Raw Ewe's Milk Research Articles

Purification and characterization of an extracellular tributyrin esterase produced by a cheese isolate, Micrococcus sp. INIA 528

Abstract Micrococcus sp . INIA 528, a microorganism isolated from raw ewe's milk Manchego cheese, produced an extracellular tributyrin esterase. The enzyme was purified to homogeneity from culture supernatant in two chromatographic steps, with a 296-fold increase of specific activity and a 79.6% recovery of the esterase activity. The homogeneous protein was characterized biochemically. Its molecular mass was estimated to be 44.6 kDa by SDS-polyacrylamide gel electrophoresis. The amino acid composition of the enzyme was determined, but its N -terminus could not be sequenced. Optimal conditions for activity of the enzyme on α -naphtyl butyrate were 30°C and a pH of 7.5. The purified enzyme was strongly inhibited by EDTA, dithiothreitol, Cu 2+ , Zn 2+ , Ni 2+ , Fe 2+ and Co 2+ , and lost 50% activity in the presence of 7.5% NaCl. It was heat-labile, retaining only 50% of its maximum activity after 5 min at 50°C. The enzyme hydrolysed α - and β -naphtyl esters of fatty acids from C4 to C18, with preference for α -naphtyl butyrate. K m values for the hydrolysis of α -naphtylbutyrate and α -naphtylcaprilate at pH 7.5 and 30°C were 80 and 60 μ m , respectively. The maximum activity on triglycerides was recorded on tributyrin, considerably higher than on tricaprylin or trilaurin. K m values for the hydrolysis of tributyrin and tricaprylin at pH 7.5 and 30°C were 5 and 0.6 m m , respectively.

A case of sporadic ovine mastitis caused by Listeria monocytogenes and its effect on contamination of raw milk and raw-milk cheeses produced in the on-farm dairy.

We describe a case of listerial mastitis in a flock of 130 sheep. The animals were housed at a farm where the bulk raw ewe milk was processed to produce raw milk soft cheese. List. monocytogenes was shed from the right mammary complex. Shedding was observed over a period of 99 d. A mean level of 4-56 x 10(4) cfu (colony forming units) Listeria monocytogenes/ml was recovered from the raw milk originating from the infected udder. The numbers ranged from 9 x10(1) to 2.95 x 10(5). The bulk milk was contaminated by approx. 5.7 x 10(3) cfu/ml. In the cheese product, 2.0 x 10(2) cfu List. monocytogenes/g were constantly detectable for a period of 7 d post manufacture. The starter culture used for coagulation had a pivotal influence on the behaviour of List. monocytogenes during cheesemaking. Using the same mesophilic buttermilk culture as used by the farmer allowed numbers of Listeria to increase 60-fold within 12 h owing to a delayed acidification of the bulk milk. Addition of a thermophilic yogurt culture reduced the numbers of Listeria within 8 h of incubation.

Serpa Cheese: Technological, biochemical and microbiological characterisation of a PDO ewe's milk cheese coagulated with Cynara cardunculus L.

Portugal has a strong tradition of cheesemaking from raw ewe's milk; most of these cheeses are still made on a traditional farmhouse scale. Their production is protected by Protected Designation of Origin (PDO) but the specific biochemical aspects of the majority still need to be characterised. Two different cheesemaking procedures, traditional and semi-industrial, were compared technologically, biochemically and microbiologically. It was observed that, despite the highly significant difference between artisanal and semi-industrial cheeses (P < 0.001), both products were within the limits of national regulations for most parameters except maturation temperature, humidity and the value for the maturation index. Although the present study was not fully representative of the region, the results obtained suggest that the specific regulations for Serpa cheese should be revised and that other parameters, such as moisture and salt-in-moisture content, which are very much dependent on the cheesemaking process, should be included in order to characterise better this traditional cheese.

