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Tips from the journals of the American Society for Microbiology

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American Society for Microbiology

Streptococcus Enzyme Could Compete With Toothbrushes, Dental Floss

Investigators from Japan show in vitro that the bacterium Streptococcus salivarius, a non-biofilm forming, and otherwise harmless inhabitant of the human mouth, actually inhibits the formation of dental biofilms, otherwise known as plaque. Two enzymes this bacteria produces are responsible for this inhibition. The research is published in the March 2011 issue of the journal Applied and Environmental Microbiology.

"FruA may be useful for prevention of dental caries," corresponding author Hidenobu Senpuku, of the National Institute of Infectious Diseases, Tokyo says of one of the enzymes. "The activity of the inhibitors was elevated in the presence of sucrose, and the inhibitory effects were dependent on the sucrose concentration in the biofilm formation assay medium," the researchers write.

"We show that FruA produced by S. salivarius inhibited S. mutans biofilm formation completely in the in vitro assay supplemented with sucrose," the researchers write. S. salivarius is the primary species of bacteria inhabiting the mouth, according to the report.

The authors suggest that FruA may actually regulate microbial pathogenicity in the oral cavity. They found that a commercial FruA, produced by Aspergillus niger, was as effective as S. salivarius FruA at inhibiting S. mutans biofilm formation, despite the fact that its amino acid composition is somewhat different from that of S. salivarius.

FruA is produced not only by S. salivarius, but by other oral streptococci. Much of the oral microbial flora consists of many beneficial species of bacteria that help maintain oral health and control the progression of oral disease.

(A. Ogawa, S. Furukawa, S. Fujita, J. Mitobe, T. Kawarai, N. Narisawa, T. Sekizuka, M. Kuroda, K. Ochiai, H. Ogihara, S. Kosono, S. Yoneda, H. Watanabe, Y. Morinaga, H. Uematsu, and H. Senpuku, 2011. Inhibition of Streptococcus mutans biofilm formation by Streptococcus salivarius FruA. Appl. Environ. Microbiol. 77:1572-1580.)

A Better Test for HPV

A new test for human papillomavirus (HPV) is just as sensitive as the old one, but more specific for detecting cervical cancer, meaning that it has fewer false positive results, according to a paper in the February 2011 Journal of Clinical Microbiology.

"This is important because reducing false positive results avoids unnecessary additional tests and follow-up, the associated health care costs, and distress to women," says first author Sam Ratnam, of the Faculty of Medicine, Memorial University, St. John's, Newfoundland and Labrador. HPV infection, he explains, is highly prevalent, but "only a small fraction of the infected are at risk of developing HPV-associated cancers."

The investigators report that the new test, called the Aptima HPV test, detected 96.3 percent of women with high-grade cervical intraepithelial neoplasia or worse (CIN 2+) compared to 94.3 percent for the old test, the Hybrid Capture 2 DNA test (HC2), among 1418 women studied. But Aptima has far fewer false positives than HC2. "This difference could be attributed to the fact that the Aptima test detects the expression of two oncogenes, E6 and E7, via their messenger RNAs," says Ratnam. "These proteins are involved in initiation and mediation of oncogenic process that leads to cervical cancer, and to other HPV-associated cancers. The HC2 test, on the other hand, detects the viral DNA which is not as discriminating. The Pap smear, the traditional common screening method for cervical cancer, has few false positives, but fails to detect nearly half of all CIN 2+ cases."

While HPV is the single most common sexually transmitted virus, its spread is increasing due to rising oral sex among young people, according the Oral Cancer Foundation. "We're seeing more and more cases of tonsilar cancers in Newfoundland," a cancer which is frequently caused by HPV, says coauthor Adrian Lear of the Dr. H. Bliss Murphy Cancer Centre, St. John's, Newfoundland. In people under the age of 50, HPV-associated oral cancers may even be replacing tobacco as the primary causative agent according to the Oral Cancer Foundation.

While the role of HPV is most recognized in cervical cancer, it is also associated with anal and penile cancers, and cancers of the vagina and vulva. The test could detect HPV infections that have begun to progress towards these other HPV-associated cancers, says Ratnam.

Currently, two vaccines are available against HPV: Gardasil, which is active against four types, 16, 18, 6 and 11, and Cerverix, which is active against two types, 16 and 18. Types 16 and 18 account for about 70% cervical cancer world-wide, and types 6 and 11 account for over 90% of genital warts. These vaccines are now approved in many countries around the world but offered only to females. "I'm convinced the day is coming when the vaccine will be offered for both males and females through publicly funded programs," says Lear. "In the meantime, the use of a more accurate test such as the Aptima test should improve the efficiency and cost-effectiveness of cervical cancer screening around the world, and should help prevent cervical cancer," says Ratnam.

