Microbial Mechanisms of Pathogenicity Chapter 15 Microbial Mechanisms of Pathogenicity

Microbial Mechanisms of Pathogenicity Pathogenicity The ability to cause disease Virulence The extent of pathogenicity Many properties that determine a microbe’s pathogenicity or virulence are unclear or unknown But, when a microbe overpowers the hosts defenses, disease results! They need to gain entry, adhere, penetrate and cause damage to cause disease.

Disease: Pathogens may cause damage to host Direct damage in the immediate vicinity Grow and multiply and clog cells and passageways Far removed from site of invasion by toxins Toxins spread through blood and lymph By hypersensitivity The host’s reaction may cause the damage

Portals of Entry Entry of a Microbe Need to adhere, penetrate, and then cause damage Gain access via portal of entry and may a have preferred portal of entry - Streptococcus pneumoniae via GI tract? Small pox via vein? Portals of Entry: Mucous membranes Respiratory GI Urogenital conjunctiva Skin Tough so rare - Necator americanus - hookworm Parenteral route Puncture or injection

Mucous Membranes: Respiratory Respiratory Tract microbes inhaled into mouth or nose in droplets of moisture or dust particles Easiest and most frequently traveled portal of entry Common cold Flu Tuberculosis Whooping cough Pneumonia Measles Strep Throat Diphtheria

Mucous membranes: G.I. Tract Salmonellosis Salmonella sp. Shigellosis Shigella sp. Cholera Vibrio cholorea Ulcers Helicobacter pylori Botulism Clostridium botulinum Fecal - Oral Diseases These pathogens enter the G.I. Tract at one end and exit at the other end. Spread by contaminated hands & fingers or contaminated food & water Poor personal hygiene.

Mucous Membranes of the Genitourinary System - STD’s Gonorrhea Neisseria gonorrhoeae Syphilis Treponema pallidum Chlamydia Chlamydia trachomatis HIV Herpes Simplex II

Mucous Membranes: Conjunctiva mucous membranes that cover the eyeball and lines the eyelid Trachoma Chlamydia trachomatis

2nd Portal of Entry: Skin Skin - the largest organ of the body. When unbroken is an effective barrier for most microorganisms. Some microbes can gain entrance thru openings in the skin: hair follicles and sweat glands

3rd Portal of Entry: Parenteral Microorganisms are deposited into the tissues below the skin or mucous membranes Punctures injections bites scratches surgery splitting of skin due to swelling or dryness

Preferred Portal of Entry Just because a pathogen enters your body it does not mean it’s going to cause disease. pathogens - preferred portal of entry Small pox via variolation Streptococcus pneumoniae if inhaled can cause pneumonia if enters the G.I. Tract, no disease Salmonella typhi if enters the G.I. Tract can cause Typhoid Fever if on skin, no disease

Numbers of Invading Microbes ID50: Infectious dose for 50% of the test population LD50: Lethal dose (of a toxin) for 50% of the test population Example: ID50 for Vibrio cholerea 108 cells (100,000,000 cells) ID50 for Inhalation Anthrax - 5,000 to 10,000 spores ????

ID50 and LD50 for Bacillus anthracis Portal of entry ID50 Skin ??? endospores Inhalation 10,000-20,000 endospores Ingestion 250,000-1,000,000 endospores

Key traits to a pathogen The ability to: 1. Adherence To host surfaces and not be washed off 2. Avoid phagocytosis Prevent host defenses from destroying 3. Penetrate Get into host and spread 4. Produce Enzymes Spread, prevent host defenses and cause damage at or near site of infection 5. Produce Toxins Cause damage at distant site

Adherence Adhesions/ligands bind to receptors on host cells so won’t get flushed off. Mechanisms to adhere and avoid host defenses: Glycocalyx Streptococcus mutans Dextran (plaque) Waxes Mycobacteria Fimbriae Escherichia coli M protein Streptococcus pyogenes Tapered end w/ hooks Treponema pallidum

Capsules Prevent phagocytosis and help with attachment (adherence) Streptococcus pneumoniae Klebsiella pneumoniae Haemophilus influenzae Bacillus anthracis Streptococcus mutans Yersinia pestis

Enzymes to help penetration Many pathogens secrete enzymes that contribute to their pathogenicity: Increase virulence by use of enzymes And avoid phagocytosis Coagulase Coagulate blood - wall off from host make boil Kinases Digest fibrin clot - allow spreading streptokinase and staphylolinase Hyaluronidase Hydrolyses hyaluronic acid connective tissue Collagenase Hydrolyzes collagen IgA proteases Destroy IgA antibodies Hemolysins lyse RBC’s

Hemolysins Alpha Hemolytic Streptococci Beta Hemolytic Streptococci secrete hemolysins that cause the incomplete lysis or RBC’s Beta Hemolytic Streptococci - secrete hemolysins that cause the complete lysis of RBC’s

Leukocidins Enzymes that attack certain types of WBC’s 1. Kills WBC’s which prevents phagocytosis 2. Releases & ruptures lysosomes lysosomes - contain powerful hydrolytic enzymes which then cause more tissue damage

Enzymes: Necrotizing Factor “Flesh Eating Bacteria” Necrotizing fasciitis causes death (necrosis) to tissue cells

