Characterization and antimicrobial resistance analysis of avian pathogenic Escherichia coli isolated from Italian turkey flocks

Prevalence of specific serogroups, antibiotic resistance and virulence factors of avian pathogenic Escherichia coli (APEC) isolated from clinical cases: A systematic review and meta-analysis

Pathogenic strains of Escherichia coli infecting poultry, commonly called avian pathogenic E. coli (APEC) present significant risks, to the health of both poultry and the general public. This systematic review aimed to examine the prevalence of APEC serotypes, sequence types (ST), phylogenetic groups, virulence factors and antibiotic resistance patterns based on 189 research papers sourced from PubMed, Web of Science, and ProQuest. Then, data were extracted from the selected studies and analyzed to assess the global distribution and characteristics of APEC strains. The metaprop codes in the Meta and Metafor packages of R as implemented in RStudio were then used to conduct meta-analysis. Among APEC strains identified from these different research reports serogroup O78 had the highest overall prevalence (16 %), followed by serogroups O2 (10 %), and O117 (8 %). The most common ST profiles were ST117 (20 %), ST140 (15 %), ST95 (12 %), and ST131 (9 %). ST117 and ST140 are known reservoirs for pathogenic E. coli in humans. Moreover, phylogenetic assessment highlighted the prevalence of phylogroups A, A1, F, D, and B2 among APEC strains indicating diversity in phylogenetic origin within poultry populations. The presence of antimicrobial resistance was notable among APEC strains against antibiotics such as tetracyclines, penicillins, and cephalosporins. This resistance may be linked to use of antimicrobials in poultry production in certain regions presenting challenges for both animal health management and human infection control. Analysis of sequences linked to adherence or virulence indicated that genes encoding adhesins (csg, fimC), iron/metal uptake (sitB, sitC, iroD) and cytotoxicity (estB, hlyF), and serum resistance (traT, iss) were highly prevalent. These factors have been reported to contribute to APEC host colonization and virulence in poultry. In summary, this overview of the characteristics of APEC highlights the pressing importance of monitoring and implementing management approaches to reduce antimicrobial resistance considering that a phylogenetic diversity of E. coli strains causes infections in both poultry and humans and represents a risk to both animal and public health. Further, determining the major conserved aspects and predominant mechanisms of virulence of APEC is critical for improving diagnostics and developing preventative measures to reduce the burden of infection caused by pathogenic E. coli in poultry and lower risks associated with foodborne transmission of E. coli to humans through poultry and poultry products.

Role of ArcA in the regulation of antibiotic sensitivity in avian pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC) is one of the common extraintestinal infectious disease pathogens in chickens, geese, and other birds, inducing serious impediments to the development of the poultry industry. Hence, investigating how bacteria regulate themselves amidst different challenging conditions is immense essential in prevention and treatment for bacterial pathogen infections. The ArcA regulatory factor has been reported to regulate oxygen availability in strains, but its role in regulation of antibiotics resistance in APEC is unclear. This study delved into understanding how ArcA regulates antibiotic resistance in APEC. An E. coli APEC40 arcA knockout strain was constructed, and the regulatory mechanism of arcA on APEC antibiotic susceptibility was identified by drug sensitivity test, colony counting assay, real-time quantitative PCR, β-galactosidase assays and electrophoretic mobility shift assay (EMSA). The results showed that ArcA directly binds to the promoter region of the outer membrane protein OmpC/OmpW and regulates bacterial susceptibility to kanamycin and penicillin G. At the same time, the double knockout of ompW and ompW/arcA resulted in an increase in resistance to kanamycin compared to the deletion of the arcA gene. This outcome provided experimental proof suggesting that the outer membrane protein OmpW could serve as a crucial pathway for the ingress of kanamycin into cells. These results confirmed the important regulatory role of ArcA transcription factors under APEC antibiotic stress.

