Use of a modified fluorescent in situ hybridization procedure to improve the identification of Streptococcus pneumoniae in blood cultures.
Streptococcus pneumoniae is an important causative agent for bacteremia. Fluorescent in situ hybridization (FISH) is a helpful molecular technique for the rapid identification of S. pneumoniae in positive blood cultures. There are many reports concerning the application of an enzymatic treatment with lysozyme in the FISH procedure for partial cell wall digestion of S. pneumoniae. However, this study was aimed to test the FISH procedure without enzymatic treatment for the identification of S. pneumoniae in blood culture specimens. Seventy-seven positive blood culture specimens containing Gram-positive cocci were examined by both the conventional laboratory methods and FISH. Detection of S. pneumoniae was performed by two FISH procedures: one procedure was performed with an enzymatic treatment step and the other one was done without enzymatic treatment. In addition, the specimens were tested by the FISH procedure with enzymatic treatment to detect Streptococcus pyogenes and Enterococcus. The specificity of FISH in comparison with conventional culture methods was 100%. The sensitivity of the FISH procedure with enzymatic treatment for the detection of S. pneumoniae was 90%, whereas, the sensitivity of the FISH procedure without enzymatic treatment was 100%. In fact, by omission of enzymatic treatment, detection of S. pneumoniae was improved in 6 specimens. The results of the FISH and culture methods for the detection of S. pyogenes and Enterococcus were compatible. Altogether, FISH procedure without enzymatic treatment step seems to improve the detection of S. pneumoniae in some cases. Thus, for successful detection of S. pneumoniae, we suggest the application of both FISH procedures (the procedure with enzymatic treatment and the procedure without enzymatic treatment) for each blood culture specimen.
Bushehr University of Medical Sciences Department of Microbiology and Parasitology, Faculty of Medicine P. O. Box 3631 Bushehr Iran Bushehr University of Medical Sciences The Persian Gulf Tropical Medicine Research Center Bushehr Iran.
Saeed
S
Tajbakhsh
Somayyeh
S
Gharibi
Keivan
K
Zandi
Ramin
R
Yaghobi
D016470:Bacteremia / Q000382:microbiology*; D015373:Bacterial Typing Techniques; D017931:DNA Primers / Q000235:genetics; D016983:Enterococcus / Q000235:genetics / Q000302:isolation & purification; D006801:Humans; D017404:In Situ Hybridization, Fluorescence / Q000379:methods*; D009113:Muramidase; D015345:Oligonucleotide Probes; D012680:Sensitivity and Specificity; D013296:Streptococcus pneumoniae / Q000235:genetics / Q000302:isolation & purification*; D013297:Streptococcus pyogenes / Q000235:genetics / Q000302:isolation & purification
D017931:DNA Primers; D015345:Oligonucleotide Probes; D009113:Muramidase