Anaerobes, Antibiotic Susceptibility Flashcards
Which Clostridium species have myonecrosis?
C. perfringens
C. septicum
Concentration of gases for anaerobic conditions
90% nitrogen
5% CO2
5% hydrogen
How are anaerobic conditions achieved?
Anaerobic boxes and jars to prevent O2 from getting in
PRAS media
Pre Reduced Anaerobically Sterilized
Brucella, PEA, LKV
Brucella media
- Nonselective, similar to SBA
- Prevotella (fluorescence)
- Hemolysis observation
Phenyl Ethyl Agar (PEA)
- Selective for obligate anaerobes (both Gram pos and neg) and Gram (+) facultative anaerobes
- Inhibits G(-) rods - Enterobacteriaceae
- Inhibits swarming of Clostridia
Laked Kanamycin Vanvomycin (LKV) agar
- Inhibits G(+) organisms and aerobic G(-) rods
- Inhibits Porphyromonas
- Isolates Bacteroides and Prevotella (black pigmentation)
Bacteroides Bile Esculin (BBE) agar
- Bile resistance = growth on BBE agar
- Esculin hydrolysis = black pigmentation
- Bacteroides fragilis - growth and black
- Fusobacterium mortiferum - growth
- Bilophila wadsworthia - fish eye appearance
- Inhibits aerobic G(-) rods
Egg Yolk Agar
- Detects presence of lecithinase and lipase
- Lecithinase: opaque precipitate around colonies (C. perfringence)
- Lipase: iridescent sheen on colony surface (F. nacrophorum)
- Proteolysis: clearing around colonies
Chopped meat carbohydrate agar
Enrichment broth
- Detects organisms in low numbers (helps with recovery)
Thioglycolate broth
Sodium thioglycollate and L-cysteine - reducing agents, helps save anaerobes from dying
- anaerobes grow at the bottom of the tube
Acceptable specimens for anaerobes
NOT:
Sputum, feces, gastric contents, all swabs, urine
Clostridium perfringens
- GI tract: food poisoning
- Non GI tract: myonecrosis (gas gangrene)
- Found in: soil/GI tract
- Gram stain: boxcar, G(+) straight rods
- Colony morphology: double zone beta hemolysis, lecithinase (+) opaque precipitate on Egg Yolk Agar
- Reverse CAMP with Group B Strep
- alpha and beta toxins
Which organism has turbidity around colonies on Egg Yolk Agar?
Clostridium perfringens
Alpha and beta toxins for C. perfringens
Type A/Alpha toxin:
- contaminated meat/gravies
- mild cramps, diarrhea, self limiting
- from spores
> alpha toxin for non GI tract/in muscle instead —> gas gangrene/myonecrosis
Type B/Beta toxin:
- life threatening, necrotizing enterocolitis (inflamed intestines)
- bloody diarrhea with vomiting
Clostridium botulinum
- Botulism: food poisoning
- Ingestion of toxins in food, soil contaminated food or honey
- Virulence factor: neurotoxins, release of acetylcholine can cause paralysis
- “Tennis racket” gram stain
- Lipase (+) - iridescent on Egg Yolk Agar
- Adult botulism: toxin in food already
- Infant botulism: toxin released in GI tract (food has spores)
Clostridioides difficile
- AAD (antibiotic associated diarrhea), colitis
- Virulence factors: A toxin (enterotoxin), B toxin (cytotoxin)
- watery diarrhea
- pseudomembranous colitis (PMC): yellow plaques through colonic mucosa
Media:
- CCFA
- Chartreuse fluorescence
- Barnyard odor
Barnyard odor
Clostridioides difficile
Clostridium septicum
- Myonecrosis
- Typhilitis (neutropenic colitis): sepsis in immunocompromised
- Uneven gram stain, Citron bodies
- Medusa Head on Brucella
