Term
What is liquid broth media used for? |
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Definition
enrich sample
cultivate organisms present in low numbers |
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Term
What is a general purpose media? |
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Definition
Supports growth of broad range of organisms
Tryptic soy agar (TSA)
Nutrient Agar
Not selective or differentiating |
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Term
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Definition
Contains specific nutrients for the growth of particular species
SBA-TSA with 5% sheep RBC added (used for general isolation of organisms directly from specimens)
Chocolate agar- hemolyzed RBCs and supplements |
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Term
What is cultured on chocolate agar? |
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Definition
Chocolate agar supports fastidious organisms
N. gonorrheae and H. influenzae
contains hemolyzed RBCs plus supplements |
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Term
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Definition
Contains additives that enhance growth of some organisms while inhibiting others
used for contaminated samples |
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Term
What is differential media? |
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Definition
aids in presumptive ID or grouping of organisms based on the appearance of colonies
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Term
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Definition
demonstration of hemolytic properties (esp. streptococci) |
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Term
What are the types of hemolysis? |
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Definition
beta hemolysis: complete clearing of SBA
Streptolysn O: oxygen labile
Streptolysin S: oxygen stable
alpha hemolysis: incomplete lysing of RBCs leads to
greenish discoloration around colonies
gamma: non-hemolytic |
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Term
What is MacConkey Agar used for? |
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Definition
Differential AND Selective
- Selective: inhibits gram positive organisms
- Differential: lactose plus pH color changing indicator
- Lactase fermentation turns colonies magenta
- non-lactose fermenters stay clear
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Term
What is Eosin-Methylene Blue (EMB) used for? |
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Definition
- Selective-eosin and methylene dyes inhibit Gram + organisms
- Differential: lactose fermenters turn dark due to acid production
- E. coli colonies turn green w/sheen because of high amounts of acid produced
- Lactose non-fermentors are colorless
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Term
What is Columbia CNA Agar used for? |
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Definition
- Selective only: selects for G+ bacteria
- colistin and nalidixic acid inhibit G - bacteria
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Term
What is Mannitol Salt Agar (MSA) used for? |
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Definition
- Differential: mannitol fermentation produces yellow discoloration (S. aureus)
- Selective: high salt concentration selects for organisms that grow in presence of salt (S. aureus)
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Term
What genera constitute most clinically isolated aerobic G+ cocci? |
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Definition
Staphylococcus
Streptococcus
Enterococcus |
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Term
What are the characteristics of Staphylococcus?
Aerobe vs. anaerobe
Gram stain
morphology
catalase test
salt growth? |
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Definition
facultative anaerobe
Gram +
Cocci in irregular clusters
catalase +
grow in high salt media (MSA) |
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Term
What test is used to differentiate groups in the genus Staphylococcus? |
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Definition
Coagulase test
Coagulase positive=S. aureus group
Coagulase negative=S. epidermidis and S. saprophyticus groups |
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Term
How is the S. epidermidis CoNS differentiated from S. saprophyticus CoNS? |
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Definition
S. epidermidis is Novobiocin SUSCEPTIBLE
S. saprophyticus is Novobiocin RESISTANT |
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Term
What regions of the body are colonized by different Staph groups? |
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Definition
S. aureus mainly on anterior nares
S. epidermidis mainly colonized skin |
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Term
What are the characteristics of S. aureus colonies |
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Definition
mostly hemolytic
mod. large
golden yellow/white |
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Term
What is useful about the catalase reaction test? |
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Definition
Streptococci are catalase -
Staphylococci are catalase + |
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Term
What is the composition of the Staphylococcus latex agglutination test? |
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Definition
Latex beads coated with fibrinogen and Ab to Protein A (component of S. aureus cell wall)
Fibrinogen detects S. aureus coagulase
Ab detect protein A in S. aureus |
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Term
How is novobiocin resistance/susceptibility testing performed? |
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Definition
Streak colony on SBA
place 5 ug novobiocin disc on media
resistance indicated by zone of inhibition less than or equal to 16mm |
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Term
What are some general characteristics of family Enterobacteriaceae? |
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Definition
Enteric organisms
Gram - bacilli
grow well on MAC
Biochemically active
ferments glucose and other sugars (sometime with gas)
catalase +
Oxidase -
reduce nitrate->nitrite |
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Term
What genera of family Enterobacteriaceae account for most extraintestinal infections? |
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Definition
Eschericia (coli
Klebsiella
Proteus (mirabilis)
Enterobacter
Serratia |
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Term
What are the most common intestinal infections due to Enterobacteriaceae? |
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Definition
E. coli
Salmonella
Shigella
Y. enterocolitica (not covered) |
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Term
What toxins are produced by E. coli O157:H7? |
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Definition
Stx1
Stx2
also known as verocytotoxins |
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Term
What are some biochemical characteristics of O157:H7? |
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Definition
ferment lactose
do NOT ferment sorbitol overnight
SMAC colonies are colorless
Indole + (most E. coli are) |
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Term
What reaction is responsible for indole test?
