EXAM 3 Anaerobes Flashcards
describe anaerobes
- do not require oxygen for life and reproduction
- oxygen’s direct toxic effect may prohibit their growth
why is oxygen toxic?
it reacts with organic matter to produce free radicals
what are 3 toxic products and free radicals?
- O2- (superoxide)
- H2O2 (hydrogen peroxide)
- OH• (hydroxyl radical)
lack of ___, such as superoxide dismutases and peroxidases helps explain the toxic effects of oxygen, but some ___ can produce them in varying quantities
- protective enzymes
- anaerobes
in vivo, bacteria tend to ___ the redox potential at their site of growth. sites colonized with ___ of organisms frequently provide conditions favorable to the growth of anaerobes. ___ and ___ of other anaerobes contribute to this balanced environment
- lower
- mixtures
- volatile and foul-smelling metabolic byproducts
describe the two natural habitats of anaerobes
- environmental (exogenous) - clostridium species are notorious in the environment due to survival of their spores
- endogenous - most other anaerobic infections, including many clostridia are seeded from normal endogenous flora: mouth, vagina, bowel, skin
what is the significance of some anaerobe species being so specific to their normal site?
they can offer clues to the physician of a hidden locus of infection when they are recovered elsewhere in the body
what are the 4 anaerobic bacteria specific to the oral cavity?
- fusobacterium
- veilonella
- actinomyces
- pigmented porphyromonas and prevotella sp.
what is the anaerobic bacteria specific to the skin?
propionibacterium
what are the 2 anaerobic bacteria specific to the vagina?
lactobacillus and prevotella bivia
what are the 2 anaerobic bacteria specific to the colon?
bacteroides fragilis and bacteroides sp.
what are some predisposing factors of anaerobic infections?
- trauma to mucous membranes or skin
- vascular stasis
- tissue necrosis
- decrease of redox potential of tissues
- trauma allows anaerobes of the indigenous microflora or soil to gain access to deeper tissues
oxygen is ___ to anaerobic bacteria
toxic
there are degrees of anaerobiasis, from ___ to ___
strict anaerobes to aerotolerant anaerobes
anaerobes generally require ___ incubation periods in the laboratory
longer
anaerobic infections are usually ___, and often smell ___
- mixed
- bad
what are the 4 important anaerobic spore-forming gram positive rods?
clostridium species:
- tetanus - c. tetani
- gas gangrene - c. perfringenes
- botulism - c. botulinum
- antibiotic associated diarrhea and pseudomembranous colitis - c. difficile
what are the main important anaerobic species of non-spore forming gram positive rods, and how are they manifested?
- actinomyces species
- chronic granulomatous, infectious disease with sinus tracts and fistulae, which erupt to the surface and drain pus containing “sulfur granules”
- proprionibacterium species
- normal skin and respiratory flora
- scope of infection similar to coagulase negative staph species
- mobiluncus species
- act synergistically with organisms including gardnerella vaginosis to cause bacterial vaginosis
what are the 2 important anaerobic gram positive cocci species, and how are they manifested?
- peptostreptococcus species
- usually found in abscess that arise from misplaced oral flora: brain or deep lung abscess
- anaerobic and microaerophillic streptococcus species
- habitat and appearance similar to peptostreptococcus species
what is the important anaerobic gram negative cocci, and how is it manifested?
- veillonella species
- the only anaerobic genus of gram negative cocci usually implicated as pathogens
- found in mixed infections of oral origin
what are the 3 important anaerobic gram negative rods, and how are they manifested?
- bacteroides species
- b. fragilis group account for about 70% of clinically significant anaerobic bacteremias
- outnumbers e. coli in the colon by approximately 1000:1
- b. fragilis group account for about 70% of clinically significant anaerobic bacteremias
- prevotella and porphyromonas species
- include former pigmented bacteroides species
- common in mouth flora and dental abscess
- fusobacterium species
- also mouth associated; can occasionally be found mixed with actinomyces
what are the 3 main treatment options for anaerobic infections?
- create an environment in which anaerobes cannot proliferate
- arrest the spread of anaerobes into healthy tissue
- neutralize toxins
describe creating an environment in which anaerobes cannot proliferate as a treatment option for anaerobic infections
- useful measures include removing dead tissue (debridement), draining pus, eliminating obstructions, decompressing tissues, releasing trapped gas, and improving circulation in and oxygenation of tissues
- in lesser infections, surgical therapy may be all that is required
describe arresting the spread of anaerobes into healthy tissue as a treatment option for anaerobic infections
antimicrobial agents play an important role here
describe neutralizing toxins as a treatment option for anaerobic infections
- toxins are produced by the anaerobes when such toxins are present
- specific anti-toxins can be used
___ are communities of microorganisms attached to a solid surface
biofilms
the biofilm community is usually composed of numerous ___ species with intricate ___ communication (quorum sensing/pheromones)
- microbial
- inter-species
can biofilms be composed of a single species?
yes
biofilm formation is a ___ mechanism
survival
the biofilm surface can be ___ or ___ tissue
living or non-living (abiotic)
describe the formation of biofilms
- attachment of cells to substrate
- growth and aggregation of cells into microcolonies
- maturation and maintenance of architecture
what are the 5 stages of biofilm formation?
