Miscellaneous Gram-Negative Bacteria

What is the mode of transmission for Legionella?

Inhalation of contaminated water aerosols (e.g. from cooling towers, air conditioning) or aspiration of contaminated water/ice.

What type of organism is Legionella pneumophila?

A fastidious, aerobic, Gram-negative rod that requires L-cysteine and iron to grow.

What stain is used to visualise Legionella?

Silver stain (e.g. Warthin-Starry).

Where is Legionella naturally found?

Freshwater environments such as lakes, streams, warm springs, and artificial water systems.

What is the pathogenesis of Legionnaires’ disease?

Bacteria multiply inside alveolar macrophages → cytokine release → inflammatory cell influx → pneumonia and respiratory failure.

What is the morphology of Bordetella pertussis?

Small, aerobic, Gram-negative coccobacillus.

How is Bordetella pertussis transmitted?

Respiratory droplets.

What are the stages of pertussis infection?

• Catarrhal stage (1–2 weeks): Mild cough and rhinorrhoea

• Paroxysmal stage (1–6 weeks or longer): Repeated forceful coughing fits followed by “whoop” sound on inhalation

What are complications of pertussis?

Pneumonia, otitis media, asthma, exhaustion from coughing.

Why is pertussis re-emerging despite vaccination?

Acellular vaccines provide shorter immunity + vaccine hesitancy.

Where in the body are Gram-negative anaerobes most abundant?

Gastrointestinal tract, upper respiratory tract, genitourinary tract

Which genus is most commonly associated with intra-abdominal infections?

Bacteroides fragilis (80% of cases).

What types of infections are caused by Gram-negative anaerobes?

Periodontal disease, abscesses, intra-abdominal and gynecological infections, soft tissue infections.

What microorganisms commonly contribute to acute necrotizing gingivitis?

Prevotella, Fusobacterium, and spirochetes such as Treponema.