Medical Bacteriology - Bacterial Morphology

Medical Bacteriology

1. Welcome to bacterial world

2. Bacterial Morphology

3. Bacteria : Bacteria is a type of biological cell which is UNICELLUR and prokaryotic. They lack membrane – bound nucleus. Bacteria’s are microscopic and display a wide range of size, shapes and arrangements.

4. Morphology : The term Morphology comes from ‘ Greek ’ word. Morpho means – ‘shape or form’. Logy means – ‘study of something ‘. The morphology of bacteria describes the external appearance of bacterial cells including size , shape and arrangement .

5. Bacterial size : The unit of measurement used for bacteria is micron ( micrometre ). The average size of bacteria ranges from 0.5 to 5mm. In 1998 Australian scientist discovered even smaller microbes from oil drilling site (20 – 150) almost equal to the size of smallest Mycoplasma . They have been nicknamed as “ Nanobacteria ” or nanobes . The size of common bacteria like E . coli ranges in from 1.1 to 1.5mm in diameter. Epulopiscium fishelsoni is the one of the largest bacteria (0.75mm). The second biggest bacteria is ‘ Thiomargarita namibiensis ’ (0.75mm). Smallest bacteria are members of genes Mycoplasma (0.3mm).

6. Bacterial shapes : Most of the bacteria have a rigid cell wall that provides a definite shape to the bacteria while protecting the internal components. Bacteria exit in many shapes. The three basic shapes of bacteria are as follows, Cocci – eg : Staphylococcus , Streptococcus Bacilli – eg : E.coli , Clostridium Spiral or Helical – eg : Vibrio cholerae , Treponema pallidum

7. Cocci shape : These are round or spherical shaped bacteria. They may exist in singly or in pairs (diplococci) or in clusters It is assumed that coccoid forms were derived from rod – shaped organisms through evolutionary time .

8. Bacilli shape : These are rod - shaped cells that also look like a cocci, remain either single or attached to other cells. Bacillus are among the first bacteria to have arisen in rod shaped.

9. Spiral shape : This group includes bacteria that are either helical – shaped or curved (comma – shaped). Spiral bacteria are of three types, Which has only a singlet turn – eg : Vibrio cholerae , Spirilla . Rigid spirals with more than one turns – eg : Treponema pallidum . Filamentous helically coiled flexible forms – eg : Spirochaete .

10. Arrangements : The bacteria’s are arranged in various shapes due to cell division. Cocci arrangements : Coccus : This includes bacteria’s that are present as a single cell. Diplococci : This word denotes that after binary fission cells do not separate and always occur in pairs. Diplococcus means a pair of spherical cells. Eg : Neisseria , Diplococcus . Tetrads : When four cocci are arranged in two layers of four cells each, the clusters is termed as tetrads. Eg : Micrococcus , Aerococcus , Tetragenococcus .

11. Cocci arrangements : Sarcina : These are packets of eight coccoid cells arranged in the form of a cube. This happens when the cells divide in a perpendicular plane. Eg : Sarcina luteus . Staphylo : In this type of arrangement, cells occur in irregular, randomly arranged bunches just like a bunch of grapes. Eg : Staphylococcus aureus , Staphylococcus epidermidis . Strepto : Here the bacteria are arranged in long chains. Eg : Streptococcus pyogenes , Streptococcus pneumonia

12. Cocci arrangements :

13. Bacilli arrangements : Bacillus : Bacilli are the bacteria which are rod – shaped and are present as single cell. These are endospore former & facultative anaerobes. Eg : Bacillus cereus Diplobacilli : These are exists in pairs. After cell division the two cells do not divide and grow in an attached arrangement. Eg : Moraxella bovis . Streptobacilli : In this group bacteria are arranged in chains due to cell division. Eg : Streptobacilli felis .

14. Bacilli arrangements : Coccobacilli : It resemble both cocci as well as bacilli. Shorter in size & stumpy appearance. Eg : Haemoplilus influenza . Pallisades : These resemble a picket fence structure due to cell division. It’s appearance similar to Chinese letters. Eg : Corynebacterium diphtheria .

15. Bacilli arrangements :

16. Spiral arrangements : Vibrio : These are the slightly curved bacteria resembling a comma shape. Eg : Vibrio cholerae , Vibrio mytili . Spirochetes : These are spiral bacteria having a helical shape. These are flexible and have an axial filament which helps in motility. Eg : Treponema pallidum , Leptospira sp ., Spirilla : These are helical shaped/ corkScrew form. They are more rigid and similar to spirochetes.They have flagellum. Eg : Campylobacter jejuni .

17. Spiral arrangements :

18. Other shapes & arrangements: Appendaged bacteria Box/rectangular bacteria

19. Other shapes & arrangements : Club – shaped bacteria Filamentous bacteria

20. Other shapes & arrangements : Triangular bacteria Pleomorphic bacteria

21. Other shapes & arrangements : Stalked bacteria Star – shaped bacteria

22. Reference Textbook of microbiology, Author – Kanika sharma , ( Ane’s student edition) HttPs://microbenotes.com