Genetic Diversity and Antimicrobial Resistance of Extraintestinal E. coli Populations Pre- and Post-Antimicrobial Therapy on Broilers Affected by Colisepticemia

The aim of the present study was to investigate the genetic diversity and antimicrobial resistance (AMR) of E. coli during enrofloxacin therapy in broilers affected by colisepticemia. Three unrelated farms with ongoing colibacillosis outbreaks were sampled at day 1 before treatment and at days 5, 10 and 24 post-treatment. A total of 179 E. coli isolates were collected from extraintestinal organs and submitted to serotyping, PFGE and the minimum inhibitory concentration (MIC) against enrofloxacin. PFGE clusters shifted from 3-6 at D1 to 10-16 at D5, D10 and D24, suggesting an increased population diversity after the treatment. The majority of strains belonged to NT or O78 and to ST117 or ST23. PFGE results were confirmed with SNP calling: no persistent isolates were identified. An increase in resistance to fluoroquinolones in E. coli isolates was observed along the treatment. Resistome analyses revealed qnrB19 and qnrS1 genes along with mutations in the gyrA, parC and parE genes. Interestingly, despite a fluoroquinolone selective pressure, qnr-carrying plasmids did not persist. On the contrary, two conjugative AMR plasmid clusters (AB233 and AA474) harboring AMR genes other than qnr were persistent since they were identified in both D1 and D10 genomes in two farms. Further studies should be performed in order to confirm plasmid persistence not associated (in vivo) to antimicrobial selective pressure.

The Two-Component System CpxRA Affects Antibiotic Susceptibility and Biofilm Formation in Avian Pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC) is one of the common extraintestinal infectious disease pathogens in chickens, geese, and other birds. It can cause a variety of infections, and even the death of poultry, causing enormous economic losses. However, the misuse and abuse of antibiotics in the poultry industry have led to the development of drug resistance in the gut microbes, posing a challenge for the treatment of APEC infections. It has been reported that the CpxRA two-component system has an effect on bacterial drug resistance, but the specific regulatory mechanism remains unclear. In this study, the regulatory mechanism of CpxRA on APEC biofilm formation and EmrKY efflux pump was investigated. The cpxRA knockout strain of E. coli APEC40 was constructed, and the molecular regulatory mechanism of CpxR on biofilms and efflux pump-coding genes were identified by biofilm formation assays, drug susceptibility test, real-time reverse transcription quantitative PCR, and electrophoretic mobility shift assay (EMSA). The results indicated that CpxR can directly bind to the promoter region of emrKY and negatively regulate the sensitivity of bacteria to ofloxacin and erythromycin. These results confirm the important regulatory role of the CpxRA two-component system under antibiotic stress in APEC.

Associations between antimicrobial resistance in fecal Escherichia coli isolates and antimicrobial use in Canadian turkey flocks

Antimicrobial resistance (AMR) in enteric bacteria continues to be detected in turkey flocks and retail products worldwide, including in Canada. However, studies assessing linkages between on-farm antimicrobial use (AMU) and the development of AMR are lacking. This study aims to identify AMU characteristics that impact the development of AMR in the indicator bacteria Escherichia coli in turkey flocks, building on the Canadian Integrated Program for Antimicrobial Resistance Surveillance methodology for farm-level AMU and AMR data integration. Two analytic approaches were used: (1) multivariable mixed-effects logistic regression models examined associations between AMU (any route, route-specific, and route-disease-specific indication) summarized as the number of defined daily doses in animals using Canadian standards ([nDDDvetCA]/1,000 kg-animal-days at risk) and AMR and (2) multivariable mixed-effects Poisson regression models studied the linkages between AMU and the number of classes to which an E. coli isolate was resistant (nCR E. coli ). A total of 1,317 E. coli isolates from a network of 16 veterinarians and 334 turkey producers across the five major turkey-producing provinces in Canada between 2016 and 2019 were used. Analysis indicated that AMR emerged with the use of related antimicrobials (e.g., tetracycline use-tetracycline resistance), however, the use of unrelated antimicrobial classes was also impacting AMR (e.g., aminoglycosides/streptogramins use-tetracycline resistance). As for studying AMU-nCR E. coli linkages, the most robust association was between the parenteral aminoglycosides use and nCR E. coli , though in-feed uses of four unrelated classes (bacitracin, folate pathway inhibitors, streptogramins, and tetracyclines) appear to be important, indicating that ongoing uses of these classes may slow down the succession from multidrug-resistant to a more susceptible E. coli populations. The analysis of AMU (route and disease-specific)-AMR linkages complemented the above findings, suggesting that treatment of certain diseases (enteric, late-stage septicemic conditions, and colibacillosis) are influential in the development of resistance to certain antimicrobial classes. The highest variances were at the flock level indicating that stewardship actions should focus on flock-level infection prevention practices. This study added new insights to our understanding of AMU-AMR linkages in turkeys and is useful in informing AMU stewardship in the turkey sector. Enhanced surveillance using sequencing technologies are warranted to explain molecular-level determinants of AMR.

