Set 3. Ch 25/29 Pathogens and Infection/Diagnosis of Infectious Diseases

Pathogen

Disease-causing microorganism

Infection

Condition caused by a pathogen

Pathogenicity

Ability of the pathogen to inflict damage on the host

Virulence

Ability of organism to cause disease

Invasiveness

Ability of pathogen to invade the host

Bacteremia

Bacteria in the blood

Septicemia

Molecules related to the pathogen present in blood

Opportunistic pathogen

Causes disease in weakened hosts

Nosocomial infection

Hospital-acquired infection

Steps of disease process

Adherence → Colonization (making biofilms) → Infection (causes symptoms now)

Adhesins

Structures that allow bacteria to attach to host

Types of adhesins

Capsules - adhesion and protection from phagocytes

Fimbriae

Pili

Flagella

Capsule function

Sticky protective layer aiding attachment

LD50

Dose required to kill 50% of hosts (lower = more virulent)

Salmonella virulence factors

- Endotoxin - Lipid A lipopolysaccharides

- Cytotoxin

- Plasmids

- Type 1 fimbriae (adherence)

- Flagellum (motility)

Pathogenicity islands

Gene clusters encoding virulence traits

Exotoxins

Secreted protein toxins from the pathogen cell as it grows

Three categories

1. Cytolytic toxins

2. A B toxins

3. Superantigen toxins

Endotoxins

Toxic lipopolysaccharides (Lipid A component) found in the cell wall of Gram-negative bacteria

AB toxins

Two-part toxins with binding (B) and active (A) components (e coli)

Function of AB toxins

Enter cells and disrupt cellular function

Example AB toxin

- E coli

- Diphtheria

- Tetanus

- Botulism

- Cholera

Clostridium toxins

Affect nervous system

Botulism toxin

Blocks neurotransmitter release causing paralysis

How Cholera causes disease in the gut

Increases cAMP → ion imbalance → water loss → diarrhea

PPE

Personal protective equipment (gloves, gowns, masks)

BSL levels

Biosafety levels (1-4 based on risk, higher the number higher the risk)

HAI (healthcare-associated infection)

- Local or systemic infection acquired at a healthcare facility

- Most common types of infections

- Frequently resistant to antibiotics!!

HAI (healthcare-associated infection) risk factors

Immunocompromised patients, surgery, antibiotics, hospital exposure

General-purpose media

Supports growth of many organisms (e.g., blood agar)

Enrichment media

Enhances growth of specific organisms

Selective media

Inhibits some microbes while allowing others to grow

Differential media

Allows for identification of organisms based on appearance in the media

MIC

Minimum inhibitory concentration of antibiotic

Antibiotic dilution assay

Measures growth in varying antibiotic concentrations

Disk diffusion

Measures zone of inhibition around antibiotic disk

Etest

Gradient method to determine MIC

Immunoassays

Use antibodies to detect pathogens

Direct immunofluorescence

Fluorescent antibody binds directly to antigen

Indirect immunofluorescence

Secondary antibody provides fluorescence

ELISA (EIA)

Enzyme-linked assay to detect antigens or antibodies

- Very sensitive immunoassay

- Widely used in clinical diagnosis and research

- Employ covalently bonded enzymes attached to antibody molecules