Enterococcal diversity in the environment of an Irish Cheddar-type cheesemaking factory

Enterococcus and Lactobacillus contamination of raw milk in a farm dairy environment

Enterococci and lactobacilli are ubiquitously found in the intestinal microflora of humans and animals. The aim of the present study was to determine the importance of bovine faeces as a source of these organisms in raw milk. One hundred and fifty six putative enterococci and 362 lactobacilli were isolated from bovine faeces (n=26), cows' teats, raw milk, the milking machine and the milking environment on one farm. The clonal relationships of each group were investigated using Pulsed-Field Gel Electrophoresis and representatives of the different clusters were identified by repetitive DNA element (rep)-PCR fingerprinting, protein profiling, phenylalanyl-tRNA synthase (pheS) sequence analysis or 16S rDNA gene sequencing. Lactobacilli were present at approximately 3 orders of magnitude greater than enterococci in the bovine faeces. The majority of the bovine faecal enterococcal isolates were identified as Aerococcus viridans. Seven teat isolates belonged to a potential novel Aerococcus sp. and one bovine faecal isolate to a potential second novel Aerococcus sp. The lactobacilli present in the bovine faeces were predominantly Lactobacillus mucosae and Lactobacillus brevis, with small numbers of Lactobacillus plantarum. Only one Enterococcus (a strain of E. casseliflavus) out of 76 and one Lactobacillus (a strain of L. parabuchneri/kefir) out of 247 of the bovine faecal isolates was found in the milk. The major source of these bacteria in the milk was the milking equipment.

Enterococci from Appenzeller and Schabziger raw milk cheese: antibiotic resistance, virulence factors, and persistence of particular strains in the products

Enterococci are natural residents of human and animal intestinal tracts, and grow to high numbers in a variety of cheeses. The aim of this study was to determine the diversity of enterococci in two types of artisanal raw milk cheese (Schabziger and Appenzeller) and to investigate whether particular strains with triple resistance against chloramphenicol (Chl), tetracycline (Tet), and erythromycin (Ery) persist in the production system. Of 46 cheese samples, a total of 312 Enterococcus strains were isolated over a 5-month period on selective agar plates containing Chl, Tet, or, Ery. Enterococcus faecalis was the predominant species (80.7%), followed by Enterococcus faecium (5.1%), and Enterococcus durans (11.7%). According to the phenotypic resistance patterns, a selection of 150 strains was analyzed with PCR for the presence of genes encoding resistance to Ery (ereA, ereB, mphA, ermA, ermB, ermC, mrsA/mrsB, mefA/mefE), and Tet (tetM, tetL). Because virulence factors have been linked to the pathogenicity of enterococci, the strain selection was also tested for the presence of the following virulence factors: Agg, GelE, Cyl, Esp, EfaAfs, EfaAfm, Cpd, Cob, and Ccf. All tested strains contained at least two of the nine virulence genes taken into analysis. Pulsed-field gel electrophoresis patterns of the isolates showed a limited persistence of several strains over a period of 1 to 2 months in Schabziger, and more than 2 months in Appenzeller. Finally, the enterococcal flora in the two types of cheeses seems to be rather unrelated. Within 150 strains from 25 different cheese samples (11 Appenzeller and 14 Schabziger), 41 pulsed-field gel electrophoresis patterns could be identified, and only 1 of these was found in enterococci from both types of cheese.

The role and application of enterococci in food and health

The genus Enterococcus is the most controversial group of lactic acid bacteria. Studies on the microbiota of many traditional cheeses in the Mediterranean countries have indicated that enterococci play an important role in the ripening of these cheeses, probably through proteolysis, lipolysis, and citrate breakdown, hence contributing to their typical taste and flavour. Enterococci are also present in other fermented foods, such as sausages and olives. However, their role in these products has not been fully elucidated. Furthermore, the production of bacteriocins by enterococci is well documented. Moreover, enterococci are nowadays used as probiotics. At the same time, however, enterococci have been associated with a number of human infections. Several virulence factors have been described and the number of vancomycin-resistant enterococci is increasing. The controversial nature of enterococci has prompted an enormous increase in scientific papers and reviews in recent years, where researchers have been divided into two groups, namely pro and contra enterococci. To the authors' impression, the negative traits have been focused on very extensively. The aim of the present review is to give a balanced overview of both beneficial and virulence features of this divisive group of microorganisms, because it is only acquaintance with both sides that may allow their safe exploitation as starter cultures or co-cultures.

