The Achromobacter genus includes opportunistic pathogens that can cause chronic infections in immunocompromised patients, especially in people with cystic fibrosis (CF). Treatment of Achromobacter infections is complicated by antimicrobial resistance. In this study, a collection of Achromobacter clinical isolates, from CF and non-CF sources, was investigated for polymyxin B (PmB) resistance. Additionally, the effect of PmB challenge in a subset of isolates was examined and the presence of PmB-resistant subpopulations within the isolates was described. Further, chemical and mass spectrometry analyses of the lipid A of Achromobacter clinical isolates enabled the determination of the most common structures and showed that PmB challenge was associated with lipid A modifications that included the addition of glucosamine and palmitoylation and the concomitant loss of the free phosphate at the C-1 position. This study demonstrates that lipid A modifications associated with PmB resistance are prevalent in Achromobacter and that subresistant populations displaying the addition of positively charged residues and additional acyl chains to lipid A can be selected for and isolated from PmB-sensitive Achromobacter clinical isolates. IMPORTANCE Achromobacter species can cause chronic and potentially severe infections in immunocompromised patients, especially in those with cystic fibrosis. Bacteria cannot be eradicated due to Achromobacter's intrinsic multidrug resistance. We report that intrinsic resistance to polymyxin B (PmB), a last-resort antimicrobial peptide used to treat infections by multiresistant bacteria, is prevalent in Achromobacter clinical isolates; many isolates also display increased resistance upon PmB challenge. Analysis of the lipopolysaccharide lipid A moiety of several Achromobacter species reveals a penta-acylated lipid A, which in the PmB-resistant isolates was modified by the incorporation of glucosamine residues, an additional acyl chain, loss of phosphates, and hydroxylation of acyl chains, all of which can enhance PmB resistance in other bacteria. We conclude that PmB resistance, particularly in Achromobacter isolates from chronic respiratory infections, is a common phenomenon, and that Achromobacter lipid A displays modifications that may confer increased resistance to polymyxins and potentially other antimicrobial peptides.
lipid A, antibiotic resistance, Achromobacter, opportunistic infections, polymyxins
NCBI PubMed ID: 36519943Publication DOI: 10.1128/spectrum.03729-22Journal NLM ID: 101634614Publisher: Washington, DC: ASM Press
Correspondence: M.A. Valvano
Institutions: Department of Chemical Sciences, University of Naples Federico II, Naples, Italy, Task Force on Microbiome Studies, University of Naples Federico II, Naples, Italy, Wellcome-Wolfson Institute for Experimental Medicine, Queen's University Belfast, Belfast, United Kingdom, West African Center for Cell Biology of Infectious Pathogens, University of Ghana, Accra, Ghana, Antimicrobial Resistance and Healthcare Associated Infections Unit, UK Health Security Agency, London, United Kingdom, Laboratory for Disinfection and Pathogen Elimination Studies, Northern Ireland Public Health Laboratory, Belfast City Hospital, Belfast, United Kingdom, Research Group on Foods, Nutritional Biochemistry and Health, Universidad Europea del Atlantico, Santander, Spain, CIBERINFEC, Instituto de Salud Carlos III, Madrid, Spain, Department of Chemistry, School of Science, Osaka University, Osaka, Japan
Methods: PCR, DNA sequencing, GC-MS, SDS-PAGE, chemical analysis, MALDI-TOF MS, extraction, statistical analysis, assay of polymyxin sensitivity, gene annotation
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