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Applied and Environmental Microbiology, April 1999, p. 1540-1547, Vol. 65, No. 4
Departments of
Microbiology1 and Food Science and
Technology,3 and National Food
Biotechnology Centre,2 University College, Cork,
Ireland
Received 11 September 1998/Accepted 1 February 1999
The bacteriophage-host sensitivity patterns of 16 strains of
Lactococcus lactis originally isolated from a mixed strain
Cheddar cheese starter culture were determined. Using phages obtained from cheese factory whey, four of the strains were found to be highly
phage resistant. One of these isolates, Lactococcus lactis subsp. cremoris HO2, was studied in detail to determine the
mechanisms responsible for the phage insensitivity phenotypes. Conjugal
transfer of plasmid DNA from strain HO2 allowed a function to be
assigned to four of its six plasmids. A 46-kb molecule,
designated pCI646, was found to harbor the lactose utilization genes,
while this and plasmids of 58 kb (pCI658), 42 kb (pCI642), and 4.5 kb
(pCI605) were shown to be responsible for the phage resistance
phenotypes observed against the small isometric-headed phage
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Identification of Four Phage Resistance Plasmids
from Lactococcus lactis subsp. cremoris
HO2
712
(936 phage species) and the prolate-headed phage
c2 (c2 species).
pCI658 was found to mediate an adsorption-blocking mechanism and was also responsible for the fluffy pellet phenotype of cells containing the molecule. pCI642 and pCI605 were both shown to be required for the
operation of a restriction-modification system.
*
Corresponding author. Mailing address: Department of
Microbiology, University College, Cork, Ireland. Phone: 353-21-902730: Fax: 353-21-903101 or 353-21-276318. E-mail:
g.fitzgerald{at}ucc.ie.
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