Lucibelli, F. | Search bioRxiv

bioRxiv2025

First report of Photobacterium damselae subspecies damselae in Razorbill (Alca torda)

A razorbill (Alca torda) was found dead in Bacoli, Italy, on January 16, 2023, during an exceptional irruptive event. The bird, a young female weighing 800 g with a moderate nutritional status and no external traumatic injuries underwent a post-mortem examination, which revealed coelomitis with severe congestion of the liver, lungs, kidneys, and myocardium. Lung, liver, kidney, and heart samples were collected for microbiological and histopathological analyses. Bacterial isolation on blood agar showed the growth of spherical/ovoid colonies after 48 hours, consistent with the Photobacterium genus. Identification by MALDI-TOF MS and PCR confirmed the presence of Photobacterium damselae subsp. damselae (Pdd), supported by 16S gene sequencing and detection of the ureC gene. PCR screening for virulence factors identified the hlyAch gene in lung samples, suggesting a potentially pathogenic strain in avian species. Histopathological examination showed severe, inflammatory infiltrates and widespread hemorrhages in the liver, the lung tissue and kidneys. In the myocardium, mild and multifocal lymphocytic infiltrates were present. These findings suggest a significant role of P. damselae subsp. damselae in the observed lesions. The results of the study revealed a new cross-species transmission of this potential zoonotic bacterium and the need for further research in this field. ImportanceWith this study we revealed the first isolation of Photobacterium damselae subsp. damselae in a razorbill but especially the first in a migratory bird. We documented a new cross-species transmission of P. damselae subsp. damselae and the need for further research, highlighting its zoonotic potential and therefore raising concerns about potential implications for marine wildlife, aquaculture and human health. Considering the role of migratory birds in the spread of infectious diseases even over long distances and the effect of climate change on marine ecosystems, and consequently on the circulation of pathogens, it is essential to adopt a preventive approach to mitigate this potential zoonotic risks.

microbiology↗

bioRxiv2024

Simultaneous silencing of gut nucleases and a vital target gene by adult dsRNA feeding enhances RNAi efficiency and mortality in Ceratitis capitata adults.

Ceratitis capitata, known as Mediterranean fruit fly (Medfly), is a major dipteran pest significantly impacting fruit and vegetable farming. Currently, its control heavily relies mainly on chemical insecticides, which pose health risks and have effects on pollinators. A friendly and species-specific alternative strategy involves providing double-stranded RNA (dsRNA) through feeding to disrupt essential functions in pest insects, which is poorly explored in dipteran species. Previous reports in Orthoptera and Coleoptera species suggested that dsRNA degradation by two specific nucleases in the intestinal lumen is among the major obstacle to feeding-mediated RNAi in insects. In our study, we experimented with three-day adult feeding using a combination of dsRNA molecules that target the expression of the ATPase vital gene and two intestinal dsRNA nucleases. These dsRNA molecules were recently tested separately in two Tephritidae species, showing limited effectiveness [1,2]. In contrast, we observed 79% mortality over seven days, which was associated with a decrease in mRNA levels of the three targeted genes. As expected, we also observed a reduction in dsRNA degradation following RNAi against nucleases. This research illustrates the potential of utilizing molecules as pesticides to achieve mortality rates in Medfly adults by targeting crucial genes and intestinal nucleases. Furthermore, it underscores the importance of exploring RNAi-based approaches for pest management Simple SummaryThe control of insect pest species, mainly belonging to Orthoptera, Hemiptera, and Coleoptera species, can be based on novel emerging species-specific pesticides. These consist of dsRNA molecules delivered by feeding to insect larvae or adults, which suppress vital gene functions by RNA-RNA sequence complementarity and RNA interference. However, fewer studies of dsRNA feeding have been performed in dipteran pest insects. Two studies in Orthoptera and Coleoptera species have shown that suppressing intestinal enzymes degrading external dsRNA can improve insect mortality rates. Ceratitis capitata (Tephritidae), the Mediterranean fruit fly (Medfly), is a major dipteran pest significantly impacting fruit and vegetable farming. Currently, its control heavily relies mainly on chemical insecticides, which pose health risks and have effects on beneficial pollinators. Previous attempts to induce mortality by adult dsRNA-feeding in this and other Tephritidae species, such as Bactrocera tryoni and B. dorsalis, showed some effectiveness, but were often limited. We improved this method by simultaneously silencing two intestinal nucleases and a vital gene. We have found a mix of three dsRNAs able to induce much higher mortality (79%) within one week, following only three days of adult feeding.

genetics↗