Identification of Pasteurella multocida Serogroup F isolates in rabbits

In field evaluation of impact on clinical signs of an inactivated autogenous vaccine against Pasteurella multocida in rabbits

In Italy, the use of autogenous inactivated vaccines prepared with the bacterial strains isolated from affected animals is authorized by the Ministry of Health in farms where bacterial diseases occur frequently. The autogenous vaccine performed using Pasteurella multocida is frequently used in rabbit farms, but the feedback of its application is not available. Therefore, the aim of this study is to give information about the impact on the clinical signs of a bivalent autogenous vaccine in rabbits of a genetic centre. The vaccine was prepared using two P. multocida strains belonging to serogroups A and F, equipped with virulence genes and responsible for cyclical outbreak of pasteurellosis in the farm. The vaccine was administered with a first injection, followed by another one after 15 days, then another one four months after the first injection, and then continuing with a further injection every six months to all rabbits. Clinical conditions and mortality rates were monitored for two years after the first vaccination. The improvement in clinical condition and the decrease of the mortality rate were significant especially in the first year post-vaccine. In addition, the number of animals removed due to the disease decreased greatly. Based on the finding of P. multocida strains belonging to serogroup D and serogroup A equipped with different virulence-gene patterns from those previously found, we suggest that the vaccine was unable to prevent the introduction and spreading of new strains among the rabbits.

Characterisation of Pasteurella multocida Strains from Different Lesions in Rabbits

Pasteurellosis, a disease caused by Pasteurella multocida, is responsible for economic losses in rabbit industrial farms due to rhinitis, conjunctivitis, pneumonia, metritis, mastitis, orchitis, subcutaneous abscesses, otitis, encephalitis, and septicaemic forms. Although the occurrence of the disease is conditioned by predisposing factors that affect the rabbit immune response, the strains of P. multocida involved in the infection may have a different pathogenic ability. Therefore, typing of strains spread among the rabbits is important to assess their pathogenic potential. The aim of this study is to investigate the P. multocida strains responsible for disease in rabbit industrial farms. A total of 114 strains identified from different lesions were serotyped. Additionally, the presence of virulence-associated genes was investigated using three PCR (polymerase chain reaction) protocols. Capsular type A was prevalently found in strains from respiratory lesions while types D and F in those from metritis, mastitis, and other lesions. Different associations between some virulence-associated genes and both capsular type and lesions found in rabbits were detected. The presence of 8 virulence-associated genes seems to increase the occurrence of metritis. In addition, strains belonging to capsular type A and responsible for respiratory disorders especially, were found equipped with 10 and 11 virulence-associated genes. Nevertheless, the presence of strains responsible only for rhinitis was also detected among the latter, suggesting that the pathogenic ability of the bacteria depends on the expression rather than the presence of a gene.

Pathogenic and genomic characterization of rabbit-sourced Pasteurella multocida serogroup F isolates recovered from dead rabbits with respiratory disease

Pasteurella multocida serogroup F can infect a number of animals. However, the pathogenicity and genomic features of this serogroup are still largely unknown. In the present study, the pathogenicity and genomic sequences of 19 rabbit-sourced P. multocida serogroup F isolates were determined. The 19 isolates were highly pathogenic for rabbits causing severe pathologic lesions and high mortality in inoculated rabbits. Nevertheless, the pathologic lesions in rabbits caused by the 19 isolates were distinct from those caused by the previously reported high-virulent serogroup F strains J-4103 (rabbit), P-4218 (turkey), and C21724H3km7 (chicken). Moreover, the 19 isolates were avirulent to white feather broilers. The genomes of the 19 isolates were determined to understand the pathogenicity of these isolates. The finding of a number of functional genes in the 19 isolates by comparison with the low-virulent rabbit-sourced serogroup F strain s4 might contribute to the high virulence of these isolates. Notably, polymorphisms were determined in the lipopolysaccharide outer core biosynthetic genes natC and gatF among the serogroup F strains of different hosts. However, the sequences of natC and gatF from rabbit-sourced strains (except for SD11) were identical, which might be responsible for the host specific of the 19 isolates. The observations and findings in this study would be helpful for the understanding of the pathogenicity variation and host predilection of P. multocida.

