چكيده فارسي :
Human listeriosis caused by Listeria monocytogenes is a sporadic disease with a mortality rate of approximately 20%. It has been considered that nearly all cases of human listeriosis are foodborne and associated with consumption of contaminated dairy products, unwashed raw vegetables, and under-cooked meat, seafood, and poultry products. The susceptible groups to listeriosis are pregnant women and their unborn children, neonates, immunocompromised individuals and the elderly (Painter Slutsker, 2007; Todd Notermans, 2011). Antibiotic resistance particularly multi-resistance of the pathogenic microorganisms is considered a hazardous worldwide problem for public health in recent decades (Capita Alonso-Calleja, 2013). Improper or increased application of antibiotics in human and veterinary medicine lead to dissemination of drug-resistant microorganisms, which is a great hazard to public health due to transmission of resistant strains to humans via the food chain (Perreten, 2005). Therefore, regular monitoring of multi-drug resistance in microorganisms isolated from environment and food products is necessary in order to understand the patterns of resistance to antibiotics; and plan the strategies for prevention of their environmental spread. This study aimed to determine the antibiotic resistance patterns of L. monocytogenes isolated from poultry and seafood products in central part of Iran.Materials and Methods The different serotypes of L. monocytogenes isolated from poultry products (49 strains) and seafood products (68 strains) were used. Susceptibility to different antibiotics was determined for all the isolates by a disc-diffusion method according to the guidelines of the Clinical and Laboratory Standards Institute (CLSI, 2006). The following antibiotic discs were used: ampicillin (10 µg), tetetracyclin (30 µg), erythromycin (15 µg), ciprofloxacin (5 µg), enrofloxacin (5 µg), clindamycin (2 µg), penicillin (10 U/IE), chloramphenicol (30 µg), gentamycin (10 µg), vancomycin (30 µg), trimethoprim/sulfamethoxazole (1.25/23.75 µg), and rifampin (5 µg). Each strain of L. monocytogenes was streaked on Mueller-Hinton agar(Merck, Darmstadt, Germany) plates supplemented with 5% defibrinated horse blood; and the discs were placed on the surface of each plate (5 antibiotic discs per each plate). After incubation at 35 ºC for 24 h, the diameter of growth inhibition zone around each disc was measured. The results were interpreted according to the criteria provided by CLSI (2007). Results and conclusionIn the present study, a total of 49 and 68 strains of L. monocytogenes isolated from poultry and seafood products, respectively, were examined for susceptibility to 12 different antibiotics by the disc diffusion method. It was found that 7 (14.2%) isolates of L.monocytogenes from poultry products and 10 (14.7%) from seafood products were susceptible to all used antibiotics. The other strains were found to have resistance against 1 (40.3%), 2 (18.4%), 3 (12.2%), 4 (4.31%), and 5 (3.24%) different antibiotics.The results of this study indicate a high resistance of L. monocytogenes to ampicillin and penicillin (Tables 1 and 2), the first-choice antibiotics used alone or in combination with gentamycin for treatment of human listeriosis. Rodas-Suárez et al. (2006) reported a high resistance of L. monocytogenes strains isolated from food products to ampicillin and penicillin, whereas the other researchers (Chen et al., 2010; Davis Jackson, 2009; Filiousis et al., 2009) found the susceptibility of L. monocytogenes to these antibiotics. A combination of trimethoprim and sulfamethoxazole is generally used for treatment of listeriosis in patients having allergy to penicillin. Erythromycin is another choice to treat the pregnant women infected with L. monocytogenes (Alonso-Hernando et al., 2012). In this study, the high sensitivity of L. monocytogenes to gentamycin, trimethoprim/sulfamethoxazole, and erythromycin is in agreement with the reports of filiousis et al. (2009), Davis and Jackson (2009), Altuntas et al. (2012), and Chen et al. (2010).Vancomycin is one of the last therapeutic options for the treatment of human listeriosis (Alonso-Hernando et al., 2012). The high rate of resistance to vancomycin observed in the seafood products (Table 2) could be considered as a major medical concern. The resistance to tetracycline, enrofloxacin, and ciprofloxacin might be due to the frequent use of tetracycline as a growth supplement, and fluoroquinolones as therapeutic agents in Iranian poultry and fish farms. In conclusion, the resistance of L. monocytogenes isolates to commonly used antibiotics could be a major public health and medical concern. Emergence of the multi-drug resistant strains indicates that L. monocytogenes is gradually becoming resistant to antibiotics. Therefore, the use of antibiotics for therapeutic purposes should be monitored and controlled to reduce the hazard of drug-resistant bacteria. ReferencesAlonso-Hernando, A., Prieto, M., García-Fernández, C., Alonso-Calleja, C., Capita, R. (2012). Increase over time in the prevalence of multiple antibiotic resistance among isolates of Listeria monocytogenes from poultry in Spain. Food Control, 23, 37–41.Altuntas, E. G., Kocan, D., Cosansu, S., Ayhan, K., Juneja, V. K., Materon, L. (2012). Antibiotic and bacteriocin sensitivity of Listeria monocytogenes strains isolated from different foods. Food and Nutrition Sciences, 3, 363–368.Capita, R. Alonso-Calleja, C. (2013). Antibiotic-resistant bacteria: A challenge for the food industry. Critical Reviews in Food Science and Nutrition, 53, 11–48.Chen, B. Y., Pyla, R., Kim, T. J., Silva, J. L., Jung, Y. S. (2010). Antibiotic resistance in Listeria species isolated from catfish fillets and processing environment. Letters in Applied Microbiology, 50, 626–632.Clinical and Laboratory Standards Institute (CLSI). (2007). DiskDiffusion Supplemental Tables. Document M100-S17. CLSI, Wayne, PA. Davis, J. A., Jackson, C. R. (2009). Comparative antimicrobial susceptibility of Listeria monocytogenes, L. innocua, and L. welshimeri. Microbial Drug Resistance, 15, 27–32.
