A Year in the Lab: Identifying Bacterial Collection

After spending my first week re acquainting myself with important techniques I will need for identifying, this week I began working through the collection of samples. As I was working as a lab demonstrator on Monday and Tuesday, I had to carefully plan my week in order to utilise my time effectively.

Monday 21st October

After demonstrating, I started my own work at around 5pm, by making up more MacConkey agar, autoclaving and pouring agar plates for tomorrow. I left these to dry completely before inverting and leaving them to dry further at 15ºC overnight.

Tuesday 22nd October 

Like Monday I began my own work at around 5pm, by labelling up my MacConkey agar plates with my initials, the date, the sample number and MAC (For MacConkey). I then removed my chosen samples from the freezer, allowing them to warm for a few minutes and vortexing each to ensure homogeneity. After photographing and describing the appearance of the samples, I spread plated 50μl of each sample onto individual MacConkey agar plates. I allowed the plates around 15 minutes to absorb the sample, and then incubated them all at 30ºC overnight.

IMG_2879Bacterial samples in the collection

Wednesday 23rd October 

I started the day by making up more MacConkey agar and putting it on to autoclave. I then got my spread plates out of the incubator and began observation. Using the colony counter I carefully observed the plates, took photographs of the whole plate as well as individual colonies and then began to select samples I wanted to Gram stain. As my agar had autoclaved and cooled by this point, I then poured plates and allowed them to set completely before inverting.

100 - Possibly salmonella or proteusLactose negative spread plated sample on MacConkey agar

IMG_3032Observation of spread plated samples on MacConkey agar

Once finished I began to segregate the two batches of samples I had processed into categories. I separated plates into three rough categories: Yellow (Lactose negative), Red (No reaction) and Pink (Lactose positive). Within these categories I ended up with three more specific categories, which allowed me to begin identifying specific organism colony characteristics.

IMG_2921Collection of samples, spread plated on MacConkey agar

I then selected the next set of samples to be spread plated, and as before allowed them to warm before vortexing. Again, I photographed and described the appearance of the samples and spread plated 50μl of each sample onto individual MacConkey agar plates. After allowing the plates time to absorb the sample, I incubated them overnight at 30ºC.

Thursday 24th October

On Thursday my day ran pretty much the same way as Wednesday. Making up and pouring more MacConkey agar plates, observing my incubated spread plates, Gram staining, processing my new chosen samples before spread plating and incubating overnight at 30ºC. I also re evaluated my collection categories, adding my new batch of processed samples and making small tweaks.

IMG_3120Viewing Gram stained samples

Friday 25th October

As it was the end of the week, and I couldn’t continue work over the weekend my day didn’t include production of new MacConkey agar plates and processing of new samples. Instead I got my spread plated plates out of the incubator, carefully observed, took photographs and then Gram stained. After this, I re evaluated my collection categories, adding my new batch of processed samples and ensuring I was happy with the results so far.

Next week…

I am very happy with the progress I have managed to make this week, as I have nearly spread plated all the collection onto MacConkey agar. After continuous daily practise, I feel really comfortable with the techniques required for this part of my project: Agar production, Pouring plating, Heat fixing slides, Gram staining and Spread plating.

I am very glad I took such detailed notes and photos of each plate as this has allowed me to always be able to view any plate, whether I am in the lab or working elsewhere. From this I have managed to start identifying the samples within the collection, both initially in the lab and then more definitely afterwards. I think the categories I have established in order to help me process the collection have worked well and I will continue to use this system as I begin further confirmatory processes.

A Year in the Life…


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