Enterobacteriaceae Exam 2 Flashcards
Enterobacteriaceae spp. general characteristics?
Gram - bacilli
Non-spore forming
Facultative anaerobes that ferment glucose
Reduces nitrates to nitrites
Oxidase neg
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?
Proteus spp.
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.
Peptones
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
True/false? E. coli causes both intestinal and extrainestinal pathologies.
True
What is Enteropathogenic (EPEC)?
Primarily in infants and children; outbreaks in hospital nurseries and day care centers; stool has mucous but NOT blood.
What is Enterotoxigenic (ETEC)?
“Travelers diarrhea” Watery diarrhea without blood self-limiting; travelers are going to underdeveloped countries.
What is Enteroinvasive (EIEC)?
Produce dysentery-bloody stools, may contain mucus does NOT ferment lactose. Harder to get EIEC than Shigella.
What is Enterohemorrhagic (EHEC)?
Associated with hemorrhagic diarrhea and hemolytic uremic syndrome (HUS). Does NOT sorbitol. Does NOT contain leukocytes which distinguishes it from dysentery caused by Shigella.
What is the treatment for E. coli 0157:H7?
Usually fluids, possibly IV, in cases of HUS may need dialysis.
How does 0157:H7 differs from other E. coli species?
Doesn’t ferment sorbitol creating CLEAR colonies.
What is the treatment for ETEC, EIEC, EPEC, EHEC, and EAEC?
Rehydration
Antibiotics is contradicted-resistance
What is Enteroaggregative (EAEC)?
Causes diarrhea by adhering to the mucosal surface of the intestine; watery diarrhea
What is the most common cause of UTI’s and kidney infections?
UPEC-E. coli
What plate should urine specimens incubated to?
SBAP and MacConkey
What is the significance of finding 3 different colonies on a culture plate?
It is considered contaminated and not worked up
What are the 2 species for Salmonella?
S. enterica (human pathogen) and S. bongori (animal pathogen)
What are the 3 important serotypes of S. enterica?
Typhimurium, Enteritidis, and Typhi
What species has been tied to contaminated milk?
Salmonella serotype Typhimurium
What is salmonellosis?
Accumulation of Salmonella bacteria causing gastroenteritis aka food poisoning.
Most cases resolved without antibiotics.
Which Salmonella serotype is the most common in the US?
Enteritidis
Which Salmonella serotype only lives in humans but is not normal flora? What disease does it cause?
Salmonella serotype Typhi
Causes Typhoid fever
Spread from person to person
Who would be the primary reservoir for Shigella?
Humans; flies may spread bacterium from feces to food as well.
General characteristics of Shigella?
Grows well on MacConkey’s, HE, XLD
Non-lactose fermenter, non-motile
Methyl red +, VP -, citrate -
Why would you need to boil Shigella spp.?
Boiling removes the capsule. Boiling kills the organism but doesn’t alter the antigen.
General characteristics for Klebsiella, Enterobacter, Serratia, and Hafnia spp.?
Some are non-motile
Citrate + H2S - VP + Urease + Phenylalanine deaminase -
What is Klebsiella pneumoniae resistant to? What do the colonies look like?
Ampicillin
Large, mucoid, stringy colony
Lactose fermenter, non-motile, encapsulated.
Indole - MR variable VP + Citrate +
What organism causes Donovanosis aka granuloma inguinale (STI)?
Klebsiella granulomatis
ID for Enterobacter spp.?
Lactose fermenter
Mucoid colonies
VP +, Indole -, Motile
Often associated with contaminated medical devices
ID for Serratia spp.?
Motile, DNase and OPNG +
Variable lactose fermenter
Once considered nonpathogenic; now virulent, antibiotics strains exist. Associated with contaminated catheters.
ID for Hafnia alvei?
Non-lactose fermenter
Citrate -
Has been recovered from stools/wounds
ID for Citrobacter spp?
Slow lactose fermenter
Opportunistic, nosocomial acquired, UTI, respiratory tract, neonatal meningitis
ID for Proteus mirabilis?
Swarming growth
Urease + INDOLE -
UTI, wound infection, pneumonia, septicemic
Antibiotic SUSCEPTIBLE
ID for Proteus vulgaris?
Swarming growth
Urease + INDOLE +
UTI, nosocomial, immunosuppressed
More antibiotic RESISTANT
ID for Yersinia spp?
Safety pin appearance
Small, pin-point colonies, may or may not produce alpha hemolysis.
Non-lactose fermenting
Bile salts enhance growth
ID for Yersinia enterocolitica?
Growth on CIN yields bull’s eye colonies (dark red center with surrounding clear halo).
What disease is associated with Yersinia pestis?
Plaque
What BS level should Yersinia pestis be handled?
BS level 3
Which form of plaque is the most severe?
Pneumonic-pulmonary
Which organism is associated with cold blooded animals and is uncommon in humans?
Edwardsiella tarda
ID for Edwardsiella tarda?
Non-lactose fermenter
VP - Indole +
