Chapter 15 UTA Microbiology

Disease

a condition where normal structure and/or function are damaged or impaired

Infection

invasion of pathogen or parasite that lead to disease

Signs

things that can be directly measured by clinician (e.g. body temperature)

Symptoms

things felt by patient that cannot be clinically measured (e.g. nausea)

Syndrome

groups of signs and symptoms that help indicate a particular disease

Signs and symptoms help direct towards:

Diagnosis

Asymptomatic/subclinical

only signs can be observed through correct testing

WHO's International Classification of Diseases (ICD) is used globally to:

classify and monitor diseases

Infectious

disease is directly affected by pathogens

Communicable

capable of spreading person-to-person

Iatrogenic

acquired as result of medical procedure

Nosocomial

acquired from hospital setting

Zoonotic

acquired from animal

Non-communicable

obtained from non-living thing such as soil or contaminated object

Non-infectious

not caused by pathogen

Periods of Disease

1) Incubation

2) Prodromal

3) Illness

4) Decline

5) Convalescence

Incubation

intial entry of pathogen; replication begins

Prodromal

Replication continues; host shows signs and symptoms

Illness

signs and symptoms are most severe in host

Decline

pathogen number starts to decrease; host's immune system is weak and vulnerable to secondary infection

Convalescence

host starts to recover

Acute disease

relatively short; influenza

Chronic disease

longer time; cancer, HIV

Latent disease

comes in episodes; pathogen replicates when disease is active; herpes

Koch's Postulates

set of standards that must be met to demonstrate that X pathogen causes X disease

Koch's Postulates list

1) pathogen must be found in every case of disease; not found in healthy individuals

2) pathogen can be isolated and grown in pure culture

3) healthy test subject infected with suspected pathogen; must develop same signs and symptoms as seen in postulate 1

4) pathogen must be re-isolated from new host and must be identical to pathogen from postulate 2

Koch's (wrong) assumptions

1) Pathogens are found only in disease individuals

2) All subjects are equally susceptible to infection

3) All pathogens can be grown in culture

Molecular Koch's Postulates

1) sign or symptom of disease should be associated only with pathogenic strains of a species

2) Inactivation of suspected gene associated with patho should result in measurable loss of patho

3) Reversion of inactive gene should restore the disease phenotype

Pathogenicity

ability of pathogen to cause disease

Virulence

degree of pathogenicity; continuum among many pathogen types

Example of Highly Virulent Pathogen

Bacillus anthracis; induces severe signs and symptoms

Example of Low Virulent Pathogen

Rhinovirus; induces low signs and symptoms

Median Infectious Dose (ID50)

number of pathogens required to infect 50% of population

Median Lethal Dose (LD50)

number of pathogens required to kill 50% of population

Example of Primary Pathogen

enterohemorrhagic E. coli (due to Shiga toxin)

Example of Opportunistic pathogen

S. aureus (common cause of nosocomial infections)

What can influence susceptibility to disease?

Drugs, resident microbiota, genetics, age

Stages of Pathogenicity

1. Exposure to Host

2. Adhesion and colonization

3. Invasion

4. Infection

5. Transmission

Stages of Pathogenicity: Exposure to Host

pathogens are exposed to portals of entry to begin adhesion; Some portals are worse than others; mucosa

Describe TORCH infections

pathogens that can cross placental barrier as portal of entry

TORCH Infections: T

Toxoplasmosis; Toxoplasma gondii (protozoan)

TORCH Infections: O

Syphillis; Treponema pallidum

Chickenpox; Varicella-zoster; herpesvirus3

Hep B; hepadnavirus

HIV; Retrovirus

Fifth disease-erythema; Parvovirus B19

TORCH Infections: R

Rubella; German measles

Togavirus

TORCH Infections: C

Cytomegalovirus; herpesvirus 5

TORCH Infections: H

Herpes simplex viruses HSV 1 and 2

Stages of Pathogenicity: Adhesion

Adhesins: molecules/structures that bind to certain host receptors

Biofilm: production of community glycocalyx

Stages of Pathogenicity: Invasion

occurs when colonization is established; Pathogens produce toxins to allow further colonization into body/tissue; Helicobacter pylori urease production

Stages of Pathogenicity: Invasion: Mechanisms of Invasion

1) Endocytosis

2) Effector proteins- secreted to trigger entry; Salmonella and Shigella

3) Surface proteins allow for binding to host cell; trojan horse approach

Some pathogens are able to?

survive lysosomes that engulf; Mycobacterium TB

Stages of Pathogenicity: Infection

Multiplication leads to established host infection

Stages of Pathogenicity: Transmission

Skin, respiratory, urogenital & gastrointestinal tracts; coughing, sneezing, secretions & excretions

What does the root -emia mean?

