Evaluation of a PCR assay for identification and differentiation of Campylobacter fetus subspecies

Application of a multiplex PCR assay for Campylobacter fetus detection and subspecies differentiation in uncultured samples of aborted bovine fetuses

Campylobacter (C.) fetus (epsilonproteobacteria) is an important veterinary pathogen. This species is currently divided into C. fetus subspecies (subsp.) fetus (Cff) and C. fetus subsp. venerealis (Cfv). Cfv is the causative agent of bovine genital Campylobacteriosis, an infectious disease that leads to severe reproductive problems in cattle worldwide. Cff is a more general pathogen that causes reproductive problems mainly in sheep although cattle can also be affected. Here we describe a multiplex PCR method to detect C. fetus and differentiate between subspecies in a single step. The assay was standardized using cultured strains and successfully used to analyze the abomasal liquid of aborted bovine fetuses without any pre-enrichment step. Results of our assay were completely consistent with those of traditional bacteriological diagnostic methods. Furthermore, the multiplex PCR technique we developed may be easily adopted by any molecular diagnostic laboratory as a complementary tool for detecting C. fetus subspecies and obtaining epidemiological information about abortion events in cattle.

Validation of the EntericBio Panel II® multiplex polymerase chain reaction system for detection of Campylobacter spp., Salmonella spp., Shigella spp., and verotoxigenic E. coli for use in a clinical diagnostic setting

A total of 717 faeces samples were tested prospectively using the EntericBio Panel II® detection system (Serosep, Limerick, Ireland), in parallel with routine laboratory testing, which combines the EntericBio® system with retrospective culture of each specimen where a target is detected. Discrepancy analysis was conducted using molecular methods. The EntericBio Panel II® assay produced 585 negative and 132 positive results, namely, Campylobacter spp. (n = 66); SLT 1 and/or SLT 2 (n = 64); Salmonella spp. (n = 5); and Shigella spp. (n = 0). Three samples were positive for more than 1 target. Of these results, 4 Campylobacter spp. detections and 4 SLT 1/ SLT 2 detections remained unconfirmed, and the system failed to detect 2 Campylobacter spp. targets detected by routine laboratory detection. The sensitivity, specificity, positive predictive value, negative predictive value, and efficiency were calculated to be 98.4%, 98.7%, 93.9%, 99.7%, and 98.6%, respectively.

So close and yet so far - Molecular Microbiology of Campylobacter fetus subspecies

Campylobacter fetus comprises two subspecies, C. fetus subsp. fetus and C. fetus subsp. venerealis, which are considered emerging pathogens in humans and animals. Comparisons at the genome level have revealed modest subspecies-specific variation; nevertheless, these two subspecies show distinct host and niche preferences. C. fetus subsp. fetus is a commensal and pathogen of domesticated animals that can be transmitted to humans via contaminated food. The clinical features of human infection can be severe, especially in impaired hosts. In contrast, C. fetus subsp. venerealis is a sexually transmitted pathogen essentially restricted to cattle. Infections leading to bovine venereal campylobacteriosis cause substantial economic losses due to abortion and infertility. Recent genome sequencing of the two subspecies has advanced our understanding of C. fetus adaptations through comparative genomics and the identification of subspecies-specific gene regions predicted to be involved in pathogenesis. The most striking difference between the subspecies is the highly subspecies-specific association of a pathogenicity island in the C. fetus subsp. venerealis chromosome. The inserted region encodes a Type 4 secretion system, which contributes to virulence properties of this organism in vitro. This review describes the main differences in epidemiological, phenotypic, and molecular characteristics of the two subspecies and summarizes recent advances towards understanding the molecular mechanisms of C. fetus pathogenesis.

New molecular microbiology approaches in the study of Campylobacter fetus

Campylobacter fetus infection is a substantial problem in herds of domestic cattle worldwide and a rising threat in human disease. Application of comparative and functional genomics approaches will be essential to understand the molecular basis of this pathogen's interactions with various hosts. Here we report recent progress in genome analyses of C. fetus ssp. fetus and C. fetus ssp. venerealis, and the development of molecular tools to determine the genetic basis of niche‐specific adaptations. Campylobacter research has been strengthened by the rapid advancements in imaging technology occurring throughout microbiology. To move forward in understanding the mechanisms underlying C. fetus virulence, current efforts focus on developing suitable in vitro models to reflect host‐ and tissue‐specific aspects of infection.

