RESUMEN
Moraxella catarrhalis is a human respiratory tract pathogen that causes otitis media in children and lower respiratory tract infections in adults with chronic obstructive pulmonary disease. We have identified and characterized a zinc uptake ABC transporter that is present in all strains of M. catarrhalis tested. A mutant in which the znu gene cluster is knocked out shows markedly impaired growth compared to the wild type in medium that contains trace zinc; growth is restored to wild-type levels by supplementing medium with zinc but not with other divalent cations. Thermal-shift assays showed that the purified recombinant substrate binding protein ZnuA binds zinc but does not bind other divalent cations. Invasion assays with human respiratory epithelial cells demonstrated that the zinc ABC transporter of M. catarrhalis is critical for invasion of respiratory epithelial cells, an observation that is especially relevant because an intracellular reservoir of M. catarrhalis is present in the human respiratory tract and this reservoir is important for persistence. The znu knockout mutant showed marked impairment in its capacity to persist in the respiratory tract compared to the wild type in a mouse pulmonary clearance model. We conclude that the zinc uptake ABC transporter mediates uptake of zinc in environments with very low zinc concentrations and is critical for full virulence of M. catarrhalis in the respiratory tract in facilitating intracellular invasion of epithelial cells and persistence in the respiratory tract.
Asunto(s)
Transportadoras de Casetes de Unión a ATP/metabolismo , Proteínas Portadoras/metabolismo , Moraxella catarrhalis/metabolismo , Infecciones por Moraxellaceae/metabolismo , Infecciones del Sistema Respiratorio/metabolismo , Zinc/metabolismo , Transportadoras de Casetes de Unión a ATP/genética , Animales , Proteínas Portadoras/genética , Línea Celular , Células Epiteliales/metabolismo , Células Epiteliales/microbiología , Humanos , Ratones , Ratones Endogámicos BALB C , Moraxella catarrhalis/genética , Moraxella catarrhalis/patogenicidad , Infecciones por Moraxellaceae/genética , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Sistema Respiratorio/metabolismo , Sistema Respiratorio/microbiología , Infecciones del Sistema Respiratorio/genética , Infecciones del Sistema Respiratorio/microbiología , Virulencia/genéticaRESUMEN
An urgent need exists for vaccines to prevent infections caused by nontypeable Haemophilus influenzae and Moraxella catarrhalis. These bacteria cause otitis media in children, a clinical problem associated with enormous morbidity and cost. H. influenzae and M. catarrhalis also cause lower respiratory tract infections in adults with chronic lung disease. Infections in this clinical setting are associated with disability and death. Recent progress in identifying potential vaccine antigens in both bacteria raises great promise in developing effective vaccines. This paper reviews the key issues in vaccine development for H. influenzae and M. catarrhalis, including areas where progress has been stalled, and proposes areas that deserve investigation in the next 5 years.