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What are the better ways to preserve shrimp samples?

The shrimp samples could be preserved in a -20C freezer.  If the interested target is a DNA virus such as WSSV, the samples can be kept in frozen form for at least one year without thawing.  If the interested target is a RNA virus such as YHV, the samples can only be preserved for 2 to 3 months in a -20C freezer.

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What care should be taken when we preserved samples by ethanol?

The samples can also be preserved in 95% ethanol.   However, this method is only good for WSSV and other DNA viruses.  The RNA viruses infected samples should not be preserved in ethanol because the sensitivity of the test will drop 10 to 100 times.

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Can I preserve the sample in Lysis Buffer or DTAB solution instead of ethanol?

Be sure to use the GC grade ethanol to fix samples.  Either 95% or absolute ethanol is suitable.  Industrious ethanol might inhibit PCR because of the additives.  The volume of ethanol should be at least twice of the sample volume.  And the bigger tissue nugget should be cut into smaller pieces before preservation.

If the samples will be extracted within 24 hours, users can use Lysis Buffer or DTAB solution to preserve samples.  Room temperature is good for these samples.  Do not store the Lysis Buffer or DTAB solution preserved samples in a freezer or a refrigerator. 

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Can we use TE buffer instead of ddH2O to dissolve the DNA pellet?

Yes.  TE buffer is even better than ddH2O for dissolving the DNA pellet.  If you want to preserve the DNA samples for longer period (from 1 week to 1 year), TE buffer is highly recommended.  But for the routine diagnosis, ddH2O is more convenient.

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Can I preserve my samples with davidson's fixative?

Davidson’s fixative is not recommended for sample preservation, especially when you want to extract DNA from the sample. One of the components of Davidson’s fixative is Formalin which has already been confirmed of DNA damage in recent research reports. Formalin forms monomethylol adducts with nucleotide rings. This reaction is reversible in aqueous solutions, which is typically used for DNA extraction, though, less reverse reactions occur. Base damage caused by Formalin may impair PCR by halting polymerase elongation, but an insidious possibility is error prone translation synthesis across sites of damage, producing in vitro, artificial mutations. In another word, the PCR diagnosis with DNA extracted from Davidson’s fixed sample will be easily become false-negative results by conventional PCR methods. As for our IQ2000^TM serial PCR detection systems, the built-in internal control mechanism can monitor the quality of extracted DNA.  These Davidson’s fixed samples will not be able to get the internal control, and therefore can avoid the false-negative interpretation.

Hence, we don’t recommend Davidson’s fixative for sample preservation.

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