Assessment of rapid methods of pneumococcal antigen detection in routine sputum bacteriology

Prospective study to determine clinical relevance of detection of pneumococcal DNA in sera of children by PCR

We undertook a prospective study to evaluate the accuracy of PCR of serum (aimed at the pneumococcal pneumolysin gene) at detecting pneumococcal infections in infants and children. The assay was positive for all blood and cerebrospinal fluid culture-positive samples and for 38 and 44% of patients with lobar pneumonia and acute otitis media, respectively. It was positive for 17% of healthy controls. There was a marked effect of age on the rate of positivity among healthy controls, with the highest rate (33%) being in 2-year-old children, the age group with the highest rate of nasopharyngeal (NP) carriage; the lowest rate was found among infants <2 months of age (13%) and adults ages 18 to 50 years (0%), age groups with the lowest NP pneumococcal carriage rates. Carriers of pneumococci in the nasopharynges had a higher rate of positivity than noncarriers of pneumococci in the nasopharynges for all groups. Our results suggest that although PCR of serum is a sensitive test for the detection of Streptococcus pneumoniae in sterile fluids, its high rate of positivity for healthy controls, related to NP pneumococcal carriage, might exclude it from being useful in detecting deep-seated pneumococcal infections.

Immunoreactivity of five monoclonal antibodies against the 37-kilodalton common cell wall protein (PsaA) of Streptococcus pneumoniae

Five monoclonal antibodies (MAbs) were produced against the Streptococcus pneumoniae pneumococcal surface adhesin A (PsaA) 37-kDa common cell wall protein. These antibodies were used in a dot immunoblot and Western blot study of clinical isolates of S. pneumoniae to detect the presence of the protein. By both assays, the MAbs reacted with clinical isolates representing the 23 type-specific serotypes present in the licensed pneumococcal polysaccharide vaccine. Western blot analysis confirmed the presence of a protein migrating in the gel with a molecular mass of 37 kDa. An extension of the study by using dot immunoblot analysis that included an analysis of the 90 serotypes of S. pneumoniae showed that all five MAbs reacted with 89 of the 90 serotypes tested. MAb 1B6, the exception, did not react with S. pneumoniae serotype 16F. Dot immunoblot analysis of the MAbs with Enterococcus faecalis and viridans streptococci showed varied reactivity patterns, depending on the species. The MAbs against the 37-kDa antigen did not react with Escherichia coli, respiratory pathogens, or nonpathogens representing 22 genera and 29 species of bacteria. All five MAbs also reacted with five multidrug-resistant strains of S. pneumoniae. In summary, these MAbs may be useful for detection of pneumococcal antigen and may lead to the development of diagnostic assays for pneumococcal disease.

Pneumococci in nasopharyngeal samples from Filipino children with acute respiratory infections

The presence of Streptococcus pneumoniae in the upper respiratory tract was studied in 318 Filipino children less than 5 years old with an acute lower respiratory tract infection. Nasopharyngeal samples were obtained from 292 children. With both quantitative bacterial culture and detection of capsular polysaccharide antigens by coagglutination, counterimmunoelectrophoresis, and latex agglutination, pneumococci were found in 160 (70%) of the 227 samples eligible for analysis. Culture was positive in 115 samples and antigen was positive in 140 samples. The culture isolation rate was significantly lower if the patient had received antimicrobial agents in the 48 h prior to the sampling. The seven most common types or groups of pneumococci were 6, 14, 19, 23, 15, 7, and 11, which together accounted for 64% of all pneumococcal findings.

Evaluation of polymerase chain reaction for diagnosis of pneumococcal pneumonia

To test the ability of the polymerase chain reaction (PCR) to detect Streptococcus pneumoniae in blood, we generated two sets of nested primers. The first defined 559-bp and 649-bp regions of the pneumolysin gene, and the second defined 445-bp and 553-bp regions of the autolysin gene. These nucleotide segments were detected in DNAs from isolates of all 20 pneumococcal serotypes tested, but they were not detected when used to test DNAs from 41 isolates of nonpneumococcal bacteria and fungi. The sensitivity was evaluated by using purified pneumococcal DNA. We were able to detect 10 fg of S. pneumoniae DNA, or 4.3 genome equivalents. Blood samples were obtained from 16 patients with culture-proven pneumococcal bacteremia and were subjected to PCR analysis. Of eight buffy coat fractions tested, six showed reactivity in the PCR with the pneumolysin primers, and five of the eight produced the expected products when tested with the autolysin primers (sensitivities, 75 and 63%, respectively). Of the eight whole-blood specimens tested, only three produced the expected products with either set of primers. Additionally, we tested 14 samples from patients with bacteremia that were culture positive for nonpneumococcal bacterial species, and 13 were negative (specificity, 93%). This combination of sensitivity and specificity may make detection of S. pneumoniae in blood by PCR in comparison with that by blood culture a very promising alternative for a means of definitive diagnosis.

