ARCHIVED REPORTS XR0012746 - Laserfiche WebLink

Home Browse Search

.: _ r r t Issued: 8/18/87 MICRO SOP-P19 o Cool the bent glass rod (e.g., by rubbing it on the inside of the petri dish lid). o Place the inoculated plate on the turntable and while spinning the petri dish, spread the inoculum over the surface of the TSA plate until resistance is felt and/or the liquid is absorbed. o Discard the contaminated bent glass rod .into a container of appropriate disinfectant. o Invert and place the +.noculated petri diahes in a rack for storage and transport and incubate at the appropriate temperature (e.g., room temperature, 25°C) overnight or for a previously chosen time. Counting and Recording Colonies o After the required incubation p:riod (e.g., 24 h, 1 week, etc.), promptly examine the plates and select those with 30-300 CFU's. (If / counting must be delayed temporarily, refrigerate plates for no more ;? ;> than 24 h, but this should be avoided as a routine practice.) o Using a colony counter equipped with a guide plate, appropriate smagnification, light and a hand or automatic tally, count all colonies Or the colonies of interest). If replicate plates are countable, sum.the plate counts from both plates and calculate the mean plats count for that-.1ilution. a Compute the CFU/ e,L by multiplying the mern plate count (PC) by the 3 reciprocal of the dilution used and then by 10 if 0.1 mL was originally plated. x s f. CFU/ mL = PC x reciprocal of dilution x 10 For example, Tf PC 35 0 10'2 dilution, then 4 CFU/ mL = 35 x 102 x 10 = 3.5 x 104 s o Record the dilutions plated and plate counts in the notebook. o If plates from all dilutions have no colonies, report the count as zero but when computing the density, use the value 9f less than one (0). s For example, if no colonies develop on the 10 dilution plates, calculate the densit _�a_.less...ahan_._1000__.(<1U�0)_.CFU/.:mL�_ -- _--- -. _ t t: » 4 _