- attachment (seconds)
- irreversible binding (minutes)
- layering/maturation 1
- ultimate thickness/maturation 2 (days)
- dispersion (several days)
describe the attachment stage of biofilm formation
- stage 1, seconds
- reversible binding
- logarithimic growth
- pili and bacterial adhesion molecules
- changes in gene expression: decrease flagella, increase adhesion molecules
describe the irreversible binding stage of biofilm formation
- stage 2 (minutes)
- exopolysaccharides (EPS) trap nutrients and planktonic bacteria
- cells are sessile
describe the layering/maturation 1 stage of biofilm formation
- stage 3
- greater than 10 micrometer thickness
describe the ultimate thickness/maturation 2 stage of biofilm formation
- stage 4 (days)
- greater than 100 micrometer thickness
- some cells released from substrate, but trapped in the EPS
describe the dispersion phase of biofilm formation
- stage 5, several days
- cells leaving
- as nutrtiion becomes scarce, there are changes in gene expression
- cells again become planktonic
describe the construction of biofilms
- stalks and mushroom-shaped microcolonies attached to the substratum
- matrix contains EPS, proteins, and DNA
- viable? but non-culturable organisms
- fluid-filled channels
- exchange nutrients, dispose of wastes, some motile organisms
describe the 3 layers fo mature biofilm
- outer - most exposure to nutrients, most active organisms, some become planktonic
- intermediate - metabolism is down-regulated, but still using nutrients and exchanging genes
- innermost - attached, earliest and least active, includes the persister cells
what are some examples of the variety of environments where biofilms are found?
- ship hulls, rocks in rivers and streams, sludge in potable water supplies, lungs of cystic fibrosis patients, dental plaque
- variety of environments, but interplay of biofilm and planktonic phenotypes and 3D architecture are universal
which cell types are free living?
planktonic
which cell types are attached/participating in the biofilm community?
sessile
which cell types are metabolically inert, present in all biofilms, potential for maintenance of gene pool, resist environmental stress (including antibiotics), and are possibly able to disable apoptosis?
persister
what are the advantages to living in a biofilm?
- protection from host defenses - including protection from oxygen-reactive molecules
- physical barrier to PMNs and phagocytes
- potential to outcompete normal biota
- gene transfer spread resistance in community
- provide protective enzymes
- perform as organic polymers - creeping like a lava flow on inanimate surface without detachment
as a biofilm forms, streamers of cells extend from the surface and break away to form what?
new biofilms elsewhere
___ can transmit already up-regulated resistant aggregates of organisms to other body sites
disaggregation
what are the most well-studied natural human biofilms?
dental biofilms aka plaque
what can happen to anaerobic bacteria if you have poor oral hygiene?
poor oral hygiene → blood stream → heart valves (cardiovascular disease)
poor oral hygiene is a sequelae to ___
periodontitis
- intimate relationship with ulcerated gums
- likely hematogenous spread of adherant bacteria
- heart valves, prosthetic joints
- immune mimicry leading to atherosclerosis
after teeth cleaning, the pellicle forms almost immediately. what is the pellicle?
coating of proteins and glycopeptides of host origin
what are the primary colonizers of dental plaque?
- s. mutans and actinomyces
- pili and adhesion molecules
- glucan polymer glycocalyx (EPS)
what are the bridge bacteria in the formation of dental plaque?
- glucan-binding proteins
- fusobacterium
bridge bacteria can’t bind to the ___, but can bind to ___
- pellicle
- primary colonizers
the late colonizers in the development of dental plaque are generally considered ___, and consist of what bacteria?
- non-pathogenic
- s. salivarius, propionibacterium, prevotella, veillonella, selenomonas
the development of dental plaque with good oral hygiene is not usually associated with ___ due to a balance between ___ and ___. this mostly consists of gram ___ organisms.
- disease
- host defenses
- bacterial growth
- positive
describe the changes of the microbiota if dental plaque remains undisturbed on teeth for several days
mainly anaerobic and facultative gram negative bacilli and spirochetes
if plaque remains undisturbed on teeth for several days, the microbiota are now considered pathogens. what are the 4 main pathogenic bacteria, and what do they require in order to attach?
- porphyromonas gingivalis
- bacteroides forsythia
- aggregatibacter actinomycetemcomitans (aa)
- treponema denticola
- they require the late colonizers (strep salivarius, proprionibacterium, prevotella, veillonella, selenomonas) to attach
what are the virulence factors of pathogenic bacteria that result from undisturbed dental plaque?
- adhere to the gingival epithelium
- invade tissue
- initiate an inflammatory response
pathogenic bacteria that result from undisturbed dental plaque primarily cause ___, but with continued poor hygiene, inflammation extends to ___ and can lead to eventual ___
- reversible, relatively mild gingivitis
- periodontal support structures
- tooth loss