Epidemiology of bovine venereal campylobacteriosis: geographic distribution and recent advances in molecular diagnostic techniques

Bovine venereal campylobacteriosis (BVC) is a major cause of economic loss to the cattle industries in different parts of the world. Camplylobacter fetus subsp. venerealis (Cfv), the main causative agent of BVC, is highly adapted to the genital tract of cattle and is transmitted by carrier bulls. However, infertility and abortions can also be caused by the intestinal pathogens C. fetus subsp. fetus (Cff), and C. jenuni, which are not venereally transmitted. Bovine venereal campylobacteriosis, caused by Cfv associated with lowered fertility, embryo mortality and abortion, repeated returns to service, reduced pregnancy rates and extended calving intervals, has the highest prevalence in developing countries where natural breeding in cattle is widely practised. The epidemiology, pathogenesis and diagnosis of the disease have been the subject of previous reviews. The main focus of this review is to highlight the epidemiology of this disease with particular reference to geographical distribution and recent advances in molecular diagnostic techniques. It is hoped that further research interest of scientists will be stimulated with a view to finding lasting solutions to the reproductive problems associated with the disease for better livestock productivity, particularly in developing endemic countries.

Molecular-based detection of non-culturable and emerging campylobacteria in patients presenting with gastroenteritis

From January 2009 to May 2010, 436 faecal samples from patients with diarrhoeal illness in Southern Ireland were identified as Campylobacter genus-positive by an automated multiplex PCR; however, 204 (46·8%) of these samples were culture-negative for campylobacters. A combination of Campylobacter-specific uniplex PCR and 16S rRNA sequencing confirmed the presence of Campylobacter DNA in 191 (93·6%) of the culture-negative samples. Species-specific PCR identified C. jejuni (50·7%) C. ureolyticus (41%) and C. coli (5·7%) as the most prevalent species while C. fetus, C. upsaliensis, C. hyointestinalis and C. lari accounted for 10% of culture-negative samples; mixed Campylobacter spp. were detected in 11% of samples. We conclude that non-culturable Campylobacter spp. are responsible for a considerable proportion of human enteritis and the true incidence of infection is likely to be significantly underestimated where conventional Campylobacter culture methods are used in isolation.

Campilobacteriose genital bovina e tricomonose genital bovina: epidemiologia, diagnóstico e controle

A presente atualização trata de duas das mais importantes doenças sexualmente transmitidas de bovinos, a campilobacteriose genital bovina e a tricomonose genital bovina. São abordados aspectos relacionados à epidemiologia destas doenças, principalmente em relação a sua distribuição no Brasil. Também são revisados aspectos importantes de diagnóstico, incluindo as técnicas e interpretação dos resultados, além de medidas de controle para ambas as doenças.

Emerging thermotolerant Campylobacter species in healthy ruminants and swine

Campylobacters other than Campylobacter jejuni or C. coli were isolated in 35% of 343 farms recently analyzed in northern Spain. This study was aimed at identifying at the species level the 120 isolates collected (21 ovine, 52 beef cattle, 44 dairy cattle, and 3 porcine) by species-specific polymerase chain reaction and 16S rRNA gene sequencing analysis. Thus, five species were identified: Campylobacter hyointestinalis (90 isolates), Campylobacter lanienae (12), Campylobacter fetus subsp. fetus (10), Campylobacter lari (1), and Campylobacter sputorum (1). Ambiguous results were obtained for six isolates. Phylogenetic analyses of the 16S rRNA gene sequence placed three of them (cattle isolates) as an intermediate clade between C. hyointestinalis subsp. hyointestinalis and C. fetus, two ovine isolates formed a new clade clustering with Campylobacter concisus despite sharing higher similarity with Campylobacter mucosalis, and one porcine isolate shared similarly high homology with C. lanienae and C. hyointestinalis subsp. lawsonii. C. hyointestinalis was the predominant species, particularly in cattle, but it was also isolated from sheep and swine. C. lanienae was only found in sheep, C. fetus in cattle and sheep, and C. lari in a single dairy cattle farm. Although previously reported, the isolation of C. lari from cattle is not common, and this is the first report of C. lanienae and C. hyointestinalis in sheep. This study demonstrated the wide distribution in livestock of several emerging zoonotic Campylobacter species and provided valuable information on their host animal reservoirs.

Polymerase chain reaction for the diagnosis of bovine genital campylobacteriosis

Bovine genital campylobacteriosis is a common venereal disease of cattle; the prevalence of this disease can be underestimated mostly because of the nature of the etiological agent, the microaerobic Campylobacter fetus subspecies venerealis. The purpose of the current study was to evaluate the utilization of polymerase chain reaction (PCR) in the diagnosis of genital campylobacteriosis in samples obtained from bull prepuce aspirate, cow cervical mucus, and abomasum contents of aborted fetuses, collected into enrichment medium. Five different DNA extraction protocols were tested: thermal extraction, lysis with proteinase K, lysis with guanidine isothiocyanate, lysis with DNAzol, and lysis with hexadecyltrimethylammonium bromide (CTAB). The specificity, sensitivity, and technical application of the PCR assay were also evaluated with clinical samples and compared to bacterial isolation by standard culture. DNA extraction by the CTAB protocol provided better results in PCR, and it was able to detect 63 colony-forming units per ml of C. fetus. Out of 277 clinical samples tested, 68 (24%) were positive for Campylobacter fetus using PCR, while only 8 (2.8%) of the samples were positive by bacterial isolation in solid medium, proving the superiority of the PCR technique when compared to the standard isolation method, and providing evidence for its usefulness as a better screening test in cattle for the diagnosis of bovine genital campylobacteriosis.

