Pathogen 2
Virulence 2
Virulence factors
Microbe able to cause infection and disease
- Primary pathogen =causes disease when present
- Opportunistic pathogen = requires help to cause disease (weak IS)
quantitative measure of disease causing ability (measure by mortality rate, disease severity)
- low-virulence = mild symptoms no long term effects
- high virulence = severe symptoms, high death rate
Any microbial product/structure that is required for disease
Localized infection
Systemic infection
Asymptomatic (subclinical) infection
Terms ending in Emia
Terms ending in itis
- microbe in one site of body
- spread throughout body
- infection with no obvious symptoms (mild they escape diagnosis)
- microbe in bloodstream
- inflammation of
How do bacteria cause disease 5 steps
Must complete this
- Transmitted and enter suitable host
- Avoid being removed after entry (attachment)
- Migrate to a site within the host to be able to support growth
- Overcome host defenses and multiply
- Exit host and transfer to new host
-disease not seen till stage 3-5
1 Transmission and entry into host
Point of entry determined by mechanism of transmission
- microbes have preferred points
- most common tract =resp, uro-genital, intestinal
infectious dose varies
- Cholerae (intestinal) = 10^8 bacteria
- tuberculosis = 10 bacteria
2 Strategies for avoiding removal after entry 3
Host will expel if not attached to tissue
-pilli
-bacterial surface proteins
capsular polysaccharide
3 Strategies for migrating to other body sites
2 ase
- invasion of surface tissues and moving within host(optional, needing bacterial tissue degrading enzyme)
- Hyaluronidase, Collagenase
degrades hyaluronic acid & collagen which holds connective tissues together
4 Strategies for growing and surviving inside the host 2
Requires that bacteria be able to:
- Get nutrients from host (hemolysins = lysis of red blood cells)
- Evade the hosts immune system
- Bacterial capsule =block phagocytosis
- bacterial toxins = kill phagocytes
- strategies for exiting the host
routes 4
Routes vary:
- mucus, saliva (respiratory pathogens)
- feces (intestinal pathogens)
- semen, vaginal discharges (STI’s)
- pus, blood, urine, etc.
-large number released
How do bacterial pathogens dmg the host 2
- Result of host immune response to pathogen
- inflammation, fever
- side effect of phagocytic attack on bacteria - Direct result of pathogens actions
- production of tissue degrading enzymes and lytic molecules (collagenase, hyaluronidase, hemolysin)
- production of bacterial toxins (dmgs host or alters metabolism
Endotoxins
lipid attached to a bacterial outer membrane
- lipopolysaccharide (LPS)
- only on gram negative bacteria
- released from outer membrane
All LPS has same biological effect:
Immune system increases cytokine production
- interleukin 1 - hypothalamus - fever
- tumor necrosis factor - low blood pressure - shock
Activates blood coagulation pathway, complement proteins
=TOXIC SHOCK(hypotension, fever, chills, vasodilation, intravascular coagulation)
Exotoxins
Toxic proteins secreted by bacteria as they grow
-gram negative/positive
Potent in small amount (1 microgram)
Act on eukaryotic cells to kill or alter metabolism
Types of Exotoxins 3
Cytotoxins (diphtheria toxin)
-block protein synthesis (death)
Enterotoxins (cholera toxin)
-hyper section of water from intestinal cells (diarrhea)
Neurotoxins (botulinum toxin)
-neurotransmitter interference in nerves (paralysis)
2 notes on Exotoxins
- Soluble and can be carried by bloodstream
(clostridium tetani (tetanus toxin))
-bacteria stay at would
-toxin released to CNS - Exotoxins (not Endotoxins) can be chemically inactivated
- Exotoxin (active) + formaldehyde = Toxoid (inactive)
Useful in vaccines
Bacteria can have LPS and produce exotoxins
Laboratory Diagnosis of Bacterial Infections
- Gram Stain + microscopy
- fast and easy
- good for sterile bacteria
- not useful for normal flora
- doesn’t id
Laboratory Diagnosis of Bacterial Infections
- Serology, Nucleic Acid amplification
ELISA assays (serology)
- detect antibodies produced
- cant tell current and past infection
Nucleic acid amplification test (NAAT)
- detect DNA sequences
- PCR tech (polymerase chain reaction)
- fast, sensitive, complex, expensive
- best for bacteria that cant be detected
Require presumptive diagnosis, must tell lab what to look for, not form of screening
Laboratory Diagnosis of Bacterial Infections
- Bacterial growth Culture
- grow all bacteria present
- identify using indicators
- can screen for many different bacteria at once
- slow
- most often used
Laboratory Diagnosis of Bacterial Infections
Other Tests 3
Antibiotic susceptibility testing
- disc diffusion essays
- where resistance is know
Bacterial enumeration
- number of cells
- special situation (urinary tract infection
- yes or no
Genetic comparisons of different strains or isolates
- tracking outbreaks, sources of infection
- done in reference labs