Evolution of the volatile components of ewe raw milk La Serena cheese during ripening. Correlation with flavour characteristics

La Serena cheese is a soft to semi-soft Spanish variety manufactured from Merino ewe raw milk coagulated with an extract of Cynara cardunculus. In the present work a purge and trap ex- traction procedure coupled to gas chromatography - mass spectrometry was used to study the volatile fraction evolution during ripening of La Serena cheese. A total of 112 compounds were identified. Al- cohols were quantitatively the main chemical family in the volatile fraction, increasing significantly during ripening. Ethanol, 1-propanol, 2-propenol, 2-propanol, 2-butanol, 2-pentanol and the branched chain 2-methyl-1-propanol and 3-methyl-1-butanol, were abundant at the end of ripening. Esters, especially ethyl esters of acetic, butanoic, hexanoic and octanoic acids and 3-methyl-1- butanol acetate, were found at high levels in the headspace of La Serena cheese. Concentrations of most esters increased dramatically during ripening, and, given their low perception thresholds, may be considered as key constituents of the aroma of this cheese variety. The principal component analy- sis of sensory attributes and volatile compounds extracted 3 functions. Linear aldehydes and alco- hols, 2-alkanols, branched-chain alcohols, 2-methyl-ketones, alkanes, terpenes and esters other than ethyl esters correlated positively with function 1 (25.8% of the variance explained). Odour and aroma quality, along with the sensory attributes lactic, fruits-flowers, and clean cheese flavour, and the volatiles ethanol and ethyl esters, had a high correlation coefficient with function 2 (14.8% of the vari- ance explained). 2-Butanone and the sensory attributes fishy and putrid had a negative correlation co- efficient with this function. Odour and aroma intensity, along with the sensory attributes animal, pungent and fishy, and the volatile compounds branched chain aldehydes, n-alkanols, 2-butanol and esters, were positively correlated with function 3 (11.0% of the variance explained). Terpenes had a negative correlation coefficient with this function. Volatile compound / ewe raw milk / La Serena cheese / ripening / flavour

Seasonal variation of volatile compounds in ewe raw milk La Serena cheese

La Serena cheese is a soft to semi-soft variety made in Extremadura (western Spain) from Merino ewe raw milk using an extract of Cynara cardunculus as milk coagulant. A purge and trap ap- paratus coupled to a GC-MS was used to study the seasonal variation of the volatile fraction of La Serena cheeses made at four artisan dairies. Alcohols and esters were the main chemical families found in La Serena cheese. Most volatile compounds were detected in cheeses made during the whole year, although at different concentrations. Abundances of hydrocarbons, primary alcohols, second- ary alcohols of an uneven number of carbon atoms, terpenes, 2,3-butanedione, free fatty acids, nitro- gen compounds and aromatic compounds were generally higher in cheeses made during spring. Aldehydes reached the highest levels in spring and summer cheeses. Ethanol and ethyl esters were more abundant in spring and autumn cheeses, while branched chain alcohols and branched chain alkyl esters were more abundant in summer cheeses. Cheeses made in winter showed a lower abun- dance of most volatile compounds, except dimethyl sulphide and dimethyl disulphide. Cheeses made in spring received the highest scores for odour and aroma quality, and cheeses made in winter re- ceived the lowest scores. High amounts of 2,3-butanedione, medium concentrations of most terpenes and alcohols, low levels of methyl ketones, especially of 2-butanone, and very low concentrations of 2-butanol were generally recorded for cheeses with the highest quality scores in sensory evaluation. Concentrations of most ethyl esters and branched chain alkyl esters in the highest scored cheeses were above the mean values in cheeses made during the whole year. However, levels of propyl esters and ethyl esters of branched chain acids were lower in the highest scored cheeses. Volatile compound / ewe raw milk / La Serena cheese / seasonal variation

Evaluation of the Spiral Plating System for the Routine Assessment of Indicator Microorganisms in Raw Ewe's Milk

The numbers of members of different microbial groups in bulk raw ewe's milk used for cheesemaking (46 samples, taken on receipt at the dairy over 1 year) were assayed by the spiral plating system to determine the effectiveness of this method compared with that of widely accepted conventional methods in providing counts. The results indicated that for ewe's milk, the suitability of the spiral plating system depends to a great extent on the microbial group studied. Although “spiral” counts of mesophiles, psychrotrophs, coliforms, and Enterobacteriaceae could be considered equivalent to those obtained by conventional techniques (r ≥ 0.90; variance between replicate platings ≈ 0.005), the automated method was found not to be suitable for the assessment of other groups of indicator bacteria (thermodurics and enterococci). Counts of lactic acid bacteria and yeasts and molds were affected significantly (P < 0.05) by the plating method, although other statistical parameters were more favorable (r = 0.88 and r = 0.82, respectively; 95% confidence limits within 0.5 log units). Finally, counts of staphylococci, particularly on Baird-Parker medium, showed less variation and higher reproducibility with the spiral method. Nevertheless, for the routine microbiological analysis of ewe's milk, the spiral plating system, with its time-, effort-, and material-saving advantages, is preferred over the conventional method.

