Laboratory procedures from which the data was obtained

All microbiological data were extracted directly from institutional reports. The institutional protocols used for isolation and identification of Salmonella spp. serovars are summarized below. Laboratory procedures were divided into two phases: isolation and subspecies identification. The consistency of the fecal samples was evaluated to determine the culture process. Liquid samples were seeded on culture media for Campylobacter spp., Vibrio cholerae, blood agar, MacConkey agar (MAC), hektoen enteric agar (HEA), and selenite agar and incubated at 37 °C. Non-liquid samples were seeded on blood agar, MAC agar, HEA agar and selenite agar. Salmonellosis was considered possible when growth was identified on blood agar, MAC agar and selenite agar. To confirm the diagnosis, a colony of selenite agar was used for subspecies identification.

Secretion samples (e.g., orotracheal secretion) were seeded on blood agar, MAC agar and Columbia Nalidixic Acid (CNA) agar. Colonies suggestive of Salmonella spp. were obtained from blood agar and MAC agar media for subspecies identification. Sterile fluid samples (e.g., cerebrospinal fluid, urine) were seeded on chocolate agar and PHI-enriched culture medium. Finally, the blood culture sample was incubated at 37 °C in automated BioMerieux equipment. Positive samples (growth alert) were evaluated by Gram staining and culture on blood agar and MAC agar.

Once the colony was obtained, the VITEK®MS automated equipment was used to identify the bacterial genus and species by mass spectrometry, which has reported a sensitivity of over 98% for genus and species identification in enterobacterial isolates [15]. Sometimes Salmonella spp. was identified without determining the subspecies, so it was proceeded to confirmation using VITEK®2, which has a sensitivity of 98.1% with a positive predictive value of 99.3% and a specificity of 99.7% with a negative predictive value of 99.3% [14], if the subspecies still not identified, it was used a third platform (MicroScan WalkAway plus system). When identification was not achieved with any of the three equipments, it was registered as Salmonella spp.

After confirmation of the species, an antibiogram was performed and resistance was determined according to the current cut-off points recommended by The Clinical & Laboratory Standards Institute (CLSI) [16]. In addition, the CARBA NP test (CNPt) or the rapidec test (bioMerieux), and the NG-test CARBA 5 were performed. CNPt, is a novel phenotypic method developed for carbapenemase detection based on in vitro hydrolysis of imipenem by a bacterial lysate, which is detected by changes in pH values [17]. While NG-test CARBA 5 a rapid in vitro multiplex immunoassay for the phenotypic detection and differentiation of five common carbapenemase families [18].