Genomic epidemiology of Methicillin Susceptible Staphylococcus aureus (MSSA) isolates from blood cultures in two hospitals in Argentina shows a high prevalence of CC398

VIELMA VALLENILLA J; NICOLA F; HAIM MS; RAGO L; BUES F; BONVEHI P; CAMPOS J; MOLLERACH M; DI GREGORIO S

Conferencia; Applied Bioinformatics & Public Health Microbiology 2023; 2023

Wellcome Connecting Science Conferences

Introduction: Staphylococcus aureus is the leading cause of death from bacterial infections worldwide. Currently, an increase in the number of bacteremias due to MSSA in hospitals has been observed. Objective: We aim to characterise phenotypically and genotypically all S. aureus isolated from blood cultures in two hospitals (A and B) in Buenos Aires (January-July 2021), and to determine the clonal relationship among them. Methods: Antibiotic susceptibility was determined by Phoenix and interpreted using the CLSI-2021. PFGE was performed for 31/35 isolates, using SmaI and Cfr9I, for those non-typable isolates. Subsequently, all the MSSA isolates were sequenced with Illumina NovaSeq platform. Relevant information [resistome, virulome, MLSTs, spatype and the phylogeny of prevalent clonal complexes], was determined by using ARIBA-v2.14.6 , spaTyper-1.0 and the SNP-phylogeny GHRU pipeline. Results: MSSA rate was 85.7% (30/35). Nine of these isolates displayed iMLSb phenotype and 4/30 were resistant to gentamicin. MRSA isolates represented 14.3% (5/35) of which 1/5 was resistant to clindamycin and 2/5 resistant to erythromycin, gentamicin and ciprofloxacin. Eight out of 9 isolates showing an iMLSb phenotype were non-typable by PFGE with SmaI. Cfr9I-PFGE of non tipable SmaI isolates showed that they all belonged to the pulse type A, related to CC398-MSSA. Bioinformatics analysis revealed that 8/9 isolates with the iMLSb phenotype carried the ermT gene (and belonged to CC398), and 1/9 carried the ermC gene (and belonged to CC8). Remaining MSSA isolates, belonged to other clonal complexes: CC8 (n=4), CC1 (n=4), CC15 (n=3), CC5 (n=2), CC30 (n=2), CC45 (n=1), CC97 (n=1), CC121 (n=1), CC22 (n=1), ST20 (n=1) and ST72 (n=1). CC398-t1451-PVL- (7/30) was the most prevalent genotype followed by CC15-t084-PVL- (3/30), CC1-t189-PVL- (3/30), CC8-t024-PVL- (2/30), all others were single genotypes. The phylogenetic analysis showed that CC398 isolates were highly related with previously reported strains circulating during 2019 in South-America. Moreover, a high clonality in two CC398-t1451-PVL- isolates (100% bootstrap) from hospital “A” could be correlated with a strong epidemiological link. Conclusion: We observed a high rate of bacteraemias caused by MSSA. 88.8% of isolates displaying iMLSb phenotype belonged to CC398, which is the major clonal complex among the MSSA isolates recovered from blood cultures from patients attending both hospitals. Our results also show evidence of possible within-hospital transmission of CC398-t1451-PVL-.