Manufacture of Spanish hard cheeses from CO 2-treated milk

The suitability of milk preserved by refrigeration and CO 2 addition for the manufacture of rennet-coagulated Spanish hard cheeses was evaluated. Two types of cheeses were produced from milk preserved by refrigeration and CO 2 addition (pH 6.2) and were compared with controls made from fresh milk. Degasified (50–52 °C and 300 mm Hg) and pasteurised milk was employed for the manufacture of 30-day-old cheeses using a commercial starter. A degasified (30–32 °C and 350–375 mm Hg) mixture of 90% cow's and 10% ewe's raw milk was used for the manufacture of starter-free 75 day-old cheeses. Milk preservation did not affect multiplication and acidification capacity of lactic acid bacteria in cheeses from pasteurised milk but promoted lower levels of lactococci at first days of ripening in cheeses from raw milk and rendered lower amounts of lactic, pyruvic and succinic acids. Preservation did not affect the evolution of volatile compounds. Cheeses from preserved milk showed reduced clotting time, slightly higher cheese yields and increased curd hardness and whey losses during cheesemaking. The taste panel accepted cheeses from preserved milk. These results support the interest of CO 2-addition in preservation of milk for the manufacture of Spanish hard cheeses.

Listeria in ready-to-eat and unprocessed foods produced in Portugal

Between October 1998 and April 2000, 429 food samples were investigated for the presence ofListeria spp. The foodstuffs included 138 ready-to-eat foods (68 traditional hard and semi-hard Portuguese cheeses, 23 salad vegetables and 47 cooked and/or cured meats) and 291 uncooked foods (14 raw vegetables, 65 raw chicken and 212 raw ewe's, cow's or goat's milk). Listeria spp. were recovered from 63 samples (15%). Listeria monocytogenes was present in 39 (9%) samples, Listeria innocua in 12 (3%), Listeria seeligeri in 23 (5%), Listeria ivanovii in seven (2%) and Listeria grayi in two (0·5%). More than one Listeria species was recovered from 18 samples. A combination of serotyping, phage-typing, cadmium and arsenic sensitivities were used to subtype 36 of the L. monocytogenes isolates: at least nine different strains were recognized. Four food samples yielded two different L. monocytogenes strains.

Microbiology of “Orinotyri”, a ewe's milk cheese from the Greek mountains

The microflora of five batches of Orinotyri, a cheese made from raw ewe's milk, was studied in ten day and three-month-old cheese. Mean log counts of 7·94 for Enterobacteriaceae and 7.41 for coliforms in fresh cheese were reduced (P<0·05) by 3·02 and 2·76 log units, respectively, during ripening. It also seems that high cheese pH (means: ten days, 6·31; three months, 5·79) did not favour the growth of yeasts. These organisms were found at low levels only in fresh cheese. Lactic acid bacteria numbers of the cheese at ten days decreased significantly (P<0·05) in the three-month-old cheese, but they were still present at high levels (mean log counts: lactobacilli, 5·78; lactococci, 8·24; enterococci, 6·20). Enterococci predominated in the fresh cheese, but they were outnumbered by lactococci in three-month-old cheese. Enterococcus faecalis and Lactococcus lactis subsp. lactis were the most frequently isolated species. Acid production by Lc. lactis subsp. lactis strains varied considerably and the same was observed for their caseinolytic, lipolytic and peptidolytic activities. The results suggest the possibility of choosing strains for industrial fermentation.

Characterization of non-starter lactic acid bacteria from Italian ewe cheeses based on phenotypic, genotypic, and cell wall protein analyses.

Non-starter lactic acid bacteria (NSLAB) were isolated from 12 Italian ewe cheeses representing six different types of cheese, which in several cases were produced by different manufacturers. A total of 400 presumptive Lactobacillus isolates were obtained, and 123 isolates and 10 type strains were subjected to phenotypic, genetic, and cell wall protein characterization analyses. Phenotypically, the cheese isolates included 32% Lactobacillus plantarum isolates, 15% L. brevis isolates, 12% L. paracasei subsp. paracasei isolates, 9% L. curvatus isolates, 6% L. fermentum isolates, 6% L. casei subsp. casei isolates, 5% L. pentosus isolates, 3% L. casei subsp. pseudoplantarum isolates, and 1% L. rhamnosus isolates. Eleven percent of the isolates were not phenotypically identified. Although a randomly amplified polymorphic DNA (RAPD) analysis based on three primers and clustering by the unweighted pair group method with arithmetic average (UPGMA) was useful for partially differentiating the 10 type strains, it did not provide a species-specific DNA band or a combination of bands which permitted complete separation of all the species considered. In contrast, sodium dodecyl sulfate-polyacrylamide gel electrophoresis cell wall protein profiles clustered by UPGMA were species specific and resolved the NSLAB. The only exceptions were isolates phenotypically identified as L. plantarum and L. pentosus or as L. casei subsp. casei and L. paracasei subsp. paracasei, which were grouped together. Based on protein profiles, Italian ewe cheeses frequently contained four different species and 3 to 16 strains. In general, the cheeses produced from raw ewe milk contained a larger number of more diverse strains than the cheeses produced from pasteurized milk. The same cheese produced in different factories contained different species, as well as strains that belonged to the same species but grouped in different RAPD clusters.

