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enteric gnr
Enterobacteriaceae
| Question | Answer |
|---|---|
| What are the key characteristics of Enteric Gram Negative rods? | facultative anaerobes, most are motile, ferment glucose, reduce nitrates to nitrites, oxidase negative (except Pleisomonas) |
| What will Enterobacteriacea look like on blood agar? | enriched agar like blood agar: wet,gray,circular, convex, and smooth with definite edges; nonhemolytic |
| What will Enterobacteriacea look like on EMB or Mac agar? | it depends on whether the organism is a lactose fermenter or not. Lactose fermenters will be pink on MAC or purple on EMB. Nonlactose fermenters will be colorless on both. E. coli has a metallic sheen on EMB |
| What will Salmonella/Shigella look like on selective agar? | Salmonella is a H2S producer--so it will be black on HE, BS, or SS. Shigella will be colorless |
| Which Enterobacteriaceae are not lactose fermenters? | Salmonella, Shigella, Edwardsiella, Yersinia,Serratia, Proteus, Providencia, Morganella--acronym:YES3P2M |
| Which Enterobacteriaceae are H2S producers? | Salmonella, Edwardsiella, Citrobacter freundii,Proteus mirabilis, Proteus vulgaris |
| What is the IMViC reaction for E. coli? | IMViC + + - - |
| Which Enterobacteriaceae are PDA positive? | All Proteus, Providencia, and Morganella species are positive |
| Which Enterobacteriaceae are urease producers? | Most Proteus and Morganella species are positive plus Yersinia enterocolitica, some Citrobacters, and Klebsiellas are weakly positive |
| What are the O, H, K, and Vi antigens? | O= somatic (cell wall); H= flagella; K= capsular; Vi is an antigen found with Salmonella typhi |
| Which Enterobacteriaceae are nonmotile? | Shigella and Klebsiella |
| Which Enterobacteriaceae are PAD positive? | Proteus, Providencia, and Morganella |
| Which Enterobacteriaceae are urease positive? | Proteus, Providencia stuartii, Klebsiella pneumoniae (wk), and Yersinia (wk) |
| What does the ONPG test detect? | test for slow lactose fermentation. Helpful in differentiating Citrobacter (+) from Salmonella (-) |
| What are the reactions in TSI (triple sugar iron agar)? | Yellow=Acid (A); Red= Alkaline (K) Slant reaction/butt reaction. Lactose fermentation is in the slant (A=positive;K=negative). Glucose fermentation in the butt (A=+; K=-) H2S pos if black; Gas if bubbles |
| What does the indole test check for? | the enzyme tryptophanase (deaminates tryptophan). Pink ring (pos) with Indole/Kovac's reagent. |
| What does the methyl red test check for? | If glucose is metabolized by the mixed acid fermentation pathway, acidic end products are produced, which result in a low pH (Positive==red color after methyl red indicator added) |
| What does the Voges-Proskauer test detect? | Acetoin is produced from an alternate pathway for glucose metabolism. Positive=red color when KOH and alpha-napthol are added. Organisms that are VP positive are MR negative and vice versa. |
| What does the citrate test detect? | If the organism can use citrate as its sole source of carbon, the pH increases and the pH indicator changes color. Positive=change from green to blue, or growth. |
| What does the urease test detect? | Urease breaks down urea. Ammonia is released and pH increases. Change in color of pH indicator. Positive=change from yellow to pink |
| What does the PAD test detect? | Phenylalanine deaminase deaminates phenylalanine to phenylpyruvic acid. Phenylpyruvic acid reacts with ferric chloride to produce a green color. |
| What does the motility test detect? | Motile organisms grow away from the stab line in medium with an agar concentration of 0.4% or less |
| What are key reactions for E. coli? | Positive: lactose fermentation, gas, indole, MR, motility green metallic sheen on EMB |
| What diseases are caused by E. coli? | Urinary tract infections, neonatal sepsis, others E. coli O157:H7 Hemolytic Uremic Syndrome (HUS) |
| What are key reactions for Shigella? | Positive: MR Negative: lactose fermentation, gas, H2S, VP, citrate, PD, urease, motility |
| What diseases are caused by Shigella? | Bacillary dysentary (very infectious) |
| What are key reactions for Edwardsiella tarda? | Positive: gas, H2S, indole, MR, motility |
| What diseases are caused by Edwardsiella tarda? | Opportunistic. GI and Wound infections. Chief reservoir are reptiles and fresh water fish. Infections often involve aquatic environments |
| What are key reactions for Salmonella? | Positive: H2S, motility, MR Most citrate positive except S. typhi |
| What diseases are caused by Salmonella? | Typhoid fever (S. typhi). Septicemia, enteric fever, diarrhea, food poisoning. Found in poultry. May be transmitted by reptiles. S. typhi has Vi antigen |
| What are key reactions for Citrobacter freundii? | Positive: gas, H2S, MR, citrate, motility, ONPG Lactose variable. |
| What diseases are caused by Citrobacter? | Opportunistic and nosocomial infections. Sepsis, gastroenteritis, wound infections |
| What are key reactions for Klebsiella pneumoniae? | Positive: Lactose, gas, VP, citrate, urease (slow) encapsulated, usually mucoid colonies Non-motile! |
| What diseases are caused by Klebsiella pneumoniae? | Pneumonia, urinary tract infections, |
| What are key reactions for Enterobacter aerogenes (now K. mobilis)? | Positive: Lactose, gas, VP, citrate, motility, ODC |
| What diseases are caused by Enterobacter aerogenes? | Opportunistic and nosocomial infections. |
| What are key reactions for Serratia marcescens? | Positive: VP, citrate, motility Some produce a red pigment when incubated at room temperature |
| What diseases are caused by Serrratia marcescens? | opportunisitc pathogen. Pneumonia and septicemia in immunosuppressed. |
| What are key reactions for Proteus vulgaris and mirabilis? | Positive: H2S, MR, PD, urease, motility Negative: lactose swarming. Burned chocolate odor. P. mirabilis most common; indole negative. P. vulgaris indole positive |
| What are key reactions for Morganella morganii? | Positive: indole, MR, PD, urease, motility, ODC |
| What diseases are caused by Morganella? | Mainly nosocomial infections. UTI and wound |
| What are key reactions for Providencia? | Positive for indole, MR, citrate, PD, motility P. rettgeri is urease positive |
| What diseases are caused by Providencia? | urinary tract infections |
| What are key reactions for Yersinia enterocolitica? | Positive: MR, urease Negative: lactose, H2S, VP, citrate, PD Motile at RT but not 35 C. |
| What diseases are caused by Yersinia? | Y. pestis--bubonic plague Y. enterocoliticca- diarrhea and pseudoappendicitis |
| What is the appearance of E. coli on TSI, Mac, and HE agars? | TSI: A/A, gas Mac: flat, dry, pink with darker pink halo HE: yellow |
| What is the appearance of Shigella on TSI, Mac, and HE agars? | TSI: K/A Mac: colorless HE: green |
| What is the appearance of Edwardsiella on TSI, Mac, and HE agars? | TSI: K/A, gas, H2S Mac: colorless HE: green |
| What is the appearance of Citrobacter on TSI, Mac, and HE agars? | TSI: A/A or K/A, gas, H2S (or no H2S) Mac: colorless HE: green |
| What is the appearance of Salmonella on TSI, Mac, and HE agars? | TSI: K/A, gas, H2S (S. typhi tiny bit of H2S) Mac: colorless HE: green |
| What is the appearance of Klebsiella on TSI, Mac, and HE agars? | TSI: A/A, gas Mac: pink and mucoid HE: yellow |
Created by:
gleystem