Achromobacter spp. in Cystic Fibrosis: Investigating Pathogenicity, Host Response, and Molecular Identification

Achromobacter spp. are non-lactose fermenting, catalase and oxidase-positive Gram-negative bacilli commonly found in various environments. They play a significant role in human infections, particularly in cystic fibrosis (CF) patients, where they can cause chronic respiratory infections. Notably, these bacteria exhibit considerable antibiotic resistance due to both innate and adaptive mechanisms. The Achromobacter genus includes 22 species, with A. xylosoxidans being the most prevalent in CF clinical samples, linked to increased pulmonary exacerbations and hospitalizations. Other relevant species include A. dolens and A. insuavis. Current identification methods, such as VITEK 2 and MALDI-TOF MS, often struggle to accurately differentiate between species. This research includes several studies examining the virulence, antimicrobial resistance, host immune response, and species identification of Achromobacter spp. The first study compared phenotypic characteristics of CF clinical isolates, revealing critical differences in virulence and antibiotic resistance, which may correlate with bacterial persistence in the lungs. A second study investigated the host inflammatory response in CFTR-knockout and wild-type mice exposed to selected isolates, finding that virulent strains induced higher lung inflammation and mortality, particularly in knockout mice. This highlights the importance of understanding the pathogenic mechanisms of Achromobacter spp. Further research utilized an in vivo zebrafish model to explore host interactions, revealing varying levels of host mortality and bacterial persistence. Our findings demonstrated that highly virulent strains led to significant host mortality, whereas less virulent strains caused limited infections. Importantly, macrophages played a crucial role in controlling bacterial growth; their depletion resulted in increased bacterial burden and mortality, even with less virulent strains. Finally, the development of a quantitative PCR (qPCR) protocol for species-level identification addressed challenges in accurately diagnosing Achromobacter infections. This research enhances our understanding of Achromobacter spp. in CF and other infections, informing clinical management and future therapeutic strategies.