31. Bacterial Structure and Function Flashcards
steps of prokaryotic cell division?
- replication of the bacterial chromosome is initiated at the CYTOPLASMIC MEMBRANE - this triggers cell division
- each daughter chromosome is anchored to a different portion of the membrane
- as the membrane grows, the daughter chromosomes are pulled apart
- SEPTUM GROWS FROM OPPOSITE SIDES TOWARD THE CENTER OF THE CELL AND DIVIDES THE DAUGHTER BACTERIA INTO TWO CELLS
- PCN binding protein cleaves this
- incomplete cleavage causes bacteria to remain linked, forming chains (streptococci) or clusters (staphylococci)
- cell division requires transpeptidases (PBPs) and other enzymes
obligate anaerobes ___ O2
will be killed by O2 - obtain energy from fermentation
obligate aerobes ____ O2
require
facultative anaerobes ____O2
prefer O2 but can grow in absence of O2 via respiration or fermentation
microaerophiles ____ O2
can withstand low levels of O2
why is oxygen toxic to anaerobes?
don’t have syperoxide dismitase (so can’t converte superoxide to O2 and hydrogen peroxide)
and don’t have catalase of peroxidase to decompose hydrogen peroxide into water
thermophilic vs mesophilic vs psychrophilic
thermophilic: optimum temp 55-75C and minum of 35-40C
mesophilic: grow well in us - optimum 30-45C, minimum 10-15C, most pathogenic bacteria
psychrophilic: facultative - similar to mesophils but can grow slowly near 0C; obligate - optimum temp is 15-18C and killed above 20C
pour plate method?
orig sample
dilute with water to make a 10^-1 dilution
dilute that with water to make a 10^-2 dilution
etc etc
mix dilution with warm agar and pour
Count CFUs and multiply by dilution factor to get viable count/mL of bacteria
____ is the state of being free of microorgs
aspesis
____ is the inactivation or elim of ALL viable organisms and their spores
sterilization (you can’t be a little pregnant, or a little sterile)
____ is the process of removing or killing MOST microorgs on or in a material
disinfection
______ is a cleaning process which REDUCES pathogen levels to produce a healthy clean env’t
sanitization
a _____ kills vegetative bacteria and SOME SPORES
germicide (attains disinfection)
a _____ is used on non-living objects to render them infectious; kills vegetative bacteria, fungi, viruses but NO SPORES
disinfectant
a _______ is used to prevent multiplication of microorgs when applied to living systems.
antiseptic (it is BACTERIOSTATIC and not bactericidal)
arrange most resistant to least resistant:
spores, hydrophilic viruses (non-liquid, non-enveloped), vegetative bacteria, mycobacteria, lipophilic viruses (lipid containing, enveloped)
most: spores
mycobacteria
hydrophilic viruses
vegetative bacteria
least: lipophilic viruses
autoclave
15lbs/sq inch pressure for 15-20 min at 121C
- sterilizes with moisture, microorgs are destroyed at a lower temperature than in dry heat
- method of choice when product can withstand such treatment since it is fast, least toxic, cheap, and can be performed on a large spectrum of instruments
hot air sterilization
160C for 1-4 hours
- sterilizes and used on materials that would be damaged by moist heat (gauzes, dressings, powders)
filtration disinfection
via
radiation disinfection
used on materials that would be destroyed by heat (petri dishes, gloves, syringes)
- UV = thymine dimers but poor penetration and so not sterilizing
- Ionizing (beta rays, GAMMA RAYS, x-rays) = breaks in DNA backbone and can STERILIZE
ethylene oxide (C2H4O)
sterilizes via its action as a powerful alkylating agent
- low temperature sterilization: use for heat-labile materials na delicate instruments
(but carcinogenic and explosive)
alcohols
disrupts cellular membranes, solubilization of lipids, and denaturation of proteins by acting on S-H functional groups
evaporate quickly - extended contact times hard to achieve
- inefective vs spore-forming bacteria
halogens
chlorine = 1:10 good as disinfectant
must be made fresh daily and iodine is just as good as a disinfectant and antiseptiv
method of action: oxidizes microbial proteins
disinfecting the skin?
alcohol scrub is better than soap and water, but need soap for C.diff to wash it off of your hands
use of chlorhexidine alcohol for skin antisepsis, NOT providone-iodine for surgical = significant reductions in hospital acquired infections
what is a biofilm?
a microbially derived sessile community ,typified by cells that are attached to a substratum, interface, or to each other, are embedded in a matrix of extracellular polymeric substance, and exhibit an altered phenotype with regard to growth, gene expression, and protein production
microbes that are
- attached to a hydrated surface
- embedded in a polysaccharide slime
- behave as a community
- demonstrate antibiotic resistance and resistance to clearance by the host immune system
biofilm disease examples?
CF endocarditis osteomyelitis chronic UTI prostatitis otitis media dental infections endophthalmitis serious skin infections indwelling medical device infection
biofilm infection resolution?
cut it out
what % of all infections are biofilm related?
65-80
why are biofilms resistant to antibiotics?
biofilms reduce antibiotic penetration
cells withina biofilm are super slow growing (so not susceptible to things like rifampcin that inhibit RNA pol)
cells within a biofilm express many stress response genes that resist antibiotic action
why are there inaccurate MIC/MBC predictoin of bacterial populatoins in situ?
biofilms are in situ and MBC/MIC are calculated invitro
why are there inaccurate CFU determinants from clinical samples like a UTI?
one clump can have a million bacteria, but only count the one clump on the plate if not homogenized first
sometimes bacteria are viable but not culturable
missing the nidus of infection