Summary of How Bacterial Pathogens Penetrate Host Defenses 1. Adherence 2. Capsule 3. Enzymes leukocidins Hemolysins Coagulase Kinases Hyaluronidase Collagenase Necrotizing Factor

Penetration into the Host Cell Figure 15.2

Toxins Provide properties to spread and cause damage to the host. Compare endotoxins and exotoxins Endotoxins from inside the cell. Released upon cell lysis. Exotoxins are secreted out of the cell during cell life. Toxin Substances that contribute to pathogenicity Toxigenicity Ability to produce a toxin Toxemia Presence of toxin the host's blood Toxoid Inactivated toxin used in a vaccine Antitoxin Antibodies against a specific toxin

Exotoxins Mostly seen in Gram (+) Bacteria Most gene that code for exotoxins are located on plasmids or phages Figure 15.4a

Exotoxin Exotoxin Source Mostly Gram + Metabolic product By-products of growing cell Chemistry Protein Water soluble Fever? No Neutralized by antitoxin Yes LD50 Small - Very potent 1 mg of Clostridium botulinum toxin can kill 1 million guinea pigs

Exotoxins - three types 1. Cytotoxins kill cells 2. Neurotoxins interfere with normal nerve impulses 3. Enterotoxins effect cells lining the G.I. Tract Many toxins have A-B subunit toxins or type III toxins A - active Causes change in host B - binding Figure 15.5

Exotoxins Superantigens or type I toxins Cause an intense immune response due to release of cytokines from host cells Fever, nausea, vomiting, diarrhea, shock, death

Exotoxins Cholera enterotoxin Membrane-disrupting toxins or type II toxins Lyse host’s cells by: Making protein channels in the plasma membrane (e.g., leukocidins, hemolysins) Disrupting phospholipid bilayer Cholera enterotoxin Vibrio cholerae Gram (-) comma shaped rods

Exotoxins Exotoxin Lysogenic conversion • Corynebacterium diphtheriae A-B toxin type III. Inhibits protein synthesis. + • Streptococcus pyogenes Membrane-disrupting. Type II Erythrogenic. • Clostridium botulinum A-B toxin. Neurotoxin - flaccid paralysis Botox • C. tetani A-B toxin. Neurotoxin - prevents CNS inhibition - spastic paralysis • Vibrio cholerae A-B toxin. Enterotoxin. Stimulates cAMP to cause severe diarrhea • Staphylococcus aureus Superantigen. Type I. Enterotoxin.

Botox Botulism Clostridium botulinum Gram (+), anaerobic, spore-forming rod, found in soil works at the neuromuscular junction prevents impulse from nerve cell to muscle cell results in muscle paralysis Botulus – latin word for sausage (first known as sausage disease) C. botulinum does not grow in sausage today mainly due to nitrites added. Infant botulism 250 per yr., most associated with honey due to little microbial flora in G.I.

Tetanus (Lock Jaw) Clostridium tetani Gram (+), spore-forming, anaerobic rod neurotoxin acts on nerves, resulting in the inhibition of muscle relaxation Tetanospasmin - “spasms” or “Lock Jaw” 50 cases a yr. in U.S. 1 million per yr. Worldwide 50% in newborns – because they dress severed umbilical cord with soil, clay or cow dung Tetanospasmin inhibits the release of acetylcholine by interfering with activity of cholinesterase (enzyme that normally breaks down acetylcholine)

Endotoxin Figure 15.4b

Endotoxins Source Gram– Metabolic product Present in LPS of outer membrane Chemistry Lipid Fever? Yes Neutralized by antitoxin No LD50 Relatively large

Endotoxins - part of the Gram (-) Bacterial cell wall LPS (Lipopolysaccharides) O Antigen Lipid A Heat Stable (exotoxins are typically heat liable) Lipid A - Toxin portion of the LPS responsible for Fever that is associated with many Gram (-) Bacterial infections Gram (-) cells are “digested” endotoxins are released - fever Antibiotics E. coli (0157:H7) enterotoxin causes a hemolytic inflammation of the intestines results in bloody diarrhea

Endotoxins Figure 15.6

Non bacteria pathogens Viruses Protozoa Fungi Algae Helminths

Cytopathic Effects of Viruses Table 15.4

Pathogenic Properties of Fungi Fungal waste products may cause symptoms Chronic infections provoke an allergic response Tichothecene toxins inhibit protein synthesis Fusarium Proteases Candida, Trichophyton Capsule prevents phagocytosis Cryptococcus Ergot toxin Claviceps

Pathogenic Properties of Fungi Aflatoxin Aspergillus on peanuts? Mycotoxins Neurotoxins: Phalloidin, amanitin Amanita “death angel” - Liver damage

Pathogenic Properties of Protozoa Presence of protozoa Protozoan waste products may cause symptoms Avoid host defenses by Growing in phagocytes Antigenic variation

Pathogenic Properties of Helminths Use host tissue Presence of parasite interferes with host function Parasite's metabolic waste can cause symptoms Death can cause excessive immune reaction leading to more symptoms

Pathogenic Properties of Algae Neurotoxins produced by dinoflagellates Saxitoxin Paralytic shellfish poisoning

Portals of Exit Respiratory tract Coughing, sneezing Gastrointestinal tract Feces, saliva Genitourinary tract Urine, vaginal secretions Skin Blood Biting arthropods, needles/syringes

Mechanisms of Pathogenicity Figure 15.9