THE INCIDENCE, NUMBERS AND TYPES OF LISTERIA-MONOCYTOGENES ISOLATED FROM FARM BULK TANK MILKS

Bulk tank milk from 160 producers was tested for Listeria monocytogenes at three monthly intervals over 1 year. Twenty-five producers were positive, most on a single occasion, only seven were positive on three or more of the four samplings. Listeria monocytogenes numbers were low, usually < 1 ml(-1), the highest was 35 ml(-1). All isolates were serotype 1, the use of multilocus enzyme electrophoresis on representative isolates gave nine different electrophoretic types, two have been associated with listeriosis in humans or animals, a further two had only been isolated from one other source (silage or faeces), while the majority (5) were unique to milk.