The most clinically important speciies of this genus is Klebsiella pneumoniae. This large, non-motile bacterium produces large sticky colonies when plated on nutrient media. Klebsiella's pathogenicity can be attributed to its production of a heat-stable enterotoxin. K. pneumoniae infections are common in hospitals where they cause pneumonia (characterized by emission of bloody sputum) and urinary tract infections in catheterized patients. In fact, K. pneumoniae is second only to E. coli as a urinary tract pathogen. Klebsiella infections are encountered far more often now than in the past. This is probably due to the bacterium's antibiotic resistance properties. Klebsiella species may contain resistance plasmids(R-plasmids) which confer resistance to such antibiotics as ampicillin and carbenicillin. To make matters worse, the R-plasmids can be transferred to other enteric bacteria not necessarily of the same species.