Fighting bacteria with viruses
Researchers at the National Institutes of Health are using viruses to attack antibiotic-resistant bacteria. Working with scientists from Exponential Biotherapies in Pt. Washington, New York, they have successfully used bacteriophage therapy to treat mice experimentally infected with a fatal vancomycin-resistant infection. They report their results in the January 2002 issue of the journal Infection and Immunity.
Bacteriophage are viruses that can attack and kill bacteria, but they don't cause disease in humans. Researchers began exploring the potential of these viruses as antibacterial therapies in the early 20th century, but a combination of factors, not the least of which was the discovery of penicillin and the age of antibiotics, made that that interest short-lived. The rise of antibiotic resistance in the 1980s and 1990s has renewed scientific interest in the development of these alternative therapies.
In this study, the researchers experimentally infected mice with a strain of vancomycin-resistant enterococci (VRE) and injected treated them with bacteriophage at varying times after initial infection. Those mice that did not receive treatment died within 48 hours. All the mice that were treated within 5 hours of infection and half of those treated 24 hours after infection survived.
"The emergence of antibiotic-resistant bacterial strains requires the exploration of alterative antibacterial therapies," say the researchers. "In the present study we report the isolation of bacteriophage that are safe and effective as bactericidal agents for animals with lethal VRE infections. The results warrant a reexamination of the potential application of bacteriophages in Western medicine."
(B. Biswas, S. Adhya, P. Washart, B. Paul, A.N. Trstel, B. Powell, R. Carlton and C.R. Merril. 2002. Bacteriophage therapy resuces mice bacteremic from a clinical isolate of vancomycin-resistant Enterococcus faecium. Infection and Immunity, 70: 204-210.)
Lettuce plants internalize bacteria
Lettuce that has been fertiziled with manure or irrigated with water that is contaminated with E. coli O157:H7 can take the bacteria up through its root system and internalize it inside its leaves, resisting traditional external sanitizing methods. Researchers from Rutgers University report their findings in the January 2002 issue of the journal Applied and Environmental Microbiology.
"In recent years, E. coli O157:H7 has been isolated with increasing frequency from fresh produce, including bean sprouts, cantloupes, apples and leaf lettuce. The mechanisms by which the pathogen is introduced into the lettuce plant are not fully understood," say the researchers.
The researchers tested the hypotheses that the source of the contamination may be poorly treated manure (it is estimated that the pathogen is present in over 8 percent of dairy and beef cattle) or irrigation water that has been contaminated with cattle feces. The bacteria were isolated from plants grown using either medium, but interestingly, the researchers found bacteria in the inner tissues of the plants.
"We have demonstrated that lettuce grown in soil containing contaminated manure or irrigated with contaminated water results in contamination of the edible portion of the lettuce plant," say the researchers. "Moreover, the results suggest that edible portions of a plant can become contaminated without direct exposure to a pathogen but rather through transport of the pathogen into the plant by the root system. The inaccessibility of a large number of organisms, as a consequence of their subsurface location, is perhaps the reason for the lack of effectiveness of surface-sanitizing treatments."
(E.B. Solomon, S. Yaron, K.R. Matthews. 2002. Transmission of Escherichia coli O157:H7 from contaminated manure and irrigation water to lettuce plant tissue and its subsequent internalization. Applied and Environmental Microbiology, 68: 397-400.)
Wild ducks not a source of Cryptosporidium for humans
Over half of wild ducks on the lower Rio Grande River around Las Cruces, New Mexico are carriers of the waterborne parasites Cryptosporidium and Giardia, but the parasites are not of the species most commonly associated with human infection, say researchers from New Mexico State University. They report their findings in the January 2002 issue of the journal Applied and Environmental Microbiology.
Cryptosporidium parvum and Giardia lamblia are enteric parasites that can cause persistent diarrhea in humans, lasting anywhere from 1 to 3 weeks. The most common mode of transmission is consumption of contaminated water. Previous studies have identified wild Canadian geese as one source of contamination.
"The purpose of this study was to determine to what extent Cryptosporidium and Giardia could be isolated from wild ducks," say the researchers. "Because of the large number of ducks and the diversity of their habitats, it is possible that if ducks do vector Cryptosporidium and Giardia at levels demonstrated in geese, they may have a significant microbiological impact on water quality and in turn on public safety."
The researchers tested 69 ducks from the lower Rio Grand River around Las Cruces for the presence of the parasites over a 3-month period. While 49% tested positive for Cryptosporidium carriage and 28% tested positive for Giardia carriage, none of the parasites were of the species most commonly associated with human infection.
"Unlike Canada geese, which have been shown to carry infectious C. parvum, wild ducks do not seem to carry these pathogens," say the researchers.
(R.C. Kuhn, C.M. Rock and K.H. Oshima. 2002. Occurrence of Cryptosporidium and Giardia in wild ducks along the Rio Grande river valley in southern New Mexico. Applied and Environmental Microbiology, 68: 161-165.)
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