Assignment: Staphylococcus Unknown Dichotomous Key (flow diagram) Objective: • Using selected physiological traits and a

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Assignment: Staphylococcus Unknown Dichotomous Key (flow diagram) Objective: • Using selected physiological traits and a list of coagulase negative Staphylococcus species, students will produce a dichotomous key separating all possible Staphylococcus species. Overview: This assignment is the first of two assignments relevant to the identification of an unknown bacterium in the genus Staphylococcus. In this handout, students will have a list of the species of genus Staphylococcus that are coagulase negative. The coagulase test is used to separate the genus Staphylococcus into two groups, either coagulase positive or coagulase negative. It is not necessary at this time to perform and interpret the coagulase test, however we will do so in lab 13. Subsequent pages of this handout include 1) A list of the possible unknown Staphylococcus species, and 2) A list of tests and traits that cannot be performed or used to determine the identity of the Staphylococcus unknown. 3) Following an introduction to Bergey's Manual of Determinative Bacteriology and an introduction to dichotomous keys, students will produce and turn in a dichotomous key that separates the possible Staphylococcus unknown species. This dichotomous key will be used to complete a later assignment called Staphylococcus Unknown ID. Students will be expected to use Table 17.15 in Bergey's Manual of Determinative Bacteriology to produce their dichotomous key. This book is located in the lab, and two copies are available at the Reserve Desk in the library at the Rancho Campus. 1. List of Possible Staphylococcus Unknowns The list of Staphylococcus species shown below are all coagulase negative Staphylococcus species that can cause infections in humans. In contrast, Staphylococcus aureus is coagulase positive and is not included in the list. S. capitis subsp. capitis S. capitis subsp. ureolyticus S. cohnii subsp. cohnii S. cohnii subsp. urealyticus S. epidermidis S. lentus S. lugdunensis S. saccharolyticus S. saprophyticus S. schleiferi subsp. schleiferi S. sciuri S. simulans 2. Use Table 17.15 from Bergey's Manual of Determinative Bacteriology to create a dichotomous key that will initiate the process of the identification of the Staphylococcus unknown. The dichotomous key will show you the steps to take to identify your Staphylococcus unknown. 1, SP 16
3. Tests to Omit: The following tests are listed in the Bergey's Table 17.15 but are tests we cannot perform and so cannot be used in your dichotomous key. 1. Colony diameter >5 mm 2. Lactic acid production L(+) isomer or D (-)-isomer 3. FDP-aldolase 4. Acid (anerobically) from: a. Cellobiose b. Fucose c. Raffinose d. Salicin. e. Melezitose f. Turanose & Xylitol . . 5 Hyaluronidase 6. Growth on (NH4)2SO4 7. Alkaline phosphatase 8. Arginine dihydrolase 9. Coagulace Recommendations: Begin with the table from Bergey's and mark out the species not on our list (columns). Consult the list of tests we cannot perform and mark them out as well (rows). Use the remaining information to make a dichotomous key (two-branch diagram) that separates all the possible species from each other. 10. Clumping factor 11. Fibrinolysin 12. Deoxyribonuclease Agar 13. Heat Stable Nuclease 14. B-Glucosidase 15. B-Glucouronidase 16. Novobiocin resistance Table 17.15 uses symbols to indicate what the expected test outcome will be. The interpretation for these symbols should be read carefully at the end of the table. I will require that you treat specific symbols accordingly. Failure to follow the directions below will result in a loss of points: 1. +indicates that the expected result is positive and the species name will be listed on the positive side only. 2. - indicates that the expected result is negative and the species name will be listed on the negative side. 3. D, d, ND, ds indicates that between 11-89% of the strains test positive or that not enough information is known. Treat this as a 50/50 outcome, and write the notation (D/d/ND/ds) next to the species name and include the species name on both the positive and negative sides. Write the letter "d" for the expected test result next to the species name on the dichotomous key. 2, SP 16 4. ) indicates a delayed result (test will run longer than typical). Include the parentheses next to the species name on the dichotomous key. 5. w/+w indicates that the result might produce a weak positive result, that MIGHT possibly be interpreted as not clearly positive. Include the species on the positive side only, Write the notation "w" or "+w+ for the expected test result next to the species name on the dichotomous key. 6. -w indicates the organism may appear negative OR may appear with a weak positive. Treat this as a 50/50 outcome and write the "-w" next to the species name and include the species name on both the positive and negative sides.
X Cocci Gram Stain Gram negative cocci yellow Į Staphylococcus aureus Gram positive cocci Mannitol Salt pink Simple Stain Gram negative bacilli MacConkey's No color change Salmonella pullorum Staphylococcus epidermis Dichotomous Key Pink colonies E. coli Bacilli Gram Stain Acid Fast stain ↓ Acid Fast Enterobacter aerogenes Gram positive bacilli Not acid Mycobacterium fast Endospore stain Forms endospores Bacillus subtilus