Objectives: The presence of carbapenemase-producing bacterial isolates is found not only in hospital and community settings but also in the environment. Carbapenemase production may be related to acquired, usually plasmid-borne, β-lactamase genes or to chromosomal genes intrinsic to various species. The aim of this study was to evaluate the occurrence of such carbapenemase-producing bacterial isolates among environmental samples from Nigeria.

Methods: A total of 122 environmental samples were plated on carbapenem-containing media. A total of 259 isolates were recovered, among which 124 were carbapenemase-producers according to the results of the Rapidec® Carba NP test.

Results: The majority of isolates (n=112) recovered corresponded to natural producers of carbapenemases, i.e. Stenotrophomonas maltophilia (n=108), Burkholderia cepacia (n=1), Shewanella sp. (n=1), Sphingobacterium sp. (n=1) and Chryseobacterium gleum (n=1). Ten isolates (mainly Enterobacteriaceae and Acinetobacter baumannii) produced an acquired carbapenemase, most commonly of the NDM type. In addition, two Pseudomonas otitidis isolates were identified as producing the Ambler class B carbapenemase POM-1, further confirming that this carbapenemase is naturally produced in this environmental species. Finally, several isolates co-producing 16S rRNA methylases (ArmA, RmtC) and/or extended-spectrum β-lactamases (CTX-M-9, CTX-M-15) were also identified.

Conclusion: This study revealed the presence and diversity of clinically-relevant antimicrobial-resistant bacteria in the environment in Nigeria.