Seasonal changes in the composition of bulk raw ewe's milk used for Idiazabal cheese manufacture

Seasonal changes in the composition of bulk raw ewe's milk used for Idiazabal cheese manufacture and its influence on the cheese yield are reviewed. This review is based on biochemical and microbiological data previously published on the composition of a bulk raw ewe's milk collected at three different times of the year. In order to characterize, in a more extensive perspective, the seasonal changes in the composition of this bulk raw ewe's milk and its influence on actual cheese yield, multivariate statistical analyses were applied to the compositional data of the milk and the actual cheese yield obtained at the factory. The results show pronounced seasonal changes in the composition of bulk raw ewe's milk. Changes in cheese yield, lipolytic activity and microbiological quality of the bulk raw ewe's milk are the principal aspects seasonally affected during the cheesemaking period. Also, the seasonal changes observed in the bulk raw ewe's milk composition strongly affect the quality of Idiazabal cheeses manufactured over the cheesemaking period.

Influence of rennet milk-clotting activity on the proteolytic and sensory characteristics of an ovine cheese

Abstract Roncal cheese (regulated by an Apellation of Origin) is a traditional hard cheese manufactured from raw ewe's milk in the region of Navarre in Spain. Roncal cheeses, manufactured using two lamb rennets with different milk-clotting activity levels, were evaluated to compare their chemical, proteolytic, and sensory characteristics. A preliminary study of samples of lamb rennets indicated that a large proportion of such rennets did not fulfil current microbiological requirements and likewise revealed considerable variation in the milk-clotting activity of the samples examined. Trends in the overall physicochemical parameter values (pH, dry matter, fat, and protein) were similar in both cheese batches. Proteolysis of the nitrogen fractions was observed to take place at a faster rate in the cheeses made using the rennet with the higher milk-clotting activity (soluble nitrogen, non-protein nitrogen, and amino acid nitrogen values around 13–20% higher than in the cheeses made using the rennet with the lower milk-clotting activity after 180 days of ripening). Urea-PAGE electrophoretic analysis of the caseins from the cheeses manufactured using both types of rennet showed that the β-caseins were less susceptible to proteolysis than the α s -caseins. The effect of the different milk-clotting activity levels was most pronounced on the α s -caseins, in which the rennet with the higher milk-clotting activity gave higher breakdown. Nevertheless, the differences in the proteolysis rates did not yield any appreciable sensory differences.

On the microbiology of Serra da Estrela cheese: geographical and chronological considerations

Serra da Estrela cheeses, produced following artisanal practices from raw ewe's milk in two consecutive years in five selected dairies, were sampled throughout a 60-day ripening period. The viable numbers of the major microbial groups (Enterobacteriaceae, staphylococci and yeasts, as well as such lactic acid bacteria as lactobacilli, lactococci and enterococci) were determined and statistical significance of the results was assessed. Significant differences in the viable counts of lactococci, lactobacilli, enterococci, Enterobacteriaceae and staphylococci were found for the various geographical locations, whereas the year of manufacture played a significant role only upon the viable numbers of yeasts and staphylococci. These data back up the claim that those microbial families usually implicated with health hazards are prone to a wide variability, which reflects the intrinsic heterogeneity associated with production and handling of raw milk in traditional cheesemaking.

