Lecture 5 Bacterial Growth (2) - Microbiology Lecture Notes PDF

Microbiology & Immunology Unit Lecture 5 Bacterial Growth (2) Bacterial Genetics and Virulence Factors Dr. Rasha Mokhtar Elnagar M.B.B.C, MSc, PhD, MD Medical Microbiology and Immunology Associate Professor of Medical Microbiology & Immunology Consultan...

Microbiology & Immunology Unit Lecture 5 Bacterial Growth (2) Bacterial Genetics and Virulence Factors Dr. Rasha Mokhtar Elnagar M.B.B.C, MSc, PhD, MD Medical Microbiology and Immunology Associate Professor of Medical Microbiology & Immunology Consultant Microbiology & Immunology 1-Bacterial Virulence Factors The Bacterial Virulence Factors:  Virulence factors are cellular structures, enzymes, and toxins that enhance bacterial pathogenicity. The Most Important Virulence Factors are: 1-The capsule. 2- Fimbriae (pili). 3- Teichoic acid. 4- Enzymes. 5- Bacterial toxins: exotoxins / endotoxins. 6- Pigments 1- Microbial capsule: Resist phagocytosis. Resist the hydrolytic enzymes (lysozymes) that lyse the cell wall. Adherence to the host cells 2- Fimbriae (Pili): Adhesion to the host cell surface. 3- Teichoic acid (Gram positive bacteria): Adhesion to the host cell surface. 4- Microbial Enzymes: o Collagenase: enhances microbial invasion by degradation of extracellular matrix (collagen). o Urease: neutralization acidic pH in urine & stomach. o Hemolysin: degrade RBCs and release hemoglobin. o Haemagglutinin and coagulase enzyme: Agglutination of RBCs and coagulation of the plasma→ the microbe escapes humoral immunity. o Catalase: H₂ O ₂ → H ₂ O + O ₂. o The Beta-Lactamases: Some microbes have ability to resist antibiotics due to production of Beta lactamase enzymes. The beta-lactamases hydrolyze beta- lactam ring of antibiotics. Example: Penicillinase produced by Staphylococci.  5- Bacterial Toxins Exotoxins Endotoxins Produced Gram positive and Gram Gram negative by negative bacteria bacteria Diffusion Diffuse outside the Part of the cell wall bacteria Nature Protein Lipopolysaccharid es Effect of Heat labile Heat stable heat Effect of Detoxified forming No effect formalin toxoid which used in vaccination Antigenici More Less ty Examples Clostridium botulinum Gram-negative  6- Bacterial Pigments  Cytotoxic  Exopigment: diffuse into the surrounding medium. -Ex. Blueish green: Pseudomonas aeruginosa.  Endopigment: localize to the colony. - Ex. Golden yellow. e.g. Staphylococcus aureus. 2-Bacterial Genetics Bacterial Genome:  Bacterial chromosome is a single circular double stranded DNA. Many bacteria contain additional genes on plasmids. Plasmid is an extra-chromosomal, circular, supercoiled DNA that carries some important genes such as the antibiotics resistance genes. Gene Transfer: Transfer of genetic material from one bacterium to another. Mechanisms of Gene Transfer: 1. Conjugation 2. Transduction 3. Transformation 1- Conjugation: Plasmid will be transferred from one bacterial cell to another by sex pili (in gram negative bacteria). 2- Transduction: Genetic material transfer from one bacterium to another through a virus (bacteriophage).  3- Transformatio  Naked DNA transferred from lysed donor n: cell to recipient cell. bacterial Q: Corynebacterium diphtheriae causes the disease diphtheria by producing diphtheria toxin. The gene encode the toxin is transferred to other bacteria through a virus named bacteriophage by a process called: A.Conjugation B.Transduction C.Transformation D.Translocation Reference Lippincott Illustrated Microbiology 4th edition, Chapters: 3 and 7.