L15 Bacterial Reproduction, Growth & Pathogenesis PDF

Microbiology BMF VI Bacterial Reproduction, Growth, and Pathogenesis endo us and sopes g9rem Lta g some but exotoxin endosporiction us fission binary oxygen factors to Responses virulence and Photons exostenser Malabika Maulik, PhD Clinical Assistant Professor 1 Assigned Reading Medical Microbiology...

Microbiology BMF VI Bacterial Reproduction, Growth, and Pathogenesis endo us and sopes g9rem Lta g some but exotoxin endosporiction us fission binary oxygen factors to Responses virulence and Photons exostenser Malabika Maulik, PhD Clinical Assistant Professor 1 Assigned Reading Medical Microbiology, 9th edition, (2020) Murray et al: Parts of Chapter 12,13,14,15. Sherris Medical Microbiology, 7th edition, (2018): Parts of Chapter 21, 22. 2 Learning Objectives Bacterial Reproduction, Growth, and Pathogenesis 1. Understand the different kinds of bacterial reproduction 2. Understand both cellular and population growth of bacteria. 3. Explain the terminologies associated with the nutritional requirements of bacteria. 4. Explain the observations underlying the germ theory of disease. 5. Explain the terminologies describing bacterial pathogenesis. 6. Explain the observations accompanying sepsis leading to septic shock. Bacterial Reproduction LO1 on the basis of perpetuation of the species. Ensuring that a complete and accurate copy of the genome be passed on to common  both progeny cells during transverse binary fission  one progeny cell during endosporulation. most Because bacteria are unicellular, cell division is equivalent to reproduction (i.e., one cell is equivalent to one entire organism). There are two major types of cell division: 1. 2. Transverse binary fission - division of the parental cell at the midpoint, two progeny cells of equal biomass. Endosporulation - when a bacterium detects that environmental conditions are becoming unfavorable, it may start the process of endosporulation. Fig. 13.8, Murray et al. Bacterial cell division. Requires extension of the cell wall and replication of the chromosome with septum formation. Membrane attachment of the DNA pulls each daughter strand into a new cell (?). Cellular growth as replication, increase in surface area, and midpoint septation occur concomitantly. A cell envelope phenomenon. LO1 Bacterial Reproduction - binary fission Most common mode and it is always an asexual process (as are all types of bacterial cell division). Duplication of parental nucleoid (bacterial chromosome) must occur thru the process of replication Each “daughter” cell receives a complete copy of the genome. Erwinia carotovora cells undergoing synchronous growth in classic work published in J. Bacteriol. (1965) by Dr. E.A.Grula and his doctoral student G.L. Smith at Oklahoma State University. Go Pokes! Transmission electron micrographs of synchronously-growing Erwinia carotovora during active transverse binary division. Figs. 1-6. Grula and Smith. 1965. J. Bacteriol. Bacterial Reproduction - endosporulation LO1 Some gram-positive, but never gram-negative bacteria Exclusive in the genera Bacillus and Clostridium Yields an extremely heat and chemical resistant cell type which contains a complete copy of the genome. Cell types (vegetative cell and endospore) are physiologically and morphologically disparate Heat resistance due to the desiccated condition of the spore, presence of calcium dipicolinate (dipicolic acid) and a complex, seven-layered cell envelope. The function of endosporulation is two-fold: 1) Specialized form of reproduction. 2) Mechanism by which the genome can be dispersed in the environment in a refractory condition which allows for its survival. Process of cellular endosporulation after the final replication of exponentialphase growth and after the culture has entered stationary-phase. Bacterial Growth  Growth requires metabolism, regulation, and division by binary fission 1. Cell growth-The orderly increase in all macromolecular components of the cell whereby individual cells increase with regard to surface area while concomitantly forming a division septum. LO2 Bacterial Growth 2) Population growth - Increase in the number of cells (equivalent to number of organisms due to their unicellular nature, therefore equivalent to reproduction). Occurs in four phases under closed conditions (i.e., batch culture, meaning no nutrient replenishment or metabolic waste removal):​ Lag phase of acclimation to cultivation conditions, upregulation of genes necessary for growth under given physiological environment.