structure & classification of microbes

chapter 2 of fy bsc nursing

1. Structure & C lassification of M icrobes - Khyati Chaudhari

2. MICROORGANISM……? Micro means small , very small, can’t see by naked eyes. Which can be seen by using electron microscope..

3. Classification of Microorganism All living organisms are classified into the five kingdoms of life : Monera Protista F ungi P lantae Animalia

4. Kingdom Monera Monera is non-nucleated unicellular organisms. They are prokaryotes. They have a cell wall. They have no membrane-bound organelles such as mitochondria, Golgi complex. They lack a true nucleus. Instead, they have nucleoid, genetic material without a nuclear membrane. Examples include Bacteria, cyanophyceae (Blue-Green algae), Nitrogen-fixing organisms etc.

5. Kingdom Monera Some examples include: Helicobacter pylori. E. coli. Hay bacillus. Salmonella. Staphylococcus aureus.

6. Kingdom Protista Protista are simple eukaryotic organisms that are neither animals, plants nor fungi . Protista are unicellular in nature, or they can be found as a colony of cells. Most Protista live in water, damp terrestrial environments, or even as parasites . The term ‘Protista’ is derived from the Greek word “protistos”, meaning “ the very first “.  The cell of these organisms contain a nucleus which is bound to the organelles. Some of them even possess structures that aid locomotion like  flagella  or cilia.

7. Kingdom Protista Examples of protists  include algae, amoebas, euglena, plasmodium, and slime molds. 

8. Kingdom Monera

9. Kingdom Fungi A fungus is any member of the group of eukaryotic organisms that includes microorganisms such as  yeasts  and  molds , as well as the more familiar  mushrooms . These organisms are classified as a kingdom, fungi. Fungi are  eukaryotic , non-vascular, non-motile and heterotrophic organisms. They may be unicellular or filamentous. They reproduce by means of spores. Fungi exhibit the phenomenon of alternation of generation.

10. Kingdom Fungi

11. Kingdom Plantae Plants :  Kingdom Plantae . Kingdom Plantae  includes all the plants on the earth . They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae . They are multicellular, eukaryotes and consist of a rigid structure that surrounds the cell membrane called the cell wall . Plants also have a green colored pigment called chlorophyll that is quite important for photosynthesis.

12. Kingdom Plantae

13. Kingdom Animalia All animals are members of the  Kingdom Animalia , also called Metazoa. This   Kingdom  does not contain prokaryotes.  There are over 9 million  species  of  animals  found on Earth. They range from tiny organisms made up of only a few cells, to the polar bear and the giant blue whale . All of the organisms in this  kingdom  are multicellular and heterotrophs - that means they rely on other organisms for food.

14. Kingdom Animalia

15. Classification of Microbes Microorganisms are a varied group of several distinct classes of living beings classified under the Kingdom Protista. Based on differences in cellular organization & biochemistry, Protista has been divided into two groups : Prokaryotes & Eukaryotes.

16. Cont.… Bacteria & blue-green algae are prokaryotes & while fungi, slime molds & protozoa are eukaryotes.

17. Character Prokaryotes Eukaryotes Nucleus Nuclear membrane Absent Present Nucleolus Absent Present Chromosome Circular (1) Linear (>1) Cytoplasm Mitochondria Absent Present Lysosomes Absent Present Golgi apparatus Absent Present Endoplasmic reticulum Absent Present Chemical composition Sterols Absent Present Muramic acid Present Absent Some differences between prokaryotes & eukaryotes

18. Prokaryotic cell

19. Size of bacteria The unit of measurement used in bacteriology is the micron (micrometer, µm). The limit of resolution with the unaided eye is about 200 microns. Bacteria, being much smaller, can be visualized only under magnification. Bacteria of medical importance generally measure 0.2-1.5 µm in diameter & about 3-3 µm in length.

20. Morphology is a branch of biology that deals with the form of living organisms & with relationships between their structures. Particular form, shape or structure. Morphological types of bacteria

21. Morphological types of bacteria Bacteria are classified according to their shape. Cocci – from kokkos meaning berry. They are spherical or oval cells.

22. Morphological types of bacteria Bacilli -From baculus meaning rod. -They are rod shaped cells .

23. Morphological types of bacteria Vibrio - They are comma-shaped curve rods & derive their name from their characteristic vibratory motility.

24. Morphological types of bacteria Spirilla - They are rigid spiral forms.

25. Morphological types of bacteria Spirochetes - word came from speira means coil & chaite means hair. -they are flexuous spiral forms.

26. Morphological types of bacteria Actinomycetes - This word came from Actis means ray & Mykes means fungus. - They are branching filamentous bacteria, so called because of their resemblance to the radiating rays of the sun, when seen in tissue lesions.

