Tips from the journals of the American Society for Microbiology

Bacteria in Household Dust May Help or Hinder Childhood Asthma

Bacterial populations found in household dust may determine whether or not a child living in that home develops asthma according to research published in the April 2010 issue of the journal Applied and Environmental Microbiology.

Recent studies have shown household dust to be a source of highly diverse and abundant bacteria, yet it remains largely unexplored. In the study, testing on samples of collected house dust demonstrated that bacterial populations are greatly impacted by the presence of dogs and cats and whether or not children attend day care. Additionally, dust samples collected from homes of infants, with or without pets and varying day care attendance, showed differences in dust bacteria were linked with asthma development in children

“These results provide the first evidence that the dominant bacterial populations in household dust are significantly influenced by environmental variables such as domestic animals and day care attendance,” say the researchers. “Further, the dominant bacterial populations are significantly correlated to asthma-related outcomes, supporting the hypothesis that the types of microorganisms present in homes in early life may play key roles in the development of childhood asthma.”

Asthma has risen drastically in the last decade and some are attributing the increase to an altered immune response triggered by exposure to evolving microbial communities. Farms and day care centers are associated with asthma prevention due to high levels of microbial exposure, while actions that reduce bacterial populations in the home may actually increase allergy development.

“These parallels suggest that unidentified differences in exposure to microbial communities in the industrialized world may have fundamentally changed human immune responses, thereby enhancing susceptibility to autoimmune and allergic diseases,” say the researchers.

(R.M. Maier, M.W. Palmer, G.L. Andersen, M.J. Halonen, K.C. Josephson, R.S. Maier, F.D. Martinez, J.W. Neilson, D.A. Stern, D. Vercelli, A.L. Wright. 2010. Environmental determinants of and impact on childhood asthma by the bacterial community in household dust. Applied and Environmental Microbiology, 76. 8: 2663-2667.)

Oral Bacteria Linked to Intrauterine Infections and Pre-term Birth

Bacteria in the mouths of pregnant women can contribute to pre-term birth according to researchs from Case Western Reserve University, Cleveland, Ohio, and Hathaway Brown School, Shaker Heights. The findings are published in the April 2010 issue of the journal Infection and Immunity.

Approximately 12.7% of births in the U.S. are pre-term deliveries, a rate that reflects a 36% increase over the last 25 years. Intrauterine infection is recognized as a main cause of pre-term birth as well as late miscarriage and still birth. The cause of intrauterine infections has long been attributed to bacteria ascending into the uterus from the lower genital tract, however, recent studies indicate such infections are caused not only by bacteria found in the vaginal tract, but also in the mouth.

The human mouth is home to approximately 700 bacterial species. Gingivitis, a common problem associated with pregnancy, increases bacterial concentrations in the mouth further enhancing the possibility of transmission to the placenta through the blood stream. In the study saliva and plaque samples were injected into the tails of pregnant mice to determine what bacteria are capable of oral-uterus transmission. Researchers identified a diverse group of bacterial species colonizing the mouse placenta, of which the majority originate in the oral cavity and are associated with adverse pregnancy outcomes in humans.

“This study provides the first insight into the diversity of oral bacteria associated with intrauterine infection,” say the researchers. “Based on our findings, we postulate that periodontal therapies targeted at consistently reducing the total bacterial load in the mother’s oral cavity may be effective in improving birth outcomes.”

(Y. Fardini, P. Chung, R. Dumm, N. Joshi, Y.W. Han. 2010. Transmission of diverse oral bacteria to murine placenta: evidence for the oral microbiome as a potential source of intrauterine infection. Infection and Immunity, 78. 4: 1789-1796.)

Aerosols: A New Tool Against TB?

Scientists have developed a new strategy for treating tuberculosis using dry powder aerosols that could be delivered with an inhaler. The researchers from the University of North Carolina School of Pharmacy, Chapel Hill, North Carolina; and Harvard School of Engineering and Applied Sciences, Cambridge, Massachusetts, report their findings in the April 2010 issue of the journal Antimicrobial Agents and Chemotherapy.

Epidemic rates of HIV/TB coinfection as well as emerging multidrug-resistant (MDR) and extensively drug-resistant (XDR) TB strains are contributing to increased TB-associated deaths worldwide. PA-284, a compound capable of being formulated into a dry powder, has not only shown promising activity against MDR and XDR but has also proven safe and effective in patients coinfected with HIV and TB. Previous studies showed that PA-284 was well-tolerated in tablet form, however, side effects such as headache and stomach discomfort were reported. Aerosol delivery of PA-284 directly to the primary site of infection would limit systemic exposure and ultimately eliminate potentially bothersome side effects.

In the study guinea pigs were used to evaluate the effects of PA-284 aerosols on TB infection. One month following infection with TB some guinea pigs received high daily aerosol treatments while others received low daily treatments for 4 weeks. Lung and spleen analysis of guinea pigs receiving the high dose of aerosol PA-284 showed less inflammation, bacterial burden and tissue damage.

“The present studies indicate the potential use of PA-824 dry powder aerosols in the treatment of TB,” say the researchers.

(L. Garcia-Contreras, J.C. Sung, P. Muttil, D. Padilla, M. Telko, J.L. VerBerkmoes, K.J. Elbert, A.J. Hickey, D.A. Edwards. 2010. Dry powder PA-824 aerosols for treatment of tuberculosis in guinea pigs. Antimicrobial Agents and Chemotherapy, 54. 4: 1436-1442.)

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