Laboratory Investigations for Pneumococcal Disease

Introduction:

Pneumococcal disease is a major health concern. Streptococcus pneumoniae causes pneumococcal disease. It can cause serious invasive pneumococcal diseases such as bacteremia, meningitis, or pneumonia and non-invasive pneumococcal conditions such as otitis media and sinusitis. There is a need for accurate laboratory tests to diagnose and treat pneumococcal diseases. The article discusses laboratory investigations for pneumococcal disease.

What Are the Laboratory Investigations for Pneumococcal Disease?

Laboratory investigations for pneumococcal disease involve a combination of sample collection and microbiological, molecular, and serological methods. Several laboratory diagnostic methods are described below:

1. Sample Collection and Preparation: The first step in diagnosing pneumococcal disease is the sample collection. It aids in effective diagnosis. The laboratory personnel may collect the following samples to detect the presence of the culprit bacteria.

• Blood: A blood sample can be collected to check for the presence of bacteria, such as Streptococcus pneumoniae, bacteremia, or sepsis (when the body responds abnormally to an infection and causes organ damage).

• Sputum: The sputum sample is collected in suspected pneumonia cases.

• Cerebrospinal Fluid (CSF): CSF can be collected to diagnose pneumococcal meningitis (bacterial infection of the meninges, which is the outer covering of the brain and spinal cord).

• Pleural and Synovial Fluids: Pleural and synovial fluids can be collected in the case of localized infections.

• Nasopharyngeal Swabs: The nasopharyngeal swabs are mainly taken in the cases of asymptomatic carriers.

2. Microscopy Method: The doctor can guess the patient's condition by microscopy. This method is quick, and the sensitivity of the method depends on the type of sample and bacterial load.

• Gram Staining: Gram staining of the sputum appears as gram-positive, lancet-shaped cocci in pairs (diplococci). Antimicrobial therapy alters the appearance of these cocci. In addition, over-colorization of the stain can give false results and show that they are Gram-negative diplococci. For the identification of pneumococci, fresh emulsified sputum can be mixed with antiserum and cause swelling. To identify acute pneumococcal otitis media, Gram staining of the fluid smear from the middle ear is done to find the culprit bacteria.

• Capsule Stain: The polysaccharide capsule is demonstrated to diagnose pneumococcal meningitis in cerebrospinal fluid patients.

3. Culture Method: The culture method is the gold standard method to find Streptococcus pneumoniae. It provides a definite diagnosis of pneumococcal disease.

• Blood Agar Plates: The sputum or blood sample is plated on the blood agar plates and incubated overnight at 37 degrees Celsius in the presence of five percent carbon dioxide. Streptococcus pneumonia appears to be small and greyish in color, surrounded by a greenish zone of alpha hemolysis (partial hemolysis).

4. Identification of Bacteria:

• Bile Solubility Test: This test is performed to identify the presence of the bacteria. It is based on Streptococcus pneumoniae autolysis. It identifies autolytic enzymes present in the pneumococci by breaking the bond between the muramic and alanine acids of the pneumococcal cell wall. After exposure to bile, S. pneumoniae is isolated.

• Optochin Sensitivity Test: Pneumococci are sensitive to optochin. Optochin is an antibacterial agent that helps find Streptococci. Blood agar plates are used, and a disk-saturated optochin is placed in the middle of the inoculum. After overnight incubation, the zone of bacterial inhibition around the disk is seen.

• Inulin Fermentation Test: The test helps in inulin fermentation and differentiates it from other types of streptococci bacteria.

5. Antigen Detection: This is a rapid diagnostic method performed on a urine sample. It is also performed if bacterial culture is unavailable.

• Latex Agglutination Test: It uses latex particles to find pneumococcal capsular antigens with high specificity.

• Immunochromatographic Assays: The urine sample is taken to find pneumococcal antigens in the cases of invasive pneumonia.

6. Antibody Detection: During this test, an indirect fluorescent antibody test and ELISA (enzyme-linked immunosorbent assay) are used to find specific pneumococcal antibodies in cases of invasive pneumonia.

7. Molecular Diagnostics: Due to its specificity and sensitivity, this test is gaining prominence.

• Polymerase Chain Reaction: A nucleic acid amplification test like polymerase chain reaction (PCR) is an important diagnostic tool. It identifies even minute amounts of nucleic acid in all types of pneumococcal pathogens. It provides results in a short time. In blood samples, PCR provides sensitivity for detecting Streptococcus pneumoniae. This test identifies pneumococcal deoxyribose nucleic acid (DNA) in samples. Real-time PCR assays can find serotypes and differentiate pneumococci bacteria from other types of related bacteria.

What Are the Challenges in Laboratory Diagnosis for Pneumococcal Disease?

Despite several advancements, laboratory diagnosis for pneumococcal disease faces several challenges that are described below:

• Some laboratory tests show false negative results. This can be due to previous antibiotic use or a low bacterial load.

• Some laboratory tests for pneumococcal disease can be costly and require skilled personnel.

• Sample collection can be challenging because the sample could be contaminated with other microorganisms and show false negative results.

• In low- and middle-income countries, the resources are scarce.

• Improper sample storage and delay in sample transport can show false negative results.

How to Overcome Challenges Associated With Laboratory Diagnosis for Pneumococcal Disease?

Several strategies to overcome challenges associated with laboratory diagnosis for pneumococcal disease are as follows:

• Trained personnel or healthcare workers in sample handling, storage, and transportation.

• Provide portable kits in rural or remote areas to detect pneumococcal antigens.

• Regular surveillance of antibiotic resistance patterns.

• Proper communication between laboratory technicians and clinicians is necessary to help interpret results better.

• Promote pneumococcal vaccination to decrease pneumococcal disease cases.

Conclusion

Pneumococcal disease is a bacterial infection caused by Streptococcus pneumoniae. The person may experience a blocked nose, headache, and headache. Several diagnostic tests may help detect pneumococcal disease. These include sample collection, microscopy method, culture method, bile sensitivity test, optochin test, antigen detection, and antibody detection. There are several challenges associated with laboratory diagnosis for pneumococcal disease, such as its cost, less resources, and unskilled personnel. To overcome this, healthcare providers should receive training and awareness of pneumococcal vaccination should be promoted among the public.