Laboratory-acquired infections of Salmonella enterica serotype Typhi in South Africa : phenotypic and genotypic analysis of isolates
Date
2017-9
Journal Title
Journal ISSN
Volume Title
Publisher
BioMed Central
Abstract
Background: Workers in clinical microbiology laboratories are exposed to a variety of pathogenic microorganisms.
Salmonella species is among the most commonly reported bacterial causes of laboratory-acquired infections. We
report on three cases of laboratory-acquired Salmonella enterica serotype Typhi (Salmonella Typhi) infection which
occurred over the period 2012 to 2016 in South Africa.
Methods: Laboratory investigation included phenotypic and genotypic characterization of isolates. Phenotypic
analysis included standard microbiological identification techniques, serotyping and antimicrobial susceptibility
testing. Genotypic analysis included the molecular subtyping methodologies of pulsed-field gel electrophoresis
analysis, multilocus sequence typing and whole-genome sequencing (WGS); with WGS data analysis including
phylogenetic analysis based upon comparison of single nucleotide polymorphism profiles of isolates.
Results: All cases of laboratory-acquired infection were most likely the result of lapses in good laboratory practice
and laboratory safety. The following critical issues were highlighted. There was misdiagnosis and misreporting of
Salmonella Typhi as nontyphoidal Salmonella by a diagnostic laboratory, with associated public health implications.
We highlight issues concerning the importance of accurate fluoroquinolone susceptibility testing and interpretation
of results according to updated guidelines. We describe potential shortcomings of a single disk susceptibility
screening test for fluoroquinolone susceptibility and suggest that confirmatory minimum inhibitory concentration
testing should always be performed in cases of invasive Salmonella infections. These antimicrobial susceptibility
testing issues resulted in inappropriate ciprofloxacin therapy which may have been responsible for failure in
clearance of pathogen from patients. Salmonella Typhi capsular polysaccharide vaccine was not protective in one
case, possibly secondarily to a faulty vaccine.
Conclusions: Molecular subtyping of isolates proved effective to investigate the genetic relatedness of isolates.
Molecular subtyping data interpreted together with epidemiological data allowed us to pinpoint the most likely
sources for our cases of laboratory-acquired infection.
Description
CITATION: Smith, A.M. et al. 2017. Laboratory-acquired infections of Salmonella enterica serotype Typhi in South Africa: phenotypic and genotypic analysis of isolates. BMC Infectious Disease, 17(656):1-9. doi:10.1186/s12879-017-2757-2.
The original publication is available at https://bmcinfectdis.biomedcentral.com/
The original publication is available at https://bmcinfectdis.biomedcentral.com/
Keywords
Salmonella typhimurium, Laboratory infections
Citation
Smith, A.M. et al. 2017. Laboratory-acquired infections of Salmonella enterica serotype Typhi in South Africa: phenotypic and genotypic analysis of isolates. BMC Infectious Disease, 17(656):1-9. doi:10.1186/s12879-017-2757-2.