Mycobacterium bovis cultured from commercially pasteurized cows' milk: laboratory cross-contamination.
The ability of Mycobacterium paratuberculosis to survive the commercial pasteurization process of raw milk remains controversial. In a study undertaken in Venezuela to culture M. paratuberculosis from commercially pasteurized cows' milk, 83-200 ml containers of milk were processed and cultured on Herrold's egg yolk slants. No M. paratuberculosis was cultured but a total of six colonies of Mycobacterium bovis were isolated from one container each from two different milk providers. Because laboratory cross-contamination was suspected, the laboratory records were reviewed and spoligotyping was carried out on the isolated individual colonies. On the day before these milk specimens were processed, the biological safety cabinet had been used for the isolation of M. bovis from lymph nodes from infected cattle. Spoligotyping showed that that the colonies isolated from the milk all had the same pattern as the strains isolated from the lymph nodes that were processed the previous day. As far as we know, this is the first report of cross-contamination in a veterinary mycobacterial laboratory. False-positive cultures in the mycobacterial laboratory are not rare. In this setting M. bovis was isolated because it is the most common manipulated organism in this laboratory. We believe that reports on the isolation of M. paratuberculosis from commercially pasteurized milk should exclude cross-contamination before reporting, especially when this organism is routinely isolated from animal material in the same lab.
Méndez
Darling
D
Laboratorio de Zoonosis Angel Melénez, Decanato Veterinario Universidad Centrooccidente Lisandro Alvarez, Barquisimeto, Venezuela.
Giménez
Francisco
F
Escalona
Arnelly
A
Da Mata
Omaira
O
González
Alexandra
A
Takiff
Howard
H
de Waard
Jacobus H
JH
D000818:Animals; D015373:Bacterial Typing Techniques / Q000662:veterinary*; D002417:Cattle; D019411:Clinical Laboratory Techniques / Q000592:standards*; D005506:Food Contamination / Q000032:analysis*; D008892:Milk / Q000382:microbiology*; D009163:Mycobacterium bovis / Q000145:classification / Q000302:isolation & purification*; D010802:Phylogeny