Help needed interpreting Rodac Plates results

Hello All,


I am not a microbiologist but i want to learn more about it.
I use the rodac Plates PCA,VRBL,VRBG to test the hygiene of the surfaces and peoples hands.

I would like to know your oppinion on the bellow photos.

It is a rodac plate VRBL for Enterobacteriaceae.What happened?

I would like also to learn how to count UFC in these rodac plates.Can anyone help me with this.
opinions, books...

Thanks

Best Regards

Andreia

you can see in this link

http://www.fda.gov/F...BAM/default.htm

Thanks AS Nur for the link, but i don't do any diluition and the plates aren't in spiral.

The method i use is by direct contact of the plate with a surface area of my choice,and then the plates will incubate at 35-37ºC for 24-48 hours.

BR

Andreia

Dear Andreia:

You need to carry out serial dilution if the surfaces are too 'dirty' otherwise you will get this - 'TNTC' (Too Numerous To Count) as your picture showed.....

Thanks AS Nur for the link, but i don't do any diluition and the plates aren't in spiral.

The method i use is by direct contact of the plate with a surface area of my choice,and then the plates will incubate at 35-37ºC for 24-48 hours.

BR

Andreia

dear andreia..

IMEX i use swab test method to measure hygiene level of surface area.. this method is simply enough..and we can do many level of serial dilution. here is the simply method :

1. first you have to prepare swab stick steril and BPW solution steril (10 ml).
2. swab your surface area ± 10 x 10 cm and put your swab stick to BPW solution aseptically
3. pippet 1 ml of your BPW solution to petri dish and pour ± 15 ml of your media (PCA, VRBL or VRBA), shake the plate ( i am using eight number pola). you can make serial dilution from BPW + sample solution for example if you need 10 times dilution, you just pippet 1 ml of sample solution to 9 ml BPW solution etc..

4. Incubate and read the result..

The other method is using ATP method.. You can buy the equipment from MErck or Biotrace etc.. Principle of this method is measure the ATP and its correlate with your hygiene status, this method only need 1 minute to get the result...

hope can help you

rgds

Asep S Nur

Did you get the answer Andreia?

Dear Andreia,

Yr info is rather inadequate to make any helpful prediction. Offhand, it looks like you placed the plate on the hands of the garbage disposal operative. VRBL responds to a very wide range of Ent..ae species of course. I certainly hope it was not a just washed/sanitised stainless steel table used to process a RTE food.

As AS NUR comments, the most likely result is TNTC (= > than a number [depending on the plate area]) This number will almost certainly be outside yr target limits so I guess you have achieved a meaningful result, namely unsatisfactory. Personally my experience is mainly with Petrifilm plates, my only knowledge of VRB type systems concerns it's ability to give different results as compared to MPN methods (product/procedure related).

Rgds / Charles.C

Dear Asep S Nur,

Would like to know what standard is your procedure based on? I would really love to get a reference for that to come up with a instruction to my fellow workers.

Very appreciate it.

Regards,
Shar

Dear Asep S Nur,

Would like to know what standard is your procedure based on? I would really love to get a reference for that to come up with a instruction to my fellow workers.

Very appreciate it.

Regards,
Shar

AS Nur can you help Sharleen?

AS Nur can you help Sharleen?

Dear sharleen.

My procedures based on BAM ( here is the link) http://www.fda.gov/F...BAM/default.htm And I just modified on sample preparation...

hope can help you..

Dear sharleen.

My procedures based on BAM ( here is the link) http://www.fda.gov/F...BAM/default.htm And I just modified on sample preparation...

hope can help you..

Dear AS Nur,

Thanks for helping out. But it was the sampling procedure that am looking for the standard. How do you justify the size of the surface area you'd like swab and the diluent to use?

Thanks again, really appreciate it.

Shar

Dear Sharleen,

Yr question is philosophical and statistical. I think you should appreciate in the following that bacteriological assessment is quantitatively not a very exact science compared to, say, weighing objects.

There is the usual statistical requirement of achieving a representative sample and also which can be “reliably” counted. I hv hardly ever seen the question of statistical number of locations addressed, this may possibly reflect the known large variances involved . Frequently IMEX, the locations are grouped by risk assessment such as via probability of direct food contact / ease of cleaning etc, eg tables, hands and an average of 2 or 3 duplicate samples taken for comparison to appropriate levels. Statistically, bacteriological theory requires a minimum number of colonies to grow on the standard plate used for counting so as to provide a desired nominal accuracy. The logic is validated in most standard textbooks. Practically, the ease of provision of a suitable sample concentration will obviously vary between a slaughterhouse reception and a fully cooked product packaging room. The typical choice of quantity of wiped surface area as referred has been found to provide a suitable practical compromise for many food situations. It can presumably be enlarged if required to increase sensitivity although in practice, the use of “less than (a specified maximum level of the cleanliness parameter /unit area” tends to be a more common solution. Hence the type of procedure referred in this thread.

Concerning the dilution liquid, this also has to possess certain specified characteristics. Over time, the choices hv narrowed. The details / validation are, I think, less common in text books. Maybe someone knows a literature ref? (I cannot remember if given in BAM, probably not since this aspect is a recognised standard setup already). Suppliers product manuals, eg Difco, Oxoid etc probably cover it but these are not available on-line i think.

Rgds / Charles.C

Dear AS Nur,

Thanks for helping out. But it was the sampling procedure that am looking for the standard. How do you justify the size of the surface area you'd like swab and the diluent to use?

Thanks again, really appreciate it.

Shar

Dear Sharleen..
For swab area based on your equipment and your cleaning process, first you have to make sure that celaning process is equal for any place.. so you can get same result for cleanliness at any place that your swabbing and ussually for swab test we use 10 x 10 cm area (based on our ATP equipment reference).. or the other way is make some small research you cantake swabing at any posiiton in equipment, assume it is plannar.. so you can take sample at 5 position ( 4 at corner and 1 at centre).. after that you can threat the data statistically.. and i am sure the result is not significant different.. you can try it..

and for diluent depend on your micro content in your product.. first you have to try without dilution, if the result is TMTC (To many to count) you have to prepare for dilution series and ussually starting in 10 times dilution..and for 10 times dilution is mean 1 part of sample on 10 ml solution (1 ml sample + 9 ml BPW)..

hope can help you a


rgds

AS Nur