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