What is this sulfameth trimethoprim used for?

It works for a wide variety of infections. Here are some uses:

Oral treatment of urinary tract infections due to E. coli, Klebsiella and Enterobacter sp, M. morganii, P. mirabilis and P. vulgaris; acute otitis media in children; acute exacerbations of chronic bronchitis in adults due to susceptible strains of H. influenzae or S. pneumoniae; treatment and prophylaxis of Pneumocystis jiroveci pneumonitis (PCP); traveler's diarrhea due to enterotoxigenic E. coli; treatment of enteritis caused by Shigella flexneri or Shigella sonnei.