Detection of the apr gene in proteolytic psychrotrophic bacteria isolated from refrigerated raw milk.
Bacteria of the genus Pseudomonas have been associated with the spoilage of raw milk and dairy products due to the production of thermostable proteolytic enzymes. The apr gene encodes for alkaline metalloprotease in Pseudomonas and other related bacteria. Its presence in psychrotrophic proteolytic bacteria isolated from raw milk collected from cooling tanks was verified. A polymerase chain reaction (PCR) technique was used with degenerate primers. Total DNA from 112 isolates was pooled in different groups and then used as template for the amplification reactions. Controls consisted of DNA extracted from 26 cultures. An expected DNA fragment of 194 bp was detected in groups that contained bacteria identified as Pseudomonas. The PCR product was observed only when DNA from control cultures of Pseudomonas aeruginosa, Pseudomonas fluorescens, Serratia marcescens and Aeromonas hydrophila were used. A detection limit assay indicated that the apr gene could be directly amplified from pasteurized milk inoculated with 10(8) CFU/ml of P. fluorescens. With this method it was possible to detect proteolytic bacteria at 10(5) CFU/ml in reconstituted skim milk powder if cells were recovered for DNA extraction before amplification.
Department of Microbiology, Federal University of Viçosa, Viçosa, MG, 36570.000, Brazil.
Maurilio L
ML
Martins
Elza F
EF
de Araújo
Hilário C
HC
Mantovani
Célia A
CA
Moraes
Maria C D
MC
Vanetti
D000818:Animals; D015373:Bacterial Typing Techniques; D002374:Catalase / Q000378:metabolism; D004269:DNA, Bacterial / Q000032:analysis*; D005506:Food Contamination / Q000032:analysis*; D005784:Gene Amplification; D008892:Milk / Q000201:enzymology / Q000382:microbiology*; D010088:Oxidoreductases / Q000378:metabolism; D016133:Polymerase Chain Reaction / Q000379:methods; D011549:Pseudomonas / Q000145:classification / Q000201:enzymology / Q000235:genetics / Q000302:isolation & purification; D012034:Refrigeration; D013045:Species Specificity; D013696:Temperature
D004269:DNA, Bacterial; D010088:Oxidoreductases; D002374:Catalase