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  1. marrium shahbaz
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    2019-09-24T12:10:48+00:00
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    Antibiotics:

    Antibiotics are the chemical substances that are synthesized by bacteria or chemically synthesized in labs to kill or stop the bacterial growth.

    Bacterial growth phases:

    Bacteria growth is divided into four phases. The logarithm analysis is done by growing the bacteria into the broth culture. That analysis showed that bacterial growth occurs in four phases.

    1. Lag phase
    2. Log phase
    3. Stationary phase
    4. Decline phase

    Lag phase:

    It is the growth phase in which the bacteria prepare itself for growth. During this phase, bacteria

    • Grow in size
    • Don’t undergo binary fission
    • Prepare its cells for enzymes
    • Prepare ribosomes and cellular component for the cell division.
    • Growth is restricted.

    Log phase:

    It is the growth phase in which the bacteria starts growing exponentially. During this phase, bacteria

    • Increase its cell number
    • Undergo binary fission
    • Utilize all the enzymes for division that are synthesized in lag phase
    • Prepare the proteins for cell
    • Growth is not restricted
    • Cell size is small and uniform
    • Represent as generation time of bacteria

    Stationary phase:

    It is the phase in which the bacteria death also occur. During this phase,

    • No net increase or decrease in cell number
    • The number of division is equal to the number of cell death
    • Available of limited nutrient
    • Lack of space in the culture
    • Preparation of secondary metabolites
    • Due to storage of granules, variable staining is done.

    Death phase:

    It is the phase in which the bacteria death occur. During this phase,

    • Increase in number of bacterial death
    • Unavailability of nutrients for growth
    • Increase in secondary metabolites

    How does antibiotic works?

    Bacteria growth occurs in 4 phases as described above. During log phase, antibiotics enter in bacterial cell because

    • Bacteria grow exponentially and increase it cell mass.
    • Cell is small in size.
    • Cell produces its proteins, amino acids and other precursor units.
    • Cell membrane is less permeable at that time, because cell need nutrient from the environment.
    • When nutrients are taken up by cell, antibiotics also move inside the cell.
    • Penicillin when enter, it degrades its cell wall subunit.
    • Bacterial cell become weak and die
    • This phase is medically important as in this phase, bacteria is sensitive to drugs.

    Antibiotics that works on Salmonella:

    As salmonella is gram-negative bacteria, penicillin groups don’t work on it. The effective antibiotics are as follows:

    1. Macrolides:

    Macrolides act on ribosomes 50S subunit and stop the protein synthesis. Cell stops its growth when protein synthesis inhibits and thus cell deaths occur.

    1. Streptogramins

    Streptogramins also act on ribosomes 50S subunit and stop the protein synthesis. Cell stops its growth when protein synthesis inhibits and thus cell deaths occur.

    1. Lincosamids:

    It also acts on ribosomes 50S subunit and stop the protein synthesis. Cell stops its growth when protein synthesis inhibits and thus cell deaths occur.

    1. Tetracycline:

    Tetracycline also stops the protein synthesis but act on 30S ribosomal unit of cells. Cell stops its growth when protein synthesis inhibits and thus cell deaths occur.

    1. Aminoglycosides:

    It also stops the protein synthesis but act on 30S ribosomal unit of cells. Cell stops its growth when protein synthesis inhibits and thus cell deaths occur.

    1. Chloramphenicol:

    Chloramphenicol inhibits the peptidyl-transferase enzymes that are responsible for protein synthesis. Cell stops its growth when protein synthesis inhibits and thus cell deaths occur.

    1. Quinolones:

    Quinolones have different mode of action. These antibiotics target the nucleic acid and stop the DNA gyrases enzymes. This antibiotics inhibits the supercoiling of DNA and kill the cell.

    Resistance:

    But nowadays, bacteria are resistant to antibiotics. There are two types of resistance in bacteria.

    • Natural resistance is the type in which the bacteria are naturally resistant to the antibiotics. It is non-transferable to the other bacteria. For example; gram negative bacteria have small peptidoglycan content, so penicillin doesn’t work on them.
    • Acquired resistance is the type in which bacteria acquired or adapted resistant from the environment. When antibiotics are used for long term, the bacteria become resistant to them. This resistant is transferable to other bacteria and most of the bacteria acquired resistant from the misuse of antibiotics.

    Resistance mechanism:

    There are three commonly resistant mechanisms that are adapted by gram positive bacteria for the survival.

    1. Production of Inhibitory enzyme:

    Bacteria synthesize the enzymes that degrade the active compound of antibiotics. Antibiotic activity depends on the active compound that is responsible for the antibiotics mode of action. Its activity stop and bacteria survive in the environment when the active compound broken by enzymes. For example, amino-glycosidase enzymes are synthesized by Salmonella to break the aminoglycosides antibiotics.

    1. Modified target site:

    Antibiotics always work by binding to its target site. Bacteria change its target site for the antibiotics. When the target sites are changed, antibiotics are unable to bind with them. The unbinding of antibiotic with the target site destroys the effect of antibiotic. For example, bacteria change its ribosomal unit so that antibiotics don’t get attach to them and target them.

    1. Efflux pump:

    Bacteria have some modified proteins that pump the antibiotics out from the cell. Bacteria survive and able to grow when antibiotics move out. It is the common mechanism that is used for the resistance against tetracycline.

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