Enumeration and Confirmation of Aeromonas hydrophila, Aeromonas caviae, and Aeromonas sobria Isolated from Raw Milk and Other Milk Products in Northern Greece

A total of 138 raw cow's and 57 raw ewe's milk samples; 80 pasteurized cow's milk samples; 39 Anthotyros cheese, 36 Manouri cheese, and 23 Feta cheese samples; and 15 rice pudding samples were examined for the presence and any countable population of Aeromonas species. Twenty-two (15.9%) of the 138 cow's milk samples analyzed were contaminated with A. hydrophila. In 13 of these samples, populations of 3.0 × 102 to 5.0 × 103 CFU/ml were counted in starch ampicillin agar (SAA). Eighteen cow's milk samples (13.0%) were contaminated with A. caviae, and in eight of these samples, populations of 2.0 × 102 to 3.0 × 103 CFU/ml were counted in SAA. Five cow's milk samples (3.6%) were contaminated with A. sobria, and in two of these samples, populations of 2.5 × 103 and 5.0 × 103 CFU/ml were counted in SAA. Eleven cow's milk samples (7.9%) were contaminated with other Aeromonas spp. not classified. Eight (14.0%) of the 57 ewe's milk samples analyzed were contaminated with A. hydrophila. In these samples, populations of 5.0 × 102 to 5.0 × 103 CFU/ml were counted in SAA. Six ewe's milk samples (10.5%) were contaminated with A. caviae, and populations of 1.5 × 102 to 1.0 × 103 CFU/ml were counted in SAA. Two ewe's milk samples (3.5%) were contaminated with A. sobria, and populations counted in SAA were 5.0 × 102 and 1.0 × 103 CFU/ml. Four samples (7.0%) were contaminated with other Aeromonas spp. not classified. A. hydrophila was recovered in 4 (10.2%) and 3 (8.3%) of the Anthotyros and Manouri cheese samples analyzed, respectively, but no countable populations were noted in SAA. None of the pasteurized milk, Feta cheese, and rice pudding samples yielded Aeromonas spp. The results of this work indicate that motile Aeromonas are common in raw milk in Greece. Also, the presence of A. hydrophila in the whey cheeses Anthotyros and Manouri indicates that postprocessing contaminations of these products with motile Aeromonas may occur during production.

Changes in microbial flora during manufacture of a traditional fermented milk from ewe's milk

Changes in the microbial flora during the manufacture of a sour milk from raw ewe's milk were studied. Mean log counts of lactic acid bacteria, lactobacilli and streptococci (respective values in milk 4.55, 3.19 and 5.56) increased significantly (P<0.05) to 8.46, 6.98 and 8.46, respectively, at 5 days and at the same time the pH decreased from 6.58 in milk to 4.71 in the final product. Levels of total counts, coliforms and psychrotrophs also increased to 108, 107and 106cfu/ml, respectively. Halotolerants and yeasts were counted at quite low numbers throughout manufacture.Isolates of lactic acid bacteria were classified as lactococci, lactobacilli, leuconostocs and enterococci. Enterococci predominated (58.9% of the isolates) over the other lactic acid bacteria after 1 day meanwhile leuconostocs became predominant (46.9%) after 5 days, followed by lactobacilli (29.7%), lactococci (17.2%) and enterococci (6.2%).Lactobacillus plantarumandLeuconostoc mesenteroidessub-spp.cremoriswere the species most frequently isolated. Enzyme activities (API-ZYM tests) of lactococci and leuconostocs were low, in general, but activities ofLb. plantarumstrains were considerably higher. ThreeLc. lactissub-spp.lactisstrains produced diacetyl, four of them formed acetoin, and one was characterized as good active, concerning acidification ability.Results presented here suggest the necessity of using a starter culture, consisting of selected strains of lactococci, leuconostocs and possibly lactobacilli, and pasteurized milk for the production of a high quality product.

Formation of Biogenic Amines in Idiazábal Ewe's-Milk Cheese: Effect of Ripening, Pasteurization, and Starter

The importance of biogenic amines stems from their toxicity and their potential as a cause of food poisoning. After fish, cheese has been the foodstuff most often responsible for cases of food poisoning caused by ingestion of biogenic amines. Changes in biogenic amine (histamine, tyramine, putrescine, cadaverine, tryptamine, isopentylamine, spermidine, and phenylethylamine) content during the ripening of a cheese made from raw ewe's milk were studied, together with the effects of pasteurization and a commonly used commercial starter and indigenous starter cultures. Biogenic amines were determined by high-pressure liquid chromatography following extraction from the cheese and derivatization with dansyl chloride. Levels of histamine, potentially the most toxic amine, in the semihard Idiazábal cheese were very low. Tyramine, putrescine, and cadaverine were the main amines present in this type of cheese. Levels of those amines increased during ripening. Pasteurization of the milk brought about a reduction in the biogenic amine content of the ripened cheese, irrespective of the starter culture employed. The indigenous starter cultures considered in this study produced higher levels of histamine and cadaverine and lower levels of tyramine and putrescine than the commercial starter culture tested.

