The drug tolerant persisters of Riemerella anatipestifer can be eradicated by a combination of two or three antibiotics

Repurposing antimicrobials with ultrasound-triggered nanoscale systems for targeted biofilm drug delivery

Chronic infections represent a major clinical challenge due to the enhanced antimicrobial tolerance of biofilm-dwelling bacteria. To address this challenge, an ultrasound-responsive nanoscale drug delivery platform (nanodroplets) is presented in this work, loaded with four different antimicrobial agents, capable of simultaneous biofilm disruption and targeted antimicrobial delivery. When loaded, a robust protective effect against clinically-derived MRSA and ESBL Gram-positive and Gram-negative planktonic isolates was shown in vitro. Upon application of therapeutic ultrasound, an average 7.6-fold, 44.4-fold, and 25.5-fold reduction was observed in the antibiotic concentrations compared to free drug required to reach the MBC, MBEC and complete persister eradication levels, respectively. Nanodroplets substantially altered subcellular distribution of encapsulated antimicrobials, enhancing accumulation of antimicrobials by 11.1-fold within the biofilm-residing bacteria's cytoplasm compared to treatment with unencapsulated drugs. These findings illustrate the potential of this multifunctional platform to overcome the critical penetration and localization limitations of antimicrobials within biofilms, opening potential new avenues in the treatment of chronic clinical infections.

Unveiling the silent threat: A comprehensive review of Riemerella anatipestifer - From pathogenesis to drug resistance

Riemeralla anatipestifer, a predominant bacterium with multidrug resistance, has caused tremendous economic losses in the poultry farming industry. However, there are few studies on its identification, pathogenic mechanisms, and virulence factors and effective and systematic prevention and control strategies. The emergence and spread of antibacterial resistance has prompted increased focus on R. anatipestifer. However, studies on the mechanisms underlying gene aggregation and dissemination are lacking. This review summarizes recent studies on R. anatipestifer and explores its epidemiology, pathobiology, serotype classification, and preventive and treatment measures. Our findings illuminate the characteristics of virulence-related and drug resistance factors that have pivotal roles in the pathogenesis of R. anatipestifer infection. This study provides a comprehensive reference and guidance for in-depth research on R. anatipestifer.

Ornithobacterium rhinotracheale in Moroccan Poultry: Antimicrobial Susceptibility Profiles, Characterization of Recent Isolates, and Retrospective Study (2019-23) of Its Occurrence in Different Poultry Production Systems

Ornithobacterium rhinotracheale (ORT) is one of the most important respiratory pathogens of poultry, notably in turkeys, while Riemerella anatipestifer (RA) is the etiologic agent of infectious serositis, the most economically significant disease of domestic ducks and, to a lesser extent, geese and turkeys. Currently, little is known about ORT and RA infections in Moroccan poultry. Thus, the main aim of this study was to describe ORT incidence in Moroccan poultry flocks during the period from 2019 to 2023 and gain better insights into genetic characteristics in combination with assessment of antimicrobial susceptibility of Moroccan ORT isolates during 2023 outbreaks. In addition, we report the first detection of RA in Moroccan turkeys and caged layer chickens. For this purpose, poultry flocks exhibiting elevated mortality rates along with respiratory clinical signs were necropsied. Additionally, the birds presenting fibrinous pleuropneumonia were investigated for ORT infection during the period from January to December 2023. Samples of the lungs, air sacs, and tracheas were collected for bacteriology testing, and the antimicrobial susceptibility testing was conducted on the isolates. Furthermore, trachea and lung samples were subjected to real-time quantitative polymerase chain reaction (qPCR), and positive qPCR samples were then selected for further amplification of the rpoB gene, followed by sequencing. Moreover, a retrospective study of the incidence of ORT from 2019 to 2023 was carried out. The results showed a significant increase of ORT cases (p , 0.001); additionally, age was identified as the sole significant risk factor associated with ORT diagnosis in the multivariable logistic regression analysis (odds ratio = 4.87, 95% confidence interval = 2.54-9.37, p , 0.001). Bacteriology confirmed 10 ORT isolates. Additionally, antimicrobial susceptibility testing revealed complete resistance to several antibiotics, with varying levels of resistance and sensitivity across isolates, including 100% sensitivity to florfenicol in broilers and turkeys. Sequencing of the rpoB gene revealed that 10 ORT isolates had nucleotide similarity ranging from 98% to 100% with other known ORT isolates from chickens and turkeys reported in the U.K., Chile, China, Portugal, and the United States. On the other hand, two ORT isolates were found to be genetically very close to known RA strains, despite testing positive for ORT by real-time qPCR. Amino acid sequence comparisons for these isolates reached 83.10% similarity with Riemerella sp. strain WJ4 isolated in China and 98.79% similarity with strain IPDH 98/90 isolated in Germany. In conclusion, the prevalence of ORT in Moroccan poultry flocks increased over the 5-yr period covered by this retrospective study, contributing significantly to recent respiratory disease outbreaks. Additionally, RA may also contribute to polyserositis in poultry; however, further studies are needed to determine its pathogenicity.

