Listeria monocytogenes: Its importance in the dairy industry

Abstract

K e y words: Listeria monocytogenes, heat resistance, incidence, growth, milk. cheese. INTRODUCHON Morphological and biochemical characteristicsCurrently five species of Listeria are recognised (Seeliger and Jones 1986) of which three may be pathogenic for man. Listeria iuuriouii has neurotrophic activity in mice and sporadically has been involved in human disease (Seeliger 1984), and recently L seeligeri has been implicated as the causative agent for meningitis in man (Kluge and Hof 1986; Rocourt et a1 1986). However, the most important species of the group is L monocytogenes, and this review will concentrate on this organism.Listeria mortocytogenes Pirie 1940, 383AL is a small, coccoid to rod-shaped, Gram-positive organism exhibiting a tumbling motility at room temperature. The organism is often designated as a coryneform contaminant because of its unique morphology. Identification of new isolates may be achieved by examination of cellular morphology, colonial morphology and haemolytic reaction on sheep or horse blood agar and blue-green coloration of colonies when viewed

Retention of Listeria and Salmonella cells contaminating skim milk by tangential membrane microfiltration ("Bactocatch" process)

“…Such a bacterial reduction is not as effective as pasteurization, but it could be relatively satisfactory when cheesemaking with raw milk is envisaged. "Bactocatch" treatment of raw milk containing 0.5-10 CFU/ml of potentially pathogenic Listeria and Salmonella species (Griffiths, 1989), according to the process described by Maubois (1991) with an UHT sterilization of cream to be added for fat standardization and a MF treatment of skim milk will allow a count between 2-40 CFU/1 000 ml in cheese milk. Envisaging that 90% of these contaminating bacteria will be kept in the 100 9 of cheese resulting from the original 1 000 ml of cheesemilk leads to 0.2-4 Listeria or Salmonella cells per 10 9 of cheese.…”

“…Despite an extended variation reported accarding to country, Griffiths (1989) estimated that Listeria monocytogenes occurs in less than 5% of collected milks. The level of Listeria in raw milk is estimated to be 10 CFUlml (Beckers et al, 1987).…”

“…Thus, bulked silo milk probably contains 0.5 CFU/ml of Listeria. But Listeria monocytogenes is able to grow at low temperatures (Donnelly and Briggs, 1986) and taking into account a lag phase of 24-48 h and a generation time of 20 h, it can be assumed that even after 96 h of low temperature storage, untreated milk would approach levels of 5 to 10 CFU/ml (Griffiths, 1989). Information on the concentration of Salmonella cells in raw milk supplies seems to be lacking in the literature (Marth, 1969) but it is likely that contamination of raw milk by Salmonella is similar to that of Listeria (Johnson et al, 1990).…”

Türkiye’nin Güneydoğu Bölgesi’nde Üretilen Mısır Silajı ve Çiğ Sütlerde Listeria Türlerinin Varlığı

“…On the other hand, Aygun and Pehlivanlar [21] found one (2.12%) positive sample for L. ivanovii and L. grayi among 47 raw milk samples. Faecal or environmental contamination during milking, storage and transport, infected cows in dairy farms and poor silage quality have been reported [7,14,17,[19][20][21] as contamination sources of Listeria spp. to raw milk.…”

Microbiological, physical and chemical studies on fresh red meats packaged under different modified gas atmospheres

“…The higher growth rates of other psychrotrophic spoilage flora than Listeria in the modified gas atmospheres is desirable in that the packaging can extend the storage life of pork chops by restricting the possibilities for Listeria to grow to high numbers before the product is spoiled. However, it must be noted that Listeria grew even though at a slower rate, and considering the relatively low infectious dose of this pathogen for humans (about 102 to 103 cells; Griffith, 1989), particularly for imunocompromized persons , the risk of human infection may not be reduced by modified atmosphere packaging of fresh pork chops. The higher growth rates of Listeria in the gas atmosphere packages than in the vacuum package is also an indication that fresh meats packaged in MA may be susceptible to growth of Listeria if the package Is subjected to moderate thermal abuse.…”