27. Morphological types of bacteria Mycoplasma - are bacteria that do not have a cell wall & hence do not possesses a fixed shape. They occur as round or oval bodies & as interlacing filaments. - Mycoplasma are bacteria that have no cell wall and therefore have no definite shape.

28. Arrangement of cocci Bacteria sometimes show characteristics cellular arrangement or grouping . Thus, cocci may be arranged in pairs, chains, group of four, group of eight, or grape like clusters.

29. Arrangement of cocci In pair- d=Diplococci In chain- Streptococci

30. Arrangement of cocci Group of 4- Tetrads Group of 8- Sarcina

31. Arrangement of cocci In grape like clusters- staphylococci

32. Arrangement of bacteria Some bacilli are arranged at angles to each other, presenting a Chinese latter pattern. They called corny bacterium.

33. Bacterial cell structure & functions

34. Cell wall It is outer covering of most cells that protects the bacterial cell and gives it shape. Bacterial cell walls are made of  peptidoglycan ( polysaccharides +n protein)   AKA murein. Mycoplasma are bacteria that have no cell wall and therefore have no definite shape . The rigid structure of peptidoglycan gives the bacterial cell shape, surrounds the plasma membrane and provides prokaryotes with protection from the environment.

35. Cell wall Going further out, the bacterial world divides into two major classes: Gram-positive and Gram-negative . Amount and location of peptidoglycan in the cell wall determines whether a bacterium is G+ve or G-ve.

36. Gram-positive G+ve bacteria have a simpler chemical nature. G+ve bacteria possess thick cell wall containing many layers of peptidoglycan and teichoic acids . In G+ ve cells, peptidoglycan is the outermost structure and makes up as much as 90% of the thick compact cell wall . The cell wall caries bacterial antigens that are important in their ability to cause disease & protect against disease.

37. Gram-negative G- ve bacteria have relatively thin cell wall consisting of few layers of peptidoglycan surrounded by a second lipid membrane containing lipopolysaccharides and lipoproteins The LPS present on the cell walls of G-ve bacteria account for their endotoxic activity & O antigen specificity. Peptidoglycan makes up only 5 – 20% of the cell wall and is not the outermost layer, but lies between the plasma membrane and an outer membrane. The endotoxins are responsible for inducing fever, tissue necrosis &death.

38. Gram-negative The outermost layer of the G- ve bacterial cell wall is called the outer membrane . It is s imilar to the plasma membrane, but is less permeable . It contains various proteins called outer membrane proteins (OMP) .

39. Cell wall characteristics Gram-positive Gram-negative Thickness Thicker Thinner Variety of amino acids Few Several Aromatic & Sulphur containing amino acids Absent Present Lipids Absent or scanty Present Teichoic acid present Absent

40. Cell wall Antibiotics such as penicillin inhibit the formation of peptidoglycan cross-links in the bacterial cell wall. The enzyme lysozyme , found in human tears, also digests the cell wall of bacteria and is the body's main defense against eye infections.

41. Cytoplasmic membrane The cytoplasmic membrane or plasma membrane is a thin layer lining the inner surface of the cell wall. Which separating it from the cytoplasm. It works as semipermeable membrane by regulating the flow of substances in and out of the cell . It c onsists of both lipids and proteins . It p rotects the cell from its surroundings .

42. Periplasmic space Gram- nagative bacteria : -space between the cytoplasmic membrane and the cell wall and space found between cell wall and the outer membrane. Gram-positive bacteria : - space between the cytoplasmic membrane and the cell wall . The periplasm is filled with water and proteins.

43. Periplasmic cell However periplasm contains proteins and other molecules distinct from those in the cytoplasm because the membrane prevents the free exchange between these two compartments . Periplasmic proteins have various functions in cellular processes including: transport, degradation and motility . Periplasm controls molecular traffic entering and leaving the cell .

44. Cytoplasm Cytoplasm is p ortion of the cell that lies within the plasma membrane. substances within the plasma membrane, excluding the genetic material . It is gel-like matrix composed of mostly water(4/5 th ), enzymes , nutrients, wastes, and gases. It c ontains cell structures - ribosomes, chromosome and plasmids , as well as the components necessary for bacterial metabolism . It carries out very important functions for the cell - growth , metabolism, and replication .

45. Constituents of cytoplasm are… Proteins including enzymes Vitamins Ions Nucleic acids and their precursors Amino acids and their precursors Sugars , carbohydrates and their derivatives Fatty acids and their derivatives

46. Ribosomes- protein synthesis machinery It consists of RNA and protein. S maller than the ribosomes in eukaryotic cells-but have a similar function. They are centers of protein synthesis.

