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Diversity, antimicrobial activity, and susceptibility of culturable soil actinobacteria isolated from Sichang Island

Wongsakorn Phongsopitanun^a,*, Paranee Sripreechasak^b, Ek Sangvichien^c, Somboon Tanasupawat^a

 
ABSTRACT:     Actinobacteria are a promising source of novel antibiotics. The study of diverse actinobacteria from Sichang Island may lead to a discovery of new microbes with pharmaceutical applications. Some actinobacteria, especially those in the genus Nocardia, can cause infection in humans and animals. A total of 55 actinobacteria were isolated from six soil samples collected from Sichang Island, Chonburi Province, Thailand. Based on the morphological characteristics and 16S rRNA gene analysis, the actinobacterial isolates were classified into three genera including Streptomyces (32 isolates), Nocardia (22 isolates), and Saccharothrix (1 isolate). Most of the Streptomyces and the Saccharothrix isolates exhibited antimicrobial activity, with none observed among the Nocardia strains. The 16S rRNA gene similarity suggested three strains represented candidates of novel taxa. Moreover, most of the Nocardia were rare environmental species. Antimicrobial susceptibility testing revealed that amoxicillin/clavulanate (2/1), imipenem, and linezolid were active against Nocardia strains, but they were not susceptible to ceftriaxone, cefotaxime, clarithromycin, ciprofloxacin, and trimethoprim/sulfamethoxazole. The susceptibility profiles vary between strains and species.

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* Corresponding author, E-mail: Wongsakorn.p@chula.ac.th

Received 16 Apr 2021, Accepted 26 Jul 2021