Molecular identification and diversity of enterococci isolated from Slovak Bryndza cheese

Three hundred and eight presumed enterococcal isolates were recovered from Bryndza, a soft sheep milk cheese. The cheese samples were obtained from five different commercial distributors in Slovakia and were taken at three different seasonal intervals. All isolates were identified to the species level using genotypic tools. Species-specific PCR using ddl genes highlighted the predominance of Enterococcus faecium (176 isolates) and assigned 50 isolates to the species Enterococcus faecalis. The remaining 82 isolates were classified using repetitive element sequence-based polymerase chain reaction (PCR) with primer (GTG)(5)-(GTG)(5)-PCR, in combination with phenylalanyl-tRNA synthase gene (pheS) sequence analysis and by whole-cell protein analysis (SDS-PAGE). These strains were identified as Enterococcus durans (59 strains), Enterococcus italicus (8 strains), Enterococcus casseliflavus (3 strains), Enterococcus gallinarum (3 strains), Enterococcus hirae (1 strain), and 8 strains were members of the species Lactococcus lactis. Of the seven enterococcal species isolated, three of them, E. durans, E. faecalis and E. faecium were present in all samples studied, with E. faecium as the predominant one. The precise identification of enterococci in Bryndza cheese is an essential step in the process of evaluation of their functional properties which will be further studied and assessed.

Enterococci from Tolminc cheese: Population structure, antibiotic susceptibility and incidence of virulence determinants

Microbiological analysis of ripened artisanal Tolminc cheese revealed the presence of an enterococcal population in numbers of up to 10(6) per g. All colonies, isolated from the citrate azide tween carbonate (CATC) enterococcal selective medium were Gram positive and coccal-shaped and were analysed with PhenePlate FS system. This system discriminated 10 PhP clusters among the 90 enterococcal isolates. From each cluster the most representative isolate for that particular type was selected for further study. The 10 representative enterococci were catalase negative and grew in the presence of NaCl (2%, 4% and 6.5%) and bile salts (0.06%). Genus specific primers confirmed all 10 enterococcal representatives as Enterococcus members, while species specific primers determined them further as strains of Enterococcus faecalis species. PCR for vanA and vanB genes detection, respectively, amplified no PCR products. The absence of van genes was confirmed with both disc and E-test, as isolates were susceptible to vancomycin according to the National Committee for Clinical Laboratory Standards (NCCLS). The results of disc tests with other antimicrobial agents (ampicillin, vancomycin, kanamycin, penicillin, erythromycin, neomycin, chloramphenicol, clindamycin, rifampin) did not differ much among the tested enterococci: they were all very resistant to clindamycin only. The incidence of enterococcus virulence determinants was as expected: all of the 10 E. faecalis strains tested possessed multiple determinants (between 7 and 11).

Antibiotic resistance and virulence traits of enterococci isolated from Baylough, an Irish artisanal cheese

Eight representative Enterococcus strains from a collection of over 600 previously isolated from an Irish artisanal cheese were subjected to phenotypic and genotypic analysis of antibiotic resistance and virulence properties. Genes encoding resistance to tetracycline (tet(M) and tet(L)) and/or erythromycin (erm(B)) were detected in five strains. In addition, all strains contained two or more of the virulence genes tested (agg, gel, cyl, esp, ace, efaAfs, and efaAfm). Further investigation into the transferability and environmental dissemination of these resistance and virulence traits will allow risk assessment and safety evaluation of artisanal cheeses.

