Question

Design and submit a concept map on what you have learned. It should include concepts and connections between concepts including: Microbiology testing techniques Types of microbes identified by each technique

Answer 1

Answer: Microbiology testing techniques are used to identify different microbes. Traditionally, microbes were mostly identified using phenotype (based on external characteristics). The characteristics used were shape, size, smell and colour. These techniques include culturing, staining, and simple biochemical tests. One of the most important technique is staining. Staining differentiates different bacterial cells based on the cell wall composition. Gram staining is used to differentiate Gram-positive bacteria (Clostridium spp., Bacillus spp., Staphylococcus ssp., Streptococcus spp., etc.) and Gram-negative bacteria (Salmonella ssp., Helicobacter spp., Escherichia spp., etc.). Many bacteria are Gram-variable.

Endospore staining technique is used to differentiate spore-producing and non-spore producing bacteria. Malachite green stain is most commonly used in this technique.

Many staining techniques stains a single particular bacterial species. Ziehl-Neelsen staining is used specifically stain Mycobacterium tuberculosis.

Some stains isolate fungi. Lactophenol cotton blue is a blue coloured stain that stains the carbohydrates of the fungal cell wall. Other stains specific to fungi are Trypan blue, periodic-acid Schiff stain, aniline blue, calcofluor white stain, and Grocott’s methenamine silver stain.

The modern methods include biochemical, immunological, and molecular techniques. The biochemical tests are more specific in microbe’s identification. Catalase testing is done to identify the bacteria that have catalase activity. Oxidase testing is done to identify bacteria with cytochrome c oxidase (an enzyme in electron transport chain) activity. Substrate utilization tests are done using a different panel of the substrates, like, different carbon and nitrogen source. Different bacteria use different substrate and according to the colour of the substrates used changes after incubation.

Molecular techniques like polymerase chain reaction can differentiate different strains of bacteria. There are different sets of sequence-specific primers. In this technique, 16S ribosomal RNA is used. Microarray-based microbial identification is use hybridization of pre-amplified microbial DNA sequences to arrayed species-specific oligonucleotide probes.

The immunological technique includes ELISA method for microbial detection. The concept map of different techniques is shown in the below figure.