Lec15 Anaerobes and Gram + Bacilli Flashcards
What are some general characteristics of anaerobes?
- often normal human commensals
- cause disease when in high levels or introduced to sterile site
- form abscesses
- their toxins can cause tissue destruction
- metabolism leads to gas production
How do you treat anaerobic infections?
- penicillin [amoxi, ampi, piper, ticar]
- combo of penicillin and beta lactamase inhibitor [for serious intestinal infection]
- 2nd gen cephalosporins
- carbapenems [imi, erta, mero]
not as highlighted:
metronidazole
clindamycin
oral vancomycin
What is metronidazole? mech of action?
- interrupts electron transport chain in bacteria
- generates toxic metabolites that cause DNA fragmentation
Where does clindamycin act on bacteria?
protein synthesis inhibitor at translocation step
What are micro characteristics of clostridium difficile?
- gram positive
- anaerobic
- spore forming
- bacillus
What is pathogenesis of c. difficile?
- can colonize colon of asymptomatic patients at low levels
- pathogenic when normal flora of colon destroyed by systemic antibitiocs
What drugs is c. diff usually resistant to?
- many!
- beta lactams, clindamycin, cephalosporins, fluoroquinolones
How is C. difficile diagnosed?
- by pseudomembranous colitis
- by EIA toxin assay [enzyme immunoassay] = most often
- by cytotoxicity assay
- by PCR
What are the two c diff toxins? functions?
toxin A = enterotoxin
- chemotactic for neutrophils
toxin B = cytotoxin
- disrupts tight cell junctions
- increases permeability of intestinal wall and causes diarrhea
What is worst case complication associated with C diff?
- toxic megacolon –> massive dilation of colon and septic shock
How is toxic megacolon treated?
- by bowel resection
- if bowel not removed may cause death
What are standard treatments for c difficile?
- metronidazole
- oral vancomycin
What is cause of c difficile relapses? how can you avoid?
- due to spore formation
- avoid by: probiotics, intravenous immune globulin, fecal transplant
What makes strains of c diff hypervirulent?
mutation in regulatory gene leads to loss of regulation of toxin production
What are micro properties of clostridium perfringens?
- gram positive rectangular rod [but often decolorizes]
- double zones of hemolysis on blood culture plate
= zone of complete hemolysis by theta toxin, wider zone of partial hemolysis by alpha toxin - india ink prep to highlight capsule
What makes up the double zone of hemolysis with c. perfringens?
zone of complete hemolysis by theta toxin
wider zone of partial hemolysis by alpha toxin
What is function of c. perfringens alpha toxin?
- mediates hemolysis, vascular permiability, tissue destruction
What diseases are caused by clostridium perfringens?
- soft tissue infections: cellulitis, fasciitis, suppurative myositis, gas gangrene [myonecrosis]
- food poisoning
- necrotizing enteritis
- bacteremia/septicemia
In what circumstance does c. perfringens infect gall bladder?
- often in conjunction with other GI organisms like E coli or klebsiella
What is mech of food poisoning from c. perfringens?
- short incubation period [8-24 hrs]
- abdominal cramps and watery diarrhea
- usually lasts 24-48 hrs
- enterotoxin is heat labile but spores can survive at low temp
How do you treat c. perfringens?
penicillin
What is effect of clostridium tetani = tetanus? how is it transmitted?
- produces toxin tetanospasmin that upregulates excitatory synaptic activity, decreases inhibitory
- -> spastic paralysis
- classic finding: risus sardonicus = sardonic grin from face muscles being permanently flexed
- organism can survive in soil as terminal spores, get from rusty nail in soil
What is effect of clostridium botulinum?
- has AB toxin that prevents release of acetylcholine at synapse –> flaccid paralysis
- botulism
What causes botulism from clostridium botulinum
- foodborne botulism associated with improperly canned foods
- infant botulism associated with spore contamination of honey, infant powder milk
- rarely, wound botulism
- inhalational botulism [potential bioterrism]
What is stridor?
high pitched sound made when patient with airway compression inhales
What is ludwig’s angina?
- consequence of severe mixed anaerobic infections of pharyngeal space
What are micro properties of bacteroides fragilis?
- pleomorphic gram negative rod
- has polysaccharide capsule
- has catalase and superoxide dismutase so oxygen tolerance
What is the most common anaerobic gram negative to cause disease?
bacteroides fragilis
What are actinomyces? micro properties?
- gram positive
- branching filamentous rod
- molar teeth colonies on agar
- sulfur granules = colonies of actinomyes
Where can you get actinomyces infection?
spreads from sterile site like mouth to cerebral, cervicofacial, thoracic, abdominal, pelvic
who is at risk for nocardia infection?
happens a lot in patients who are immunocompromised
mirco properties of nocardia?
- beaded, branching, filament structure
- gram positive bacili
- stain with modified acid fast stain
- stain weakly positive with regular acid fast stain
- dry colonies
Where do you get nocardia infection?
lungs
brain
How do you treat nocardia?
high dose trimethoprim-sulfamethoxazole for months
How do you treat actinomyces?
treat with penicillin
How do actinomyces and nocardia differ?
both gram pos branching bacillus
actinomyces: anaerobic only
nocardia: aerobic and anaerobic
actinomyces: does not stain acid fast
nocardia: will stain acid fast
treat:
actinomyces: penicillin
nocardia: trimethoprim-sulfamethoxazole
What are properties of myobacterium fortuitum? treat?
- faster growth than myobacterium tuberculosis
- gram positive beaded bacilli [like nocardia]
- environmental organism that can contaminate surgical sites
- treat with surgical debridement, macrolides, and beta lactams
- usually very resistant to antibiotics
What are properties of corynebacterium diphtheriae? diseases?
- gram positive bacillus
- organisms do not invade
- produce exotoxin
- cause tough pharyngeal membrane –> lead to airway constriction and death
- cardiac and neurotoxicity
How do you treat corynebacterium diphtheriae? prevent?
- treat with antitoxin
- prevent with vaccine
What is DTaP?
toxin based vaccine for:
diphtheria: diphtheria toxin
tetanus: tetanus toxoid
acellular pertussis: pertussis toxin
