Fighting the Resistance

Wigle works to inhibit growth of antibiotic-resistant bacteria

Before penicillin was introduced during World War II, soldiers were just as likely to die from infections as from battle wounds. The introduction of penicillin was a medical breakthrough; many once-fatal infections could be easily cured, and penicillin earned a label as a “miracle drug.”

Tim Wigle is looking for ways to inhibit the activity of a protein called RecA, which is vital to the development of antibiotic resistance in bacteria.

Today, it’s hard to imagine life without penicillin and numerous other antibiotics that battle bacterial infections. But as antibiotics have become more commonly used (and misused), bacteria have started to fight back. Today, antibiotic resistance quickly is becoming one of the world’s most serious health problems.

“Antibiotic resistant bacteria pose an alarming threat to public health all over the world,” explains Tim Wigle, a fourth-year graduate student in the Division of Medicinal Chemistry and Natural Products. “We now live in an era where factors such as international travel, overcrowding, and the menace of bioterrorism have the potential to unleash these pathogens on millions of unsuspecting people.”

Wigle conducts research in the lab of associate professor Scott Singleton, PhD. The lab studies the development and transmission of microbial drug resistance and searches for new strategies to control drug-resistant microorganisms.

Wigle’s dissertation research is focused on the activity of a bacterial protein called RecA, which is vital to the development and spread of antibiotic resistance. Wigle explains that when bacteria experience stress, such as when an antibiotic is being used to treat an infection, the resulting DNA damage to the bacteria activates the RecA protein.

Once activated, RecA performs two major functions. It signals for the bacterial SOS response that initiates the transcription of genes instrumental in allowing the bacteria to bypass the stress and continue to proliferate.  If that doesn’t work, this RecA-initiated response eventually will cause the bacteria to mutate its own DNA in an attempt to bypass the stress. This leads to the creation of genes encoding antibiotic-resistant proteins that allow the bacteria to start proliferating again. Through a DNA strand-exchange reaction called a recombination reaction, RecA also facilitates the sharing of this resistant DNA between bacteria of the same and even different species.

“RecA helps bacteria become resistant to antibiotics and it helps them survive through conditions of stress,” Wigle says. “So we’re looking for ways to knock out RecA so that any bacteria under stress from an antibiotic will not become resistant to that antibiotic and instead will become weakened so that it can be killed by your own body or by another antibiotic.”

Wigle says that up to this point, researchers have not successfully identified a molecule capable of inhibiting RecA in bacteria.

“In our lab we are searching for small molecule inhibitors that will either prevent the activation of RecA or will interfere with the activated form of RecA,” Wigle explains.

He hopes to discover a RecA inhibitor that will ultimately either slow down the rate at which bacteria become resistant to antibiotics or make bacteria more susceptible to current frontline antibiotics and therefore easier to kill -- thus extending the effective lifetime of current antibiotics. Wigle says there is also a chance that a RecA inhibitor could be used as a standalone antibiotic.

To identify potential RecA inhibitors, Wigle has developed procedures, or assays, capable of identifying and quantifying the inhibition of RecA caused by small molecules. The assays have been used to screen a library of approximately one hundred compounds against RecA. He says that so far he has successfully identified two classes of compounds that inhibit RecA in the lab. However, the compounds are not practical for use outside the laboratory.

“The inhibitors we’ve discovered won’t penetrate the bacterial cell membrane because they’re negatively charged compounds, and charged compounds won’t pass through the membranes of bacterial cells,” Wigle explains. “Whereas they’re useful to study RecA in a test tube setting, they’re not useful for studies on living bacteria.”

Wigle now hopes to find more drug-like compounds that can cross into bacteria and allow study in a living setting. He recently acquired and screened approximately three thousand compounds from the National Institutes of Health and is now busy chasing down several promising leads from this set.

At present, Wigle’s research focuses primarily on RecA isolated from Escherichia coli bacteria, but he says he is studying the application of his research to other species of notorious bacteria, including Streptococcus pneumoniae, Staphylococcus aureus and Bacillus anthracis (Anthrax).  He says that initial results suggest that small molecule inhibitors of E.coli RecA will be universal for all bacterial species.

The potential impact of Wigle’s research is already being recognized. Last year, he received a Graduate Education Advancement Board Recognition Award, a privately funded prize given by the Graduate School to recognize graduate student research that benefits North Carolina communities. He also served as first author on a paper published in Biochemistry, a highly renowned American Chemical Society journal. Singleton and postdoctoral researcher Andrew Lee, PhD, served as coauthors on the paper.

Wigle is optimistic about the prospective benefits of his research to extend current antibiotic treatment and pave the way for the future of antibiotic medicine.

“Eventually we believe that we will discover a small molecule inhibitor of RecA that can serve as a lead candidate for the development of a new class of antibacterial therapeutics,” he says.