Sunday, July 29, 2007

Microbiology and Accreditation of Labs

Hi all. It’s nice meeting everyone again. You people must have missed school a lot. I'm currently doing in house SIP. So far, I'm spending most of my time doing literature review. I do not really have interesting things to share because I’m just looking at different protocols for food analysis and doing a little read up on accreditation of labs. So pardon me if this entry gets boring. Unlike many others, I do not have to deal with machines. Things that I’ve done require basic skills only.

For my SIP, I am a TSO for Basic Microbiology as well as Human Anatomy and Physiology practical lessons. For B Mic, i did streak plate for Bacillus Subtilis, subcultured of E. coli on nutrient agar and broth. Because of the shortage of slides for viewing, I had to do gram staining for S. aureus, E. coli and Bacillus Subtilis. All the slides were mount using DPX to preserve the stains. I also prepare agar plates and dry agar plates. Agars were prepared by weighing the dehydrated media and suspend them in distilled water. Molten agar is then sterilized by autoclaving at 121°C for 15 mins.

As for HAP practical, I prepare the required reagent or equipment required for that day’s practical. Boiled starch, pepsin, pancreatin, egg albumin, litmus milk were prepared and dispensed into the bottles.

As a TSO, there are also some general duties for me to do. Housekeeping, clearing the oven, refilling the DI water, ethanol as well as washing up are some of the things expected to be done every week.

What I’ve done in AS4 is microbial food analysis testing. This is done by using AOAC official methods to find out the total plate count, coliform count and E. coli count. The test selected is 989.10 (total plate and coliform) and 991.14 (E. coli). The food sample used is different flavours of ice cream. The steps for performing this test are quite straight forward.

First, dilution of ice cream is done by weighing a certain required amount into Butterfield’s buffered Phosphate diluent. Mix well. Inoculate homogenate onto petrifilm. Incubate the petrifilm. Read the results.

The picture above is an example of one of the results. This result is for chocolate ice cream. 1 and 2 are results for TPC, 3 for CC and 4 for EC. For CC, only red colonies with air bubbles next to the colonies will be counted. The counting range for TPC, CC and EC are 25 to 250 colonies. Anything below 25 will not be counted and anything above 250 will be reported as estimated count. In this case, of all the 36 petrifilms, only 6 had readings, whereas the rest were not counted due to the low amount of colonies growing on the petrifilms. (so the ice cream are still consumable. this is considered low as compared to char kway teow. i heard the microbial count for the latter could be more than 10X more.)

To get a lab accreditated, certain standards have to be met. Some of which include validity of agar, microbial count of water, sterility of autoclaved bottles. I did a trial test for validity of agar by streaking microbes (E. coli and S. aureus) on general agar (TSA) as well as selective agar (MacConkey agar and Baird Parker agar). This is to ensure that the agar is correctly enhancing and inhibiting the growth of the different microbes.

Also, I did microbial testing of water. Choices of water used were milliQ water, DI water from RO tank, DI water from container and tap water. The results are as follow

Pic 1 and 2: milliQ water, Pic 3 and 4: DI water from RO tank, Pic 5 and 6: DI water from container, Pic 7 and 8: Tap water

Since microbial food analysis is involved, it is very important that test or experiment is done in a controlled environment. There must be a microbial quality monitoring program for the laboratory environment as well as the de-ionized water used in the laboratory. This is done by establishing and verifying suitable and effective protocols based on standards methods to measure microbial bioburden in the air, work surfaces, and de-ionized water. Using the data collected, statistical analysis may be applied to determine the monitoring frequency, alert and action limits, etc, all of which will contribute to an effective monitoring program.

15 weeks of SIP left. All the best to everyone. enjoy. =)

Suat Fang
0503328G
TG01

7 comments:

Star team said...

hey,

Just want to know how does The MacConkey agar act as a selective medium for E.Coli?

Randall
Tg02
0503272G

The Lab Freaks said...

lessy!

HAHA. erm may i know what are some other things/ test involve in accreditation of lab?
TELL ME MOREEEEEEEE! hehs. (:

Natalie
TGO1

VASTYJ said...

hey suat fang!

seems like u do more work than i do at my lab. haha.

what is in the petrifilm? how can the colonies grow? do u put it in a container for incubation? or the film itself is just directly put into the incubator?

maybe after quite some time u will not eat ice cream made by TP anymore. haha!

Ying Ying
TG01

The Lab Freaks said...

hey gal!

u mentioned TPC, CC and EC..what are they ah? and u are super free.....haha....

charmaine
TG01

we are the XiaoBianTai-7! said...

Hey,

What is Butterfield’s buffered Phosphate diluent?

and

For CC, why is it that only red colonies with air bubbles next to the colonies will be counted?

Adrian TG01

ALsubs said...

hey hi
i have the same quest to ask (as adrain) what is Butterfield’s buffered Phosphate diluent? wats the purpose of using it as a diluent??

Vinodhini
TGO2

The Lab Freaks said...

hello Randall =D

MacConkey agar is selective for E.coli as it supports the growth of gram negative bacteria that ferment lactose. the production of acid during fermentation causes a colour change in the agar, thus distingush it from other kind of bacteria which doesnt ferment lactose.


hello Nat!! =)

accreditation of labs includes montioring of environment too. this can be done by using settle plates and RODAC plates to test the microbial air quality.


hello Ying Ying =]

i haven really had much hands on yet.. i assume we are almost equally "busy"..

petrifilm is basically a thin film that has agar in the centre of the film. (i didnt know such things existed.. hee) the agar contains the required nutrients to support the various growth. we incubate them just like how we incubate the petri dishes but there's no need for us to turn it upside down during incubation.

i have nv ate the ice cream b4.. haha..


hi charmaine. ;)

they are just short forms of the different counts.
TPC: total plate count
CC: coliform count
EC: E.coli count

i make myself busy by doing lit research which is so difficult to find info!!


hello Adrian and Vino :]

Butterfield’s buffered Phosphate diluent is just a solution which is a buffer/diluent used to do serial dilution of food.

Suat Fang
tg01
0503328G