Biology Reference
In-Depth Information
and also provided both cellular and humoral immune defense responses
(Rengpipat
et al
.
, 1998; Rengpipat
et al
.
, 2000).
Streptococcaceae
Streptococcus phocae
(PI80) was isolated from the intestine of shrimp
(
Penaeus indicus
) and conferred protection to
Penaeus monodon
postlarvae
(PL-55, 55 d after they molted from the last mysis stage) when challenged
with a
V. harveyi
strain (Swain et al., 2009). The survival attained with this
strain was 92% against 60% in the control (
V. harveyi,
only). However, this
strain did not protect the postlarvae against a strain of
V. parahaemolyticus
.
The authors speculated that the mode of action is the production of
bacteriocins and other substances capable of making a pore in the cell
membrane of pathogens, which leads to the effl ux of K + ions, although no
evidence is presented.
PROBIOTIC IN LARVAL CULTURE: GRAM-NEGATIVE
BACTERIA
Vibrios (Vibrionaceae)
Turbot larvae often experience mass mortalities apparently caused by
different pathogenic vibrios and other Gram-negative bacteria (Hjelm
et
al., 2004). To control these pathogens, several Gram-negative and positive
bacteria have been tested. A strain of
Vibrio pelagius
introduced in the
rearing water improved the survival of larvae compared to fi sh exposed
to
Aeromonas caviae
, a species associated with high larval mortalities, and
with the control group (Ringo and Vadstein, 1998). This result might point
out that
V. pelagius
served more as a feed additive than a true probiont. A
very desirable and maybe indispensable requirement for a probiotic strain
to function as such is its ability to colonize the gut of the host. A strain of
V. mediterranei
(Q40) was observed as a fi rst colonizer of the gut of turbot
larvae and thus be able to prevent the colonization of potential pathogens
(Huys
et al
.
, 2001). Larvae treated this way also showed improved
survival, but since no infection challenges were done, it is diffi cult to say
that this strain is indeed a probiont. “Vibrio E” (phenotypically close to
V. alginolyticus
) was challenged against the pathogenic strain “Vibrio P”
described previously (Gatesoupe, 1997). In this case, a higher survival
percentage was observed when a higher density of the probiont was
inoculated, but in any case, signifi cantly lower than uninfected larvae.
Vibrio E is a siderophore producing strain that can grow in iron-chelating
media and it was proposed that both strains competed for iron, and since
