Microbiology book Flashcards
Media for gram-negative rods
MAC
Result of lactose fermenters on MAC
pink, dark pink, or red colonies
Result of non-lactose fermenters on MAC
clear and colorless
SBA and CHOC gram-negative rods produce large colonies that appear
gray and sometimes mucoid
dry, pink colonies with a surrounding “halo” of pink, precipitated bile salts
Escherichia/Citrobacter-like
large, mucoid pink colonies that occasionally have cream-colored centers
Klebsiella/Enterobacter
partial lysing of RBCs in an SBA plate around
green discoloration of the medium
a-hemolysis
complete clearing of erythrocytes in SBA
b-hemolysis
produce a wide, deep, clear zone of β-hemolysis
group A β-hemolytic streptococci (Streptococcus pyogenes)
a narrow, diffuse zone of β-hemolysis close to the colony
group B β-hemolytic streptococci (Streptococcus agalactiae and Listeria monocytogenes)
shows medusa head (filamentous appearance)
Bacillus anthracis
Dry appearance of colonies
Diphtheroids
moist, creamy white to yellowish colonies
Staphylococci
produce colonies that are brittle, crumbly, and wrinkled, resembling bread crumbs on a plate.
Nocardia spp.
Pigment: green, sometimes a metallic sheen
P.aeruginosa
Pigment: brick red especially at room temperature
Serratia rubidaea
Kluyvera spp pigment
blue
Chromobacterium violaceum pigmentation
purple
Pigment is brown-black (anaerobic)
Pigment production for these organisms is variable
Prevotella melaninogenica
Odor: old sock (stocking that has been worn continuously for a few days without washing); this odor is evident when bacteria are growing on mannitol salt agar
S. aureus
Odor: fruity or grapelike
P. aeruginosa
Odor: putrid
P. mirabilis
Odor: musty basement, “mousy” or “mouse nest” smell
Haemophilus spp
Odor: freshly plowed field
Nocardia
phenotypic testing for identifying different strains of bacteria
uses antibodies to detect specific antigens located on the bacterial surface
serotyping
genotype testing; more accurate than examining the phenotype
Molecular bioiogy
utilize carbohydrates by oxidation (aerobically), fermentatively (anaerobically), or both
Oxidation-Fermentation Test
useful in the presumptive identification of gram-negative enteric bacteria (intestinal pathogens)
TSI and KIA
TSI difference from KIA
TSI contains sucrose
Carbohydrate present in KIA
glucose and lactose
KIA: lactose is present in a concentration
10:1 (glucose)
TSI: sucrose is also present in a ___ concentration
1%
1% lactose and 0.1% glucose, 1% sucrose
Detect production of H2S in TSI and KIA
Ferrous sulfate and sodium thiosulfate
pH indicator for KIA and TSI
Phenol red
Reactions on TSI Agar or KIA:
No fermentation
Red/Red
alkaline slant/alkaline butt (K/K)
alkaline slant/no change (K/NC).
Reactions on TSI Agar or KIA:
Glucose fermentation only, no lactose (or sucrose in TSI) fermentation
Red/Yellow
alkaline slant/acid butt (K/A)
Reactions on TSI Agar or KIA:
Lactose (or sucrose or both) fermentation
Yellow/Yellow
acid/acid (A/A)
Reactions on TSI Agar or KIA:
alkaline slant/acid butt, H2S in butt
K/A, H2S
Reactions on TSI Agar or KIA:
acid slant/acid butt, H2S in butt
A/A H2S
determine presence of B-galactosidase; lacks presence of B-galactoside
Ortho-Nitrophenyl-β-D Galactopyranoside Test
ONPG is structurally similar to
lactose
β-Galactosidase hydrolyzes ONPG to
galactose and o-nitrophenol
Positive result of ONPG
yellow
Methyl Red Test positive reaction
red color
Voges-Proskauer Test positive result
red
added first as a catalyst or color intensifier for VP
a-napthol
determine whether the bacterial species possess enzymes capable of decarboxylating (removing the carboxyl group, COOH) specific amino acids in the test medium.
