A long-term survey of
Serratia
spp. bloodstream infections revealed an increase of antimicrobial resistance involving adult population
Authors: Pérez-Viso Blanca , Hernández-García Marta , Rodríguez Concepción M. , D. Fernández-de-Bobadilla Miguel , Serrano-Tomás María Isabel , Sánchez-Díaz Ana María , Avendaño-Ortiz José , Coque Teresa M. , Ruiz-Garbajosa Patricia , del Campo Rosa , Cantón Rafael 
Published: January 2024

Serratia
spp. is a well-recognized pathogen in neonates; however, limited data are available in adults. We studied microbiological and clinical characteristics of
Serratia
spp. causing bloodstream infections (BSI) in our institution (January 2005–July 2020). Overall, 141 BSI episodes affecting 139 patients were identified and medical records reviewed. Antimicrobial susceptibility was recovered from our informatics system and 118 isolates from 116 patients were available for further microbiological studies. Whole genome sequencing (WGS) was completed in 107 isolates. Incidence of
Serratia
BSI was 0.3/1000 overall admissions (range 0.12–0.60), with maximum prevalence (27 episodes, 19.1%) during 2017–2018. Relevant patients’ clinical characteristics were 71.9% ≥60 years (
n
= 100), with high comorbidity rates (49%, ≥2), 23 (74.2%) of them died within 1 month of the BSI episode. WGS identified all isolates as
Serratia marcescen
s when Kraken bioinformatics taxonomic tool was used despite some which were identified as
Serratia nematodiphila
(32/118) or
Serratia ureilytica
(5/118) by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Nevertheless, when using MASH distance,
Serratia nevei
(63/107),
S. ureilytica
(38/107), and
S. marcescens
(6/107) were assigned. Carbapenemase (
bla
VIM-1
) and extended-spectrum β-lactases (ESBL) (
bla
SHV-12
) genes were found in seven and three isolates, respectively, one of them expressing both genes. The worldwide-disseminated IncL/M scaffold plasmid was identified in six VIM producers. Four genotypes were established based on their virulence factors and resistome.
Serratia
spp. emerged as a relevant nosocomial pathogen causing BSI in elderly patients in our hospital, particularly in recent years with a remarkable increase in antibiotic resistance. ESBL and carbapenemases production related to plasmid dissemination are particularly noteworthy.

IMPORTANCE

Serratia
spp. is the third most frequent pathogen involved in outbreaks at neonatal facilities and is primarily associated with bacteremia episodes. In this study, we characterized all causing bloodstream infection (BSI) in patients admitted to our hospital during a 16-year period (2005–2020). Despite having no neonatal intensive care unit in our hospital, this study revealed that
Serratia
spp. is a relevant pathogen causing BSI in elderly patients with high comorbidity rates. A significant increase of antimicrobial resistance was detected over time, particularly in 2020 and coinciding with the coronavirus disease (COVID-19) pandemic and nosocomial spread of multidrug-resistant
Serratia
spp. isolates. extended-spectrum β-lactases and carbapenemases genes associated with plasmid dissemination, typically detected in other Enterobacterales species, were also identified, reinforcing the role of
Serratia
spp. in the antimicrobial resistance landscape. Additionally, this work highlights the need to reclassify the species of
Serratia
, since discrepancies were observed in the identification when using different tools.