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News From The Journals Of The American Society For Microbiology

August 04th, 2010

Organic and Natural Beef Cattle Production Systems Offer No Major Difference in Antibiotic Susceptibility of E. coli

A new study suggests that when compared to conventionally raised beef cattle, organic and natural production systems do not impact antibiotic susceptibility of Escherichia coli O157:H7. This discovery emphasizes that although popular for their suggested health benefit, little is actually known about the effects of organic and natural beef production on food-borne pathogens. The researchers from Kansas State University detail their findings in the August 2009 issue of the journal Applied and Environmental Microbiology.

Increased outbreaks of foodborne illness, as well as the growing awareness and popularity of organic and natural foods, have forced many cattle farmers to adopt new production methods to meet consumer demand for safe and healthy beef. Organic food sources receive only certified organic feed, are raised without the use of antibiotics, hormones, and other veterinary products, and are regulated by the U.S. Department of Agriculture. Natural production guidelines completely restrict the use of antibiotics and hormones, but do allow nonorganic food sources and are only regulated by the brand name owner.

Cattle are major reservoirs of E. coli O157:H7 and their feces are the main source of food and water contamination that lead to foodborne illness in humans. In the study fecal samples were collected from organically and naturally raised cattle and tested for the presence of E. coli O157:H7. Results showed prevalence rates of 14.8 % in organically raised and 14.2 % in naturally raised cattle. These E. coli O157:H7 levels were comparable to those previously identified in conventionally raised cattle. Additionally, the minimum inhibitory concentration of a variety of antibiotics for E. coli O157:H7 isolates were analyzed to determine the effects of all three production systems and no significant difference in antibiotic susceptibility was noted.

“The prevalences of E. coli O157:H7 that we observed in organically and naturally raised beef cattle were similar to the previously reported prevalence in conventionally raised cattle,” say the researchers. “No major difference in antibiotic susceptibility patterns among the isolates were observed.”

(S. Reinstein, J.T. Fox, X. Shi, M.J. Alam, D.G. Renter, T.G. Nagaraja. 2009. Prevalence of Escherichia coli O157:H7 in organically and naturally raised beef cattle. Applied and Environmental Microbiology, 75. 16: 5421-5423.)

New Study Finds Wild Pikas Are Natural Mammalian Hosts to H5N1 Avian Influenza Virus

For the first time a new study suggests that when exposed in their natural ecosystem, wild pikas (a species closely related to rabbits) are mammalian hosts of H5N1 subtype avian influenza viruses and may also be a source of transmission to domestic mammals and humans. The researchers from China report their findings in the September 2009 issue of the Journal of Virology.

Wild birds are the known natural reservoirs for the H5N1 subtype avian influenza virus, however, researchers are unsure of their role in the spread of the virus to other free-ranging wild mammals within their natural habitats. Highly pathogenic H5N1 avian influenza viruses are now endemic in bird populations throughout Southeast Asia and 391 human cases, of which 60% were fatal, have been reported since 2003. Although human-to-human transmission has yet to occur, H5N1 viruses pose a serious public heath threat.

In the study researchers traced the circulation of the H5N1 virus in wild pikas and confirmed a natural H5N1 virus infection in their native environment. Genetic testing of the H5N1 virus isolated in pikas revealed two distinct evolutionary groups, a mixed/Vietnam H5N1 virus sublineage (MV-like pika virus) and a wild bird Qinghai-like H5N1 sublineage (QH-like pika virus). Further analysis of the MV-like pika virus found it to be the same as goose H5N1 virus. When tested in mice the MV-like pika virus was nonpathogenic, however, the QH-like pika virus was highly pathogenic in mice. Finally, in an attempt to recreate the virus infection of pikas, rabbits were intranasally vaccinated with the H5N1 virus of pika origin resulting in infection.

“Our findings first demonstrate that wild pikas are mammalian hosts exposed to H5N1 subtype avian influenza viruses in the natural ecosystem and also imply a potential transmission of highly pathogenic avian influenza virus from wild mammals into domestic mammalian hosts and humans,” say the researchers.

(J. Zhou, W. Sun, J. Wang, J. Guo, W. Yin, N. Wu, L. Li, Y. Yan, M. Liao, Y. Huang, K. Luo, X. Jiang, H. Chen. 2009. Characterization of the H5N1 highly pathogenic avian influenza virus derived from wild pikas in China. Journal of Virology, 83. 17: 8957-8964.)

New Study Suggests an Unidentified Source as Cause of Residual Viremia in HIV-1 Patients on HAART

A new study suggests that an unidentified cellular source may be responsible for residual viremia in HIV-1 patients on highly active antiretroviral therapy (HAART). This discovery disputes previous theories that attributed residual viremia to latent proviruses in resting CD4+ T cells and could significantly impact eradication efforts. The researchers from The Johns Hopkins University School of Medicine, Baltimore, Maryland; The University of Texas, Austin; and the Howard Hughes Medical Institute, Baltimore, Maryland report their findings in the September 2009 issue of the Journal of Virology.

When successful, HAART can reduce HIV-1 levels in the blood to undetectable amounts, however, HIV-1 still persists as latent proviruses in resting CD4+ T cells, also known as residual viremia. Current eradication strategies have focused on these latent T cell reservoirs, however, treatment failure has prompted researchers to examine other cellular reservoirs as potential sources of residual viremia.

Using two different methods, researchers analyzed viral sequences from individual patients to determine whether residual viremia was stemming from a source other than latent resting CD4+ T cells. Results showed residual viremia to be genetically distinct from proviruses in activated CD4+ T cells.

“The finding that some of the residual viremia in patients on HAART stems from an unidentified cellular source other than CD4+ T cells has implications for eradication efforts,” say the researchers.

(T.P. Brennan, J.O. Woods, A.R. Sedaghat, J.D. Siliciano, R.F. Siliciano, C.O. Wilke. 2009. Analysis of human immunodeficiency virus type 1 viremia and provirus in resting CD4+ T cells reveals a novel source of residual viremia in patients on antiretroviral therapy. Journal of Virology, 83. 17: 8470-8481.)

Source:
Carrie Slijepcevic

American Society for Microbiology
The research was supported by the Australian Stem Cell Centre, the Juvenile Diabetes Research Foundation and the National Health and Medical Research Foundation.

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