Identification of emerging Acinetobacter johnsonii virulence and antibiotic resistance genes associated with high mortality in cultured Oreochromis niloticus

Abstract

The present study was planned to investigate the causative agent of Oreochromis niloticus summer mortality that resulted in significant economic losses in Port Said Governorate, Egypt during 2017. Many bacterial isolates were identified, among which Acinetobacter johnsonii has been selected to be the focus of the current study. Acinetobacter johnsonii_Egy was isolated and identified using the analytical profile index (API) 20 E, sequencing 16S ribossomal RNA gene fragment and phylogenetic analysis. A drug resistance evaluation revealed that A. johnsonii was resistant to ampicillin, gentamicin, lincomycin, nalidixic acid, tetracycline, and oxytetracycline among the tested antibiotics. Experimental infection was performed and challenged fish revealed similar clinical signs as seen in naturally infected ones. The disease appears to be highly infectious and lethal, causing 100% cumulative mortality during experimental infections. Virulence genes (fimH, traT, and iutA) and antibiotic resistance genes (qacED1, qnrS, sul1, dfrA, and aadA1) presence was confirmed in the A. johnsonii_Egy isolate.In conclusion, A. johnsonii is highly infectious to O. niloticus and might have a great influence on transfer of the antibiotic resistance in aquaculture. According to the available knowledge, this study is first to report A. johnsonii as emerging opportunistic pathogen in the Egyptian Nile tilapia (in Port Said).

Antibiotic resistance in bacteria isolated from the skin of trout in León Province, Spain

“…Also, our results agreed with findings of Kozińska et al (2014) and Borella et al (2020) who found that all A. johnsonii and A. sobria isolates respectively were resistant to ampicillin and sensitive to gentamicin. While in contrast to our results, Elabd et al (2020) and Dhanapala et al (2021) found that all A. johnsonii and A. sobria isolates were resistant gentamycin and enrofloxacin respectively. These differences in the antimicrobial susceptibility may be attributed to some differences including the used antimicrobials, management practices, and time of examination where antimicrobial resistance is increasing over time (Ali et al, 2017).…”