Characterization of Listeria monocytogenes isolated from production lines of fresh and cold-smoked fish.
OBJECTIVE
The aims of this study were to characterize strains of Listeria monocytogenes isolated from cold-smoking fish plants to establish possible routes of contamination through the processing chain.


RESULTS
Listeria monocytogenes from fresh fish suppliers, raw materials, factory sites and finished products isolated in Portugal (162 isolates) and England (28 isolates) were characterized by serotyping, phage typing, tetracycline, cadmium and arsenic resistance, and plasmid profiling. On the basis of serotyping and phage typing, the isolates were categorized into eight groups. Although cultures within some of the groups could be further differentiated on the basis of plasmid profiling and cadmium and arsenite typing, consideration of all typing data predominantly clustered together isolates from a single location. L. monocytogenes strains: from fresh salmon suppliers were not found in the processing lines; from fresh salmon from different locations differed; and from the water where salmon trout were farmed differed from those isolated from the fish samples.


CONCLUSIONS
No clear source or route of contamination in the cold-smoked processing chain could be established; however, these results highlight the complexity in tracking this bacterium through food chains.
Vaz-Velho
M
M
Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Porto, Portugal. manuela@esb.ucp.pt
Duarte
G
G
McLauchlin
J
J
Gibbs
P
P
D000818:Animals; D015373:Bacterial Typing Techniques; D004739:England; D005399:Fishes / Q000382:microbiology*; D005511:Food Handling; D005516:Food Microbiology; D005519:Food Preservation; D005525:Food-Processing Industry; D008089:Listeria monocytogenes / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D011174:Portugal; D012474:Salmon / Q000382:microbiology; D014337:Trout / Q000382:microbiology