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Lab Practical
Module 1 ID Lab
64
Microbiology
Graduate
03/06/2016

Additional Microbiology Flashcards

 


 

Cards

Term
What is liquid broth media used for?
Definition

enrich sample

cultivate organisms present in low numbers

Term
What is a general purpose media?
Definition

Supports growth of broad range of organisms

Tryptic soy agar (TSA)

Nutrient Agar

Not selective or differentiating

Term
What is enriched media?
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

Term
What is cultured on chocolate agar?
Definition

Chocolate agar supports fastidious organisms

N. gonorrheae and H. influenzae

contains hemolyzed RBCs plus supplements

Term
What is selective media?
Definition

Contains additives that enhance growth of some organisms while inhibiting others

 

used for contaminated samples

Term
What is differential media?
Definition

aids in presumptive ID or grouping of organisms based on the appearance of colonies

 

 

Term
What is SBA used for?
Definition
demonstration of hemolytic properties (esp. streptococci)
Term
What are the types of hemolysis?
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

Term
What is MacConkey Agar used for?
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
Term
What is Eosin-Methylene Blue (EMB) used for?
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
Term
What is Columbia CNA Agar used for?
Definition
  • Selective only: selects for G+ bacteria
  • colistin and nalidixic acid inhibit G - bacteria
Term
What is Mannitol Salt Agar (MSA) used for?
Definition
  • Screens for S. aureus
  • Differential: mannitol fermentation produces yellow discoloration (S. aureus)
  • Selective: high salt concentration selects for organisms that grow in presence of salt (S. aureus)
Term
What genera constitute most clinically isolated aerobic G+ cocci?
Definition

Staphylococcus

Streptococcus

Enterococcus

Term

What are the characteristics of Staphylococcus?

Aerobe vs. anaerobe

Gram stain

morphology

catalase test

salt growth?

Definition

facultative anaerobe

Gram +

Cocci in irregular clusters

catalase +

grow in high salt media (MSA)

Term
What test is used to differentiate groups in the genus Staphylococcus?
Definition

Coagulase test

 

Coagulase positive=S. aureus group

 

Coagulase negative=S. epidermidis and S. saprophyticus groups

Term
How is the S. epidermidis CoNS differentiated from S. saprophyticus CoNS?
Definition

S. epidermidis is Novobiocin SUSCEPTIBLE

 

S. saprophyticus is Novobiocin RESISTANT

Term
What regions of the body are colonized by different Staph groups?
Definition

S. aureus mainly on anterior nares

 

S. epidermidis mainly colonized skin

Term
What are the characteristics of S. aureus colonies
Definition

mostly hemolytic

mod. large

golden yellow/white

Term
What is useful about the catalase reaction test?
Definition

Streptococci are catalase -

Staphylococci are catalase +

Term
What is the composition of the Staphylococcus latex agglutination test?
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

Term
How is novobiocin resistance/susceptibility testing performed?
Definition

Streak colony on SBA

place 5 ug novobiocin disc on media

resistance indicated by zone of inhibition less than or equal to 16mm

Term
What are some general characteristics of family Enterobacteriaceae?
Definition

Enteric organisms

Gram - bacilli

grow well on MAC

Biochemically active

ferments glucose and other sugars (sometime with gas)

catalase +

Oxidase -

reduce nitrate->nitrite

Term
What genera of family Enterobacteriaceae account for most extraintestinal infections?
Definition

Eschericia (coli

Klebsiella

Proteus (mirabilis)

Enterobacter

Serratia

Term
What are the most common intestinal infections due to Enterobacteriaceae?
Definition

E. coli 

 

Salmonella

Shigella

 

Y. enterocolitica (not covered)

Term
What toxins are produced by E. coli O157:H7?
Definition

Stx1

Stx2

 

also known as verocytotoxins

Term
What are some biochemical characteristics of O157:H7?
Definition

ferment lactose

do NOT ferment sorbitol overnight

SMAC colonies are colorless

 

Indole + (most E. coli are)

Term

What reaction is responsible for indole test?

How do you know if it is indole +?

Definition

metabolic degradation of tryptophan

 

Tryptophanase breaks down tryptophan->indole

blue green color is +

Term
What is the MUG test and what is it used for? How do you know if a sample is MUG +?
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+

Term
How is salmonella serotyping performed?
Definition

Somatic O antigen (cell wall antigen-outer portion of LPS)

 

H antigen (flagella)

Term
What is used for serogrouping vs serotyping? how is it reported?
Definition
  • Serogrouped based on O antigens
  • Serotyped based on flagella H antigens
  • reported by genus and serotype to state for tracking outbreaks
Term
What are the key biochemical reactions defining the Salmonella genus?
Definition

Non-lactose fermenter (clear on MAC)

Ferments glucose WITH production of H2S gas

Agglutination of antisera for Salmonella O groups

Term
What does a TSI slant look like when inoculated with Salmonella? A urease tube?
Definition

TSI: blackening and gas bubble in the deep (H2S  production)

 

No change in slant color (non-fermenter)

 

Urease - (no pink color)

Term
What are the 4 serogroups of Shigella sp.?
Definition
A-D
Term

What are the key biochemical reactions of Shigella?

