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 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 w 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!

Molecular Determinants of Pathogenicity Production and delivery of various factors Attachment to host tissues 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 Common cold w Flu w Tuberculosis w Whooping cough w Pneumonia w Measles w 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 Botulism Clostridium botulinum

Fecal - Oral Diseases w These pathogens enter the G.I. Tract at one end and exit at the other end. w Spread by contaminated hands & fingers or contaminated food & water w Poor personal hygiene.

Mucus Membranes of the Genitourinary System - STD’s Gonorrhea Neisseria gonorrhoeae Syphilis Treponema pallidum Chlamydia 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

2nd 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

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

Preferred Portal of Entry w Just because a pathogen enters your body it does not mean it’s going to cause disease. w 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 w 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 Example: ID 50 for Vibrio cholerea 10 8 cells (100,000,000 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 w Neisseria gonorrhoeae w ETEC (Entertoxigenic E. coli) 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 Prevent phagocytosis w attachment w Streptococcus pneumoniae w Klebsiella pneumoniae w Haemophilus influenzae w Bacillus anthracis w Streptococcus mutans K. pneumoniae

Avoidance of Phagocytosis Capsules are Involved in avoidance of phagocyte- mediated 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 w 1. Kills WBC’s which prevents phagocytosis w 2. Releases & ruptures lysosomes 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 w Blood clots protect bacteria from phagocytosis from WBC’s and other host defenses w Staphylococcus aureus - are often coagulase positive Fibrinogen Fibrin ( Clot)

D. Kinases - enzymes that dissolve blood clots w 1. Streptokinase - Streptococci w 2. Staphylokinase - Staphylococci 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) w “Spreading Factor” w mixed with a drug to help spread the drug through a body tissue w Streptococci, Staphylococci, Clostridia and pneumococci.

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

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

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

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

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

4. Toxins w Poisonous substances produced by microorganisms w toxins - primary factor - pathogenicity w 220 known bacterial toxins 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 w 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.

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

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

Lysogenic Convergence w Scarlet Fever w Streptococcus pyogenes 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 w Gram (+), spore-forming, anaerobic rod w neurotoxin acts on nerves, resulting in the inhibition of muscle relaxation w tetanospasmin - “spasms” or “Lock Jaw”

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

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

Cholera toxin w Converts ATP into cAMP 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.

Severe cases, 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

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 Vibrio Enterotoxin Causes Profuse Watery Diarrhea

EHEC (Enterohemorrhagic E. coli) w E. coli (0157:H7) w enterotoxin causes a hemolytic inflammation of the intestines w results in bloody diarrhea Toxin alters the 60S ribosomal subunit inhibits Protein Synthesis Results in cell death lining of intestine is “shed” Bloody Diarrhea (Dysentary)

More on Toxins

II- Endotoxins Part of outer membrane surrounding gram-negative bacteria. Endotoxin is lipid portion of lipopolysaccharides (LPS), called lipid A. Effect exerted when gram-negative cells die and cell walls undergo lysis, liberating endotoxin. All produce the same signs and symptoms: Chills, fever, weakness, general aches, blood clotting and tissue death, shock, and even death. Can also induce miscarriage. Fever: Pyrogenic response is caused by endotoxins.

Exotoxins vs. Endotoxins

Endotoxin is LPS

Endotoxins (Continued) Endotoxins do not promote the formation of effective antibodies. Organisms that produce endotoxins include: Salmonella typhi Proteus spp. Pseudomonas spp. Neisseria spp. Medical equipment that has been sterilized may still contain endotoxins. Limulus amoebocyte assay (LAL) is a test used to detect tiny amounts of endotoxin.

Events leading to fever: Gram-negative bacteria are digested by phagocytes. LPS is released by digestion in vacuoles, causing macrophages to release interleukin-1 (IL-1). IL-1 is carried via blood to hypothalamus, which controls body temperature. IL-1 induces hypothalamus to release prostaglandins, which reset the body’s thermostat to higher temperature.

Microbial Mechanisms of Pathogenicity: How Microorganisms Cause Disease

III. B. The Normal Flora of Humans w Types of Symbiosis Mutualism A symbiotic relationship in which both species benefit Commensalism A symbiotic relationship in which one species benefits, and the other species is neither helped nor harmed

III. B. The Normal Flora of Humans w Types of Symbiosis (cont.) Parasitism A symbiotic relationship in which one species benefits, and the other species is harmed Generally, the species that benefits (the parasite) is much smaller than the species that is harmed (the host)

III. B. The Normal Flora of Humans w Normal flora is present in skin upper respiratory tract oral cavity intestine, especially large intestine vaginal tract w Very little normal flora in eyes & stomach

III. B. The Normal Flora of Humans w Notably absent in most all internal organs Absent in: lower respiratory tract muscle tissue blood & tissue fluid cerebrospinal fluid peritoneum pericardium meninges

III. B. The Normal Flora of Humans w Benefits of the normal flora Nutrient production/processing eg Vitamin K production by E. coli Competition with pathogenic microbes Normal development of the immune system w Normal flora and opportunistic infections

III. C. Generalized Stages of Infection 1.Entry of Pathogen Portal of Entry 2.Colonization Usually at the site of entry 3.Incubation Period Asymptomatic period Between the initial contact with the microbe and the appearance of the first symptoms

III. C. Generalized Stages of Infection 4.Prodromal Symptoms Initial Symptoms 5.Invasive period Increasing Severity of Symptoms Fever Inflammation and Swelling Tissue Damage Infection May Spread to Other Sites

III. C. Generalized Stages of Infection 6.Decline of Infection 5.Convalescence

Course of Infectious Disease Incubation period is the interval between exposure and illness onset. Convalescence is a time of recuperation and recovery from illness. Depending on various factors an individual may still be infectious during either incubation or convalescence.