Persistent cough, and cough with sputum is the most common symptom of bacterial pneumonia.

The color of the sputum can help determine the type of pathogen that has caused the infection, for example: rust-colored sputum is due to Streptococcus pneumonia, while if the infection is caused by Pseudomonas, Haemophilus, and pneumococcal species, the color of sputum is green. Infections due to anaerobic bacteria produce foul-smelling sputum.

Some of the other symptoms of bacterial pneumonia are yperthermia or hypothermia, tachypnea, tachycardia, central cyanosis, and mental impairment.

Physical findings in patient with bacterial pneumonia are significant breath sounds such as wheezes, crackles or rhonchi, reduction in the intensity of the sound, lymphadenopathy and deviation of the trachea [7].

Severity Assessment: There are some tools to assess the severity of the bacterial pneumonia and the risk of death associated with it. They include:

• PSI/PORT: Pneumonia severity index/Patient Outcomes Research Team score
• CURB-65 system: Confusion, urea, respiratory rate, blood pressure, and age >65 years
• APACHE: Acute physiology and chronic health evaluation

Laboratory tests: Some of the important laboratory tests to assess the severity of illness of the bacterial pneumonia are: Serum chemistry panel, determination of arterial blood gas (ABG) and venous blood gas, complete blood count (CBC) with differential, serum lactate and free cortisol value. 

Sputum evaluation: Before initiating the antibiotic therapy, the sputum is subjected to Gram stain and culture. In Gram staining, a single microbe must be identified, though mixed flora is observed in patients infected with anaerobic bacteria.

Imaging Studies: Chest radiography and chest ultrasonography are some of the imaging tests that can also be performed. 

Bronchoscopy: The bronchial specimen can be obtained with the help of fiberoptic bronchoscope. The bronchoalveolar lavage can be used to perform the fluid analysis and culture.

Thoracentesis: In patients with parapneumonic pleural effusion, the analysis of the fluid is beneficial in identifying between the simple and complicated effusions. 

Pathogen specific tests: Sputum, serum, serologic and urine tests are considered as pathogen specific tests [8].

• Antibiotics: The mainstay of the treatment of bacterial pneumonia is antibiotics. For managing infections by Streptococcus pneumoniae (most common cause of bacterial pneumonia), the first line of treatment is penicillin-G and amoxicillin. For penicillin-resistant form of this bacterium, sensitivity tests for identifying the appropriate antibiotics are conducted.
• Supportive measures to manage bacterial infections are symptomatic treatment with analgesia, antipyretics, oxygen supplementation, intravenous fluids, respiratory therapy, suctioning and ventilation, use of intravenous fluids and chest physiotherapy. 
• Proper hydration and nutrition also are important to manage the problems associated with bacterial pneumonia [9].

Most of the patients who suffer from bacterial pneumonia recuperate well with antibiotics. Patients, who develop complications of bacterial pneumonia, including sepsis, lung failure and meningitis, often die.

Though there is no possible method to predict the severity of the complications, patients with chronic medical conditions, or with low immunity is at a higher risk of complications.

Complications

Patients with pneumonia are often treated successfully with antibiotics, though some people may develop complications. Some of the complications of bacterial pneumonia are:

• Bacteremia: In some patients, the bacteria can enter the bloodstream from the lungs parenchyma, thus spreading to the other organs, causing organ failure, a condition referred to as bacteremia.
  
• Lung abscess: When pus forms in the cavity of the lungs, it is called an abscess. This condition can be successfully treated with antibiotics or by surgery. 
• Pleural effusion: In this condition, fluid is accumulated around the lungs. In pneumonia, fluid is built up in the thin space between the linings of the lungs and the chest called pleura. If this fluid is infected, it must be drained with the help of a chest tube or surgery. 
• Breathing problems: Patients with pneumonia often complain about difficulty in breathing enough oxygen. In severe cases, the patients are hospitalized and mechanical ventilator is used to assist breathing.

