Bacteria.pptx

Bacteria are small single-celled organisms. Bacteria are found almost everywhere on Earth and are vital to the planet's ecosystems. Some species can live under extreme conditions of temperature and pressure. The human body is full of bacteria, and in fact is estimated to contain more bacterial cells than human cells.

1. Presented By: Jagruti Marathe Bacteria

2. All livings things (Single and multicellular) are made of cells that share the same Common Characteristic. Characteristics of cell and life

3. Characteristics of cell and life

4. Characteristics of life #455a64 #cccccc Reproduction and heredity- genome composed of DNA packed in chromosomes , produce offspring sexually Growth and Development Metabolism – Chemical and physical life processes

5. Characteristics of life #455a64 #cccccc Movement and /or irritability – respond to internal/ external stimuli, self-propulsion of organisms Cell support, protection, and storage mechanisms cell walls, vacuoles, granules, and inclusions Transport of nutrients and waste

6. They are as unrelated to human beings as living things can be, but bacteria are essential to human life and life on planet Earth. Although they are notorious for their role in causing human diseases, from tooth decay to the Black Plague, there are beneficial species that are essential to good health. Bacterial cell

7. Bacteria are unicellular, free-living, microorganisms capable of performing all the essential functions of life. They possess both DNA and RNA. Both are Prokaryotic microorganisms that do not contain chlorophyll. They occur in water, soil, air, food, and all-natural environments. They can survive extremes of temperature, PH, Oxygen tension, and atmospheric pressure. Bacterial cell

8. Bacteria are very small microorganisms that are visible only under a microscope. Cocci – 1 μm Bacilli – 1 to 10 μm Vibrio’s –  0.5–0.8 μm in width and 2–3 μm in length. Spirilla – 1.4 to 1.7 μm in diameter and up to 60 μm in length, while Spirochetes – spirochetes are giants, 0.2-0.3 μm in diameter and 20-30 μm in length SIZE OF Bacterial cell Cocci Bacilli Vibrio's Spirilla Spirochetes

9. Actinomycetes – 1–2 μ m diameter Mycoplasma – E longated or filamentous forms (up to 100 μm long and about 0.4 μm thick) SIZE OF Bacterial cell Actinomycetes Mycoplasmas

10. Classification of Bacteria Bacteria can be classified into various categories based on their features and characteristics. The classification of bacteria is mainly based on the following: Shape Composition of the cell wall Mode of respiration Mode of nutrition CLASSIFICATION OF Bacterial CELL-

11. Classification of bacteria based on Shape Type of Classification Examples Bacillus (Rod-shaped) Escherichia coli (E. coli) Spirilla or spirochete (Spiral) Spirillum volutans Coccus (Sphere) Streptococcus pneumoniae Vibrio (Comma-shaped) Vibrio cholerae

12. Classification of bacteria based on composition of cell wall Type of Classification Examples Peptidoglycan cell wall Gram-positive bacteria Lipopolysaccharide cell wall Gram-negative bacteria

13. Classification of bacteria based on mode of respiration Type of Classification Examples Anaerobic Bacteria Actinomyces Aerobic Bacteria Mycobacterium

14. Classification of bacteria based on mode of nutrition Type of Classification Examples Autotrophic Bacteria Cyanobacteria Heterotrophic Bacteria All disease-causing bacteria

15. In bacteria,  the cell wall forms a rigid structure of uniform thickness around the cell and is responsible for the characteristic shape of the cell (rod, coccus, or spiral) . Structure of bacterial cell

16. Bacteria are  single-celled, or simple, organisms that are invisible to the naked eye . Many bacteria are found both inside and outside of organisms, including humans. Bacteria are also found on surfaces and in substances like water, soil, and food, making them key players in the Earth's ecosystems. Structure of bacterial cell

17. Internal Structure In bacteria, the cell wall forms a rigid structure of uniform thickness around the cell and is responsible for the characteristic shape of the cell (rod, coccus, or spiral). Inside the cell wall (or rigid peptidoglycan layer) is the plasma (cytoplasmic) membrane; this is usually closely opposed to the wall layer. Structure of bacterial cell