Lactose fermentation

other Fermentation

Motility

Gas production

Agglutination

Definition

Non-lactose fermenter

ferments GLUCOSE without gas

non-motile

biochemically inactive

H2S negative

Agglutinates with grouping antisera for Shigella

Term

What does a TSI slant look like when inoculated with Shigella?

 

Urease slant?

Definition

Red in the slant (oxidation of peptones)

Yellow in the deep (production of acid due to glucose fermentation)

 

Urease -

Term
What media are used to culture and isolate Shigella and Salmonella?
Definition

enrichment broth (maximal recovery)

 

selective media (MAC, HK)

 

biochemical screening

 

serogrouping/(serotyping for Salmonella)

Term
What do Salmonella and Shigella look like on MAC?
Definition

Gram -

lactose negative=clear colonies on MAC (no acid)

Term
What is Hektoen Enteric Agar? What does it select for/differentiate?
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

Term

What do Salmonella and Shigella look like on HK agar?

What about E. coli?

Definition

Salmonella: clear/green with black center

Shigella: clear green

E. coli (non-O157:H7): yellow

Term
What are the contents of TSI agar?
Definition

Glucose, lactose, and sucros

phenol red pH indicator

Term
How do you read TSI?
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

Term
How do you read a Urease test?
Definition

Positive:media turns hot pink if urea->ammonia+CO

Negative: no color change, yellow

Term
Which Strep are beta, alpha, and gamma hemolytic?
Definition

Beta: S. pyogenes (GAS) and S. agalactiae (GBS)

Alpha: S. pneumoniae and "viridans" strep

Gamma: S. bovis

Term

What are the key characteristics of Streptococci?

Gram

Colony morphology

Catalase

an/aerobic

 

Definition

Gram positive cocci, spherical/ovoid

usually in pairs or chains

Grey/white translucent colonies

Catalase -

Facultative anaerobes

 

Term
How are Beta hemolytic strep grouped?
Definition

Lancefield System

Detects cell wall polysaccharides A,B,C,F,G

Cell wall lipteichoic acids (D and Enterococci)

Term
How is Lancefield grouping performed?
Definition

Extract antigens enzymatically by incubating for 10min-1hr

 

use latex agglutination to identify via homologous antisera

Term
What clinical syndromes are caused by Group A Strep?
Definition

S. pyogenes

pharyngitis, impetigo

cellulitis/necrotizing fasciitis

endocarditis, sepsis

scarlet vever

streptococcal TSS

Sequelae: ARF, glomerulonephritis

Term
What is the PYR test? What is it used for?
Definition

Determines the activity of prrolidonyl aminopeptidase enzyme

 

Presumptive ID of GAS and Enterococci

Term
How do you isolate GAS?
Definition

Blood agar with sulfamethoxazole trimethoprom (STX) to inhibit normal flora

 

Select colonies with beta hemolysis

Term
What are the biochemical findings that indicate GAS?
Definition

Catalase -

 

PYR +

Term
What species of Streptococcus is GBS? What clinical significant syndromes does it cause?
Definition

LOS NICU

Transmission from Mother to child during birth

Sepsis, amnionitis, UTI in pregnant women

Term
How is GBS isolated and identified?
Definition

Colony morphology on SBA: narrow B hemolysis (some are non-hemolytic)

 

Lancefield grouping (positive for B antigen)

 

CAMP +

 

Term
How does the CAMP test work? What does it identify?
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 

Term
What species comprise the alpha hemolytic strep?
Definition

Streptococcus pneumoniae

"viridans" strep

Term
What are the biochemical characteristics of S. pneumo?
Definition

Optochin sensitive

Bile sensitive
Quellung reaction positive 

Term

What syndromes does S. pneumoniae cause?

Definition

**Community acquires pneumonia

Otitis media, sinusitis

meningitis, peritonitis, arthritis

Oropharyngeal carriage common

Term
What is the colony morphology of S. pneumoniae?
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

Term
What is the quellung reaction?
Definition
Anticapsular antibodies applied to S. pneumo cause capsule to swell and become more conspicuous under microscopy
Term
What special cellular morphology identifies S. pneumo vs. other strep species?
Definition

Pairs of coccobacilli

non-staining halo indicates capsule

Term
What does the Optochin test allow you to do?
Definition

Presumptive ID of S. pneumo

 

Disk with optochin placed on media plated with colony

 

Zone of inhibition >14mm = presumptive ID of S. pneumo

Term
How is the bile solubility test performed?
Definition

Addition of 10% Na desoxycholate (bile salt)

 

activates lytic enzymes in S. pneumo and causes colonies to disappear

Term
What are the biochemical characteristics of viridans sp. strep?
Definition

alpha or gamma hemolytic

bile esculin and optochin -

Term
what are the biochemical characteristics of Serogroup C and G strep? Group D?
Definition

C and G: beta hemolytic, bile esculin and optochin -

 

D: gamna hemolytic, Bile Esculin + optochin -

Term

What characteristics describe Enterococci?

 

Gram/morphology

hemolysis

catalase

lancefield group

pyr

bile esculin

salt tolerance

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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