Multidrug-Resistant Salmonella enterica Serovar Rissen Clusters Detected in Azores Archipelago, Portugal

Abstract

Gastrointestinal infections caused by nontyphoidal Salmonella (NTS) remain one of the main causes of foodborne illness worldwide. Within the multiple existing Salmonella enterica serovars, the serovar Rissen is rarely reported, particularly as a cause of human salmonellosis. Between 2015 and 2017, the Portuguese National Reference Laboratory of Gastrointestinal Infections observed an increase in the number of clinical cases caused by multidrug-resistant (MDR) S. enterica serovar Rissen, particularly from the Azores archipelago. In the present study, we analyzed by whole genome sequencing (WGS) all clinical, animal, food, and environmental isolates received up to 2017 in the Portuguese Reference Laboratories. As such, through a wgMLST-based gene-by-gene analysis, we aimed to identify potential epidemiological clusters linking clinical and samples from multiple sources, while gaining insight into the genetic diversity of S. enterica serovar Rissen. We also investigated the genetic basis driving the observed multidrug resistance. By integrating 60 novel genomes with all publicly available serovar Rissen genomes, we observed a low degree of genetic diversity within this serovar. Nevertheless, the majority of Portuguese isolates showed high degree of genetic relatedness and a potential link to pork production. An in-depth analysis of these isolates revealed the existence of two major clusters from the Azores archipelago composed of MDR isolates, most of which were resistant to at least five antimicrobials. Considering the well-known spread of MDR between gastrointestinal bacteria, the identification of MDR circulating clones should constitute an alert to public health authorities. Finally, this study constitutes the starting point for the implementation of the “One Health” approach for Salmonella surveillance in Portugal.

Occurrence and distribution of Salmonella serovars in carcasses and foods in southern Italy: Eleven-year monitoring (2011–2021)

“…Interestingly, S. Enteritidis, the most commonly reported serovar from confirmed human cases in Europe since 2011 [ EFSA and ECDC (European Food Safety Authority and European Centre for Disease Prevention and Control), 2021 ] was not frequently detected in the present study, and comparing the period 2011–2015 with 2016–2021, a decreased, although not significative, occurrence was observed ( p > 0.05). By contrast, S. Rissen, frequently detected here, is often associated with human infections in the United States of America and Asia ( Silveira et al, 2019 ), but not in the European Union.…”

“…S. Infantis, S. Derby, monophasic S. Typhimurium, S. Typhimurium, and S. Rissen were the most frequently found. S. (Silveira et al, 2019), but not in the European Union.…”

Serotyping and Evaluation of Antimicrobial Resistance of Salmonella Strains Detected in Wildlife and Natural Environments in Southern Italy

“…Moreover, S. Typhimurium, S. Enteritidis and S. Derby, along with monophasic S. Typhimurium, S. Infantis, S. Newport, S. Stanley, S. Kentucky and S. Virchow, which were also detected in the present study, are frequently reported in human cases in Europe [ 13 ]. By contrast, S. Rissen is frequently reported in human infections in the United States of America and Asia [ 23 ], but not in the European Union.…”

Antimicrobial Susceptibility Testing for Salmonella Serovars Isolated from Food Samples: Five-Year Monitoring (2015–2019)

“…S. Newport, S. Infantis, and monophasic S. Typhimurium belong to the five most commonly reported serovars in human cases, and S. Brandenburg has also been frequently reported during confirmed cases of human salmonellosis in the EU [1]. S. Rissen, which is frequently reported in the United States of America and Asia, is rarely isolated during human infection in Europe [18]. Since the role of food in Salmonella transmission to humans has been demonstrated, the high resistance rate and MDR reported among these serotypes is a matter of great concern [19].…”