​ Exponential phase - growth is at steady state due to (1) transverse binary fission, (2) constant generation time, and (3) unicellular nature of bacteria. Stationary phase - cessation of growth due to either nutrient depletion or toxic waste accumulation.​ Death phase (decline) - Fraction of population loses viability at each​ time increment. During the death phase, some bacteria stop dividing but remain viable and are often insensitive to antibiotics LO2 LO3 Fig. 13.9, Murray et al. Phases of bacterial growth, starting with an inoculum of stationary-phase cells. Bacterial growth requirements Nutrients are exogenous chemicals which must be provided for growth because they are essential for maintenance of bacterial metabolism. Oxygen availability- Aerobe vs anaerobe Some bacteria have very extensive nutritional requirements and are therefore considered nutritionally fastidious. For example: Most pathogenic organisms would serve as good examples. Other bacteria are more saprophytic in that they have very simple nutritional requirements because they are able to synthesize most or all of the compounds necessary for growth from a single carbon source. For example: Wild-type Escherichia coli and Pseudomonas aeruginosa are both able to grow with glucose as the sole carbon, energy, and electron source. LO3  Pathogenic bacteria are typically chemoheterotrophic; therefore growth is dependent on the conversion of organic substrate(s) to: a. Precursors of macromolecules that comprise the cell. b. ATP which are stored forms of energy necessary for biosynthesis of macromolecules and other energy-requiring processes. c. Reducing power (NADH+H+ and FADH2) which is the stored form of electrons necessary for biosynthesis of macromolecules and oxidative phosphorylation. LO3 Bacterial response to oxygen  Bacterial metabolism 1. Aerobic respiration 2. Fermentation  Fermentation and respiration pathways each regenerate ATP and NAD+.  Bacteria exhibit different characteristic responses to oxygen.  Aerobic metabolism produces peroxide and toxic oxygen radicals  Oxygen resistance vs ability to use O2 as final acceptor. LO3 LO4 Bacterial response to oxygen table Very examples Important not LO4 Bacterial Pathogenesis  The German Physician Robert Koch conclusively demonstrated the etiology of anthrax in 1876, thereby providing the first unequivocal proof of the germ theory of disease.  Koch’s Postulates 1. Organism must be present in every case of the disease. 2. Organism must be isolated from the infected host and cultivated in pure culture. 3. Specific disease must be reproduced upon re-inoculation into healthy host. 4. Organism must be recoverable from experimentally-infected host by cultivating in pure culture. The Koch Institute, Wedding-Berlin Robert Koch LO4  Molecular Koch’s Postulates (as first proposed in the 80s by Dr. Stanley Falkow): 1. Virulence gene is associated with microbe that causes disease but is absent or inactive in strains that fail to cause disease in animal model. 2. Disruption of gene function in virulent strain results in avirulence (or a measurable decrease in virulence if multiple virulence factors). 3. Introduction of cloned gene into avirulent strain restores original virulence level. 4. Gene is expressed during infection. Koch’s postulates in this century will involve genomics, metagenomics, and proteomics. Stanford microbiologist Stanley Falkow receives the National Medal of Science. Bacterial Pathogenesis  All host-associated bacteria must be considered when discussing infectious diseases.  The human commensal microbiota become secondary (opportunistic) pathogens when normal barriers are compromised and they enter otherwise sterile sites.  Pathogenesis – process of disease development in a host LO5 LO5 Bacterial Pathogenesis Primary pathogens are able to cause disease in healthy individuals by virtue of their ability to: 1. enter the host, 2. colonize by either adhesion to or invasion of healthy tissues while concomitantly causing deleterious effects, and/or 3. introducing endotoxins or exotoxins, 4. all while evading host defense mechanisms to include primarily the immune system which itself can cause cellular and tissue damage. Glycan-mediated molecular interactions in bacterial pathogenesis, Lee, Sohyoung et al.Trends in Microbiology, Volume 30, Issue 3, 254 - 267 Table 14.1, Murray et al. Bacterial Port of Entry Bacterial Pathogenesis- entry Route Examples Ingestion Salmonella spp., Shigella spp., Yersinia enterocolitica, enterotoxigenic Escherichia coli, Vibrio spp., Campylobacter spp., Clostridium botulinum, Bacillus