Chlamydia cell culture. Immunofluorescent light micrograph of chlamydia bacteria (Chlamydia psittaci, yellow) cultured in McCoy cells. The C. psittaci bacteria were first found in parrots. They also occur in pigeons and poultry. When transmitted to humans, they cause a rare type of pneumonia, called psittacosis, that may be fatal in the elderly and weak. Treatment is with suitable antibiotics. Immunofluorescence is a staining technique that uses antibodies to attach fluorescent dyes to cells and tissues. Chlamydia bacteria only live inside cells. McCoy cells are cells cultured for diagnostic purposes, including the culturing of bacteria. Magnification unknown.