Biol 241L: Exp 5-8

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What makes water potable?

absence of human pathogens

What is used as indicators of fecal matter?

coliforms

What is the presumptive test in analysis for potable water?

inoculation into lauryl tryptose broth tubes

What are the results for the presumptive test in analysis for potable water?

production of gas after incubation at 37 °C for 24-48h

What is the confirmed test in analysis for potable water?

inoculation into brilliant green lactose bile broth or streak culture on EMB agar

What are the results for the confirmed test in analysis for potable water?

gas after 48±3h/37±0.5 °C, typical coliform colonies after 24h/37 °C

Why is the confirmed test done after a presumptive test?

positive results may be from Clostridium or Bacillus

What is the completed test in analysis for potable water?

inoculation into lauyrl trptose broth and gram-stain

What are the results for the completed test in analysis for potable water?

gram-negative, nonsporeforming bacilli, production of acid and gas from lactose fermentation

What do E. coli colonies look like on EMB agar?

small, metallic sheen, flat, green

What do Enterobacter aerogenes colonies look like on EMB agar?

large, mucoid, pink

Which coliform is the more reliable sewage indicator and why?

E. coli because Enterobacter can be isolated from soil and grains

What is the Endo medium?

selective medium containing lactose and basic fuchsin

How is Endo medium used to identify coliforms?

aldehydes from coliform breakdown of lactose react with basic fuchsin to form metallic green sheen

What identifies total coliforms?

ferment lactose + acid/gas in 48h/35 °C, green colonies on Endo in 24h/35 °C

What identifies fecal coliforms?

ferment lactose + acid/gas, blue colonies on m-FC in 24±2h/44.5±0.2 °C

What advantages are there to the membrane filter test in analysis for potable water?

greater sensitivity, larger volumes tested, higher degree of reproducibility, shorter time

What disadvantages are there to the membrane filter test in analysis for potable water?

filter can be plugged by cyanobacteria or extraneous debris

Which organisms from Exp. 7 grow on EMB agar?

E. coli (green), S. typhimurium (colourless), P. aeruginosa (colourless), C. freundii (red)

Which organisms from Exp. 7 grow on Endo agar?

E. coli (green), S. typhimurium (pink), P. aeruginosa (red), C. freundii (green)

Which organisms are not lactose fermentors from Exp. 7?

B. subtilis, S. aureus, S. typhimurium, P. aeruginosa

Which organisms are lactose fermentors from Exp. 7?

E. coli, C. freundii

What is the IMViC test used for?

differentiation between coliforms

What does the Indole test do?

presence of tryptophanase to break down tryptophan into pyruvic acid, ammonia & indole

What is the procedure for the Indole test?

inoculation into tryptone broth, add Kovac's reagent to react with indole

What does the Methyl red test do?

fermentation of glucose to acidic products to limit pH (<4.5)

What is the procedure for the Methyl red test?

inoculation into MRVP tubes, add methyl red

What does the Voges-Proskauer test do?

presence of acetylmethylcarbinol (acetoin) from sugar fermentation

What is the procedure for the Voges-Proskauer test?

inoculation into MRVP tubes, add KOH+alphanaphthol, wait 20 min

What does the Citrate test do?

utilization of citrate as carbon source

What is the procedure for the Citrate test?

inoculation into sodium citrate slant with bromothymol blue

What are the IMViC test results for E. coli?

++--

What are the IMViC test results for E. aerogenes?

--++

What are the IMViC test results for C. freundii?

-+-+

What are results of the Indole test?

[✓] red ring

What are results of the Methyl Red test?

[✓] red [x] yellow

What are results of the Voges-Proskauer test?

[✓] red [x] brown

What are results of the Citrate test?

[✓] blue slant

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