Secondary flora of Casar de Cáceres cheese: Characterization of Micrococcaceae

We have identified 190 Micrococcaceae isolates made during the ripening of Casar de Caceres cheese, a semisolid cheese made from raw ewe's milk. The identification revealed that only 7 isolates (3.7%) belonged to micrococci and 183 (96.3%) to staphylococci. Among the staphylococci, only 7, isolated in the early stages of ripening, were coagulase positive. One was identified as Staphylococcus intermedius and the remaining 6 as S. aureus. The coagulase-negative staphylococci included among the most abundant species were: 115 isolates identified as S. xylosus, 36 isolates as S. caseolyticus though certain characteristics differed from the original description of the species and 10 isolates as S. saprophyticus. Some other isolates were identified as the following species of staphylococci: 4 as S. cohnii subsp. urealyticus, 1 as S. cohnii subsp. cohnii, 3 as S. lentus, 3 as S. sciuri, 2 as S. gallinarum, 1 as S. capitis subsp. capitis and 1 as S. caprae. The lipolytic activity of many S. xylosus isolates and the caseolytic activity of the S. caseolyticus isolates make them feasible candidates to be used with starters to improve the flavour of pasteurized-milk cheeses.

Bactericidal Effect of Enterocin 4 on Listeria monocytogenes in a Model Dairy System

Enterococcus faecalis INIA 4 produced the bacteriocin enterocin 4 during growth in raw ewe's milk at 30°C. Enterocin activity reached 2,200 to 3,600 AU/ml after 8 h, with a 1 to 8% (vol/vol) level of inoculum from an 18-h culture. An enterocin activity of 500 AU/ml significantly decreased counts of Listeria monocytogenes Ohio when incubated for 6 h in a model system consisting of filtrates from cultures of E.faecalis INIA 4 in raw ewe's milk, at pH 6.0 and 30°C. However, an enterocin activity of 2,400 AU/ml was needed in the same conditions to significantly decrease counts of L. monocytogenes Scott A. All 22 wild L. monocytogenes strains isolated from ewe's milk and tested were inhibited by a filtrate containing 400 AU/ml of enterocin 4. Incubation in the filtrate for 6 h significantly lowered counts of 16 L. monocytogenes strains, and incubation for 24 h, counts of 21 strains.

Villalón, a Fresh Ewe's Milk Spanish Cheese, as a Source of Potentially Pathogenic Aeromonas Strains

Presumptive aeromonads were detected in 8 batches of Villalón cheese produced in dairy plants from pasteurized ewe's milk, the mean count being 2.85±0.24 log CFU/g. Only four isolates from 2 batches were confirmed as motile aeromonads and they fitted the description of Aeromonas hydrophila. During cheese making of 5 batches of farmhouse-made raw milk Villalón cheese, presumptive aeromonads decreased in numbers from 3.6 log CFU/ml in raw ewes' milk to 2.2 log CFU/g after salting, but after storage for 48 h at 4°C, multiplication occurred in all cheeses (mean count, 3.7 log CFU/g). Motile aeromonads were detected in raw ewe's milk, curd, and cheese. Identification to species' level of 38 isolates which shared the properties of A. hydrophila and A. caviae was based on the “suicide phenomenon” (22 strains were identified as A. hydrophila and 16 as A. caviae). All strains of A. caviae were β-hemolytic, showed suicidal activity, and failed to produce caseinase.

Exogenous Sources of Listeria Contamination in Raw Ewe's Milk

Water, feeds, milking equipment, environmental samples and feces from 15 farms producing ewe's milk contaminated by Listeria spp. were examined over a 1-year period, using a two-step enrichment procedure followed by a DNA hybridization test. Listeria spp. were isolated from 19.6% of trough-water samples, 13.1% of feed samples, 36.4% of bedding samples, 80.6% of farmyard-soil samples, and 16.2% of ewe's feces samples. The contamination rates of these samples by L. monocytogenes were 7.8%, 1.2%, 11.4%, 8.3%, and 2.7%, respectively. Tap water and milking equipment were free from Listeria spp. Fecal samples from poultry and birds in the farms exhibited a high incidence of Listeria spp. (72.7% for hens, 28.6% for pigeons and 48.3% for sparrows) and could be responsible for the contamination of trough water and some feeds by these microorganisms.