Microbial Mechanisms of Pathogenicity Prof Khaled H AbuElteen

Microbial Mechanisms of Pathogenicity Prof. Khaled H. Abu-Elteen

Infection and Disease A. Definitions B. Generalized Stages of Infection C. Virulence Factors and Toxins

A. Definitions w Disease and Infectious Disease • Any deviation from a condition of good health and well-being • Infectious Disease · A disease condition caused by the presence or growth of infectious microorganisms or parasites

A. Definitions w Pathogenicity and Virulence • Pathogenicity • The ability of a microbe to cause disease • This term is often used to describe or compare species • Virulence • The degree of pathogenicity in a microorganism • This term is often used to describe or compare strains within a species

Definitions w Acute infection vs. chronic infection • Acute Infection • An infection characterized by sudden onset, rapid progression, and often with severe symptoms • Chronic Infection • An infection characterized by delayed onset and slow progression

Definitions w Primary infection vs. secondary infection • Primary Infection • An infection that develops in an otherwise healthy individual • Secondary Infection • An infection that develops in an individual who is already infected with a different pathogen

Definitions w Localized infection vs. systemic infection • Localized Infection • An infection that is restricted to a specific location or region within the body of the host • Systemic Infection • An infection that has spread to several regions or areas in the body of the host

Definitions w Clinical infection vs. subclinical infection • Clinical Infection • An infection with obvious observable or detectable symptoms • Subclinical Infection • An infection with few or no obvious symptoms

Definitions w Opportunistic infection • An infection caused by microorganisms that are commonly found in the host’s environment. This term is often used to refer to infections caused by organisms in the normal flora.

Definitions w The suffix “-emia” • A suffix meaning “presence of an infectious agent” • Bacteremia = Presence of infectious bacteria • Viremia = Presence of infectious virus • Fungemia = Presence of infectious fungus • Septicemia = Presence of an infectious agent in the bloodstream

Definitions w The suffix “-itis” • A suffix meaning “inflammation of” • Examples: – Pharyngitis = Inflammation of the pharynx – Endocarditis = Inflammation of the heart chambers – Gastroenteritis = Inflammation of the gastointestinal tract

Definitions w Epidemiology • The study of the transmission of disease w Communicable Disease • A disease that can be transmitted from one individual to another w Noncommunicable Disease • A disease that is not transmitted from one individual to another

Definitions w Endemic Disease • A disease condition that is normally found in a certain percentage of a population w Epidemic Disease • A disease condition present in a greater than usual percentage of a specific population w Pandemic Disease • An epidemic affecting a large geographical area; often on a global scale

Definitions w Reservoir of Infection • The source of an infectious agent w Carrier • An individual who carries an infectious agent without manifesting symptoms, yet who can transmit the agent to another individual w Fomites • Any inanimate object capable of being an intermediate in the indirect transmission of an infectious agent

Definitions • Animal Vectors • An animal (nonhuman) that can transmit an infectious agent to humans • Two types: mechanical and biological • Mechanical animal vectors: The infectious agent is physically transmitted by the animal vector, but the agent does not incubate or grow in the animal; e. g, the transmission of bacteria sticking to the feet of flies • Biological animal vectors: The infectious agent must incubate in the animal host as part of the agent’s developmental cycle; e. g, the transmission of malaria by infected mosquitoes

Definitions w Direct Mechanisms of Disease Transmission • Directly From Person to Person • Examples: Direct Skin Contact Airborne (Aerosols)

Definitions w Indirect Mechanisms of Disease Transmission • Examples: Food & Waterborne Transmission Fomites Animal Vectors

Pathogenicity - ability to cause disease Virulence - degree of pathogenicity Many properties that determine a microbe’s pathogenicity or virulence are unclear or unknown w But, when a microbe overpowers the hosts defenses, infectious disease results! w

Molecular Determinants of Pathogenicity Attachment to host tissues Production and delivery of various factors Replication and evasion of immunity Damage to host tissues

Microbial Mechanisms of Pathogenicity: How Microorganisms Cause Disease

Portals of Entry w 1. Mucus Membranes w 2. Skin w 3. Parentarel

1. Mucus Membranes w A. Respiratory Tract • microbes inhaled into mouth or nose in droplets of moisture or dust particles • Easiest and most frequently traveled portal of entry

Common Diseases contracted via the Respiratory Tract w w w w Common cold Flu Tuberculosis Whooping cough Pneumonia Measles Diphtheria

Mucus Membranes w B. Gastrointestinal Tract • microbes gain entrance thru contaminated food & water or fingers & hands • most microbes that enter the G. I. Tract are destroyed by HCL & enzymes of stomach or bile & enzymes of small intestine