Rapid detection of pneumococcal antigen in pleural fluid of patients with community acquired pneumonia

BACKGROUND

Detection of pneumococcal antigen may help to increase the rate of diagnosis of pneumococcal pneumonia. This study was designed to determine the value of rapid detection of pneumococcal antigen in pleural fluid from patients with community acquired pneumonia.

METHODS

Thoracentesis was performed in patients suspected of having empyema and in patients with pneumonia of unknown aetiology. Pneumococcal capsular antigen was detected by latex agglutination and this method was compared with Gram staining and culture, specimens of pleural fluid being examined in parallel by the three methods.

RESULTS

Pleural fluid was radiographically identified in 63 of 135 patients with community acquired pneumonia. In nine of 45 patients with pneumococcal pneumonia and pleural fluid pneumococci were identified by Gram stain in two and by culture in one specimen of pleural fluid, whereas antigen was detected in eight of these specimens. In 12 of 33 patients with pneumonia of other known aetiology only one pleural fluid specimen was antigen positive, providing a specificity of 92% for this test. Pleural fluid obtained from 12 of 58 patients with pneumonia of unknown aetiology yielded detectable antigen in seven cases.

CONCLUSIONS

Detection of pneumococcal antigen by latex agglutination in pleural fluid may yield important and rapid information in patients with community acquired pneumonia.

Pneumococcal antigen persistence in sputum from patients with community-acquired pneumonia

The purpose of this study was to establish the diagnostic value of pneumococcal capsular antigen by comparing this with the results of Gram stain and culture in representative and nonrepresentative sputa during follow-up in patients with community-acquired pneumonia. Antigen was detected by a latex particle agglutination test. At the time of hospital admission, antigen was detected in 17 representative sputum specimens from 30 patients with pneumococcal pneumonia, which was comparable to the results of Gram stain and culture. In five additional patients, antigen was demonstrated in nonrepresentative specimens. During follow-up under antibiotic treatment, this number increased by six: three patients with representative and three patients with nonrepresentative sputum, respectively. Two of the 22 patients with pneumonia of other known cause had an antigen-positive sputum on admission and in another two patients, sputum antigen was detected during follow-up. Ten of 34 patients with pneumonia of unknown cause had detectable antigen in representative or nonrepresentative sputum on admission. During follow-up, antigen was detected in sputa of an additional seven patients. There was no difference in duration of antigen persistence between patients with pneumococcal pneumonia and pneumonia of unknown cause. It was observed that the first antigen-positive sputum specimen was always detected within the first five days of the hospital stay. We conclude that antigen detection in both representative and nonrepresentative sputum specimens at the time of hospital admission and during follow-up is of additional value for the diagnosis of pneumococcal pneumonia. It markedly increases the number of patients with pneumococcal pneumonia detected, who would otherwise be considered to have pneumonia of unknown cause. However, antigen-positive results should be interpreted carefully, especially in those pneumonia patients with chronic bronchitis, because detectable antigen may be caused by pneumococcal carriership of the lower respiratory tract.

Evaluation of a latex test for rapid detection of pneumococcal antigens in sputum

A latex agglutination test (Directigen) for detection of pneumococcal capsular polysaccharide antigens in sputum was evaluated in comparison to culture and Gram stain using 121 sputum specimens. The sensitivity, specificity and rate of agreement of the latex test compared to culture were 90%, 79% and 81%, respectively. The results suggest that the latex test may be useful for detecting pneumococcal antigen in sputum.