cereus, Listeria spp., Brucella spp. Inhalation Mycobacterium spp., Nocardia spp., Mycoplasma pneumoniae, Legionella spp., Bordetella, Chlamydophila psittaci, Chlamydophila pneumoniae, Streptococcus spp. Trauma Clostridium tetani Needlestick Staphylococcus aureus, Pseudomonas spp. Arthropod bite Rickettsia, Ehrlichia, Coxiella, Francisella, Borrelia spp., Yersinia pestis Sexual transmission Neisseria gonorrhoeae, Chlamydia trachomatis, Treponema pallidum FIG. 14.1 Body surfaces as sites of microbial infection and shedding. Red arrows indicate infection; purple arrows indicate shedding. Modified from Goering, R.V., Dockrell, H.M., Zuckerman, M., et al., 2019. Mims’ Medical Microbiology, sixth ed. Elsevier, Philadelphia, PA. LO5 Bacterial Pathogenesis- adhesion and colonization LO5 Howboditi.se  Virulence factor- ability to produce a product or strategy that contributes to a pathogenic process. Box 14.1, Murray, et al.  Renders the bacterium pathogenic. Bacterial Virulence Factors Adherence Invasion Byproducts of growth (gas, acid) Toxins Degradative enzymes Cytotoxic proteins Endotoxin Superantigen Induction of excess inflammation Evasion of phagocytic and immune clearance Capsule Resistance to antibiotics Intracellular growth Biofilm production Bacterial Pathogenesis- pathogenic actions LO5  Toxins are bacterial products that directly harm tissue or trigger destructive biological activities.  Exotoxins - a can be produced by gram-positive or gram-negative bacteria and include cytolytic enzymes and receptor-binding proteins that alter a function or kill the cell.  Toxin gene is encoded on a plasmid (tetanus toxin of C. tetani, heat-labile [LT] and heat-stabile [ST] toxins of enterotoxigenic E. coli)  For many bacteria, the effects of the toxin determines the disease (e.g., C. diphtheriae, C. tetani). Bacterial Pathogenesis- pathogenic actions LO5  Toxins are bacterial products that directly harm tissue or trigger destructive biological activities.  Endotoxins – lipopolysaccharide component on outer membrane, lipid A is toxic.  Only gram-negative bacteria make endotoxin.  Weaker, endotoxin-like responses may result from gram-positive bacterial structures, including lipoteichoic acids. LO5 Bacterial Pathogenesis- host defense LO5 Primary barriers to infection. LO5 Key Definitions LO5 Disease- An interruption, cessation, or disorder of body functions, systems, or organs characterized by at least two of the following criteria: a recognized etiologic agent(s), an identifiable group of signs or symptoms, and/or consistent anatomical alterations. Infection- Population growth of a bacterium to the detriment of the host (endoparasitism). Pathogenicity- Ability of a bacterium to produce an infectious disease in an organism (qualitative term). Virulence- Degree of pathogenicity (quantitative term). Infective dose- Number of pathogenic organisms necessary to initiate an infection in a susceptible host. The ability to produce a product or strategy that contributes a pathogenic process is referred to as a virulence factor and renders the microorganism pathogenic. Incubation period- Time elapsed between infection and onset of symptoms. Septic Shock LO6 Highly lethal complication of localized infections which disseminate by bacteremia to sepsis with high levels of LTA or LPS systemically leading to an overpowering pro-inflammatory response throughout the body. Often nosocomial in nature. Severe sepsis involves when one of the following indicates organ failure: decrease urine, change in mental status, decreased platelets, dyspnea, abnormal heart function, pain. Box 14.3, Murray et al. Endotoxin-Mediated Toxicity Patient is diagnosed with septic shock when severe sepsis is accompanied Fever by extremely low blood pressure refractory to fluid replacement. Leukopenia followed by leukocytosis Activation of complement Thrombocytopenia Disseminated intravascular coagulation Decreased peripheral circulation and perfusion to major organs Shock Death SIRS, systemic inflammatory response syndrome. LO5 doi: https://doi.org/10.1136/bmj.i1585 1. Endosporulation is common in ______________ genera of bacteria A. B. C. D. E. Bacillus Clostridium Staphylococcus Streptococcus A and B never gron e 2. Which of the following kind of bacteria grows best in limited oxygen supply ? A. B. C. D. E. Microaerophilic Aerobe Anaerbe Facultatively anaerobe Facultatively aerobe For further questions, please contact : Malabika Maulik, PhD, Clinical Assistant Professor Forensic Science & Biomedical Research Building, E-421 Email: [email protected] Thank you