Increased detection of invasive enteropathogenic bacteria in pre-incubated blood culture materials by real-time PCR in comparison with automated incubation in Sub-Saharan Africa

Abstract

Background: Invasive enteropathogenic bacteria can cause systemic infections. Data from studies with PCR detection suggest, at least for Salmonella enterica, that blood culture may lead to underestimation in the tropics. Corresponding data are lacking for other invasive enteropathogenic bacteria. We compared classical blood culture and molecular methods for the diagnosis of blood infections. Methods: A real-time multiplex PCR for Salmonella spp., Shigella spp./entero- invasive Escherichia coli (EIEC), Yersinia spp., and Campylobacter jejuni was applied to 2321 retained blood culture samples from Ghanaian patients, after enrichment by automated culture. Results: PCR detected Salmonella DNA in 56 out of 58 pre-incubated Ghanaian blood cultures with growth of S. enterica. In 2 samples molecular diagnosis was only possible after 1:10 dilution. Twenty-two samples negative by blood culture and 1 positive with Micrococcus spp. were PCR-positive for Salmonella spp. In addition, 3 Shigella spp./EIEC, 2 Yersinia spp., and 1 C. jejuni were detected by PCR but not by culture growth. Conclusions: Real-time PCR was more sensitive in identifying invasive enteropathogenic bacteria than automated blood culture, which is hampered by a lack of evidence-based standardization of pre-analytic conditions in the tropics. Primary agar culture and Gram-staining prior to automated blood culture is advisable in cases where transportation times are long.

Keywords::

• Enteropathogenic bacteria
• PCR
• blood culture
• Sub-Saharan Africa
• epidemiology

Acknowledgements

The authors are grateful for the excellent technical assistance provided by Simone Priesnitz and Annett Michel in performing the sample preparations and the PCR analyses.

Declaration of interest: The FISA study, from which the Ghanaian samples were taken, was funded by the International Vaccine Institute (IVI). DNA preparation and PCR analysis was funded by the German armed forces, scientific project number 03K2-S-450709 ‘Evaluation of real-time/multiplex PCR for the diagnosis of infections in tropical medicine under field/deployment conditions’.