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BMC Infect Dis. 2017 Sep 29;17(1):656. doi: 10.1186/s12879-017-2757-2.

Laboratory-acquired infections of Salmonella enterica serotype Typhi in South Africa: phenotypic and genotypic analysis of isolates.

Author information

1
Centre for Enteric Diseases, National Institute for Communicable Diseases, National Health Laboratory Service, Private Bag X4, Sandringham, Johannesburg, Gauteng, 2131, South Africa. anthonys@nicd.ac.za.
2
Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa. anthonys@nicd.ac.za.
3
Centre for Enteric Diseases, National Institute for Communicable Diseases, National Health Laboratory Service, Private Bag X4, Sandringham, Johannesburg, Gauteng, 2131, South Africa.
4
Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.
5
National Health Laboratory Service (Groote Schuur Hospital), Cape Town, South Africa.
6
Division of Medical Microbiology, University of Cape Town, Cape Town, South Africa.
7
AMPATH Laboratories, Cape Town, South Africa.
8
Department of Health, Communicable Disease Control, Cape Town, South Africa.
9
Division of Public Health Surveillance and Response, National Institute for Communicable Diseases, National Health Laboratory Service, Johannesburg, South Africa.
10
National Health Laboratory Service (Tygerberg Hospital), Cape Town, South Africa.

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.

KEYWORDS:

Genotyping; Laboratory-acquired infection; MLST; Molecular subtyping; PFGE; Salmonella Typhi; South Africa; WGS; Whole-genome sequencing

PMID:
28962627
PMCID:
PMC5622435
DOI:
10.1186/s12879-017-2757-2
[Indexed for MEDLINE]
Free PMC Article

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