- Beta hemolytic
- Swarming within 24 hours
Clostridium tetani
- Wound/puncture contaminated in soil
- Tetanus: trismus (lockjaw) and Rudy’s sardonicus (distorted grin)
- G(+) but turns G(-) after 24 hours
- Oval spores, drumstick appearance
- Narrow zone of beta hemolysis
Cutibacterium (Propionibacterium) acnes
- Joint infection
- “Palm of Hands” in bunches on gram stain
- Catalase and Indole (+)
- Gram (+) non-spore forming rods
Bacteroides fragilis
- Mucosal surfaces of oral cavity and GI tract
- Abscesses
- Foul odor
- Bacteremia, septic arthritis, aspiration pneumonia, chronic sinusitis, decubitus ulcers
- Black colonies on BBE agar (bile esculin resistant and hydrolyzes esculin
Prevotella
- Normal flora of oral cavity
- Black colonies on agar
- Brick-red fluorescence
- Colistin S (KV - R)
- Lipase (+)
Porphyromonas
- UV fluorescence (pink/orange/red)
- Some species pigmented/black and mask UV pigment
- Asaccharolytic
- Vancomycin S, KC - R
- Does not grow on BBE/LKV
Fusobacterium nucleatum
- Isolated from oral cavity (biofilms)
- KC (S), V (R)
- Beta hemolytic
- Chartreuse fluorescence
- Ground glass/bread crumb colonies
- Indole (+)
- No growth on PEA/LKV/BBE except F. mortiferum (also indole (-))
- Long, tapered thin rods
What are the Gram (+) anaerobic cocci?
Peptostreptococci (brain abscess)
Finegoldia
Parvimonas
Peptoniphilus
Murdochiella
Staphylococcus
Anaerococcus
What are the Gram (-) anaerobic cocci?
Veillonella
Megasphaera
Anaeroglobus
Negativicoccus
Acidaminococcus
How MIC is performed
MIC - minimum inhibitory concentration, the first tube without organisms growing
Broth dilution
Same inoculum, different concentrations of antibiotics.
Bactericidal
Kills bacteria
Bacteriostatic
Inhibits bacteria, reversible
Difference between Prevotella and Porphyromonas?
Prevotella: vancomycin resistant, brick red fluorescence
Porphyromonas: vancomycin susceptible, pink red orange fluorescence
Beta lactam resistance
Beta lactams bind enzymes (PBPs - penicillin binding proteins) which inhibit cell wall synthesis
- weaken cell wall and cause cell death
ESBLs (Extended Spectrum Beta- lactamases)
Organisms can hydrolyze beta lactam rings
Resistance to penicillin, cephalosporin and aztreonam
CRE - carbapenem resistant enterobacteriales
WITH carbapenemase enzyme: Inactivate carbapenems and other beta lactam antibiotics
WITHOUT carbapenemase: mutations in porin gene prevent carbapenems/antibiotic from entering bacterial cell wall
Protein synthesis inhibitors
Aminoglycosides: gentamycin, kanamycin, tobramycin, streptomycin, amikacin
Macrolides: erythromycin, clindamycin
Streptogramins: dalfopristin, quinopristin
Oxazolidinones: linezoid
Chloramphenicol: chloramphenicol
Tetracyclines: doxycycline, tigecycline, tetracycline
Glycylglycines: improved tetracyclines
What do beta lactams inhibit?
Cell wall
Examples of beta lactams
Penicillin, cephalosporin, carbapenems, monobactams
Cell wall inhibitors
Beta lactams
Glycopepetides
Cell membrane inhibitor
Lipopeptides
Inhibitors of DNA/RNA synthesis
Disrupt DNA -
- Fluoroquinolones: ciprofloxacin, levofloxacin
- Metronidazole
Inhibits RNA/protein synthesis -
- Rifamycin
Metabolic inhibitors
Folic acid inhibitors -
- Sulfonamide
- Trimethoprim
- Nitrofurantoin
