Cork-borne bacteria and yeasts as potential producers of off-flavours in wine

Bacteria and yeasts were found to be present within cork lenticels, covered by mucous or fibrous substances. They survived heating, peroxide treatment and contact with the alcohol and sulfur dioxide of wine. 187 bacteria and 36 yeast strains were isolated from cork stoppers of wine bottles and, during various stages of production, from corkwood and new cork stoppers. After culturing, a number of isolates showed the ability to modify the aroma of model systems consisting of dilute or full strength wine and pulverised cork. The aromas produced by isolates of varying cork origin are tabled. A small number of isolates methylated 2,4,6-trichlorophenol, yielding 2,4,6-trichloroanisole, responsible for the typical cork taint. During the boiling of cork slabs, the internal temperature on the inside of a box made from cork slices did not exceed 87°C.     

Transformation ability of fungi isolated from cork and grape to produce 2,4,6-trichloroanisole from 2,4,6-trichlorophenol

The ability of eight fungal strains to transform 2,4,6-trichlorophenol (TCP) to 2,4,6-trichloroanisole (TCA) was studied. These fungi were isolated from cork, belonging to the genera Penicillium, Aspergillus, Trichoderma and Chrysonilia, and from grapes Botrytis cinerea. All, except Chrysonilia, produced TCA when grown directly on cork in the presence of TCP, Aspergillus and Botrytis cinerea being the ones with the highest level of production. It is the first time that Botrytis cinerea, a microorganism often present on grapes and in winery environments, has been shown to transform TCP into TCA. This result can partially explain the wine cork taint before being bottled.     

Epidemiological investigation of Streptococcus equi subspecies zooepidemicus involved in clinical mastitis in dairy goats

An outbreak of clinical mastitis was observed in dairy goats due to the zoonotic pathogen Streptococcus equi ssp. zooepidemicus. Affected goats were culled to prevent transmission of infection to other animals or humans. The objective of the study was to determine whether horses on the same farm were the source of the pathogen. Streptococcus equi ssp. zooepidemicus was obtained from milk of 10% of goats in the herd and from feces of 3 of 7 healthy horses that shared pasture and housing with the goats. Isolates of caprine and equine origin had identical biochemical profiles, including the ability to ferment sorbitol and lactose, which distinguishes S. equi ssp. zooepidemicus from S. equi ssp. equi. Sequencing of the 16S-23S intergenic spacer region and results from sodA-seeI multiplex PCR supported identification of isolates as S. equi ssp. zooepidemicus. Based on random amplified polymorphic DNA typing and rpoB and sodA sequencing, caprine isolates were indistinguishable from each other, but distinct from equine isolates. Further analysis of equine fecal samples showed that multiple strains of S. equi ssp. zooepidemicus can be present in a single sample or in sequential samples obtained from a single horse. Failure to detect the mastitis-causing strain in equine feces may indicate that horses were not the source of the mastitis outbreak in goats. Alternatively, the outbreak may be due to presence of multiple S. equi ssp. zooepidemicus strains in equine feces and a failure to detect all strains when analyzing a limited number of isolates per sample.     

Development of a DNA microarray for detection and identification of Legionella pneumophila and ten other pathogens in drinking water

The safety and accessibility of drinking water are major concerns throughout the world. Consumption of water contaminated with infectious agents, toxic chemicals or radiological hazards represents a significant health risk and is strongly associated with mortality. Therefore, we have developed an oligonucleotide-based microarray using the sequences of 16S-23S rDNA internal transcribed spacer regions (ITS) and the gyrase subunit B gene (gyrB) found in the most prevalent and devastating waterborne pathogenic agents. This new diagnostic contains 26 specific probes and can simultaneously detect Aeromonas hydrophila, Klebsiella pneumoniae, Legionella pneumophila, Pseudomonas aeruginosa, Salmonella spp., Shigella spp., Staphylococcus aureus, Vibrio choleraeo, Vibrio parahaemolyticus, Yersinia enterocolitica and Leptospira interrogans. Testing was carried out against a total of 218 bacterial strains, including 53 representative strains, 103 clinical isolates and 62 strains of other bacterial species belonging to 10 genera and 48 species. The results were specific and reproducible, with a detection sensitivity of 0.1 ng DNA or 10⁴ CFU/ml achieved for pure cultures of each target organism. The diluted cultures and real drinking water samples were tested by the microarray with 100% accuracy. This novel diagnostic method is superior in time- and labor-efficiency to conventional bacterial culture and antiserum agglutination, and can be readily applied to epidemiological surveillance and other food safety applications.     

