Genetic and phenotypic analysis of the pathogenic potential of two novel Chlamydia gallinacea strains compared to Chlamydia psittaci

Abstract

Chlamydia gallinacea is an obligate intracellular bacterium that has recently been added to the family of Chlamydiaceae. C. gallinacea is genetically diverse, widespread in poultry and a suspected cause of pneumonia in slaughterhouse workers. In poultry, C. gallinacea infections appear asymptomatic, but studies about the pathogenic potential are limited. In this study two novel sequence types of C. gallinacea were isolated from apparently healthy chickens. Both isolates (NL_G47 and NL_F725) were closely related to each other and have at least 99.5% DNA sequence identity to C. gallinacea Type strain 08-1274/3. To gain further insight into the pathogenic potential, infection experiments in embryonated chicken eggs and comparative genomics with Chlamydia psittaci were performed. C. psittaci is a ubiquitous zoonotic pathogen of birds and mammals, and infection in poultry can result in severe systemic illness. In experiments with embryonated chicken eggs, C. gallinacea induced mortality was observed, potentially strain dependent, but lower compared to C. psittaci induced mortality. Comparative analyses confirmed all currently available C. gallinacea genomes possess the hallmark genes coding for known and potential virulence factors as found in C. psittaci albeit to a reduced number of orthologues or paralogs. The presence of potential virulence factors and the observed mortality in embryonated eggs indicates C. gallinacea should rather be considered as an opportunistic pathogen than an innocuous commensal.

Experimental inoculation of chicken broilers with C. gallinacea strain 15-56/1

“…Similarly, Heijne et al . 11 observed C. gallinacea -induced mortality in experimentally infected embryonated chicken eggs, which was potentially strain dependent but lower than C. psittaci -induced mortality. According to You et al .…”

“…However, experimentally infected broilers showed reduced body-weight gains (BWG); this was the sole symptom and they did not exhibit any clinical signs of disease 5 . Mortality in embryonated chicken eggs after inoculation with different C. gallinacea strains has also been described 5 , 11 . Laroucau et al .…”

Experimental Chlamydia gallinacea infection in chickens does not protect against a subsequent experimental Chlamydia psittaci infection

“…Chlamydia gallinacea NL_G47 and NL_F725 were isolated from caecal material from laying hens as described earlier [ 17 ]. Chlamydia psittaci strain NL_Borg is an in-house reference strain of ompA genotype D and is closely related to the turkey outbreak strain C. psittaci NJ1 with only 65 Single Nucleotide Polymorphisms (SNPs) [ 17 ].…”

“…Chlamydia gallinacea NL_G47 and NL_F725 were isolated from caecal material from laying hens as described earlier [ 17 ]. Chlamydia psittaci strain NL_Borg is an in-house reference strain of ompA genotype D and is closely related to the turkey outbreak strain C. psittaci NJ1 with only 65 Single Nucleotide Polymorphisms (SNPs) [ 17 ]. All strains were passaged three times in the yolk sac of embryonated SPF chicken eggs and stored at -80 °C in a 20% yolk sac suspension in Sucrose Phosphate Glutamate (SPG) until inoculation [ 18 ].…”

“…All strains were passaged three times in the yolk sac of embryonated SPF chicken eggs and stored at -80 °C in a 20% yolk sac suspension in Sucrose Phosphate Glutamate (SPG) until inoculation [ 18 ]. The infectious dose of the suspensions was calculated via egg titration experiments and expressed as the Egg Infectious Dose 50 (EID 50 ) [ 17 , 19 , 20 ].…”