Abstract
Klebsiella spp. is a relevant pathogen that can present acquired resistance to almost all available antibiotics, thus representing a serious threat for public health. While most studies have been focused on isolates causing community-acquired and nosocomial infections, little is known about the commensal isolates colonizing healthy subjects. We describe the molecular identification and the phenotypic characterization of commensal Klebsiella spp. from breast milk of healthy women and faeces from healthy breast-fed infants, which were compared with isolates from community-acquired infections and from a nosocomial NICU outbreak. The phylogenetic analysis of a 454-bp sequence of the rpoB gene was useful for species identification (K. pneumoniae, K. variicola, K. quasipneumoniae, K. oxytoca, K. grimontii, K. michiganensis, Raoultella planticola and R. ornithinolytica), previously misidentified as K. pneumoniae or K. oxytoca by biochemical methods. Globally, we report that commensal strains present virulence traits (virulence genes, siderophores and biofilms) comparable to community-acquired and NICU-infective isolates, thus suggesting that the human microbiota could constitute a reservoir for infection. Isolates causing NICU outbreak were multi-drug resistant (MDR) and ESBLs producers, although an imipenem-resistant commensal MDR K. quasipneumoniae isolate was also found. A commensal K. pneumoniae strain showed a potent bacteriocin-like inhibitory activity against MDR Klebsiella isolates, thus highlighting the potential role of commensal Klebsiella spp. in health and disease.
Highlights
IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
Among the 21 isolates initially identified as K. oxytoca by routine biochemical methods, just 1 isolate was identified as K. oxytoca sensu stricto by rpoB sequencing
The rest of the isolates were identified as K. michiganensis (n = 16), K. grimontii (n = 2), K. pneumoniae (n = 1)
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The major species of this genus is Klebsiella pneumoniae, followed by Klebsiella oxytoca, both considered as opportunistic pathogens with major relevance in community- and hospital-acquired (nosocomial) infections, which are severe in immunocompromised subjects such as those hospitalized in transplant, intensive care (ICU), or neonatal units (NICU) [2]. Phylogenetic analyses have shown that K. pneumoniae complex comprises seven phylogenetic groups (Kp1 to Kp7). Kp1 is the most abundant and includes K. pneumoniae sensu stricto; Kp2, Kp3, Kp4, Kp5, Kp6 and Kp7 include K. quasipneumoniae subsp. The K. oxytoca complex comprises six phylogroups, Ko1, Ko2, Ko3, Ko4, Ko6 and Ko8, 4.0/)
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