Effect of exopolysaccharides (EPSs) produced by Lactobacillus delbrueckii subsp. bulgaricus strains to bacteriophage and nisin sensitivity of the bacteria

Lactobacillus strains used in this study were isolated from village-type yogurt and raw milk. The isolates were identified as Lactobacillus delbrueckii subsp. bulgaricus by 16 s rDNA sequence analysis and API 50 CHL identification systems. The exopolysaccharide (EPS) production of the strains growth in skim milk were investigated. In addition sensitivity and insensitivity of these strains against domestic bacteriophages and nisin were examined. It was deduced that those strains which had relatively high EPS-producing capacity were insensitive against phages and nisin. Linear relationships were determined between EPS production of the bacteria and bacteriophage and nisin insensitivity of the bacteria.There was a negative correlation between EPS production quantity and phage and nisin sensitivity of the bacteria. Of all the strains, L. delbrueckii subsp bulgaricus B3 produced the highest EPS quantity, and it was insensitive against phages and nisin. Based on these results, it is suggested that L. delbrueckii subsp bulgaricus B3 can be used with the starter culture in dairy industry for stable and high-quality yogurt production.     

Enterococcus populations in artisanal Manchego cheese: biodiversity, technological and safety aspects

Enterococci represent a considerable proportion of the microbiota in Manchego cheeses. In this study, a total of 132 enterococci isolated from good quality Manchego cheeses from two dairies at different ripening times were genotypically characterized and identified using molecular techniques. Representative isolates from the clusters obtained after genotyping were assayed for some enzymatic activities considered to have a potential role in cheese ripening, and for 2,3-butanedione and acetoin production, evaluation of odor intensity and appearance in milk and safety evaluation. Enterococcus faecalis was the predominant specie, accounting for 81.8% of the total isolates, while Enterococcus faecium, Enterococcus hirae and Enterococcus avium were present in low proportions. The number of genotypes involved at each ripening time varied both between dairies and with the ripening times; genotype E. faecalis Q1 being present in almost all the samples from both dairies. Eight isolates showed a higher proteolytic activity and 3 isolates produced high quantities of acetoin-diacetyl, for which reason they are interesting from a technological standpoint. A low antibiotic resistance was found and almost all the strains were susceptible to clinically important antibiotics. On the contrary, only four isolates (E. faecalis C4W1 and N0W5, and E. faecium N32W1 and C16W2) did not harbor some of the virulence genes assayed.     

Genotypic and technological characterization of Leuconostoc isolates to be used as adjunct starters in Manchego cheese manufacture

Twenty-seven Leuconostoc (Ln.) isolates from Manchego cheese were characterized by phenotypic and genotypic methods, and their technological abilities studied in order to test their potential use as dairy starter components. While phenotypic diversity was evaluated by studying the biochemical characteristics of technological interest (i.e. acidifying and aminopeptidase activities), genotypic diversity was evidenced by using Randomly Amplified Polymorphic DNA-Polymerase Chain Reaction (RAPD-PCR). Additional technological abilities such as lipolytic, proteolytic and autolytic activities, salt and pH tolerance and production of dextran, flavour compounds and biogenic amines, were investigated. The marked differences among strains reflected the existing biodiversity in naturally fermented products. After statistically evaluating their performance, strains C0W2, belonging to Ln. lactis, and C16W5 and N2W5, belonging to Ln. mesenteroides subsp. dextranicum, revealed the best properties to be used in mixed dairy starter cultures. This study evidences the fact that natural environments can be considered as a proper source of useful strains, for the dairy industry.     

Interactions in biofilms of Lactococcus lactis ssp. cremoris and Pseudomonas fluorescens cultured in cold UHT milk

Three Lactococcus lactis ssp. cremoris isolates from refrigerated bulk raw milk were cultured separately and in association with a known psychrotrophic dairy Pseudomonas fluorescens strain, in skim UHT milk for 72 h at 7°C, to determine mutual influences in both the planktonic and biofilm phases. Two levels of inoculum of each culture partner were combined. Protocooperation and commensalism cases were found, all of them in the biofilm phase. Type and intensity of the interactions depended on Lactococcus strain and on the cell density of each partner. Maximum enhancement of attachment was observed to be approximately 100-fold for P. fluorescens and 20,000-fold for one of the L. lactis strains. Confocal scanning laser microscopy images show compact masses of Pseudomonas trapping lactococci cells in cooperative biofilms.     

