A startup received a big funding boost for its work aimed at combating a serious threat to public health.

GV, the venture capital arm of Google, led an estimated $51 million investment round in Spero Therapeutics, a Cambridge, Massachusetts-based biotech developing a new class of antibiotic treatments targeting some of the toughest drug-resistant bacterial infections.

“We are grateful for the continued strong support from our existing investors as we welcome new partners who share our vision for building a multi-program approach to the major unmet need in drug-resistant bacterial infections,” said  Spero’s President and CEO Ankit Mahadevia, M.D., in a statement.

The financing will help Spero further advance its assets into the different stages of clinical testing.

One of Spero’s lead programs,Potentiator is using innovative technology to boost the spectrum and potency of over two dozen classes of gram-positive antibiotics so they could also become potential treatments for infections.

The difference between the two pathogens is the gram-positive bacterium lack an outer membrane, while gram-negative bacterium possess a thick plasma membrane capable of shielding the microbe from antibiotics and similar drugs.

Spero started a Phase I clinical trial in December 2016 to evaluate this molecule’s safety, tolerability and pharmacokinetic profile. Results from the investigation will be presented later in 2017.

Another candidate in Spero’s pipeline is a novel oral agent called SPR994, which has shown promise against a number of gram-negative bacterium in the lab, including extended spectrum beta lactamases (ESBLs). The new funding will help the company launch the first stage of clinical trials.

The World Health Organization recently released a list of 12 superbugs that pose a considerable threat to human health in an effort to highlight areas where potent treatments need to be developed.

The organization split these entrants into three categories called CRITICAL, HIGH, and MEDIUM. ESBLs are in the critical part of the list.

Spero joins GV’s growing Life Science & Health Portfolio, which is filled with other firms researching novel medical tools like liquid biopsy specialist Grail and gene editing upstart Editas Medicine.