Characterization of a DHA-1-Producing Klebsiella pneumoniae Strain Involved in an Outbreak and Role of the AmpR Regulator in Virulence

Abstract

A clonal strain of Klebsiella pneumoniae producing the plasmid-encoded cephalosporinase DHA-1 was isolated from four patients admitted to the teaching hospital of Clermont-Ferrand, France, in 2006. It was responsible for severe infections in three of the patients; the fourth was colonized only in the gastrointestinal tract. The strain had at least two plasmids encoding resistance to antibiotics (quinolones, aminoglycosides, chloramphenicol, sulfonamides, and trimethoprim), as shown by disk diffusion assay, and harbored only a few genes for virulence factors (wabG and mrkD), as shown by PCRs. DHA-1 synthesis is regulated by an upstream, divergently transcribed gene, ampR, which is also involved in the expression of virulence factors in Pseudomonas aeruginosa. To investigate the role of AmpR in K. pneumoniae, we cloned the wild-type ampR gene from the DHA-1 clonal isolate into a previously characterized K. pneumoniae background plasmid-cured strain, CH608. ampR was also introduced into a CH608 isogenic mutant deleted of ampD, in which AmpR is present only in its activator form, resulting in constitutive hyperproduction of the ␤-lactamase. We showed that ampR was involved in the upregulation of capsule synthesis and therefore in resistance to killing by serum. AmpR also modulated biofilm formation and type 3 fimbrial gene expression, as well as colonization of the murine gastrointestinal tract and adhesion to HT-29 intestinal epithelial cells. These results show the pleiotropic role of ampR in the pathogenesis process of K. pneumoniae.

First characterization of CTX-M-15 and DHA-1 -lactamases among clinical isolates of Klebsiella pneumoniae in Laghouat Hospital, Algeria

“…Our results are comparable with those of other studies in Spain, China, and France, which observed the diffusion of DHA-1 plasmid-mediated cephalosporinases in K. pneumoniae strains (Hennequin et al, 2012;Guo et al, 2012;Tobes et al, 2013). There are few studies concerning the cephalosporinases AmpC diffusion in this species in Algeria.…”

Biofilm formation and antibiotic resistance inKlebsiella pneumoniaeurinary strains

“…Sahly et al (2008) have also observed an upregulation of type 3 fimbriae expression, pivotal for biofilm formation, upon acquisition of ESBL (SHV-12)-encoding plasmids. Moreover, plasmids encoding cephalosporinases have been demonstrated to get transcriptional factors, that is, AmpR, involved in the upregulation of capsule synthesis and resistance to killing by serum as well as in the modulation of biofilm formation and expression of type 3 fimbriae, thus increasing virulence of K. pneumoniae (Hennequin et al 2012b;Compain et al 2014).…”

Interplay between Peptidoglycan Biology and Virulence in Gram-Negative Pathogens

“…More specifically, ampR from a plasmid containing the DHA-1 enzyme in a clinical strain of K. pneumoniae was shown to be involved in capsule synthesis and the derived serum resistance, biofilm formation, type 3 fimbrial gene expression, adhesion to cells in culture, as well as colonization of the gastrointestinal tract in mice (287). These results add strength to the previously mentioned idea on the wide pleiotropic power of ampR (and other LysR regulators) to regulate not only intrinsic or horizontally acquired ␤-lactamases expression but also many other bacterial processes, including virulence.…”