I was advised to store at 4 degrees Celsius and some said to freeze at -20 degrees. I did store it at first in the refrigerator but later transferred them into the deep freezer. I want to later do bacterial counts and am afraid I may have lost some of the bacteria but I have already cultured and subcultured the samples with lots of bacteria colonies seen before attempting to preserve the water for further analysis. Can I still recover as many bacteria as possible after thawing the water as I did not add glycerol to the water before freezing?
For water samples, the time between sample collection and analysis should, in general, not exceed 6 hours, and 24 hours is considered the absolute maximum. The samples must immediately be placed in a lightproof insulated box containing ice-packs with water to ensure rapid cooling.
I personally don't think you will get accurate results from your freeze thawed samples. see attached WHO guidance.
http://www.who.int/water_sanitation_health/dwq/2edvol3d.pdf
Thank you very much for your answers. I collected the samples in an ice box and cultured them after arrival at the lab same day to isolate bacteria and after that i decided to store them. I guess I may not bother to do any further analysis on the water since they have been frozen for days and hopefully I already have the bacteria I am looking for.
I advise you to collect the literature and consult standard books for planning your future work. Kindly read this book:
APHA, Standard Methods for the Examination of Water and Waste Water, American
Public Health Association, Washington, 1992, 18 edn,
Water sampling and its preservation is very important parameter for any reliable measurements and conclusions.
For microbiological analyses of water samples, the rules should be the following:
DO NOT : freeze samples (except for viruses); put ice-packs in direct contact with samples; transport warm and cold samples together.
DO ALWAYS : cool samples — ideally (5 ± 3) °C — during transport and protect samples from sunlight.
After the arrival in lab, store at (5 ± 3) °C and analyse water samples within a maximum of 24 h. In reality, each microorganism has a different maximum time. For ex., for culturable microrganisms at 22°C or 36°C analysis should be done within 8 h with a maximum of 12 h.
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