IMPORTANCE

The 19 rabbit-sourced Pasteurella multocida serogroup F isolates showing high virulence to rabbits were avirulent to the broilers. Notably, polymorphisms were determined in the lipopolysaccharide outer core biosynthetic genes natC and gatF among all serogroup F strains of different hosts. However, the sequences of natC and gatF from rabbit-sourced strains (except for SD11) were identical, which might be responsible for the host specific of the 19 isolates.

Experimental pathogenicity and comparative genome analysis of high- and low-virulence strains of rabbit-origin Pasteurella multocida

Pasteurella multocida, the causative pathogen of rabbit pasteurellosis, causes significant economic losses in the commercial rabbit industry. However, the associated pathogenic mechanism of P. multocida remains unclear. The aim of this study is to compare the genomes and pathogenicity of high- and low-virulence strains of P. multocida to advance the current understanding of rabbit pasteurellosis. The high-virulence strain rapidly proliferates in the lung and spleen of infected mice within approximately 9 h, maintaining a high bacterial load until host death. Meanwhile, the low-virulence strain only proliferates in mouse organs for a short time, with the bacterial load beginning to decrease 13 h post-infection. Moreover, the expressions of inflammatory cytokines MCP-1, TNF-α, and IL-1β are upregulated in all infected mouse lung and spleen tissue, however, the high-virulence strain induced significantly higher expression than the low-virulence strain. Histopathological analysis revealed greater inflammation and tissue lesions in the lung and spleen of mice infected with the high-virulence strain. Two pathogenicity-associated regions unique to the genome of the high-virulence strain harbor approximately 199 genes, including functional genes related to virulence factors, such as lipopolysaccharide biosynthesis, iron acquisition, biosynthesis of outer membrane proteins, and adhesion. These two genomic regions are shared by three previously sequenced, highly virulent P. multocida strains in rabbits. In conclusion, the increased pathogenicity of high-virulence P. multocida may be due to the presence of virulence-associated genes in two unique genomic regions, resulting in strong proliferative activity, significant inflammation, and pathological lesions in the mouse model. These findings provide important insights regarding the pathogenic mechanism underlying rabbit pasteurellosis.

Spreading of Pasteurella multocida Infection in a Pet Rabbit Breeding and Possible Implications on Healed Bunnies

The number of pets such as dogs, cats, rabbits, and parrots has increased in European families. Social benefits to owners such as decreasing feelings of loneliness and anxiety are provided by pets which are also used in Animal-assisted Therapy (AAT). Nevertheless, human-animal interactions are also associated with health problems including allergies, asthma, and zoonosis. Rabbits may carry potential pathogens for humans. One of the most common bacteria that colonizes the oro-pharynx and the upper respiratory tract of rabbits is Pasteurella (P.) multocida. Transmission of the infection to humans results from scratches, licks, and bites but it also can occur from the inhalation of air particles containing the microorganism. Immunocompromised people or persons with pulmonary disorders are particularly susceptible to the infection. Infected rabbits may carry P. multocida with or without clinical signs. In this paper, the sensitivity to antibiotics and the invasiveness ability of P. multocida identified in a farm of pet rabbits affected by severe pasteurellosis were investigated. The strain was P. multocida belonging to capsular type A which is the type most often detected in humans. The identified strain was susceptible to the tested antibiotics, but it appeared equipped with several virulence genes which are responsible for fimbriae production, adhesion processes to host cells, enzyme production, and are involved in iron acquisition processes. These findings are of particular interest because rabbits recovered from pasteurellosis very often become carriers of the bacteria. Therefore, we suggest considering P. multocida screening in the routine medical checks of rabbits, especially if they are meant to be companion animals for children and elder people, given that the transmission of the pathogen cannot be excluded.

