A very important technique in Microbiology laboratories is identifying unknown bacteria cultures. Unknown identification is used for practical purposes, such as diagnosing diseases or determining treatment of an infection. Microbiologists identify unknown bacteria to determine new and emerging infectious diseases and current diseases to determine if any kind of treatment or antibiotics can be used. Some bacteria do not have distinguishing morphological features, so there are different kinds of test that can be performed to distinguish the differences of bacteria. The types of identification methods used to identify bacteria are cell wall composition, differential staining, biochemical testing, and morphology. Some other tests that are used to identify bacteria are serological testing, flow cytometry, DNA fingerprinting, Ribosomal RNA sequencing, and phage typing.
Determining the chemical composition of the cell wall is an important aspect in identifying unknown bacteria, but it corresponds with differential staining. In differential staining the one type of stain that is very useful is the gram stain. Gram stains are done in order to distinguish bacteria based on the composition of cell wall they have. They are two types of gram stains the gram-positive and gram-negative. The gram-positive bacteria cell walls mainly consist of many layers of peptidoglycan, which forms a thick rigid structure. Cell walls of gram-positive bacteria contain teichoic acids, which primarily consist of an alcohol and phosphate. The teichoic acids provide much of the cell wall's antigenic specificity making it possible to identify bacteria by certain laboratory tests. The gram-negative bacteria consist of one or a very few layers of peptidoglycan and an outer membrane. The outer membrane consists of lipopolysaccharides, lipoproteins, and phospholipids. The polysaccharide portion is composed of sugars that function as antigens and are useful in distinguishing species of gram- negative bacteria. Based upon the characteristics, microbiologists perform gram stains to characterize bacteria in one of the groups.
Morphology is useful in identifying bacteria because it tells the shape and arrangement of the bacteria. You can also determine if your organism possesses flagella or endospores. Biochemical testing provides insight into a species niche in the ecosystem. Enzymatic activities are used to differentiate bacteria. Biochemical test are used to find out the oxygen requirements for your bacteria, which are also very helpful in identifying bacteria.
Serological testing differentiates among microbial species and strains within species. This test also screens bacterial isolates for possible similarities. This test detects serum antibodies or antibody-like substances that appear specifically in association with certain diseases and bacteria. Flow cytometry is used to identify bacteria in a sample without culturing the bacteria. The simplest method detects the presence of bacteria by detecting the difference in electrical conductivity between cell and surrounding medium. DNA fingerprinting is used to determine the source of hospital-acquired infections. The restriction enzymes enable researchers to compare the base sequences of different organisms. The number and sizes of restriction enzymes provide information about their genetic similarities and differences. Ribosomal RNA sequencing determines the diversity of organisms and their phylogenetic relationships. All cell contain ribosomes. Related organisms will have fewer different bases in their rRNA than organisms that are distantly related. The RNA genes have undergone few changes over time. The phage-typing test determines which types of phages a bacterium is susceptible to. The phages are able to infect and lyse the bacterial cells. This aids in the prediction of the source of infection.
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