flowchart (1) organism recognition
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Microbiology Lab Diagnostic Flowchartsby Shishin Yamada
last updated: September 23, 1998
Gram Positive Lab Flowchart
Gram Negative Lab Flowchart
© "First Aid for the USMLE Step 1" by Appleton and Lange.
Bacterial Cocci*Many thanks to Jason Collins for citing reference material for these charts
(from "The Microbiology Companion" book by ALERT and ORIENTATED publishers)
Species Gram DiagnosticReactions
Diseases
Staphylococcus–aureus (coagulase +, beta)–epidermidis (coagulase –)–saprophyticus (coagulase –)
+pale yellowcolonies, cocciin grape-likeclusters
Catalase + AbcessesFood poisoningToxic shock syndromePneumonia
Streptococcus–pyogenes (group A, beta)–agalactiae (group B, beta)–bovis (group D, alpha)–pneumoniae (alpha)–viridans (alpha)
+off-white smallcolonies, cocciin grape-likeclusters
Catalase – Pharyngitis, rheumatic feverPyoderma, acute glomeronephritisPneumoniaMeningitisSubacute bacterial endocarditis
Enterococcus–enterococcus faecalis
+white mediumcolonies, cocciin long chains
Catalase – EndocarditisUTI
Neisseria–meningitidis (ferments maltose)–gonorrhoeae (cannot ferment maltose)
–small, kidney-bean shapeddiplococci
Oxidase + MenigitisUrethritisPID
*KEY:Catalase = Mix with 3% hydrogen peroxide. Catalase + if forms bubbles.Coaguase = Check for coagulase enzyme. Coagulase + if plasma clots, clumps or forms precipitate.Oxidase = Determines presence of cytochrome-c in bacteria. Oxidase + if paper turns dark purple quickly.
Alpha = alpha hemolysis (very small clear area of hemolysis around colonies on blood agar)Beta = beta hemolysis (large clear area of hemolysis around colonies on blood agar)Gamma = NO hemolysis (no signs of hemolysis around colonies on blood agar)
Fermentation of specific sugars means that they change the pH of the tube over 48 hours. Fermentation is + forwhen the upper third of the tube turns yellow, while the bottom two-thirds remains red.
Gram Positive Rods*Many thanks to Jason Collins for citing reference material for these charts
(from "The Microbiology Companion" book by ALERT and ORIENTATED publishers)
Species Spores Diagnostic Reactions DiseasesBacillus–anthracis (non-motile, catalase +)–cereus (motile!)
YES Only AEROBIC Gram +rod that forms spores.
Colonies grow in longchains.
Anthrax exotoxinFood poisoning
Clostridium–botulinun (blocks Ach at NM junction)–tetani (Inhibits GABA, glycine)–perfringens (food poisoning, necrosis)–difficile (inflammatory lesion of colon)
YES Only ANAEROBIC G+rod that forms spores.
When inhibitsneurotransmitters, often seeflaccid paralysis (Ach) orspastic paralysis (GABA,glycine)
BotulismFood poisoningWound infectionsGas gangrenePseudomembranous colitis
Corynebacterium–diptheriae
NO Selective medium:Loeffler's agar; sincedifficult to separate
Diptheria (URI).CDEF = CorynebacteriumDiptheriae blocks ElongationFactor; so inhibits protein synth inall eukaryotic cells
Listeria–monocytogenes
NO Catalase +Beta hemolyticTumble-weed motilityLPS-like componentIntracellular reproductionin mononuclear phagocytes
DOES NOT produce exotoxinsOpportunistic meningitis
ENTERIC Gram Negative Rods*Many thanks to Jason Collins for citing reference material for these charts
(from "The Microbiology Companion" book by ALERT and ORIENTATED publishers)
Species Oxidase Growth onMacConkey
GlucoseMetabolism
Diseases
Enterics–Escherichia coli (metallic-green on EMB)–Shigella (non-motile, no flagella)–Salmonella (S. typhi makes a little H2S, swims like a salmon in body for systemic infection)–Klebsiella pneumonia–Enterobacter aerogenes–Proteus vulgaris(H2S gas, "swarms")–Yersinia pestis
– + Fermentsglucose
Traveller's diarrhea (ETEC)Dysentery (EIEC)Diarrhea and vomiting (EPEC)Hemolytic colitis (EHEC)Very bloody diarrhea (Shigella)Enterocolitis/gastritis (Salmonella)Nosocomial/pneumonia (Kleb)UTI (Enterobacter, Proteus)Bubonic plague (Yersinia)Many other shitty effects!
Pseudomonoadaceae–Pseudomonas aeruginosa (smells like grapes, procyanin)
+ + Oxidizesglucose
Pneumonia, meningitisUTI, Burn infections
Vibrionaceae–Vibro cholera (comma-shaped)
+ + Fermentsglucose
Cholera ("rice-water" stools)Diarrhea
Campylobacteraceae–Campylobacter jejuni (curved or S-shaped)–Helicobacter pylori (curved or S-shaped)
+ + Inert toglucose
Diarrhea (C. jejuni)Gastritis (H. pylori)
RESPIRATORY Gram Negative Rods*Many thanks to Jason Collins for citing reference material for these charts
(from "The Microbiology Companion" book by ALERT and ORIENTATED publishers)
Species Lab findings DiseasesHaemophilus influenza Coccobacillus
Growth requires factor V (NAD) andfactor X (heme). Found in old fashioned(not modern) chocolate agar
URIPneumoniaMeningitis
Legionella pneumophila Stains very lightly Legionaire's diseasePneumonia with fever, headache,diarrhea, vomiting
Bordetella pertusis Selective medium: Bordet-Gengou agar Whooping cough (only humans)
ZOONOTIC (associated with an animal)Gram Negative Rods
Species Lab findings DiseasesFrancissella tularensis From rabbits, e.g. Lawnmover-vs-rabbit
nest case. Spread by ticks.Caseating granulomas can formthroughout body. Intracellulargrowth in monocytes and PMNsallow it to evade antibodies andcomplement-mediated lysis.
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