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To analyze distribution of Listeria monocytogenes serotypes and antimicrobial susceptibility of Listeria isolates from a domestic swine processing facility.
Presumptive Listeria isolates (314) were molecularly identified to discriminate among L monocytogenes, Listeria ivanovii, and Listeria species. Listeria monocytogenes serotypes were identified by polymerase chain reaction (PCR) and PCR-restriction enzyme analysis (PCR-REA) and tested for antimicrobial susceptibility.
Isolates were identified as L monocytogenes (259; 82.5%), L ivanovii (2; 0.6%), and Listeria species (53; 16.9%). Distribution of L monocytogenes serotypes: 4a/4c (0.4%), 4b (11.2%), 4d/4e (14%), 4b/4d/4e (9.3%), 1/2a (26.3%), 3a (7.7%), 1/2a/3a (6.2%), 1/2b/3b (1.2%), 1/2c (5%), 3c (1.2%), and 1/2c/3c (5.4%). Thirty-two L monocytogenes isolates (12.4%) were not typeable by PCR-REA, suggesting the possibility of serotypes 4ab/7. Susceptibility was 84.2% to 100% for most antimicrobials. Major resistance (R) and intermediate (I) susceptibility were found for clindamycin (R = 36.7%, I = 39.8% for L monocytogenes; R = 100% for L ivanovii; and R = 14%, I = 86% for Listeria species). Drugs of choice for treatment of human listeriosis (penicillin, ampicillin, and trimethoprim-sulfamethoxazole) remained effective; 1.2% of L monocytogenes were β-lactam resistant. Multidrug resistance was found only in L monocytogenes (26.6%) and Listeria species (26.4%), with (clindamycinI or R -erythromycinR-azithromycinR) and (ciprofloxacinI-clindamycinI) the most frequent phenotypes.
Resistance to clindamycin and ciprofloxacin are shared between L monocytogenes and untyped Listeria. Although erythromycin is a drug of choice for prophylaxis in Colombian swine, resistance is low. No specific relationships between serotypes, sources, and antimicrobial susceptibility were found.
Gamboa-Marín A, Mejía-Wagner DC, Moreno-Ocampo PA, et al. Antimicrobial susceptibility of Listeria monocytogenes, Listeria ivanovii, and Listeria species isolated from swine processing facilities in Colombia. J Swine Health Prod. 2013;21(1):10–21.