Pathogenic bacteria in Finnish bulk tank milk.

While the quality of raw cow milk in Finland is known for its high hygienic standard, with the national average total bacterial count being below 10(4) CFU/mL annually, the prevalence of pathogenic bacteria in Finnish raw milk is underreported. The aim of this study was to determine the occurrence of Listeria monocytogenes, thermophilic Campylobacter spp., Salmonella spp., stx-positive Escherichia coli (STEC), coagulase-positive staphylococci, Yersinia spp., and Bacillus cereus group in raw cow milk samples collected from bulk tanks at 183 Finnish farms. Additionally, the hygienic quality of the milk was studied by determining the total bacterial and E. coli counts. L. monocytogenes was detected in 5.5% of the milk samples, with concentrations varying from <1 to 30 CFU/mL. Thermophilic Campylobacter spp. or Salmonella spp. were not detected in any of the samples. STEC with Shiga toxin-encoding stx2 was detected in 2.7% of the samples. Yersinia enterocolitica was detected in 7.7% of the samples; however, all isolates were negative for ail, suggesting that they were non-pathogenic. Coagulase-positive staphylococci were detected in 34.4% of the samples, with an average concentration of 25 CFU/mL in the positive samples. Members of the B. cereus group were detected in 20.8% of the samples, with an average concentration of 1 CFU/mL in the positive samples. No relationship was detected between E. coli or the total bacterial count and the presence of pathogenic bacteria, which suggests that pathogens can be present also in farms with excellent production hygiene. Although the concentration of pathogenic bacteria in fresh raw milk was mainly relatively low, it should be borne in mind that some of the pathogenic bacteria can survive and multiply at refrigeration temperatures and may cause a disease with a very low infectious dose. Thus, consumption of raw milk and related products poses a potential risk for food poisoning.

Occurrence and growth of Listeria monocytogenes in packaged raw milk.

The increased availability of packaged raw drinking milk necessitates the investigation of the occurrence and growth of Listeria monocytogenes in raw milk during distribution and storage. The occurrence of L. monocytogenes in 105 retailed raw milk bottles, 115 bulk tank milk samples, 23 in-line milk filter socks and in 50 environmental samples collected from an on-farm dairy establishment were investigated. Growth of inoculated low-level L. monocytogenes contamination was also investigated in two types of raw milk packaging, namely in 1-litre plastic bottles and 3-litre bag-in-boxes, both stored at three different storage temperatures of 6, 8 and 10°C. The occurrence of L. monocytogenes was higher (4.8%) in bottled raw milk stored until the use-by-date of the package compared to fresh bulk tank milk (1.7%). L. monocytogenes counts were ≤13CFU/ml in bottled raw milk and ≤1CFU/ml in bulk tank milk. L. monocytogenes was not detected in the packaging facility, but occurred very frequently (39%) in the milk filter socks. Subtyping of L. monocytogenes isolates using pulsed-field gel-electrophoresis revealed seven pulsotypes, of which two occurred in multiple samples. Targeted inoculum levels of 1-2CFU/ml yielded L. monocytogenes counts≥100CFU/ml within seven days of storage in 22% of the raw milk packages stored at 6°C, and in all of the raw milk packages stored at 8°C. The frequent occurrence of L. monocytogenes in raw milk and the ability of a low-level L. monocytogenes contamination to grow at refrigeration temperatures highlight the importance of consumer education regarding the appropriate raw milk storage and handling.

Arcobacter species and their pulsed-field gel electrophoresis genotypes in Finnish raw milk during summer 2011.

The aim of this study was to investigate the occurrence of Arcobacter species in raw milk in Finland. A total of 177 raw milk samples, each from a separate farm, were examined from June to August 2011. Arcobacter species were isolated using an enrichment and selective detection procedure. Overall, 26 (15 % ) of the 177 samples yielded Arcobacter spp. Samples from 25 farms were positive for Arcobacter butzleri and from 1 farm for Arcobacter cryaerophilus. Moreover, both Arcobacter butzleri and A. cryaerophilus were recovered from 1 positive sample. To evaluate a possible genetic variability, one strain of A. butzleri from each farm and the A. cryaerophilus sample were analyzed by pulsed-field gel electrophoresis. Genotyping revealed that Arcobacter spp. populations are heterogeneous, and no dominant clone has spread in the investigated samples. Our study is the first report on the isolation of both A. butzleri and A. cryaerophilus in raw milk in Finland. Based on our findings, the presence of Arcobacter species in raw milk may pose a potential hazard for human health, in particular for consumers who prefer drinking unpasteurized milk.

Clostridium tyrobutyricum strains show wide variation in growth at different NaCl, pH, and temperature conditions.

Outgrowth from Clostridium tyrobutyricum spores in milk can lead to butyric acid fermentation in cheeses, causing spoilage and economical loss to the dairy industry. The aim of this study was to investigate the growth of 10 C. tyrobutyricum strains at different NaCl, pH, and temperature conditions. Up to 7.5-fold differences among the maximum growth rates of different strains in the presence of 2.0% NaCl were observed. Five of 10 strains were able to grow in the presence of 3.0% NaCl, while a NaCl concentration of 3.5% was completely inhibitory to all strains. Seven of 10 strains were able to grow at pH 5.0, and up to 4- and 12.5-fold differences were observed among the maximum growth rates of different strains at pH 5.5 and 7.5, respectively. The maximum growth temperatures varied from 40.2 to 43.3°C. The temperature of 10°C inhibited the growth of all strains, while 8 of 10 strains grew at 12 and 15°C. Despite showing no growth, all strains were able to survive at 10°C. In conclusion, wide variation was observed among different C. tyrobutyricum strains in their ability to grow at different stressful conditions. Understanding the physiological diversity among the strains is important when designing food control measures and predictive models for the growth of spoilage organisms in cheese.