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Tips from the journals of the American Society for Microbiology

American Society for Microbiology

Salt and Organic Acids May Increase Pathogen Virulence

Salt and organic acids may increase the virulence of Listeria monocytogenes, one of the most harmful food-borne pathogens plaguing the U.S. today, say researchers from New York. They report their findings in the August 2006 issue of the journal Applied and Environmental Microbiology.

L. monocytogenes is attributed to 28% of all deaths in the U.S. related to food-borne illnesses. Foods considered to be at greatest risk for transmission are ready-to-eat products (RTE), with RTE meat products being the single most common cause of human infection. Researchers believe L. monocytogenes can grow in refrigerated temperatures and in the presence of organic acids and salt, indicating that exposure to certain environmental stress conditions may in fact enhance the organism's survival and induce expression of virulence genes.

In the study researchers measured the effects of temperature (7 or 37 degrees Celsius), pH (5.5 or 7.4), and the presence of salt and organic acids on the ability of L. monocytogenes to grow, invade cells, and survive exposure to synthetic gastric fluid. Results showed that the ability of L. monocytogenes to invade cells is affected by all elements with highest invasion occurring at 37 degrees Celsius and a pH level of 7.4. Although salt and organic acids appear to increase virulence during cell invasion, they alternately reduce the bacterium's ability to survive exposure to gastric fluid.

"Our results suggest that environmental stress conditions from specific foods may influence the L. monocytogenes infectious dose and thereby contribute to the association of food-borne infections with specific foods," say the researchers.

(M.R. Garner, K.E. James, M.C. Callahan, M. Wiedmann, K.J. Boor. 2006. Exposure to salt and organic acids increases the ability of Listeria monocytogenes to invade Caco-2 but decreases its ability to survive gastric distress. Applied and Environmental Microbiology, 72. 8: 5384-5395.)

New Vaccine Protects Pigs from Nipah Virus

Researchers from the U.S. and abroad suggest for the first time that a canarypox virus-based vaccine protects pigs from Nipah virus infection. Their findings appear in the August 2006 issue of the Journal of Virology.

Nipah virus (NiV) was isolated and identified in Malaysia in 1999 following an outbreak of human encephalitis believed to be transmitted from pigs to humans. Research indicates that the virus may have emerged as early at 1996 or 1997 but due to nonspecific clinical signs and low mortality it went undetected. Due to its undetermined route of transmission to humans, high virulence, and lack of vaccine or treatment, the virus is also currently classified as a biosafety level 4 agent.

In the study pigs were vaccinated with a canaryppox-virus based vaccine containing the NiV gene and then boosted after 14 days. Two weeks later they were challenged with the Nipah virus and results showed that all vaccinated animals appeared to be protected, the virus was not found in the tissue of any of the immunized pigs. In contrast, the virus was identified in challenge control pigs.

"The present study indicates that the tested recombinant canarypox (ALVAC-vectored) NiV vaccine candidates have the potential to protect pigs from disease and to restrict virus replication and nasal and pharyngeal shedding, thereby strictly limiting the chance for spread of the virus to uninfected animals/individuals," say the researchers.

(H.M. Weingartl, Y. Berhane, J.L. Caswell, S. Loosmore, J.C. Audonnet, J.A. Roth, M. Czub. 2006. Recombinant Nipah virus vaccines protect pigs against challenge. Journal of Viroloy, 80. 16: 7929-7938.)

FluChip May Offer Rapid Detection of Multiple Influenza Virus Strains

U.S. researchers have developed a new diagnostic method capable of rapid identification of influenza A and B subtypes that may ultimately reduce the impact of a potential influenza pandemic. They report their finding in the August 2006 issue of the Journal of Clinical Microbiology.

Annual influenza outbreaks, and the threat of a pandemic as new strains continue to emerge and mutate, are of great worldwide concern. An estimated 36,000 people die from influenza-related illnesses each year in the United States alone and increased awareness has prompted international efforts in developing effective monitoring and preparedness measures. To date, the most reliable method for identifying influenza virus strains takes 3 to 7 days and can only test a few samples simultaneously.

In this blind study researchers used the FluChip-55 microarray to test 72 influenza virus isolates for A and B subtypes including H1N1, H3N2, as well as avian A/H5N1 which has become enzootic in poultry in certain parts of the world. In less than twelve hours combined results provided correct types and subtypes for approximately 72% of the isolates and the correct type and partially correct subtype for 13% of the isolates. Incomplete subtyping in most cases was attributed to failure relating to nucleic acid amplification as opposed to testing limitations.

"By using the FluChip-55 microarray in conjunction with a well-established RNA amplification method, RNA from viruses of interest, including influenza viruses A/H1N1, A/H3N2, and A/H5N1 and influenza B virus, was typed and subtyped in 11 hours," say the researchers. "The ability to rapidly identify new, potentially pandemic strains of influenza virus will allow health care officials to more rapidly respond and, potentially, reduce the spread and human impact of the disease."

(M.B. Townsend, E.D. Dawson, M. Mehlmann, J.A. Smagala, D.M. Dankbar, C.L. Moore, C.B. Smith, N.J. Cox, R.D. Kuchta, K.L. Rowlen. 2006. Experimental evaluation of the FluChip diagnostic microarray for influenza virus surveillance. Journal of Clinical Microbiology, 44. 8: 2863-2871.)


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