Molecular and Serological Characteristics of Avian Pathogenic Escherichia coli Isolated from Various Clinical Cases of Poultry Colibacillosis in Poland

Escherichia coli infections are a major problem in modern poultry production. Avian pathogenic E. coli (APEC) strains have several mechanisms that enable them to colonize various ecosystems. In this study, 290 E. coli isolates were recovered from clinical cases of colibacillosis in chicken and turkey broilers and from laying and breeding hens. The samples were taken from organs with pathological changes suggesting colibacillosis. The lesions were assigned to three groups depending on their advancement, of which the largest (60% of the isolates) was group 3, with the most extensive changes. The most common serotype was shown to be O78 (14%). The most frequently detected gene among those tested was iss, while papC was the least prevalent. An analysis of the number of genes present per isolate revealed that the presence of four genes was the most common (22%), while only 1% of the strains tested had all eight genes. The most frequently detected genes for each serotype were iss and iucD for O78; irp2 and cvi/cva for O1; irp2, iucD, and iss for O2, and iss and iucD for O8, for which the least frequent was papC. All O18 serotype strains had the iss gene, while none had the vat gene.

Investigation of Serotype Prevalence of Escherichia coli Strains Isolated from Layer Poultry in Greece and Interactions with Other Infectious Agents

Colibacillosis is the most common bacterial disease in poultry and it is caused by avian pathogenic Escherichia coli (APEC), which is assigned to various O-serogroups. Previous studies have shown that APEC strains are more often related to certain O-serogroups such asO78, O2 and O1. E. coli has been reported to act either as a primary or secondary agent in complicating other infections. The aim of this study was to investigate the occurrence of and characterize the O-serogroups of E. coli strains isolated from commercial layer and layer breeder flocks showing macroscopic lesions of colibacillosis and increased or normal mortality in Greece. Furthermore, we attempted to assess the interaction between infectious agents such as Mycoplasma gallisepticum (MG), Mycoplasma synoviae (MS), infectious bronchitis (IBV) and infectious laryngotracheitis (ILT) with E. coli infections in layer flocks with increased mortality. Our study revealed that in addition to the common serogroups (O78, O2), many other, and less common serogroups were identified, including O111. The O78, O111 and O2 serogroups were frequently detected in flocks with lesions of colibacillosis and increased mortality whereas O2, O88 and O8 were reported more commonly in birds with colibacillosis lesions but normal mortality rates. These data provide important information for colibacillosis monitoring and define preventative measures, especially by using effective vaccination programs because E. coli vaccines are reported to mainly offer homologous protection. Finally, concerning the association of the four tested infectious agents with E. coli mortality, our study did not reveal a statistically significant effect of the above infectious agents tested with E. coli infection mortality.

Prevalence of poultry Escherichia coli isolates producing extended-spectrum beta-lactamases and their public health importance

Recently, different reports highlighted the problem with dissemination of Escherichia coli producing extended spectrum beta-lactamases (ESBL) in poultry farms in Europe. The high incidence of Escherichia coli among poultry in Europe harbouring blaCTX-M-1 and the occurrence of ESBL and AmpC-producing Escherichia coli in raw meat samples collected from slaughterhouses in Europe have been discussed. ESBL-producing Enterobacteriaceae can be transmitted along the broiler production chain. Plasmids responsible for ESBL production frequently carry genes coding resistance to other antimicrobial classes, such as fluoroquinolones, aminoglycosides, sulphonamides. Resistance to cephalosporins in Enterobacteriaceae is of special concern for public health, because these anti­microbial agents are critically important. The aim of this mini review was to describe the mechanisms of resistance and prevalence of ESBL-producing E. coli. It is important to investigate the spread of these bacteria among poultry, the role of farm birds as reservoir of E. coli and the risk for people.