18. All bacteria, both pathogenic and saprophytic, are unicellular organisms that reproduce by binary fission. Most bacteria are capable of independent metabolic existence and growth, but species of  Chlamydia  and  Rickettsia  are obligately intracellular organisms. Structure of bacterial cell

19. Bacterial cells are extremely small and are most conveniently measured in microns (10 -6  m). They range in size from large cells such as  Bacillus anthracis  (1.0 to 1.3 µm X 3 to 10 µm) to very small cells such as  Pasteurella tularensis   (0.2 X 0.2 to 0.7 µm)   Mycoplasmas  (atypical pneumonia group) are even smaller, measuring 0.1 to 0.2 µm in diameter. Bacteria, therefore, have a surface-to-volume ratio that is very high: about 100,000. Structure of bacterial cell

20. External Structure Structure of bacterial cell

21. Two types of surface appendage can be recognized on certain bacterial species: the flagella, which are organs of locomotion, and pili (Latin hairs), which are also known as fimbriae (Latin fringes). Flagella occur on both Gram-positive and Gram-negative bacteria, and their presence can be useful in identification. Structure of bacterial cell

22. For example, they are found on many species of bacilli but rarely on cocci. In contrast, pili occur almost exclusively on Gram-negative bacteria and are found on only a few Gram-positive organisms (e.g.,  Corynebacterium renale ). Some bacteria have both flagella and pili. e.g.: Escherichia coli. Structure of bacterial cell

23. Bacterial Flagella Bacterial flagella are long, thin (about 20 nm), whip-like appendages that move the bacteria towards nutrients and other attractants. Flagella are free at one end and attached to the cell at the other end.   Flagellum can never be seen directly with the light microscope but only after staining with  special flagella stains that increase their diameter . Flagella can be seen easily with the  electron microscope . Structure of bacterial cell

24. F lagella Structurally, bacterial flagella are long (3 to 12 µm), filamentous surface appendages about 12 to 30 nm in diameter. The protein subunits of a flagellum are assembled to form a cylindrical structure with a hollow core. Structure of bacterial cell

25. A flagellum consists of three parts: T he long filament, which lies external to the cell surface; T he hook structure at the end of the filament; and The basal body, to which the hook is anchored and which imparts motion to the flagellum. The basal body traverses the outer wall and membrane structures. Structure of bacterial cell

26. Basal Body It is attached to the cell membrane and cytoplasmic membrane. It consists of rings surrounded by a pair of proteins called Mot . The rings include: L-ring:  Outer ring anchored in the lipopolysaccharide layer and found in gram +ve bacteria. P-ring:  Anchored in the peptidoglycan layer. C-ring:  Anchored in the cytoplasm M-S ring:  Anchored in the cytoplasmic membrane Structure of bacterial cell

27. Basal Body It is attached to the cell membrane and cytoplasmic membrane. It consists of rings surrounded by a pair of proteins called Mot . The rings include: L-ring:  Outer ring anchored in the lipopolysaccharide layer and found in gram +ve bacteria. P-ring:  Anchored in the peptidoglycan layer. C-ring:  Anchored in the cytoplasm M-S ring:  Anchored in the cytoplasmic membrane Structure of bacterial cell

28. Hook It is a broader area present at the base of the filament. Connects filament to the motor protein in the base. The hook length is greater in  gram +ve bacteria . Filament Thin hair-like structure arising from the hook. Structure of bacterial cell

29. Arrangement and Types Flagella are attached to cells in different places. As the number and location of flagella are distinctive for each genus, they can be used in the classification of bacteria. There are four types of flagellar arrangement. Monotrichous (Mono means one) : Single polar flagellum e.g.  Vibrio cholerae ,  Campylobacter spp .  (polar flagella often in pairs to give a “seagull” appearance). Amphitrichous : Single flagellum at  both ends  e.g.  Alcaligenes faecalis  (note: amphibians live both on land and in water).  Lophotrichous:  Tuft of flagella at one or both ends e.g.  Spirilla  spp Peritrichous (flagella in the periphery) : Flagella surrounding the bacterial cell. All the members of the family  Enterobacteriaceae ,  if motile have peritrichous flagella. e.g.  Salmonella  Typhi ,   Escherichia coli,   Proteus  spp (highly motile organism; shows swarming motility)

