Stains
Why do gram positive organisms stain purple ?
because they have a thick peptidoglycan wall that retains the primary crystal violet stain
Test used to distinguish Staphylococcus aureus from other staph is
Coagulase
MacConkey media for screening suspected cases of hemorrhagic E.coli O157:H7 must contain
Sorbitol - O157:H7 does NOT ferment Sorbitol - others do
This is the cause of whooping cough.
Bonus: what do the colonies look like ?
Bordetella pertussis
Mercury drops
Which of the following groups of specimens would be acceptable for anaerobic culture?
a. vaginal swab, eye swab
b. intraoral surface swab, leg swab
c. pleural fluid, brain abscess fluid
d. urine , sputum
C
Some organisms do not stain with Gram stain because they have mycolic so we do acid fast staining . there are different types: which type uses heat?
Ziehl-Neelsen
The optochin disk is used for the identification of what?
Strep pneumoniae
an organism is isolated from surface of a skin burn and found to produce a blue/green pigment on blood agar plate. what is the most likely organism
Also what carbohydrates does this organism ferment?
Pseudomonas aeruginosa
None
A patient came in with a genital ulcer that was swabbed and sent to lab. The gram stain showed a GNB that looked like a school of fish . What is the most likely organism
Bonus: What is required for growth
Haemophilus ducreyi
Increased CO2
A 45-year-old man presents with a hard, non-tender "lumpy jaw" swelling of several weeks' duration, accompanied by sinus tracts draining thick yellow pus. Gram stain reveals branching, filamentous Gram-positive rods. Which of the following is the most likely diagnosis?
Actinomyces israelli
* molar tooth colony
Which type of acid fast staining uses a high phenol concentration but no heat ?
Kinyoun
gamma hemolytic strep that blacken bile esculin agar but does not grow in 6.5% NaCl broth is most likely
Group D strep ( Strep bovis)
Optimal incubator temp for Campylobacter jejuni is
42C
Media used to support growth of Legionella pneumophila should contain the additives
a. X and V factor
b. hemin and Vit K
c. charcoal and yeast extract
d. dextrose and laked blood
C
Which anaerobic bacteria is inhibited by SPS ( found in blood culture bottles )
Peptostreptococcus anaerobius
The gram stain in imagine one is most likely of :
a. streptococcus
b. staphylococcus
c. corynebacterium
d. listeria
Staphylococcus : gram pos in clusters
an isolate of unknown beta hemolytic strep is streaked perpendicular to a staph aureus . after incubation a zone of arrowhead hemolysis is noted at the interface of the two streaks. What is this test called and what is presumptive identification of the unknown streptococcus?
CAMP test : S. agalactiae ( Group B )
Biochemical reactions of an organism are consistent with Salmonella. A suspension is tested in polyvalent antiserum A through G and in Vi antiserum. There is agglutination in the Vi antiserum only. What should be done next?
Boil the suspension of the organism for 10 minutes to inactivate the Vi antigen.
A Gram-negative coccobacillus is found on a sheep blood agar plate showing "satellitism" around a streak of Staphylococcus aureus. What is the most likely identification of the organism?
H. influenzae
A black-pigmented, anaerobic, Gram-negative rod is isolated from a periodontal pocket. It is asaccharolytic and sensitive to vancomycin. What is it?
Porphyromonas
* pigmented anaerobic GNR either Porphyromonas or Prevotella
-Porphyromonas is asaccharolytic and sensitive to Vancomycin
The gram stain on image 2 is most likely :
a. Vibrio cholera
b. Neisseria gonnorhea
c. Corynebacterium diptheriae
d. Streptococcus pneumoniae
C
It is important to differentiate between Enterococcus and Group D strep because?
Enterococcus shows antibiotic resistance
A blood culture bottle with macroscopic signs of growth is Gram stained and the technician notes small, curved gram-negative bacilli resembling “gull wings.” It is subcultured to blood and chocolate agar, and incubated aerobically and anaerobically. After 24 hours, no growth is apparent. The next step should be to:
incubate in microaerophilic conditions - this is required for growth of Campylobacter
* microaerophilic = decreased O2 and increase CO2
also Campylobacter jejuni grows best at 42C
A patient develops a hand infection after a fist fight. A Gram-negative rod is isolated that produces a bleach-like odor and pits the agar. What is the organism?
Eikenella corrodens
This gram-positive, spore-forming anaerobic bacillus known for producing a characteristic double zone of hemolysis on blood agar.
Clostridium perfringens
* causes gas gangrene
* pos lecithinase test ( on egg yolk agar) opaque zone seen