Determination of some characteristics coccoid forms of lactic acid bacteria isolated from Turkish kefirs with natural probiotic

In this study, a total of 21 coccoid forms of lactic acid bacteria (lactococci) were isolated from Turkish kefir samples. As a result of the identification tests, 21 lactococci isolates were identified as Lactococcus cremoris (11 strains), Lactococcus lactis (4 strains), Streptococcus thermophilus (3 strains) and Streptococcus durans (3 strains). The amount of produced lactic acid, hydrogen peroxide, proteolytic activity, diacetyl and acetaldehyde productions of the lactococci were determined. Different amounts of lactic acid were produced by strains studies; however, lactic acid levels were 2.3-9.9 mg/ml. While Lac. lactis Z13S, Str. durans Z7S, Z8S, Z15S, Lac. cremoris Z9S, Z16S, Z17S, Z19S, Z20S and Z21S strains were not shown hydrogen peroxide, Lac. lactis Z1S and Z2S strains had a maximum hydrogen peroxide (0.17 μg/ml). Lac. lactis Z2S, Z3S, Str. thermophilus Z5S, Z12S, Str. durans Z7S, Z8S, Lac. cremoris Z14S and Z16S strains were not show proteolytic activity, Lac. cremoris Z20S strain produced the maximum amount (0.09 mg/ml) of proteolytic activity. Acetaldehyde concentration produced in Lactobacillus strains ranged between 0.18 and 3.96 μg/ml. Antimicrobial effects of the lactococci on Escherichia coli NRLL B-704, Staphylococcus aureus 4-63, Pseudomonas aeruginosa ATCC 29212 were also determined by an agar diffusion method. All of the strains were able to inhibit S. aureus, while Lac. lactis Z1S, Z2S and Lac. cremoris Z6S strains were able to inhibit E. coli and P. aeruginosa. Also, Str. thermophilus Z5S strain were able to inhibit P. aeruginosa.     

High genetic and phenotypic variability of Streptococcus thermophilus strains isolated from artisanal Yuruk yoghurts

Streptococcus thermophilus is a commonly used starter bacterium in dairy industry. It reduces the pH of milk rapidly and equilibrates the medium for the growth of Lactobacillus delbrueckii subsp. bulgaricus during yoghurt fermentation. Efforts to increase the diversity of artisanal yoghurt starters are not only important to bring new strains with novel and desirable characteristics, but also for the preservation of natural diversity which diminishes with the overuse and spread of industrial starters to natural resources. In the present study, 14 artisanal yoghurt samples were processed for the isolation of promising strains for yoghurt starter culture production and 66 strains were subsequently characterized. They were all identified as S. thermophilus using species-specific PCR and 16S rRNA gene sequencing. Genotypic diversity at the strain level was investigated by pulsed field gel electrophoresis (PFGE), and 22 homology groups were obtained. Further phenotypic characterization unearthed a significant phenotypic heterogeneity within homology groups, mostly with atypical novel character. Only 7 out of 66 strains showed S. thermophilus type-strain like phenotypic traits. Majority of the isolates were determined to be protease positive and fast milk acidifier to be used as yoghurt starter culture.     

16S rRNA partial gene sequencing for the differentiation and molecular subtyping of Listeria species

Use of 16S rRNA partial gene sequencing within the regulatory workflow could greatly reduce the time and labor needed for confirmation and subtyping of Listeria monocytogenes. The goal of this study was to build a 16S rRNA partial gene reference library for Listeria spp. and investigate the potential for 16S rRNA molecular subtyping. A total of 86 isolates of Listeria representing L. innocua, L. seeligeri, L. welshimeri, and L. monocytogenes were obtained for use in building the custom library. Seven non-Listeria species and three additional strains of Listeria were obtained for use in exclusivity and food spiking tests. Isolates were sequenced for the partial 16S rRNA gene using the MicroSeq ID 500 Bacterial Identification Kit (Applied Biosystems). High-quality sequences were obtained for 84 of the custom library isolates and 23 unique 16S sequence types were discovered for use in molecular subtyping. All of the exclusivity strains were negative for Listeria and the three Listeria strains used in food spiking were consistently recovered and correctly identified at the species level. The spiking results also allowed for differentiation beyond the species level, as 87% of replicates for one strain and 100% of replicates for the other two strains consistently matched the same 16S type.     