30. Functions of Bacterial Flagella Organs of locomotion:  Many   prokaryotes are motile, and the majority of motile prokaryotes move by means of flagella. Role in Pathogenesis:   Escherichia coli  and  Proteus  spp are common causes of urinary tract infections. The flagella of these bacteria help the bacteria by propelling the bacteria from the urethra into the bladder. Roles in Organism identification Some species of bacteria, e.g.  Salmonella  species are identified in the clinical laboratory by the use of specific  antibodies  against flagellar proteins. Organisms such as  Vibrio cholerae  (darting motility) and  Proteus  species (swarming growth in common culture media) are easily identified by their  characteristics motility pattern .

31. Properties Bacterial flagella Archeal flagella Flagellar filament Flagellar filament is made up of a single type of protein Several different flagellin proteins are found. Diameter of Flagella The diameter of bacterial flagella is 15-20 nm depending on the species. Archaeal flagella is roughly half the diameter of bacterial flagella, measuring only 10–13 nm in width. Source of energy for the rotation of flagella Proton motive force ATP

32. Fimbriae and Pili Fimbriae and pili, both are appendages on the cell wall of the bacteria. These thin protein tubes originate from the cytoplasmic membrane of several bacteria, protruding out after it penetrates the peptidoglycan layer of the cell wall. While the fimbriae are bristle-like short fibers occurring on the bacterial surface, Pili are long hair-like tubular microfibers found on the surface of bacteria. Structure of bacterial cell

33. The pili are found in some gram-negative bacteria only, whereas the fimbriae are found in both the gram-negative and gram-positive bacteria. Both fimbriae and pili are capable of sticking to the bacterial surface. Pili are usually longer and less in number compared to the fimbriae. Virtually, they are found in all gram-negative bacteria but not as much in gram-positive bacteria. Structure of bacterial cell

34. Pilli Pili are hair –like microfibrils, 0.5-2 µm in length and 5 to 7 nm in diameter. They are thinner, shorter and more numerous than flagella. They are present only on gram -ve bacteria. It composed of Protein known as pillin and its molecular weight is 18,000 daltons . Structure of bacterial cell

35. Pili or fimbriae are unrelated to motility and are found on motile as well as non-motile cells. Fimbriae and pili, these two terms are used interchangeably but they can be distinguished. Fimbriae can evenly distributed over the entire surface of the cell or they occur at poles of the bacterial cell . (100 to 200) Pili are usually longer than fimbriae and only 1 or 2 per cell. They join the bacterial cell for transfer the genetic material(DNA)- (Bacterial conjugation) from one cell to another cell. Structure of bacterial cell

36. Pili are of two types – the long conjugation pili and the short attachment pili. The F or sex pili (Long conjugation pili) are long and a few in number. This conjugation pilus facilitates conjugation. Genetic recombination is enabled in gram-negative bacteria through the transfer of DNA from the male bacterium to a female bacterium. Structure of bacterial cell

37. A few names are given to different types of pili by their function. The classification does not always overlap with the structural or evolutionary-based types, as  convergent evolution  occurs. Structure of bacterial cell

38. Fimbriae and Pili – Structure Pili and flagella are different in being thinner and shorter, less rigid and straight, and large in number. Their occurrence is either at the poles of a bacterial cell or is evenly distributed over the cell’s enteric surface. The pili have a diameter of close to 250 Å and lengthwise they are 0.2-20 µm. Plasmids genetically govern Pili and vary in number, ranging between 1 and 10. The molecular weight of Fibrillin is close to 16,000 Daltons . The Long conjugation pili are helical tubes having a hollow core. These structures are the cylinder of repeating protein units. The filamentous structure of these is administered by the  plasmid  of the bacterium. The diameter of the Long conjugation pili is 65-135 Å and close to 20 µm lengthwise, which is greater in comparison to fimbriae.

