Tamilselvam Batcha - Prevalence of antimicrobial resistance genes in Listeria monocytogenes isolated from dairy farms

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      Foodborne Pathog Dis. 2005   Fall;2(3):201-11.


      ms to 15 antimicrobial agents was evaluated. All 38 L.   monocytogenes isolates from the four farms evaluated were   resistant to more than one antimicrobial in different   combinations. All L. monocytogenes isolates evaluated were   resistant to cephalosporin C (minimum inhibitory concentration   [MIC] > or = 512 microg/mL), streptomycin (MIC > or = 32)   and trimethoprim (MIC > or = 512). Most L. monocytogenes   isolates were resistant to ampicillin (92%, MIC > or = 2),   rifampicin (84%, MIC > or = 4), rifamycin (84%, MIC > or =   4), and florfenicol (66%, MIC > or = 32) and some were   resistant to tetracycline (45%, MIC > or = 16), penicillin G   (40%, MIC > or = 2) and chloramphenicol (32%, MIC > or =   32). All L. monocytogenes isolates were susceptible to   amoxicillin, erythromycin, gentamicin, kanamycin and vancomycin.   Susceptibility of L. monocytogenes to the antimicrobials   evaluated was quite consistent among the dairy farms evaluated.   However, some variability in antimicrobial susceptibility among   dairy farms was noted. Nineteen of 38 L. monocytogenes isolates   contained more than one antimicrobial resistance gene sequence. A   high frequency of floR (66%) was found in L. monocytogenes   followed by penA (37%), strA (34%), tetA (32%), and sulI (16%).   Other tetracycline resistance genes (tetB, tetC, tetD, tetE, and   tetG) and other antimicrobial resistance genes (cmlA, strB, aadA,   sulI, vanA, vanB, ampC, ermB, ereA, and ereB) were not found in   any of the L. monocytogenes isolates from the four dairy farms.   Results of the present study demonstrated that L. monocytogenes   isolated from the dairy farm environment were resistant to many   antimicrobials and contained one or more antimicrobial resistance   genes.

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