Verification of the effectiveness of SCAR (sequence characterized amplified region) primers for the identification of Polish strains of Fusarium culmorum and their potential ability to produce B-trichothecenes and zearalenone

Rapid and sensitive methods to detect Fusarium culmorum and trichothecene and zearalenone producing strains in food and feed are valuable in predicting potential contamination. In this study the effectiveness of primers, recommended in the literature, for species identification of F. culmorum and basic genes encoding for mycotoxin production was tested. A total of 68 isolates of F. culmorum were collected from cereals and potato between 2005 and 2008 from different Polish provinces. It was shown that from among the four primer pairs enabling the identification of F. culmorum, and therefore also to establish its presence in the material, only primers Fc01F/Fc01R seem to be fully effective in the case of Polish strains. Determination of material contamination by F. culmorum, however, is only a first step in determining food safety. It is also extremely important to identify genes encoding the potential ability to produce mycotoxins. It was shown that three pairs of primers (tox5-1/tox5-2, HATriF/HATriR and Tri5F/Tri5R) enable a fully effective identification of the presence of the Tri5 gene responsible for producing trichothecenes. Determination of the DON-chemotype, and thus identification of the strains of F. culmorum potentially producing deoxynivalenol, is enabled equally by MinusTri7F/MinusTri7F, Tri7F/Tri7DON and Tri13F/Tri13DONR. However, a determination of the NIV-chemotype, and thus identification of the strains potentially producing nivalenol, is enabled by Tri7F/Tri7R, Tri7F/Tri7NIV and Tri13NIVF/Tri13R. The potential ability of isolates to produce ZEA can be determined to the same degree in assay with PKS4-PS.1/PKS4-PS.2 and F1/R1.     

Incidence, diversity and toxin gene characteristics of Bacillus cereus group strains isolated from food products marketed in Belgium

The major objectives of this study were to determine the incidence, diversity and characteristics of Bacillus cereus group spp. isolated from food products marketed in Belgium. The food products investigated in this study included cooked pasta, lasagna, béchamel sauce, bolognaise sauce, fresh minced beef, fresh-cut vegetables and raw basmati rice. B. cereus group spp. were detected in 56.3% (324 of 575) of the samples giving rise to 380 strains. The highest incidence (100%) occurred in the raw basmati rice. Although only 10 (2.6%) of the 380 isolates were determined to be psychrotolerant (able to grow at ≤ 7 °C), 25 (6.2%), 189 (49.7%) and 334 (87.9%) isolates were able to grow at mild temperature abuse conditions of 8 °C, 9 °C and 10 °C, respectively. The large diversity of the isolates obtained (overall and between isolates obtained from the same product type) was highlighted by the results of the (GTG)₅ PCR fingerprinting of 80 selected isolates. Sixty-one of these 80 isolates belonged to 15 distinct clusters (≥ 85% Pearson correlation) whereas the remaining 19 were each clustered separately. Further diversity was also found in the distribution of toxin genes as 16 different profiles were observed in the 80 selected isolates. Whilst none of 80 selected strains harboured the ces gene required for the production of the emetic toxin cereulide, 42 strains (52.5%) carried all seven genes required for the production of the diarrhoeal enterotoxins: haemolytic BL, non-haemolytic enterotoxin and cytotoxin K. The results of this study highlight not only the omnipresence but also the highly diverse ecology of B. cereus spp. within and across several food product types available on the retail market in Belgium. They should also provide the impetus for more studies to enable detailed risk assessment studies to be performed.     

The microflora of fresh and spoiled sardines (Sardina pilchardus) caught in Adriatic (Mediterranean) Sea and stored in ice

