Gram Positive Cocci

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STAPHYLOCOCCI

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• Gram positive cocci in grape like clusters

• Non-motile

• Catalase Test (+) – presumptive test to differentiate Staphylococci and Micrococcus from Streptococci

• Principle: H2O2 is converted to water and oxygen by the presence of enzyme Catalase

• Reagent: 3% H2O2 - can be directly add to the culture media or in the slide; (+) result: vigorous bubbling

• Colonies from Blood test agar plates can cause False (+) reaction in this test .

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As to Pigment formation / Growth on Leoffer’s Serum Slant (LSS)

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°Staphylococcus aureus – golden yellow °Staphylococcus citreus – lemon yellow °Staphylococcus albus – white

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Staphylococcus aureus' GROWTH/COLONY MORPHOLOGY:

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• Normal flora of anterior nares and nasopharynx

• PCR will enable detection from nasal swab

• Uniform turbidity on broth

• On plates, they produced smooth circular and opaque colonies with oil-like or butyrous appearance

• Jet black colonies on tellurite agar

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TEST FOR IDENTIFICATION (S. aureus)

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• Catalase (+)

• Coagulase (+)

• Mannitol Fermentation (+)

• DNase Test (+)

• VP and Nitrate (+)

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HEMOLYSIS ON BAP:

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Beta – hemolytic

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SUSCEPTIBILITY TEST:

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 Sensitive to Lyostaphin and Novobiocin

 Resistant to Polymyxin

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VIRULENCE FACTORS:

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• Catalase is produced by S. aureus BUT it has never been a virulence factor! It has nothing to do with the ability of the organism to produce a disease .

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ENZYMES:

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Lipase – initiates skin infection

Hyaluronidase – spreading factor; it enhances the invasion into the tissues

Beta lactamase/ penicillinase – makes the S. aureus resistant to penicillin

Staphylokinase – promotes fibrinolysis (dissolution of clot)

Coagulase – it causes the bacterial cells to agglutinate in the plasma; it also converts fibrinogen to fibrin.

Beta-hemolysin – responsible for the β-hemolytic property of S. aureus

Protein A – prevents phagocytosis

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TOXINS:

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• Enterotoxin A and B – food poisoning

• Enterotoxin F / TSST – causes the Toxic Shock Syndrome

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Exfoliation

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– epidemolytic toxin that causes desquamation (or exfoliation) of the skin in Scalded Skin Syndrome aka Ritter’s disease .

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– incomplete/partial hemolysis on BAP causing the greening of the agar

• Streptococcus pneumoniae, Viridans Streptococci – S. mitis and S. mutans

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Alpha hemolytic Streptococci

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– complete hemolysis showing clear zones around the colony

• Streptococcus pyogenes and Streptococcus agalactiae

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Beta hemolytic Streptococci

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– unable to cause hemolysis on BAP

Ex: E. faecalis, E. faecium, S. bovis

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Gamma hemolytic Streptococci

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– when a colony is surrounded by an inner alpha and outer beta zone. This may occur due to prolonged refrigeration

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Alpha prime

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– based on the hemolytic pattern of the organisms

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Smith and Brown Classification

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– based on the physiologic needs of the organism

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Academic or Bergey’s Classification

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= (-) 10 and 45°C but (+) in 37°C i.e. S. pyogenes

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Pyogenic

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= (+) 45°C but (-) in 10°C i.e. S. mitis, S. mutans. S. sanguis, S. salivarius, S. constellatus S. intermedius

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Viridans

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= (+) 10 and 45°C i.e. E. faecalis

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Enterococci

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= (+) 10°C but (-) in 45°C i.e. S. lactis and S. cremoris

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Lactic group

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– based on the extraction of C Carbohydrate from Streptococcal cell wall

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Lancefield Classification

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All Streptococci are placed under Lancefield EXCEPT:

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Viridans and S. pneumoniae

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Other Gram (+), Catalase (-) organisms isolated from Clinical Specimens (that can cause infection in immunocompromised):

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• Pediococcus

• Lactococcus

• Aerococcus

• Rothia

• Leuconostoc

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– broth: (Histopathology) use as an adhesive in exfoliative cytology; low virulence potential

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Leuconostoc

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- Aka Thiol-requiring Streptococci / Pyridoxal Streptococci / Satelliting Streptococci

- These are S. adjacens and S. defectives

- These are viridans needing Vitamin B-6 in their media

- When mixed with S. aureus they satellite around the colonies of S. aureus

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Abiotrophia

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– known to cause liver, spleen and brain abscesses

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Milleri Streptococci Complex

Colonies: “caramel” / “butter scotch” odor

Species: S. constellatus, S. intermedius, S. anginosus

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Hemolytic Pattern:

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• Alpha – Viridans and S. pneumoniae

• Beta – Group A, B, C and some Group D (Lancefield)

• Gamma – mostly Group D

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– targets WBC, causing its destruction; associate with MRSA (Methicillin-resistant S. aureus) infection

- It can be Community-acquired / Hospital-acquired.

The Hospital acquiredMRSA is difficult to treat due to its resistant to almost all antibiotics except Glycopeptides (vancomycin)

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PVL/ Panton Valentine Leucocidin

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TOXIC MEDIATED DISEASES:

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• Food poisoning

• Toxic Shock Syndrome

• Scalded Skin Syndrome

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– skin infection of epidermidis, involving epithelial cells

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Bullous impetigo

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Coagulase- Negative Staphylococci (CONS)

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