Distinct species turnover patterns shaped the richness of antibiotic resistance genes on eight different microplastic polymers

Elucidating the formation mechanism of plastisphere antibiotic resistance genes (ARGs) on different polymers is necessary to understand the ecological risks of plastisphere ARGs. Here, we explored the turnover and assembly mechanism of plastisphere ARGs on 8 different microplastic polymers (4 biodegradable (bMPs) and 4 non-biodegradable microplastics (nMPs)) by metagenomic sequencing. Our study revealed the presence of 479 ARGs with abundance ranging from 41.37 to 58.17 copies/16S rRNA gene in all plastispheres. These ARGs were predominantly multidrug resistance genes. The richness of plastisphere ARGs on different polymers had a significant correlation with the contribution of species turnover to plastisphere ARGs β diversity. Furthermore, polymer type was the most critical factor affecting the composition of plastisphere ARGs. More opportunistic pathogens carrying diverse ARGs on BMPs (PBAT, PBS, and PHA) with higher horizontal gene transfer potential may further magnify the ecological risks and human health threats. For example, the opportunistic pathogens Riemerella anatipestifer, Vibrio campbellii, and Vibrio cholerae are closely related to human production and life, which were the important potential hosts of many plastisphere ARGs and mobile genetic elements on BMPs. Thus, we emphasize the urgency of developing the formation mechanism of plastisphere ARGs and the necessity of controlling BMPs and ARG pollution, especially BMPs, with ever-increasing usage in daily life.

Genomic analysis and experimental pathogenic characterization of Riemerella anatipestifer isolates from chickens in China

Waterfowl have a high likelihood of being infected with Riemerella anatipestifer. Although the pathogen is found in domestic ducks, turkeys, geese, and wild birds, there is little information available about the consequences of infection during egg laying and hatching in chickens. Here, we present the first report of a novel sequence type of R. anatipestifer S63 isolated from chickens in China. On the basis of pan-genome analysis, we showed S63's genome occupies a distinct branch with other R. anatipestifer isolates from other hosts. Galleria mellonella larval tests indicated that S63 is less virulent than R. anatipestifer Ra36 isolated from ducks. Ducks and hens are susceptible to S63 infection. There is no mortality rate for chickens or ducks, but adult chickens experience neurological symptoms that reduce egg production and hatching rates. In chickens, S63 might be passed vertically from parents to offspring, resulting in "jelly-like" lifeless embryos. Using quantitative PCR, S63 was detected in the brain, liver, reproductive organs, and embryos. As far as we know, this is the first report of R. anatipestifer in hens, a disease that can reduce egg productivity, lower hatching rates, and produce jelly-like lifeless embryos, and the first report to raise the possibility that hens can be infected by roosters via semen.

Antibacterial activity of isopropoxy benzene guanidine against Riemerella anatipestifer

Introduction: Riemerella anatipestifer (R. anatipestifer) is an important pathogen in waterfowl, leading to substantial economic losses. In recent years, there has been a notable escalation in the drug resistance rate of R. anatipestifer. Consequently, there is an imperative need to expedite the development of novel antibacterial medications to effectively manage the infection caused by R. anatipestifer. Methods: This study investigated the in vitro and in vivo antibacterial activities of a novel substituted benzene guanidine analog, namely, isopropoxy benzene guanidine (IBG), against R. anatipestifer by using the microdilution method, time-killing curve, and a pericarditis model. The possible mechanisms of these activities were explored. Results and Discussion: The minimal inhibitory concentration (MIC) range of IBG for R. anatipestifer was 0.5-2 μg/mL. Time-killing curves showed a concentration-dependent antibacterial effect. IBG alone or in combination with gentamicin significantly reduced the bacterial load of R. anatipestifer in the pericarditis model. Serial-passage mutagenicity assays showed a low probability for developing IBG resistance. Mechanistic studies suggested that IBG induced membrane damage by binding to phosphatidylglycerol and cardiolipin, leading to an imbalance in membrane potential and the transmembrane proton gradient, as well as the decreased of intracellular adenosine triphosphate. In summary, IBG is a potential antibacterial for controlling R. anatipestifer infections.

Lactobacillus plantarum supernatant inhibits growth of Riemerella anatipestifer and mediates intestinal antimicrobial defense in Muscovy ducks