A total of 1500 strains were isolated from the skin and gills of fresh, ice-stored (4 days) and spoiled (8 days) Adriatic sardines, and were identified at different taxonomic levels. Fresh sardine microflora found included mostly non-fermenting Gram-negative bacteria, (Pseudomonas, Flavobacterium, Psychrobacter, Acineobacter, Shewanella), and a minor proportion of Enterobacteriaceae and Gram-positive bacteria. The highest increase in microflora frequency, after 8 days in ice, was observed for thePseudomonas fragigroup (8–30·8%) andShewanella putrefaciens(1·8–11%). A significant presence was also noted for fluorescentPseudomonas(15·6–18·4%) andPsychrobacter immobilis(16·4–23·4%). The isolation frequency of the other groups decreased during storage. The most important proteolytic species werePseudomonas fluorescensandShewanella putrefaciensand the most lipolytic bacteria werePsychrobacter immobilisand again,P. fluorescensandS. putrefaciens. A total of 288 isolates, representative of the main groups, were tested for potential spoiling activity (H₂S and off-odour production, TMAO reduction).Shewanella putrefacienswas the strongest spoiler, followed byPseudomonas fluorescens. A weaker activity was observed for strains ofPseudomonas fragi, enterobacteriaceae and non-saccharolytic pseudomonads. The contribution of weak spoiler bacteria can be undermined by the activity of the strongest spoilers, but in some cases the considerable incidence of the former group suggests their effective role.Morganella morganiiwas the only histamine-producing species among 57 screened strains representative of different taxa.     

Identification of lactic acid bacteria involved in the spoilage of pasteurized “foie gras” products

The spoiling microflora of a re-packaged French “foie gras” product was studied. A total of 54 isolates, originating from two different factories, were identified using phenotypical and molecular methods (partial 16S rDNA sequencing). Weissella viridescens was the main species detected in the products from factory 1 (64% of the isolates). These products had a low lactic acid concentration and were considered as non-spoiled. The microflora of factory 2 was dominated mainly by the genus Lactobacillus (95% of the isolates), and the high lactic acid concentration of these products was linked with a strong spoilage. Among the 30 Lactobacillus strains, three species were predominant: Lactobacillus sakei (nine isolates), Lactobacillus coryniformis (eight isolates) and Lactobacillus paraplantarum (five isolates). Challenge tests were performed to confirm the involvement of the Lactobacillus strains in the spoilage of the product. Sterile “foie gras” samples were inoculated with 14 LAB strains from the collection. The most acidifying strains belonged to the species L. sakei, Lactobacillus plantarum and L. paraplantarum. This confirmed the role of the strains from the Lactobacillus genus as the main spoilers of “foie gras” products and will be useful to design new quality protocols and extend the shelf-life of these products.     

Conventional identification of Streptococcus uberis isolated from bovine mastitis in Argentinean dairy herds

The objective of this study was to evaluate a conventional scheme for identifying Streptococcus uberis strains isolated from bovine mastitis. Seventy-five gram-positive, catalase-negative cocci were collected from cows with mastitis from 19 dairy herds located in the east-central region of Argentina. Five American Type Culture Collection strains and bovine isolates were identified by the API 20 Strep system and by restriction fragment length polymorphism analysis of 16S rDNA. A conventional scheme based on 11 biochemical tests was selected for identification of Strep. uberis strains: the Christie-Atkins-Munch-Petersen reaction; hydrolysis of Arg, esculin, and sodium hippurate; growth in inulin, mannitol, raffinose, salicin, and sorbitol; and growth at 45°C and in 6.5% NaCl. Reference strains and 25 bovine isolates were classified accurately to the species level by the conventional scheme in a blind assay. Each reference strain and each bovine isolate were identified as belonging to the same species following these 3 methods. The remaining 50 isolates identified as Strep. uberis by the API 20 Strep system and 16S rDNA RFLP were assayed by the conventional scheme. This scheme correctly identified 47 (94%) of 50 isolates as Strep. uberis by comparing their biochemical profile with that of the reference strain. Three (6%) of the 50 isolates were classified as Strep. uberis by the API 20 Strep system and by 16S rDNA RFLP and were identified as Enterococcus faecalis by the conventional scheme. Thirty percent of the Strep. uberis strains showed biochemical profiles identical to the Strep. uberis American Type Culture Collection 27958 strain. Seventy percent of the Strep. uberis strains demonstrated variability compared with the reference strain, resulting in 19 different biochemical profiles. The conventional scheme proposed in this study resulted in a relatively low number of misidentifications and could biochemically identify not only typical, but also atypical Strep. uberis strains. This conventional scheme can be considered an adequate method for identifying Strep. uberis strains isolated from bovine mastitis because of its affordable cost in developing countries, and it may contribute to determining the frequency of isolation of Strep. uberis strains in Argentinean dairy herds.     