Functionality of enterococci in dairy products

Enterococci have important implications in the dairy industry. They occur as nonstarter lactic acid bacteria (NSLAB) in a variety of cheeses, especially artisan cheeses produced in southern Europe from raw or pasteurised milk, and in natural milk or whey starter cultures. They play an acknowledged role in the development of sensory characteristics during ripening of many cheeses and have been also used as components of cheese starter cultures. The positive influence of enterococci on cheese seems due to specific biochemical traits such as lipolytic activity, citrate utilisation, and production of aromatic volatile compounds. Some enterococci of dairy origin have also been reported to produce bacteriocins (enterocins) inhibitory against food spoilage or pathogenic bacteria, such as Listeria monocytogenes, Staphylococcus aureus, Vibrio cholerae, Clostridium spp., and Bacillus spp. The technological application of enterocins, shown to be produced during cheese manufacture, led to propose enterococci as adjunct starter or protective cultures in cheeses. There is evidence that enterococci, either added as adjunct starters or present as nonstarter NSLAB, could find potential application in the processing of some fermented dairy products. Literature suggest that the complex biochemical and ecological phenomena explaining the technological functionality of the enterococci in dairy products, are still to be fully understood. Clearly, the clinical research on enterococci underlines also that the safety of dairy products containing enterococci is an issue that the industry must carefully address before proceeding to their application.

Methods used for the isolation, enumeration, characterisation and identification of Enterococcus spp

This paper reviews the methodology applied for the identification and characterisation of enterococci and covers phenotypic, genotypic and phylogenetic techniques. Although conventional phenotypic typing schemes are useful for rapid and simple identification of enterococcal species for routine applications, other methods like standardised sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE), multilocus enzyme electrophoresis (MLEE), antimicrobial susceptibility testing, serotyping, pyrolysis mass spectrometry (pyMS) and vibrational spectroscopic methods allow a more in-depth characterisation of enterococci. Many of the recently described enterococcal species exhibit deviations from hitherto so-called classical enterococci with regard to their phenotypical properties. Therefore, genotypic methods have to be used to clarify their possible assignment to the genus Enterococcus. In this review, special emphasis is given on recently developed polymerase chain reaction (PCR)-based typing methods such as random amplified polymorphic DNA (RAPD), amplified fragment length polymorphism (AFLP), specific and random amplification (SARA) and modifications of PCR-ribotyping as well as pulsed-field gel electrophoresis (PFGE) and partial sequence analysis. The use of PCR and probes for genus and species identification of enterococci is also considered like the application of sequence data of conserved DNA regions (e.g., ribosomal ribonucleic acid (rRNA) genes) in the case of species identification.

Genotypic and phenotypic characterization of the dynamics of the lactic acid bacterial population of adjunct-containing Cheddar cheese manufactured from raw and microfiltered pasteurised milk

AIMS

This study investigates the dynamics of the microflora, particularly the lactobacilli, in Cheddar cheese manufactured from raw and microfiltered milk containing different adjunct cultures.

METHODS AND RESULTS

Sixteen cheeses - raw milk, adjunct and control cheeses - were manufactured in four trials. Lactobacilli were identified by PCR methods in one trial, and by phenotypic typing for all trials. Numbers of lactobacilli were significantly different at day 1 and 3 months in the control and adjunct-containing cheeses. In the raw milk cheeses, Lactobacillus paracasei was detected throughout ripening, Lact. curvatus at the end, and Lact. plantarum at day 1 only. Lactobacillus strain diversity decreased from raw, control to adjunct cheeses. Enteroccoci and coliform numbers further differentiated raw cheeses from the others. Lactococcal starter numbers also differed in the three cheese types and differences were observed within adjunct cheeses. Although adjunct lactobacilli dominated in the cheese to which they were added, strains with similar phenotypic profiles were also detected on occasions in some of the control cheeses.

CONCLUSIONS

The addition of adjunct lactobacilli modified the growth kinetics of both adventitious lactobacilli and starter lactococci during ripening. Appropriate strain tracking is necessary to monitor changes in the population profiles of control and experimental cheeses in trials utilizing adjunct cultures.

SIGNIFICANCE AND IMPACT OF THE STUDY

Investigations of the role of adjunct strain(s) in cheeses may be complicated by the interactions between the adjunct and the other cheese strains, and effective strain monitoring by genotypic or phenotypic methods is essential if valid comparisons are to be made.

