L5: Principles of Microbiology Flashcards
acellular microbes
- need host cells to propagate
- viruses
- prions
viruses
- nucleic acid packaged in protein coat
prions
- pure protein
- pathogenesis arises from accumulation in CNS of abnormal isoforms
- Mad Cow
- CJD
Cellular organisms
- prokaryotes
- eukaryotes
prokaryotes
- include archaea & bacteria
- do not have a nucleus
- very little intracellular organization
eukaryotes
- include Eukarya
- contain a nucleus
- visible subcellular organelles (mitochondria, chloroplasts)
archaea
- more primitive
- currently no known human pathogens among the archaea
membrane of bacteria
- peptidoglycan in the cell call
why don’t we have uncontrolled growth of microbes?
- circumstances are not ideal
- nutrients are limited
- host defenses protect us
- even microbes get infections
- carrying capacity!
bacteria central dogma
- single circular bacterial chromosome
- DdRp translates genes into RNA
- ribosomes translate to protein
- structural proteins and enzymes do most of the work
plasmids
- extrachromosomal genetic elements
- usually circular
- autonomously replicating
- may encode virulence factors or antibiotic resistance genes
- source of mobile genetic information that can be transferred from one cell to another
vertical gene transmission
- from parent to progeny
- through cell division
horizontal gene transfer
- lateral
- foreign donor gives DNA to recipient
- three mechanisms
transduction
- done by phage
- phage lands on bacteria and shoots DNA into cell
- phage DNA integrates into bacterial DNA
- new phages form with some bacterial DNA packaged
- donor cell lysis
- phage lands on new donor cell and inserts the newly hybridized DNA
transformation
- uptake of naked DNA by the cell
- different mechanism for gram negatives versus gram positives
conjugation
- structure forms between two bacterial cells
- DNA is transferred
- slightly different in gram positives versus gram negatives
what can mobile genetic elements encode?
- antibiotics resistance
- toxins
- other virulence factors
microbe reproduction
- microbes reproduce rapidly
- mutations continually arise from replication errors
health consequences
- drug resistance
- emergency infectious diseases
what are viruses made out of?
- protein
- nucleic acids (DNA or RNA)
- lipids
- sugars
is a virus that infects the fecal-oral route more likely to be enveloped or not?
- not
- envelope contains important information that would be degraded by stomach acid
generic virus life cycle
- attachment to cell - based on viral receptor on the host surface
- entry into the cell
- uncoating - once it gets into the cell, it falls apart
- host cell machinery takes over and synthesizes new protein and nucleic acids of the virus
- all the proteins and nucleic acids come together in assembly and the virus exits the cell
functions of the viral genome
- genome replication
- genome assembly and packaging
- regulation of replication cycle
- modulation of host defenses
what is not in the viral genome
- genes that code for protein synthesis machinery, energy metabolism, or membrane biosynthesis
viral genome replication
- in many cases the virus uses the host cell polymerases
modulation of host cell defenses
- some viruses make proteins that tell the host cell to turn down the host cell response
what do human cells lack the ability to do?
- replicate RNA or make DNA from RNA
- no RdR/Dp
- viruses that need these enzymes must encode them in their own genome
positive sense RNA
- mRNA
- can be directly translated into protein
- also must be replicated to make new virus
- requires viral RdRp
negative sense RNA
- must first be copied to positive sense
- negative polarity not recognized by the ribosome
- intact virus must include viral RdRp
coating and packaging of viruses
- happens inside the host cell and not in the viral particle
viruses classification
- obligate intracellular parasites
viral outside structure
- may be enveloped or naked
viral genomes
- can be DNA or RNA
different steps in the viral life cycle may provide
- targets for antiviral therapy
encounter
- infectious agent meets host
entry
- agent enters host
spread
- agent spreads from site of entry
multiplication
- agent multiplies within host
damage
- agent, host response, or both cause tissue damage
outcome
- agent or host wins or they learn to coexist
what is the most common type of infection?