How do you know if it is indole +? |
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Definition
metabolic degradation of tryptophan
Tryptophanase breaks down tryptophan->indole
blue green color is + |
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Term
What is the MUG test and what is it used for? How do you know if a sample is MUG +? |
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Definition
- Used to differentiate other E. coli from O157:H7
- beta-D-glucuronide enzyme in E. coli degrades MUG and produces fluorescence when incubated overnight
O157:H7 isolates are MUG-
Other E. coli are MUG+ |
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Term
How is salmonella serotyping performed? |
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Definition
Somatic O antigen (cell wall antigen-outer portion of LPS)
H antigen (flagella) |
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Term
What is used for serogrouping vs serotyping? how is it reported? |
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Definition
- Serogrouped based on O antigens
- Serotyped based on flagella H antigens
- reported by genus and serotype to state for tracking outbreaks
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Term
What are the key biochemical reactions defining the Salmonella genus? |
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Definition
Non-lactose fermenter (clear on MAC)
Ferments glucose WITH production of H2S gas
Agglutination of antisera for Salmonella O groups |
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Term
What does a TSI slant look like when inoculated with Salmonella? A urease tube? |
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Definition
TSI: blackening and gas bubble in the deep (H2S production)
No change in slant color (non-fermenter)
Urease - (no pink color) |
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Term
What are the 4 serogroups of Shigella sp.? |
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Definition
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Term
What are the key biochemical reactions of Shigella?
Lactose fermentation
other Fermentation
Motility
Gas production
Agglutination |
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Definition
Non-lactose fermenter
ferments GLUCOSE without gas
non-motile
biochemically inactive
H2S negative
Agglutinates with grouping antisera for Shigella |
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Term
What does a TSI slant look like when inoculated with Shigella?
Urease slant? |
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Definition
Red in the slant (oxidation of peptones)
Yellow in the deep (production of acid due to glucose fermentation)
Urease - |
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Term
What media are used to culture and isolate Shigella and Salmonella? |
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Definition
enrichment broth (maximal recovery)
selective media (MAC, HK)
biochemical screening
serogrouping/(serotyping for Salmonella) |
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Term
What do Salmonella and Shigella look like on MAC? |
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Definition
Gram -
lactose negative=clear colonies on MAC (no acid) |
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Term
What is Hektoen Enteric Agar? What does it select for/differentiate? |
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Definition
Selects for enteric pathogens
contains lactose, sucrose and salicin + pH indicator
Fermenters produce yellow colonies
non-fermenters are green/transparent
Na thiosulfate and ferric ammonium citrate indicate H2S production through black center of colony |
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Term
What do Salmonella and Shigella look like on HK agar?
What about E. coli? |
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Definition
Salmonella: clear/green with black center
Shigella: clear green
E. coli (non-O157:H7): yellow |
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Term
What are the contents of TSI agar? |
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Definition
Glucose, lactose, and sucros
phenol red pH indicator |
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Term
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Definition
Reaction in the deep: anaerobic fermentation (yellow if acid production due to fermentation)
Reaction on slant: yellow if glucose and lactose/sucrose fermenter, reverts to red if oxidation of peptones causes pH increase
Blackening: H2S production
Gas production: lifting or cracking of media |
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Term
How do you read a Urease test? |
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Definition
Positive:media turns hot pink if urea->ammonia+CO2
Negative: no color change, yellow |
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Term
Which Strep are beta, alpha, and gamma hemolytic? |
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Definition
Beta: S. pyogenes (GAS) and S. agalactiae (GBS)
Alpha: S. pneumoniae and "viridans" strep
Gamma: S. bovis |
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Term
What are the key characteristics of Streptococci?
