EPIDEMIOLOGY, ECOLOGY, AND MOLECULAR GENETICS OF ANTIMICROBIAL RESISTANCE IN PATHOGENIC AND COMMENSAL BACTERIA FROM FOOD ANIMALS
Location: Bacterial Epidemiology and Antimicrobial Resistance
Title: Susceptibility of Listeria monocytogenes, L. innocua, and L. welshimeri Isolated from Various Sources to Antibiotics
Submitted to: Interscience Conference on Antimicrobial Agents & Chemotherapy Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: June 29, 2007
Publication Date: September 17, 2007
Citation: Davis, J.A., Jackson, C.R., Bailey, J.S., Berrang, M.E., Frye, J.G., Englen, M.D., Meinersmann, R.J., Cray, P.J. 2007. Susceptibility of Listeria monocytogenes, L. innocua, and L. welshimeri Isolated from Various Sources to Antibiotics [abstract]. Interscience Conference on Antimicrobial Agents & Chemotherapy Proceedings. 225 p.124 E-2085.
Background: Listeriosis is a leading cause of death from foodborne illnesses in the United States. Emergence of antimicrobial resistant strains of Listeria monocytogenes could cause major public health concerns. Few studies have examined antimicrobial susceptibility of L. monocytogenes isolated from various sources. The current study determined antimicrobial susceptibility of three Listeria species isolated from manure, food, and humans.
Methods: From December, 2006 to March, 2007, three species of Listeria from various sources were obtained. L. innocua and L. welshimeri were isolated from swine and dairy manure, respectively, using standard protocols. L. monocytogenes isolated from humans and foods (e.g. dairy, meat and produce) were donated. Antimicrobial susceptibility testing was performed using Sensititre® MIC plates containing 18 antimicrobials. Resistant isolates were analyzed for the presence of antimicrobial resistance genes (tetM, penA, aadA, strA and strB) using PCR.
Results: A total of 57 L. monocytogenes, four L. innocua and six L. welshimeri were tested. The majority of L. monocytogenes isolates were resistant to oxacillin (98%, 57/58) and ceftriaxone (84%, 48/57) while few L. monocytogenes isolates were resistant to clindamycin (16%, 9/57) and ciprofloxacin (2%, 1/57). All L. welshimeri isolates were resistant to streptomycin, quinupristin/dalfopristin, ciprofloxacin, rifampin, oxacillin, penicillin G and clindamycin. Most L. welshimeri isolates were resistant to trimethoprim/sulfamethoxazole (67%, 4/6). All L. innocua isolates were resistant to oxacillin and penicillin G and 75% of the L. innocua isolates were resistant to tetracycline,ceftriaxone or clindamycin. Among streptomycin resistant L. welshimeri, aadA, strA and strB were not detected. However, tetM was detected among tetracycline resistant L. innocua.
Conclusions: The results show that L. welshimeri had the broadest range of resistance and resistance to tetracycline in L. innocua was due to the presence of tetM. Increased antimicrobial resistance in L. monocytogenes may occur from the transfer of resistance genes from other Listeria species.