39. Fimbriae and Pili – Function The role of fimbriae and pili is not limited, they are involved in many activities. The Fimbriate bacteria are the bacterium having fimbriae. These fimbriae are adhesive in nature attaching the entity to the substrate that naturally occurs or to any other entity. Additionally, the fimbriae cause agglutination of the blood cells such as leukocytes, epithelial cells, erythrocytes, etc. The fimbriae are armed with antigenic traits as they serve as thermolabile nonspecific agglutinogen. The fimbriae affect the metabolic processes. The cells that contain fimbriae are referred to as Fim cells. They have a high rate of metabolic action compared to the cells which do not contain fimbriae (Fim– cells). They operate as aggregation organelles, forming stellate aggregation on a static liquid medium. These pili connect two cells due to their hollow cores serving as conjugation tubes. The female cell is identified by the tip of the pilus from where the genetic content of the donor cell transfers to the female cell.

40. Capsule Many prokaryotic microorganisms synthesize amorphous organic exopolymers which are deposited outside the cell wall called capsules or slime layers or glycocalyx coats. The term capsule refers to the layer tightly attached to the cell wall while the slime layer is the loose structure that often diffuses into the growth medium. Structure of bacterial cell

41. The capsule layer may be thin of a size less than 0.2 µm called a microcapsule and the thick layer of size more than 0.2 µm to 10 µm called a microcapsule. Structure of bacterial cell

42. Composition of the capsule: Complex polysaccharide ( Klebsiella pneumoniae ) Or Polypeptide ( Bacillus anthracis ) Or Hyaluronic acid ( Streptococcus pyogenes ). Water(98%) Structure of bacterial cell

43. The capsule or slime layer has less affinity for basic dyes and is not visible in Gram staining. Special capsule staining techniques are used by using copper salts as mordants. Structure of bacterial cell

44. Capsules may be easily observed by negative staining in wet films with Indian ink. They are seen as clear halos around the bacteria against a black background. Capsular material is antigenic and may be demonstrated by the serological method. It is visualized by the reaction with a specific antibody which causes a characteristic swelling of the capsule. It is known as a quelluing reaction. Structure of bacterial cell

45. The function of Capsule: Capsules protect the bacteria from antibacterial agents such as lytic enzymes. They inhibit phagocytosis and contribute to the virulence of pathogenic bacteria. They may provide protection against temporary drying by binding water molecules. They may block the attachment of bacteriophages. They may promote the stability of bacterial suspension by preventing the cells from aggregation and settling. They may promote the attachment of bacteria to surfaces. Structure of bacterial cell

46. Cell wall: A cell wall is a rigid structure that gives a definite shape to the cell, situated between the capsule and cytoplasmic membrane. It is about 10-20 nm in thickness and constitutes Structure of bacterial cell

47. It is important to note that not all bacteria have a  cell wall . Having said that though, it is also important to note that  most  bacteria (about 90%) have a cell wall and they typically have one of two types: a  gram positive  cell wall or a  gram negative  cell wall. Structure of bacterial cell

48. The two different cell wall types can be identified in the lab by a differential stain known as the  Gram stain . Developed in 1884, it’s been in use ever since. Originally, it was not known why the Gram stain allowed for such reliable separation of bacterial into two groups. Once the electron microscope was invented in the 1940s, it was found that the staining difference correlated with differences in the cell walls.  Structure of bacterial cell

49. After this stain technique is applied the gram positive bacteria will stain purple, while the gram negative bacteria will stain pink. Structure of bacterial cell

50. Gram Stain Process Gram staining steps Cell effects Gram-positive Gram -negative Step 1 Crystal violet Primary stain added to specimen smear. Stain cells purple or blue Purple or blue purple or blue Step 2 Iodine Mordant makes dye less soluble so it adheres to cell walls. Cells remain purple or blue purple or blue purple or blue Step 3 Alcohol Decolorize washes away stain from gram-negative cell walls . Gram –Positive cells remain purple or blue. Gram-negative cells are colorless. Purple or blue Colorless Step 4 Safranin Counterstain allows dye adherence to gram-negative cells. Gram –Positive cells remain purple or blue. Gram-negative cells appear pink or red. Purple or blue Pink or red

