Perreten, V. | bioRxiv Science

bioRxiv2023

Ancient methicillin-resistant Staphylococcus aureus: expanding current knowledge using molecular epidemiological characterization of a Swiss legacy collection

Few methicillin-resistant Staphylococcus aureus (MRSA) from the early years of its global emergence have been sequenced. Knowledge about evolutionary factors promoting the success of specific MRSA multi-locus sequence types (MLSTs) remains scarce. We aimed to characterize a legacy MRSA collection isolated from 1965 to 1987 and compare it against publicly available international and local genomes. We accessed 451 ancient (1965-1987) Swiss MRSA isolates, stored in the Culture Collection of Switzerland. We determined phenotypic antimicrobial resistance (AMR) and performed Illumina short-read sequencing on all isolates and long-read sequencing on a selection with Oxford Nanopore Technology. For context, we included 103 publicly available international genomes from 1960 to 1992 and sequenced 1207 modern Swiss MRSA isolates from 2007 to 2022. We analyzed the core genome (cg)MLST and predicted SCCmec cassette types, AMR, and virulence genes. Among the 451 ancient Swiss MRSA isolates, we found 17 sequence types (STs) of which 11 have been previously described. Two STs were novel combinations of known loci and six isolates carried previously unsubmitted MLST alleles, representing five new STs (ST7843, ST7844, ST7837, ST7839, and ST7842). Most isolates (83% 376/451) represented ST247-MRSA-I isolated in the 1960s, followed by ST7844 (6% 25/451), a novel single locus variant (SLV) of ST239. Analysis by cgMLST indicated that isolates belonging to ST7844-MRSA-III cluster within the diversity of ST239-MRSA-IIII. Early MRSA were predominantly from clonal complex (CC) 8. From 1980 to the end of the 20th century we observed that CC22 and CC5 as well as CC8 were present, both locally and internationally. The combined analysis of 1761 ancient and contemporary MRSA isolates across more than 50 years uncovered novel STs and allowed us a glimpse into the lineage flux between Swiss and international MRSA across time.

microbiology↗

bioRxiv2020

Addition of Daptomycin to Levofloxacin Increased the Efficacy of Levofloxacin Monotherapy against a Methicillin-Susceptible Staphylococcus aureus Strain in Experimental Meningitis and Prevented Development of Resistance

Daptomycin and levofloxacin were tested as monotherapies and in combination against the antibiotic-susceptible S. aureus strain MSSA 1112 in a rabbit meningitis model and the effect of the combination on induction of resistance was determined in vitro. Changes of the susceptibility to fluoroquinolones and daptomycin was determined by the measurement of the MIC and mutations were detected by whole genome sequence comparison of the mutants with the parent strain MSSA 1112. Meningitis was induced by intracisternal inoculation of 105 CFU of MSSA 1112 and treatment was started 10 h later by injection of daptomycin (15 mg/kg) and levofloxacin (10 mg/kg) standard doses. Cerebrospinal fluid (CSF) samples were repeatedly collected during therapy in order to determine killing rates and results of bactericidal activity were expressed in {Delta}log10 CFU/ml over 8 h. The combination of daptomycin with levofloxacin was significantly (p< 0.001) superior to levofloxacin monotherapy and increased the antibacterial activity of daptomycin. In vitro, MSSA 1112 was cycled over six days with either increasing concentrations of levofloxacin or daptomycin or with a combination of levofloxacin with half of the MIC of daptomycin or daptomycin with half of the MIC of levofloxacin leading to mutations in target genes as identified by whole genome sequence analysis. Addition of low concentration of daptomycin (0.25 mg/L) reduced levofloxacin-induced resistance in vitro. Addition of levofloxacin in low concentration (0.125 mg/L) did not influence daptomycin-induced resistance. These findings highlight the lack of reciprocal interference of antibiotics in combination with regard to the development of resistance.

microbiology↗