Micro Lab Notes Final - Microbiology Lab Notes Intro To...

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Microbiology Lab Notes Intro To Micro (Lab 1 & 2) Gram stain is the most critical identifier while waiting for culture results Heating wetted slides can kill bacteria & alter gram stain & morphology Gram Stain Technique o Flood with crystal violet (rinse) o Flood with gram’s iodine (rinse) o Apply acetone-alcohol dropwise o Flood with safranin (rinse) Gram Stained Organisms o Staphyloccocus (all members of the genus)------------------------------------ Gm (+), cocci occurring mainly in pairs, tetrads or grape-like clusters o Streptococcus (all members of the genus) Gm (+), cocci in chains Cocci are more elongated along the chain (vs. staph is very round) S. pneumoniae has shorter chains than most in the genus and are often found as lancet-shaped diplococci (may see halo) o Neisseria Large Gm (-) cocci in pairs (one cocci is generally smaller than the other in the pair) Resemble kidney beans with long axis parallel to plane of division May sometimes appear gm (+) o E. Coli Gm (-) rods with bipolar staining present----------------- Difficult to distinguish between species of Gm(-) rods Rules-of-thumb o All cocci are Gm (+) except Neisseria- aerobe Veillonella- anaerobe Any normal gm (+) cocci that have aged or have been grown in an acidic environment can stain Gm(-) o Some rods are Gm(-), some are Gm(+), memorize the different genera o Spores are generally unstained, but can be stained using malachite green Clostridium & Bacillus are the main spore producers Clostridium tetani has terminal spores (tennis racket), other Clostridia are subterminal Acid-Fast Bacteria o Bacteria with high concentrations of waxes & lipids makes them resistant to staining & decolorization o Mycobacterium & Nocardia are the main genuses Patient Cases
o Case 1: BPH patient has right flank tenderness & UTI Clean catch of urine shows gram negative rods that are short & fat Dx: E. coli pyelonephritis o Case 2: RA patient has sudden onset of swelling in her left knee. Aspiration of the knee shows cloudy fluid with leukocytosis, low sugar & high protein signaling septic arthritis Aspirate showed Gram positive cocci in clusters Dx: S. aureus soft tissue infection o Case 3: Post-splenectomy patient presents with cough with rust-colored, purulent sputum & consolidated right lower lobe pneumonia. Gm stain and culture were non-dx, but blood was positive within 24 hours Blood culture was made to show gram positive cocci mostly in singles ↓, but some pairs Dx. S. pneumonia (bacteremia common in these patients) Note: Splenectomy predisposes patients to encapsulated bacteria (especially streptococci) Enteric Bacteriology (Lab 3 & 4) Enteric bacteria are those that colonize or infect the GI tract Enterobacteriaceae are Gm (-) rods that ferment glucose, reduce nitrate and have peritrichous flagella when motile (except Shigella & Klebsiella) o They are facultative with an electron transport chain (not CytC) Enterococci, lactobacilli, certain obligate anaerobes & P. aeruginosa are also commonly found in the colon

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