Salmonella Heidelberg is frequently found in poultry and poultry products and is associated with antimicrobial resistance strains and infections and mortality in humans. Whole-genome sequencing is used to monitor and understand epidemiological factors related to antimicrobial resistance. This study aimed to characterize the phenotypic resistance and sequence the whole genome of Salmonella Heidelberg strains isolated from poultry products in Brazil. Fourteen Salmonella Heidelberg strains isolated from whole broiler chicken carcasses and portions in Brazil between 2013 and 2019 were used in this study. Genus confirmation was performed by polymerase chain reaction. The disk diffusion test was conducted to assess the phenotypical antimicrobial susceptibility of the strains. Whole-genome sequencing was carried out to investigate the presence of antimicrobial resistance genes, plasmids, multilocus sequence typing, and virulence-associated genes. A high frequency of phenotypic resistance to cephalosporins, tetracyclines, and sulfonamides was detected. All strains had mutations in gyrA and parC and contained the genes tet(A), fosA7, and sul. The presence of genes originating from Yersinia pathogenicity islands was also detected. This study identified a high frequency of antimicrobial resistance in Salmonella Heidelberg strains from broilers slaughtered in different regions of Brazil, all belonging to the same sequence type (ST15) and associated with multiple resistance and virulence genes. The presence of the Yersinia high-pathogenicity island was detected, indicating potential virulence. These findings highlight the importance of continuously monitoring antimicrobial resistance to control and prevent foodborne infections and maintain the efficacy of treatments for human salmonellosis.

Salmonella spp. is one of the major bacterial causes of foodborne gastroenteritis in humans. The aim of this study was to investigate antimicrobial susceptibility to cephalosporins and quinolones, and to identify the genetic mechanisms related to this resistance in strains of Salmonella spp. Seventy chicken carcass samples were collected from slaughterhouses in the state of Rio de Janeiro, Brazil. The phenotypic profile was detected by the disk-diffusion method and the search for genes encoding betalactamases, and resistance to quinolones was evaluated by PCR. The search for mutations in gyrA and parC was carried out by sequencing these genes. Eleven strains of Salmonella spp. of different serotypes were isolated. All the strains were resistant to at least one of the antimicrobials tested, and 63.64% (7/11) showed resistance to three or more antimicrobials. In the phenotypic test for ESBL production, 36.36% (4/11) of the strains were considered positive. PCR detected the resistance genes bla _CMY-2, qnrB, bla _CTX-M, and bla _TEM. Among the isolates, 45.45% (5/11) simultaneously presented the bla _CTX-M, bla _TEM, qnrB genes and a mutation (Thr-57→Ser) in parC. Point mutations in the parC gene were detected in all the analyzed samples. Genes such as bla _SHV, qnrA, qnrC, qnrD, qnrS, aac(6’)-Ib, qepA, and oqxAB were not detected. The study identified Salmonella spp. resistant to cephalosporins and quinolones, with resistance genes and mutations in parC, highlighting concerns about the adoption of biosecurity measures, responsible use of antimicrobials, and surveillance of resistant strains in the poultry chain.

1. This study evaluated the minimal inhibitory concentration (MIC) of ciprofloxacin and the presence of plasmid-mediated quinolone resistance (PMQR) mechanisms in 97 nontyphoidal Salmonella spp. isolated from broilers and carcasses from three different regions in Brazil. The presence of mutations in quinolone resistance determination regions (QRDRS) was investigated in the ciprofloxacin-resistant strain by DNA sequencing. 2. Most of the Salmonella spp. (85.6%) had intermediate resistance to ciprofloxacin and only one isolate was resistant. MIC breakpoints ranged from ≤0.03 to 1 µg/ml and 67.01% of the strains had a MIC of 0.25 µg/ml (n=65). Thirteen strains (13.40%) were susceptible to ciprofloxacin with MIC ≤0.06 µg/ml. The qnrB gene was detected in eight isolates with intermediate resistance and in two susceptible strains. The other PMQR genes, qnrA, qnrC, qnrD, qnrS, qnrVC, aac(6′)-Ib, qepA, oqxAB and mutations in QRDR were not detected in any strain. 3. There was a high frequency of ciprofloxacin intermediate resistant Salmonella from broiler and broiler carcasses from Brazil. The presence of these strains in poultry and derived products poses a risk to public health.

