Identification of Salmonella sp. in stool samples for parasitological and biochemical tests: situation due to pre-analytical and analytical errors

The intestine is a complex organ of the gastrointestinal tract. It is rich in microorganisms that constitute its microbiota, which, is essential for the absorption and protection from
pathogens. The imbalance of the intestinal microbiota enables infection by pathogens such as Salmonella spp., a Gram-negative bacterium commonly not identified by clinical
laboratories. The absence of a diagnosis of this pathogen is primarily due to the request for tests to search for parasites without considering the importance of pathogenic bacteria; sometimes, the absence of parasites and the similarity in symptoms can lead to an incorrect diagnostic hypothesis of a viral disease. To confirm the above-mentioned
diagnostic deficiency, we carried out the bacterial analysis in stool samples sent to a clinical analysis laboratory in the interior of São Paulo (Presidente Prudente) to perform
Occult Blood Research (PSO) and Fecal Parasitological Examination (EPF). Approval by research ethics committees was waived as this was a clinical sample without access to patient identification data. Therefore, these samples were cultured on classical media: Salmonella and Shigella agar (SS), deoxycholate-lysine-xylose agar (XLD), MacConkey agar (MC), and enrichment with iodinated tetrathionate broth. Of the total of 80 samples analyzed, 61 showed bacterial growth of enterobacteria, and 2 showed growth of Salmonella sp. in SS and XLD media, with no agreement of positivity between cultures. This inconsistency of results can lead to laboratory errors and a lack of diagnosis of salmonellosis since SS and XLD are not used concomitantly for the same sample. Positive samples for Salmonella sp. are from women aged 48 and 59 already in menopause; the physiological hormonal change experienced during this period may be associated with changes in the enteric microbiota that would enable the proliferation of pathogens like Salmonella spp. and its infections. The absence of a request for a stool culture by the medical group is crucial for the correct laboratory test to be carried out in this and many other cases of bacterial infections. Consequently, the patient may experience severe consequences since the therapeutic choice of parasitosis and or a virus is completely different from a bacteriosis. Furthermore, the choice of culture medium can be crucial to identifying Salmonella spp. Parallel cultures performed in different media can help to increase the detection rate of this enteropathogen. Given the problems presented and the results obtained, we suggest that clinical and laboratory protocols be revised to improve the diagnosis and treatment of salmonellosis.