Role of McbR in the regulation of antibiotic susceptibility in avian pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC) causes a variety of bacterial infectious diseases known as avian colibacillosis leading to significant economic losses in the poultry industry worldwide and restricting the development of the poultry industry. The development of efflux pumps is one important bacterial antibiotic resistance mechanism. Efflux pumps are capable of extruding a wide range of antibiotics out of the cytoplasm of some bacterial species, including β-lactams, polymyxins, tetracyclines, fluoroquinolones, aminoglycosides, novobiocin, nalidixic acid, and fosfomycin. In the present study, we constructed the mcbR mutant and the mcbR-overexpressing strain of E. coli strain APECX40 and performed antimicrobial susceptibility testing, antibacterial activity assays, real-time reverse transcription PCR, and electrophoretic mobility shift assays (EMSA) to investigate the molecular regulatory mechanism of McbR on the genes encoding efflux pumps. Our results showed that McbR positively regulates cell susceptibility to 12 antibiotics, including clindamycin, lincomycin, cefotaxime, cefalexin, doxycycline, tetracycline, gentamicin, kanamycin, norfloxacin, ofloxacin, erythromycin, and rifampicin by activating the transcription of acrAB, acrD, emrD, and mdtD (P < 0.01). Additionally, EMSA indicated that McbR specifically binds to the promoter regions of acrAB, acrD, acrR, emrD, and mdtD. This study suggests that, in APECX40, McbR plays an important role in the regulation of bacterial susceptibility by directly activating the transcription of efflux pumps genes.

Characterization of Avian Pathogenic Escherichia coli (APEC) Associated With Turkey Cellulitis in Iowa

Turkey cellulitis, also known as clostridial dermatitis is a significant cause of morbidity, mortality, and carcass condemnation at slaughter resulting in considerable losses for turkey producers. Here, we assessed the potential role of Avian Pathogenic Escherichia coli (APEC) in a cellulitis outbreak on a turkey farm in Iowa. Birds from one farm with a history of cellulitis and one farm with no history of disease (for comparison) were followed from the age of 10 weeks (before the outbreak) to 18 weeks (just prior to slaughter). E. coli recovered from the litter, from skin lesions of birds with cellulitis, and from systemic lesions of birds submitted for necropsy, were assessed. A total of 333 isolates were analyzed and screened for virulence-associated genes, antimicrobial resistance genes including heavy metal resistance, adhesins, invasins, and protectins, iron acquisition systems and their phylogenetic group through multiplex PCR. In addition, PCR was used to serogroup the isolates, and pulsed field gel electrophoresis (PFGE) was used to analyze a subset of strains from the farm environment (litter) and birds at 17 and 18 weeks of age when the cellulitis infection appeared to peak. Overall, E. coli isolates recovered from cellulitis lesions and systemic infection were identified as APEC, while a lower prevalence of E. coli recovered from the litter met the criteria of APEC-like. Direct comparison of E. coli isolates from the litter, lesions, and systemic strains using PFGE failed to find identical clones across all three sources reflecting the diversity of strains present in the poultry environment causing disease. This study highlights the role of APEC in turkey cellulitis and should not be overlooked as a significant contributor to the disease in turkeys.

Role of LsrR in the regulation of antibiotic sensitivity in avian pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC) is a specific group of extraintestinal pathogenic E. coli that causes a variety of extraintestinal diseases in chickens, ducks, pigeons, turkeys, and other avian species. These diseases lead to significant economic losses in the poultry industry worldwide. However, owing to excessive use of antibiotics in the treatment of infectious diseases, bacteria have developed antibiotic resistance. The development of multidrug efflux pumps is one important bacterial antibiotic resistance mechanism. A multidrug efflux pump, MdtH, which belongs to the major facilitator superfamily of transporters, confers resistance to quinolone antibiotics such as norfloxacin and enoxacin. LsrR regulates hundreds of genes that participate in myriad biological processes, including mobility, biofilm formation, and antibiotic susceptibility. However, whether LsrR regulates mdtH transcription and then affects bacterial resistance to various antibiotics in APEC has not been reported. In the present study, the lsrR mutant was constructed from its parent strain APECX40 (WT), and high-throughput sequencing was performed to analyze the transcriptional profile of the WT and mutant XY10 strains. The results showed that lsrR gene deletion upregulated the mdtH transcript level. Furthermore, we also constructed the lsrR- and mdtH-overexpressing strains and performed antimicrobial susceptibility testing, antibacterial activity assays, real-time reverse transcription PCR, and electrophoretic mobility shift assays to investigate the molecular regulatory mechanism of LsrR on the MdtH multidrug efflux pump. The lsrR mutation and the mdtH-overexpressing strain decreased cell susceptibility to norfloxacin, ofloxacin, ciprofloxacin, and tetracycline by upregulating mdtH transcript levels. In addition, the lsrR-overexpressing strain increased cell susceptibility to norfloxacin, ofloxacin, ciprofloxacin, and tetracycline by downregulating mdtH transcript levels. Electrophoretic mobility shift assays indicated that LsrR directly binds to the mdtH promoter. Therefore, this study is the first to demonstrate that LsrR inhibits mdtH transcription by directly binding to its promoter region. This action subsequently increases susceptibility to the aforementioned four antibiotics in APECX40.

