Enteric and Anaerobe Lab Flashcards Preview

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Flashcards in Enteric and Anaerobe Lab Deck (65)
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Describe Enterobacteriaceae

These are facultative anaerobes that:

-ferment glucose

-have peritrichous or no flagella

-oxidase negative

-reduce nitrate to nitrite


Where are Enterobacteriaeceae found?

most are found as normal flora or pathogens in the vertebrate gut. A few can survive in the environment



What are the lactose fermenting enterobacteriaceae?

-E. Coli

-Klebisella pneumoniae





Describe Klebsiella pneumoniae

Mainly an opportunist causing:

community and nosocmial pneumonoa


-wound infections




What are the nonlactose fermenters of enterbactericeae?

-Salmonella Typhi and Enteritidis


-Proteus and Morganella

-Yersinia Pestis and enterocolitica

-Edardsiellla and Hafnia


The presence of E. coli in surface or well water is an indication of what?

animal or human fecal contamination


How can E. Coli be tested for in water?

by performing a coliform count by plating samply on media that are selective for Enterobacteriaceae and differential for lactose fermenters (note that other bugs such as Klebsiella and Enterobacter may add colonies to this test since they can also ferment lactose)


How can you distinguish between E. coli colonies and other lactose-fermenting colonies?

IMViC test (Indole production from tryptophan, Methyl red (large amount of acid from glucose), Voges-Proskauer (test that detects the production of acetylmethyl carbinol from glucose) and Citrate (utilization)



T or F. The IMViC rxns are used to distinguish between the fecal coliform E. Coli and Klebisella or Enterobacter (not neccessary fecal coliforms)



How would E. Coli react to a IMViC?

Indole and Methyl Red +

VP and Citrate -


How would klebisella and Enterobacter react to a IMViC?

Indole and Methyl red -

Citrate and VP +


How can E Coli and E. Coli coliforms be differentiated?

A Colilert test, a broth-based test that distinguishes between coliforms and E. Coli based on the ability of coliform B-galactosidase to degrade ONPG subtrate and E. Coli B-glucuronidase to degrade MUG substrates


Where do anaerobes generally cause infection?

in sites continguous to a surface harboring indigious anaerobic flora when the surface has been breached and conditions favor growth

Specimens MUST be obtained from the acutal site of infection (e.g. abscess, internal body space) anf free from contaminating normal anaerobic flora. In the lab, special anaerobic collection dervies are required for collection ant special techniques are needed for ID


Strict anaerobes account for __% of bacteria in a fecal specimen



What ANAEROBES do cause GI disease?

-Clostridium Perfringens (foodbourne diarrhea)

-C. diff 

-C. botulinum (not normal flora; infent and wound botulism, an infection; foodbourne botulism in adult, an intoxication)


How should C. perfringens be ID'd?

Stool culture and suspect foods to detect high conc of C. perfringens


How should C. diff be ID'd?

Culture: Selective culture and cytotoxin production by isolates

Culture Independent: Toxin detectio, C. diff antigen detection, and/or NAAT of C. diff markers


How should C. botulinum be ID'd?

Culture: Selective culture and toxin testing by isolates from suspect food or stool (or wounds)

Culture independent: Toxin detection (mouse bioassay or toxin antigen test) in stool, serum, or suspect foods


Info on suspected diagnoses and tx are important to include with requests on the specimens being sent to labs. For ex., labs will not attempt to ID organisms that compete poorly with normal gut flora on typical enteric media (Vibrio and Yersinia)


As a general rule, stool specimens should be:

-selected from the actual site of infection

-collected appropriately and in a timely manner


Stool sampling

Stool specimens to detect enteric pathogens should be collected from from extaneous material (urine, barium preps, laxatives) and submitted to the lab ASAP


T or F. Gram +, - and anaerobes can cause bacteremia



Describe a proper blood draw for bacteremia

-properly decontaminate puncture site 

-collect 8-10 mL/set

- collect into appropriate media types (aerobic or anaerobic)

-collect 2-3 sets from different puncture sites


How are blood draws from suspected bacteria handled?

Almost always cultures from primary isolation and purification of potential pathogens from other flora. This generally takes 18-24 hrs (longer for slowing growing organisms). After isolation of potential pathogens, additional ID procedures and sometimes secondary isolations are needed. These may add an additional 18-24 hrs


T or F. Most enteric-related bacteria can be distinguished from each other just using a BAP 



Describe MacConkey Agar

It contains bile salts and crystal violet which inhibit the growth of most gram + bacteria (selects for gram neg enterics) It also has glucose and lactose and a pH indicator which permit differentiation of lactose utilizing and lactose non-utilizing bacteria (however both Lac+ and Lac- enterobacteriaceae will grow due to the presence of other nutrients)


What is one very important use of MacConkey agar/

Distinguishing between E. Coli (lactose +, red/pink) and Shigella/Salmonella (both lactose negative, white/colorless)


How is E. Coli O157 ID'd?

A special MacConkey agar in which sorbitol is substituted for lactose because more E. Coli CAN ferment sorbitol (pink/red) while O157 cannot (white)


What is EMB agar used for?

semi-selective and differential plating medium for preliminary ID of enteric-related GRAM NEGATIVE rods

Similar in utility to MacConkey