Effect of temperature modulation and bvg mutation of Bordetella bronchiseptica on adhesion, intracellular survival and cytotoxicity for swine alveolar macrophages

Abstract

Bordetella bronchiseptica causes respiratory disease in swine, yet there are no studies examining the interaction of B. bronchiseptica with swine alveolar macrophages. A swine isolate of B. bronchiseptica was able to adhere to, and survive intracellularly in, swine alveolar macrophages, but the relative ability of the bacteria to accomplish these functions was dependent on its phenotypic phase and culture conditions. More bacteria were observed extracellularly as well as intracellularly by immunofluorescent staining when B. bronchiseptica was cultured at 23°C as compared to 37°C. However, more bacteria cultured at 37°C were found surviving intracellularly after the macrophages were cultured with polymyxin B to kill extracellular bacteria. Similar results were seen in experiments performed with an isogenic Bvg − phase-locked mutant of B. bronchiseptica cultured at 37 or 23°C, indicating that another temperature dependent mechanism in addition to bvg may play a role in adhesion and intracellular survival . B. bronchiseptica was cytotoxic for swine alveolar macrophages in the Bvg + phase only. The cytotoxicity of B. bronchiseptica for alveolar macrophages, and its ability to survive phagocytosis, are no doubt important to escape from immune clearance mechanisms and establish infection, and could leave the host susceptible to secondary respiratory pathogens.