Antimicrobial in vitro activities of condensed tannin extracts on avian pathogenic Escherichia coli

Condensed tannins (CTs), which extracted from yew leaves, tilia flower and black locust leaves, were examined for their antimicrobial in vitro activity against avian pathogenic Escherichia coli (APEC). Past research demonstrated that CTs which contain procyanidins and prodelphinidins that could inhibit the growth of a wide range of bacteria. However, there is no information on how these affect pathogenic bacteria from chickens such as APEC. The high concentration of extracts, 10, 5, 2·5 mg ml^-1 , affected the growth curves of APEC, which gave different inhibition values for the three CT extracts. Furthermore, these CTs had significant effects (P ≤ 0·05) on APEC biofilm and motility depending on each CT concentration and composition. However, at low concentration (0·6 mg ml^-1 ), the tilia flowers, a high molar percentage of procyanidins, enhanced bacterial cell attachment and improved the swimming motility of APEC. In contrast, yew, an equal molar percentage of procyanidins/prodelphinidins, and black locust, a high molar percentage of prodelphinidins, interrupted and blocked swarming and swimming motility. The data suggested that the antimicrobial activity of the CT extracts was elicited by a positive relationship between anti-biofilm formation and anti-motility capacities. SIGNIFICANCE AND IMPACT OF THE STUDY: This study showed that condensed tannins (CTs), which were a group of secondary metabolites of many plants and rich in prodelphinidins (PD), had greater antibacterial activity against avian pathogenic Escherichia coli (APEC) than CTs that were rich in procyanidins (PC). The mode of action of the CTs was to inhibit the swimming and swarming motility of APEC, and its ability to form biofilms. The significance of this finding is that the use of PD-rich CTs to control APEC should not encourage the development of antibiotic resistance by APEC because a different mechanism is used. If confirmed in vivo, this could provide the poultry industry with a valuable and novel means of controlling the antibiotic resistance.

Extended-spectrum beta-lactamase and Class 1 integrons in multidrug-resistant Escherichia coli isolated from turkeys

AIM

This study aimed to investigate the prevalence and implication of extended-spectrum beta-lactamase (ESBL) producing and Class 1 integrons (int1) gene carriers Escherichia coli isolates that demonstrated multidrug resistance (MDR) phenotypes and was isolated from turkeys that suffered from respiratory manifestations.

MATERIALS AND METHODS

A total of 120 freshly dead turkey poults that suffered from respiratory manifestations, with a history of treatment failure at Hefna, Belbis, Sharqia (Egypt) were sampled. From each bird lung and liver were aseptically collected and transported for laboratory investigations.

