Identification and pathogenicity study of emerging fish pathogens Acinetobacter junii and Acinetobacter pittii recovered from a disease outbreak in Labeo catla (Hamilton, 1822) and Hypophthalmichthys molitrix (Valenciennes, 1844) of freshwater wetland in West Bengal, India

Abstract

The disease outbreaks in aquaculture system of wetlands are the major cause of fish mortality. Among various bacterial septicaemic diseases, fish mortality caused by Acinetobacter spp. is recently reported in different fish species. Fish disease outbreak was investigated in a wetland of West Bengal, India to identify the aetiological factors involved. The moribund fish were examined and subjected to bacterial isolation. Two bacterial causative agents were identified as Acinetobacter junii and Acinetobacter pittii by biochemical characterization and 16S rRNA gene amplification. Both the isolates were oxidase-negative, nitrate-negative, catalase-positive and indole-negative. The molecular identification using 16S rRNA gene sequencing and phylogenetic tree analysis further confirmed the two Acinetobacter spp. with 97%-99% similarity. The antibiotic resistance patterns of these two bacteria revealed that both of them were resistant to β-lactam, cefalexin, cephalothin, amoxyclav, cefuroxime, cefadroxil, clindamycin, vancomycin and penicillin. In addition, A. pittii was also resistant to other antibiotics of cephams group such as ceftazidime and cefotaxime.In the challenge experiment, both A. junii and A. pittii were found to be pathogenic with LD 50 of 1.24 × 10 5 and 1.88 × 10 7 cfu/fish respectively. Histopathological examination of gill, liver and kidney revealed prominent changes supporting bacterial septicaemia. The investigation reports for the first time on concurrent infection by A. junii and multidrug-resistant (MDR)-A. pittii as emerging fish pathogens to cause severe mortality in Labeo catla and Hypophthalmichthys molitrix in a freshwater wetland.

Dynamics of Bacterial and Fungal Communities and Metabolites During Aerobic Exposure in Whole-Plant Corn Silages With Two Different Moisture Levels

“… Xu et al (2019 , 2020b) , using SMRT sequencing, revealed that L. parafarraginis , L. silage , L. buchneri , L. farciminis , and L. paralimentarius were the main species and predominant bacterial community in whole-plant corn silage after ensiling for 90 day. Acinetobacter species are a group of Gram-negative, strictly aerobic, non-fermenting organisms that are ubiquitous in polluted aquatic environments, sewage, vegetables, and can be pathogenic in animals and humans ( Xia et al, 2008 ; Malick et al, 2020 ). In the present study, they might have been present in the materials before ensiling, have greater acid resistance than other bacteria in silages and therefore dominated the bacterial community during aerobic exposure ( Figure 3B ).…”

The Alteration of Intestinal Microbiota Profile and Immune Response in Epinephelus coioides during Pathogen Infection

“…was clearly superior to the NNV group, whereas the vibrio group was enriched with Ralstonia spp., some species reported as infectious bacteria on human, which cause meningitis, respiratory infection and catheter related infection [ 94 ]. Acinetobacter spp., which are abundant in NNV, GIV and Vibrio-infected grouper, were identified as serious pathogens that could lead to major disease outbreak in Labeo catla [ 95 ]. In the Vibrio group, Ralstonia spp.…”

Relationships between pond water and tilapia skin microbiomes in aquaculture ponds in Malawi

“…Namely, Plesiomonas (shigelloides) (Liu et al, 2015), Flavobacterium (columnare) (Dong et al, 2015) and Acinetobacter spp. an emerging group of freshwater fish pathogens (Malick et al, 2020). Likewise, among the detected microeukaryotic genera, there were species pathogenic to tilapia, including the parasitic ciliate Ichthyophthirius multifiliis (El-Dien and Abdel-Gaber, 2009) and two skin-targeting pathogenic oomycetes, Aphanomyces invadans (OIE, 2013) and Saprolegnia parasitica (Ellison et al, 2018) but the metabarcoding of short hypervariable regions of marker genes does not allow us to accurately assign species or strain level classifications to determine their pathogenicity.…”