Bathing seawater and sand as reservoirs of clinically relevant and antimicrobial resistant Klebsiella pneumoniae strains

Klebsiella pneumoniae is included in the ESKAPE list of bacteria, which are currently considered the greatest threat to human health. It is widely distributed in the environment, including waters, soils, and plants. According to the One Health concept, it is essential to enhance our understanding of the distribution and genetic characteristics of this human pathogen in aquatic ecosystems, particularly in environments with frequent human contact, such as beaches and seawater used for recreational purposes. The aim of this study is to investigate whether bathing seawater and sand could serve as reservoirs for antimicrobial- resistant and clinically relevant K. pneumoniae strains. A total of 60 seawater and 54 sand samples were collected along the Abruzzo Region (Central Italy) shoreline during the bathing season. K. pneumoniae was detected at 13 seawater and 12 sand sites, mainly in areas heavily impacted by anthropogenic pollution and close to river mouths. Several strains belonged to sequence types (STs) of clinical interest, and one classified as ST348 was multidrug-resistant and harbored multiple antimicrobial resistance genes (ARGs). All the collected strains had ARGs in their genome, several of which were located on putative plasmids or phages, enhancing the potential for their horizontal gene transfer. This study confirms that bathing seawater and sand could contribute to the selection and spread of clinically relevant K. pneumoniae, with anthropogenic pollution influencing its presence. These environments should be recognized as important reservoirs and monitored for their potential to transmit this pathogen to humans.