Pneumonia is an infection of the lungs typically caused by a bacteria, virus, or inhaled substances. Here is a look at some gram-negative bacterial causes.

What Is Pneumonia?

Pneumonia occurs when the lungs' air sacs and small airways fill with liquid and cannot function properly. When gas exchange is impeded, the body cannot take in oxygen as it normally would, and our cells must have oxygen to carry out aerobic respiration; the breakdown of glucose to obtain energy for cellular work. Viruses, bacteria, fungi or inhaled substances can all lead to pneumonia.

Bacterial Pneumonia

Bacteria are primitive prokaryotic organisms that are structurally simple and lacking a nucleus. Of the different types of pneumonias, bacterial tend to be the most serious, and, in adults, the most common. Bacterial pneumonia may follow influenza or even a common cold, particularly in the elderly or immune compromised.

Gram-Positive and Gram Negative Bacteria

Bacterial cell walls are the target of many antibiotics, and a primary component of the cell walls is the molecule peptidoglycan, a huge polymer that is found only in bacteria.

From the peptidoglycan inwards all bacterial cells are very similar. Going further out, the bacterial world divides into two major classes: Gram positive and Gram negative.

Gram-positive Cells

In Gram-positive cells, peptidoglycan makes up as much as 90% of the thick, compact cell wall, which is the outermost structure of Gram + cells.

Gram-negative Cells

The cell walls of gram-negative bacteria are more chemically complex, thinner and less compact. Peptidoglycan makes up only 5 – 20% of the cell wall, and is not the outermost layer, but lies between the plasma membrane and an outer LPS membrane.

Antibiotics Gram-Negative Cells

Penicillins and cephalosporins interfere with the structure of peptidoglycan, but because of the LPS membrane, these antimicrobials can’t access the peptidoglycan of Gram-negative bacteria. Gram-positive bacteria, with no membrane outside the peptidoglycan cell wall, are more susceptible to these antibiotics.

Gram Negative Pneumonia

Gram-negative bacteria can cause serious pneumonia most often occurring in people who are hospitalized, infants, the elderly, alcoholics, and those with chronic diseases, particularly immune system disorders. These bacteria rarely infect the lungs of healthy adults.

The symptoms of Gram-negative bacterial pneumonia are the same as for gram-positive, except that people tend to be sicker and worsen quickly, as Gram-negative bacteria can rapidly destroy lung tissue. Even with treatment, about 25 to 50% of people with Gram-negative pneumonia die.

Some Types of Gram-Negative Pneumonia

Legionnaire’s Disease

Organism: Legionella pneumophila

L. pneumophila is a flagellated bacterium that spreads via water and can contaminate air-conditioning systems. Symptoms begin with aches, pains, fever and headache, followed by a cough that eventually produces phlegm. Although usually mild, the disease can be severe, with extreme breathlessness, diarrhea and confusion. About 20% of people who develop Legionnaire’s disease die.

Haemophilus Pneumonia

Organism: Haemophilus influenzae

The name of this type of pneumonia is a misnomer, as H. influenzae does not cause flu; instead it is a major cause of pneumonia in children under 6 years of age. Illness begins with sneezing and a runny nose; then develops into the common symptoms of pneumonia. In addition, some fluid commonly develops around the lung, called a 'pleural effusion'.

This bacterium is present in approximately 75 percent of healthy children and adults. Usually nonencapsulated strains are harbored as normal flora, but 3 – 7% of healthy individuals have dangerous H. influenzae type b (Hib) encapsulated strains upper respiratory tract.

Friedländer's Pneumonia

Organism: Klebsiella pneumoniae

The organism causing Friedländer's Pneumonia, also called Klebsiella Pneumonia, is an anaerobic rod shaped bacterium found in the normal flora of the mouth, skin, and intestines. It naturally occurs in the soil and about 30% of strains can fix nitrogen in anaerobic condition. New antibiotic resistant strains of K. pneumoniae are increasingly prevalent, and this organism is becoming more of a problem in hospital-acquired (nosocomial) infections.

Pseudomonas Pneumonia

Organism: Pseudomonas aeruginosa

P. aeruginosa is a rod-shaped bacterium found in soil, water, plants, and animals. It is an opportunistic pathogen, rarely causing disease in healthy persons, but infecting those who have weakened immune systems.

This bacterium is the second most common cause of nosocomial pneumonia and the most common cause of pneumonia in intensive care units. Many Pseudomonas are resistant to certain antibiotics, making infections difficult to treat.

Pneumonia Resources

For more information on pneumonia, see the Mayo Clinic: Infectious Diseases or Science Prof Online. For additional material on other types of pneumonia see the Suite101.com articles Gram Positive Bacterial Pneumonia, Primary Atypical Pneumonia and Endemic Fungal Pneumonia.

Sources

Bauman, R. (2005) Microbiology.

Park Talaro, K. (2008) Foundations in Microbiology.