Common bacteria that causes foodborne diseases are resistant to antibiotics, according to research that identified 39 genes responsible for this resistance. Brazil's Ministry of Health received reports of 11,524 outbreaks of foodborne diseases between 2000 and 2015, with 219,909 individuals falling sick and 167 dying from the diseases in question.

Bacteria caused most outbreaks of such illnesses, including diarrhea and gastroenteritis. The most frequent were Salmonella spp., With 31,700 cases diagnosed in the period (14.4% of the total), Staphylococcus aureus (7.4%), and Escherichia coli (6.1%).

According to a survey by the Ministry of Social Development, bacteria of the genus Salmonella were the etiological agents in 42.5% of the laboratory-confirmed foodborne disease outbreaks reported in Brazil between 1999 and 2009.

Whole-genome sequencing of the main bacterium that causes acute diarrhea is the research focus for a group at the University of São Paulo led by Juliana Pfrimer Falcão, a professor at the university's Ribeirão Preto School of Pharmaceutical Sciences (FCFRP-USP).

In an article published in  PLOS ONE, biomedical scientists Amanda Aparecida Seribelli and Fernanda Almeida, who belongs to Falcão's lab, describe how they sequenced and investigated the genomes of 90 strains of a specific serovar of  Salmonella enterica known as  S. Typhimurium  (an abbreviation of  Salmonella enterica subspecies serovar Typhimurium).

When the action of antibiotics in each of the 90 strains was tested, it was discovered that the vast majority were resistant to different classes of antibiotics that are part of the arsenal of medicine. The study also identified 39 genes responsible for resistance to antibiotics.

Researchers affiliated with Fiocruz, São Paulo State University's School of Agrarian and Veterinary Sciences (FCAV-UNESP) and Adolfo Lutz Institute participated in the study. The 90 strains of  S. Typhimurium  were sequenced at the United States Food and Drug Administration (FDA) during Almeida's doctoral stay.

Salmonellosis

Salmonella comprises two species,  S. bongori  and S. enterica. The latter is the type species, with a large number of subspecies and serovars that cause more foodborne infections than any other species in Brazil and worldwide. The human and animal intestinal tract is the main natural reservoir for this pathogen, with poultry, pork and related food products served as major transmission vectors.

The six subspecies of  S. enterica are subdivided into 2,600 serovars. A serovar (short for serological variant) is a distinct variation within a species of bacterium or virus characterized by having the same number of specific surface antigens.

The most important subspecies of  S. enterica from the epidemiological standpoint is  S. enterica subspecies enterica, which causes the foodborne infection known as salmonellosis. The symptoms are diarrhea, fever, stomach cramps, and vomiting.

According to Almeida, all 90 strains analyzed in the study belonged to  S. Typhimurium. Another researcher at FCFRP-USP (also working at the university's Clinical, Toxicological and Bromatological Analysis Laboratory) is currently sequencing and analyzing samples containing the serovar  S. Enteritidis.

According to Almeida, the technique used was high-throughput genotyping with SNPs (pronounced "snips" and short for single-nucleotide polymorphisms), which enabled them to identify the genetic composition (genotype) of each strain by means of DNA sequencing. SNPs are the most common markers of genetic variation. The phylogenetic results separated the 90 strains of  S. Typhimurium into two groups, A and B.

Origin of resistance

The analysis of SNPs identified 39 genes for resistance to different classes of antimicrobial or antibiotic, such as aminoglycoside, tetracycline, sulfonamide, trimethoprim, beta-lactam, fluoroquinolone, phenicol and macrolide. Point mutations were also found in some of the genes, such as gyrA, gyrB, parC and parE.

S. Enteritidis has been known since the 1950s, but for a time, it caused fewer cases of the disease. This was radically changed by the  S. Enteritidis pandemic, which began in the late 1980s and early 1990s in Europe and then spread around the world.

"The key finding of this research is the discovery of a large number of resistance genes in the samples, considering that they were isolated from humans and food. are resistant to antimicrobials, "Almeida said.