Showing the limitations of available phenotypic assays to detect B. pseudomallei from clinical specimens in Nigeria

Abstract

Burkholderia is a genus comprising Gram-negative bacteria that are metabolically complex and versatile, thriving in frequently hostile settings. Burkholderia pseudomallei, the causative agent of melioidosis, is a prominent member of the genus and a clinical pathogen of tropical and sub-tropical regions. This pathogen is well known for its multidrug resistance nature and possible bioweapon potential. There is currently no report of the pathogen from clinical specimens in Nigeria, this might be due to misdiagnosis with phenotypic assays. This study aims to explore the accuracy in the use of phenotypic assays to accurately diagnose B. pseudomallei in Nigeria. Two hundred and seventeen (217) clinical samples and twenty-eight (28) Gram-negative clinical isolates were collected and analysed using Ashdown selective agar and monoclonal antibody-based latex agglutination. The species-level identification was achieved using the Analytical profile index (API) 20NE system. The susceptibility of the isolates to nine different antimicrobial agents was determined using the disk diffusion method. Sixty-seven (74) culture-positive isolates were obtained using Ashdown selective agar. Twenty-two isolates were believed to be B. pseudomallei through the monoclonal antibody-based latex agglutination test and API 20NE system subsequently identified 14 isolates as Burkholderia. The predominant Burkholderia species was B. cepacia with isolation rate of 30.8% (8/26). No isolate was distinctively identified as B. pseudomallei but five isolates were highly suspected to be B. pseudomallei with similarity indices ranging from 81.9 – 91.3%. Other bacterial species with definitive identity include Aeromonas sp., Sphingomonas sp. and Pseudomonas aeruginosa. The antibiotic susceptibility results revealed an overall resistance to amoxicillin-clavullanic acid (71.4%), cefepime (33.3%), trimethoprim-sulfamethoxazole (38.1%), piperacillin-tazobactam (33.3%), imipenem (66.7%), doxycycline (57.1%), and ceftazidime (66.7%). The highest intermediate resistance was observed for cefepime and piperacillin-tazobactam with a value 66.7% each while no intermediate-resistance for gentamicin, colistin and imipenem. Our findings, therefore, show that phenotypic assays alone are not enough in the diagnosis of melioidosis. Additionally, it provides a robust basis for supporting present and future decisions to expand diagnostic capability for melioidosis beyond phenotypic assays in low-resource settings.