Common diseases contracted via the G. I. Tract w Salmonellosis • Salmonella sp. w Shigellosis • Shigella sp. w Cholera • Vibrio cholorea w Ulcers • Helicobacter pylori w Clostridium botulinum Botulism • Clostridium botulinum

Fecal - Oral Diseases w 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 w Poor personal hygiene. w

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

Mucus Membranes w D. Conjunctiva – • mucus membranes that cover the eyeball and lines the eyelid w Trachoma • Chlamydia trachomatis

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

3 rd Portal of Entry: Parentarel w w w Microorganisms are deposited into the tissues below the skin or mucus membranes Punctures and scratches injections bites surgery

Preferred Portal of Entry w w Just because a pathogen enters your body it does not mean it’s going to cause disease. pathogens - preferred portal of entry

Preferred Portal of Entry w Streptococcus pneumoniae • if inhaled can cause pneumonia • if enters the G. I. Tract, no disease w Salmonella typhi • if enters the G. I. Tract can cause Typhoid Fever • if on skin, no disease

Number of Invading Microbes LD 50 - Lethal Dose of a microbes toxin that will kill 50% of experimentally inoculated test animal w ID 50 - infectious dose required to cause disease in 50% of inoculated test animals w • Example: ID 50 for Vibrio cholerea 108 cells (100, 000 cells) • ID 50 for Inhalation Anthrax - 5, 000 to 10, 000 spores ? ?

How do Bacterial Pathogens penetrate Host Defenses? 1. Adherence - almost all pathogens have a means to attach to host tissue Binding Sites adhesins ligands

Some cells use fimbriae to adhere. Fimbriae can play a role in tissue tropism. Example attachment of Candida to vaginal epithelial cells

Adhesins and ligands are usually on Fimbriae Neisseria gonorrhoeae w ETEC (Entertoxigenic E. coli) w w Bordetello pertussis

Bacteria typically employ proteins known as Adhesins to attach to host tissues, which usually are located on ends of fimbriae. Alternatively, adhesins can consist of glycocalyx.

2. Capsules w w w w K. pneumoniae Prevent phagocytosis attachment Streptococcus pneumoniae Klebsiella pneumoniae Haemophilus influenzae Bacillus anthracis Streptococcus mutans

Avoidance of Phagocytosis Capsules are Involved in avoidance of phagocytemediated recognition and attachment.

Cell Wall Components M protein: Found on cell surface and fimbriae of Streptococcus pyogenes. Mediates attachment and helps resist phagocytosis. M-protein is heat and acid resistant Waxes [ Mycolic Acid]: In cell wall of Mycobacterium tuberculosis helps resist digestion after phagocytosis and can multiply inside WBC.

3. Enzymes w Many pathogens secrete enzymes that contribute to their pathogenicity

Enzymes and toxins that harm eukaryotic cells.

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

B. Hemolysins - cause the lysis of RBC’s Streptococci

1. Alpha (α) Hemolytic Streptococci - secrete hemolysins that cause the incomplete lysis or RBC’s Incomplete Lysis of RBC

2. Beta (β) Hemolytic Streptococci - secrete hemolysins that cause the complete lysis of RBC’s Complete Lysis of RBC

3. Gamma (γ) Hemolytic Streptococci do not secrete any hemolysins

C. Coagulase - cause blood to coagulate Blood clots protect bacteria from phagocytosis from WBC’s and other host defenses w Staphylococcus aureus - are often coagulase positive Fibrinogen --------- Fibrin ( Clot) w

D. Kinases - enzymes that dissolve blood clots 1. Streptokinase - Streptococci w 2. Staphylokinase - Staphylococci w w Helps to spread bacteria - Bacteremia w Streptokinase - used to dissolve blood clots in the Heart (Heart Attacks due to obstructed coronary blood vessels)

E. Hyaluronidase w Breaks down Hyaluronic acid (found in connective tissues) “Spreading Factor” w mixed with a drug to help spread the drug through a body tissue w Streptococci, Staphylococci, Clostridia and pneumococci. w

F. Collagenase w Breaks down collagen (found in many connective tissues) w Clostridium perfringens - Gas Gangrene • uses this to spread through muscle tissue

Tissue Damage Caused by Microbial Enzymes of Clostridium perfringens Severe gangrene caused by Clostridium perfringens. Source: Tropical Medicine and Parasitology, 1997

G. Necrotizing Factor - causes death (necrosis) to tissue cells “Flesh Eating Bacteria” Necrotizing fasciitis

H. Lecithinase Destroys lecithin ( phosphatidylcholine) component of plasma membrane. w Allowing pathogen to spread w Clostridium perfringens w

Summary of How Bacterial Pathogens Penetrate Host Defenses 1. Adherence w 2. Capsule w 3. Enzymes w • • A. leukocidins B. Hemolysins C. Coagulase D. Kinases E. Hyaluronidase F. Collagenase G. Necrotizing Factor H. Lecithinase

4. Toxins Poisonous substances produced by microorganisms w toxins - primary factor - pathogenicity w 220 known bacterial toxins w • 40% cause disease by damaging the Eukaryotic cell membrane w Toxemia • Toxins in the bloodstream • Toxigenicity: Capacity of microorganisms to produce toxins.