Characterization of Pasteurella multocida isolated from dead rabbits with respiratory disease in Fujian, China

Background

Pasteurella multocida is one of the important pathogens that infect rabbits, causing major economic losses in commercial rabbit farming. In this study, 205 P. multocida isolates recovered from lungs of dead rabbits with respiratory disease were defined by capsular serogroups, lipopolysaccharide (LPS) genotypes, multi-locus sequence types and screened virulence factors by using PCR assays, and tested antimicrobial susceptibility.

Results

The 205 isolates were assigned into 2 capsular types, A and D, and 2 LPS genotypes, L3 and L6. When combining capsular types with LPS genotypes, 4 serotypes were detected. A:L3 (51.22%, 105/205) was the most predominant serotype, followed by A:L6 (24.88%, 51/205), D:L6 (19.02%, 39/205) and D:L3 (4.88%, 10/205). The 205 isolates were grouped into 3 sequence types, ST10, ST11 and ST12. ST12 (56.10%, 115/205) was the most prevalent sequence type, followed by ST10 (24.88%, 51/205) and ST11 (19.02%, 39/205). In the 205 isolates, virulence associated genes ptfA, fur, hgbB, ompA, ompH and oma87 were positive in the PCR screening, whereas the toxA and tbpA genes were negative. Notably, the 156 capsular serogroup A isolates carried the pmHAS gene. All the 205 isolates were susceptible to most of the used antibiotics, except for streptomycin, gentamycin, kanamycin and ceftriaxone, and the resistance rates of which were 27.80, 15.61, 9.27 and 2.44%, respectively.

Conclusions

This study, for the first time, described the prevalence and characteristics of P. multocida causing respiratory disease in rabbits in Fujian Province, which might be useful for tracking the epidemic strains and development of efficient vaccines and methods to prevent and control the pathogen.

Immunohistochemical and molecular analysis of Pasteurella multocida in a rabbit with suppurative pleuropneumonia

A 1-month-old rabbit, imported as a pet by a distributor, died suddenly in the quarantine period in Japan due to suppurative pleuropneumonia. A bacterial isolate from its right lung was identified as Pasteurella multocida serotype A: 11. The isolate was classified as ST204 using the RIRDC scheme of multilocus sequence typing, suggesting that the isolate was genetically related to European isolates of the same sequence type listed in the PubMLST database and not to four other isolates that originated from past imported rabbits. In the immunohistochemical assay, an antiserum recognizing the somatic serotype 11 antigen generated from chicken could specifically detect P. multocida, indicating that the antiserum for somatic serotyping was useful for immunohistochemical diagnosis of rabbit pasteurellosis.

Pasteurella multocida: Genotypes and Genomics

Pasteurella multocida is a highly versatile pathogen capable of causing infections in a wide range of domestic and wild animals as well as in humans and nonhuman primates. Despite over 135 years of research, the molecular basis for the myriad manifestations of P. multocida pathogenesis and the determinants of P. multocida phylogeny remain poorly defined. The current availability of multiple P. multocida genome sequences now makes it possible to delve into the underlying genetic mechanisms of P. multocida fitness and virulence. Using whole-genome sequences, the genotypes, including the capsular genotypes, lipopolysaccharide (LPS) genotypes, and multilocus sequence types, as well as virulence factor-encoding genes of P. multocida isolates from different clinical presentations can be characterized rapidly and accurately. Putative genetic factors that contribute to virulence, fitness, host specificity, and disease predilection can also be identified through comparative genome analysis of different P. multocida isolates. However, although some knowledge about genotypes, fitness, and pathogenesis has been gained from the recent whole-genome sequencing and comparative analysis studies of P. multocida, there is still a long way to go before we fully understand the pathogenic mechanisms of this important zoonotic pathogen. The quality of several available genome sequences is low, as they are assemblies with relatively low coverage, and genomes of P. multocida isolates from some uncommon host species are still limited or lacking. Here, we review recent advances, as well as continuing knowledge gaps, in our understanding of determinants contributing to virulence, fitness, host specificity, disease predilection, and phylogeny of P. multocida.

