Flashcards in Enterobacteriaceae Exam 2 Deck (66)
Enterobacteriaceae spp. general characteristics?
Gram - bacilli
Facultative anaerobes that ferment glucose
Reduces nitrates to nitrites
Catalase pos (except for Shigella dysenteriae)
Which organism is the most common cause of nosocomial infections?
E. coli (Enterobacteriaceae spp. are the majority of nosocomial infections)
ID for Enterobacteriaceae spp.?
Large, gray, smooth colonies on SBAP and chocolate agar.
Which organisms are lactose fermenters?
E. coli, Klebsiella pneumoniae, Enterobacter aerogenes, Enterobacter cloacae, and Citrobacter spp.
Which organisms are non-lactose fermenters (lack beta-galactosidase)?
Proteus spp., Salmonella spp., Shigella spp., Serratia marcescens, Yersinia enterocolitica.
*Shigella does contain beta-galactosidase but not permease so with ONPG is a late lactose fermenter.*
What is lactose composed of?
Glucose and galactose
What are the 2 enzymes required for lactose to be utilized by bacteria?
Lactose permease- Allows for penetration of lactose molecule into bacterial cell.
Beta-galactosidase- Hydrolyzes lactose once within the bacterial cell wall resulting in formation of glucose + galactose.
What are coliforms?
Coliform bacteria are non-pathogenic strains of microorganisms (not E. coli 0157:H7).
When are coliforms usually used?
As a bacterial indicator of sanitary quality of foods, water, and processing environments.
General characteristics for coliforms?
Rod-shaped, gram neg, non-spore forming bacteria which can ferment lactose with the production of acid and gas.
Common coliforms include?
Escherichia, Citrobacter, Enterobacter, Klebsiella, and Serratia.
How does disease transmit in Enterobacteriaceae spp.?
Endogenous infections-normal flora going into sterile sites
Ingestion of contaminated foods-Shigella and Salmonella
Insect vector- Yersinia pestis transmitted by fleas
Horizontal transmission- person to person; nosocomial infections.
Which organisms are not motile?
Klebsiella, Shigella, Yersinia
Which organism creates a swarming effect on blood and chocolate agars?
If not processed quickly, what media should the specimens should be collected and transported in?
Cary-Blair, Amies, or Stuart media
Which media can be used on Enterobacteriaceae spp.?
SBAP, Chocolate, MacConkey, HE, XLD, TSI, Salmonella-Shigella agar, Hektoen enteric agar, eosin-methylene blue agar, cefsulodin-irgasan-novobiocin agar, Citrate agar, and phenylalanine agar.
What does ONPG test for?
Tests for beta-galactosidase activity and identifies late lactose fermenters (lack permease-color change) from non-fermenters (lack both-no color change).
**OPNG is substituted for lactose and enters bacterial cell walls more easily without need for permease.**
*Shigella sonnei is a late lactose fermenter*
What does TSI contain?
Contains glucose, lactose, sucrose, and phenol red as pH indicator; starts red in color.
Why do some slants convert to yellow and back to red in 18-24 hours.
TSI slant for E. colK i
A/A gas +, H2S -
TSI slant for Salmonella
K/A gas +, H2S +
TSI slant for Shigella
K/A gas -, H2S -
True/false? Most hospital labs will perform gram stains of stool specimens as non-pathogenic intestinal flora look similar to enteric pathogens.
False. Will NOT.
If you do a gram stain, look for presence of WBC's which could indicate invasive pathogen.
Which antigens do Enterobacteriaceae possess?
O antigen- somatic (cell wall), heat-stable antigen.
H antigen- flagellar, heat liable antigen
K antigen- capsular, heat-labile antigen
O antigen is used to group which organisms?
E. coli, Salmonella, and Shigella
H antigen can be used to group which organisms?
Salmonella and E. coli (Shigella non-motile)
K antigen is used to type which organism
Klebsiella pneumoniae, K1 antigen of E. coli
Presumptive ID for E. coli?
Oxidase -, Indole +
Gram neg rods
Growth on MacConkey (pink)
*Other characteristics: Simmons citrate negative. Usually motile. Voges-Proskauer test negative.*
Definitive ID for E. coli?
Beta-hemolysis or lactose positive AND PYR negative