Bacteria culture from urine. Coloured scanning electron micrograph (SEM). Here large numbers of mixed bacteria are shown. Urinary tract infections (UTIs) are a severe public health problem and are caused by a range of pathogens, but most commonly by Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Enterococcus faecalis and Staphylococcus saprophyticus. High recurrence rates and increasing antimicrobial resistance among uropathogens threaten to greatly increase the economic burden of these infections. Staphylococcus species are implicated in 10 to 20 percent of urinary tract infections. In females between the ages of 17 and 27, it is the second most common cause of these infections. It may also reside in the urinary tract and bladder of sexually active females. Magnification: x4000 when printed at 10 centimetres wide.