- asymptomatic
spectrum of relationship between microbes and hosts?
- Essential and mutually beneficial
- Colonization
- Infection (active or latent)
- Disease
active infection
- active and growing inside the patient
- asymptomatic versus symptomatic
latent infection
- asymptomatic with pathogen present, but little or no replication
- pathogen can re-activate if immune responses wane
variety of host susceptibility
- Host genetics
- Immune status
- Microbiota
- Co-infections
transmission of microbial agents
- person to person (communicable)
- horizontal or vertical
- animal to person (zoonoses)
- insect to person (vector borne)
- environmental (nosocomial, fomite)
Routes of transmission
- entry via epithelial surfaces (inhalation/ingestion/sexual contact)
- deeper tissue penetration (insect bites, cuts/wounds, organ transplants and blood transfusions)
entry via epithelial surfaces
- inhalation
- ingestion
- sexual contact
deeper tissue penetration
- spread from epithelia
- insect bites
- cuts and wounds
- organ transplants and blood transfusions
spread of infections
- Efficiency of transmission
- Duration of infectiousness
- Number of people exposed
how might we change the duration of infectiousness
- antimicrobial therapy
- immunomodulatory therapy
- some vaccines don’t prevent infection, but reduce duration or severity
- screening for important symptomatic infection
- important for immunocompromised
how might we change the number of exposed, susceptible individuals?
- vaccination
- chemoprophy
- environmental/structural control
- public health policies
environmental/structural controls?
- quarantine
- PPE
public health policies
- contact tracing
- partner treatment
- DOT
population level factors that influence infectious diseases
- time
- place
time
- time of year
- incubation period
place
- geographic distribution of some infectious agents (vectors and/or pathogens)
- occupation related exposures
- travel
prevention strategies
- education and public health awareness
- hygiene
- limit exposure
- improve host defenses (vaccines)
education and public health awareness
- scientific literacy
- reporting and surveillance
hygiene
- handwashing
- sanitation
limit exposure
- insecticide-treated bed nests
- PPE
improve host defenses
- vaccines
obligate versus facultative
- obligate always does
- facultative may or may not
asymptomatic infection
- also called subclinical infection
- without subjective symptoms
- patient decides symptoms
- often used to also include without objective signs
prodromal infection
- early signs and symptoms that appear before full-blown disease
symptomatic infection
- accompanied by signs and/or symptoms of disease
are asymptomatic diseases medically irrelevant?
- no!
- asymptomatic infections are frequently transmissible
- the next host may not experience asymptomatic infection
What are 4 major pathogen categories?
- Bacteria
- Viruses
- Fungi
- Parasites
Name 3 modes of transmission of infectious diseases.
- Person to person (communicable); horizontal or vertical
- Anima to person (zoonoses)
- Insect to person (vector borne diseases)
- Environmental (nosocomial, fomite)
Why is understanding infection important?
Infection can affect every body system.
What is AMR?
Antimicrobial resistance,
What do drugs target in bacteria?
Prokaryotic ribosomes and cell wall.
Bacteria have unique ribosomes (e.g. 70s) and a peptidoglycan cell wall.
What are the 3 phylogenetic domains?
Bacteria, Archaea and Eukarya
Examples of Eukarya
Fungi, protozoa and helminths
Obligate human parasites
Found only in humans (no animal or environmental reservoirs)
Obligate aerobe
must use oxygen for growth
Obligate anaerobe
must avoid oxygen for growth
Obligate intracellular pathogen
only replicates inside eukaryotic cells (may be human or animal)
Name 3 microbiological stains
- Gram’s stain
- Acid-fast stains
- Silver stain (GMS)
Gram’s stain
Results determined by bacterial cell wall structure (bacteria either gram-positive or gram-negative)
Acid-fast stains
- Include Ziehl-Neelsen & Auramine-Rhodamine
- Used for Mycobacterium species
Silver stain
Used for many fungi, protozoa and some bacteria
