Infection and Disease II Pathogenicity and Infection

ELISA -- Enzyme-Linked Immunosorbent Assay Direct ELISA -- detects __________ (i.e. virus, bacterium) Indirect ELISA -- detects ______________ to the antigen. HIV ELISA is an example. Antibody-based detection methods

HIV Indirect ELISA animation activities/elisa/technique.html? activities/elisa/technique.html?

Pathogenicity and Infection Non-specific host defenses Non-specific host defenses Entry of the pathogen into the host Entry of the pathogen into the host Colonization and growth Colonization and growth Virulence Virulence Toxins Toxins

Some terms Pathogen (or ‘true pathogen’) -- can cause infection and disease in a _____________ host Opportunistic pathogen -- only pathogenic to non- ______________ individuals or when introduced into a normally ___________ part of the body Virulence -- degree of __________________ of a parasite Virulence factors -- _________________ of the pathogen which allow it to successfully invade and colonize a host

Non-specific host defenses Anatomical defenses Anatomical defenses Effect of age, stress, and diet on susceptibility Effect of age, stress, and diet on susceptibility

Physical Barriers and Anatomical Defenses

Compound in Saliva Protects Against E. coli Scientists from the University of Calgary have identified a protein produced by salivary glands that, when administered orally, can significantly reduce diarrhea and weight loss associated with Escherichia coli infection. They report their findings in the October 1998 issue of the journal Infection and Immunity. In the study, the researchers investigated the ability of the protein, known as epidermal growth factor (EGF), to protect rabbits from the effects of an experimental E. coli infection. The researchers found that daily treatment with EGF prevented the occurrence of diarrhea and weight loss. They also found lower colonization rates in the intestines of treated rabbits. "The findings demonstrate that oral EGF administration inhibits the production of diarrhea and reduction in weight gain seen in weanling rabbits infected with attaching-effacing E. coli, " say the researchers. "These observations suggest a role for EGF in protecting the gastrointestinal tract from colonization from bacterial pathogens.” (A. Buret, M.E. Olson, D. Grant Gall, and J.A. Hardin Effects of orally administered epidermal growth factor on enteropathogenic Escherichia coli infection in rabbits. Infection and Immunity. 66: )

Susceptibility to Infectious Disease Age -- ___________ and ____________ more susceptible. Why?  infants -- undeveloped normal flora,undeveloped immune system  elderly -- immune response declines, anatomical changes Stress -- in rats: fatigue, exertion, poor diet, dehydration, drastic climatic changes increase_________________ and___________________ of infections.  Hormone imbalance plays important role. Diet -- famine and infectious disease correlated (e.g. cholera). Overeating may have also an effect.  Key may be disruption of __________________ ______________  Not eating a particular substance needed by normal flora can have effect (e.g. a vitamin)

How they get in Tissue specificity (of the pathogen) is a serious barrier to the entry of most microorganisms (more on this later) l Discussed in viruses, also true of other pathogenic microorganisms: often (usually) only infect specific tissues and cell types. l Notable (mainly bacterial) exceptions exist, e.g. Streptococcus pyogenes and Staphylococcus aureus. So, how do microorganisms “get into” (colonize and establish in) the host?? l In the first place some of them don’t have to “get in” to be pathogenic… How can this be? They might already be there (in the normal flora or as latent infections) Called infection from an “endogenous” source

Exogenous infections Skin: portals are bites, digestive enzymes, needles, surgery, wounds, and catheters. High speed photo of unstifled sneeze Respiratory tract: location (upper or lower) somewhat dependent on size, attachment. Portal of entry to the greatest ________________ of pathogens. GI tract: ________ production (e.g. Staph. aureus, Clostridium perfringens) or directly through intestinal (and stomach, in the case of Helicobacter) epithelium

