A modified PCR-based method for rapid non-radioactive detection of clinically important pathogens

Molecular diagnostics of clinically important staphylococci

Bacterial species of the genus Staphylococcus known as important human and animal pathogens are the cause of a number of severe infectious diseases. Apart from the major pathogen Staphylococcus aureus, other species until recently considered to be nonpathogenic may also be involved in serious infections. Rapid and accurate identification of the disease-causing agent is therefore prerequisite for disease control and epidemiological surveillance. Modern methods for identification and typing of bacterial species are based on genome analysis and have many advantages compared to phenotypic methods. The genotypic methods currently used in molecular diagnostics of staphylococcal species, particularly of S. aureus, are reviewed. Attention is also paid to new molecular methods with the highest discriminatory power. Efforts made to achieve interlaboratory reproducibility of diagnostic methods are presented.

Accuracy of a polymerase chain reaction-based assay for detection of pneumococcal bacteremia in children

OBJECTIVE

To evaluate the utility of a polymerase chain reaction (PCR)-based assay for identifying pneumococcal DNA in the blood of pediatric patients with suspected bacteremia.

METHODS

Children evaluated at the Children's Hospital of Pittsburgh who were having blood drawn for culture had an additional 2 to 3 mL of blood (from the same sampling) obtained and placed in a sodium citrate tube for PCR processing (study group). The control group for this study consisted of children having blood drawn for biochemical analysis who were afebrile, well-appearing, and had no recent illnesses. Specimens were frozen at -70 degrees C and then batch-processed for PCR-based analyses with the JM201/202-204 primer/probe set. Amplified products were detected after liquid hybridization format wherein a 32P end-labeled probe was annealed to the amplified DNA and visualized by autoradiographic analysis after gel retardation.

RESULTS

Four hundred eighty study group patients and 103 controls had specimens tested by both PCR and blood culture. Twenty-six (5%) patients had a positive blood culture for a pathogenic organism (21 of which were Streptococcus pneumoniae). Twelve (57%) of the 21 patients with blood cultures positive for S pneumoniae also were positive by PCR. In addition, 206 study group patients and 16 controls with negative blood cultures had positive PCR results. A greater proportion of study group patients were PCR-positive/culture-negative than were controls (206/459 vs 16/103).

CONCLUSION

Although this assay currently lacks adequate sensitivity and specificity for clinical use, the high frequency of PCR-positive cases in patients with suspected bacteremia may indicate a greater role for S pneumoniae than had previously been appreciated. Further refinement of this assay as well as the development of a rapid PCR-based assay appears warranted.