Characterization of Pasteurella multocida involved in rabbit infections

In rabbit, P. multocida is considered a predominant pathogenic agent; despite this, few data on the molecular epidemiology are available so far. The aim of this work was to characterize P. multocida isolates from rabbit affected by various diseases in Italy. Comparison was made to reference strains from other countries. Thirty-nine isolates were tested using PCRs to detect the genes coding capsular antigens, virulence factors and lipopolysaccharide structures (LPS). Multilocus sequence typing (MLST) was performed and 19 STs registered that belonged to 9 clonal complexes. Italian isolates were all related to P. multocida subsp. P. multocida. Three sequence types dominated (ST9, ST50 and ST74). The isolates were assigned to capsular types A (20/39), D (9/39) and F (10/39), to virulence genes pfhA (13/39), hgbB (21/39) and pfhA+hgbB (4/39) (one without virulence factors) and the isolates either belonged to the LPS genotypes 3 (22/39) or 6 (17/39). The clonal relationships of the Italian strains from rabbit had similarity to previously reported rabbit isolates that belonged to ST9, ST74, ST204 and ST206, however, they differed from other rabbit references strains that belonged to six other STs. In particular, ST9 with capsular type F has been previously reported from diseased rabbit in Czech Republic and ST74 has been observed for older rabbit isolates. ST50 has probably been reported from Spain. ST9 and ST50 have previously also been reported from birds and pig, respectively, whereas ST74 has exclusively been reported from pig. It remains to be investigated if the isolates obtained from diseased rabbit in Italy represent introductions from other host or they are primarily of rabbit origin.

Experimental pathogenicity and complete genome characterization of a pig origin Pasteurella multocida serogroup F isolate HN07

Pasteurella multocida serotype F isolates are predominately prevalent in avian hosts, but rarely seen in pigs. However, we isolated several strains of P. multocida serotype F from clinical samples of pigs in China. To understand the pathogenicity of these strains, one of the serotype F isolates designated HN07, was used to challenge experimental chickens, as P. multocida of this serotype is predominately prevalent in avian hosts. However, strain HN07 could not resulted in significant clinical signs in experimental chickens even at an infective dose of ∼10⁹ CFU, suggesting the isolate was avirulent to chickens and therefore raising the possibility that the porcine serotype F isolate is not transmitted by chickens. We then used HN07 to challenge experimental pigs, as this strain was isolated from pigs. As expected, the strain led to the clinical signs and the pathological lesions in experimental pigs that are similar to the pasteurellosis disease. We then determined the complete genome sequence of the pig origin serogroup F isolate HN07 for the first time. Genome comparison between HN07 and the avian serotype F P. multocida Pm70 identified a novel integrative conjugative element (ICE) ICEpmcn07 which was likely to harbor a series of genes responsible for a putative type IV secretion system (T4SS) in HN07. This is the first time that we determined an ICE carrying a T4SS in P. multocida. Besides, comparative analysis also defined a number of virulence-associated genes in HN07 but absent in Pm70 which may have a contribution to the pathogenicity of the strain. This is the first report of the pathogenicity and genome characterization of a pig origin Pasteurella multocida serogroup F isolate. The pathogenic and genomic definition of the pig origin P. multocida serogroup F in our study would have significance on the pathogenesis and genetic diversity and virulence variability of P. multocida.

An ST11 clone of Pasteurella multocida, widely spread among farmed rabbits in the Iberian Peninsula, demonstrates respiratory niche association

Pasteurella multocida is a veterinary pathogen causing diseases with considerable economic repercussions in a wide range of animal hosts. In rabbits, P. multocida infections cause a variety of clinical manifestations including rhinitis, pneumonia, septicemia, abscesses, mastitis, and pyometra. In this study, 100 P. multocida isolates from different commercial rabbit farms located throughout the Iberian Peninsula were molecularly characterized by capsular typing, detection of four virulence-associated genes (tbpA, toxA, hgbB, and pfhA), and multilocus sequence typing (MLST). Rabbit P. multocida isolates belonged to three different capsular types: A (47.0%), D (28.0%), and F (25.0%). One group of P. multocida isolates of capsular type D and positive for the hgbB gene was significantly associated with the clinical presentation of respiratory disease (OR 5.91; 95%CI, 1.63-21.38). These isolates belonged to same sequence type, ST11, in the P. multocida Multi-host MLST database. The ST11 clone also includes isolates from porcine and avian pneumonia. This clonal group of epidemiologically unrelated P. multocida isolates could be a virulent clone with some degree of specificity for respiratory disease. These findings could be relevant in the development of vaccines for pasteurellosis prevention, especially respiratory disease.