Riemerella anatipestifer (RA) is an important pathogen of waterfowl, with multiple serotypes and a lack of cross-protection between each serotype, which leads to the continued widespread in the world and causing significant economic losses to the duck industry. Thus, prevention and inhibition of RA infection are of great concern. Previous research has established that Lactobacillus plantarum supernatant (LPS) can prevents the pathogenic bacteria infection. However, LPS whether inhibits RA and underlying mechanisms have not yet been clarified. In this study, we investigated the direct and indirect effects of LPS-ZG7 against RA infection in Muscovy ducks. The results demonstrated that LPS-ZG7 prevented RA growth in the presence of pH-neutralized, and the inhibition was relatively stable and unaffected by heat, acid-base and ultraviolet light (UV). Following flow cytometry data found that LPS-ZG7 increased RA membrane permeability and leakage of intracellular molecules. And scanning electron microscopy revealed LPS-ZG7 damaged the RA membrane integrity and leading to RA death. Furthermore, quantitative real time polymerase chain reaction (qPCR) analysis represented that LPS-ZG7 upregulated mucosal tight junction proteins occludin, claudin-1, and Zo-1 in Muscovy ducks, and increasing mucosal transport channels SGLT-1, PepT1, AQP2, AQP3, and AQP10 in duodenum, jejunum, and colon, then decreased the intestinal permeability and intestinal barrier disruption which were caused from RA. From the data, it is apparent that LPS-ZG7 enhanced intestinal mucosal integrity by rising villus height, villus height-to-crypt depth ratio and lower crypt depth. LPS-ZG7 significantly decreased intestinal epithelia cells apoptosis caused by RA invasion, and enhanced intestinal permeability and contribute to barrier dysfunction, ultimately improving intestinal health of host, indirectly leading to reduce diarrhea rate and mortality caused by RA. Overall, this study strengthens the idea that LPS-ZG7 directly inhibited the RA growth by increased RA membrane permeability and damaged the RA membrane integrity, and then indirectly enhanced intestinal mucosal integrity, improved intestinal health of host and mediated intestinal antimicrobial defense.

Immunogenicity of live phoP gene deletion strain of Riemerella anatipestifer serotype 1

Duck infectious serositis is an acute and infectious disease caused by Riemerella anatipestifer (R. anatipestifer) that leads to perihepatitis, pericarditis, meningitis, and airbag inflammation in ducks, which causes serious economic losses to the global duck industry. The phoP/phoR is a novel 2-component signal transduction system first reported in gram-negative bacteria, of which phoP acts as a global regulator and virulence factor. In this study, the phoP gene from the R. anatipestifer YM strain was knocked out using homologous recombination technology and replaced with the spectinomycin resistance gene (Spec). The virulence of the R. anatipestifer YMΔphoP strain was reduced by approximately 47,000 times compared to that of the wild-type R. anatipestifer YM strain. Ducks were immunized with live R. anatipestifer YMΔphoP strain by subcutaneous inoculation at a dose of 10⁶ to 10⁷ CFU (0.2 mL per duck) and challenged with the wild-type R. anatipestifer YM strain 14 days later. The protection rate in the immunized group was 100%. The growth characteristics of ducks in the immunized and negative control groups were normal, and the research demonstrated R. anatipestifer YMΔphoP strain have suitable immunogenicity and protective effects. Thus, the study findings suggest that the novel R. anatipestifer YMΔphoP strain may provide a candidate for the development of a gene deletion activated vaccine against duck infectious serositis.

PK/PD integration of florfenicol alone and in combination with doxycycline against Riemerella anatipestifer

Riemerella anatipestifer (RA) is an important pathogen found in poultry. RA infection can kill ducks and lead to significant economic losses. Seven RA strains with different susceptibility phenotypes were chosen to study the pharmacokinetic/pharmacodynamic (PK/PD) integration of florfenicol (FF) alone and in combination with doxycycline (DOX). The checkerboard assay indicated that synergy [fractional inhibitory concentration index (FICI) ≤ 0.5] was detected in the CVCC3952 strain of RA and that additivity (FICI >0.5 to ≤ 1) was observed in other strains. Static time–kill curves showed that the bactericidal effect of FF against RA was produced at a FF concentration ≥4 MIC, and the antibacterial activity of FF against RA was enhanced from the aspects of efficacy and efficacy in combination with DOX. Dynamic time–kill curves indicated that FF elicited bactericidal activity against the CVCC3857 strain with a reduction ≥4.88 log₁₀CFU/ml when the dose was ≥8 mg/L. However, a bactericidal effect was not achieved at the maximum administered dose of FF monotherapy (20 mg/L) for isolates with a MIC ≥4 μg/ml. The effect of FF against RA was enhanced upon combination with DOX. The combination of FF with DOX reduced the bacterial burden ≥4.53 log₁₀CFU/ml for all strains with a MIC ≥4 μg/ml. Data were fitted to a sigmoidal E_max model. The PK/PD parameters of AUC_24h/MIC (the area under the concentration–time curve over 24 h divided by the MIC) and %T >MIC (the cumulative percentage of time over a 24-h period at which the concentration exceeded the MIC) of FF for eliciting a reduction of 3 log₁₀CFU/ml was 40.10 h and 58.71, respectively. For strains with a MIC ≤ 16 μg/ml, the magnitude of the AUC_24h/MIC and C_max/MIC required for a 3 log₁₀CFU/ml of bacterial killing was 34.84 h and 4.74 in the presence of DOX at 0.5 MIC, respectively. These data suggest that combination of FF with DOX enhanced the activity against RA strains with various susceptibilities to FF and DOX.