Cubist Pharmaceuticals unloaded a lot of cash today in a buying spree which netted it biotechs Optimer and Trius in a bid to expand its anti-infective portfolio and hit a goal of $2 billion in revenue by 2015. The drug maker acquired Optimer for $535 million, with possible sales milestones, and Trius for another $707 million.

Cubist CEO Michael Bonney speculated in an analyst call yesterday that if all the products from the deal are ultimately approved by regulators, Cubist could provide four out of 10 of the antibiotics the Infectious Disease Society of America has said the world will need by 2020. Cubist’s current top-seller is Cubicin for MRSA (Methicillin-resistant Staphylococcus aureus), which generated 93% of the company’s revenue last year—$859.7 million.

The Lexington, MA-based manufacturer has been in cahoots with Optimer for the past two years as a co-marketer for Dificid—an antibiotic for diarrhea-causing infections in hospitals. The existing marketing infrastructure in place for Dificid made it an obvious takeover target, some said. Optimer anticipates Dificid will hit $250 million in cumulative sales by the end of the year.

Analysts are a bit more confused by the acquisition of Trius. Its primary asset, tedizolid phosphate—which is currently in late-stage trials for certain gram-positive infections—will likely face generic competition right out of the gate. Jefferies analyst Eun Yang wrote in an investor note today,  “[the] acquisition of Trius Therapeutics is perplexing. With the main competitor Zyvox [from Pfizer] going generic in 2015/2016, we see little value in TSRX’s tedizolid.”

Trius is expected to file an NDA for tedizolid by the end of the year in the US and a marketing application in the EU by the first half of 2014. Trius is currently in a partnership with Bayer AG for the development and commercialization of tedizolid outside of the US, Canada and EU.

Cubist management said during a conference call that they expect both drugs, tedizolid and Dificid, to eventually hit annual sales of $600 million to $1 billion.