Characterization of Lancefield Group C and G Streptococci Causing Invasive Infections in Humans and Genomic Analysis of Macrolide Resistance, Portugal

Maria Inês Filipe Mendes

Key information

Authors:

Maria Inês Filipe Mendes (Maria Inês Filipe Mendes)

Supervisors:

Marcos Daniel Caetano Borges de Pinho; Ana Cristina Anjinho Madeira Viegas (Ana Cristina Anjinho Madeira Viegas)

Published in

December 6, 2024

Abstract

Streptococcus dysgalactiae subsp. equisimilis (SDSE) is a bacterium whose pathogenesis and capacity of infection in humans has been overlooked, but several studies have shown an increasing number of infections. In 2019-2022, 183 SDSE isolates causing invasive infections in Portugal were recovered, mostly from patients over 65 years-old (68%). Most presented the Lancefield group G antigen (68%), while the remaining were group C. No resistance to penicillin, vancomycin, linezolid, trimethoprim/sulfamethoxazole and chloramphenicol was found. High antimicrobial resistance rates to erythromycin and clindamycin were detected (45% and 43%, respectively), with an increase in resistance to both these antimicrobials since 2011. Resistance rates of 28% to tetracycline and 1% to levofloxacin were registered. Around 1% of isolates presented high-level resistance to gentamycin and 3% to streptomycin. Among macrolide and lincosamide resistant isolates, 72.3%, 24.1% and 3.6% presented the iMLSB, cMLSB and M phenotypes, respectively. The erm(A) gene was the most common (73.5%), followed by erm(B) (19.3%), erm(T) (3.6%) and mef(A) (3.6%) genes. Genomic analysis of SDSE invasive isolates recovered in Portugal (2011-2018) showed that macrolide and lincosamide resistance was found in different genetic backgrounds, although clonal complex 17 was associated with the high prevalence of resistance, mainly mediated by erm(A). The characterization of resistance genes genomic context showed that most isolates harboring the erm(A) gene seemed to carry ICESp2907, while the presence of the erm(B) gene was mainly associated to Tn3872. erm(T) presence in this population was due to plasmid p5580, while mef(A) was associated to the presence of distinct mobile genetic elements.