Serratia marcescens colonization in preterm neonates during their neonatal intensive care unit stay

Background Nosocomial sepsis is the main problem that preterms have to face during their stay at neonatal intensive care units (NICU). Serratia marcescens is an emerging cause of preterm sepsis but its epidemiology is still largely unknown. Consequently, the aims of this study were to know the rate of preterms colonized by S. marcescens during their stay at the NICU and the characteristics and evolution of the S. marcescens population, including the susceptibility to clinically relevant antibiotics. Methods Twenty-six preterm infants born with a gestational age <= 32 weeks and/or weigh <= 1500 g were included in the study. Samples of meconium and feces (n = 92) were collected during their first month of life of the infants, together with feeding samples after their pass through enteral feeding tubes (n = 37). Samples were inoculated on MacConkey agar plates. The isolates identified as S. marcescens were genotyped using RAPD and PFGE; and antibiotics susceptibility was performed in a Vitek 2 system. Results A total of 179 S. marcescens isolates were obtained from the samples. PFGE profiling and cluster analysis allowed the classification of the isolates into 7 different S. marcescens clones. PFGE patterns 1 and 3 were the dominant strains in the fecal samples colonizing 31 and 35% of the infants, respectively. Those isolates causing bacteremia in two infants clustered in PFGE pattern 3. Conclusion S. marcescens is a bacterial species closely associated to the NICU environment. It can be frequently isolated from preterm's feces although only some genetic lineages seem to be associated to sepsis. Enteral feeding tubes act as important reservoirs to keep the S. marcescens population in the NICU.