The battle to discover new antibiotics.
Most of our antibiotics, and practically all of the different classes of antibiotics (ie the different families with different modes of action) were discovered over a period of three decades from the early 1940's to the late 1960's. No new classes of antibiotics were discovered for over thirty years and only two new classes have been discovered since 1968 - the Oxazolidinones in the late 1990's (although one of them was used against Tuberculosis since 1956) and the Lipopeptides approved in 2003.
a similar article in the New York Times in 2010 and shows the steep decline in the number of antibiotics approved for sale over the last three decades. This is the absolute number of antibiotics, not different classes, most of these antibiotics are variations on existing themes.
Interestingly both these articles make the same point that it is not necessarily the science that is lacking but the financial incentive:
While the notion of directly subsidizing drug companies may be
politically unpopular in many quarters, proponents say it is necessary
to bridge the gap between the high value that new antibiotics have for
society and the low returns they provide to drug companies.