Gram-Negative Bacteria

Gram-Negative Bacteria

Proteobacteria

• Escherichia (E. coli) is a heterotrophic, facultative anaerobic, Gram-negative rod-shaped bacterium that inhabits the gut of humans and animals.

• It can cause diarrhea, fever, and produces endotoxin and enterotoxin (in some strains).

• E. coli is part of the Enterobacteriaceae family and has peritrichous flagella for motility.

• Most strains are normal flora, but some can be pathogenic, with infection occurring through animal contact or contaminated food (e.g., 0157, 0111).

• Salmonella (S. enterica) is a heterotrophic, facultative anaerobic, Gram-negative rod-shaped bacterium that is a normal flora in animal gut.

• It can cause food-borne infections and self-limiting diarrhea, with endotoxin and enterotoxin production.

• S. typhi is a water-borne infection that causes typhoid fever, which can be fatal.

Vibrio

• Vibrio (V. cholera) is a heterotrophic, facultative anaerobic, Gram-negative curved rod-shaped bacterium that is mainly found in marine environments.
• It can cause gut infections, cholera, and severe diarrhea, with exotoxin production.
• V. cholera is often found in sewage contamination and can cause seafood-borne disease.

Pseudomonas

• Pseudomonas (P. aeruginosa) is a heterotrophic, aerobic, Gram-negative curved rod-shaped bacterium that is commonly found in soil and water.
• It can cause hospital-acquired infections, such as burns and contact lenses infections, and has innate antibiotic resistance.
• P. aeruginosa has low membrane permeability, produces haemolysin, and proteases, and has a large genome (6mb) making it metabolically versatile.

Neisseria

• Neisseria is a heterotrophic, aerobic, Gram-negative diplococci bacterium that inhabits mammalian mucous membranes.
• It has a capsule that aids in evading the immune response and fimbriae that allows adhesion to tissues.
• N. gonorrhoeae causes gonorrhoea (STD) and N. meningitis causes meningitis (meningococcal disease).

Rickettsia

• Rickettsia is a heterotrophic, aerobic, Gram-negative coccobacillus bacterium that is dependent on host metabolism and cannot be grown in vitro.
• It causes various fever diseases, such as arthropod-borne diseases, and produces phospholipase.
• R. prowazekii causes diseases with symptoms like headache, fever, and rash.