Chapter 1 - Bacteria Flashcards
Leading causes of death globally
non communicable disease accounted for 74% of deaths globally
Most deadly communicable disease
Lower respiratory infections
Neonatal
less than 28 days old
Leading causes of death in low-income countries
People living in a low-income country are far more likely to die of a communicable disease than a non-communicable disease
Bacterial diseases: Terminology
- Encounter: the agent “meets” the host
- Entry: the agent enters the host’s body (or remains on the skin)
- Multiplication: the agent multiplies in the host
- Spread:the agent spreads from the site of entry (for some)
- Damage: the agent, the host response, or both cause damage
- Outcome: the agent or host wins out, or they learn to co-exist
Infection
pathogen colonizes the body (but not necessarily causes disease)
Colonize
becomes part of the microbiota, maybe transient, maybe permanent
Disease
overt symptoms caused by infection, impairment of the host - causes damage
Pathogen
bacterium capable of harming a healthy host
Opportunistic Pathogen
harms a weakened or immunocompromised host, but not a healthy host
Pathogenicity
The ability of an organism to cause disease and represents a genetic component of the pathogen (qualitative). - cannot be calculated
The overt damage done to the host is a property of the host-pathogen interactions
Disease is not an inevitable outcome of the host pathogen-interaction
Pathogens can express a wide range of virulence
Virulence
The degree of pathology caused by the organism (quantitative) - can be calculated
The extent of the virulence is usually correlated with the ability of the pathogen to multiply within the host and may be affected by other factors
Pathogens may exhibit different levels of virulence
Virulence is a quantitative concept, so we must be able to quantify it in some way.
ID50 and LD50
Virulence factors
Gene products that enable bacterium to establish itself within or on a host and enhance its potential to cause disease
eg toxins, flagella
Would the same number of bacteria cause disease regardless of its portal entry into the body?? → aka does route of entry effect its virulence/matter
Not necessarily, if bacteria are ingested much more is sully needed to cause disease
If bacteria are injected into the blood steam, much less is needed to cause disease
The bacteria would have to overcome host’s physiological anatomical defences
If a species of bacteria are pathogenic to mice, would they also be pathogenic to humans?
depends
- could cause different diseases or not at all
A bacterium may be a pathogen to mice, but be part of the microbiota of a different species of host.
Host susceptibility
Host susceptibility varies between individuals:
- underlying disease/infection
- stress
- diet
- Age
altered immune system due to disease or therapy
Hosts genetics and resistance genes (eg TLRs
microbiota plays a role
- creates competition
Risk factors for disease that you might have some control over include:
- nutritional status
- Environmental conditions
Streptococcus pyogenes
Causes numerous disease in humans include:
Pharyngitis - strep throat Tonsillitis Scarlet fever Cellulitis Rheumatic fever
Streptococcus pyogenes
This bacteria species is found on skin and mucous membrane of healthy people - thus an opportunistic pathogen
What is Streptococcus pyogenesknown for?
Bacterium can cause both non-invasive and invasive types of infections
The bacterium causes skin diseases when there is a breach in the skin or mucus membrane and the bacteria enter the tissue
The other bacteria of the microbiota may keep it “in check”
-meaning that the number of bacteria present in the body is controlled
-
Primary infection
Initial infection event, may or may not lead to disease
Secondary Infection
Opportunistic organism causes a second infection following a primary infected
- infects weakened host
Subclinical Infection
No obvious symptoms
Nosocomial infection
Acquired in a hospital/medical clinic setting (e.g., a complication of a reason for being in the hospital)
eg C. difficile infections
Local infection
Common type of infection
is restricted to a relatively small area of the body.
Non-invasive organisms usually cause these infections
These organisms express virulence factors –but tend to cause less severe disease (they may be highly contagious)
These infections are usually managed with antimicrobial compounds ( eg antibiotics)
Systemic infection
Spread throughout the body. This is a less common types of infection
Invasive organisms usually cause these infections
The bacteria are found in normally sterile body fluids (e.g.,blood, joint fluid, cerebrospinal fluid) or a deep tissue abscess (e.g., muscle or fat)
- uses the circulatory system to spread
The pathogen possess (and expresses) virulence factors that enable it to spread throughout the body
These types of infections are extremely serious and sometimes difficult to treat (i.e.treatment might lead to complications for the patient)
