Development of bacteriophage resistant starter cultures – genetic ...

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11 Δεκ 2012 (πριν από 8 χρόνια και 7 μήνες)

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Phage typing of

Lactococcus lactis

strains
with a new
ly

developed microtiter
plate system



Thomas Janzen
,
Ulf Houlberg,

Christina Lenhard,
Pia Rasmussen, Mette Dines Cantor, and
Ilka Eppert

Chr. Hansen A/S,
Innovation
, Bøge Allé 10
-
12, 2970 Hørsholm, Den
mark

Tel.: +45
-
45748463; e
-
mail:
dkthj@chr
-
hansen.com



Infection with bacteriophages
is

still a major pro
blem during dairy fermentations making the
development of new starter cultures belonging to different lytic groups a challenge for the
starter culture

producers.

To be able to test a high number of lactococcal strains we have developed a high throughput
phage typing method based on a
patented
microtiter plate system.
B
romo cresol purple and
b
romo cresol green
were added
to milk
as pH indicators.
The
pH

of the indicator added milk
in the microtiter plates was estimated using image analysis of digital picture recorded by flat
bed scanner
s
.


The phage typing
itself
was made by pipetting 44 phages from mainly different lytic groups
into the micr
o
titer plate
s with the help of a liquid handling robot.

558
Lactococcus lactis

strains from Chr. Hansen
’s

culture collection were added (two strains per plate)
,

and
acidification followed
over time
with the automised system.


7
6

of the strains were attacked by one or
more of the test phage
s

leaving 482 (86%) strains
phage resistant
.

The system delivers in parallel acidification data which can be used to preselect strains with a
certain acidification rate.
Subtracting slow and medium acidifying strains from the non
-
att
acked
strains
, 72 (13%)
lactococcal
strains remained with good acidification properties in
addition to the phage resistance.

The poster discusses also the distribution of the
sensitivity of the single test strains regarding
the three main phage species c2,

936
, and P335.