Microbiology #1 | What are BACTERIA ? Harmful or Helpful ?
Before jumping straightly into the topic, (i.e. Bacteria), I really want to know about the basics. So, let's start with a brief history about the "Living things". Earlier in ancient times, living things were roughly classified into Plants and Animals . But, after the revolutionary invention of microscope, in 1866, Ernst Haeckel, a biologist, proposed a third kingdom of living things and named it as "Protista". This kingdom included those organisms which were neither plants nor animals. Later, after the development of electron microscope, in 1938, Herbert F. Copeland modified the kingdom Protista and proposed a four-kingdom classification system, with the new one named as "Monera". This included all the prokaryotic (meaning: without true nucleus) organisms like BACTERIA and Blue green algae. Finally, after about three decades, in 1969, a scientist named Robert Whittaker proposed an additional kingdom named "Fungi" resulting into the widely recognised, "Five-kingdom classification system" !
*So what actually are BACTERIA??
- Speaking in the simplest way, BACTERIA are prokaryotic microorganisms that do not contain chlorophyll. They are unicellular (one celled) and do not show true branching, except the so called 'Higher bacteria' (actinomycetes).
*Can we see them??
- Of course, we do can see them. But it is not possible with our naked eyes. We need to stain bacteria first and see under the microscope.
*What microscopes are used for observing them??
The microscopes used are:
- Optical microscope
- Phase contrast microscope
- Dark field microscope
- Electron microscope
*What is staining??
- It is the process by which microorganisms are made visible under the microscope, esp. by adding colours to them. Some common stains include: Gram stain, Giemsa stain, ZN stain, negative stain with India ink
*How do they look like??
- Their description is given under the following heading:
Size: They are not visible to naked eye. Their size is expressed in micron (10^-6)
Shape: According to shape, they are classified into bacilli(rod shaped), cocci(round shaped), vibrios(comma shaped), spirilla, spirochete (spiral shaped) and mycoplasma (without definite shape)
-Bacteria usually show characteristic cellular arrangement or grouping:
COCCI in:
- pairs > diplococci
- chain > streptococci
- cluster > staphycocci etc.
The type of cellular arrangement is determined by the plane through which binary fission takes place and by the tendency of the daughter cells to remain attached even after division
*What are the parts of bacteria??
- They consist of the following parts:
1) Outer membrane:
(Cell wall)
- It gives shape, rigidity and ductility to bacteria. It cannot be seen by direct microscopy. It is only demonstrated by a process called Plasmolysis. Cell wall carries bacterial antigen that are important in virulence and immunity.
2) Cytoplasm:
- No mitochondria and Endoplasmic Reticulum are present.
It contains:
a) Ribosomes: They are centres of protein synthesis.
b) Mesosomes: These are vesicular, convulated or multilaminated structure formed by invagination of the plasma membrane into cytoplasm. Mesosomes are analogous to mitochondria of eukaryotes.
c) Intracytoplasm inclusions:
May be of various types :
- Volutin granules: characteristically present in Diphtheria bacilli. perhaps they serve as a reserve of energy and phosphate
- Polysaccharides granules
- Vacuoles: fluid containing cavities separated from cytoplasm by a membrane
3) Nucleus:
- It is seen only by electron microscope. No nuclear membrane or nucleolus is present. Haploid no. of chromosome are present.Nucleus may possess extranuclear genetic elements consisting of DNA called Plasmids or Episomes. These are not required for survival. may confer certain properties like toxigenicity and drug resistance which may constitute a survival advantage.
4) Slime layer and capsule:
- Many bacteria secrete a viscid material around the cell surface. When this is organised into a sharply defined structure, it is called Capsule which is seen by negative staining with India ink.
E.g: Pneumococcus
- It acts as a protective barrier and also contributes to virulence by inhibiting phagocytosis
5) Flagella:
- They are the organs of locomotion. Presence or absence of flagella and their number and arrangement are characteristic of different genera of bacteria
E.g:
- Monotrichous: Cholera vibrio
- Amphitrichous: Alkaligenes faecalis
- Lophotrichous: Spirilla
- Peritrichous: Typhoid bacilli
Flagella can be seen by special staining in which thickness is increased by mordanting, or by electron microscopy
6) Fimbriae:
- They are the organs of adhesion. They are shorter and thinner than flagella. They also help in conjugation.
*Gram positive bacteria v/s Gram negative bacteria
- A list of them is shown in the chart below :
*Are bacteria harmful ??
- Yessss....of course...Here's a list of 25 common diseases caused by bacteria.
Disease Pathogen
1. Cellulitis - Group A Streptococcus and Staphylococcus
2. Anthrax - Bacillus anthracis
3. Botulism (and Infant botulism) - Clostridium botulinum
4. Cat-scratch disease - Bartonella henselae
5. Chancroid - Haemophilus ducreyi
6. Chlamydiasis - Chlamydia trachomatis
7. Cholera - Vibrio cholerae
8. Clostridium perfringens infection (Food poisoning) - Clostridium perfringens
9. Diphtheria - Corynebacterium diphtheriae (Gram +ve non-capsulated)
10. Epidemic typhus - Rickettsia prowazekii (louse-borne bacteria)
11. Gonorrhea - Neisseria gonorrhoeae
12. Leprosy (Hansen's disease) - Mycobacterium leprae
13. Leptospirosis - Leptospira genus
14. Lyme disease - Borrelia burgdorferi and other Borrelia species
15. Meningitis (Bacterial) - Streptococcus pneumoniae (pneumococcus), Neisseria meningitidis (Meningococcal disease), Haemophilus influenzae, Listeria monocytogenes
16. Pertussis (Whooping cough) - Bordetella pertussis
17. Plague - Yersinia pestis
18. Pneumonia - Diplococcus pneumoniae
19. Scarlet fever - Streptococcus pyogenes
20. Shigellosis (Bacillary dysentery) - Shigella genus
21. Syphilis - Treponema pallidum
22. Tetanus (Lockjaw) - Clostridium tetani (Gram +ve)
23. Trachoma - Chlamydia trachomatis
24. Tuberculosis - Mycobacterium tuberculosis
25. Typhoid fever - Salmonella typhi
*Are bacteria helpful too???
- And the answer is again a YESSS !!!...Did you know that there are certain bacteria which reside in different parts of our body and help in immunity. Such bacteria are known as Normal Flora. These Normal Flora do not allow growth of other foreign organisms in our body, and neither they do any harm to us unless they are transferred from their original site to another site.
A list of them is shown in the chart below:
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