Antimicrobial resistance (AMR) is a pressing global public health issue, driven by the widespread use of antibiotics in both human and veterinary medicine. Tetracyclines, widely used in livestock for growth promotion and disease treatment, have contributed significantly to the emergence of resistant bacterial strains. This study aimed to evaluate the tetracycline resistance profiles of Salmonella spp. and Escherichia coli isolates from the poultry supply chain in Brazil, and identify the primary tetracycline resistance genes involved. A total of 97 Salmonella strains and 195 E. coli strains were analyzed for tetracycline resistance using the disc diffusion method and PCR to detect resistance genes (tetA, tetB, tetC, tetD, tetE, and tetG). The results revealed high tetracycline resistance rates, with 88.66% of Salmonella strains carrying the tetA gene, 4.12% harboring tetB and 1.03% carrying tetD. Among E. coli isolates, 64.62% carried tetA, 65.13% carried tetB, and 43.59% exhibited both genes. The tetE gene was detected in 1.03% of E. coli strains. These findings highlight the widespread presence of tetracycline resistance determinants in poultry-associated bacteria, underscoring the need for stricter antimicrobial use regulations and enhanced AMR monitoring in animal production systems to mitigate public health risks.

Enteropatogenic Escherichia coli (EPEC) and shigatoxigenic E. coli (STEC), are generally poultry and poultry product isolate and can cause serious human infections. Many strains may become resistant to various antimicrobials, which can hinder the treatment of bacterial diseases. Organic farming seeks to avoid the selection and frequency of antimicrobial-resistant bacteria. This study aims to verify the resistance of EPEC and STEC from organic and conventional (industrial) broiler isolates to antimicrobials. All isolates were submitted to disk diffusion test with tetracycline, gentamicin, enrofloxacin, ceftriaxone and amoxicillin + clavulanate (TET, GEN, ENO, CTX, AMC) and PCR to detect specific virulence genes for EPEC and STEC. A total of 297 E. coli strains were isolated, 213 from conventional. In organic broiler, 84 strains were isolated. The strains from the conventional broiler isolates were resistant to five antimicrobials tested: TET 48.82% (104/213), ENO 28.17% (60/213), CTX 15.49% (33/213), GEN 14.55% (31/213), and AMC 7.04% (15/213), and 9.86% (21/213) were considered multidrug-resistant. Organic chicken strains were resistant to four of the antimicrobials tested: TET 35.7% (30/84), ENO 9.5% (8/84), CTX 2.4% (2/84), GEN 4.8% (4/84). Of the strains from the organic broiler chicken isolates, only 1.2% (1/84) was considered multidrug-resistant. No EPEC and STEC were found in the organic chicken samples. The multidrug resistance was characterized in 9.52% (2/21) of the EPEC and 4.76% (1/21) of the STEC. The study demonstrated the absence of EPEC and STEC strains in organic broilers and carcasses and a lower frequency of multiresistant strains compared to conventional breeding.

Broiler chickens and derived products are a key source of Shiga toxin-producing Escherichia coli (STEC) in humans. This pathotype is responsible for causing severe episodes of diarrhea, which can progress to systemic complications. A rapid and accurate diagnosis of the disease, and early treatment of the infection with antimicrobials, can prevent it worsening. However, multidrug-resistant strains have potentially negative implications for treatment success. In this context, the aim of the present study was to isolate and identify multidrug-resistant STEC strains from broiler chickens and carcasses. Of 171 E. coli strains, isolated by conventional microbiological techniques and submitted to Polymerase Chain Reaction (PCR), for detection of stx1 and stx2 genes, 21.05% (36/171) were STEC pathotype, and most of them (66.67% - 24/36) carried both stx1 and eae genes. The multidrug resistance pattern was observed in 75% (27/36) of STEC strains. The presence of STEC in broiler chickens and carcasses reinforces that these sources may act as reservoirs for this pathotype. Multidrug-resistant bacteria contaminating animal products represent a public health issue because of the possibility of spread of multidrug-resistant determinants in the food chain and a higher risk of failure in human treatment when antimicrobials are needed.