), primarily urinary problems ( Escherichia coli , Proteus mirabilis , Enterobacter cloacae , Serratia marcescens ), and primarily gastrointestinal problems ( Helicobacter pylori , Salmonella enteritidis , Salmonella typhi ). Gram-negative bacteria associated with nosocomial infections include Acinetobacter baumannii , which cause bacteremia, secondary meningitis, and ventilator-associated pneumonia in intensive-care units