51. A cell wall, not just of bacteria but for all organisms, is found outside of the cell membrane. It’s an additional layer that typically provides some strength that the cell membrane lacks, by having a semi-rigid structure. Both gram positive and gram negative cell walls contain an ingredient known as  peptidoglycan  (also known as  murein ). This particular substance hasn’t been found anywhere else on Earth, other than the cell walls of bacteria. But both bacterial cell wall types contain additional ingredients as well, making the bacterial cell wall a complex structure overall, particularly when compared with the cell walls of eukaryotic microbes. The cell walls of eukaryotic microbes are typically composed of a single ingredient, like the cellulose found in algal cell walls or the chitin in fungal cell walls.

52. The bacterial cell wall performs several functions as well, in addition to providing overall strength to the cell. It also helps maintain the cell shape, which is important for how the cell will grow, reproduce, obtain nutrients, and move. It protects the cell from  osmotic lysis , as the cell moves from one environment to another or transports in nutrients from its surroundings. Since water can freely move across both the cell membrane and the cell wall, the cell is at risk for an osmotic imbalance, which could put pressure on the relatively weak plasma membrane. Studies have actually shown that the internal pressure of a cell is similar to the pressure found inside a fully inflated car tire. That is a lot of pressure for the plasma membrane to withstand! The cell wall can keep out certain molecules, such as toxins, particularly for gram negative bacteria. And lastly, the bacterial cell wall can contribute to the pathogenicity or disease –causing ability of the cell for certain bacterial pathogens.

53. Structure of Peptidoglycan peptidoglycan, since it is an ingredient that both bacterial cell walls have in common. Peptidoglycan is a polysaccharide made of two glucose derivatives,  N-acetylglucosamine (NAG)  and  N-acetylmuramic acid (NAM) , alternated in long chains. The chains are cross-linked to one another by a  tetrapeptide  that extends off the NAM sugar unit, allowing a lattice-like structure to form.

54. The four amino acids that compose the tetrapeptide are:  L-alanine, D-glutamine, L-lysine or  meso -diaminopimelic acid (DPA),  and  D-alanine . Typically only the L-isomeric form of amino acids are utilized by cells but the use of the mirror image D-amino acids provides protection from proteases that might compromise the integrity of the cell wall by attacking the peptidoglycan. The tetrapeptides can be  directly cross-linked  to one another, with the D-alanine on one tetrapeptide binding to the L-lysine/ DPA on another tetrapeptide. In many gram positive bacteria there is a cross-bridge of five amino acids such as glycine ( peptide interbridge ) that serves to connect one tetrapeptide to another. In either case the cross-linking serves to increase the strength of the overall structure, with more strength derived from  complete cross-linking , where every tetrapeptide is bound in some way to a tetrapeptide on another NAG-NAM chain.

55. Gram Positive Cell walls The cell walls of gram positive bacteria are composed predominantly of peptidoglycan. In fact, peptidoglycan can represent up to 90% of the cell wall, with layer after layer forming around the cell membrane. The NAM tetrapeptides are typically cross-linked with a peptide interbridge and complete cross-linking is common. All of this combines together to create an extremely strong cell wall.

56. The additional component in a gram-positive cell wall is  teichoic acid , a glycopolymer, which is embedded within the peptidoglycan layers. Teichoic acid is believed to play several important roles for the cell, such as the generation of the net negative charge of the cell, which is essential for development of a proton motive force. Teichoic acid contributes to the overall rigidity of the cell wall, which is important for the maintenance of the cell shape, particularly in rod-shaped organisms.

