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Bacterial structure and growth
This document discusses various aspects of bacterial structure and growth. It describes the key differences between gram-positive and gram-negative bacteria, including their cell wall structures. It also outlines the organelles and inclusions found within bacterial cells, such as the cell membrane, cytoplasm, ribosomes, and plasmids. External structures like flagella, pili, capsules, and endospores are also defined. The document concludes by examining the requirements and conditions necessary for bacterial growth, including nutrients, temperature, pH, oxygen levels and generation times.
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Bacterial structure and growth
- 1. BACTERIAL STRUCTURE & GROWTH MEDI3104 Dr Meher Rizvi Associate Professor Deptt of Microbiology and Immunology Response to infection and pathobiology
- 2. GRAM’S Gram positive cocciin chains Gram positive cocci in clusters Gram negative bacilli in no specific arrangement Zeihl Neelsen stain: Acid fast bacilli
- 3. Spiral bacteria: Treponema pallidum Silverimpregnation Capsulated bacteria: Streptococcus pneumoniae
- 4.
- 5. Eukaryote vs Prokaryote EukaryotesProkaryotes True nucleus Primitive nucleus Nuclear membrane No Nuclear membrane Chromosomes Single strand of DNA Cytoplasmic structures present Absent 80S Ribosomes 70S Ribosomes Asexual & Sexual Reproduction Asexual Respiration via Mitochondria Cytoplasmic membrane
- 6. Parts of acell Cell wall Cell membrane Cytoplasm Nucleiod Ribosomes Granules/inclusion bodies Mesosomes Appendages Pili Flagella Capsule Spores Plasmids
- 8.
- 12. Antigenic Structure ofEnterobacteriaceae S. typhi O antigen side chain (Fimbriae) Somatic O antigen raises good specific antibodies. Serological diagnosis of Vibrio, Salmonella, Shigella, E. coli depends on O antigen
- 13. Cell wall • Peptidoglycan •N acetyl glucosamine & N acetyl Muramic acid • Protect the cell from osmotic changes • Rigidity • Multilayered in Gram positive • Teichoic acid • Mono to bi layered in Gram negative
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- 15. Special components ofGram positive cell wall Teichoic acid SPA / M PROTEIN
- 16. GRAM NEGATIVE CELLWALL Outer membrane- Gram negative bacteria only 2 layers of lipids Inner layer-phospholipids Outer layer- Lipopolysaccharide: 3 regions Lipid A (endotoxin: pyrogenic, lethal, necrotic, anticomplementary) Core polysaccharide O antigen (Somatic O antigen)
- 17. Functions of Bacterialcell Wall Rigid structure •Maintains cell shape •Protects the bacteria from the effects of osmotic pressure •Takes part in cell division •Virulence: •Endotoxin in Gram negative bacteria •Protein M of Streptococcus pyogenes •Protein A of Staphylococcus aureus •Supports the surface appendages like pili , fimbriae, flagella •Immunity (Antibodies raised against LPS, Teichoic acid)
- 18. A double layerof lipids - present in all bacteria Cytoplasmic membrane
- 19. Cytoplasmic membrane :Cytoplasmicmembrane : • Selective permeability • Contains proteins which transport metabolites • Into the cell : e.g. nutrient uptake • Out of the cell: e.g. waste excretion • Performs the functions of respiration, lipid & cell wall synthesis • electron transport • energy production (site of ATP production) • Detects and responds to chemicals in surroundings
- 20.
- 21. Plasmids: Small,circular,extrachromosomal ， double- strandedDNA molecules Capable of self-replication Contain genes that confer properties: •Antibiotic resistance ， •Virulence factors Plasmids are not essential for cellular survival The bacterial genome consists of a single, double stranded circular molecule without a nuclear membrane
- 22. CYTOPLASMIC STRUCTURES • Nucleiod •Chromosomal DNA • Plasmids • Ribosome – 70S :50S & 30S ( Site of protein synthesis) • Intracytoplasmic Inclusion bodies • Storage of excess food and energy • Metachromatic granules/ Babes ernst granules Accumulates when a cell is grown in nutritional deficiency • Mesosomes: respiration, cell wall formation, • Chromosome replication
- 23. External structures :Externalstructures : Capsule: lies external to the cell wall Consists of polysachharide layers Bacillus spp: polypeptide layers Protects bacteria against phagocytosis- virulence factor Uses: Vaccine production as capsule is antigenic Used for serological diagnosis: (Neisseria meningitidis, Haemophilus influenza, Str pneumoniae)
- 24. Flagella Monotrichate Amphitrichate LophotrichatePeritrichate • Originates from cytoplasmic membrane • Provides motility to bacteria • Bacteria move towards food – chemotaxis • Identification of bacteria (H antigen) • Can have one or many flagella • Pathogenesis: Motility is a virulence factor • H antigen: Raises good antibodies. Used in serological diagnosis ( Salmonella)
- 25. Fimbriae :Fimbriae : •Short protein fibres- fimbriae cover the whole surface of bacterial cell • Help bacteria to adhere to surface of host cells • Are important virulence factors • Pili : Protein fibres, longer than fimbriae, one or few per bacterial cell • F ( Fertility ) pili allow bacteria to transfer chromosomal and extra-chromosomal genetic material to other bacteria
- 26. Common pili orfimbriae: fine , rigid numerous, related to bacterial adhesion Sex pili: longer and coarser, only 1-4, related to bacterial conjugation Sex pili
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- 28. Chapter 4 ExtremelyResistant structures Heat, irradiation, cold Boiling >1 hr still viable Produced in unfavourable conditions Location important in classification Central, Subterminal, Terminal Bacillus stearothermophilus -spores Used for quality control of heat sterilization equipment Bacillus anthracis - spores Used in biological warfare
- 29. Endospores (spores) • Produced whenstarved • Contain Dipicolinic acid • Bacillus and Clostridium Identification of Bacteria
- 30. BACTERIAL GROWTHBACTERIAL GROWTH Bacteriamultiply by binary fission
- 32. Stationary Phase Storage granulesform Sporulation occurs Exotoxins, antibiotics, bacteriocins produced Stationary Phase: Growth stops Nutrients exhausted Toxic products accumulate
- 33.
