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Tips from the Journals of the American Society for Microbiology

American Society for Microbiology

Gastric Acid May Help Protect Against Foodborne Diseases

A new study suggests that low levels of gastric acid in the stomach can increase one's likelihood of getting a foodborne infection. The researchers from Australia report their findings in the February 2008 issue of the journal Infection and Immunity.

The belief that gastric acid forms a barrier against bacterial pathogens is widespread among the healthcare community, however no previous experimental data has been reported. One of the three main functions ascribed to gastric acid is inhibiting infectious agents from reaching the intestine and distribution levels noted in fish, amphibians, reptiles, birds and mammals indicate evolutionary advantages.

Hypochlorhydria is a condition that occurs when gastric acid levels in the stomach are abnormally low and is commonly associated with increased risk of infection. In the study healthy mice and hypochlorhydric mice were infected with Yersinia enterocolitica, Salmonella enterica serovar Typhimurium, Citrobacter rodentium and Clostridium perfringens and then monitored for their ability to fight infection. Results showed that significantly higher numbers of all four pathogens survived in the hypochlorhydric mice. Further studies indicated that infected mice treated with antacids were more sensitive to infection due to the absence of stomach acid.

"Apart from establishing the role of gastric acid in nonspecific immunity to ingested bacterial pathogens, our model provides an excellent system with which to investigate the effects of hypochlorhydria on susceptibility to infection and to evaluate the in vivo susceptibility to gastric acid of orally administered therapies, such as vaccines and probiotics," say the researchers.

(S.M. Tennant, E.L. Hartland, T. Phumoonna, D. Lyras, J.I. Rood, R.M. Robins-Browne, I.R. van Driel. 2008. Influence of gastric acid on susceptibility to infection with ingested bacterial pathogens. Infection and Immunity, 76. 2: 639-645.)

Higher Rates of MRSA Among Drug Users Than Six Years Ago

A new comparative study suggests that rates of MRSA infection in injection drug users in Vancouver have significantly increased over the last six years highlighting the need for interventional methods in high-risks groups. The researchers from the University of British Columbia, Vancouver General Hospital, and Vancouver Coastal Health report their findings in the February 2008 issue of the Journal of Clinical Microbiology.

Current statistics show that there are an estimated 13 million injection drug users worldwide. Past studies indicate that nasal or skin colonization with Staphylococcus aureus occurs at a higher rate in people who abuse drugs and in addition poses an increased risk of subsequent infections in injection drug users.

In a study conducted in 2000, researchers found that among 229 injection drug users, 27% had S. aureus nasal colonization and an overall MRSA colonization rate of 7.4%. In the current study researchers collected 301 samples from injection drug users and found an S. aureus colonization rate of 39.5%. Further testing of the S. aureus isolates showed an overall MRSA rate of 18.6% indicating a significant increase over the last six years.

"MRSA nasal colonization in this population has increased significantly within the last six years," say the researchers. "This study highlights the need for interventional measures in high-risk groups, not only to minimize further acquisition in these populations but also to prevent the spread of community strains within health care facilities and the general population."

(G.N. Al-Rawahi, A.G. Schreader, S.D. Porter, D.L. Roscoe, R. Gustafson, E.A. Bryce. Methicillin-resistant Staphylococcus aureus nasal carriage among injection drug users: six years later. Journal of Clinical Microbiology, 46. 2: 477-479.)

Copper May Inhibit the Transmission of HIV Through Breast Milk and Blood

Researchers from the U.S. and abroad have developed an inexpensive copper-based filter that may prevent HIV from being passed through breast milk and blood. They report their findings in the February 2008 issue of the journal Antimicrobial Agents and Chemotherapy.

Worldwide statistics of HIV transmission through breast milk and blood transfusions are at a disastrous high, especially in developing countries. In 2001 breast-feeding was attributed to up to 50% of the 700,000 mother-to-child transmission cases reported. The World Health Organization has estimated that blood transfusions are responsible for 80,000 to 160,000 HIV infections each year, while the Center for Disease Control reports that transfusions are the cause of 5 to 10% of HIV infections in developing countries.

In previous studies copper has shown potent antibacterial and antiviral activity. In this study viral levels of HIV-1 in cultures were noted both before and after exposure to copper oxide powder, copper oxide fibers and copper-based filters. Researcher's determined HIV-1 inhibition occurred following dose-dependant exposure to both copper oxide and copper fibers. Following filtration with copper powder or copper fibers viral deactivation of all isolates was observed.

"This inexpensive methodology may significantly reduce HIV-1 transmission from mother-to-child and/or through blood donations if proven to be effective in breast milk or plasma and safe for use," say the researchers. "The successful application of this technology may impact HIV-1 transmission, especially in developing countries where HIV-1 is rampant."

(G. Borkow, H.H. Lara, C.Y. Covington, A. Nyamathi, J. Gabbay. 2008. Deactivation of human immunodeficiency virus type 1 in medium by copper oxide-containing filters. Antimicrobial Agents and Chemotherapy, 52. 2: 518-525.)


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