bacterial genetics and bacterial pathogenesis Flashcards
what are the three ways the bacteria can do horizontal gene transfer
transduction
conjugation
transformation
transformation
DNA is taken up directly by cells
- competent cells
- naturally competent (transform a lot)
- DNA taken up is mostly linear, not plasmids or phage DNA
transduction
viruses replicate in bacteria
lytic or lysogenic phases
-occurs when bacterial genes are packaged by phage and subsequently transferred to other bacteria
what is a prophage
the phage genome once it is incorporated into bacteria genome
generalized transduction
any random bit of bacterial DNA can be excised with the prophage
specialized transduction
that phage has a specific loci and thus the phage will always have the same bit of DNA from the bacteria with it
conjugation
bacterial sex via pilus
transposable elements
DNA elements that move from one place in bacterial DNA to another
- can transfer genes to a new location or disrupt genes when they insert
- can carry virulence and ABX resistance genes
direct transposons
moves the transposon to a new site
replicative transpostions
transposon leaves a copy in place upon movement
pathogenicity islands (PAIs)
virulence genes compact in distinct genomic islands
- acquired by horizontal gene transfer
- differ in GC content from rest of bacterial chromosome
mutualistic symbiosis
host receives goods and or services while bacteria may receive goods in return
-both benefit
commensalism
bacteria benefit while host is unaffected
disease (pathogens)
due to interactions that damage the host directly or indirectly via stimulation of host inflammatory response
opportunists and pathobionts
an organism which under normal circumstances does not cause disease, but can be pathogenic under some conditions
as you go further down the GI tract what happens to the number of bacteria?
it increases
- helps extract nutrients
- required for proper immune system development
- affect metabolism of some drugs
- protects against pathogens
coloniziation resistance
microbiota inhibits colonization by newcomers
- high diversity
- high density
- high colonization resistance
Clostridium difficile
gram positive anaerobe found in GI tract
-only causes pathogenesis following antibiotic tx that depresses the rest of the microbiota of the gut
psuedomembranous colitis
caused by C. difficile
severe ulceration of the colon
- initially associated with clindamycin, now associated with other ABX
- can be acquired in hospital as spores
symptoms of psuedomembranous colitis
use of broad spectrum ABX
diarrhea
abdominal pain
fever
how does C. difficile survive antibiotics
resistance genes
biofilm formation
spore formation
how can C. difficile be spread?
via spores that are excreted by infected pts
-the spores can persist in the environment and are highly resistant to commonly used disinfectants and ABX
spore components (5) of C. difficile
cell membrane thick peptidoglycan mesh another cell membrane wall of keratin like protein outer layer called exosporium
how do you get rid of spores?
via autoclave
121 C for 15 min
-most ABX and hand sanitizers will not kill spores
factors that facilitate bacterial infection and survival within a host
- outcompete commensals
- attachment to host cells and tissues via -adhesins
- evasion of innate and adaptive immune sys
- acquisition of limiting nutrients eg: Fe, AAs
- dissemination within a host and transmission to new host eg: ability to break down or cross tissue barrier)
how to pathogens defend against phagocytosis?
capsules
survival strategies within extracellular environments?
- capsules
- vary surface exposed antigens
- secret molecules that interfere with host defenses eg: toxins, enzymes
survival strategies within intracellular environments
- resistance to ROS and NO eg: superoxide dismutase, suppression of host NO synthase expression
- neutralized phagolysosome contents
- prevent phagolysosome fusion
- escape phagolysosme
toxins
virulence factors excreted or not that are toxic to human or animal or plant cells
what are some toxin types
endotoxin
super antigens
action on host cell membrane
A-B type toxins
staphylococcus aureus
1/3 of population colonized
survives on skin, surfaces, environment
-can cause food poisoning, bacteremia/sepsis, toxic shock syndrome, abscesses and cellulitis
what is Hospital acquired methicillin resistant S. aureus
HA-MRSA is when a patient gets MRSA from a staff at a hospital
what is community acquired MRSA
MRSA from the environment eg: daycare, wrestlers
-colonizes in the skin more than nose
how many death are HA-MRSA and CA-MRSA responsible for per year?
20,000
A/B toxins
a two component toxin
A subunit of A/B toxin
responsible for the enzymatic activity of the toxin
B subunit of A/B toxin
mediates binding to a specific receptor and transfer of the A subunit across the membrane
**B subunit Breaks cell membrane
