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Open Access Research article

Identification of Streptococcus agalactiae by fluorescent in situ hybridization compared to culturing and the determination of prevalence of Streptococcus agalactiae colonization among pregnant women in Bushehr, Iran

Saeed Tajbakhsh12*, Marjan Norouzi Esfahani1, Mohammad Emaneini3, Niloofar Motamed4, Elham Rahmani5 and Somayyeh Gharibi2

Author Affiliations

1 Department of Microbiology and Parasitology, Faculty of Medicine, Bushehr University of Medical Sciences, Moallem Street, P. O. Box 3631, Bushehr, Iran

2 The Persian Gulf Tropical Medicine Research Center, Bushehr University of Medical Sciences, Bushehr, Iran

3 Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran

4 Department of Community Medicine, Faculty of Medicine, Bushehr University of Medical Sciences, Bushehr, Iran

5 Department of Obstetrics and Gynecology, Faculty of Medicine, Bushehr University of Medical Sciences, Bushehr, Iran

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BMC Infectious Diseases 2013, 13:420  doi:10.1186/1471-2334-13-420

Published: 8 September 2013

Abstract

Background

Pregnant women colonized by Streptococcus agalactiae (group B streptococci [GBS]) may transfer this microorganism to their newborns. S. agalactiae is an important cause of pneumonia, sepsis, and meningitis in newborns. Fluorescent in situ hybridization (FISH) is considered as a method of identification in the field of diagnostic microbiology. In this paper, we have designed a study to compare the DNA FISH after 7 h Lim broth enrichment and culturing for the identification of S. agalactiae and to determine the prevalence of vaginal colonization by S. agalactiae among pregnant women in Bushehr, Iran.

Methods

Vaginal swab specimens were obtained from 285 pregnant women at 35 weeks or more than 35 weeks of gestation. The specimens were inoculated into Lim broth. In order to evaluate the sensitivity and specificity of GBS DNA FISH after 7 h Lim broth enrichment, the specimens were tested using both FISH and conventional culture methods. In addition, the prevalence of GBS colonization was determined.

Results

Based on the results of this study, both the sensitivity and specificity of FISH were 100%. S. agalactiae was detected by both culture and FISH in 27 of the 285 pregnant women. Thus, the prevalence of GBS colonization was 9.5%.

Conclusions

Since short-term (7 h) Lim broth enrichment followed by FISH using oligonucleotide probes showed a high sensitivity and specificity, this protocol is therefore a highly accurate and relatively rapid method for the detection of S. agalactiae. Our analysis suggests that the use of DNA FISH to screen for S. agalactiae colonization in pregnant women may be considered in the absence of GBS culture availability.

Keywords:
Streptococcus agalactiae; Prevalence; Pregnant women; Fluorescent in situ hybridization; FISH