Syndicate content

Archive - Apr 16, 2012

DNA Sequencing Allows ID of Unusual, Oft-Fatal Pathogen in Patient

A 14-year-old Texas girl was finally cured of an oft-fatal emerging disease when doctors amputed her lower leg, where the infection arose, after various antimicrobials proved ineffective. The culprit was Pythium insidiosum, a fungus-like microbe which rarely causes disease in humans and then primarily in Thailand. The case "clearly highlights the need for clinicians to have the best support possible from the clinical microbiology lab," says Dr. Don Murphey of Cook Children's Medical Center, who served as attending physician during the case. The case report is published in the April 2012 issue of the Journal of Clinical Microbiology. The girl, otherwise healthy, presented to an urgent care facility with a 2-week history of a continuously enlarging erythematous bump on her lower leg, having reported recently swimming in an algae-filled pool. "Over the course of several weeks, what started as a very small lesion grew to involve most of her leg," says first author Dr. Stephen J. Salipante, of the University of Washington, Seattle. "Initial cultures of the wound suggested that this was a bacterial infection, and it was treated as such, but without success. She eventually needed to be hospitalized," says Dr. Salipante. Her treatment team at Cook Children's hospital tried increasingly aggressive medical and surgical management, including different antibiotic regimens, antifungals, and surgical debridements, but the infection simply didn't respond. "Given the microscopic appearance of the organism, our working hypothesis was that this was some kind of unusual, and very aggressive fungus," says Dr. Salipante. However, sequencing a segment of DNA that is useful for categorizing fungi, the ITS1 sequence, "revealed that this was not a fungus at all—rather, the DNA sequence very closely matched… P. insidiosum," says Dr.

Promiscuous Queen Bees Maintain Genetic Diversity in Island Environment

By mating with nearly 100 males, queen bees on isolated islands avoid inbreeding and keep colonies healthy. The results, published online in PLoS ONE, focused on giant honey bee colonies on Hainan Island, off the coast of China. Because these bees have long been separated from their continental cousins, it was thought that the island bees would be prime candidates for inbreeding as well as having very different genes, said Dr. Zachary Huang, Michigan State University (MSU) entomologist. “We believed that the island bees would show evidence of the founder effect, or random genetic changes in an isolated population, on a unique sex determination gene from the mainland bees,” he said. “At first we were surprised when we couldn’t document this effect. Looking at it further, I asked myself, ‘Why didn’t I think of this before?’” When compared to bees, humans have a rather simplistic sex-determination process. In females, the two sex-determination chromosomes are the same, and in males the two chromosomes are different. With bees, however, the combinations of complementary sex determination genes, or CSDs, determine the sex and the societal role of the bees. One particular gene can have alleles – the “flavor” of genes. In humans, they dictate hair and eye color. In bees, though, they are responsible for creating females (worker bees), fertile males (that mate with the queen) or infertile males (diploid males which serve no purpose). The “voila” moment came once Dr. Huang estimated the bees’ mating habits and the potential of CSD allele combinations. That’s when he understood why he couldn’t confirm the founder effect. Keeping the CSD mix diverse is one of the keys to maintaining a healthy hive, he said. The island queens carry around 40 CSD alleles.