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Isolation of Some Antibiotic Resistant Staph Aureus

Staphlococcus aureus is bacteria that causes numerous infections, including osteomyelitis, abscesses, scalded-skin syndrome, and bacterial endocarditis. S. aureus is treated by physicians with antibiotics, usually a choice from the "-cillin" group. Since penicillin has been around for many years, some bacteria have developed resistance against penicillin by producing enzymes called beta-lactamases.

  1. Gram Stain

    • S. aureus is differentiated from numerous other bacteria using a technique called a gram stain. Gram-staining distinguishes between S. aureus and -- among other bacteria -- streptococci. The procedure involves preparing a microscopic slide by adding crystal violet stain, alcohol, and a red dye called saffrin. In gram-positive bacteria such as S. aureus the stain is violet-colored, whereas gram-negative bacteria such as streptococci are stained red.

    Antibiotic Resistance S. Aureus

    • Isolating antibiotic-resistant S. aureus bacteria involves culturing them on an agar medium, which allows lab personnel to test different antibiotics to see which most effectively penetrate the bacterial cell wall. For S. aureus, the agar is prepared with penicillin, a cephalosporin, and vancomycin. S. aureus is then added to the agar and cultured for 24 hours. Results of antibiotic-resistant S. aureus will show penetration of only vancomycin into the cell wall, because these bacteria have developed resistance to penicillin and cephalosporins through beta-lactamase production.

    Treatment

    • Antibiotic resistant S. aureus is a common cause of nosocomial, or hospital-related, infections. Treating these infections can be difficult. However, successful treatment has been observed with the use of the antibiotics vancomycin and rifampin.

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