Chapter 22 - Staphylococcus and Micrococcus

How do we detect for fermentation?

Phenol red carbohydrate assays. Yellow = positive Orange = red

What are common factors between Staphylococcus and Micrococcus?

1. Gram positive cocci 2. Tetrads (micro) Clusters (staphylo) 3. No endospores 4. Live in high salt (human skin) 5. aerobic respiration 6. positive catalase

What are the 3 ways we distinguish within Staphylococcus?

1. Mannitol Fermentation 2. Novobiocin sensitivity and resistance 3. Coagulase Assay

Name important staphylococcus species

1. Staphylococcus aureus: Infections can include skin infections, septicemia, and pneumonia. Some strains cause toxic shock syndrome. - becoming antibiotic resistant (MRSA) 2. Staphylococcus epidermis: most common. Rarely infectious, but can be opportunistic. 3. Staphylococcus saprophyticus: normal flora of female genitalia. Possible UTI's

What are differences between staphylococcus and micrococcus?

How they ferment sugars. - Micrococcus are strict aerobes, in the absence of oxygen they cannot switch to fermentation. - Staphylococcus are facultative anaerobes, they use oxygen when present but switch to fermentation in its absence. *Micrococcus = nonfermenters. Staphylococcus = fermenters.

Describe the reaction and results on Mannitol salt agar

If the cells ferment mannitol, they produce organic acids as end products. The acids will lower the pH below 6.8 and the media will turn yellow.

Describe Novobiocin sensitivity and resistance

Novobiocin is affective against some staphylococcus. We need to calculate a zone of inhibition to determine sensitivity, intermediate, or resistant. (at least 18-20mm = sensitive)

Besides the gram stain and catalase assay, how do we distinguish between staphylococcus/micrococcus + streptococcus/enterococcus?

Salt tolerance. Can use a mannitol salt agar (a selective medium for staphylococcus and micrococcus)

Describe the coagulase assay

Virulence factors (that enhance ability to cause disease) include 2 types of coagulase: bound or free 1. bound: aka clumping factor is a receptor for fibrinogen (involved in blood clotting) - this binding causes blood clots. 2. free or secreted: catalyzes a reaction that converts fibrinogen into insoluble stringy fibrin. Fibrin coats bacteria. - coagulases make s. aureus a potent pathogen.

What is the only species that carries coagulase?

s. aureus

Describe mannitol salt agar

selective for Staphylococcus and Micrococcus 7.5% NaCl differential because it contains sugar mannitol and pH indicator phenol red - able to test isolates for their ability to ferment mannitol (differentiates within staphylococcus)