Characterisation of Chlamydia psittaci isolated from a horse.

The research article discusses the isolation and characterization of a strain of the bacterium Chlamydia psittaci, collected from a horse with a nasal discharge.

Isolation and initial characterisation

• The bacterium Chlamydia psittaci was isolated from a nasal swab taken from a horse exhibiting a serous, or clear, nasal discharge. The nasal swab was first cultured in cycloheximide-treated McCoy cell monolayers, a particular strain of cells used for growing bacteria and virus samples in a laboratory setting.
• Immunofluorescence staining techniques were employed to identify the presence of Chlamydia psittaci in the sample. A rabbit antiserum bred to react against C. psittaci as well as a monoclonal antibody that reacts with a certain type of antigen unique to the Chlamydia genus were used. These stains showed clear and compact chlamydial inclusions or aggregates.
• The bacterium did not react with a stain designed to react with iodine or with a strain of monoclonal antibodies engineered to react against Chlamydia trachomatis, confirming its specific identity as C. psittaci and not C. trachomatis.

Further characterisation and identification

• The isolated C. psittaci bacterium was then further grown in the yolk sacs of embryonated hens eggs and given the designation N16.
• Identification was further confirmed through the use of electron microscopy, a high-resolution technique allowing visualization of the bacterium at a sub-micron level.
• The researchers prepared plasmid DNA from purified chlamydial elementary bodies (the infectious form of the bacterium) and analysed it using gel electrophoresis, a procedure that separates DNA fragments by their size. The results were visualized using ethidium bromide, a DNA-binding dye that fluoresces when exposed to ultraviolet light.

Growth rate and yield

• This particular strain of C. psittaci, N16, was noted to grow relatively slowly in the cycloheximide-treated McCoy cells originally used for its isolation.
• The yield of elementary bodies over one growth cycle was also lower compared to other strains of the bacterium, indicating that this strain may have adapted to a slower growth rate or less optimal conditions within the horse’s nasal environment.