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Principle of Infectious Diseases Bacteriology I: Overview and basic concepts Dr. Ricardo Gutiérrez, Microb., MSc, Ph.D. Assistant Professor [email protected] Summer semester, 2024  (Infectious) disease triangle Pathogens Overview Bacteria are unicellular organisms...

Principle of Infectious Diseases Bacteriology I: Overview and basic concepts Dr. Ricardo Gutiérrez, Microb., MSc, Ph.D. Assistant Professor [email protected] Summer semester, 2024  (Infectious) disease triangle Pathogens Overview Bacteria are unicellular organisms that lack of membranous organelles and true nucleus Small in size / large in number Evolved to survive in a variety of ecologic niches (habitats) Some grow rapidly / other slowly Some require minimal (basic) nutrients to grow / others are fastidious Most are beneficial / some can be pathogenic  Bacteria Small in size Invisible to the naked eye! 1676 – Antoni van Leeuwenhoek  Bacteria in numbers 1.3×1029 bacteria in oceans = 100 million times more cells than stars in vis Universe There are more microbes in a teaspoon of soil than there are people on the earth Human adults excrete their own weight in fecal bacteria every year ~1×1011: the same number of bacteria in 1 g of dental plaque as there are humans that have EVER lived 16,000,000 people worldwide die from infectious disease every year Microbiology by numbers. Nat Rev Microbiol 9, 628 (2011). Microbiology by numbers. Plos Biology 14, 18 (2016). https://doi.org/10.1038/nrmicro2644 https://doi.org/10.1371/journal.pbio.1002533  Bacteria Bacteria can be true pathogens, Opportunistics Pathogens opportunistic pathogens or Commensals commensals: Opportunistic pathogens: organisms that True pathogens: organisms Commensal bacteria: organisms that reside on under usual conditions do not cause that can cause disease in either surface or internal mucosae of the host disease, but are inclined to induce an healthy immunocompetent without harming it. infectious process in weaken individuals individuals Commensal → mutualistic relationship Today´s topics Section 1. Bacterial cell structure Section 2. Bacterial cell and colony morphology Section 3. Bacterial growth and metabolism Section 1. Bacterial cell structure Cell structure Prokaryotes (pro – before; karyote – nucleus) Unicellular Lack of membranous organelles Section 1. Bacterial cell structure Eukaryote vs prokaryote cells Section 1. Bacterial cell structure All bacteria have: Cytoplasm Ribosomes Nucleoid (DNA) Plasma membrane Complex and rigid cell wall (one exception) Some bacteria have: Capsule Flagella Pili/fimbriae Plasmids Some bacteria are able to produce: Endospores Section 1. Bacterial cell structure Cytoplasm: Jelly-like aqueous solution (cytosol) Three main components: 1. Macromolecules (proteins, mRNA, tRNA) 2. Small molecules: precursors of macromolecules, Cytoplasm metabolites, ATP, etc. 3. Inorganic ions: co-factors for metabolic activities Functions: Facilitate major chemical reactions of the cell Contains: nucleoid (DNA) and ribosomes Section 1. Bacterial cell structure Nucleoid Nucleoid (DNA): The bacterial chromosome Supercoiled to be fixed in a small area (nucleoid associated proteins) Double-stranded DNA Contains the essential genes for the life of the bacteria (core-genome) Section 1. Bacterial cell structure Plasmid Plasmid (“extra” DNA): Circular DNA molecule Replicates independently from the chromosome Several different plasmids may be present in each cell Each plasmid can be as a single copy or multiple copies Double-stranded DNA Some are conjugative, others not Contains additional genes, not essential Functions: Provide virulence factors (genes) Antibiotic resistance (genes) Others additional functions... Section 1. Bacterial cell structure Plasmid (“extra” DNA): conjugation Section 1. Bacterial cell structure Ribosomes: Ribosomes The cellular protein factory Proteins + rRNA = Ribosome Two subunits = large (50S) and small (30S) Conserved genetic code Two main applications = therapy + phylogeny Section 1. Bacterial cell structure Can you recognize the ribosomes?  