Two Types of Toxins w 1. Exotoxins • secreted outside the bacterial cell w 2. Endotoxins • part of the outer cell wall of Gram (-) bacteria. ? ?

Exotoxins versus Endotoxins

I- Exotoxins w Mostly seen in Gram (+) Bacteria w Most gene that code for exotoxins are located on plasmids or phages

Three Types of Exotoxins w 1. Cytotoxins • kill cells e. g. Diphtheria toxin w 2. Neurotoxins • interfere with normal nerve impulses. e. g. Botulinum Toxin w 3. Enterotoxins • effect cells lining the G. I. Tract. e. g. Cholera toxin or choleragen.

Response to Toxins If exposed to exotoxins: antibodies against the toxin (antitoxins) w Exotoxins inactivated ( heat, formalin or phenol) no longer cause disease, but stimulate the production of antitoxin • altered exotoxins - Toxoids w Toxoids - modified toxin by heat, chemical, radiation, that have lost their toxicity. Injected to stimulate the production of antitoxins and provide immunity. w

Example: DPT Vaccine w D - Diphtheria • Corynebacterium diphtheriae w P - Pertussis • Bordetello pertussis w T - Tetanus • Clostridium tetani DPT - Diphtheria Toxoid Pertussis Antigen Tetanus Toxoid

Required Immunizations in Jordan w w w 1. Diphtheria 2. Pertussis 3. Tetanus 4. Measles 5. Mumps 6. Rubella w w w Corynebacterium diphtheriae Bordetello pertussis Clostridium tetani Measles virus Mumps virus Rubella virus • German Measles 7. Polio w 9. Hepatitis B w Polio virus w Hepatitis B Virus w

Most genes that code for exotoxins - plasmids or phages Lysogenic convergence w Diphtheria w Cytotoxin inhibits protein synthesis resulting in cell death w Pseudomembrane w • fibrin, dead tissue, bacterial cells

Lysogenic Convergence Scarlet Fever w Streptococcus pyogenes w • lysogenic convergence w cytotoxin - damages blood capillaries and results in a skin rash • Strep Thoat with a rash

Rash of Scarlet Fever Caused by Erythrogenic Toxins of Streptococcus pyogenes

Diseases Caused by Staphylococcal Toxins Scalded Skin Syndrome Toxic Shock Syndrome

Diseases caused by Neurotoxins w 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

Tetanus (Lock Jaw) w Clostridium tetani Gram (+), spore-forming, anaerobic rod w neurotoxin acts on nerves, resulting in the inhibition of muscle relaxation w tetanospasmin - “spasms” or “Lock Jaw” w

Muscle Spasms of Tetanus are Caused by Neurotoxin of Clostridium tetani Neonatal Tetanus (Wrinkled brow and risus sardonicus) Source: Color Guide to Infectious Diseases, 1992

Diseases caused by Enterotoxins w Cholera • Vibrio cholerae • Gram (-) comma shaped rods

Cholera toxin Converts ATP into c. AMP w causes cells to excrete Cl- ions and inhibits absorption of Na+ ions w Electrolyte imbalance w H 2 O leaves by osmosis w H 2 O Loss (Diarrhea) w Two polypeptides: A (active) and B (binding). The A subunit of enterotoxin causes epithelial cells to discharge large amounts of fluids and electrolytes. w

Severe cases, 12 - 20 liters of liquid lost in a day w Untreated cases - Mortality Rate about 50% w Mortality may be reduced to about 1% • administering fluids and electrolytes

Vibrio Enterotoxin Causes Profuse Watery Diarrhea Rice-water stool of cholera. The A subunit of enterotoxin causes epithelial cells to discharge large amounts of fluids and electrolytes. Source: Tropical Medicine and Parasitology, 1995

EHEC (Enterohemorrhagic E. coli) E. coli (0157: H 7) w enterotoxin causes a hemolytic inflammation of the intestines w results in bloody diarrhea w • Toxin • • • alters the 60 S ribosomal subunit inhibits Protein Synthesis Results in cell death lining of intestine is “shed” Bloody Diarrhea (Dysentary)