require reduced oxygen tension for growth (<10%). do not durvive in ambient air.
extremely oxygen sensitive species
like some clostridia, cannot survive even 0.5% oxygen.
anaerobes as part of normal flora
obligate anaerobes outnumber facultative anaerobes in the gut, and are the prdeominant type of bacteria in the oral cavity, GI tract and genital tract.
02 solubilty and and anaerobes
02 solubility in H2O is low, and poorly diffusable, so anaerobes can live mm below the surface.
microbial biofilm of complex composition. more than 700 species that can colonize.
oral colonization timing
neonates oral cavity is sterile, but is colonized soon after birth. microbiota stable in composition.
pellicle forms from saliva proteins. serves as scaffold for biofilm. Then comes primary, secondary, and tertiary colonizers.
Strep and actinomyces. Have adhesins that directly atach to salivary proteins.
allow coadhesion and coaggregation between bacterial species. "bridge" species, usually fusobacterium.
G-, including porphyromonas. Tend to be strict anaerobes, depend on 1 and 2 colonizers to deplete oxygen. more proinflammatory.
removes biomass but no evidence that it changes bicrobiot over time.
different in different parts of the gut. highest in the large intestine (500-1000 species). Dominated by bacteriodes and firmicutes.
2/3 anaerobic infections are mixed. Abscess formation almost always mixed (E. coli and Bacteriodes).
obligate anaerobe benefits from synergy
lower redox pot of environment, necessary growth factors, impairment of local host defenses
facultative bacteria benefits from anaerobes
enhanced growth, protection from phagocytoccis as bystanders, protection from antibiotics.
G- rods, sim. to E. coli. Microflora in mouth and GI tract. Predominant genus in the GI tract.
Bacteriodes under normal conditions
involved in metabolic activities (ferment CH20, N acquisition, recycle bile), compete w/ pathogens (attachment sites, nutrients, produce volatile FA lowering pH, release free bile acids)
bacteriodes and disease
most common genus isolated from anaerobic infections, including bacteremia. Not invasive, but events compromising intestinal barrier provide access. Rely on synergism w/ aerobic for disease.
most important opportunistic Bacteriodes pathogen. 1-2% of normal flora, but 80% of anaerobic infections.
most produce beta-lactamases, so treat w/ beta-lactam and inhibitor (ampicillin + sublactam), or metronidazole. most are resistant to aminoglycosides.
G+ rods, hyphae like filaments. "ray fungus." non-motile, non-spore forming. commonly found in mouth, part of oral flora. opportunistic, esp. after dental procedure. causes periodental disease and caries. relies on synergy.
abscess formation when oral health is compromised.
may be confused w/ nocardi. differentiation important because of treatment.
long term penicillin treatment. resistant to metronidazole.
G+ spore forming rods. vary in O2 sensitivity. clostridial spores ubiquitous in the environment
C. perfingens/C. septicum
produced by B. fragilis and peptrostrep, can protect from phagocytocis, enhances abscess formation, increase liklihood of systemic infection. Important in peritoneal abcess formation.
G-, some like B. Fragilis have LPs that is less toxic and thus less immunostimulatory.
often produced by anaerobes to protect them from reactive O2 species created by the host.
fatty acid produced by B. fragilis, decreases phagocyte function and neutrophil migration. enhances not only B. fragilis but other nearby species.
actinomycosis caused by A. israelii (usually). Swelling of tissues, abcess, or mass lesion. Abcess may break through skin in chronic infections.
lumpy jaw diagnosis
inspection of abscess fluid shows yellowish granules of clumped organisms. called "sulfur granules"
lumpy jaw treatment
long term treatment w/ penicillins. (4-6 weeks IV followed by oral therapy).
oropharynx usual source of anaerobes in brain. caused by anatomically adjacent infection, or septic emboli from the lung. prevotella, porphyromonas, peptrostrep most common.
follows aspiration of lung or gut contents. pneumonitis first, then abcess in 1-2 weeks if untreated.
in many patients with lung abscess there are expectorations with horrible odor, giving patient fetid breath.
aspiration pneumo organisms
prevotella, porphyromonas, fusobacterium, peptostrep. mixed w/ strep viridians and other anaerobes.
intra abdominal infection usually following trauma or necrosis w/ GI flora entering peritoneum. Most frequently B. fragilis and E. coli.
facultative anaerobe (E. coli, enterobacter) typically responsible for early infection, and anaerobe (b. fragilis) infection leads to abcess formation.
chronic wounds in poor wound healing
individuals w/vascular disease (diabetes), typically mixed infection, w/ S. aureus, pseudomonas, peptostrep, and GBS. grow in mixed biofilms.
stages in development of chronic infection
contamination, colonization, local infection, infection.
organisms present but not replicating
organisms present in the wound but are not causing tissue damage.
local infection stage
transition between colonization and infection stages, infectious signs absent but wound healing is delayed
bacteria are replicating at high numbers and are causing tissue damage.
traumatic gas gangrene
C. perfingens, crush type injury reducing perfusion. Spores from enviroment germinate, producing myonectoric factors, mass myonecrosis/shock