47. Mesosomes Mesosomes are seen as vesicular folds within the plasma membrane, protruding into the cytoplasm. They are more prominent in Gram-positive bacteria. They are the principal sites of the respiratory enzymes in bacteria & are like the mitochondria of eukaryotes in function.

48. Mesosomes Mesosomes also coordinate nuclear & cytoplasmic division during binary fission due to their position near the nuclear body.

49. Intracytoplasmic inclusions Inclusion bodies: Bacteria can have within their cytoplasm a variety of small bodies collectively referred to as inclusion bodies. Some are called granules and other are called vesicles . Inclusions are considered to be nonliving components of the cell that do not possess metabolic activity and are not bounded by membranes . The most common inclusions are volutin, glycogen, lipid droplets, crystals and pigments .

50. Intracytoplasmic inclusions Volutin granules need special staining techniques such as Albert’s or Ponder’s stain to demonstrate the granules more clearly . Volutin granules are characteristically present in corynebacterium diphtheria & are believed to store energy for cell metabolism. Polysaccharides granules & lipid granules are storage product. Vacuoles are fluid containing cavities separated from the cytoplasm by a membrane. Their function & significance are uncertain.

51. Nucleus Bacterial nuclei may be seen by electron microscopy. They appear as oval or elongated bodies, generally one per cell. The bacterial chromosome is haploid & replicates by simple binary fission instead of mitosis as in other cells.

52. N ucleus Bacteria may possess extra-nuclear genetic elements consisting of DNA, called plasmids, which carry genetic information. They can be transmitted to daughter cells during binary fission & also transferred from one bacterium to another, either through conjugation or by bacteriophages. They confer properties such as toxigenicity & drug resistance on the cell.

53. Slime layer & capsule Many bacteria secrete a sticky material around the cell surface. When this is organized into a sharply defined structure, as in streptococcus pneumonia, it is known as the capsule . Capsules may be polysaccharide or polypeptide. Large capsules may be readily demonstrated by negative staining with India ink, when they are seen as clear halos around organism, against a black background.

54. Slime layer & capsule Capsules protect bacteria from lytic enzymes found in nature & also contribute to the virulence of pathogenic bacteria by inhibiting phagocytosis.

55. Flagella Made up of protein subunits called flagellin. Each flagellum is attached to cell membrane with the help of proteins other than flagellin . Flagella are the organ of the locomotion. The basal region has a hook like structure and a complex basal body. The basal body consists of a central rod or shaft surrounded by a set of rings.

56. Flagellar Arrangement Bacterial species differ in the number and arrangement of flagella on their surface. Bacteria may have one, a few, or many flagella in different positions on the cell .

57. Flagellar Arrangement Atrichous – no flagella Monotrichous - single flagellum A mphitrichous a flagellum at each end Lophotrichous - clusters of flagella at the poles of the cell Peritrichous - flagella distributed over the entire surface of the cell .

58. Fimbriae Hollow , hair like structures made of protein is called fimbrie or pili. They are shorter & thinner than flagella (about 0.5 µm long & less than 10 nm thick) & project from the cell surface as straight filaments. They arise from the cell membrane.

59. Fimbriae Fimbriae can be seen only under the electron microscope. They function as organs of attachment, helping the cell adhere firmly to particles of various kinds.

60. Spores Some bacteria, particularly members of the genera Bacillus & Clostridium have the ability to from highly resistant resting stages called spores.

61. Spores Sporulation (formation of spores) helps bacterial survival for long periods under unfavorable conditions. Each bacterium forms one spore, which on germination forms a method of reproduction. As bacterial spores are formed inside the parent cell, they are called endospores.

62. Spore The fully developed spore has at its core the nuclear body, surrounded by the spore wall. Outside this spore cortex, which is enclosed by multi layered tough spore coat. Some spore have an additional outer covering called exosporium, which may have distinctive ridges & grooves. E.g. B. anthracis.

63. Shape & position

64. Resistance They are extremely resistant to drying & relatively resistant to chemicals & heat. Though some spores may resist boiling for prolonged periods, spores of all medically important species are destroyed by autoclaving at 120 ° C for 15 minutes. Methods of sterilization & disinfection should ensure that spores are destroyed in addition to vegetative cells. Spores germinate in optimal conditions.

65. Resistance The spore wall is shed & the germ cell appears by rupturing the spore coat & elongates to form the vegetative bacterium.

66. Pleomorphism Pleomorphism  is the ability of some microorganisms to alter their morphology( shape & size), biological functions or reproductive modes in response to environmental conditions.