Some properties of Plesiomonas shigelloides treated with aminoglycosides

First report of multidrug-resistant and pathogenic Plesiomonas shigelloides from endangered crested ibis (Nipponia nippon)

Plesiomonas shigelloides (P. shigelloides) is a gram-negative, thermotolerant, motile, and pleomorphic microorganism that acts as an opportunistic pathogen, capable of causing abscesses, enteric infections, and even sepsis in humans and other animals, thereby posing a threat to human and animal health worldwide. The crested ibis (Nipponia nippon) is a globally endangered avian species with a limited population and is vulnerable for various infections. To gain a better understanding of the prevalence of P. shigelloides in the endangered crested ibis, fecal samples from the crested ibis at the Xiazhu Lake Crested Ibis Breeding Research Center, China were collected and analyzed. The results confirmed that 45.6% (36/79) of the fecal samples tested positive for P. shigelloides. Antibiotic susceptibility testing showed that 27.8% (10/36) of P. shigelloides isolates were multidrug-resistant, with resistance to ampicillin and amikacin being 100% and 77.8%, respectively. Subsequently, ten representative isolates were subjected to whole genome sequencing, and resistance and virulence genes were analyzed. The evolutionary tree of the genomes show that these strains have different origins, with one strain closely related to a strain from human. Finally, the pathogenicity experiment demonstrated that several strains exhibit pathogenicity in both mice and waterfowl, with two strains displaying lethal pathogenicity in mice. To the best of our knowledge, this is the first report of multidrug-resistant and pathogenic P. shigelloides isolated from the crested ibis, suggesting a potential threat to this endangered species and broader public health implications.

Influence of subinhibitory concentrations of amikacin and ciprofloxacin on morphology and adherence ability of uropathogenic strains

The influence of subinhibitory concentrations (1/2, 1/4, 1/8, 1/16 and 1/32 MIC) of amikacin and ciprofloxacin on the morphology and adherence of uropathogenic strains was studied. Intensity of morphological changes was proportional to the concentrations of these antibiotics. Morphological changes were the most prominent after bacterial exposure to sub-MICs of ciprofloxacin. These concentrations, especially 1/2 MIC of ciprofloxacin, induced the formation of filaments of E. coli, K. pneumoniae, K. oxytoca, E. cloacae and A. calcoaceticus biotype anitratus. No morphological changes were observed in P. aeruginosa, S. epidermidis and S. aureus cells after exposure to subinhibitory concentrations of both antibiotics. Sub-MICs of amikacin affected the changes in cell shape only slightly. The exposure of bacterial strains to 1/2 MIC of ciprofloxacin induced increased vacuolation of the cells. We observed shrinkage of the protoplasm and the pleated cell walls in comparison with control cells. The greatest loss of adherence ability occurred at 1/2 MIC of ciprofloxacin after a 1-d incubation.

Potential virulence-associated properties of Plesiomonas shigelloides strains

Serotyping and some potential virulence-associated markers were investigated in Plesiomonas shigelloides strains isolated from humans, animals and aquatic environments. Surface properties of these strains were evaluated using Congo red binding, salt-aggregation test, bacterial adherence to xylene and motility. Production of pancreatic elastase, proteinase (consistent with subtilisin Carlsberg), triacylglycerol lipase, histidine decarboxylase and beta-hemolysin was also determined. In addition, detection of signal molecules such as C4-C8 unsubstituted N-acylhomoserine lactones (AHLs) was performed. The serological typing of the P. shigelloides strains showed that the isolates belonged to 13 different serovars. The majority of the strains were hydrophobic and motile. The strains produced low levels of elastase, proteinase and histidine decarboxylase whereas triacylglycerol lipase activity was relatively high. Only 23.3 % of the strains produced hemolysin. The AHLs signal molecules were not detected. P. shigelloides strains were able to produce a variety of potential virulence markers which may be involved in the pathogenesis of Plesiomonas-associated infections.