Wk 1 Clinical Bacteriology

Question 1

What is darkfield microscopy used for?

Answer 1

When organism is difficult to see with bright field
Borrelia, Treponema, Mycoplasma

Question 2

Gram stain examples

Answer 2

Question 3

What color are acid fast negative and positive bacteria?

Answer 3

negative = blue
positive = red

Question 4

What do mycobacterium species cell walls contain?

Answer 4

mycolic acids, fatty acids, and lipids
-they are acid-fast positive

Question 5

What are non-acid fast bacteria counter stained with?

Answer 5

Methylene blue

Question 6

What does hemolysis on blood agar look like?

Answer 6

Question 7

What are 2 types of non-selective media?

Answer 7

1. tryptic soy broth - widely used to isolate bacteria
2. thioglycolate broth - can differentiate b/w species based on O2 requirements
   3-anaerobic bacteria (like Gram-positive spore formers)

Question 8

3 types of selective and differential media

Answer 8

1. CNA agar - selects for Gram-positive bacteria (Colistin and** N**alidixic acid inhibit Gram-negative bacteria) (Gram + Staphylococcus, Streptococcus)
2. MacConkey agar - selects Gram-negative, lactose, bile salts inhibit Gram + bacteria (differentiates lactose fermenters (pink) vs non-lactose fermenters (not pink)
3. Thayer-Martin media - chocolate agar supplemented w/ antibiotics (used to culture and isolate Neisseria sp), Vancomycin kills Gram-positives, Trimethroprim and Colistin kill most Gram-negative organisms except Neisseria) - think Neisseria sp. with this!!

Question 9

Common clinically important anaerobes

Answer 9

Question 10

What are 3 biochemical tests?

Answer 10

1. Catalase test
2. Coagulase test
3. Oxidase test

Question 11

Catalase test

Question 12

Coagulase Test

Question 13

Oxidase Test

Question 14

Oxidative-Fermentation test

Question 15

TSI

Answer 15

=triple sugar iron

Question 16

Agglutination tests

Question 17

What are 5 serologic tests

Answer 17

Antigensoftheorganismintissues or body fluids
* Antibodiesinpatient’sserum
Tests:
1. Agglutination (rapid)
2. Enzyme immunoassay (ELISA)
3. immunofluorescence (IF)
4. Immunohistochemistry (IHC)
5. Western blot

Question 18

Review

Answer 18

Question 19

Most common staphylococcus

Answer 19

-are catalase positive
S. aureus
S. epidermidis
S. saprophyticus

Question 20

Staphylococcus aureus

Answer 20

• Catalase positive
• Coagulase positive
• β-Hemolytic

Question 21

MRSA (Methicillin-Resistant S. aureus)

Answer 21

• Highly antibiotic resistant=SUPER BUG
• Resistant to the penicillinase-stable penicillins (methicillin, nafcillin, and oxacillin) and all beta-lactam drugs
• Altered penicillin-binding protein PBP2A encoded by mecA

Question 22

Staphylococcus epidermidis

Answer 22

• Non-hemolytic
• Catalase positive
• Coagulase negative
• Novobiocin sensitive
• Normal skin flora (epidermis=skin)
• Contaminates blood cultures
• Skin/wound infections
• Biofilms on plastic devices: catheters, prostheses (hip implant, heart valve)

Question 23

Staphylococcus saprophyticus

Answer 23

*Gram-positive
Catalase positive
* Coagulase negative
* Novobiocin resistant

• Normal flora of female genital tract
• Urinary tract infection or Uncomplicated cystitis, second most common cause
• Peritonitis

Question 24

Streptococcus and Enterococcus

Answer 24

• S. pyogenes (Group A Strep)
• S. agalactiae (Group B Strep)
• S. pneumoniae (pneumococcus)
• Viridans Streptococci group
• Enterococcus species

Question 25

Streptococcus classification

Answer 25

Question 26

Streptococcus agalactiae (Group B Streptococcus)

Answer 26

* Catalase negative * β-hemolytic * Narrow zone of hemolysis * Bacitracin resistant * Lancefield Group B * Polysaccharide capsule is a significant virulence factor * Colonizes genital and lower GI tracts of 10-40% of women; also found in oropharynx, upper GI * Pregnant women screened at 36-38 weeks for GBS * Intrapartum penicillin prophylaxis if positive

Question 27

Streptococcus pyogenes (Group A Streptococcus, GAS)

Answer 27

* Group A Strep, human-restricted pathogen * β-hemolytic * Bacitracin sensitive * Differentiate from other β-hemolytic streptococci * Lancefield Group A * Virulence factors – Capsule – M protein: Antiphagocytic, inhibits complement – Enzymes for tissue invasion: Streptolysin, DNAses, Streptokinase (dissolves clots) – Superantigens

Question 28

S. pyogenes (Group A Streptococcus)

Answer 28

* Pyogenic * Pharyngitis* * Impetigo (honey crusted lesions) * Cellulitis * Scarlet fever (strawberry tongue) * Bacteremia, toxic shock-like syndrome * Necrotizing fasciitis

Question 29

Streptococcus pneumoniae (pneumococcus)

Answer 29

* Lancet-shaped diplococcus * No Lancefield group * α hemolytic (partial) * Optochin sensitive * Differentiate from α-hemolytic Viridans Streptococci * Bile soluble * Autolysin activated by bile * * Meningitis, otitis media, pneumonia, sinusitis (MOPS)