.
Significance and Importance of the Study:  This study demonstrates that probiotic bacteria are able to efficiently generate important flavour and aroma compounds and therefore has implications for the development of probiotic containing foods.     

Lactic acid bacteria associated with vacuum-packed cooked meat product spoilage: population analysis by rDNA-based methods

AIM: To determine the lactic acid bacteria (LAB) implicated in bloating spoilage of vacuum-packed and refrigerated meat products. METHODS AND RESULTS: A total of 18 samples corresponding to four types of meat products, with and without spoilage symptoms, were studied. In all, 387 colonies growing on de Man, Rogosa and Sharpe, yeast glucose lactose peptone and trypticase soy yeast extract plates were identified by internal spacer region (ISR), ISR-restriction fragment length polymorphism and rapid amplified ribosomal DNA restriction analysis profiles as Lactobacillus (37%), Leuconostoc (43%), Carnobacterium (11%), Enterococcus (4%) and Lactococcus (2%). Leuconostoc mesenteroides dominated the microbial population of spoiled products and was always present at the moment bloating occurred. Lactobacillus sakei, Lactobacillus plantarum and Lactobacillus curvatus were found in decreasing order of abundance. The analysis of two meat products, 'morcilla' and 'fiambre de magro adobado' obtained from production lines revealed a common succession pattern in LAB populations in both products and showed that Leuc. mesenteroides became the main species during storage, despite being below the detection level of culture methods after packing. CONCLUSIONS: Our results pointed to Leuc. mesenteroides as the main species responsible for bloating spoilage in vacuum-packed meat products. SIGNIFICANCE AND IMPACT OF THE STUDY: Prevention of bloating spoilage in vacuum-packed cooked meat products requires the sensitive detection of Leuc. mesenteroides (i.e. by PCR).     

Molecular source tracking of predominant lactic acid bacteria in traditional Belgian sourdoughs and their production environments

Aims:  To investigate the circulation of predominant sourdough lactic acid bacteria (LAB) species in the production environment of two Belgian artisan sourdough bakeries.
Methods and Results:  Isolates were collected from sourdoughs, flour, hands of the baker and air in the bakery setting and taxonomically characterized using repetitive element sequence-based PCR fingerprinting, pheS and/or 16S rRNA gene sequencing and amplified fragment length polymorphism (AFLP) analysis. In parallel, PCR-DGGE (denaturing gradient gel electrophoresis) analysis of V3-16S rDNA amplicons was applied to visualize the predominant bacterial population in the sourdoughs and the corresponding bakery environment (flour, hands of the baker, air and bakery equipment). Both approaches revealed that sourdoughs produced at D01 and D10 were mainly dominated by Lactobacillus spicheri and L. plantarum and by L. sanfranciscensis , respectively, and that these LAB species also circulated in the corresponding bakery environment. Furthermore, AFLP fingerprinting demonstrated that sourdough and bakery environment isolates of these species were genetically indistinguishable. For more sensitive source-tracking, SYBR Green-based real-time PCR assays were developed using species-specific primers targeting the pheS gene of L. plantarum and L. sanfranciscensis, detected in air samples from D01 and D10, respectively.
Conclusions:  The results obtained in this study indicate that specific strains of LAB persist in artisan doughs over years and circulate in the bakery environment. Furthermore, the importance of air as a potential carrier of LAB in artisan bakery environments was demonstrated.
Significance and Impact of the Study:  PheS -based real-time PCR can be used to detect, quantify and/or monitor specific LAB species (e.g. starter cultures) in sourdough and bakery environment samples.     

