Avian pathogenic Escherichia coli (APEC) is a bacterium that is responsible for colibacillosis in birds. However, information about broiler breeder APEC isolates is limited, but the data is critical due to the transfer of this bacteria down the production pyramid to progenies resulting in high mortality. Therefore, we evaluated the phenotypic virulence characteristics of 28 isolates using embryo lethality and day-old chick challenge assays. Also, the in vitro adhesion and invasion potential of selected nine isolates were identified. Results showed more than 1/3rd of the isolates were highly virulent and the virulence increased as the number of virulence-associated genes increased. High adhesion and invasion rates were observed among the isolates. Overall, the study helped us to evaluate the virulence characteristics of APEC from broiler breeders. However, future studies based on whole genome approach would help to identify the specific targets which can be used to develop effective interventions.

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Chlamydia trachomatis is the most common sexually transmitted bacterial disease agent worldwide, and, though frequently asymptomatic, can cause extreme pathology including infertility. Chlamydial species exhibit a unique biphasic developmental cycle. Once attached to a cell surface, infectious elementary bodies (EB) are internalized within an inclusion, the membrane-bound structure in which EB transform to noninfectious, replicable reticulate bodies (RB). After multiple rounds of division, RB condense to form EB, which are released and can infect new host cells. In culture, exposure to stressors, such as beta-lactam antibiotics, induce chlamydiae to reversibly detour from normal development into a noninfectious, viable state termed persistence. Cell culture data suggest that persistent forms are resistant to azithromycin (AZM), a front-line antibiotic, and are able to alter the host transcriptome. Though persistence has been described in culture for over 50 years, whether or not it: i) occurs in vivo; and ii) influences chlamydial pathogenesis, transmission and therapy has remained unresolved. To address these questions, we developed an animal model of persistent chlamydial infection using amoxicillin (AMX) treatment. AMX exposure decreased shedding of infectious chlamydiae in C. muridarum-infected mice without affecting chlamydial viability, demonstrating the presence of persistent chlamydiae. Shedding of infectious EB resumed following AMX cessation. Shedding data and microarray analyses suggested that host immunity might limit chlamydia’s exit from persistence in our model. Thus, we hypothesized that cyclophosphamide (CTX) treatment would increase the magnitude of chlamydial shedding observed after AMX-treatment cessation. CTX treatment increased post-AMX shedding by more than 10-fold compared to AMX-only controls. To determine whether persistent chlamydiae are resistant to antibiotic eradication in vivo, we induced persistence by administering AMX and treated mice with various AZM dosing regimes. Persistently infected mice demonstrated increased treatment failure following AZM therapy compared to productively infected controls. These data suggest that persistent chlamydiae are refractory to treatment in vivo and provide an explanation for the observation that treatment fails in some patients. In addition to creating the first fully characterized, experimentally tractable, in vivo model of chlamydial persistence, these experiments provide evidence that persistent/stressed chlamydial forms may serve as a long-term reservoir of infectious organisms in vivo.

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