Aerobes

Aerobes are organisms that rely on oxygen (O₂) to produce energy in the form of adenosine triphosphate (ATP). They use an O₂-dependent system to generate ATP, primarily through the process of aerobic respiration. This metabolic pathway is critical for the survival and functioning of aerobic bacteria and other organisms.

ATP Generation in Aerobes

Oxygen as Terminal Electron Acceptor: Aerobes utilize molecular oxygen (O₂) as the final electron acceptor in the electron transport chain, a process that occurs in the mitochondria (in eukaryotes) or the cell membrane (in prokaryotes).
Energy Production: The process generates large amounts of ATP, the cell’s main energy currency, through oxidative phosphorylation.

Examples of Aerobic Bacteria

The following bacteria are well-known examples of aerobic organisms that depend on oxygen for ATP production:

Bacteria	Characteristics
Nocardia	Gram-positive, filamentous bacteria; causes pulmonary infections
Pseudomonas aeruginosa	Gram-negative; opportunistic pathogen; associated with lung infections in cystic fibrosis patients
Mycobacterium tuberculosis	Causes tuberculosis; survives in oxygen-rich environments like the lungs
Bordetella pertussis	Gram-negative; causes whooping cough (pertussis)

Examples of Aerobic Bacteria

Special Note on Mycobacterium tuberculosis

Reactivation: Mycobacterium tuberculosis (M. tuberculosis) has a unique relationship with oxygen. Reactivation of latent tuberculosis infections, often seen in patients with compromised immune systems or after TNF-α inhibitor therapy, has a predilection for the apices of the lung. The lung apices have higher oxygen concentrations, making them an ideal site for M. tuberculosis growth.

Points to Remember

Aerobes depend on oxygen to generate ATP through an oxygen-dependent electron transport system.
Nocardia, Pseudomonas aeruginosa, Mycobacterium tuberculosis, and Bordetella pertussis are key examples of aerobic bacteria.
Reactivation of M. tuberculosis often targets the oxygen-rich apices of the lungs, particularly in immunocompromised patients.
Immunocompromised states or TNF-α inhibitor therapy can trigger the reactivation of latent tuberculosis.

Bibliography

Kumar, V., Abbas, A. K., Aster, J. C. (2014). Robbins and Cotran Pathologic Basis of Disease. 9th Edition. Elsevier.
Ryan, K. J., & Ray, C. G. (2010). Sherris Medical Microbiology. 5th Edition. McGraw-Hill.

USMLE Step 1 Review Series

Curriculum

Aerobes

ATP Generation in Aerobes

Examples of Aerobic Bacteria

Special Note on Mycobacterium tuberculosis

Points to Remember

Bibliography

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