Tag: #microbe

ANTI-CELL WALL ANTIBACTERIAL DRUGS

Selective toxicity is the important characteristic of antimicrobial drugs which means that any drug is selective against a particular microorganism and also selectively act on a particular site. Not all drugs can act on every site. There are many sites at which any drug acts such as cell wall, cell membrane of the bacterial cell. Basically selective toxicity explains that any drug will only act on the pathogen and not on the host.
ANTI-CELL WALL DRUGS
Anti-cell drugs are those drugs which act on the cell wall of the bacterial pathogen and not the host. There are variety of drugs which fall under this category. The major class is of beta-lactam antibiotics among which penicillin is the drug which is studied the most. The drugs can be administered into the patient’s body by different ways like intramuscular, intravenous, or can be applied as topical preparations. But mostly, these drugs are intramuscular or intravenous drugs. The following points explain the further different mechanisms of anti-cell wall drugs.
There are 3 different mechanisms by which anti-cell wall drugs work and thus they are also classified as following:

  1. First classification involves the drugs that directly interact with Penicillin-Binding-Proteins (PBPs) and inhibit the transpeptidase activity which in turn inhibits the attachment of newly formed peptidoglycan subunit to the pre-existing one.
    This is the main mechanism of β-lactam antibiotics. These antibiotics include Penicillin (penams), cephalosporins, Penems, Carbapenems, and monobactams.
    These antibiotics bind to the penicillin-binding proteins which are enzymes present in the bacterial cell wall. Different β-lactam antibiotics bind in a different way. After the antibiotics bind to the enzyme, it changes the morphological response of the bacteria to the antibiotic.
  2. Second classification involves the drugs that bind to the peptidoglycan subunit, blocking different processes.
    The important class of compounds called as glycopeptides are mainly involved in this mechanism of anti-cell wall antibiotics.
    Vancomycin and Teicoplanin are the major examples of glycopeptide antibiotics.
    Vancomycin kills only gram-poitive bacteria whereas Teicoplanin is active against both. The overall mode of action of glycopeptides antibiotics is blocking transpeptidation i.e. similar to β-lactam antibiotics, they also inhibit the transpeptidase activity, and transglycosylation i.e. they being large in size attach to the peptidoglycan subunits thus creating a blockage which does not allow the cell wall subunits to attach to the growing peptidoglycan backbone.
  3. Third classification involves the drugs that block the transport of peptidoglycan subunits across cytoplasmic membrane.
    The main example of such type of drugs is bacitracin, which is a simple peptide antibiotic originally isolated from Bacillus subtilis.
    The mode of action of these class of drugs is blocking the activity of specific cell membrane lipid carriers which act as the attachment surface for peptidoglycan precursors and help in their movement from cell cytoplasm to exterior of the cell. This activity of lipid carriers is inhibited by bacitracin like drugs and they finally prevent the incoroporation of those precursors into cell wall thus inhibiting its biosynthesis.

Although, its route of administration is mostly oral or intramuscular, bacitracin is also known to show its effects when used as topical ointments like Neosporin.

GRAM STAINING

Bacteria can be classified into two different categories i.e. gram-positive bacteria and gram-negative bacteria. To differentiate the type of bacteria present in any collected sample there is a technique known as GRAM STAINING OR GRAM STAIN. It is sometimes also known as gram’s method. This technique is a different step process which can easily distinguish and classify between different types of bacteria. This was named after the great scientist Hans Christian Gram.
Gram Staining method differentiates bacteria on the basis of their physical and chemical structure of cell wall. They are stained with different reagents and are observed in different colors when seen under the microscope. It is due to the fact that gram positive bacteria have a thick layer of peptidoglycan which allows it to retain the primary stain which is crystal violet and thus they appear purple whereas on the other hand, gram-positive bacteria have thin peptidoglycan cell wall and thus only retain the secondary or counter stain which is Safranin and thus they appear slightly pinkish when observed under microscope. Gram staining is the basic technique which is widely used in the microbiology labs to distinguish between both the types of bacteria. It provides a great help to microbiologists to perform their clinical tasks. If any infection is suspected in the patient then after the collection of sample, the gram staining is done and the type of bacteria is observed.
Gram staining is completed in the various steps –

