Abstract
The first documented nosocomial outbreak caused by Serratia marcescens in Spain occurred in 1969 at the neonatal intensive care unit (NICU) of the tertiary La Paz Children’s Hospital in Madrid, Spain, and based on the available phenotyping techniques at this time, it was considered as a monoclonal outbreak. Only 47 years later, another S. marcescens outbreak of an equivalent dimension occurred at the same NICU. The aim of the present study was to study isolates from these historical and contemporary outbreaks by phenotypic analysis and whole-genome sequencing techniques and to position these strains along with 444 publicly available S. marcescens genomes, separately comparing core genome and accessory genome contents. Clades inferred by both approaches showed high correlation, indicating that core and accessory genomes seem to evolve in the same manner for S. marcescens. Nine S. marcescens clusters were identified, and isolates were grouped in two of them according to sampling year. One exception was isolate 13F-69, the most genetically distant strain, located in a different cluster. Categorical functions in the annotated accessory genes of both collections were preserved among all isolates. No significant differences in frequency of insertion sequences in historical (0.18–0.20)—excluding the outlier strain—versus contemporary isolates (0.11–0.19) were found despite the expected resting effect. The most dissimilar isolate, 13F-69, contains a highly preserved plasmid previously described in Bordetella bronchiseptica. This strain exhibited a few antibiotic resistance genes not resulting in a resistant phenotype, suggesting the value of gene down expression in adaptation to long-term starvation.
Highlights
Serratia marcescens is a ubiquitous environmental microorganism, and a relevant nosocomial pathogen able to cause a broad spectrum of infections, in neonates (Zingg et al, 2008)
These historical strains were grouped in five Pulse-field gel electrophoresis (PFGE) patterns, and the five contemporary isolates were grouped into three pulsotypes (Figure 1)
Bacterial typing techniques have evolved over time— from phenotypic tests in the 70s of the previous century to current molecular studies based on DNA, with a superior discrimination capacity, better interlaboratory reproducibility, and greater cost-effectiveness (Mellmann et al, 2017; Pérez-Losada et al, 2017)
Summary
Serratia marcescens is a ubiquitous environmental microorganism, and a relevant nosocomial pathogen able to cause a broad spectrum of infections, in neonates (Zingg et al, 2008). The main concerns regarding this opportunistic pathogen are its capability to spread in the hospital environment, to cause outbreaks, and its potential for expressing and disseminating antibiotic resistance, combining intrinsic mechanisms and acquired antimicrobial genes (Mahlen, 2011). The first documented S. marcescens outbreak affecting pediatric patients in Spain occurred in 1969 at the neonatal intensive care unit (NICU) of La Paz Children’s Hospital, the main pediatric university hospital in Madrid. The outbreak lasted, with oscillations, until late 1974 (>5 years), with a high incidence of S. marcescens bacteremia (9.16% of all early neonatal sepsis during the period), frequently associated with gut colonization during the first 3 days of life (12.5% of 120 children tested) (Baquero et al, 1969). The recovered isolates were considered as a single clone causing a monoclonal outbreak according to the available bacterial typing techniques, based on phenotypic tests that included biochemical reactions and antimicrobial susceptibility testing
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