- 34. Generation time Time takenby a particular organism to double its number Escherichia coli- Vibrio cholerae - 20 min (Disease develops in few hours ) Mycobacterium tuberculosis- 20 hours ( Disease develops in months ) Mycobacterium leprae- 20 days ( Disease develops in years)
- 35. Practical implications Escherichia coliand Vibrio cholerae grow in the laboratory in 18-24 hours Results of culture available in 24-48 hours Mycobacterium tuberculosis requires 4-6 weeks to grow in the laboratory Results of culture are available in 8 weeks or more
- 36. REQUIREMENT FOR BACTERIALGROWTH - proper nutrients ( carbon, nitrogen ) - proper pH ( optimum 6.8 – 7.2 ) - proper temperature - optimum 370 C - proper atmosphere (aerobic , anaerobic, micro-aerophilic ) - proper osmolality • Culture medium - Solid , Liquid ( Broth )
- 37. Nutritional Requirement forGrowth: Autotrophs : Can manufacture their own food (free living in nature, in soil, water etc.) Heterotrophs : Require organic ready made food Most medically important bacteria are heterotrophs Oxygen requirement: Aerobes : Require oxygen Anaerobes: Grow in the absence of oxygen Microaerophilic : Reduced concentration of O2: 5-7% Anaerobic jarIncubator Oil as preservative
- 38. Temperature requirement forgrowth :Temperature requirement for growth : • Psychrophiles : Optimum temperature : 15-200 C • Mesophiles: Optimum temperature : 30-370 C • Medically important bacteria are mesophiles, adapted to the human body normal temperature • Thermophiles: Optimum temperature : 50-600 C
- 39. Temperature requirement forgrowthTemperature requirement for growth
- 40. pH • Most pathogenicbacteria grow between pH 6.5 and 7.5 • Acid (below pH 4) good preservative for pickles, sauerkraut, cheeses • Exceptions to the rule: • Acidophiles can live at low pH • Many bacteria and viruses survive low pH of stomach to infect intestines • Helicobacter pylori lives in stomach under mucus layer
- 42.
Editor's Notes
- #2 Bacteria were earlier considered to be nothing more than a bag of enzymes until the electron microscope was discovered when it was discovered that it is a complex well defined structure.
- #6 Cytoplasmic structures: mitochondria, golgi apparatus and endoplasmic reticulum, food vacuole etc
- #11 Figure: 04-28 Caption: Cell walls of Bacteria. (a,b) Schematic diagrams of gram-positive and gram-negative cell walls.
- #12 Bacterial cell wall is more complex than eukaryotic cell wall. Peptidoglycan does not exist in any other living thing. Good news. Because cell wall acting antibiotics will not damage host cells Caption: Teichoic acids. (b) Summary diagram of the gram-positive cell wall.
- #13 Figure: 04-36 Caption: The gram-negative cell wall. Note that although the outer membrane is often called the "second lipid bilayer," the chemistry and architecture of this layer differs in many ways from that of the cytoplasmic membrane. (a) Arrangement of lipopolysaccharide, lipid A, phospholipid, porins, and lipoprotein in the outer membrane. See Figure 4.35 for details of the structure of LPS. Lipid A can be toxic in humans, and if so, is referred to as endotoxin (Section 21.12). (b) Molecular model of porin proteins. Note the three pores present, one formed from each of the proteins forming a porin molecule. The view is perpendicular to the plane of the membrane. Model based on X-ray diffraction studies of Rhodobacter blasticus porin.