First report on antimicrobial resistance and molecular characterisation of Salmonella enterica serotype Typhi isolated from human specimens in Luanda, Angola

Abstract

Objectives: Typhoid fever is a common infection in Africa and, despite scarce surveillance reports, its incidence is commonly considered high by the Angolan health system. Drug-resistant Salmonella enterica serotype Typhi has emerged, making antimicrobial susceptibility testing essential to provide clinical guidance. This is the first report analysing the antimicrobial resistance patterns and population structure of the few S. enterica ser. Typhi isolated from patients with typhoid fever in Luanda, Angola.

Methods: Isolates were collected by the Angolan National Institute of Public Health between September 2013 and May 2014. Ten isolates were identified by the API 20E system and serotyping, and the genus was confirmed by PCR. All isolates were tested for antibiotic susceptibility, and the presence of resistance genes [bla_CTX-M, bla_SHV, bla_TEM, bla_OXA-1, several plasmid-borne genes encoding AmpC β-lactamases, sul and qnr genes, dfrIa, dfrA12, aac(6')-Ib, cmlA and floR] were screened by PCR. Isolates were typed by PFGE and MLST.

Results: Several isolates were identified with resistance to trimethoprim/sulfamethoxazole (n=6), β-lactams (n=5) and chloramphenicol (n=1) and reduced susceptibility to ciprofloxacin (n=2). PFGE revealed eight closely related restriction patterns, and MLST grouped these into three sequence types (ST1, ST2 and ST8), with ST2 being predominant.

Conclusion: This first epidemiological report provides a preliminary description of S. enterica ser. Typhi strains circulating in Luanda and emphasises the need for continuous monitoring of this pathogen to provide information in order to implement better epidemiological strategies for the control of typhoid fever in Angola.

Keywords: Angola; Antimicrobial resistance; Enteric fever; Human specimens; Molecular typing; Salmonella enterica serotype Typhi.