First report of cross resistance to silver and antibiotics in Klebsiella pneumoniae isolated from patients and polluted water in Tunisia

Klebsiella pneumoniae, ubiquitously found in a variety of environmental sources, is an important pathogen in burn wounds and nosocomial infections. Burn wounds have been commonly treated with silver compounds, which are also used in a multitude of (non)medical products. As the latter increased silver discharge into different environments, we evaluated and compared silver resistance in K. pneumoniae isolates collected from patients hospitalized at the Charles-Nicolle hospital (Tunis, Tunisia) with isolates collected from different metal polluted waters in the north and south of Tunisia. All K. pneumoniae isolates harboured blaTEM-1 and blaSHV-1. In addition, all clinical isolates showed a multidrug phenotype and harboured the blaCTX-M-15, blaOXA-1 and blaNDM-1. Furthermore, all isolates showed resistance to silver nitrate. The silver resistance determinant, screened via the silE gene, was located for all isolates on a large plasmid with a size similar to pMG101. This study showed cross-resistance between silver and beta-lactams in clinical as well as environmental K. pneumoniae isolates from Tunisia and showed for the first time that NDM-1-producing K. pneumoniae developed resistance to silver.