Behaviour of Listeria spp. in naturally contaminated chorizo (Spanish fermented sausage)

Counts of Listeria spp. were determined during the manufacture and drying of 21 lots of five chorizo varieties produced by three different manufacturers. Presumptive Listeria were not isolated from any of the batches produced in a large factory (F3) using starter, sorbate and controlled ripening at high temperatures. Initial levels in factory 1 (F1), with no starter added, but controlled ripening at low temperatures, were ca 3.5 log10 cfu/g while those in factory 2 (F2), with no starter added and ripening under natural climatic conditions, were 1.17 log10 cfu/g. Numbers of listeriae in batches obtained from F1 remained almost constant before decreasing by ca 0.5 log units/g in the finished product (32 days), while the levels in F2 increased by 1.47 log units/g after 11 days of ripening and declined further to levels above the original amount. Manufacturing procedure and smoking significantly affected presumptive listeriae counts. Thirteen strains recovered from F1 batches were identified as: Listeria monocytogenes (three strains of serovar 1/2c), Listeria innocua (eight strains of serovar 6b) and Listeria welshimeri (two strains of serovar 6b). Listeria strains from F2 were assigned to L. innocua and L. welshimeri.