A differential medium for lactic acid-producing bacteria in a mixed culture

Aims:  Modified deMan-Rogosa Sharpe agar containing bromophenol blue (mMRS-BPB) was tested as a medium for counting and differentiation of each lactic acid-producing bacterium (LAB), especially in a mixed culture.
Methods and Results:  Type strains of 10 LAB species ( Lactobacillus acidophilus , L. brevis , L. bulgaricus , L. gasseri , L. paracasei , L. plantarum , L. reuteri , Weissella confusa , Bifidobacterium bifidum and B. infantis ) and five commercial yogurts were inoculated on plate count agar with bromocresol purple, mMRS, and mMRS-BPB. Each type strain showed more clearly formed colonies on the three media under anaerobic conditions than under aerobic conditions. Especially each type strain produced colonies with specific characteristics of each species on mMRS-BPB. Commercial yogurts produced the largest number of colonies with various shapes and colours on mMRS-BPB.
Conclusions:  Modified deMan-Rogosa Sharpe agar containing bromophenol blue under anaerobic conditions is appropriate for counting and differentiating each LAB in a mixed culture.
Significance and Impact of the Study:  Modified deMan-Rogosa Sharpe agar containing bromophenol blue will be useful in isolation and enumeration of each LAB from fermented foods as well as intestinal microflora.     

PCR-DGGE analysis of lactic acid bacteria and yeast dynamics during the production processes of three varieties of Panettone

Aims:  To study lactic acid bacteria (LAB) and yeast dynamics during the production processes of sweet-leavened goods manufactured with type I sourdoughs.
Methods and Results:  Fourteen sourdough and dough samples were taken from a baking company in central Italy during the production lines of three varieties of Panettone. The samples underwent pH measurements and plating analysis on three solid media. The microbial DNA was extracted from both the (sour)doughs and the viable LAB and yeast cells collected in bulk, and subjected to PCR-denaturing gradient gel electrophoresis (DGGE) analysis. The molecular fingerprinting of the cultivable plus noncultivable microbial populations provide evidence of the dominance of Lactobacillus sanfranciscensis , Lactobacillus brevis and Candida humilis in the three fermentation processes. The DGGE profiles of the cultivable communities reveal a bacterial shift in the final stages of two of the production processes, suggesting an effect of technological parameters on the selection of the dough microflora.
Conclusions:  Our findings confirm the importance of using a combined analytical approach to explore microbial communities that develop during the leavening process of sweet-leavened goods.
Significance and Impact of the Study:  In-depth studies of sourdough biodiversity and population dynamics occurring during sourdough fermentation are fundamental for the control of the leavening process and the manufacture of standardized, high-quality products.     

Characterization of bacteriocin-like inhibitory substances (BLIS) from sourdough lactic acid bacteria and evaluation of their in vitro and in situ activity

AIMS: To identify and characterize bacteriocion-producing lactic acid bacteria (LAB) in sourdoughs and to compare in vitro and in situ bacteriocin activity of sourdough- and nonsourdough LAB. METHODS AND RESULTS: Production of antimicrobial compounds by 437 Lactobacillus strains isolated from 70 sourdoughs was investigated. Five strains (Lactobacillus pentosus 2MF8 and 8CF, Lb. plantarum 4DE and 3DM and Lactobacillus spp. CS1) were found to produce distinct bacteriocin-like inhibitory substances (BLIS). BLIS-producing Lactococcus lactis isolated from raw barley showed a wider inhibitory spectrum than sourdough LAB, but they did not inhibit all strains of the key sourdough bacterium Lb. sanfranciscensis. Antimicrobial production by Lb. pentosus 2MF8 and Lc. lactis M30 was also demonstrated in situ. CONCLUSIONS: BLIS production by sourdough LAB appears to occur at a low frequency, showing limited inhibitory spectrum when compared with BLIS-producing Lc. lactis. Nevertheless, they are active BLIS producers under sourdough and bread-making conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: The activity of BLIS has been demonstrated in situ. It may influence the complex sourdough microflora and support the implantation and stability of selected insensitive bacteria, such as Lb. sanfranciscensis, useful to confer good characteristics to the dough.     

