First Report of Aeromonas veronii as an Emerging Bacterial Pathogen of Farmed Nile Tilapia (Oreochromis niloticus) in Brazil.

Brazil is one of the world's leading producers of Nile tilapia, Oreochromis niloticus. However, the industry faces a major challenge in terms of infectious diseases, as at least five new pathogens have been formally described in the last five years. Aeromonas species are Gram-negative anaerobic bacteria that are often described as fish pathogens causing Motile Aeromonas Septicemia (MAS). In late December 2022, an epidemic outbreak was reported in farmed Nile tilapia in the state of São Paulo, Brazil, characterized by clinical signs and gross pathology suggestive of MAS. The objective of this study was to isolate, identify, and characterize in vitro and in vivo the causative agent of this epidemic outbreak. The bacterial isolates were identified as Aeromonas veronii based on the homology of 16S rRNA (99.9%), gyrB (98.9%), and the rpoB gene (99.1%). A. veronii showed susceptibility only to florfenicol, while it was resistant to the other three antimicrobials tested, oxytetracycline, enrofloxacin, and amoxicillin. The lowest florfenicol concentration capable of inhibiting bacterial growth was ≤0.5 µg/mL. The phenotypic resistance of the A. veronii isolate observed for quinolones and tetracycline was genetically confirmed by the presence of the qnrS2 (colE plasmid) and tetA antibiotic-resistant genes, respectively. A. veronii isolate was highly pathogenic in juvenile Nile tilapia tested in vivo, showing a mortality rate ranging from 3 to 100% in the lowest (1.2 × 104) and highest (1.2 × 108) bacterial dose groups, respectively. To our knowledge, this study would constitute the first report of highly pathogenic and multidrug-resistant A. veronii associated with outbreaks and high mortality rates in tilapia farmed in commercial net cages in Brazil.

Different virulence genetic context of multidrug-resistant CTX-M- and KPC-producing Klebsiella pneumoniae isolated from cerebrospinal fluid.

Information regarding resistance and virulence traits of meningitis-causing enterobacteria in hospital environment remains scarce. The aim of this study was to characterize virulence and acquired resistance genes of carbapenem-resistant and/or 3rd to 4th generation cephalosporin-resistant Klebsiella pneumoniae isolated from the cerebrospinal fluid of inpatients. Antimicrobial susceptibility testing was performed by disk diffusion. The string test was performed to identify hypermucoviscous phenotype. Galleria mellonella infection model was used to evaluate the virulence profile of the isolates. Screening for virulence determinants and acquired resistance genes were performed by PCR. The blaCTX-M and/or blaKPC and/or rmtG were detected in all the isolates. Genetic virulence determinants, including mrkD, entB, iroD, fecIRA, uge, wabG, fimH, ureA, ybtS, and clb were detected in the majority of multidrug-resistant K. pneumoniae isolates. One isolate presented hypermucoviscous phenotype, and several isolates showed enhanced virulence in G. mellonella infection model. The combination of the virulence genes found here seems to support not only the known virulence genetic context among nosocomial infections-causing K. pneumoniae but also the role that clb and ybtS may play in K. pneumoniae virulence.

Extensively drug-resistant IMP-16-producing Pseudomonas monteilii isolated from cerebrospinal fluid.

IMP-1-producing Pseudomonas aeruginosa was first reported in Japan and since then, bacteria with this metallo-ß-lactamase have been detected worldwide. Pseudomonas monteilii (part of P. putida group) were considered an environmental pathogen with low virulence potential; however, multidrug-resistant and carbapenem-resistant P. monteilii have emerged. The present study reports the draft sequence of an extensively drug-resistant IMP-16-producing P. monteilii 597/14 isolated from cerebrospinal fluid in 2014. The sequencing data revealed blaIMP-16 as a gene cassette on class 1 integron, In1738 characterized in this study. Furthermore, the resistome of Pm597/14 consisted of 7 resistance genes (aadA1b, strA, strB, aacA4, blaIMP-16, blaOXA-2, sul1) and diverse virulence determinants involved in the adherence, LPS, antiphagocytosis, iron uptake and mercuric resistance. Although different virulence determinants were found in this study, using Galleria mellonella infection model, Pm597/14 did not kill any larvae between 7 days post-infection. P. monteilii isolates have been reported from clinical and environmental sources, carrying different MBL genes showing its potential role as their reservoir.