Quantitation of pneumococcal C polysaccharide in sputum samples from patients with presumptive pneumococcal pneumonia by enzyme immunoassay

Although the Gram stain and culture of expectorated sputum are considered standard methods for the diagnosis of presumptive pneumococcal pneumonia, these methods remain relatively insensitive and nonspecific. We developed an enzyme immunoassay (EIA) for the quantitation of pneumococcal C polysaccharide (PnC) in the sputum of patients with presumptive pneumococcal pneumonia. Of 34 patient sputum samples collected within 24 h of the first radiographic report of pneumonia, 12 grew Streptococcus pneumoniae on culture. By using a cutoff point of 0.5 micrograms of PnC per ml of sputum, all 12 specimens were positive (sensitivity, 100%) by EIA. PnC levels ranged from 1.43 to 57.53 micrograms/ml. Blood samples from 18 of the 34 patients were cultured. S. pneumoniae grew in the culture of a blood sample from one patient, whose sputum also had the highest PnC level. Of 22 sputum samples from patients with pneumonia that did not grow S. pneumonia, two were positive by EIA (specificity, 90.1%). Sputa from both patients had low levels of PnC (2.7 and 4.5 micrograms/ml), and both patients had received antibiotics before sputum collection. The positive predictive value of the quantitative EIA was 85.7%. Quantitation of PnC has the potential for improving the accuracy of sputum examination for S. pneumoniae, monitoring disease severity and the effectiveness of antibiotic therapy, and differentiating between those patients with invasive pneumococcal disease and those who are carriers of S. pneumoniae.

Pneumococcal capsular antigen detection and pneumococcal serology in patients with community acquired pneumonia

BACKGROUND

Methods to determine the microbial cause of community acquired pneumonia include detection of pneumococcal antigen and measurement of pneumococcal capsular antibody response. Their usefulness compared with conventional microbiological techniques was investigated in patients with pneumonia, some of whom had been treated with antibiotics.

METHODS

Pneumococcal capsular antigen was detected by latex agglutination in sputum and the results compared prospectively with results of conventional microbiological techniques in 90 patients with community acquired pneumonia. Serum, urine, and pleural fluid samples were also tested for antigen. Serum pneumococcal capsular antibody titres were measured.

RESULTS

A diagnosis was established by conventional microbiological techniques in 53 patients, 30 of whom had pneumococcal pneumonia. The sensitivity of antigen detection in first day sputum specimens (n = 18) in those with pneumococcal pneumonia was 94%; antigen was present in 23 of the 27 patients who produced representative sputum on admission and during follow up. The specificity of antigen detection in sputum in patients with non-pneumococcal pneumonia and lung infarction was 87%. Antigen was present in 12 of 25 patients with pneumonia of unknown aetiology who produced representative sputum. Antigen was rarely detected in serum and urine, but was present in pleural fluid in three of four patients with pneumococcal pneumonia and in all four patients with pneumonia of unknown aetiology. Pneumococcal antigen remained detectable in patients treated with antibiotics. Pneumococcal capsular antibody detection was as specific (85%) as antigen detection, but had a lower sensitivity (50%).

CONCLUSION

Pneumococcal antigen detection in sputum or pleural fluid is of value in making a rapid diagnosis and provides an additional diagnostic result in patients with pneumococcal pneumonia, especially those receiving antibiotic treatment.

Antigen detection in pneumococcal pneumonia

Streptococcus pneumoniae remains the commonest proven cause of community-acquired pneumonia in patients admitted to hospital, but no currently available diagnostic method can be regarded as a gold standard. Microscopy of sputum is usually considered insensitive and poorly specific, and more invasively-obtained specimens are not routinely collected. Cultures of blood and respiratory secretions, and countercurrent immunoelectrophoresis (CIE) and particle agglutination-based assays for capsular polysaccharides in serum and urine specimens, are specific but less than ideally sensitive. Some workers have reported specificity problems when immunoassays are applied to respiratory secretions. New diagnostic methods include detection of pneumococcal C polysaccharide in sputum and urine by ELISA and particle-agglutination assays, and these appear promisingly sensitive and specific in preliminary studies. Clinical assessments are now required to define the role of these techniques in guiding the treatment of individual patients.