RESULTS

Examination of samples collected from 120 freshly dead turkey poults revealed the isolation of coagulase-positive staphylococci, coagulase-negative staphylococci, Campylobacter spp., Salmonella spp., Proteus spp., Pseudomonas spp., Klebsiella spp., and E. coli with the prevalence rates of 12/120 (10%), 30/120 (35%), 17/120 (14.2%), 5/120 (4.1%), 17/120 (14.2%), 6/120 (5%), 7/120 (5.8%), and 18/120 (15%), respectively. E. coli isolates were subjected for serotyping and characterization, while the rest of isolates were preserved to be investigated later in further studies. Serogrouping of E. coli isolates revealed the identification of O119, O6, O8, and O169, while 1/18 of isolates was untypable. Studying phenotypic antibiotic susceptibility profiles of isolates revealed that 18/18 (100%) of isolates demonstrated resistance against cefuroxime, tetracycline, and trimethoprim, 16/18 (88.9%) of isolates demonstrated resistance to amoxicillin/clavulanic acid, enrofloxacin, and norfloxacin, 14/18 (77.8%) of isolates demonstrated resistance to doxycycline and ciprofloxacin, and 9/18 (50%) of isolates showed resistance to gentamycin. Double disk synergy test showed that 6/18 (33.3%), 8/18 (44.4%), and 13/18 (72.2%) of isolates demonstrated the phenotypic pattern of ESBL producers with cefepime, cefotaxime, and ceftriaxone, respectively. Genotypic attributes for beta-lactamase TEM gene and int1 gene were studied by reverse transcriptase-polymerase chain reaction and revealed that 17/18 (94.4%) of isolates were positive for both genes. Embryo lethality test indicated that the 18 studied E. coli isolates were considered primary pathogens.

CONCLUSION

The results revealed that 18/18 (100%) of E. coli isolates demonstrated MDR against three or more antibiotic groups, 9/18 (50%) of isolates showed extensive resistance against the nine tested chemotherapeutic agents from seven antibiotic groups. It is recommended to monitor the circulation of MDR and ESBL-producing pathogens in poultry production in a one health approach, as a preventive measure to mitigate the risk imposed on public health.

The association between extended spectrum beta-lactamase (ESBL) and ampicillin C (AmpC) beta-lactamase genes with multidrug resistance in Escherichia coli isolates recovered from turkeys in Brazil

1. The aim of this study was to analyse the association between Escherichia coli isolates recovered from turkeys and the expression of beta-lactamase genes, such as extended spectrum beta-lactamase (ESBL) and ampicillin class C (AmpC). The phenotype of the resistance profile was examined using the association between amoxicillin and ceftiofur resistance. 2. Results showed that 84% from the turkey isolates harboured 4 or 5 genes associated with the CoIV plasmid. In an antibiogram test, 82% of the isolates were multidrug-resistant, the highest levels of resistance being against erythromycin (99%) and amoxicillin (76.1%). ESBL-positive groups were 31% positive for the ctx-m-2 gene, 6.8% were positive for ctx-m-8 and 70% harboured the tem wild gene. 3. All positive isolates from the AmpC beta-lactamase-positive group harboured the cmy-2 gene. The presence of the cmy-2 gene was associated with both the CTX-group genes and resistance to ceftiofur. 4. There was a high prevalence of avian pathogenic E. coli in suspected cases of colibacillosis in turkeys and a high antimicrobial resistance index. The results highlighted the risk of ceftiofur resistance and the presence of both ESBL and AmpC beta-lactamase E. coli in the turkey production chain.

Longitudinal field studies of avian metapneumovirus and turkey hemorrhagic enteritis virus in turkeys suffering from colibacillosis associated mortality

The aim of this study was to evaluate if the exposure to Avian metapneumovirus (aMPV) and/or to Turkey hemorrhagic enteritis virus (THEV) was significant for the induction of episodes of colibacillosis in aMPV and THEV vaccinated turkeys. Colibacillosis-associated mortality was recorded and longitudinal virological studies performed in three consecutive turkey flocks reared in the same farm. aMPV and THEV diagnostic swabs and blood samples were made once a week up to 14 weeks of age. Swabs were processed by molecular techniques for viruses detection and antibody titres were evaluated. Field subtype B aMPVs were detected in all flocks at different ages of life always associated with respiratory signs and increase of colibacillosis-associated mortality. THEV has been consistently detected in all flocks since the 9th week of age. Vaccination with a single dose of the THEV commercial inactivated vaccine available in Italy seems does not protect the birds from the infection. Sequence comparison of the hexon protein of one of the THEV strains detected, and strains isolated worldwide, revealed high similarity between them. These results are consistent with the notion that the hexon protein, being the major antigenic component of the virus, is highly conserved between the strains. Results showed that field aMPV infection is directly correlated to colibacillosis-associated mortality. Less clear appears the role of THEV because the endemicity of aMPV makes difficult to evaluate its role in predisposing colibacillosis in absence of aMPV. It would be interesting to further investigate this issue through experimental trials in secure isolation conditions.