Investigating Feral Pigs as Animal Reservoirs for Nontuberculous Mycobacteria in Hawai’i

Abstract

Nontuberculous mycobacteria (NTM) are environmentally-acquired opportunistic pathogens that cause recalcitrant pulmonary disease in susceptible individuals. The prevalence of NTM pulmonary disease is increasing globally, and the highest rates within the US are in Hawai'i. Mycobacterium porcinum (Latin, “porcus,” pig) is the fourth most frequently isolated NTM species from the Hawai’i environment and cause lymphadenitis in pigs and wound and pulmonary infections in humans. Because Hawai’i is home to large populations of invasive feral pigs, we hypothesized pigs are animal reservoirs for NTM. This hypothesis was tested with the following aims: (i) Determine the NTM species diversity among Hawai’i feral pigs, and (ii) Assess the growth rate of feral pig, environmental, and respiratory NTM, including environmental and respiratory M. porcinum isolates, and compare survival of these isolates in human macrophages. To accomplish project aims, we collected a matched set of nasal and fecal samples from 50 deceased Hawai’i feral pigs. Samples were microbiologically cultured and NTM were identified using partial rpoB gene sequencing. A total of 20 NTM species were identified, including Mycobacterium abscessus. Five pig-derived NTM isolates and six M. porcinum isolates were selected for further characterization including tabulating their colony morphology, capacity to form biofilms, and assessing their capacity to survive in human THP-1 macrophages. We found effective control of pig-derived NTM by THP-1 macrophages, but differential production of host cytokines in response to infection. M. porcinum isolates showed significant intraspecies variation with respect to growth rate and macrophage survival. This study confirms feral pigs in Hawai’i harbor pathogenic NTM species and may contribute to the prevalence of NTM in Hawai’i.