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This study aimed to evaluate antimicrobial resistance, virulence, and the genetic diversity of Aeromonas isolated from migratory birds from Guangxi Province, Guangdong Province, Ningxia Hui Autonomous Region, Jiangxi Province, and Inner Mongolia in China. A total of 810 samples were collected, including fresh feces, cloacal swabs, and throat swabs. The collected samples were processed and subjected to bacteriological examination. The resistance to 21 antibiotics was evaluated. A phylogenetic tree was constructed using concatenated gltA-groL-gyrB-metG-PPSA-recA sequences. Eight putative virulence factors were identified by PCR and sequencing, and a biofilm formation assay was performed using a modified microtiter plate method. In total, 176 Aeromonas isolates were isolated including A. sobria, A. hydrophila, A. veronii, and A. caviae. All isolates showed variable resistance against all 16 tested antibiotic discs, and only one antibiotic had no reference standard. Six kinds of virulence gene markers were discovered, and the detection rates were 46.0% (hlyA), 76.1% (aerA), 52.3% (alt), 4.5% (ast), 54.0% (fla), and 64.2% (lip). These strains were able to form biofilms with distinct magnitudes; 102 were weakly adherent, 14 were moderately adherent, 60 were non-adherent, and none were strongly adherent. Our results suggest that migratory birds carry highly virulent and multidrug-resistant Aeromonas and spread them around the world through migration, which is a potential threat to public health.

To demonstrate the detailed genetic characteristics of a bla NDM-1-carrying multidrug-resistant Aeromonas caviae strain, the complete genome of the A. caviae strain K433 was sequenced by Illumina HiSeq and Oxford nanopore platforms, and mobile genetic elements associated with antibiotic resistance genes were analyzed by a series of bioinformatics methods. A. caviae K433 which was determined to produce class B carbapenemase, was resistant to most antibiotics tested except amikacin. The genome of K433 consisted of a chromosome cK433 (6,482-kb length) and two plasmids: pK433-qnrS (7.212-kb length) and pK433-NDM (200.855-kb length), the last being the first investigated bla NDM-carrying plasmid from Aeromonas spp. By comparison of the backbone and MDR regions from the plasmids studied, they involved a highly homologous sequence structure. This study provides in-depth genetic insights into the plasmids integrated with bla NDM-carrying genetic elements from Aeromonas spp.

The selective pressure of the living surroundings is a key factor in the development of resistance profiles in pathogenic bacteria such as Aeromonas spp. In this study, Aeromonas species were isolated from the Ba River, and their composition, resistance profiles to antibiotics, and heavy metals (HMs) were investigated. The discovery revealed that selective pressure altered the diversity of Aeromonas spp., with Aeromonas veronii being more adaptable to contaminated waters. Long-term exposure to antibiotics or HMs exerts persistent selective pressure on Aeromonas species, leading to the increase in multiple antibiotic resistance (MAR) index and multidrug-resistant (MDR) strains. Furthermore, HMs could drive the co-selection of antibiotic resistance via co-resistance or cross-resistance. blaTEM, blaSHV, blaCTX-M, sul1, czcA, mexA, and mexF were detected at high frequencies in Aeromonas species. Among these resistance phenotypes conferred genes, blaTEM may be intrinsic in the genome of Aeromonas spp., while mexA and mexF may have been acquired from surrounding environments owing to selective pressure. Resistance genes evolved as a consequence of selective pressure and have been shown to be positively correlated with their prevalence. Our study suggests that the selective pressure of living surroundings significantly contributes to the composition and resistance profiles of Aeromonas spp. in the riverine ecosystem.

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The study aimed to elucidate the species taxonomy, clinical manifestations, virulence gene profiles and antimicrobial susceptibilities of Aeromonas strains isolated from life-threatening bacteremia in southeastern China.
Clinical samples of Aeromonas causing bacteremia were isolated from a teaching hospital in Wenzhou from 2013 to 2018 and a retrospective cohort study was performed. Aeromonas strains were identified at species level by housekeeping gene gyrB. Virulence and drug resistance-associated genes were screened by polymerase chain reaction (PCR) and antimicrobial susceptibility testing (AST) was performed by the VITEK 2 Compact system.
A total of 58 Aeromonas isolated from patients with bacteremia were collected during 6 years (2013-2018). 58 isolates were identified to five different species, where Aeromonas dhakensis appeared to be the predominant species (26/58), followed by Aeromonas veronii (13/58), Aeromonas caviae (10/58), Aeromonas hydrophila (7/58) and Aeromonas jandaei (2/58). 16 of 58 patients had poor prognosis. Poor prognosis was significantly associated with liver cirrhosis and inappropriate empirical antimicrobials therapy. The progression of bacteremia caused by Aeromonas was extremely fast, especially in A. dhakensis infections. Virulence genes aer, lip, hlyA, alt, ast, and act, were detected at ratios of 24.1% (14/58), 62.1% (36/58), 65.5% (38/58), 58.6% (34/58), 15.5% (9/58) and 65.5% (38/58), respectively. Antimicrobial susceptibility testing exhibited that 9 out of 58 isolates were identified as multi-drug resistant (MDR) organism. The blaTEM gene was identified in all 9 MDR isolates. blaSHV, blaAQU-1, blaMOX, blaCepH, blaCphA and aac(6\')-Ib-cr were detected in 4 isolates, 2 isolates, 1 isolate, 3 isolates, 8 isolates, and 3 isolates, respectively. The majority of Aeromonas strains maintained susceptible to 3rd generation cephalosporins, aminoglycosides, fluoroquinolones and furantoin.
The prevalence and dangerousness of Aeromonas infections, especially A. dhakensis, are underestimated in clinic. Continuous monitoring is essential to keep track of MDR Aeromonas due to the increasing prevalence recently and a more effective measure is required to control the spread of resistance determinants.

Aeromonas and Pseudomonas are important bacterial species involved in spoilage of refrigerated freshwater fish. In this study, 10 Aeromonas and seven Pseudomonas bacterial strains were isolated from spoiled grass carp and identified. Twelve of seventeen bacterial strains showed high potential of biofilm formation and 14 of 17 can produce extracellular protease. In order to explore the spoilage capacity of dual-species, the sterile grass carp fillets were inoculated with mono- and dual-species of Aeromonas salmonicida and Pseudomonas azotoformans strains. The results revealed significantly higher levels of the total viable count and total volatile basic nitrogen in dual-species as compared to mono-species from day 6. The higher contents of histamine, cadaverine and serious degradation in muscles tissue were also observed in dual-species after 10 days of storage. Results of in vitro experiments showed that the co-culture of A. salmonicida and P. azotoformans significantly increased the bacterial maximum growth rate, promoted the biofilm formation and improved the spoilage capacity of bacterial strains. This study has revealed that the co-culture of Aeromonas and Pseudomonas bacterial strains accelerated spoilage process of grass carp and increased biofilm formation. It indicates that the mixed-cultures of spoilage micro-organisms pose a huge threat to food industry.