Lecture 2 - Basic Structural Differences Between Pathogenic Microbes PDF

Lecture 2 – Basic structural difference between pathogenic microbes What is an infectious disease? ➔ Illness caused by infectious agents, such as bacteria, viruses, parasites or fungi, which can be spread directly or indirectly from one individual to another ➔ Parasites such as protozoa...

Lecture 2 – Basic structural difference between pathogenic microbes What is an infectious disease? ➔ Illness caused by infectious agents, such as bacteria, viruses, parasites or fungi, which can be spread directly or indirectly from one individual to another ➔ Parasites such as protozoa ➔ Indirectly spreading an infectious disease by touching surfaces or walking into a sneeze ➔ Infectious disease can only be passed on to susceptible persons COVID-19 and other pandemics ➔ Presently, more than 704 million people around the world have contracted COVID-19 and more than 7 million people have died ➔ There were THREE (3) other pandemics before COVID-19: (1) Malaria (2) Tuberculosis (3) HIV/AIDS ➔ Together responsible for approx. 2.7 million deaths a year ➔ This figure could increase over the next 1-2 years due to disruptions in healthcare as a result of the COVID-19 pandemic, which mainly affect low- and middle-income countries If we take COVID out of the situation TB is the 2nd most infectious disease ➔ These are caused by infectious agents ➔ In 2016, HIV is not TOP 10 because our treatment helped (2016) ➔ HIV still present due to lack of availabilities in the lower-income countries (2016) ➔ major milestones: chloritization of water and introduction of penicillin Spanish flu: towards the end of 1920 Factors influencing decrease in infectious disease mortality/morbidity There are FOUR (4) main factors: (1) Improvements in public health systems – chlorination of water which helped combat against diarrheal diseases (2) Improved environmental conditions – helped combat against malaria like proper garbage disposal (3) Development of immunization and antimicrobial chemotherapy – E.g. measles in Minnesota 2024 (4) The increasing ability to identify new pathogenic organisms – advances in technology Factors influencing increase in infectious disease mortality/morbidity There are FIVE (5) main factors: (1) Microbial adaptation – increase in antimicrobial resistance which is causing super resistance (2) Human behavior and practices – lack of childhood immunization (eg. Measles) and increase in internation air travel (eg. SARS-CoV-2, SARS), Poverty and war (infectious disease causes outbreak cant get meds during war due to lack of availability) (3) Emergence/re-emergence of more virulent strains of pathogens – (eg. SARS_CoV-2, and Ebola) (4) Climate change (eg. Chikungunya and Zika) (5) Bioterrorism (eg. Anthrax and Botulinum toxin) Basic structural differences between prokaryotic and eukaryotic microbes No nucleus No membrane DNA freely in the cytoplasm bound organelles Extra chromosomal DNA Membrane Allows DNA to be separated bound from cytoplasm organelles Gram-positive: Teichoic acids are major cell surface antigens. Present in cell wall of most Gram- positive bacteria so make them potential antibiotic targets. ➔ Teichoic acids play an important role Gram-negative: The O-polysaccharide of the lipopolysaccharide (LPS) is antigenic (O-antigen) and the lipid portion is toxic to humans and animals (endotoxic). These features are used to help identify different microbial strains and species, eg Salmonella spp. ➔ LPS helps prevent permeability Bacterial cell member ➔ Composed of phospholipid bilayer ➔ Acts as permeability barrier ➔ Some antimicrobials work by binding to the LPS in the outer membrane and damaging both the outer and inner cell membranes of Gram-negative bacteria Bacterial cell wall ➔ The cell wall is a good target for viruses ➔ Rigid and protects the organism from differences in osmotic tension between the cell and the environment ➔ Gram-positive bacteria have thick multilayered peptidoglycan cell walls and a cell membrane ➔ Gram-negative cell walls have inner and outer membranes as well as a thinner peptidoglycan layer ➔ Some antimicrobials act by preventing synthesis of cell walls in susceptible microbes by inhibiting peptidoglycan synthesis What happens to bacterial cells during gram staining? ➔ The crystal violet binds to the peptidoglycan within the bacterial cell ➔ When the iodine mordant is added a large crystal violet and iodine complex is formed ➔ When the decolourizer is added, in the gram-positive cell the complex remains due to the thicker peptidoglycan layer whereas in gram negative the thinner peptidoglycan and also the presence of more lipids causes the complex to wash away/ be removed and the counter stain is added (safranin) and stains in the gram-negative bacteria. Bacterial morphology / shapes ➔ Shape of cells primarily determined by peptidoglycan layer ➔ Aids with identification of organism Flagella ➔ Long protein filaments of uniform length that are responsible for cell motility ➔ Propel cell by spinning around axis in corkscrew motion ➔ Virulence factor (eg V. cholera, C. jejuni) – thought to propel microbe through mucus lining of small intestine (linked to diarrheal disease) ➔ Highly antigenic (H antigen) – Used for serotyping of Salmonella Glycocalyx – External Capsule or Slime Layer ➔ Sticky, viscous material which forms an extracellular coating → usually composed of polysaccharides, polypeptides OR both ➔ If tightly bound to cell wall: capsule ➔ If unorganized and loosely bound: slime layer ➔ Virulence factor: allow cells to adhere to surfaces and protect bacteria from antibodies and phagocytosis → contributes to pathogenicity Phagocytosis: helps organisms to be infectious Viruses ➔ Possess 2 main components: (1) Genome consisting of either single/double stranded RNA or DNA (2) Protein-containing capsid designed to protect the genome ➔ May or may not be surrounded by an envelope (lipid-containing membrane surrounding capsid) ➔ Envelope derived from host cell membranes Lipid layer taken up from the host to make the envelope Virus Capsids  ➔ Composed of protein molecules → joined to make units called capsomers ➔ Capsid proteins are encoded by the virus genome ➔ Basic morphology: Tail fibres Reproduction of viruses ➔ Contain no functional organelles or carry out no metabolic processes → cannot divide ➔ Too small to carry enough genetic material to code for gene products necessary to produce new viruses ➔ Infect host cell and use the host’s replication processes to produce identical progeny virus particles (virions) ➔ Viruses do not metabolize or grow, but are assembled into their mature form Antiviral therapy ➔ Controlled measures ➔ Targets virus via replication ➔ Antivirals typically work by preventing the virus from replicating ➔ Some work by stopping virus from infecting host cell altogether Fungi ➔ Non-photosynthetic eukaryotes ➔ Multicellular/Filamentous: moulds ➔ Unicellular: yeasts ➔ Pathogenic fungi can cause diseases ranging from skin infections (superficial mycoses) to more serious systemic infections (deep mycoses) ➔ Cell wall composed of chitin (instead of bacterial peptidoglycan) and membrane contains ergosterol (instead of mammalian cholesterol) – unique features ➔ Useful features for treating fungal infections Protozoa ➔ There are THREE (3) main characteristics: (1) Eukaryotic (2) Unicellular (3) Lack cell wall ➔ Reproduce asexually but some exceptions eg Paramecium ➔ Trophozoite: Vegetative state that feeds on bacteria and particulate nutrients ➔ Cyst: Dormant stage that allows survival under adverse environmental conditions ➔ Very few species pathogenic to humans