Bailey Flashcards
6 steps in infectious disease process
- encounter
- entry
- spread
- multiplication
- damage
- outcome
encounter
natural resivoir of infectious microbe
encounter does not mean infection
entry
pathogens must enter body in order to establish infection
colonization/invasion
colonize a surface before causing disease, adhere to host tissue
colonize-patho must be adated for growth in niche
invade-must have specific virulence factors
multiplication/spread
- lateral prop to contiguous tissues
2. dissemination to distant sites, then multiple
damage
- host response (phagocytes, cytotoxic T cell)
- infectious organism
- types of toxins
outcome
resulting illness
what are the two processes for entry into a host?
- ingress of microorganisms into body cavities contiguous with outside (inhalationg/ingestion)
- penetration of microorganisms into deeper tissues after crossing epi barrier (bites, cute, transplants, transfusions)
what body areas are considered in direct contact with exterior?
nose, mouth, resp tract, alimentary cnal, anus, female genital tract, urinary tract
2 steps of penetration of bacteria into epi cells
- attachment to specific receptors
2. internalization
2 meanings of spread of infection
- lateral propagation/movement to contiguous tissues
2. dissemination to distant sites
what must microbes over come in order to multiply and spread?
host defenses
inoculum size is important in establishing _____
an infection (varies with different organisms)
4 possible outcomes of a host-parasite interaction
- host wins out and clears infection
- parasite overcomes the host
- host and parasite adapt to each other
- neither host or parasite win (chronic inf can continue indefinitely)
how can damage to the host be caused?
- infectious agent
- host response (immune system)
- both
the great majority of microorganisms are _____
commensal
commensal
exist without causing harm
gram positive bacteria have _____
thick cell wall made of murein (peptidoglycan)
composition of murein
long chains of N acetylmuramic acid and N acetylglucosamine linked by short polypeptides
gram negative bacteria have _____
thin layer of murein between two membrane lipid bilayers
what is the outer layer of gram negative bacteria made of?
lipopolysaccharide (LPS)
-is different for different bacteria
lipopolysaccharide (LPS)
- different for different bacteria
- toxic (endotoxin) even in its purified form
- Lipid A (fatty acids attached to phosphorylated disaccharide) that faces into mem and a polysaccharide core faces out
- outer (O antigen) region is variable and antigenic, provides differences between gram - bac
bactericidal
kill bacteria
bacteriostatic
inhibit growth
penicillins (and other beta lactams)
antibiotics that affect cell wall, bactericidal
how do antibiotics often work?
by targeting bacterial ribosomes
what are the 2 bacterial ribosome subunits
30S
50S
what is the 30 s subunit responsible for?
translation of mRNA
what is the 50 s subunit responsible for?
joining amino acids together and moving the complex alone the mRNA molecule
which subunit do antibiotics target?
both
what inhibits folic acid metabolism?
sulfonamides and trimethoprim
what inhibits protein synthesis?
aminoglycosides, tetracyclines, and erythromycin
what inhibits DNA synth
metronidazole
what do pili (fimbriae) do
they are specialized structures on the surface of bacteria that are involved in adhesion to cells or other surfaces
what do sex pili do?
special pili that link a donor cell to a recipient cell during transfer of DNA
flagella
surface structures used for locomotion
they cause movement when they rotate CCW and tumbling when CW
what is flagellar movement used by?
bacteria for chemotaxis- movement toward substances that attract, away from substances that repel
strict aerobes
must have O2 to grow
obligate anaerobes
cannot tolerate O2
facultative anaerobes
can grow with or without O2
obligate intracellular parasites
can only grow inside host cells
therapeutic index
ratio between effective and toxic dose of an antibiotic
what do antibiotics tend to target
structures that are unique in bacteria vs host cells
- cell wall
- enzymes for replication, transcription, translation
- essential metabolites
- ribosome structure
how penicillin disrupts cell wall
inhibits final step of peptidoglycan synthesis, prevents crosslinking of peptidoglycan molecules
how do bacteria become resistant to antibiotics?
- synthesizing enzymes that inactivate the drug
- inhibiting uptake of the drug
- increasing secretion of the drug (pumping it out of the cell)
- modifying the target of the drug
where are drug resistant genes often found?
on plasmids that can be transferred readily from one bacteria to another
in order to survive as an infective agent, bacteria must
- avoid being washed away
- find a nutritionally compatible niche
- survive host cell defenses
- transfer to a new host
what causes damage to a host cell as a result of infection?
- cell death
- pharmacologic alterations of metabolism
- mechanical causes
- host responses
- bacterial toxins
pathogen associated molecular patterns
structures on microbial surface consisting of repeated molecules
pattern recognition receptors
recognize pathogen associated molecular patterns
how are abcteria often classified?
via surface antigens (serotype)
how do pathogens adhere to host tissue?
- nonspecific adherence
2. specific adherence
nonspecific adherence
- reversible
2. docking
specific adherence
- irreversible
2. anchoring
what does specific adherence involve?
adhesins
adhesins
substances on the surface of microbes, often found on pili, interactions are specific
glucosyl binds to salivary protein in pellicle and binds strep mutans
how do bacteria take u nutrients
- carrier-mediated diffusion (facilitated)
- phosphorylation linked transport (group translocation)
- active transport (energy dependant)
types of toxins
endotoxin: component of cell wall, generally reserved for lipopolysaccharide
exotoxins: soluble substances secreted into host tissues
what makes a microbe a pathogen
- ability to adhere to host
- ability to colonize the host
- ability to replicate within given niche
- ability to cause damage
categories of bacteria based on environment
- oligotrophs: can grow w/ limited nutrients
- microaerophiles: require some O2, but low levels
- mesophiles: grow well in mild temps (15-45 C)
why are LPS important?
- considered pathogen associated molecular patterns (PAMPs)
- PRRs can recognize PAMPs
glycocalyx
substance surrounding cell, capsule when well organized, slime layer when not
why would capsules be beneficial to pathogens?
for some bact, encapsulation is a necessary virulence factor
5 ways antibiotics inhibit bacteria
- inhibit cell wall synthesis
2.
5 ways antibiotics inhibit bacteria
- inhibit cell wall synthesis
- disrupt cell membrane function
- inhibit protein synthesis
- inhibit nucleic acid synthesis
- act as antimetabolites
antibiotics commonly used in dentistry and their purpose
- penicillin: odontogenic infection
- clindamycin: odontogenic infection (bone), abscesses
- cephalosporins: odontogenic infection
- metronidazole: abscesses and periodontitis
- tetracyclines: periodontitis
mechanisms of drug resistance
- synthesis of enzymes that inactivate the drug
- prevention of access to target site (inhibit uptake or increase secretion of drug)
- modification of target site (via enzyme affinity or metabolid pathway)
how does antibiotic resistance spread?
- chromosome associated resistance
- plasmid mediated resistance
- rapid spread resistance
