Antimicrobial Susceptibility Test of an Enteric Organism
| Purpose | To determine the antimicrobial susceptibility pattern of a gram-negative enteric bacillus |
| Materials | Nutrient agar plates (Mueller-Hinton if available) Antimicrobial disks Sterile swabs Forceps Beaker containing 70% alcohol Pure plate or slant culture of unknown from Experiment 25.2 Tube of nutrient broth (5.0 ml) |
Procedures
- Using a sterile swab or inoculating loop, take some of the growth of the pure culture of your unknown organism and emulsify it in 5.0 ml of nutrient broth to equal the turbidity of a McFarland 0.5 standard. (Discard the swab.)
- Take another sterile swab, dip it in the broth suspension, drain off excess fluid against the inner wall of the tube.
- Inoculate an agar plate as described in Experiment 15.1.
- Follow steps 4 through 7 of Experiment 15.1.
- Incubate the agar plate at 35°C for 24 hours.
- Examine plates and record results for each antimicrobial disk as S (susceptible), I (intermediate), or R (resistant).
- Compare results with those obtained for the organism you tested in Experiment 15.1 and Experiment 23.3.
Results
Record your findings.
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- Judging by the results of your tests, what group of antimicrobial agents appear to be indicated for the treatment of patients with gram-negative infections? Gram-positive infections?
- What conclusions can you draw as to the importance of testing each suspected bacterial pathogen for its antimicrobial susceptibility?
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