Improved isolation of Chlamydia trachomatis from a low-prevalence population by using polyethylene glycol

The effect of polyethylene glycol (PEG) on the isolation of Chlamydia trachomatis was evaluated in our laboratory. Initial range-finding experiments demonstrated that the number of chlamydial inclusion bodies increased with increasing PEG concentrations. However, PEG concentrations above 10.5% became progressively more toxic to the McCoy cell monolayers. When 50 frozen clinical Chlamydia isolates were inoculated onto McCoy cell cultures with and without 7% PEG, the PEG-treated cultures produced three- to fivefold more chlamydial inclusions than cultures without PEG. This enhancement was also observed when 1,144 fresh clinical specimens from a low-prevalence population were tested. With fresh clinical specimens, PEG-treated cultures produced two- to sixfold more inclusions than standard cultures. The addition of 7% PEG to the chlamydial overlay medium significantly increased the number of inclusions in each culture, improved the sensitivity of the culture, and decreased the probability of missing a weakly positive specimen.