Decarboxylase test
two amino acids commonly used to test for decarboxylase activity
Lysine and Ornithine
Medium for decarboxylase test
Moeller decarboxylase base medium
pH indicator for decarboxylase
bromocresol purple and cresol red
Decarboxylase positive:
yellow
decarboxylase negative:
purple
Amino acid: Lysine
End product:
Cadaverene
Amino acid: Ornithine
End product
Putrescine
Amino acid: Arginine
End product:
Putrescine and urea
possesses the enzyme that deaminates phenylalanine to phenylpyruvic acid
phenylalanine deaminase (PAD) test
Deaminase test is used for the initial differentiation of
PPM: Proteus, Providencia, Morganella
Positive result for deaminase test
Green
Frequently used medium for citrate utilization
Simmons’ citrate medium
Positive result for Simmons’ citrate medium
Green to blue
pH indicator of Simmons’ citrate medium
Bromothymol blue
Alternative for citrate utilization test
Christensen’s citrate
Christensen’s citrate positive result
Yellow to pink
DNase test positive:
clear zone around the bacteria
Added to DNase test for detection of bacteria
1N HCl
Alternative for HCl in DNase
Methyl green
degradation product of tryptophan
Indole
Positive result for indole test:
Red color after addition of PDAB
Ehrlich reagent contains ___ for indole
p-dimethylaminobenzaldehyde
alternative that does not use xylene for indole
Kovac’s reagent
____ method is more sensitive than Kovac’s for indole
Ehrlich method
Positive result for indole nitrate
blue green color within 2 minutes
Rapid indole test: smear onto filter paper with p-dimethylaminocinnamaldehyde
positive result:
blue green color within 2 minutes
determine whether bacteria decarboxylate or deaminate lysine; H2S is also detected
LIA; Lysine Iron Agar Slant
LIA contains:
amino acid lysine
Glucose
ferric ammonium citrate
sodium thiosulfate
LIA ph indicator
bromocresol purple
LIA is used to detect (organisms)
PPM - Proteus, Providencia, Morganella
determines if organism can use sodium malonate as its sole carbon source
Malonate utilization
Malonate Utilization positive result:
Green to Blue
Motility positive result:
movement away from the stab line or a hazy appearance
useful in differentiating Klebsiella spp. from Enterobacter and Serratia spp
Motility Indole Ornithine Agar
Positive result of Motility Indole Ornithine Agar:
Clouding of the medium or spreading growth from the line of inoculation
Nitrate and Nitrite Reduction positive result:
Diazo red dye
Determines the presence of the cytochrome oxidase
Oxidase
Positive result for oxidase test:
lavender color
Kovac’s oxidase test uses
0.5% or 1% aqueous solution of tetramethyl-ρ-phenylenediamine dihydrochloride.
Sulfide Indole Motility Agar is used for differentiating gram-negative bacteria in the family:
Enterobacteriaceae
Sulfide Indole Motility Agar positive result:
Cloudiness from inoculation
H2S black precipitate
Indole: pink to red after addition of Kovac’s reagent
determines whether a microorganism can hydrolyze urea
Urease
Preferred agar for urease
Christensen’s urea agar
Indicator for Christensen’s urea
Phenol red
Small fuzzy-edged colony with an umbonate center on SBA or CHOC agar
Eikenella corrodens
Bacterial enzyme for spot indole
typtophanase
Bacterial enzyme for ONPG
B-galactosidase
Bacterial enzyme for oxidase
cytochrome oxidase
Presumptive test for S. pneumoniae in sputum, blood, and CSF cultures
Bile solubility
Identification of group A streptococci; differentiates enterococcus from group D streptococci
PYR
Screening test for cryptococcus, proteus, and klebsiella spp., and Yersinia enterocolitica
Rapid urease
Presumptive identification of E. coli and Streptococcus anginosus group; enterohemorhagic E. coli is negative
MUG
Presumptive identification of catalase negative, gram postive cocci
LAP