Untersuchungen zum Vorkommen von Listerien, Salmonellen, Campylobacter und Staphylokokken in Rohmilch im Land Brandenburg

Abstract

Due to related diseases the consumption of raw milk has recently been called into question. On the one hand there are many reports in the literature about milk-borne enteritis associated with raw milk and dairy-products manufactured from raw milk whereas heat-treated milk and dairy-products are seldom the cause for infection and intoxication. On the other hand there is a demand for natural, untreated foods on the the part of the consumer. The intention of this investigation was to examine the occurrence of certain human pathogens in raw milk from Brandenburg (Germany). Beside the total bacterial count and the coliform count as parameters of hygiene the presence of Listeria species, especially Listeria monocytogenes, Salmonella species, Campylobacter species and Staphylococcus aureus was tested. The investigation was carried out according to the Official Methods-Collection of § 35 of the German Foods and Foodstuffs Article (LMBG) which have in part been slightly changed. The research on Campylobacter was done according to the methods suggested by the Nordic Comitee on Food Analysis to the European Committee for Standardization (CEN). The research was done between June 1993 and July 1994 with 415 raw milk samples altogether taken by the dairy for their own tests from farm bulk-tanks of 82 dairy farms being investigated. The milk was then delivered to the dairy for heat-treatment and further processing and was not destined for raw consumption.

The medium bacterial count was x = 7,3 x 104 per milliliter with a central 50 %-range from 2,6 x 104 to 2,3 x 105 colony forming units per milliliter (cfu/ml). The colony count of 241 raw milk samples (= 58,1 %) was below 100.000 cfu/ml. Before the the EC-directive 92/46/EWG/EEC came into force on January 1st 1994, 242 samples (= 58,3 % out of the 415 samples) and after that date 173 raw milk samples (= 41,7 %) had been investigated. The medium bacterial count (x) dropped from 77.000 to 64.000 cfu/ml after that date and the percentage of samples showing colony counts less than 100.000 cfu/ml had risen from 55,4 % to 61,9 %. In the 374 samples tested for coliforms the medium bacterial count (x) of these bacteria was 9,3 x 102 cfu/ml with a central 50 %-range from 2,3 x 102 to 7,5 x 103 cfu/ml. Listeria was isolated from 44 out of 415 tested samples (= 10,6 %). 23 strains were confirmed as Listeria monocytogenes (= 5,5 %) and 21 as Listeria innocua (= 5,1 %). The 44 positive samples were isolated from milk samples of 28 dairy farms (= 34,1 %) with 14 farms (= 50,0 %) showing evidence of Listeria monocytogenes and 13 farms (= 46,4 %) Listeria innocua. In one farm both strains were observed. The average count of Listeria in 40 samples out of the 44 positive samples was less than 102 per milliliter raw milk. Listeria-levels of 102, 2 x 102 and twice 5,5 x 102 bacteria per milliliter raw milk were found in the remaining four samples. Salmonella could not be detected in 1 ml of 415 raw milk samples nor in 25 ml of 113 parallel investigations of raw milk samples. Nor could Campylobacter be found in any milk sample. The growth of coagulase-positive Staphylococci was observed in 349 out of 403 (= 86,6 %) tested samples so that this microorganism occurred in 78 out of 82 farms (= 95,1 %) under investigation with a maximum of 1,5 x 106 cfu/ml. The average count was x = 1,7 x 103 cfu/ml with a central 50 %-range from 630 - 4.400 cfu/ml.

Due to the findings the milk of some of the tested farms would cause a risk for human health if consumed uncontrolled especially when a possible infection with Listeria monocytogenes and Staphylococcus aures is taken into consideration. If raw milk is heat-treated according to the Milchverordnung (Milk Article, 1995) there is no risk of infection with pathogens. Nevertheless, there will always remain a small risk due to technical faults which can never be excluded.