Gram-negative Flashcards
One of the first steps in identifying an unknown bacterium
Gram Stain
Appear as rods
Enterpbacteriaceae and Pseudomonas spp.
Gram negative cocci
Nesseria spp and Moraxella catarrhalis
Oval coccobacilli
Haemophilus spp, Francisella spp and Acinetobacter spp
Large, moist and grow well on TSA with 5% sheep blood after 24hr of incubation
Enterobacteriaceae
Smaller but distinct colonies after 24hr
Neisseria spp
May require 48hr or more of incubation before growth is evident
Non fermentative gram negative rods and fastidious fermenters
Presence of clearing of the red blood cells around the colonies (B-hemolysis) on Blood agar
(EP MAN) E. Coli, Pseudomonas aeruginosa, Morganella morganii, Aeromonas hydrophila, commensal Neisseria spp
Only partial hemolysis of the cells, forming a greenish discoloration(a-hemolysis) around the colony
Eikenella corodens and Alcaligenes faecalis
“Swarming” edges that can spread to cover the entire plate
Proteus mirabilis and Proteus vulgaris
Bioluminescent
Photorhabdus spp.
Parasite associated with Photorhabdus
Nematodes
Yellow-orange pigment
Carotenoids
Violet or purple
Violacein
Red, maroon or yellow pigment
Phenazines
True or Flase: Carotenoids, Violacein and Phenazines are water soluble?
True
What are the composition of a media that detects pigment production?
- ) special peptones
2. ) inc. conc. of magnesium and sulfate ion
Pigment can also be observed in growth on TSA with?
Brain heart infusion agar
Loeffler’s agar
5% sheep blood agar
(BLS)
Bacterias with yellow pigment?
Enterobacter spp, Chryseobacterium,
Agrobacterium spp and Phingomonas spp
(E-CAP)
Bacterias with yellow-brown pigment?
Burkholderia cepacia and Burkholderia gladioli
Bacteria with violet pigment?
Chromobacterium violaceum
Bacterias with pink to red pigment?
Methylobacterium spp, Roseomonas spp, and some Serratia spp.
(MRS)
Bacteria that produces pyoverdin and pyocyanin pigment?
Pseudomonas aeruginosa
Water-soluble and diffusible pigment
Pyocyanin and Pyoverdin
sugar that is fermented in MacConkey Agar?
Lactose
Bacteria that grows in MacConkey Agar for 24hr-48hr
Enterobacteriaceae spp.
Bacteria that take up to 7 days of incubation for growth to appear in MacConkey Agar?
Fastidious fermenters and Nonfermentative gram-negative
Inability to grow on MacConkey Agar?
most Moraxella spp. and most of Neisseria spp
Gram-neg organisms that ferment lactose and have purple colonies as the neutral red indicator changes due to production of gas
Klebsiella pneumoniae and Escherichia coli
Do not ferment lactose and appear colorless or transparent on MacConkey Agar?
Proteus spp. and Pseudomonas spp.
Have acid reaction with often gas production after 24 hr incubation at 35-37 degree Celsius on Triple Sugar Iron (TSI) agar
Enterobacteriaceae and Aeromonas
Have weak acid reaction that may take up to 48hr to appear and will have no gas production on TSI agar
Fastidious fermentative gram-negative rods
Eikenella
Pasturella
(FEP)
No color change on TSI medium or will produce a pink, alkaline reaction as the bacteria break down the peptones in agar base
Pseudomonas
Moraxella
Nonfermentative gram-negative (PMN)
Negative for Oxidase
all members of Enterobacteriaceae
A member of enterobacteriaceae that is positive for oxidase
Plesiomonas shigelloides
Positive for oxidase?
(CNA MVP)
Campylobacter
Neisseria
Aeromonas
Moraxella
Vibrio
Pseudomonas spp.
Spp that can be distinguished from other similar non fermentatice gram-negative rods by negative oxidase reaction
Acinetobacter
Reason why medium containing whole blood should not be used for catalase?
RBCs have catalase that can cause false positive result
Why is Chocolate Agar used for catalase test?
Because RBCs have been destroyed while preparing the media
Spp with catalase positive?
Moraxella spp
Fastidious fermenters
Spp which is catalase negative
Kingella spp.
What bacteria is strongly positive in catalase test when used with 30% hydrogen peroxide(superoxol)?
Neisseria gonorrhoeae
Citrate Negative
Shigella spp.
Escherichia coli
Moraxella spp.
(SEM)
Citrate positive
many Enterobacteriaceae
Consistently positive for citrate utilization?
Alcaligenes faecalis
Achromobacter xylosoxidans
A positive citrate reaction helps distinguish ____ and _____
Roseomonas gilardii and Methylobacterium spp.
Indole positive
E.coli
Cardiobacterium hominis
Chryseobacterium indologenes
Nonfermentative gram-negative rods
What will be added to Ehrlich’s reagent for weakly reacting nonfermenters and fastidious organisms for Indole production?
1% p-dimethylaminobenzaldehyde
