Comprehensive Study on Gram-Negative Bacteria

Gram-negative bacteria

A significant group of microorganisms characterized by their thin peptidoglycan layer and distinctive lipopolysaccharide outer membrane.

Bacteroides

Gram-negative short rods that are obligate anaerobes, predominantly found in human feces (10^10 cells/gram), symbiotic in breaking down polysaccharides, and can cause opportunistic infections.

Campylobacter

Microaerophilic bacteria with optimum growth at 42°C, second leading cause of foodborne illness in the US, found in animals, especially birds, with sources including chicken and raw milk, and symptoms of severe, often bloody diarrhea.

Helicobacter

Closely related to Campylobacter, microaerophilic with flagellar knobs, and includes Helicobacter pylori, which is a cause of ulcers and potentially stomach cancer.

Treponema

Anaerobic and very thin bacteria that are difficult to see with light microscopy, with Treponema pallidum being the causative agent of syphilis.

Borrelia

Microaerophilic bacteria with large visible spirals, including Borrelia recurrentis, which causes relapsing fever transmitted by lice and ticks, and Borrelia burgdorferii, identified in 1982, which causes Lyme disease transmitted by ticks.

Leptospira

Aerobic, thin, finely coiled bacteria bent at the ends, causing leptospirosis, a zoonotic disease acquired through contact with contaminated urine.

Rickettsias

Gram-negative, obligate intracellular parasites transmitted by arthropod vectors, causing diseases like Rocky Mountain spotted fever and typhus.

Chlamydia

Extremely small, parasitic bacteria with a unique biphasic life cycle, transmitted airborne without arthropod vectors, causing diseases like trachoma and sexual infections.

Pseudomonas aeruginosa

Found in moist environments like whirlpool baths, it is an opportunistic pathogen that causes UTIs, skin lesions, and septicemia, and is highly resistant to antibiotics.

Legionella pneumophila

Identified in 1976, found in water systems, causing Legionnaires' disease (a severe type of pneumonia) and Pontiac fever.

Neisseria gonorrhoeae

Causes gonorrhea with no immunity or vaccine available, can lead to pelvic inflammatory disease (PID), and can be transmitted to newborns.

Neisseria meningitidis

Causes meningococcal meningitis, has high mortality if untreated, and vaccines are available.

Brucella spp.

Small, non-motile rods causing brucellosis (undulant fever), transmitted through consumption of infected meat or contact with infected animals.

Bordetella pertussis

Causes whooping cough, highly pathogenic to infants, with vaccines available (e.g., DTP, DTaP), though not lifelong.

Francisella tularensis

Causes tularemia or rabbit fever, transmitted through eating or handling infected rabbits.

Escherichia coli

Normal intestinal flora, with pathogenic strains causing diarrhea and UTIs, transmitted through contaminated water and beef.

Shigella

Closely related to E. coli, causing gastrointestinal disease.

Escherichia coli

Always pathogenic; causes bacillary dysentery, associated with poor sanitation.

Salmonella

Pathogenic, motile, and H2S producing; causes gastroenteritis and systemic infections like typhoid fever.

Klebsiella

Non-motile, urease positive; causes pneumonia, UTIs, and infant diarrhea.

Enterobacter

Yellow pigmentation, butanediol fermentation, opportunistic infections.

Serratia

Motile, red pigmentation at lower temperatures; causes opportunistic infections.

Proteus

Highly motile, urease positive; causes UTIs.

Yersinia

Causative agent of plague (bubonic, pneumonic, septicemic), found in rodents.

Vibrio

Curved rods, oxidase positive; causes diseases like cholera and gastroenteritis from raw fish.

Haemophilus

Non-motile rods requiring enriched media; causes chancroid, meningitis, conjunctivitis.

Gardnerella

Associated with bacterial vaginosis when combined with anaerobic bacteria.