Phenotypic detection and antimicrobial susceptibility of Burkholderia pseudomallei and other Gram-negative bacteria from clinical specimen on Ashdown agar in Nigeria

Abstract

Burkholderia is a genus comprising Gram-negative bacteria that are metabolically complex and versatile, thriving in frequently hostile settings. Burkholderia psudomallei, 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 are currently limited reports of this pathogen from clinical specimens in Nigeria. This study aimed to determine the occurrence of B. pseudomallei in clinical settings and characterize the pathogen using phenotypic means. 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 (67) culture-positive isolates were obtained using Ashdown selective agar. Twenty-six 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 26.9% (7/26). No isolate was distinctively identified as B. pseudomallei but four 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, provide a robust basis for not just supporting present and future decisions for expanding diagnostic capability for Burkholderia, but also for investigating the relevance of the pathogens in clinical situations.