The antimicrobial susceptibility of 73 Salmonella Typhimurium and mST strains was determined by broth microdilution method according to Clinical and Laboratory Standard Institute guidelines (CLSI, 2019) against 12 antimicrobials: amoxicillin, ampicillin, cephalothin, cefotaxime, imipenem, nalidixic acid, ciprofloxacin, chloramphenicol, erythromycin, gentamicin, streptomycin, trimethoprim/sulfamethoxazole, and tetracycline. The strains were obtained between 2010-2018 at slaughterhouses from the food-chain of pigs reared in extensive systems in the South of Spain. Minimum Inhibitory Concentration (MIC), MIC50 and MIC90 of every antimicrobial were defined. All the strains were classified as susceptible, intermediate, or resistant using the breakpoints available for this microorganism (CLSI, 2019). The antimicrobials streptomycin, tetracycline, trimethoprim-sulfamethoxazole, ampicillin, erythromycin, and chloramphenicol showed the highest MIC90 values (≥64 µg/ml). On the other hand, gentamicin, cefotaxime, imipenem, and ciprofloxacin showed the lowest ones (1-≤0.06 µg/ml). The 73 isolates were susceptible to gentamicin and imipenem, and a high percentage of them to nalidixic acid (98.63%), ciprofloxacin (97.26%) and cefotaxime (91.78%). Additionally, ampicillin, tetracycline, cephalothin, chloramphenicol and trimethoprim/sulfamethoxazole showed percentages of resistance over 78%. The 98.6% of the studied isolates were MDR. Four different resistotypes were detected, with CEP-TET-SXT-AMP-CHL being the most common one (56.9% of isolates) (resistance against cephalothin, tetracycline, trimethoprim/sulfamethoxazole, ampicillin, and chloramphenicol). For streptomycin and erythromycin there are no breakpoints available for Salmonella spp., so strains cannot be classified as susceptible or resistant to these antimicrobials. However, regarding the MIC distribution, it is observed that the isolates under study required the highest concentrations of streptomycin and erythromycin to see their growth inhibited. Gentamicin and imipenem could be selected for empirical treatment of swine salmonellosis, although other angents have shown good antimicrobial activity against this pathogen, such as nalidixic acid, ciprofloxacin, and cefotaxime. A high percentage of strains are resistant to cephalothin, which have been traditionally used for the treatment of infections caused by Salmonella spp. This fact demonstrates the importance of the appearance of antimicrobial resistance, which difficult treatments and makes useless those substances that, until now, were effective against the microorganism in question.
- Congreso: i3s salmonella and salmonellosis (20-22 June 2022, Saint Mall, France).
- Fecha: 20-22 de junio de 2022.
- Nombre: Rafael Jesús Astorga Márquez.
- Número de Colegiado: 1533
- Cargo: Catedrático. Departamento de Sanidad Animal. Facultad de Veterinaria. Universidad de Córdoba.
- Link (descarga): https://www.i3s2022.com