Flowchart 1r4m6

Microbiology Lab Diagnostic Flowcharts by 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

Diagnostic Reactions Catalase +

Diseases

Staphylococcus –aureus (coagulase +, beta) –epidermidis (coagulase –) –saprophyticus (coagulase –)

+ pale yellow colonies, cocci in grape-like clusters

Streptococcus –pyogenes (group A, beta) –agalactiae (group B, beta) –bovis (group D, alpha) –pneumoniae (alpha) –viridans (alpha)

+ off-white small colonies, cocci in grape-like clusters

Catalase –

Pharyngitis, rheumatic fever Pyoderma, acute glomeronephritis Pneumonia Meningitis Subacute bacterial endocarditis

Enterococcus –enterococcus faecalis

+ white medium colonies, cocci in long chains

Catalase –

Endocarditis UTI

Neisseria –meningitidis (ferments maltose) –gonorrhoeae (cannot ferment maltose)

– small, kidneybean shaped diplococci

Oxidase +

Menigitis Urethritis PID

Abcesses Food poisoning Toxic shock syndrome Pneumonia

*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 + for when 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 Bacillus –anthracis (non-motile, catalase +) –cereus (motile!)

Spores YES

Diagnostic Reactions Only AEROBIC Gram + rod that forms spores.

Diseases Anthrax exotoxin Food poisoning

Colonies grow in long chains.

Clostridium YES –botulinun (blocks Ach at NM junction) –tetani (Inhibits GABA, glycine) –perfringens (food poisoning, necrosis) –difficile (inflammatory lesion of colon)

Botulism Food poisoning Wound infections Gas gangrene When inhibits neurotransmitters, often see Pseudomembranous colitis flaccid paralysis (Ach) or spastic paralysis (GABA, glycine)

Corynebacterium –diptheriae

NO

Selective medium: Loeffler's agar; since difficult to separate

Listeria –monocytogenes

NO

Catalase + DOES NOT produce exotoxins Beta hemolytic Opportunistic meningitis Tumble-weed motility LPS-like component Intracellular reproduction in mononuclear phagocytes

Only ANAEROBIC G+ rod that forms spores.

Diptheria (URI). CDEF = Corynebacterium Diptheriae blocks Elongation Factor; so inhibits protein synth in all eukaryotic cells

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 on MacConkey +

Glucose Metabolism Ferments glucose

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

–

Diseases

Pseudomonoadaceae + –Pseudomonas aeruginosa (smells like grapes, procyanin)

+

Oxidizes glucose

Pneumonia, meningitis UTI, Burn infections

Vibrionaceae –Vibro cholera (comma-shaped)

+

+

Ferments glucose

Cholera ("rice-water" stools) Diarrhea

Campylobacteraceae –Campylobacter jejuni (curved or S-shaped) –Helicobacter pylori (curved or S-shaped)

+

+

Inert to glucose

Diarrhea (C. jejuni) Gastritis (H. pylori)

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!

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 Haemophilus influenza

Lab findings Coccobacillus Growth requires factor V (NAD) and factor X (heme). Found in old fashioned (not modern) chocolate agar

Diseases URI Pneumonia Meningitis

Legionella pneumophila

Stains very lightly

Legionaire's disease Pneumonia 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 Francissella tularensis

Lab findings From rabbits, e.g. Lawnmover-vs-rabbit nest case. Spread by ticks.

Diseases Caseating granulomas can form throughout body. Intracellular growth in monocytes and PMNs allow it to evade antibodies and complement-mediated lysis.