During microbial limit testing MacConkey broth and MacConkey agar are two media used for identification of E.Coli which is a pathogen. But MacConkey broth is incubated at 42-44°C and MacConkey agar is incubated at 30-35°C temperature for the identification of same pathogen. Why elevated temperature of 42-44°C is used initially and then 30-35°C is used for incubation? The reason is that there are different strain of E.coli present in the environment. E.coli is gram negative bacteria and is an indicator of fecal contamination. Such contamination could arise from poor hygiene of operators, contamination
from animals like cats, birds or a low quality water supply. E.coli is capable of causing diarrhoea and sickness also. So initially, 42-44°C temperature is provided for the incubation which is suitable for growth of fecal E.coli strain which we need to identify but other strains of E.coli couldn't grow at this high temperature. Once the enrichment of fecal E.coli has been performed in MacConkey broth then sample is streaked on MacConkey agar media and then incubate at 30-35°C which is suitable temperature for the growth of fecal E.Coli. That's why initially elevated temperature is used for the selection of fecal E.coli.
Thanks!
Dear forum,
ReplyDeleteAbout the test ME in pharmaceutical products(tablets, blisters e.t.c). The procedure is 10g of sample + 100ml Dilution=>Shaking for 30-60min=> 10ml of homogenate transfere to 100ml TSB=> Incubation for 24h/30-35oC. Subculture: 1 ml TSB to 100ml Macconkey broth and incubation at 45-44oC for 24-72h. The question is?
How we count the incubation time? We put the bottles in the incubator an we begin to count 72h? Or the time begin when the temperature in the bottle raech at 42-44oC?
Thanks in advance,
Microbiologist
M.Ch
Dear,
ReplyDeletethe incubation condition is 42-44o C for 24-72 hours that means you can take out your sample from incubator between 24-72 hours, not exact at 72 hours.
Thanks
Dear forum,
ReplyDeleteI have an other question: According to the ISO 11133:2014 (PRE-POURED CULTURE MEDIA) on the streak plate we should pour 18-20ml of agar to the petri dish (diameter 100X15mm) in order to make a depth of 3-4mm. Why is this specific depth important? the size of colonies depends on the depth of agar?
To prevent the plate from dryness. If plate become dry then we couldn't get proper recovery of microorganisms.
Deletenot clear plz explain
ReplyDeletenot clear plz explain
ReplyDeleteHi sir how to calculate the log reduction in disinfectant validation.
ReplyDeleteHi sir how to calculate the log reduction in disinfectant validation.
ReplyDeleteFor example initially, you have 1000 cfu and you recovered 100 cfu. Then it will be one log reduction. If you get 10 cfu then you will get 2 log reduction. Subtract final recovered population log from initial microbial population log. You will get log reduction.
DeleteHow many passages of the cell culture why..??
ReplyDeleteAfter 5 passage of culture has been discharced due to change in their morphology of microorganisms. Due to mutation take place ..
DeleteSir first you said 42-44 is suitable for fecal e coli and in the Last sentence you said 30-35 degrees is suitable which is correct
ReplyDelete42-44 degrees temperature is required for selection of fecal e.coli from other strains of e.coli. Once required strain remain in broth it can be easily recovered at 30-35 degree centigrade.
Delete