Comparison of vancomycin and penicillin for viral isolation

Penicillin was compared with vancomycin for use in diagnostic virology to inhibit bacterial contamination of clinical specimens. Vancomycin when combined with gentamicin and amphotericin B was found to be more effective in lowering the overall contamination rate than when penicillin was combined with these antibiotics (penicillin group, 14.9% versus vancomycin group, 6.2%; P less than 0.001). Of the contaminants grown in the presence of penicillin, 72% were gram-positive cocci, primarily coagulase-negative staphylococci. The number of gram-positive contaminants in the presence of vancomycin was reduced to zero. There was little difference in the rates of gram-negative rod or fungus contamination. The viral isolation rate in noncontaminated specimens was similar with either penicillin or vancomycin, but was reduced when specimens became contaminated. The time for virus detection and the morphology of cytopathology were similar in penicillin- and vancomycin-treated specimens. Vancomycin is an effective alternative to penicillin in reducing the growth of contaminants in viral isolation specimens.