Gram
Colony morphology
Catalase
an/aerobic
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Definition
Gram positive cocci, spherical/ovoid
usually in pairs or chains
Grey/white translucent colonies
Catalase -
Facultative anaerobes
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Term
How are Beta hemolytic strep grouped? |
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Definition
Lancefield System
Detects cell wall polysaccharides A,B,C,F,G
Cell wall lipteichoic acids (D and Enterococci) |
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Term
How is Lancefield grouping performed? |
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Definition
Extract antigens enzymatically by incubating for 10min-1hr
use latex agglutination to identify via homologous antisera |
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Term
What clinical syndromes are caused by Group A Strep? |
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Definition
S. pyogenes
pharyngitis, impetigo
cellulitis/necrotizing fasciitis
endocarditis, sepsis
scarlet vever
streptococcal TSS
Sequelae: ARF, glomerulonephritis |
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Term
What is the PYR test? What is it used for? |
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Definition
Determines the activity of prrolidonyl aminopeptidase enzyme
Presumptive ID of GAS and Enterococci |
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Term
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Definition
Blood agar with sulfamethoxazole trimethoprom (STX) to inhibit normal flora
Select colonies with beta hemolysis |
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Term
What are the biochemical findings that indicate GAS? |
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Definition
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Term
What species of Streptococcus is GBS? What clinical significant syndromes does it cause? |
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Definition
LOS NICU
Transmission from Mother to child during birth
Sepsis, amnionitis, UTI in pregnant women |
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Term
How is GBS isolated and identified? |
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Definition
Colony morphology on SBA: narrow B hemolysis (some are non-hemolytic)
Lancefield grouping (positive for B antigen)
CAMP +
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Term
How does the CAMP test work? What does it identify? |
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Definition
Streak S. aureus down middle of SBA plate
Streak Streptococcus perpendiculart to it
Look for synergistic hemolysis between GBS and S. aureus
characterized by zone of clearer media around points of intersection |
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Term
What species comprise the alpha hemolytic strep? |
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Definition
Streptococcus pneumoniae
"viridans" strep |
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Term
What are the biochemical characteristics of S. pneumo? |
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Definition
Optochin sensitive
Bile sensitive Quellung reaction positive |
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Term
What syndromes does S. pneumoniae cause? |
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Definition
**Community acquires pneumonia
Otitis media, sinusitis
meningitis, peritonitis, arthritis
Oropharyngeal carriage common |
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Term
What is the colony morphology of S. pneumoniae? |
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Definition
Large zone of alpha hemolysis
colony encapsulation gives "mucoid" wet appearance (can decrease over time)
Prolonged incubation can cause center of colonies to collapse |
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Term
What is the quellung reaction? |
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Definition
Anticapsular antibodies applied to S. pneumo cause capsule to swell and become more conspicuous under microscopy |
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Term
What special cellular morphology identifies S. pneumo vs. other strep species? |
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Definition
Pairs of coccobacilli
non-staining halo indicates capsule |
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Term
What does the Optochin test allow you to do? |
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Definition
Presumptive ID of S. pneumo
Disk with optochin placed on media plated with colony
Zone of inhibition >14mm = presumptive ID of S. pneumo |
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Term
How is the bile solubility test performed? |
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Definition
Addition of 10% Na desoxycholate (bile salt)
activates lytic enzymes in S. pneumo and causes colonies to disappear |
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Term
What are the biochemical characteristics of viridans sp. strep? |
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Definition
alpha or gamma hemolytic
bile esculin and optochin - |
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Term
what are the biochemical characteristics of Serogroup C and G strep? Group D? |
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Definition
C and G: beta hemolytic, bile esculin and optochin -
D: gamna hemolytic, Bile Esculin + optochin - |
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Term
What characteristics describe Enterococci?
Gram/morphology
hemolysis
catalase
lancefield group
pyr
bile esculin
salt tolerance |
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Definition
Gram + cocci (single, pair or short chain)
Gamma hemolytic
Catalase -
Lancefield group D (but not GDS)
facultative anaerobe
PYR+
Bile Esculin and Salt tolerant |
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