Polysulfide reduction by Clostridium relatives isolated from sulfate-reducing enrichment cultures

Sulfur is almost insoluble in water at ambient temperatures, and therefore polysulfide (S_n²⁻) has been considered as a possible intermediate that is used directly by bacteria in sulfur respiration. Sulfur-reducing reductases have been purified and characterized from a few sulfur reducers. However, polysulfide reduction has only been confirmed in Wolinella succinogenes. In our previous study, the direct production of hydrogen sulfide from polysulfide was confirmed by an enrichment culture obtained from natural samples under sulfate-reducing conditions. The present study attempted to isolate and identify polysulfide-reducing bacteria from the enrichment cultures. Almost all the isolated strains were classified into the genus Clostridium, based on 16S rRNA gene sequence analysis. The isolates, and some closely related strains, were able to reduce polysulfide to hydrogen sulfide. During production of 1 mol of hydrogen sulfide, approximately 2 mol of lactate was converted to acetate. Thus, dissimilatory polysulfide reduction occurred using lactate as an electron donor. The ability to reduce elemental sulfur was also examined with the isolates and the related strains. Although elemental sulfur reducing strains can reduce polysulfides, not all polysulfide-reducing strains can reduce elemental sulfur. These results demonstrate that the conversion of elemental sulfur to polysulfide seems to be important in the reduction process of sulfur.     

Identification, typing and characterisation of Propionibacterium strains from healthy mucosa of the human stomach

Forty two Propionibacterium isolates were recovered from biopsy samples of the gastric mucosa of eight out of 12 healthy people. Of these, 41 were identified as belonging to Propionibacterium acnes; the remaining isolate was identified as belonging to Propionibacterium granulosum. Repetitive extragenic palindromic (REP)-PCR typing suggested that up to four strains might be present in the mucosa of the same individual. Sequence analysis of either recA, tly or camp5 genes of P. acnes isolates revealed two distinct phylogenetic lineages. As per the recA, most isolates belonged to type I, while the remainder of the isolates belonged to type II. Phenotypic analyses of representative isolates showed the different strains to have diverse biochemical properties. For example, large differences were seen in carbohydrate fermentation patterns, the results of qualitative and quantitative enzymatic profiling, and survival at acidic pH. In contrast, the patterns of resistance/susceptibility to a series of 16 antibiotics were rather similar, with no atypical resistances observed. The examined strains showed limited-if any-enzymatic activities that could be ultimately related to pathogenicity (lipolytic, proteolytic or haemolytic activity). This suggests that, in the gastric ecosystem, some Propionibacterium spp. genotypes and/or phenotypes can be considered true commensals.     

Microbial background flora in small-scale cheese production facilities does not inhibit growth and surface attachment of Listeria monocytogenes

The background microbiota of 5 Norwegian small-scale cheese production sites was examined and the effect of the isolated strains on the growth and survival of Listeria monocytogenes was investigated. Samples were taken from the air, food contact surfaces (storage surfaces, cheese molds, and brine) and noncontact surfaces (floor, drains, and doors) and all isolates were identified by sequencing and morphology (mold). A total of 1,314 isolates were identified and found to belong to 55 bacterial genera, 1 species of yeast, and 6 species of mold. Lactococcus spp. (all of which were Lactococcus lactis), Staphylococcus spp., Microbacterium spp., and Psychrobacter sp. were isolated from all 5 sites and Rhodococcus spp. and Chryseobacterium spp. from 4 sites. Thirty-two genera were only found in 1 out of 5 facilities each. Great variations were observed in the microbial background flora both between the 5 producers, and also within the various production sites. The greatest diversity of bacteria was found in drains and on rubber seals of doors. The flora on cheese storage shelves and in salt brines was less varied. A total of 62 bacterial isolates and 1 yeast isolate were tested for antilisterial activity in an overlay assay and a spot-on-lawn assay, but none showed significant inhibitory effects. Listeria monocytogenes was also co-cultured on ceramic tiles with bacteria dominating in the cheese production plants: Lactococcus lactis, Pseudomonas putida, Staphylococcus equorum, Rhodococcus spp., or Psychrobacter spp. None of the tested isolates altered the survival of L. monocytogenes on ceramic tiles. The conclusion of the study was that no common background flora exists in cheese production environments. None of the tested isolates inhibited the growth of L. monocytogenes. Hence, this study does not support the hypothesis that the natural background flora in cheese production environments inhibits the growth or survival of L. monocytogenes.