Monoclonal antibody recognizing a species-specific protein from Streptococcus pneumoniae

Monoclonal antibodies (MAbs) against a nonencapsulated strain (R36A) of Streptococcus pneumoniae were produced to aid in a search for antigens common to this species. By Western immunoblot analysis, a species-specific 37-kilodalton (kDa) protein was found in lysates of 24 different encapsulated strains of S. pneumoniae. Monoclonal antibodies against the 37-kDa antigen did not react with 55 heterologous strains representing 19 genera and 36 species of bacteria that can also cause acute lower respiratory tract disease. Immunogold staining suggests that the antigen is synthesized inside the pneumococcal cell. However, MAbs to the 37-kDa antigen bound whole cells in the enzyme-linked immunosorbent assay and the indirect immunofluorescence assay. Antibody-binding epitopes of the antigen are probably exposed on the outer surface of the pneumococcus cell wall. The effectiveness of the 37-kDa antigen as a useful diagnostic marker is under study.

Rapid streptococcal antigen detection in experimental keratitis

We assessed the role of commercially available immunodiagnostic procedures in comparison to Gram stain and culture in experimental bacterial keratitis. Rabbit corneas were inoculated with Streptococcus pneumoniae, S. pyogenes, S. faecalis, or Haemophilus influenzae. Corneal scrapings were processed before and during antibacterial therapy using a coagglutination assay to detect pneumococcal capsular antigen (Phadebact Pneumococcus test) and an enzyme immunoassay to detect group A streptococcal cell-wall antigen (TestPack Strep A test). In untreated infected eyes, both immunoassays were highly specific and as sensitive as Gram stain for detection of the respective microorganisms. For S. pneumoniae keratitis, the sensitivity of coagglutination was 82% and Gram stain, 73%. For S. pyogenes keratitis, the sensitivity of enzyme immunoassay was 100% and Gram stain, 62%. Immunoassays and Gram stain were less sensitive than culture during antibacterial therapy. Successful clinical application of the coagglutination assay in a patient with pneumococcal keratitis permitted early use of specific cephalosporin treatment.

Rapid detection of pneumococcal antigens in sputa in patients with community-acquired pneumonia by coagglutination

This paper introduces the clinical use of coagglutination as a method for the rapid detection of pneumococcal antigens in patients with community-acquired pneumonia and compares it with the sputum Gram stain and culture methods. Among 105 patients, 50 (48%) were diagnosed as having pneumococcal pneumonia by at least one of the three methods. Of 95 sputa tested, 44 (46%) were found to be positive by the coagulation test, 26 (27%) by Gram staining and only 16 (17%) by the bacterial culture method. The rate of detection of pneumococcal antigens was thus greater with coagulation than with either of the other two methods. The differences were very significant (both P less than 0.01). Our study indicates that the advantages of coagglutination over the traditional bacteriological methods are its speed, sensitivity, convenience and also its relative independence of antibiotic therapy. It thus provides a new dimension in the aetiological diagnosis of pneumococcal pneumonia.

Evaluation of anaerobic culture and effect of culture medium supplementation with factor V on colonial morphology and efficacy of isolation of Streptococcus pneumoniae from sputum

The use of anaerobic incubation for the culture of Streptococcus pneumoniae from sputum was compared with incubation in carbon dioxide in air. A coagglutination test for pneumococcal antigen was used as an index of the number of specimens containing pneumococci. A total of 334 specimens were examined. There was evidence of pneumococcal colonisation by culture or coagglutination, or both, in 48 (14.37%), of which 41 (12.27%) yielded S pneumoniae on culture. Anaerobic incubation was better than incubation in carbon dioxide in air for the primary culture of S pneumoniae from sputum. Primary isolation of S pneumoniae was achieved in 11 of the 41 strains (26.82%) by anaerobic incubation alone, by incubation only in carbon dioxide in air in one strain (2.43%), and by both anaerobic incubation and incubation in carbon dioxide in air in 29 strains (70.73%). Anaerobic incubation gave large moist or mucoid colonies that were easy to recognise, but it suppressed the typical draughtsman colony of S pneumoniae. The factor V supplement routinely used in our medium also inhibited the formation of draughtsman colonies. It is suggested that draughtsman colonies occur because of a relative lack of the coenzyme nicotinamide adenine dinucleotide (factor V), which is required as a reducing agent in aspartate and glutamate metabolism. This nutritional deficiency may lead to bacterial cell wall defect and hence to the autolysis which gives the typical draughtsman colony.