Iccurrence ofaeromonas hydrophilain wild birds

Gut microbiota and age shape susceptibility to clostridial enteritis in lorikeets under human care

Background

Enteritis is a common cause of morbidity and mortality in lorikeets that can be challenging to diagnose and treat. In this study, we examine gut microbiota in two lorikeet flocks with enteritis (Columbus Zoo and Aquarium—CZA; Denver Zoo—DZ). Since 2012, the CZA flock has experienced repeated outbreaks of enteritis despite extensive diet, husbandry, and clinical modifications. In 2018, both CZA and DZ observed a spike in enteritis. Recent research has revealed that the gut microbiota can influence susceptibility to enteropathogens. We hypothesized that a dysbiosis, or alteration in the gut microbial community, was making some lorikeets more susceptible to enteritis, and our goal was to characterize this dysbiosis and determine the features that predicted susceptibility.

Results

We employed 16S rRNA sequencing to characterize the cloacal microbiota in lorikeets (CZA n = 67, DZ n = 24) over time. We compared the microbiota of healthy lorikeets, to lorikeets with enteritis, and lorikeets susceptible to enteritis, with “susceptible” being defined as healthy birds that subsequently developed enteritis. Based on sequencing data, culture, and toxin gene detection in intestinal contents, we identified Clostridium perfringens type A (CZA and DZ) and C. colinum (CZA only) at increased relative abundances in birds with enteritis. Histopathology and immunohistochemistry further identified the presence of gram-positive bacilli and C. perfringens, respectively, in the necrotizing intestinal lesions. Finally, using Random Forests and LASSO models, we identified several features (young age and the presence of Rhodococcus fascians and Pseudomonas umsongensis) associated with susceptibility to clostridial enteritis.

Conclusions

We identified C. perfringens type A and C. colinum associated with lorikeet necrohemorrhagic enteritis at CZA and DZ. Susceptibility testing of isolates lead to an updated clinical treatment plan which ultimately resolved the outbreaks at both institutions. This work provides a foundation for understanding gut microbiota features that are permissive to clostridial colonization and host factors (e.g. age, prior infection) that shape responses to infection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42523-021-00148-7.

Potential of Double-crested Cormorants ( Phalacrocorax auritus), American White Pelicans ( Pelecanus erythrorhynchos), and Wood Storks ( Mycteria americana) to Transmit a Hypervirulent Strain of Aeromonas hydrophila between Channel Catfish Culture Ponds

Aeromonas hydrophila is a Gram-negative bacterium ubiquitous to freshwater and brackish aquatic environments that can cause disease in fish, humans, reptiles, and birds. Recent severe outbreaks of disease in commercial channel catfish ( Ictalurus punctatus) aquaculture ponds have been associated with a hypervirulent Aeromonas hydrophila strain (VAH) that is genetically distinct from less virulent strains. The epidemiology of this disease has not been determined. Given that research has shown that Great Egrets ( Ardea alba) can shed viable hypervirulent A. hydrophila after consuming diseased fish, we hypothesized that Double-crested Cormorants ( Phalacrocorax auritus), American White Pelicans ( Pelecanus erythrorhynchos), and Wood Storks ( Mycteria americana) could also serve as a reservoir for VAH and spread the pathogen during predation of fish in uninfected catfish ponds. All three species, when fed VAH-infected catfish, shed viable VAH in their feces, demonstrating their potential to spread VAH.

Amplicon-based taxonomic characterization of bacteria in urban and peri-urban roof-harvested rainwater stored in tanks

Overall, 26% of Australian households use rainwater tanks as a source of potable and nonpotable water. Limited information is available on the total bacterial communities in tank water. Therefore, identification of dominant bacterial communities, diversity, and their distribution is important in understanding the microbial quality of tank water. In this study, the abundance and diversity of bacterial communities in 88 tank water samples collected from the urban areas of Brisbane (n=44) and the peri-urban center of Currumbin (n=44) in Southeast Queensland, Australia were determined using amplicon-based Illumina next-generation sequencing. In addition, the SourceTracker program was used to identify the sources of fecal contamination in tank water samples. Sequence reads were also analyzed to detect potential bacterial pathogenic genera in the tank water samples collected. Differences in sample coverage, alpha diversity, and richness did not differ significantly between the Brisbane and Currumbin tank water samples. Comamonadaceae and Planctomycetaceae were the most abundant families in all tank water samples. Curvibacter was the most abundant genus in all tank water samples. SourceTracker revealed that around 34% (Brisbane) and 43% (Currumbin) of tank water samples had a signature for bird fecal contamination. The potential opportunistic pathogenic genera including Burkholderia, Chromobacterium, Clostridium, Legionella, Mycobacterium, Nocardia, and Pseudomonas were most prevalent in tank water samples. Next-generation sequencing can be used as an initial screening tool to identify a wide array of potential pathogenic genera in tank water samples followed by quantifying specific pathogen(s) of interest using more sensitive molecular assays such as quantitative PCR (qPCR).

