Gram Positive Cocci

Question 1

Gram positive Cocci

Answer 1

-streptococcus -Staphylococcus -Enterococcus

Question 2

Chains

Answer 2

Streptococcus
Enterococcus

Question 3

Clusters

Answer 3

Staphylococcus

Question 4

Diplococcus

Answer 4

Pneumococcus

Question 5

How to decide whether to give antibiotics or not?

Answer 5

Site specimen taken from

Pathogenicity of the organism

Defense system of the host

Association of bugs to the human cells

Question 6

If the gram stain is negative, is there an infection? (meaning the stain didn’t work)

Answer 6

Could have sampling error

Background artifact

Difficult to stain organisms: atypicals

Too few organisms to catch

Gram positive in only 60% of cases with bacterial meningitis

Question 7

Gram - and Gram+ respond to different antibiotics

Answer 7

• Vancomycin: prevents peptidoglycan wall being formed (affects gram +)
• Gentamicin: Works on the ribosomes, can’t penetrate thick peptidoglycan wall (affects gram-)

(Can work on gram+ if wall is broken down first )

Question 8

Gram stain determines how the specimen is further processed

Answer 8

• Eg. Gram + cocci: catalase, coagulase, MRSA testing
• Eg. Gram - Rod: Oxidase, Urease, Gram - sensitivity test

Question 9

STREPTOCOCCUS

Clinical Determination

Answer 9

Chains or clumps?

“StrePtoCocci are seen in Pairs and Chains”

Catalase: Positive or Negative?

Coagulase (+ vs -) or Hemolysis (a,b,g)

Question 10

Results of Hemolysis testing

Answer 10

• Full or beta hemolysis: Group A
• Partial hemolysis, alpha hemolysis
• no hemolysis could be many things

Question 11

Lancefield Groups (A-G)

Answer 11

Method of grouping catalase-negative, coagulase-negative bacteria based on the carbohydrate composition of bacterial antigens found on their cell wall

Question 12

Group A: Strep Pyogenes

Answer 12

• Pyogenic = pus producing organism
• Strong Virulence Factors

Examples:

Erysipelas: Superficial skin infection

Necrotizing Fascitis

Toxic Shock Syndrome

Strep pyogenes and Staph aureus toxins 

Fever, rash, diarrhea, kidney and liver failure 

Question 13

Alpha Hemolytic Strep

Answer 13

S. Pneumoniae

S. Viridans

“Mouth Organisms”

Question 14

(Gamma) Non-hemolytic Strep

Answer 14

Enterococcus (Group D antigen)

S. Bovis (Group D antigen)

Question 15

STAPHYLOCOCCUS

Clinical Determination

Answer 15

Chains or clumps?

“STAPHylococci are in clusters, like STAFF in the hospital”

Catalase: Positive or Negative?

Coagulase (+ vs -) or Hemolysis (a,b,g)

Question 16

Staph Aureus

Answer 16

• Strong virulence factors
• MRSA (Methicillin Resistant Staph Aureus)
• “mecA” gene
• Called MSRA because methicillin was a historic chemical used to detect it
• May be more invasive that other staph aureus
• Community associated MRSA: Frequent in athletes (shared washing facilities, skin shedding)

Question 17

Quorum Sensing

Answer 17

Bacteria make and release chemicals

Chemical concentrations increase with bacterial load

Sensed by other bacteria: genes up/down regulate

Bacterial colony acts in unison

Coordinated virulence factors

Question 18

Prosthetic Materials significance?

Answer 18

Environment for bacterial proliferance

Biofilms prevent macrophage phagocytosis and attenuate inflammation in vivo

Question 19

Examples that have big fat rods? G+

Answer 19

Clostridium sp.

Bacillus sp.

Question 20

Examples that are small and thin G+

Answer 20

Corynebacteria

Question 21

Examples of branched G+

Answer 21

Actinomycetes

Nocardia