Gram (+) Cocci

Staphylococcus, Streptococcus

Staphylococcus morphology:

“Grape-like” clusters

Organism that is:

• Coagulase +

• Infections: Carbuncles, furuncles, paronychia, wounds, and bacteremia

• Intoxications: Scalded Skin syndrome, Toxic Shock syndrome, and Gastritis (enterotoxin, 1-5hrs after eating)

• Most beta lactamase +; many MSRA

• CA = community acquired; HA = hospital acquired

Staphylococcus aureus

Organism that is:

• Coagulase -

• Infections: Endocarditis, prosthetic device infections

• Intoxications: N/A

• Most methicillin resistant; sensitive to novobiocin

Staphylococcus epidermidis

Organism that is:

• Coagulase -

• Infections: UTI in young women

• Intoxications: N/A

• Resistant to novobiocin

Staphylococcus saprophyticus

Most common pathogen of Staphylococcus genus

S. aureus

Exotoxins of S. aureus

• Hemolysins

• Leukocidins

• Coagulase and hyaluronidase

• Nuclease

• Protease and lipase

S. aureus is most resistant to (—) due to plasmid mediated B-lactamase

penicillin

Some sensitive to penicillinase-resistant penicillins (PRP’s) (methicillin, oxacillin, etc.); if MRSA, (—) is drug of choice

vancomycin

S. aureus Laboratory Diagnosis (BAP, MSA Growth/Fermentation, Catalase, Coagulase)

• BAP - soft, opaque, regular colonies 2-3mm in diam; some are beta hemo-lytic and some have a golden pale color

• Growth in 7.5% NaCl and ferment mannitol

• Catalase +

• Coagulase +

Coagulase negative Staphylococcus are:

Opportunists in immunocompromised hosts and patients with prosthetic values and devices

Catalase Test

• Reagent: 3% H₂O₂

• Add one drop to colony on slide

• If catalase present, H₂O₂ is broken down to water and O₂ (which bubbles off)

If catalase is positive, then…

Organism is Staph

If catalase is negative, then…

Organism is Strep

Coagulase Test

• Reagent - EDTA rabbit plasma

• Bound coagulase - clumping on side (plasma and colony)

• Free coagulase - gels in tube test (0.5 ml plasma and colony; 35-37^oC 4-12hrs)

• Agglutination tests - detect coagulase and protein A

If coagulase is positive, then…

Organism is S. aureus

If coagulase is negative, then…

Organism is other Staph (human pathogens)

• Look for bubbles with catalase test and for clots with coagulase

• Gram (+) clusters everywhere skin and gut, nose and hair

• Protein A is my main trait and Enterotoxin in what you ate

• Penicillin won’t touch me

• Methicillin, well… maybe?

• Vancomycin killed in days of yore

• But now that drug is not for sure

• Wash your hands, don’t pick your nose

• Wear a lab coat over your clothes

S. aureus

Streptococcus morphology:

Spherical or oval; chains or pairs

Lancefield grouping based on…

C carbohydrate

• Beta hemolytic

• Streptolysin S - stable in O2; non-antigenic

• Streptolysin O - oxygen labile; antigenic

• Erythrogenic toxin - rash of scarlet fever

• Highly sensitive to penicillin

• Infections

  • Pharyngitis (Strep throat)

  • Impetigo

  • Erysipelas

  • Wounds, burns

  • Rheumatic fever (autoimmune sequalae to infection with Strep Group A)

  • Lab diagnosis - Sensitive to 0.04 units of bacitracin disc; typing

Streptococcus pyogenes (Group A)

• Narrow zone of beta hemolysis

• Neonatal sepsis and meningitis; UTI; vaginal infections

• Laboratory diagnosis

  • Serotyping

  • CAMP reaction (with S. aureus)

  • Na hippurate positive

S. agalactiae (Group B)

Group D organisms

• S. bovis

• Enterococcus

• BEM (+)

• No growth in 6.5% NaCl

S. bovis

• BEM (+)

• Growth in 6.5% NaCl

Enterococcus

• Alpha hemolytic crater-like colonies or mucoid, “water drop” colonies

• Lancet-shaped diplococci

• Check sensitivity to penicillin using oxacillin disc (≥ 20mm = sensitive)

• Causes

  • Primary lobar pneumonia (rusty sputum)

  • Meningitis

  • Bacteremia

  • Otitis media

  • Conjuctivitis

• Laboratory diagnosis

  • Typical colony morphology

  • Quellung reaction ?**

  • Sensitive to optochin

  • Bile soluble

S. pneumoniae

Subacute bacterial endocarditis

Other alpha Streptococcus (viridans group)

• Pairs or chains

• Catalase (-)

• Growth in 6.5% NaCl (Enterococcus)

Strep

• Clusters (Grape-like)

• Catalase (+)

• Growth in 7.5% NaCl

Staph

• Clusters (Grape-like)

• Catalase (+)

• Growth in 7.5% NaCl

• Coagulase (+)

S. aureus

Which Streptococci is susceptible to bacitracin?

S. pyogenes (group A)

How to distinguish S. agalactiae?

Na hippurate (+)

How to distinguish Enterococcus?

• Bile esculin (+)

• 6.5% NaCl (+)

How to distinguish Non-enterococcus

• Bile esculin (+)

• 6.5% NaCl (-)

How to distinguish S. pneumoniae?

• Susceptible to optochin

• Bile solubility (+)

How to distinguish S. viridans?

• All tests are negative

• Optochin and bacitracin are resistant