Bacti Lecture 4b

Pathogenic bacteria in nature

Only relatively few bacteria cause animal diseases

Importance of natural bacteria to animals

They form mutually beneficial symbiotic relationships critical to animal health

Microbiota

Microorganisms that naturally inhabit a region of the body

Opportunistic pathogens

Natural microbiota causing infections when entering abnormal sites or during host immunosuppression

True pathogens

Non-natural microbiota that enter the body and cause exogenous infection

Pathogenicity

Ability of a pathogen to inflict damage on its host

Virulence

Degree of pathogenicity within a group or species determined by virulence factors

Virulence factors

Molecules expressed or secreted by bacteria that aid colonization, immune evasion, host entry/exit, or nutrient acquisition

Infection

Establishment of an organism in a host whether damage occurs or not

Disease

Impairment of host function due to injury or damage

Etiology

Cause of disease due to damage or pathology

Infectious disease etiology

The microbe causing the disease

Types of infectious diseases

Nosocomial, iatrogenic, and zoonotic diseases

First stage of disease development

Exposure or contact

Second stage of disease development

Incubation period

Third stage of disease development

Prodromal period

Fourth stage of disease development

Period of illness

Fifth stage of disease development

Period of decline

Sixth stage of disease development

Period of convalescence

Shock in severe sepsis

A sign of sepsis

Main portals of entry

Mucous membranes, skin, and parenteral route

Mucous membrane portals of entry

Respiratory, gastrointestinal, urogenital, and conjunctival

Ways pathogens enter through skin

Hair follicles, sebaceous glands, skin penetration, or infection of the skin itself

Parenteral route

Entry through breaches in skin or mucous membranes

Reason pathogens prefer certain portals of entry

Some pathogens can only cause disease through specific entry sites

Pathogenesis

Series of events from initiation to development of disease

First step of pathogenesis

Contact or exposure to the pathogen

Reason adhesion is important for bacteria

Physical and mechanical barriers tend to dislodge bacteria from the body

Examples of bacterial adhesins

Pili, flagella, glycocalyx, and capsules

What adhesins bind to

Surface receptors on portal cells (the place where the bacteria enter the body, such as the respiratory tract, digestive tract, or urinary tract)

Biofilms

Microbial communities protected by extracellular polymeric substances and resistant to phagocytosis

Purpose of biofilms

Resist phagocytosis

Function of bacterial capsule

Anti-phagocytic protection

Examples of anti-phagocytic cell wall components

M proteins of Streptococci and mycolic acid of Mycobacterium tuberculosis

Reason pathogens must adhere avidly

To successfully establish infection

Where adhesion is especially important

Mucosal surfaces

Coagulase function

Clots fibrin around Staphylococcus aureus to protect against immune cells

Kinase function

Digest clots and allow bacterial spread

Hyaluronidase function

Digests polysaccharides holding cells together

Collagenase function

Breaks down collagen allowing spread into deeper tissues

IgA protease function

Cleaves IgA antibodies making them nonprotective

*NOTE: IgA protects mucosal surfaces

Antigenic variation

Change in surface antigens making antibodies ineffective

Extracellular bacteria

Bacteria that adhere to and multiply on cell surfaces

Intracellular bacteria

Bacteria that enter and proliferate inside host cells

Invasins

Surface proteins rearranging host actin filaments to promote bacterial uptake into cells

How Yersinia uses invasins

Binds host cell receptors

How Salmonella uses invasins

Injects proteins into host cells using Type III secretion

How Listeria monocytogenes moves intracellularly

Uses host actin fibers for transcytosis

How intracellular bacteria survive inside cells

Prevent lysosome-phagosome fusion

Spreading factors

Bacterial enzymes promoting spread through tissues

What hyaluronidase degrades

Hyaluronic acid in connective tissue

Bacteria producing hyaluronidase

Streptococci, staphylococci, and clostridia

What collagenase breaks down

Collagen

Bacteria producing collagenase

Clostridium histolyticum and Clostridium perfringens

What neuraminidase degrades

Neuraminic acid (sialic acid) on epithelial cells

Bacteria producing neuraminidase

Vibrio cholerae, Shigella dysenteriae, Pasteurella multocida, and Mannheimia haemolytica

Function of streptokinase and staphylokinase

Convert plasminogen to plasmin which digests fibrin

Edema factor of Bacillus anthracis

Adenylate cyclase activity promoting edema

(AC activity is in excess here)

Siderophores

Molecules used by bacteria to acquire iron from the host

Importance of iron to pathogenic bacteria

Most pathogenic bacteria require iron for growth

Ways bacteria directly damage host cells

Disrupt function, use nutrients, produce waste, and rupture cells after multiplication

Main cause of host cell damage during infection

Toxins

Toxins

Poisonous substances produced by bacteria

Three types of exotoxins

Cytotoxins, neurotoxins, and enterotoxins

Cytotoxins

Kill cells

Example of cytotoxin

Diphtheria toxin

Neurotoxins

Interfere with nerve impulses

Example of neurotoxin

Botulinum toxin

Enterotoxins

Affect cells lining the gastrointestinal tract

Example of enterotoxin

Cholera toxin (choleragen)

Disease caused by Clostridium perfringens

Severe gangrene

a serious medical condition characterized by the death of body tissue- that part of body can lose blood supply

Diseases caused by staphylococcal toxins

Scalded Skin Syndrome and Toxic Shock Syndrome

Limulus test

Test used to detect endotoxins from Gram-negative bacteria

LAL

Limulus Amebocyte Lysate

Characteristics of pathogenic bacteria

Transmissibility, adherence, invasion, immune evasion, and toxigenicity

Ways bacteria cause disease

Tissue destruction, toxin production, and overstimulation of immune responses