Normal Human Gut Bacteria May Inhibit Shiga Toxin Development Following Infection with E. coli O157:H7

A new study suggests that normal human intestinal bacteria may inhibit the development of Shiga toxin 2 (Stx2), the toxin responsible for causing the more severe symptoms associated with food-borne disease, following Escherichia coli O157:H7 infection. The researchers from France report their findings in the February 2009 issue of the journal Infection and Immunity.

Enterohemorrhagic E. coli O157:H7 causes food-borne disease with symptoms ranging from diarrhea and hemorrhagic colitis to potentially fatal hemolytic-uremic syndrome. Stx2 is released in the gut following oral ingestion of E. coli O157:H7 and is the main virulence factor responsible for the more serious complications from the disease. Despite what researchers already know about the role of Stx2 in the progression of the disease, how the molecules released by the normal intestinal bacteria impact Stx2 is largely unknown.

In the study Stx2 synthesis was analyzed following the growth of E. coli O157:H7 in contents collected from the large bowel of rats colonized with normal human intestinal bacteria. Results showed that extracellular molecules, produced in part by Bacteroides thetaiotaomicron (a predominant species of the normal human intestine), repressed Stx2 development.

"Our findings demonstrate for the first time the regulatory activity of a soluble factor produced by the complex human digestive microbiota on a bacterial virulence factor in a physiologically relevant context," say the researchers.

(T. de Sablet, C. Chassard, A. Bernalier-Donadille, M. Vareille, A.P. Gobert, C. Martin. 2009. Human microbiota-secreted factors inhibit shiga toxin synthesis by enterohemorrhagic Escherichia coli O157:H7. Infection and Immunity, 77. 2: 783-790.)

Grape Extracts May be Effective Against Harmful Gut Bacteria

In a new study researchers from Clemson University found various grape extracts and their compounds to be effective at inhibiting Helicobacter pylori, one of the leading causes of gastritis in humans. They report their findings in the February 2009 issue of the journal Applied and Environmental Microbiology.

H. pylori is the bacterial agent most commonly associated with peptic ulcers, gastritis, mucosa-associated lymphoid tissue lymphoma, and gastric cancer. Antibiotic therapy has proven effective at providing initial relief, however resistance can develop over time and relapse can occur. Previous studies have examined other natural plant extracts with anti-H. pylori activity such as garlic, broccoli, cranberries and green tea, however, grapes have yet to be evaluated despite being well known for their high levels of antioxidants and polyphenols.

The antibacterial effects of extracts from red, white, black and muscadine grapes as well as the pure compounds resveratrol, ellagic acid, and myricetin were tested for anti-H. pylori activity using agar dilution, laser scanning microscopy and cell proliferation. Following 24 hour treatment, results showed that muscadine grape skin extract had the highest anti-H. pylori effect, followed by muscadine grape synergy and seed extract. Additionally, two of the three compounds, resveratrol and ellagic acid, also inhibited H. pylori.

"In this study, grape extracts and their compounds were effective at inhibiting H. pylori in vitro, with highest efficacy by muscadine grape skin extract," say the researchers.

(J.C. Brown, G. Huang, V. Haley-Zitlin, X. Jiang. 2009. Antibacterial effects of grape extracts on Helicobacter pylori. Applied and Environmental Microbiology, 75. 3: 848-852.)

Increased Dosage of Vancomycin May Lead to Hearing Loss in Older Patients

A new study suggests that increasingly aggressive doses of vancomycin being prescribed to keep pace with the rising number of methicillin-resistant Staphylococcus aureus (MRSA) infections may cause high-frequency hearing loss in older patients. The researchers from New York Medical College, Valhalla, New York, the University of the Pacific School of Pharmacy, Stockton, and Sharp Memorial Hospital, San Diego, CA report their findings in the February 2009 issue of the journal Antimicrobial Agents and Chemotherapy.

Although vancomycin has been available to medical professionals for 50 years, the emergence and rapid rise of MRSA in both community and healthcare settings has greatly increased its use. Additionally, recent increases in vancomycin minimum inhibiting concentrations (MICs) among MRSA isolates has resulted in many clinicians upping the dosage prescribed to patients.

In the study 89 patients taking vancomycin ranging in age from 16 to 86 were evaluated for high-frequency hearing loss detected by audiometry. They were administered a baseline audiogram (3 days after initiation of therapy) and then a follow-up test after an average of 27 days of therapy. Results showed a 12% rate of high-frequency hearing loss with a trend toward a higher rate with advanced age. Further analysis demonstrated a 0% rate of high-frequency hearing loss in patients under the age of 53 and a rate of 19% for patients over the age of 53.

"We conclude that a significant rate of high-frequency hearing loss in older patients receiving vancomycin monotherapy was detected by audiometry," say the researchers. "These findings should provide an additional caution against the use of indiscriminately higher doses of vancomycin to chase increasing vancomycin MICs for MRSA strains causing serious infections, such as pneumonia or bacteremia, in older patients."

(A. Forouzesh, P.A. Moise, G. Sakoulas. 2009. Vancomycin ototoxicity: a reevalutaion in an era of increasing doses. Antimicrobial Agents and Chemotherapy, 53. 2: 483-486.)

Source: Carrie Slijepcevic
American Society for Microbiology