  1. Fixation of clinical materials i.e. the sample collected are being fixed on the glass slide by first making a smear using water and then that smear is either heat fixed or methanol fixed. It is a first and a very important step. Methanol fixation was later discovered keeping in mind its advantage of not destroying the morphology of host cell, as well as bacteria present in that. It is majorly used for the testing of blood samples collected from patients.
  2. Application of primary stain i.e. crystal violet. Primary stain means the first stain which is applied onto the fixed smear which stains all the calls purple or blue.
  3. To distinguish the slide is then washed off in a gentle and indirect stream of water for 2 seconds which removes the extra stain that is not absorbed by the cells.
  4. The next step involves the application of a mordant i.e. Iodine solution. This forms a complex with crystal violet due to which all the cells start appearing blue.
  5. Again the slide is washed for 2 seconds to remove extra stain.
  6. Addition of a decolorizing agent is the next step which will ultimately remove the excess stain which bacteria has not absorbed. The decolorizer contains the combination of acetone and alcohol. In this step, the gram positive bacteria continue appearing violet or blue in color whereas gram negative bacteria start appearing colorless.
  7. Application of counter stain or secondary stain i.e. safranin is the next step. It should let remain on the slide for 30 second to 1 minute. This will stain all the colorless gram negative bacteria pink and gram positive bacteria remains blue in color.
  8. Again the slide is washed off in a gentle stream of water.
  9. The prepared stained slide is then observed under a microscope using immersion oil (for observing under 100x).

VIRUS AND ITS TRANSMISSION

WHAT IS A VIRUS?????
A virus is referred as an infectious agent that can only replicate inside the living cells of an organism i.e. a virus is something which can not at all grow or replicate by its own. It always needs a living cell for its replication process. It is a microorganism which cannot be seen by naked eyes and can infect any life form. It can be infectious for humans, plants and even for other microorganisms like bacteria and archea. Viruses infecting bacteria are known as bacteriophage. Viruses are not restricted to a place and they can be found everywhere at every place of ecosystem whether land, or water or in air. They can cause various infections including air-borne, water-borne or even food-borne. The science dealing with the study of viruses is known as Virology and it is a branch of microbiology. A complete virus particle ranges in size from about 10-400nm in its diameter.
Viruses are near to dead when outside the living cell but once entered any living cell of an organism, they are forced to replicate using the life machinery of that particular organism and thus they produce thousands of their multiple copies and in this way infect the organism. Outside the living cells they are present in the free, independent form which may also be known as a virion.
There are 3 main parts in the structure of a virus i.e. –

  1. Genetic core which is also known as nucleic acid core containing all the genetic material whether DNA or RNA, but not both. It is known as genome.
  2. A protein coat, which is also known as capsid which surrounds the genome of a virus particle.
  3. An envelope which is made of lipid. It is an external coat surrounding the genome as well as capsid.

VIRUS TRANSMISSION
Transmission of virus particles is important for them to survive because as discussed above they can only replicate themselves inside a host living organism. The virus transmits from one organism to another in order to survive, reproduce and continue their species. The effectiveness of the transmission of viral particle depends on 2 main factors i.e. the concentration of virus and its route of transmission. More concentration of virus leads to more transmission.
There are several ways by which a virus particle may get transmitted from one organism to another.

  1. Blood – Virus particles can get transmitted through the blood. The one way is direct viral infection in blood and the other way is by arthropods like dengue or malaria is transmitted. Arthropods bite one organism and collect viral particles from them and then when they bite other organism, the same viral particles are being transmitted to the next organism and this way transmission and infection occurs. Another way is direct viral infection in blood which can be via direct infected blood exposure to a healthy individual. It may be transmitted via sexual contacts with infected person like HIV is transmitted.
  2. Saliva – It is the most commonly seen in kissing the infected individual. The saliva contains the viral particles and thus they are transmitted to healthy individual.
  3. Respiratory secretions – If any infected individual sneezes, or coughs or in any other way its respiratory secretions come in contact with the healthy individual, he may get infected by the same. It may also occur by singing or even breathing.
  4. Feces – This is not a very common method in developed countries but can infect those who do not take sanitary actions after using toilets. The virus particles secreted in feces can infect other healthy individuals if they come in contact with them.