Exogenous Infectious Agents Entering via the skin: Staph. aureus; Strep. pyogenes; herpes simplex type I, HIV, and various viruses; assorted fungi; Clostridium tetani and C. perfringens; Haemophilus aegyptum, Acanthamoeba and assorted protozoa, etc.Entering via the skin: Staph. aureus; Strep. pyogenes; herpes simplex type I, HIV, and various viruses; assorted fungi; Clostridium tetani and C. perfringens; Haemophilus aegyptum, Acanthamoeba and assorted protozoa, etc. Entering through the GI tract: various Gram-negative rods (Salmonella, Campylobacter, E. coli, Shigella dysenterae, Vibrio cholerae, etc.); assorted viruses (poliovirus, hepatitis A, rotaviruses)Entering through the GI tract: various Gram-negative rods (Salmonella, Campylobacter, E. coli, Shigella dysenterae, Vibrio cholerae, etc.); assorted viruses (poliovirus, hepatitis A, rotaviruses) Entering via the respiratory tract: Group A Strep. pyogenes; meningitis-causing bacteria such as Neisseria meningitidis, and Haemophilus influenzae; Corynebacterium diphtheriae; Bordetella pertussis; pneumonia-causing agents like Strep. pneumoniae and various viruses and fungi; Mycobacterium tuberculosis; viruses of chickenpox, measles, mumps, rubella, influenza, and common cold.Entering via the respiratory tract: Group A Strep. pyogenes; meningitis-causing bacteria such as Neisseria meningitidis, and Haemophilus influenzae; Corynebacterium diphtheriae; Bordetella pertussis; pneumonia-causing agents like Strep. pneumoniae and various viruses and fungi; Mycobacterium tuberculosis; viruses of chickenpox, measles, mumps, rubella, influenza, and common cold.

Exogenous infections (cont.) Urogenital: Enter through skin or mucosa of penis, vagina, urethra, etc. Syphilis (Treponema pallidum), gonorrhea (Neisseria gonorrhoeae), genital warts, chlamydia, herpes simplex Type II, HIV, etc. Birth-related infections: Placental (e.g. syphilis) or during birth: STORCH (syphilis, toxoplasmosis, other [HIV, hepatitis B, chlamydia], rubella, cytomegalovirus, herpes simplex II virus)

Adherence, colonization, invasion, growth, disease

Adherence Fimbriae (non-sex pili) of enteropathogenic E. coli Enteropathogenic strains are able to colonize the ___________ intestine and cause ________________ by expressing specific colonization factor antigens (proteins) on their fimbriae

Intestinal Infection by Enteropathogenic bacteria Enteropathogenic E. coli infection animation Enteropathogenic E. coli infection animation Salmonella invasion animation Salmonella invasion animation (Howard Hughes Institute web site:

Pathogens must first become established at site of infection. _____________ must be compatible with the microorganism. An infecting microorganism can’t adhere to _______ cells or hosts. Tissue and host specificity as factors in infection

Some cells are pathogenic due to the toxins they produce (e.g. Clostridia) but most need to actually ___________ and ______________ in host tissues in order to cause disease.

Colonization, Growth, and Virulence Colonization -- ____________________ of a microorganism after it has attached to host tissues or other surfaces The initial inoculum of cells is rarely sufficient to cause disease; needs to ____________. Must therefore find appropriate nutrients and environment. This not always as easy as it appears (e.g. iron) Virulence factor -- any characteristic of a pathogen that enables it to establish itself and cause disease. These are often extracellular enzymes such as hemolysin, hyaluronidase, collegenase, and coagulase. The first 3 of these allow for spread (and nutrition, to some extent), the 4th promotes localization and, probably, protection.

Summary of virulence factors important in Salmonella pathogenesis

Some pathogens are much more virulent than others

Infectious Dose -- minimum number of agents (cells, viruses) needed to cause disease Varies from 1 Rickettsia cell in Q fever to 10 cells in tuberculosis to 10 3 cells in gonorrhea, 10 4 cells in typhoid, and 10 9 cells in cholera. Smaller infectious dose = more _________ pathogen If number of cells < infectious dose no infection If number of cells >> inf. dose more rapid __________

Toxins Exotoxin -- toxin ___________ into tissue Diphtheria toxin -- extremely potent (one molecule will kill a cell). Disrupts _____________ synthesis. Caused by lysogenic phage in Corynebacterium diphtheriae. Tetanus and botulism toxins -- Causal organisms (Clostridium tetani and C. botulinum) don’t generally ______________ very much in infected tissues but instead release potent neurotoxins.

Action of Tetanus Neurotoxin Tetanus causes irreversible muscle _________________ (‘spastic paralysis’ or ‘lockjaw’)

Action of Botulinum Neurotoxin Botulinum toxin, the most poisonous substance known, causes irreversible muscle _________________ (‘flaccid paralysis’).

Toxins (cont.) Endotoxin -- toxin released only upon cell ________ and lysis These are lipopolysaccharides and thus are found only in Gram-negative organisms. Most studied in Salmonella, E. coli, and Shigella.

Toxins (cont.) Enterotoxin -- toxin that acts specifically on the ______________.  Enterotoxins are found in S. aureus, enteropathogenic E. coli, Clostridium perfringens, Salmonella spp., etc.  Most studied: cholera toxin from Vibrio cholerae

Action of cholera enterotoxin

Action of cholera enterotoxin (cont.)

Patterns of Infection