57. There is also evidence that teichoic acids participate in cell division, by interacting with the peptidoglycan biosynthesis machinery. Lastly, teichoic acids appear to play a role in resistance to adverse conditions such as high temperatures and high salt concentrations, as well as to β-lactam antibiotics. Teichoic acids can either be covalently linked to peptidoglycan ( wall teichoic acids or WTA ) or connected to the cell membrane via a lipid anchor, in which case it is referred to as  lipoteichoic acid .

58. Since peptidoglycan is relatively porous, most substances can pass through the gram positive cell wall with little difficulty. But some nutrients are too large, requiring the cell to rely on the use of  exoenzymes . These extracellular enzymes are made within the cell’s cytoplasm and then secreted past the cell membrane, through the cell wall, where they function outside of the cell to break down large macromolecules into smaller components.

59. Gram Negative Cell Walls The cell walls of gram negative bacteria are more complex than that of gram positive bacteria, with more ingredients overall. They do contain peptidoglycan as well, although only a couple of layers, represent 5-10% of the total cell wall. What is most notable about the gram-negative cell wall is the presence of a plasma membrane located outside of the peptidoglycan layers, known as the  outer membrane .  This makes up the bulk of the gram negative cell wall. The outer membrane is composed of a lipid bilayer, very similar in composition to the cell membrane with polar heads, fatty acid tails, and integral proteins.

60. It differs from the cell membrane by the presence of large molecules known as  lipopolysaccharide (LPS) , which are anchored into the outer membrane and project from the cell into the environment. LPS is made up of three different components: the  O-antigen or O-polysaccharide , which represents the outermost part of the structure , the  core polysaccharide , and lipid A , which anchors the LPS into the outer membrane.

61. LPS is known to serve many different functions for the cell, such as contributing to the net negative charge for the cell, helping to stabilize the outer membrane, and providing protection from certain chemical substances by physically blocking access to other parts of the cell wall. In addition, LPS plays a role in the host response to pathogenic gram negative bacteria. The O-antigen triggers an immune response in an infected host, causing the generation of antibodies specific to that part of LPS (think of  E. coli   O 157). Lipid A acts as a toxin, specifically an  endotoxin , causing general symptoms of illness such as fever and diarrhea. A large amount of lipid A released into the bloodstream can trigger endotoxic shock, a body-wide inflammatory response which can be life-threatening.

62. the gram negative bacteria utilize  periplasmic enzymes  that are stored in the  periplasm . Where is the periplasm, you ask? It is the space located between the outer surface of the cell membrane and the inner surface of the outer membrane, and it contains the gram negative peptidoglycan. Once the periplasmic enzymes have broken nutrients down to smaller molecules that can get past the LPS, they still need to be transported across the outer membrane, specifically the lipid bilayer. Gram negative cells utilize  porins , which are transmembrane proteins composed of a trimer of three subunits, which form a pore across the membrane. Some porins are non-specific and transport any molecule that fits, while some porins are specific and only transport substances that they recognize by use of a binding site. Once across the outer membrane and in the periplasm, molecules work their way through the porous peptidoglycan layers before being transported by integral proteins across the cell membrane. .

63. The peptidoglycan layers are linked to the outer membrane by the use of a lipoprotein known as  Braun’s lipoprotein  (good ol ’ Dr. Braun). At one end the lipoprotein is covalently bound to the peptidoglycan while the other end is embedded into the outer membrane via its polar head. This linkage between the two layers provides additional structural integrity and strength.

64. Bacterial spores are highly resistant, dormant structures (i.e. no metabolic activity) formed in response to adverse environmental conditions. When vegetative cells of certain bacteria such as  Bacillus  spp and  Clostridium  spp are subjected to environmental stresses such as nutrient deprivation, they produce metabolically inactive or dormant form-endospore. The formation of endospores circumvents the problems associated with environmental stress and ensures the survival of the organisms. During unfavourable conditions ( especially when carbon and nitrogen become unavailable ) spore-forming bacilli form endospores. The size, shape, and location of endospores are particularly useful for identifying  Clostridium, Bacillus , and related species. Bacterial Spores: Structure and Spore-Forming Bacteria

