Sale of Raw Milk in Northern Italy: Food Safety Implications and Comparison of Analytical Methods for Detecting Foodborne Pathogens

All pathogens investigated were detected in raw milk sold from vending machines, according to new research from Italy. They found that raw milk is a significant source of exposure Mycobacterium avium subsp. and that the official culture method (ISO) may be ineffective in detecting low contamination levels in milk.

27 March 2012

2 minute read

The safety of raw milk sold in Northern Italy was investigated in relation to hygiene quality parameters and presence of Salmonella spp., Listeria monocytogenes, thermotolerant Campylobacter, and Verocytotoxin–producing Escherichia coli O157:H7, explain Dr Federica Giacometti of the University of Bologna and co-authors there and at the Experimental Institute for Zooprophylaxis in Lombardy and Emilia-Romagna in Brescia in a paper published in the latest issue of Foodborne Pathogens and Disease.

They also evaluated the performance of different analytical methods used – official culture method (ISO), modified Bacteriological Analytical Manual cultural method (mBAM) and polymerase chain reaction (PCR). The presence of Mycobacterium avium subsp. paratuberculosis (Map) was investigated only by PCR.

All samples met regulations for alkaline phosphatase and inhibitory substance, while 18 per cent and 44.8 per cent of samples collected from vending machines had, respectively, somatic cell count (SCC) over 300,000 per millilitre (mL) and total bacterial count (TBC) over 50,000CFU per mL.

The correlation between hygienic quality parameters in samples collected from bulk tank and vending machines showed a significant increase of TBC in vending machines, meaning that raw milk was mishandled during distribution and sale.

All pathogens investigated were detected in raw milk sold at vending machines. A total of five samples (five per cent) had at least one pathogen, of which two were detected by PCR and three by mBAM. None of the samples was positive by cultural ISO methods.

Even if the comparison of analytical methods showed that none performs significantly better than the others, testing a higher volume of milk (25 versus 210mL) affects significantly the detection rate of pathogens.

Three samples (three per cent) were positive for Map, suggesting that raw milk is a significant source of Map exposure for consumers.

The observed TBC increase and the detection of several pathogenic bacteria pose questions on the safety of raw milk, according to Giacometti and co-authors. They continued that the use of ISO seems inefficient in detecting a low contamination level of pathogens in milk and consequently not appropriate as official method for testing.

In order to ensure consumer's safety, a new approach for the raw milk chain is required, the researchers concluded.

Reference

Giacometti F., A. Serraino, G. Finazzi, P. Daminelli, M.N. Losio, N. Arrigoni, S. Piva, D. Florio, R. Riu and R.G. Zanoni. 2012. Sale of raw milk in Northern Italy: Food safety implications and comparison of different analytical methodologies for detection of foodborne pathogens. Foodborne Pathogens and Disease. 9(4):293-297.