NOTES Selection of Mutant Cell Lines Resistant to Infection by

The lytic outcome of natural infection by Chlamydia trachomatis was exploited to select CHO (Chinese hamster ovary) cells, following chemical mutagenesis, that were deficient in their ability to sustain productive chlamydial infection. Four distinct mutant cell phenotypes with defects in either attachment or postattachment mechanisms that are required for infection by C. trachomatis and Chlamydia pneumoniae were characterized. Chlamydiae are obligate intracellular bacterial pathogens that cause a wide spectrum of diseases in humans. In the United States, genital tract infection with Chlamydia tracho-matis is the most common sexually transmitted disease, often resulting in severe human reproductive pathology (1). In de-veloping countries, ocular infection with C. trachomatis can lead to trachoma, the leading cause of preventable blindness (21). Chlamydia pneumoniae is an important cause of lower and upper respiratory tract infections in humans, and it has been implicated in the pathogenesis of atherosclerosis (17). Strains of C. trachomatis are classified into two biovariants