65. Sporulation Spore formation (sporulation) occurs when nutrients, such as sources of carbon and nitrogen are depleted. Bacterial spores are highly resistant to Heat Dehydration Radiation and Chemicals

66. Structure of the Bacterial Spore An endospore is structurally and chemically more complex than the vegetative cell.  It contains more layers than vegetative cells. Resistance of Bacterial spores may be mediated by   dipicolinic acid, a calcium ion chelator  found only in spores.  When the favorable condition prevails, (i.e. availability of water, appropriate nutrients)  spores germination occurs which forms vegetative cells of pathogenic bacteria. The following factors/constituents play  major roles in the resistance of bacterial spore:  Calcium dipicolinate in core Keratin spore coat New enzymes (i.e., dipicolinic acid synthetase, heat-resistant catalase) Increases or decreases in other enzymes.

67. A mature endospore contains a complete set of genetic material (DNA) from the vegetative cell, ribosomes, and specialized enzymes. Mature endospores  are released from the vegetative cell to become  free endospores .  When the free endospores are placed in an environment that supports growth, the endospores will revert back to a vegetative cells in a process called germination.  It should be noted that unlike the process of binary fission observed with vegetative cells, endospore formation is not a reproductive process but a process of  differentiation  that provides the bacteria with a mechanism for survival.

68. Constituents of Bacterial Spores Thick keratin-like coat Peptidoglycan Cell membrane A small amount of cytoplasm Very little water Bacterial DNA

69. Medical Importance of Bacterial Spores Important features of Spores Medical Implications Spores are highly resistant to heating; spores are not killed by boiling (100°C) but are killed at 121°C. Medical supplies must be  heated to 121°C for at least 15 minutes to be sterilized. Spores are highly resistant to many chemicals, including most disinfectants. The only solution designated as sporicidal will kill spores. Spores can survive for many years in soil and other inanimate objects. Wounds contaminated with soils can be infected with spores and cause diseases such as tetanus, and gas gangrene. Spores do not exhibit measurable metabolic activity. Antibiotics are ineffective against spores. Spores are formed only when nutrients are insufficient. Spores are not often found at the site of infection because nutrients are not limited.

70. Positions of Bacterial Spores The shape and the position of spores vary in different species and can be useful for classification and identification purposes. The position of the spores can be seen in the smear by using  the endospore staining method . Endospores may be located in the  middle  of the bacterium ( central ), at the  end  of the bacterium ( terminal ), near the end of the bacteria  (subterminal ), and maybe spherical or elliptical Central endospores  are located within the middle of the vegetative cell.   Terminal endospores  are located at the end of the vegetative cell.   Sub-terminal endospores  are located between the middle and the end of the cell

71. Examples Central or equatorial, giving the bacillus a  spindle shape  ( eg.   Clostridium bifermentans ) Sub-terminal, the bacillus appearing  Club shaped  ( eg.   Clostridium perfringens ) Oval and terminal, resembling a  tennis racket  ( eg.   Clostridium tertium ) Spherical and terminal, giving a  drumstick appearance  ( Clostridium tetani )

72. Useful Bacteria Not all bacteria are harmful to humans. There are some bacteria that are beneficial in different ways. Listed below are a few benefits of bacteria: Convert milk into curd – Lactobacillus or lactic acid bacteria Ferment food products – Streptococcus and Bacillus Help in digestion and improving the body’s immunity system – Actinobacteria, Bacteroidetes, Firmicutes, Proteobacteria Production of antibiotics, which is used in the treatment and prevention of bacterial infections – Soil bacteria

73. Harmful Bacteria There are bacteria that can cause a multitude of illnesses. They are responsible for many infectious diseases   like pneumonia, tuberculosis, diphtheria, syphilis, and tooth decay. Their effects can be rectified by taking antibiotics and prescribed medication. However, precaution is much more effective. Most of these disease-causing bacteria can be eliminated by sterilizing or disinfecting exposed surfaces, instruments, tools, and other utilities. These methods include- the application of heat, disinfectants, UV radiations, pasteurization, boiling, etc.

74. Thankyou