Microbio Section

Bacteria are ubiquitous in nature- they may sometimes be beneficial or harmful to each living organisms. The saying, “small but terrible” would best describe the nature of the action of such microorganisms. They proved that size doesn’t matter. Their minute presence may give people serious disease conditions. Hence, the first step to kill or lessen the effect done by these microorganisms is to identify, qualify and quantify them.

The supplemental discussions in this rotation made me rationalize the use of different media for a specified suspected organism. These media aid in the identification and evaluation on the pathogenicity of certain organisms.

The Blood Agar plate is an enrichment media used to allow growth of almost all organisms. Blood is being incorporated in such media to enable the examiner to observe the haemolytic action of an organism which would aid in the identification of certain species of bacteria. The MacConkey Agar is a selective media for gram negative bacilli and members of the enterobacteriaceae. This media allows the differentiation of bacteria according to their ability to ferment lactose. EMB is used to differentiate typical gram negative rods from the atypical ones. All media used in microbiology contains indicators that allow reaction with the presence of enzymatic actions. Understanding the principles and uses of each media would allow the examiner to identify and classify different species of bacteria.

Furthermore, the gram staining procedures would allow the examiner to differentiate bacteria according to its morphological structure, arrangement and reaction with the gram stain. A gram positive organisms is indicated with a purple or violet colored organisms. The violet color is due to its thick peptidoglycan layer which inhibits the decolorization of crystal violet (a primary stain in gram stain). In contrast, gram negative organisms posses a pink coloration due to its easy discoloration since it has a thin peptidoglycan layer. The pink colored is brought by the saffranin stain (a secondary stain employed after decolorizing crystal violet).

During the first day of our laboratory activity in this rotation, we were asked to prepare the different media needed for the culture and biochemical testing of bacteria. I was assigned to make the Urea broth, Citrate, SIM, Vogues Proskauer and BEA. This procedure requires enough time to be prepared. Aseptic techniques in the said preparation made me anxious in preparing the different media. Unfortunately, I and my partner have to repeat making the VP broth since it failed in the quality check.

After all the media has been prepared, the whole class was given specified bacteria coming from different specimen to be cultured and identified. I was given a lesion and wound specimen. For my lesion specimen, no growth among the three media was observed (MacConkey, EMB and BAP). However, the growth of my specimen appears to be alpha haemolytic, non lactose fermenter and a typical gram negative rod. By the aid of the biochemical testing, I was able to identify that the bacteria present in the wound specimen is a Proteus mirabilis. Such organism possess the following characteristic: Indole negative and Nitrate reductase positive (no gas bubbles produced), Methyl Red positive and Voges-Proskauer negative, Catalase positive, Phenylalanine Deaminase positive.

The rotation this week on microbiology made me proud of myself since I was able to rationalize by heart the use of the different media used in culturing bacteria. It made me more patient, more careful in doing aseptic procedures. It boosted my confidence level for the upcoming internship program this coming June 2008.