ANSWER: Klebsiella
Explanation:
A bug which was earlier treated by moderate class antibiotics has now resisted treatment from third generation antibiotics or carbapanems. The Klebsiella pathogen has led to higher mortality in patients and has become colistin resistant. Colistin is the final antibiotic for treating infections which other antibiotics have failed to treat. Klebsiella has led to UTI and ventilator acquired pneumonias and blood stream infections.