Characterisation of key genotypic and phenotypic traits of clinical cystic fibrosisStaphylococcus aureusisolates

Abstract

ABSTRACTIntroductionOne third of people with CF in the UK are co-infected by bothStaphylococcus aureusandPseudomonas aeruginosa. Chronic bacterial infection in CF contributes to the gradual destruction of lung tissue, and eventually respiratory failure in this group.Gap StatementThe contribution ofS. aureusto cystic fibrosis (CF) lung decline in the presence or absence ofP. aeruginosais unclear. Defining the molecular and phenotypic characteristics of a range ofS. aureusclinical isolates will help further understand its pathogenic capabilities.AimOur objective was to use molecular and phenotypic tools to characterise twenty-five clinicalS. aureusisolates collected from mono- and coinfection withP. aeruginosafrom people with CF at the Royal Victoria Infirmary, Newcastle upon Tyne.MethodologyGenomic DNA was extracted and sequenced. Multilocus sequence typing was used to construct phylogeny from the seven housekeeping genes. A pangenome was calculated using Roary. and cluster of Orthologous groups were assigned using eggNOG-mapper which were used to determine differences within core, accessory, and unique genomes. Characterisation of sequence type, clonal complex,agrandspatypes was carried out using PubMLST, eBURST, AgrVATE and spaTyper, respectively. Antibiotic resistance was determined using Kirby Bauer disk diffusion tests. Phenotypic testing of haemolysis was carried out using ovine red blood cell agar plates and mucoid phenotypes visualised using Congo red agar.ResultsClinical strains clustered closely based onagrtype, sequence type and clonal complex. COG analysis revealed statistically significant enrichment of COG families between core, accessory and unique pangenome groups. The unique genome was significantly enriched for replication, recombination and repair, and defence mechanisms. The presence of known virulence genes and toxins were high within this group, and unique genes were identified in 11 strains. Strains which were isolated from the same patient all surpassed average nucleotide identity thresholds, however, differed in phenotypic traits. Antimicrobial resistance to macrolides was significantly higher in the coinfection group.ConclusionThere is huge variation in genetic and phenotypic capabilities ofS. aureusstrains. Further studies on how these may differ in relation to other species in the CF lung may give insight into inter-species interactions.Data summaryThe assembled GenBank (gbk) files for all clinical isolates in this study have been deposited in ENA under the study accession PRJEB56184, accession numbers for each of the twenty-five clinical isolates have been provided in Table S1. The reference strains were collected from the NCBI BioSample database (www.ncbi.nlm.nih.gov/biosample): MRSA_252 (NC_002952.2), HO 5096 0412 (NC_017763.1), ST398 (NC_017333.1) and NCTC8325 (NC_007795.1).