Used to describe presence of pathogens in bloodstream

What does the term septicemia mean?

Bacteria are present and multiplying in blood

What determines a person going into shock?

Systolic pressure is less than 90

Local infection

small area of body

Focal infection

pathogen or toxin spreads to secondary location

Systemic infection

occurs throughout body; commonly by blood stream

What can some primary infections lead to?

secondary infections of different pathogen; HIV lowers immune system and opens door for yeast and others

Virulence factors dictate:

how severe and extensive a disease is

Examples of Virulence factors:

Adhesion factors, exoenzymes, toxins, immune evasion

Adhesins

proteins that aid in attachment to host cell receptors; found in all microbial types; commonly found on fimbriae

Exoenzymes

extracellular enzymes used to invade host tissues

Types of Exoenzymes include:

glycohydrolases, nucleases, phospholipases, proteases; Hyaluronidase

Toxins

poisons that cause host cell toxigenicity

Endotoxins

lipopolysaccharides that trigger host inflammatory responses; can cause severe fever and shock

Exotoxins

proteins mostly produced by Gram positive; targets receptors on specific cells

Exotoxins: Intracellular targeting

with A&B regions for activity and binding; diptheria and botulinum toxin

Exotoxins: Membrane disrupting

aka phospholipases that degrade bilayer membrane; Bacillus anthracis and Rickettsia

Exotoxins: Superantigen

trigger excessive production of cytokines by immune cells; S. aureus and Toxic Shock Syndrome

Host Evasion

mechanisms to evade phagocytosis

Examples of Host Evasion

1. Capsules enlarge bacterial cell so phagocytes cannot engulf pathogens

2. Proteases digest host antibody molecules

3. Mycolic acid in acid fast bacteria

4. Coagulase positive microbes coagulate blood cells to keep immune cells out of reach

5. Alteration of cell surface proteins to hide from immune cell recognition

Virulence in Viruses

similar to bacteria; adhesins and antigenic variation

Examples of Virulence in Viruses

-HIV glycoprotein 20 for binding CD4 T-cells

-Influenza high mutation of envelope spikes allows for antigenic variation

Describe antigenic drift

Slight changes in spike proteins

Describe antigenic shift

Major changes in spike proteins due to gene reassortment

When does gene reassortment occur?

When two different influenza viruses infect same host

Virulence in Fungi

Many properties similar to bacteria; adhesins, proteases, mycotoxins

Examples of Virulence in Fungi

1. Capsule gram positive Cryptococcus; cause pneumoniae and meningitis

2. Mycotoxins produced by Claviceps purpurea and Aspergillus; contaminate grains and other staple crops

Virulence in Protozoans

Unique features for attachment; Giardia lamblia uses adhesive disk of microtubules to attach to intestines

Example of Virulence in Protozoans

Plasmodium falciparum changes adhesive protein for RBCs to avoid immune recognition; causes chronicity in malaria patients

Virulence in Helminths

1. Tissue penetration achieved with proteases

2. Roundworms produce cuticle to last longer against host defense assaults

3. Schistosoma degrades host antibodies to halt immune defense

Which of the following would be a sign of an infection?

fever

Which of the following is an example of a non-communicable infectious disease?

Food poisoning due to a preformed bacterial toxin in food

What type of toxin is produced by gram-negative bacteria, composed of mostly protein, has high toxicity, targets liver cells and is not heat stable.

Exotoxin

Phospholipases are enzymes that do which of the following?

degrade cell membranes to allow pathogens to escape phagosomes

Cilia, fimbriae, and pili are all examples of structures used by microbes for ____________.

adhesion

The Shiga and diphtheria toxins target ________ in host cells.

protein synthesis

What exoenzymes can be produced by Candida to invade tissue.

Protease and phospholipase