Biology Reference
In-Depth Information
and incubated. Inhibition is determined if the inhibition halo is twice the
width of the probiotic strain growth (Hai
et al
.
, 2007).
Several other methods have been devised but with variable results,
such as well-diffusion, disc-diffusion, PCR (Nitisinprasert et al., 2006
),
spot (Prado et al., 2009) and co-culture (Hai
et al
.
, 2007).
Methods to Test Probionts
According to the defi nitions proposed earlier, to be able to prove that
an organism is indeed a probiont, it has to protect the host against the
attack of a pathogen. There are basically two ways to test this, one is to
administer the potential probiont to the host and wait until an outbreak
starts and measure signifi cant survival enhancements in those organisms
exposed to the probiont against untreated organisms. The other method
is to artifi cially challenge treated organisms with pathogens and observe
the positive effect of the probiont (Ringo and Gatesoupe, 1998). Survival
enhancements do not have to be the only parameter evaluated; less diseased
larvae, weight gain, higher molting rates, etc. are also indications that the
treated larvae coped with the infection better, although they did not die.
But a requirement is that an infection by a pathogen was established, and
this infection signifi cantly reduced the performance of the larvae. If this
cannot be proven, the microorganism can only be classifi ed as a “potential
probiont”.
Bacteria-free organisms, called “gnotobiotic”, are important as model
organisms to understand the true action of a pathogen and/or probiont,
because the results will not be masked by the normal bacteriofl ora present
in the gut. Only a few studies have been done with gnotobiotic marine
animals; germ-free sea bass (
Dicentrarchus labrax
) larvae have recently been
produced (Dierckens et al., 2009) and tested with potential pathogens.
These organisms will be of capital importance to understand host-microbe
interactions.
PROBIOTICS IN LARVAL CULTURE: GRAM-POSITIVE
BACTERIA
In the present review, only data will be presented where it has been proven
that the tested probionts do somehow protect the host against the action
of pathogens, or at least the immune system was improved, although this
last aspect is diffi cult to evaluate due to the small size of the larvae.
Lactic Acid Bacteria (LAB, order Lactobacillales)
Several species of LAB have been used as probiotics, mainly because many
of them are part of the normal microfl ora of the intestine of fi shes (Ringo
and Gatesoupe, 1998).
Carnobacterium divergens
(previously identifi ed as
