Bacterial Morphology and Cell Structure 2024 PDF

Bacterial Morphology and Structure 11/19/2024 Shafik Habal, MD...

Bacterial Morphology and Structure 11/19/2024 Shafik Habal, MD Assistant Dean for Curriculum Management and Reporting Professor, Medical Microbiology and Immunology Philadelphia College of Osteopathic Medicine Certain materials are included under the fair use exemption of the U.S. Copyright Law and have been prepared according to the fair use guidelines and are restricted from further use.  Learning Objectives 1. List the major differences between a Eukaryotic and a Prokaryotic cell 2. Describe and recognize the various bacterial shapes and arrangements 3. Describe the structure and synthesis of peptidoglycans 4. Describe the structure, function and effects of Lipopolysaccharides (LPS) 5. Compare the cell wall structure of Gram positive and Gram negative bacterial cells 6. Recognize the structure of a flagella and types of bacterial motility 7. Describe the different phases of bacterial growth curve 8. Calculate bacterial population and generation time 9. Classify bacterial organisms based on the their growth requirements Murray Medical Microbiology 9th edition – Chapter 12  Cell Theory – Historical perspective 1665 Robert Hooke All organisms are composed of one or more cells 1674 Anton van Leeuwenhoek Cells are the basic unit of life 1859 Charles Darwin 1864 Louis Pasteur All cells are derived from preexisting cells 1884 Robert Koch Modern Cell Theory: 1953 Watson and Crick 1995 Craig Venter 1. Cells contain DNA which is passed from cell to cell through cell division 2. All cells are the same in terms of chemical composition and metabolic activity 3. Physiological function is carried out inside the cell 4. Cellular activity depends on function of intracellular organelles  The Three Domain System Domain Eukarya Kingdom Animalia Phylum Chordata Class Mammalia Order Primates Family Hominidae Genus Homo Species Homo sapiens  Major features of prokaryotes and eukaryotes Characteristic Eukaryote Prokaryote Size >5 μm 0.5-3.0 μm Nucleus Present No nuclear membrane Chromosome Paired chromosomes Haploid – Chromatid Organelles Mitochondria Present Absent Golgi ER Ribosome 80S (60S + 40S) 70S (50S + 30S) Cell Wall No cell wall (present for fungi) Made of Peptidoglycans Reproduction Sexual and asexual Asexual (binary fission) Figure 12.1: Major features of prokaryotes and eukaryotes Table 12.1: Major Characteristics of Eukaryotes and Prokaryotes Gram Stain Figure 12.3: Gram-stain morphology of bacteria The bacterial cell wall Bacterial morphology https://byjus.com/neet/important-notes-of-biology-for-neet-shapes-of-bacteria/  Bacterial cell wall Provide shape, structure and rigidity, and protect against osmotic pressure gradients Almost all bacteria have cell wall. (Mycoplasma species lack cell wall) The cell wall is made of peptidoglycans Peptidoglycan synthesis  Lipopolysaccharides - LPS LPS is also called “Endotoxin” – powerful inducer of innate immunity It stimulates the release of inflammatory cytokines (IL-1b, IL-6, and TNF) Only found on Gram-negative bacteria Composed of 3 main parts: 1. O-antigen (Outer specific chain) made of repeating oligosaccharides important for bacterial typing 2. Core region composed of a short chain of polysaccharides connecting the O-antigen to the Lipid A 3. Lipid A is a disaccharide (two glucosamine molecules) with multiple fatty acid tails. It is anchored to the membrane and is responsible for eliciting the immune response Lipooligosaccharide (LOS) , which is present in Neisseria species, lacks the O-antigen portion of LPS. The shorter O antigen allows LOS aggregates to be shed and diminishes protection of the membrane, which makes Neisseria more susceptible to host-mediated complement lysis  Plasma membrane Lipid bilayer structure similar to the structure of eukaryotic membranes Unlike eukaryotic membrane, it lacks cholesterol with the exception of Mycoplasma Regulates the transport of molecules between the cytoplasm and the extracellular environment via osmosis, simple diffusion, facilitated diffusion, and active transport (ATP against a concentration gradient)  Bacterial Ribosomes Prokaryotic ribosome is composed of 30S and 50S subunits 🡪 70S Unlike eukaryotic ribosome composed of 40S and 60S subunits 🡪 80S “S” refers to Svedberg, a measurement of density based on sedimentation Ribosomal subunits are a major target for antibacterial agents  Bacterial Capsule Some bacteria (Gram + or Gram -) are surrounded by polysaccharide layer, “capsule” In cases where it is loosely adherent and non uniform in thickness 🡪 “Slime layer” The “Capsule” and “Slime layer” are referred to as “Glycocalyx” Almost always made of polysaccharides except in the case of Bacillus, its made of polypeptides Promotes adherence to host 🡪 Attachment Poorly antigenic Example of Encapsulated Bacteria Antiphagocytic 🡪 Virulence factor Streptococcus pneumoniae Can be visualized by: India Ink Streptococcus agalactiae Klebsiella pneumoniae Salmonella species Haemophilus influenzae Pseudomonas aeruginosa Neisseria meningitidis Quellung reaction  The outer membrane A phospholipid bilayer only found in Gram negative bacteria Joined to peptidoglycans by lipoproteins The outer leaflets are formed by lipopolysaccharides Arrangement of Flagella  Fimbriae and pili Fimbriae Pili Tiny, bristle-like projections Long, hair-like microfibers Occur on both Gram+ and Gram- Occur only on Gram- bacteria Made up of “fimbrillin” protein Made up of “pilin” protein Hundreds per cell Typically, 1-10 per cell Used for: Attachment Used for: Conjugation (F-pillus)  Motility Motility Stab test: A line stabbed in semisolid motility agar Growth out from the streak line 🡪 motility Motility Plate: Plate divided Bacteria inoculated on one side Use the other side as positive control. If motile 🡪 Spread out away from inoculation point.  Endospores Dormant cells produced by some Gram positive bacteria – Bacillus and Clostridium species Resistant to heat, drying, and disinfectants Formation promoted by lack of nutrients (C, N, etc.) Coxiella produce an endospore-like infectious structure enabling it survive in soil outside host  Bacterial growth requirements Mesophile 20°C – 40°C Thermophile >40°C - 65°C – Thermus aquaticus (used for PCR) Psychrophile