(Samuel Ratnam, Francois Coutlee, Dan Fontaine, James Bentley, Nicholas Escott, Prafull Ghatage, Veeresh Gadag, Glen Holloway, Elias Bartellas, Nick Kum, Christopher Giede, and Adrian Lear. 2011. Aptima HPV E6/E7 mRNA Test Is as Sensitive as Hybrid Capture 2 Assay but More Specific at Detecting Cervical Precancer and Cancer. J. Clin. Microbiol. 49: 557-564.)

Compound From Chinese Medicine Blocks Biofilm Formation on Medical Implant Materials

A compound that is an active ingredient in plants commonly used in Chinese medicine prevents biofilm formation on polystyrene and polycarbonate surfaces by Staphylococcus aureus. The research suggests that this compound, 1,2,3,4,6-Penta-O-galloyl-beta-D-glucopyranose (PGG) is highly promising for clinical use in preventing biofilm formation by S. aureus. The paper is published in the March 2011 issue of the journal Antimicrobial Agents and Chemotherapy.

S. aureus commonly forms biofilms on medical implants, causing pneumonia, meningitis, endocarditis, osteomyelitis, and bloodstream and urinary tract infections. Biofilms, which are far tougher than bacteria not incorporated into biofilms, are resistant to antibiotics even when the individual bacteria composing the biofilm lack antibiotic resistance genes. Once biofilms become attached to the surfaces of medical devices, they are extremely difficult to expunge.

PGG is "far more potent" than several other compounds found to inhibit biofilms, including IDA, NAC, and NPM, according to the report. Despite that potency, PGG did not kill S. aureus. It is also non-toxic to human epithelial and fibroblast cells. PGG likely inhibits biofilm formation during the initial attachment stage, as the investigators found PGG to be effective only when it is added to a medium within an hour after seeding. Besides polystyrene and polycarbonates, PGG inhibited biofilm formation on silicon rubber, a material commonly used in catheters, and on glass coverslips.

PGG is an active ingredient in plants that are commonly used in Chinese medicine to treat inflammation. It was one of 48 compounds purified form medicinal plants that the researchers screened for efficacy in inhibiting S. aureus biofilm formation. PGG was on sole compound from among them that did not kill the pathogens.

(M.-H. Lin, F.-R. Chang, M.-Y. Hua, Y.-C. Wu, and S.-T. Liu, 2011. Inhibitory effects of 1,2,3,4,6-Penta-O-Galloyl-beta-D-Glucopyranose on biofilm formation by Staphylococcus aureus. Antim. Agents Chemother. 55:1021-1027.)

How Different Strains of Parasite Infection Affect Behavior Differently

Toxoplasma gondii infects approximately 25 percent of the human population. The protozoan parasite is noted for altering the behavior of infected hosts. Jianchun Xiao and colleagues of the Johns Hopkins School of Medicine find clear differences in the manipulation of host gene expression among the three clonal lineages that predominate in Europe and North America, "despite the high level of genetic similarity among them," says Xiao. Type I infection largely affects genes related to the central nervous system, while type III mostly alters genes that modulate nucleotide metabolism. Type II infection does not alter expression of a clearly defined set of genes. The research is published in the March 2011 issue of the journa Infection and Immunity.

Indeed, T. gondii can play its infected rodent hosts like a piano, converting rats' and mice's natural aversion to feline odors into an attraction, presumably to enable the parasite's sexual cycle. T. gondii can reproduce sexually only in cats. Investigations of effects on humans have found an increased risk of traffic accidents, and other reckless behavior, as well as links to hallucinations.

"Toxoplasma infections, at least for mice, are so variable in their severity and heavily dependent on which strain is doing the infecting," says Xiao. "Understanding the differential effects caused by these strains could enable predicting the outcome of infection and point out directions to be explored in future studies to eliminate transmissions or cure disease. If Toxoplasma is linked to schizophrenia, this could lead to new treatments of that disease as well."

"It is noteworthy that we found vasoactive intestinal peptide receptor 2 (VIPR2) was upregulated by all three Toxoplasma strains," says Xiao. VIPR2 "is linked to schizophrenia in some recent publications. Since the tropism of Toxoplasma for brain has been linked with specific behavioral changes and psychosis in humans, this finding will have some fundamental significance for understanding the correlation between Toxoplasma and psychosis."

Type II strains cause 70-80 percent of human cases reported in North America and Europe.

(J. Xiao, L. Jones-Brando, C.C. Talbot, Jr., and R.H. Yolken, 2011. Differential effects of three canonical Toxoplasma strains on gene expression in human neuroepithelial cells. Infect. Immun. 79:1363-1373.)


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