The bacteria that cause community acquired pneumonia (CAP) in an outpatient setting are Klebsiella pneumonia, Streptococcus pneumoniae, and Haemophilus influenzae.

In non-intensive care unit, inpatient setting, the most common etiologies of CAP is Streptococcus pneumoniae, Klebsiella pneumonia, Haemophilus influenzae, Mycoplasma pneumoniae, and Legionella species. These infections are common in summer with the source of organisms arising from air conditioning systems.

In about 27% of the all the intubated patients, ventilator-associated pneumonia (VAP) develop, causing mortality as high as 30-60% [3] [4].

Acute lower respiratory tract infections are one of the leading causes of death and hospitalization across the world. In fact, this type of infection is greater burden than HIV infection, cancer or malaria. Since the epidemiology of the disease varies significantly worldwide, the discussion of the international burden of the disease becomes difficult.

Pneumonia is prevalent in the winter, often resulting in impaired host defenses to bacterial superinfection. Race, gender and age also play a role in the pathogenesis of the bacterial pneumonia. For example, though the incidence of bacterial pneumonia is more in men than women, the number of deaths is higher among females. Advanced age increases the mortality from pneumonia. Compromised immune system and comorbidity often increase the chances of infection from bacteria [3] [4] [5] [6].

The cause of bacterial pneumonia is both extrinsic and intrinsic. Several types of bacteria have been noted that can cause this type of pneumonia. While the extrinsic factors include exposure to pulmonary irritants, causative agents and/or pulmonary injury, intrinsic factors are those related to the host, such as loss of the protective airway reflexes due to the altered mental status due to intoxication or stroke.

Bacteria find their way to the parenchyma of the lungs, causing bacterial pneumonia. Impaired immune response, dysfunctioning of the defense mechanisms and poor dentition are some of the predisposing factors of the disease.

This pulmonary infection causes acute inflammation of the parenchyma, causing the neutrophils to migrate to the air spaces, ready to respond to the situation. These neutrophils kill the microbes and also form a chromatin mesh-work to entrap and kill the extracellular bacteria [6].

Bacterial pneumonia can be prevented by following the under said measures:

• Getting vaccinated: Seasonal flu-shots and pneumonia vaccine
• Quit smoking
• Maintaining proper hygiene
• Exercise regularly [10].

The inflammation of the parenchyma of the lung is defined as pneumonia. This inflammation is caused by infection by the bacteria or virus. Sometimes, inhalation of chemicals, or trauma and infection of the chest wall can also contribute to the pneumonia. When the etiology of the pneumonia is a bacterium, it is called bacterial pneumonia [1] [2] [3].

Definition

Bacterial pneumonia is the infection and inflammation of the pleura of the lungs caused by the bacteria such as Streptococcus pneumoniae, Pseudomonas, Haemophilus, and pneumococcal species. 

Cause

Both the external and the internal factors of the host are responsible for the infected associated with bacterial pneumonia. Pathogens cause the infection and a weakened immune system allows for the easier passage of these microbes to the host body causing infection.

Symptoms

The most common symptom of bacterial pneumonia is persistent cough which precipitates into production of sputum. Other symptoms are fever, altered heart rate, significant breath sounds and difficulty in breathing. Patients with bacterial pneumonia have reported mental instability.

Diagnosis

Severity of the bacterial pneumonia can be determined by severity scores such as APACHE, and PSI/PORT. There are some laboratory tests that may be performed such as blood tests to identify the serum chemistry panel, complete blood count (CBC) with differential and urine tests. Sputum of the patient is also evaluated to assess the type of bacteria. Imaging studies such as chest radiography or chest ultrasonography are also suggested. Patients may be advised to get bronchoscopy and thoracentesis done. 

Treatment

Antibiotics are the mainstay in the treatment of bacterial pneumonia with good prognosis.

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