Micro Lab Essay

Submitted By Beckaleck1
Words: 310
Pages: 2

Rebekah Ziesmer - RT
4 March 2013
Micro 233 - Dias

Selective & Differential Media Lab Report

1) Hypothesis/Objective:

2) Results:

| Organisms | | Mannitol Salt Agar (MSA) | MacConkey’s Agar | Selective/Differential? | 1. | E. Coli | Growth: | No growth | Growth | MSA inhibited growth | | | Reaction: | | Circular colonies | MacConkey’s promoted growth | 2. | Enterobacter aerogenes | Growth: | No growth | Growth | MacConkey’s promoted growth | | | Reaction: | | Circular colonies | MSA inhibited growth | 3. | Staphylococcusaureus | Growth: | Substantial Growth | No Growth | MSA promoted growth, S. aureus is halotolerant & a fermenter | | | Reaction: | Many small colonies clumped together, changed to yellos | | MacConkey’s inhibited growth | 4. | S. epidermis | Growth: | Slight growth | No Growth | MacConkey’s agar inhibited growth | | | Reaction: | Very faintly distinguishable, no color change | | MSA promoted growth, S. epidermis is not a fermenter |

3) Conclusion/Summary of Results:

Mannitol salt agar is a selective medium that contains mannitol, phenol red and sodium chloride. The high salt concentration is what makes it selective by inhibiting the growth of most types of bacteria. The S. aureus ferments the mannitol and produces an acid which turns the phenol red indicator to yellow. Neither S. epidermis nor S. aureus are inhibited by the high salt concentration, while E. coli and Enterobacter are intolerant. S.