Medically Important Gram Negative Bacteria

Gram-Negative Bacteria

Bacterium	Family	Diseases	Colony Characteristics
Escherichia coli (E. coli)	Enterobacteriaceae	UTIs, gastroenteritis, neonatal meningitis, sepsis	Lactose-fermenter; pink colonies on MacConkey agar.
Pseudomonas aeruginosa	Pseudomonadaceae	Nosocomial infections (pneumonia, sepsis, UTIs, wound infections), cystic fibrosis-related infections, burn infections.	Green pigment, grape-like odor, non-lactose fermenter.
Salmonella enterica	Enterobacteriaceae	Typhoid fever, gastroenteritis, sepsis	Black colonies on XLD, non-lactose fermenter.
Shigella dysenteriae	Enterobacteriaceae	Shigellosis (dysentery)	Colorless colonies on XLD and SS agar.
Klebsiella pneumoniae	Enterobacteriaceae	Pneumonia, UTIs, liver abscesses, sepsis	Mucoid, lactose-fermenting colonies on MacConkey agar.
Neisseria gonorrhoeae	Neisseriaceae	Gonorrhea, PID, DGI	Small, grayish colonies; oxidase-positive diplococci.
Haemophilus influenzae	Pasteurellaceae	Meningitis, pneumonia, otitis media	Requires factor V for growth; grayish colonies.
Vibrio cholerae	Vibrionaceae	Cholera	Yellow colonies on TCBS agar.
Francisella tularensis	Francisellaceae	Tularemia	Cysteine-enriched agar; non-hemolytic.
Acinetobacter baumannii	Moraxellaceae	Nosocomial infections (pneumonia, sepsis)	Smooth, grayish colonies on MacConkey agar.
Serratia marcescens	Enterobacteriaceae	Urinary Tract Infections (UTIs); Respiratory Infections; Wound Infections and Bloodstream Infections (BSIs)	Nutrient Agar: Colonies on nutrient agar exhibit the distinctive red pigmentation