Pneumonia: Definition: Pneumonia is an inflammatory condition of the lung— especially affecting the microscopic air sacs (alveoli), and the parenchyma of the lung. Lung parenchyma refers to alveolar tissue with respiratory bronchioles, alveolar ducts, blood vessels and terminal bronchioles.

Classification of pneumonia: Traditionally, clinicians have classified pneumonia by clinical characteristics, dividing them into "acute" (less than three weeks duration) and "chronic" pneumonias. Acute pneumonias are further divided into: 1- The classic bacterial broncho-pneumonias: (such as Streptococcus pneumoniae). 2- The atypical pneumonias : (such as the interstitial pneumonitis of Mycoplasma pneumoniae or Chlamydia pneumoniae). 3- The aspiration pneumonia syndromes.

nini Chronic pneumonias, on the other hand, mainly include: 1- Chronic Bacterial pneumonias: Caused by Nocardia, or Actinomyces. 2- Chronic fungal pneumonias: caused by Blastomyces dermatitidis. 3-The granulomatous pneumonias (bacterial and fungal): (Mycobacterium tuberculosis and atypical mycobacteria), Histoplasma capsulatum and Coccidioides immitis).

a Pneumonia can be also classified according to the place where it was acquired into: 1- Community-acquired pneumonia (CAP). 2- Hospital-acquired pneumonia, also called nosocomial pneumonia. CAP is the most common type of pneumonia. The most common causes of acute bacterial CAP vary depending on a person's age, but they include Streptococcus pneumoniae (50%), viruses, the atypical bacteria, and Haemophilus influenzae (20%). Gram-negative bacteria may cause CAP ( Klebsella pneumonia).

a Hospital-acquired pneumonia, also called nosocomial pneumonia, is pneumonia acquired during or after hospitalization. It occurs at least 72 hrs after admission. Hospitalized patients may have many risk factors for pneumonia, including mechanical ventilation, prolonged malnutrition, heart and lung diseases, and immune disturbances. Hospital-acquired microorganisms may include resistant bacteria such as MRSA, Pseudomonas, Enterobacter, and Serratia, and VRE.

Pathophysiology: Pneumonia frequently starts as a upper respiratory tract infection that moves into the lower respiratory tract. Bacteria can be inhaled into lung alveoli, Once inside, bacteria may invade the spaces between cells and between alveoli through connecting pores. This invasion triggers the immune system to send neutrophils. The neutrophils engulf and kill the offending organisms, and also release cytokines, causing a general activation of the immune system. The neutrophils, bacteria, and fluid from surrounding blood vessels fill the alveoli and interrupt normal oxygen transportation.

Pathophysiology: Pneumonia fills the lung's alveoli with fluid, keeping oxygen from reaching the bloodstream.

a Upper panel shows a normal lung under a microscope. The white spaces are alveoli that contain air. Lower panel shows a lung with pneumonia under a microscope. The alveoli are filled with inflammation and debris.

Etiology and diagnosis: Clinical specimens: Sputum, transtracheal aspirate, Broncheoalveolar lavage, and lung biopsy. Cultural characteristics: Streptococcus pneumonia: All species are Gram’s positive lanceolate shaped cocci arranged in pairs or chains, capsulated and non-spore formers. All species show alpha hemolytic activity on blood agar. All species are optochin sensitive.

Streptococcus pneumoniae: a

Isolation of Gram negative bacilli from sputum specimens: The most important Gram negative bacilli that associated with pneumonia are: 1- Klebsiella pneumoniae. 2- Pseudomonas aeruginosa ( Nosocomial pneumonia) 3- Escherichia coli. 4- Enterobacter and Serratia (Nosocomial pneumonia). All are Gram negative non-spore forming bacilli belong to the Family Enterobactereaceae.

Laboratory identification of Enterobactereacae: Klebsiella pneumoniae and E.coli are lactose fermenters. Pseudomonus species and serratia are none-fermenters.

Growth characteristics of Pseudomonus species on nutrient agar: The exopigment production of pseudomonas on nutrient agar discriminate it from other species. (greenish yellowish pyoverdin).

The granulomatous pneumonias: Some infectious microbes such as Mycobacterium species Cause this type of chronic pneumonia. Granuloma is defined as an aggregation of immune cells (the alveolar macrophage) that engulf invading microbes but it can not kill them. The aggregation of alveolar macrophage which contains available living microbes within lung tissue called granuloma of the lung.

The granulomatous pneumonias: Picture of a granuloma (without necrosis) as seen through a microscope on a glass slide. The granuloma in this picture was found in a lymph node of a patient With Mycobacterium avium infection.

Signs and symptoms of pneumonia: People with infectious pneumonia often have a cough producing greenish or yellow sputum, and a high fever that may be combined with chills. Shortness of breath and chest pain are also common. People with pneumonia may cough up blood, experience headaches. Other possible symptoms are fatigue, blueness of the skin, nausea, vomiting, and joint pains or muscle aches.

Signs and symptoms: a