The Animal Model Determines the Results of Aeromonas Virulence Factors

The selection of an experimental animal model is of great importance in the study of bacterial virulence factors. Here, a bath infection of zebrafish larvae is proposed as an alternative model to study the virulence factors of Aeromonas hydrophila. Intraperitoneal infections in mice and trout were compared with bath infections in zebrafish larvae using specific mutants. The great advantage of this model is that bath immersion mimics the natural route of infection, and injury to the tail also provides a natural portal of entry for the bacteria. The implication of T3SS in the virulence of A. hydrophila was analyzed using the AH-1::aopB mutant. This mutant was less virulent than the wild-type strain when inoculated into zebrafish larvae, as described in other vertebrates. However, the zebrafish model exhibited slight differences in mortality kinetics only observed using invertebrate models. Infections using the mutant AH-1ΔvapA lacking the gene coding for the surface S-layer suggested that this protein was not totally necessary to the bacteria once it was inside the host, but it contributed to the inflammatory response. Only when healthy zebrafish larvae were infected did the mutant produce less mortality than the wild-type. Variations between models were evidenced using the AH-1ΔrmlB, which lacks the O-antigen lipopolysaccharide (LPS), and the AH-1ΔwahD, which lacks the O-antigen LPS and part of the LPS outer-core. Both mutants showed decreased mortality in all of the animal models, but the differences between them were only observed in injured zebrafish larvae, suggesting that residues from the LPS outer core must be important for virulence. The greatest differences were observed using the AH-1ΔFlaB-J (lacking polar flagella and unable to swim) and the AH-1::motX (non-motile but producing flagella). They were as pathogenic as the wild-type strain when injected into mice and trout, but no mortalities were registered in zebrafish larvae. This study demonstrates that zebrafish larvae can be used as a host model to assess the virulence factors of A. hydrophila. This model revealed more differences in pathogenicity than the in vitro models and enabled the detection of slight variations in pathogenesis not observed using intraperitoneal injections of mice or fish.

Mucus accumulation and necrosis of the ventral air pouch in a marabou stork (Leptoptilos crumeniferus) with productive rhinitis

A captive-born marabou stork (Leptoptilos crumeniferus) was presented for swelling of the ventral air pouch of 1 month's duration. The pouch appeared fluid filled, and its distal third wall was markedly inspissated. The thickened distal portion of the pouch wall was removed surgically. During anesthesia, mucous discharge from the nares was evident and the nasal mucosa was hyperemic. Aeromonas and Proteus species were isolated from a nasal culture. Postoperative therapy that consisted of nasal flushing, antimicrobial agents, and nonsteroidal anti-inflammatory drugs was effective in managing the disease. On histologic examination, diffuse hemorrhage, necrosis, and multifocal vasculitis with moderate-to-severe heterophilic inflammation were present within sections of the ventral pouch. To our knowledge this is the first report of a mucus-filled ventral air pouch with associated pathologic changes secondary to a productive infection of the upper respiratory tract in a marabou stork. The unique communication between nasal cavities and the ventral air pouch should be considered in future cases of respiratory infection in marabou storks.

Population patterns and antimicrobial resistance ofAeromonasin urban playa lakes

Bacteria belonging to the genus Aeromonas are indigenous to aquatic environments. Once regarded as unimportant human pathogens, reports of opportunistic infections caused by these organisms have appeared increasingly in the medical literature. To estimate the potential for human infection by Aeromonas where limited water resources are being used intensively, we studied the spatial and temporal variation and incidence of antimicrobial resistance among environmental isolates of Aeromonas from two urban playa lakes in Lubbock, Texas. Aeromonas population densities varied seasonally, with the highest densities occurring from mid-April to late October. The greatest range of densities was 100-fold, from 2.50 to 255.17 colony-forming units per 0.1 mL of water sample. Densities also varied with water depth, although the variation did not display a consistent pattern. One hundred fifty-one Aeromonas isolates were divided into 10 species or subspecies groups by using the BIOLOG identification system. Nine isolates displayed resistance to co-trimoxazole, tetracycline, and cefuroxime, and none was resistant to more than one of these antimicrobial agents. In summary, the results of this study showed that the densities of Aeromonas peak in the late spring and again in late summer, times when human activity around the playa lakes is also high. Thus, we infer that human exposure to these potential pathogens varies seasonally. Compared to other published studies, the incidence of antimicrobial-resistant Aeromonas is relatively low in urban playa lakes in Lubbock, Texas. Nevertheless, resistant organisms were detected.Key words: Aeromonas, water, playa, antibiotic resistance, population dynamics.