Molecular typing of Portuguese clinical isolates of Salmonella spp., S. Enteritidis and S. Typhimurium

Abstract

Salmonella spp. is an important pathogen associated with human disease. It remains one of the major causes of food-borne outbreaks all over the world. In Europe two serovars are at the top of the list in number of cases per year, Enteritidis and Typhimurium. Salmonellosis is usually a self-limiting diarrheal disease requiring little or no medical intervention. However, in cases of invasive disease or infections with added complications, antimicrobial treatment may be required. Resistance to antimicrobials has been an increasing problem worldwide. Salmonella enterica from a variety of food and animal sources has been extensively characterized in terms of resistance phenotypes and numerous serotypes revealed multiple antimicrobial resistance determinants (strains resistant to two or more antimicrobials). In Europe the ECDC (European Center of Disease Control) has been in charge of the international surveillance network for human gastrointestinal infections since 2007. In Portugal the INSA (Instituto Nacional de Saúde Dr Ricardo Jorge) was the designated reference laboratory to report the epidemiological data, and though an effort was made still the actual data is not available or clearly reported. In this study 216 clinical Salmonella isolates, from Hospital de São João in Oporto (HSJ) and Hospital de São Marcos in Braga (HSM) both from the Northern region of Portugal, were tested for antimicrobial resistance and by PFGE analysis, as implemented by the CDC in the USA. The sample contained Salmonella Enteritidis, Salmonella Typhimurium and Salmonella spp. The antimicrobial susceptibility analysis to a panel of antimicrobials has confirmed European tendencies, low resistance in S. Enteritidis isolates except for nalidixic acid, and high resistance in S. Typhimurium isolates to most of the tested antimicrobials. Some of the S. Typhimurium isolates tested in this study were also tested in previous works in the lab for sulphonamides resistance and proved to have the typical DT104 resistance profile (ACSSuT). The PFGE analysis allowed the differentiation of Enteritidis and Typhimurium isolates as well as the identification of the serotype for most isolated identified has Salmonella spp. One Salmonella spp. Isolate didn’t belong to any of the two serotypes. The samples from the two hospitals showed high similarity between themselves. The discrimination of Enteritidis isolates was insufficient using XbaI enzyme leading to the conclusion that it would benefit with the analysis using a different panel of enzymes. Typhimurium isolates were well discriminated with PFGE though no correlation was possible with the resistance profile or the isolates available information.

Date of Award	2012
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Paula Teixeira (Supervisor) & Joana Silva (Co-Supervisor)