A Six-Year Investigation of the Emergence and Spread of Human Multidrug-Resistant Salmonella enterica Serovar Enteritidis in Tunisia.

The study aimed to examine the link between genetic antibiotic resistance and the prevalence of multidrug-resistant Salmonella Enteritidis in Tunisia over six years (2014-2019). About 617 clinical samples (including stools, biopsies, abscesses, and urine) were collected and analyzed using serotyping (slide agglutination method), antimicrobial susceptibility testing (disk diffusion method), and molecular techniques (PCR) for detecting antibiotic resistance genes. A total of 231 Salmonella isolates were obtained, of which serotype Enteritidis accounted for 72.3% (167/231). The majority were obtained from stool samples (70.66%, 118/167). About 59% (68/116) of the isolates were identified as multidrug-resistant, defined as exhibiting resistance to at least one agent in three or more antimicrobial classes. The antimicrobial susceptibility analysis demonstrated resistance rates of 46% for nalidixic acid (106/231), 45.5% for ofloxacin (105/231), 45% for ciprofloxacin (104/231), 43.72% for ampicillin (101/231), 43% for amoxicillin (99/231), and 43.3% for ticarcillin (100/231), highlighting a significant resistance to penicillin and fluoroquinolone classes of antibiotics. Less resistance detected to sulfonamide 16% (37/231), trimethoprim-sulfamethoxazole 8.7% (20/231), and chloramphenicol 1.73% (4/231). The most frequent genetic association was between fluoroquinolone and β-lactam resistance genes (91/116, 78.45%). The most common resistance genes that showed consistent patterns were bla (84%, 98/116), bla (84%, 98/116), bla (80.2%, 93/116), qnrA (80.2%, 93/116), qepA (80.2%, 93/116), oqxA (68.1%, 79/116), qnrB (43.1%, 50/116), qnrS (43.1%, 50/116) and aac(6')-Ib-cr (43.1%, 50/116). In contrast, bla (32%, 37/116) and bla (38.8%, 45/116) showed clear temporal fluctuations in certain years. This study provides a comprehensive overview of multidrug-resistant Salmonella Enteritidis in Tunisia and emphasizes the need for ongoing human infection surveillance.