The key surface components of Pasteurella multocida: capsule and lipopolysaccharide

The capsule and lipopolysaccharide (LPS) of Pasteurella multocida constitute the major components of the bacterial cell surface. As well as forming the basis for the most widely used classification systems, they play key roles in a range of interactions between the bacteria and the hosts they colonize or infect. Both polysaccharides are involved in the avoidance of host innate immune mechanisms, such as resistance to phagocytosis, complement-mediated killing, and the bactericidal activity of antimicrobial peptides; they are therefore essential for virulence. In addition, LPS is a major antigen in the stimulation of adaptive immune responses to infection.

Experimental study of pathogenicity of Pasteurella multocida serogroup F in rabbits

The role of Pasteurella multocida serogroup F in inducing disease in rabbits was investigated in this study. Three groups of 12 Pasteurella-free rabbits each were intranasally (i.n.), subcutaneously (s.c.), and perorally (p.o.) challenged, respectively. Six rabbits of each group were immunosuppressed using dexamethasone. Eight rabbits (four of them immunosuppressed) inoculated i.n. showed symptoms of respiratory distress resulting in respiratory failure and died or were euthanized in the terminal stage of the disease 3-6 days post-infection (p.i.). The main pathological findings were fibrinopurulent pleuropneumonia (immunocompetent rabbits) or diffuse haemorrhagic pneumonia (immunosuppressed rabbits). Septicemic syndrome ending with shock occurred in 11 rabbits (6 of them immunosuppressed) inoculated s.c., which died or were euthanized in the terminal stage of the disease 2-3 days p.i. The most significant pathological findings were extensive cutaneous and subcutaneous lesions. All of the p.o. inoculated rabbits survived the challenge showing no clinical signs of the disease and no macroscopic lesions. The observations in this study indicate that in addition to serogroups A and D of P. multocida, serogroup F also can be highly pathogenic for rabbits and therefore might be a cause of considerable economic loss in commercial rabbit production.

Diagnostic procedures in tularaemia with special focus on molecular and immunological techniques

Tularaemia is a severe bacterial zoonosis caused by the highly infectious agent Francisella tularensis. It is endemic in countries of the northern hemisphere ranging from North America to Europe, Asia and Japan. Very recently, Francisella-like strains causing disease in humans were described from tropical northern Australia. In the last decade, efforts have been made to develop sensitive and specific immunological and molecular techniques for the laboratory diagnosis of tularaemia and also for the definite identification of members of the species F. tularensis and its four subspecies. Screening for the keyword 'Francisella' a Medline search over the last decade was performed and articles describing diagnostic methods for tularaemia and its causative agent were selected. Besides classical microbiological techniques (cultivation, biochemical profiling, susceptibility testing) several new immunological and molecular approaches to identify F. tularensis have been introduced employing highly specific antibodies and various polymerase chain reaction (PCR)-based methods. Whereas direct antigen detection by enzyme-linked immunosorbent assay (ELISA) or immunofluorescence might allow early presumptive diagnosis of tularaemia, these methods--like all PCR techniques--still await further evaluation. Therefore, diagnosis of tularaemia still relies mainly on the demonstration of specific antibodies in the host. ELISA and immunoblot methods started to replace the standard tube or micro-agglutination assays. However, the diagnostic value of antibody detection in the very early clinical phase of tularaemia is limited. Francisella tularensis is regarded as a 'highest priority' biological agent (category 'A' according to the CDC, Atlanta, GA, USA), thus rapid and reliable diagnosis of tularaemia is required not only for a timely onset of therapy, the handling of outbreak investigations but also for the surveillance of endemic foci. Only very recently, evaluated test kits for serological diagnosis of human tularaemia became available, while the introduction of standardized molecular techniques for detection and typing is still missing.