Isolation and identification of cultivable lactic acid bacteria in traditional yak milk products of Gansu Province in China

Various traditional fermented yak milk and raw milk foods could be considered as an abundant resource for obtaining novel lactic acid bacteria (LAB) with unique properties. Eighty-eight samples of yak milk products were collected from Gansu Province in China. Three hundred and nineteen strains of LAB isolated from these samples were identified by phenotypic methods, 16S rRNA gene sequence analysis and PCR-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) technology. Among the isolates, one hundred and sixty-four isolates (51.41% of the total) were classified under Lactobacilli, and one hundred and fifty-five (48.59%) belonged to cocci. All the isolates were classified to six genera (Lactobacillus, Lactococcus, Leuconostoc, Streptococcus, Enterococcus and Weissella) and twenty-one species. Lactobacillus helveticus (87 strains), Leuconostoc mesenteroides subsp. mesenteroides (49 strains), Streptococcus thermophilus (39 strains), Lactobacillus casei (31 strains) and Lactococcus lactis subsp. lactis (19 strains) were considered as the predominant populations in the yak milk products. The results showed that there were abundant genus and species LAB existing in yak milk products in Gansu Province in China. The obtained LAB pure cultures may be a valuable source for further starter selection.     

The occurrence of aerolysin-positive Aeromonas spp. and their cytotoxicity in Norwegian water sources

Aims:  The aim of the study was to investigate the occurrence of Aeromonas spp. and their aerolysin status in Norwegian natural water sources.
Methods and Results:  Seventy-one samples from 33 Norwegian water sources were examined for the presence of Aeromonas spp. From most of the sample sites, the strains were isolated on blood-ampicillin-agar and Difco Aeromonas agar simultaneously. The majority of the samples (73/77) contained Aeromonas spp., with an average of 35–100 cfu 100 ml^–1. The highest counts were found in faecally-contaminated water. Using PCR, 445 isolates were screened for the presence of aerolysin, and 79% of them were found to be carriers of the aerolysin gene. A selection of the isolated strains was tested on Vero cell cultures and 83% of them showed cytotoxicity.
Conclusions:  There is widespread occurrence of aerolysin-positive cytotoxic Aeromonas spp. in many different Norwegian natural waters, including drinking water sources.
Significance and Impact of the Study:  The widespread occurrence of potentially-pathogenic Aeromonas spp. in the environment demands that these bacteria should not be ignored in drinking water supplies and in the food industry.     

Antimicrobial activity of lactic acid bacteria isolated from Tenerife cheese: initial characterization of plantaricin TF711, a bacteriocin-like substance produced by Lactobacillus plantarum TF711

AIMS: The screening and initial characterization of bacteriocins produced by lactic acid bacteria (LAB) from raw Tenerife goats' cheese with possible application as biopreservatives or ripening accelerators for Tenerife cheese. METHODS AND RESULTS: One hundred and eighty LAB of the genera Lactobacillus (95), Leuconostoc (64) and Lactococcus (21) isolated from raw Tenerife goats' cheese were screened for the production of antimicrobial substances. Lactobacillus plantarum TF711, which had the broadest spectrum of antimicrobial activity, was selected for further characterization. The antimicrobial compound was determined as a proteinaceous substance, as it was sensitive to proteases. The bacteriocin-like substance, which we called plantaricin TF711, was active against the Gram-positive bacteria Bacillus cereus, Clostridium sporogenes and Staphylococcus aureus; and against the Enterobacteriaceae Shigella sonnei and Klebsiella pneumoniae. It was stable to heat and to treatment with surfactants and organic solvents. Highest antimicrobial activity was found between pH 1 and 9. Plantaricin TF711 exhibited primary metabolite kinetics, a bacteriostatic mode of action and a molecular mass of c. 2.5 kDa as determined by tricine SDS-PAGE. CONCLUSIONS: Lact. plantarum TF711 produces a low molecular mass bacteriocin-like compound with a wide spectrum of activity and interesting technological properties (thermostability, good pH stability and stability against surfactants and organic solvents). SIGNIFICANCE AND IMPACT OF THE STUDY: Plantaricin TF711 was found to have potential for use as a biopreservative in the food industry.