Antimicrobial properties of commercial annatto extracts against selected pathogenic, lactic acid, and spoilage microorganisms

Annatto preparations are used to impart distinctive flavor and color to foods and are a primary colorant in dairy foods such as cheese and butter. There are several reports indicating that certain fractions of the annatto plant have biological activities against microorganisms of significance in food fermentation, food preservation, and human health. However, little is reported describing the nature of the antimicrobial compound(s) or their potential presence in commercial annatto colorant preparations. This study was conducted to determine whether commonly available annatto extracts are capable of influencing the outgrowth of selected lactic acid, spoilage, and pathogenic microorganisms. Disk diffusion and tube macrodilution techniques were used to determine the MICs and MBCs of double-strength water-soluble annatto extracts. Standard antibiotic disks were used as controls for the disk diffusion assay. The results demonstrate that annatto has an inhibitory effect on Bacillus cereus, Clostridium perfringens, and Staphylococcus aureus, with MICs of 0.08, 0.31, and 0.16% (vol/vol) and diameters of inhibition of 9 to 10, 12 to 13, and 15 to 16 mm, respectively. A concentration of 0.63% (vol/vol) inhibited the growth of Streptococcus thermophilus, Lactobacillus casei subsp. casei, Lactococcus lactis, and Paenibacillus polymyxa. The MICs for Listeria monocytogenes and Enterococcus durans were 1.25 and 2.5% (vol/vol), respectively. No activity was detected against Lactobacillus plantarum, Bifidobacterium bifidum, yeasts, or selected gram-negative bacteria.

Effect of raw-milk cheese consumption on the enterococcal flora of human feces

Enterococci are one of the major facultative anaerobic bacterial groups that reside in the human gastrointestinal tract. In the present study, the composition of the enterococcal fecal flora in three healthy humans was analyzed before, during, and after the daily consumption of approximately 125 g of a raw-milk Cheddar-type cheese containing 3.2 x 10(4) enterococci/g of cheese. Enterococcal counts ranged between 1.4 x 10(2) and 2.5 x 10(8) CFU/g of feces and differed from subject to subject and from week to week. The cheese contained mainly Enterococcus casseliflavus and a small population of Enterococcus faecalis. Clonal relationships were determined by pulsed-field gel electrophoresis. Before and after consumption of the cheese, samples from humans contained mainly Enterococcus faecium, with some of the clones being resident. During consumption of the cheese, one particular transient clone of E. faecalis, clone Fs2, which was present in small numbers in the cheese, largely dominated the feces. Two clones of E. casseliflavus from the cheese were also found in the feces of one of the subjects during cheese consumption. These results suggest that a clone need not be present in a food in high numbers to establish itself in the intestine.

Source of enterococci in a farmhouse raw-milk cheese

Enterococci are widely distributed in raw-milk cheeses and are generally thought to positively affect flavor development. Their natural habitats are the human and animal intestinal tracts, but they are also found in soil, on plants, and in the intestines of insects and birds. The source of enterococci in raw-milk cheese is unknown. In the present study, an epidemiological approach with pulsed-field gel electrophoresis (PFGE) was used to type 646 Enterococcus strains which were isolated from a Cheddar-type cheese, the milk it was made from, the feces of cows and humans associated with the cheese-making unit, and the environment, including the milking equipment, the water used on the farm, and the cows' teats. Nine different PFGE patterns, three of Enterococcus casseliflavus, five of Enterococcus faecalis, and one of Enterococcus durans, were found. The same three clones, one of E. faecalis and two of E. casseliflavus, dominated almost all of the milk, cheese, and human fecal samples. The two E. casseliflavus clones were also found in the bulk tank and the milking machine even after chlorination, suggesting that a niche where enterococci could grow was present and that contamination with enterococci begins with the milking equipment. It is likely but unproven that the enterococci present in the human feces are due to consumption of the cheese. Cow feces were not considered the source of enterococci in the cheese, as Enterococcus faecium and Streptococcus bovis, which largely dominated the cows' intestinal tracts, were not found in either the milk or the cheese.