Section 1. Bacterial cell structure FYI Ribosomes Poehlsgaard, J., Douthwaite, S. The bacterial ribosome as a target for antibiotics. Nat Rev Microbiol 3, 870–881 (2005). https://doi.org/10.1038/nrmicro1265  Section 1. Bacterial cell structure FYI Ribosomes: Applications = therapy & phylogeny Poehlsgaard, J., Douthwaite, S. The bacterial ribosome as a target for antibiotics. Nat Rev Microbiol 3, 870–881 (2005). https://doi.org/10.1038/nrmicro1265 Section 1. Bacterial cell structure Bacterial envelope: 1. Cytoplasmic or plasma membrane 2. Membrane-associated proteins 3. Cell wall (peptidoglycan layer) 4. In Gram negative bacteria: outer membrane + periplasmic space Bacterial envelope Gram Staining Pink: Gram-Negative Purple: Gram-Positive Section 1. Bacterial cell structure Bacterial envelope: Cell wall Composed by a unique polymer (peptidoglycan) Net or mesh-like structure Subunits: N-acetylglucosamine (NAG) + N-acetylmuramic (NAM) cross-linked with peptides Transpeptidase enzymes do the cross-liking (PBPs)* Cell wall Main function of cell wall Protection against mechanical damage and osmotic lysis Section 1. Bacterial cell structure Alternative structural bacterial envelopes Mycobacteria Mollicutes (Mycoplasma) Bacterial envelope contains mycolic acids No cell wall ~ no peptidoglycan layer Thick waxy cell wall Plasma membrane with sterols Acid-fast staining for identification Highly pleomorphic and osmotically unstable Section 1. Bacterial cell structure Flagella: Anchored to the bacterial cell envelope Multi-protein structure (engine) The number and position vary between bacteria Functions: Locomotion or bacterial motility Flagella Endoflagellum Section 1. Bacterial cell structure Pili/fimbriae: Fine, straight, hair-like appendages attached to cell wall Pili/fimbriae Known as “adhesins” Most common on Gram-negative bacteria Function Adhesion to host tissues (specificity) Contribute to antigenicity Section 1. Bacterial cell structure Endospores: Cryptobiotic state of dormancy and most durable type of cell found in nature Produced by Gram-positive bacteria Examples: pathogenic genera Bacillus and Clostridium Function Ensure survival during adverse environmental conditions Dormant highly resistant bodies Spore-producing bacteria and toxins: Once the spore has germinated, the vegetative bacilli are free to synthesize deadly bacterial toxins Today´s topics Section 1. Bacterial cell structure Section 2. Bacterial cell and colony morphology Section 3. Bacterial growth and metabolism Section 2. Bacterial cell and colony morphology Section 2. Bacterial cell and colony morphology Section 2. Bacterial cell and colony morphology Bacterial colony: “Theoretically” a bacterial colony is a macroscopic aggregate of bacteria in solid media (static), originated from a single bacterium. Bacterial colony in agar Colony Forming Unit (CFU) = 1 bacterium 1 bacterium 1 CFU Section 2. Bacterial cell and colony morphology Bacterial colony: Same species (Pseudomonas aeruginosa) different strains (genetically distinct organisms) Section 2. Bacterial cell and colony morphology Bacterial colony: Colonies may look different during time Two completely different Same species & same strain may bacterial species may produce produce different colony morphologies same colony morphology in a depending on the growth medium growth medium used. Today´s topics Section 1. Bacterial cell structure Section 2. Bacterial cell and colony morphology Section 3. Bacterial growth and metabolism Section 3. Bacterial growth and metabolism Bacterial growth: Bacteria replicate by binary fission (one mother cell results in two daughter cells) Specific environmental factors are required for the process to occurs Environmental factors 1. Nutrients (eg. glucose, nitrates) 2. pH (most pathogenic bacteria grow best at 7.2-7.4)particularlyenzymes 3. Ionic strength and osmotic pressure 4. Light 5. Temperature (most are mesophilic with growth at 30-37 °C) 6. Gaseous requirement: oxygen and carbon dioxide RaitiveOxidativespecies Section 3. Bacterial growth and metabolism Nutrient Bacterial growth curve: exhaustion & accumulation of toxic products Progressive death of cells Generation time Cells multiply at maximum rate Increase in cell size, active metabolism of cells but no Bacterial growth curve with 4 phases (in liquid medium) division Section 3. Bacterial growth and metabolism The result: (over)multiplication of bacteria in the wrong place = disease