Molecular techniques for the diagnosis of respiratory bacterial infection

Multiple peripheral pneumococcal mycotic aneurysms without aortic involvement: a unique case confirmed with the novel use of a molecular diagnostic technique

Mycotic aneurysms confer a high morbidity and mortality. Streptococcus pneumoniae aneurysms usually affect the aorta and are rare, although bacterial cultures from aneurysm tissue may be difficult following prior antimicrobial therapy. We report a unique case of mycotic femoral and popliteal artery aneurysms following pneumococcal pneumonia and meningitis, which were managed by resection, revascularization with autologous vein, and intravenous benzylpenicillin. Although blood and aneurysm sac cultures were negative, arterial wall S pneumoniae DNA was detected by polymerase chain reaction (PCR). Appropriate molecular diagnostic techniques can facilitate diagnosis and direct antimicrobial therapy; an important consideration with increasing antimicrobial resistance.

Antibiotic treatment and the diagnosis of Streptococcus pneumoniae in lower respiratory tract infections in adults

OBJECTIVE

To analyze the possible influence of antibiotic treatment on the results of different diagnostic tests for the diagnosis of lower respiratory tract infections with Streptococcus pneumoniae.

MATERIAL AND METHODS

A prospective cohort of 159 unselected adult immunocompetent patients admitted to Silkeborg County Hospital in Denmark with community-acquired lower respiratory tract infections underwent microbiological investigations with fiber-optic bronchoscopy with bronchoalveolar lavage, blood and sputum culture and urine antigen test for type-specific polysaccharide capsular antigens of S. pneumoniae.

RESULTS

When stratified for antibiotic treatment prior to microbiological sampling, three different groups of patients with documented or probable infection with S. pneumoniae could be identified. The first group comprised 14 patients who were culture positive in one or more culture tests, where most (11/14) did not receive any antibiotic treatment within 24 hours of sampling. The second group consisted of nine patients with a positive urine antigen test where 8/9 and 9/9 received antibiotic treatment 24 and 48 hours, respectively, prior to urine sampling. Only a single patient was positive in both systems, making a total of 22 patients with documented pneumococcal infection. As a positive culture test was dependent on the absence of antibiotic treatment, whereas a positive urine antigen test depended on antibiotic treatment within 48 hours, the two tests were complementary in the diagnosis of infection with S. pneumoniae. The third group of patients with probable pneumococcal infection were identified as 26% and 20% of the remaining 137 patients with unknown or known non-pneumococcal etiology, respectively, who received recent antibiotic treatment within 2-4 weeks of diagnostic sampling. By comparison, 0% (p < 0.01) with documented pneumococcal infection received antibiotic treatment in weeks 2-4 prior to microbiological sampling. As such a further eight patients should be expected to have infection with S. pneumoniae but would test negative in both culture tests and the urine antigen test because of antibiotic treatment within weeks 2-4 prior to sampling.

CONCLUSION

The diagnosis of infection with S. pneumoniae is very dependent on whether or not recent (within 2-4 weeks) or immediate (within 48 hours) antibiotic treatment has been given prior to microbiological sampling of patients. The results suggest an optimized diagnostic strategy with, if possible, sampling for culture prior to antibiotic treatment, while sampling for pneumococcal antigens should wait 24-48 hours for antibiotic treatment.

Serological expression cloning and immunological evaluation of MTB48, a novel Mycobacterium tuberculosis antigen

Improved diagnostics are needed for the detection of Mycobacterium tuberculosis, especially for patients with smear-negative disease. To address this problem, we have screened M. tuberculosis (H37Rv and Erdman strains) genomic expression libraries with pooled sera from patients with extrapulmonary disease and with sera from patients with elevated reactivity with M. tuberculosis lysate. Both serum pools were reactive with clones expressing a recombinant protein referred to here as MTB48. The genomic sequence of the resulting clones was identical to that of the M. tuberculosis H37Rv isolate and showed 99% identity to the Mycobacterium bovis and M. bovis BCG isolate sequences. The genomic location of this sequence is 826 bp upstream of a region containing the esat-6 gene that is deleted in the M. bovis BCG isolate. The mtb48 1,380-bp open reading frame encodes a predicted 47.6-kDa polypeptide with no known function. Southern and Western blot analyses indicate that this sequence is present in a single copy and is conserved in the M. tuberculosis and M. bovis isolates tested but not in other mycobacterial species tested, including Mycobacterium leprae and Mycobacterium avium. In addition, the native protein was detected in the cytoplasm, as was a processed form that was also shed into the medium during culture. Serological analysis of recombinant MTB48 and the M. tuberculosis 38-kDa antigen with a panel of patient and control sera indicates that the inclusion of recombinant MTB48 in a prototype serodiagnostic test increases assay sensitivity for M. tuberculosis infection when it is combined with other known immunodominant antigens, such as the 38-kDa antigen.

Inadequate antimicrobial treatment: an important determinant of outcome for hospitalized patients

Inadequate antimicrobial treatment, generally defined as microbiological documentation of an infection that is not being effectively treated, is an important factor in the emergence of infections due to antibiotic-resistant bacteria. Factors that contribute to inadequate antimicrobial treatment of hospitalized patients include prior antibiotic exposure, use of broad-spectrum antibiotics, prolonged length of stay, prolonged mechanical ventilation, and presence of invasive devices. Strategies to minimize inadequate treatment include consulting an infectious disease specialist, using antibiotic practice guidelines, and identifying quicker methods of microbiological identification. In addition, clinicians should determine the prevailing pathogens that account for the community-acquired and nosocomial infections identified in their hospitals. Clinicians can improve antimicrobial treatment by using empirical combination antibiotic therapy based on individual patient characteristics and the predominant bacterial flora and their antibiotic susceptibility profiles. This broad-spectrum therapy can then be narrowed when initial culture results are received. Further study evaluating the use of antibiotic practice guidelines and strategies to reduce inadequate treatment is necessary to determine their impact on patient outcomes.

Community-acquired pneumonia

Community-acquired pneumonia (CAP) remains a leading cause of morbidity and mortality worldwide and has significant financial implications for health-care systems. The epidemiology and fundamental biology of the disease has evolved, reflecting the human immunodeficiency virus pandemic, increasing world travel, and, as always, poverty. The promise held out by molecular diagnostic technology has yet to deliver in this arena, and antibiotic resistance continues to drive the quest for new antimicrobial agents. The emergence of multidrug-resistant Streptococcus pneumoniae, the microorganism most often implicated as a cause of CAP, continues to threaten treatment options. The evolution of this organism, the persistently high mortality rate associated with CAP, and increasing health-care costs have prompted the publication of guidelines by various authorities that can be used to assist in the initial assessment of the patient and then guide empirical antimicrobial therapy. It is unclear whether these guidelines will have significant impact on cost and mortality, although the trend toward a rational and evidence-based approach to antimicrobial therapy must be a goal to aspire to.