Tips from the Journals of the American Society for Microbiology

In the study researchers tested the virulence capacities of 184 human and animal S. enterica isolates in mice. Results showed that all 21 serovar typhimurium isolates derived from animals were virulent in mice, while only 16 of 41 serovar typhimurium isolates collected from human salmonellosis patients were virulent. In contrast to all animal and human bacteremia samples tested, only 10 of 29 serovar typhimurium isolates from gastroenteritis patients were virulent. Lastly, among the serovar typhimurium isolates harboring virulent Salmonella, 6 of 31 from human salmonellosis patients were avirulent in mice, in direct contrast to the virulence exhibited by all the animal isolates studied.

“These studies suggest that Salmonella isolates derived from human salmonellosis patients are distinct from those of animal origin,” say the researchers. “The characterization of these bacterial strain variants may provide insight into their relative pathogenicities as well as into the development of treatment and prophylactic strategies for salmonellosis.”

(D.M. Heithoff, W.R. Shimp, P.W. Lau, G.Badie, E.Y. Enioutina, R.A. Daynes, B.A. Byrne, J.K. House, M.J. Mahan. 2008. Human Salmonella clinical isolates distinct from those of animal origin. Applied and Environmental Microbiology, 74. 6: 1757-1766.)

New Study Compares Antibiotic Resistance in Wild American Bison and Farm Cattle

The first ever study of antibiotic-resistant bacteria in free-living American bison finds resistance rates, while relatively low, are still higher than expected. The researchers from Kansas State University report their findings in the March 2008 issue of the journal Applied and Environmental Microbiology.

Currently, over 50% of antibiotic use in the United States is attributed to the animal industry. As antibiotic resistance continues to rise researchers have extensively studied the link between humans and farm animals, however little is known about the spread of antibiotic resistance in wild animal populations.

Enterococci are one of the most common organisms associated with nosocomial infections worldwide and are also considered a reservoir for acquisition and distribution of antibiotic resistant genes. In the study enterococci isolates were collected from an American bison (Bison bison) population on a native tall-grass prairie preserve in Kansas. Bison showed resistance to tetracycline and erythromycin at rates of 8% and 4% which while higher than expected, still relatively low when compared to resistance rates of 42.9% and 12.7% in domestic cattle.

“This is the first study of antibiotic resistance in enterococci associated with American bison,” say the researchers. “The results provide us with an opportunity to gain insight into the origin of antibiotic resistance and the flow of genetic elements between environments.”

(J.F. Anderson, T.D. Parrish, M. Akhtar, L. Zurek, H. Hirt. 2008. Antibiotic resistance of enterococci in American bison (Bison bison) from a nature preserve compared to that of enterococci in pastured cattle. Applied and Environmental Microbiology, 74. 6: 1726-1730.)