Two novel antibiotic resistance genes, tet(44) and ant(6)-Ib, are located within a transferable pathogenicity island in Campylobacter fetus subsp. fetus

New tetracycline and streptomycin resistance genes, tet(44) and ant(6)-Ib, were identified in Campylobacter fetus subsp. fetus within a transferable pathogenicity island that is typically unique to Campylobacter fetus subsp. venerealis. The 640-amino-acid tetracycline resistance determinant, Tet 44, belongs to a class of proteins that confers resistance to tetracycline and minocycline by ribosomal protection. The 286-amino-acid streptomycin resistance determinant, ANT(6)-Ib, belongs to a family of aminoglycoside nucleotidyltransferases. The resistance phenotypes were demonstrated by gene inactivation and expression.

A genomic island defines subspecies-specific virulence features of the host-adapted pathogen Campylobacter fetus subsp. venerealis

The pathogen Campylobacter fetus comprises two subspecies, C. fetus subsp. fetus and C. fetus subsp. venerealis. Although these taxa are highly related on the genome level, they are adapted to distinct hosts and tissues. C. fetus subsp. fetus infects a diversity of hosts, including humans, and colonizes the gastrointestinal tract. In contrast, C. fetus subsp. venerealis is largely restricted to the bovine genital tract, causing epidemic abortion in these animals. In light of their close genetic relatedness, the specific niche preferences make the C. fetus subspecies an ideal model system to investigate the molecular basis of host adaptation. In this study, a subtractive-hybridization approach was applied to the genomes of the subspecies to identify different genes potentially underlying this specificity. The comparison revealed a genomic island uniquely present in C. fetus subsp. venerealis that harbors several genes indicative of horizontal transfer and that encodes the core components necessary for bacterial type IV secretion. Macromolecular transporters of this type deliver effector molecules to host cells, thereby contributing to virulence in various pathogens. Mutational inactivation of the putative secretion system confirmed its involvement in the pathogenicity of C. fetus subsp. venerealis.

Genomic analysis of Campylobacter fetus subspecies: identification of candidate virulence determinants and diagnostic assay targets

Background

Campylobacter fetus subspecies venerealis is the causative agent of bovine genital campylobacteriosis, asymptomatic in bulls the disease is spread to female cattle causing extensive reproductive loss. The microbiological and molecular differentiation of C. fetus subsp. venerealis from C. fetus subsp. fetus is extremely difficult. This study describes the analysis of the available C. fetus subsp. venerealis AZUL-94 strain genome (~75–80%) to identify elements exclusively found in C. fetus subsp. venerealis strains as potential diagnostic targets and the characterisation of subspecies virulence genes.

Results

Eighty Kb of genomic sequence (22 contigs) was identified as unique to C. fetus subsp. venerealis AZUL-94 and consisted of type IV secretory pathway components, putative plasmid genes and hypothetical proteins. Of the 9 PCR assays developed to target C. fetus subsp. venerealis type IV secretion system genes, 4 of these were specific for C. fetus subsp. venerealis biovar venerealis and did not detect C. fetus subsp. venerealis biovar intermedius. Two assays were specific for C. fetus subsp. venerealis AZUL-94 strain, with a further single assay specific for the AZUL-94 strain and C. fetus subsp. venerealis biovar intermedius (and not the remaining C. fetus subsp. venerealis biovar venerealis strains tested). C. fetus subsp. fetus and C. fetus subsp. venerealis were found to share most common Campylobacter virulence factors such as SAP, chemotaxis, flagellar biosynthesis, 2-component systems and cytolethal distending toxin subunits (A, B, C). We did not however, identify in C. fetus the full complement of bacterial adherence candidates commonly found in other Campylobacter spp.

Conclusion

The comparison of the available C. fetus subsp. venerealis genome sequence with the C. fetus subsp. fetus genome identified 80 kb of unique C. fetus subsp. venerealis AZUL94 sequence, with subsequent PCR confirmation demonstrating inconsistent amplification of these targets in all other C. fetus subsp. venerealis strains and biovars tested. The assays developed here highlight the complexity of targeting strain specific virulence genes for field studies for the molecular identification and epidemiology of C. fetus.

Major outer membrane proteins from many Campylobacter species cross-react with cholera toxin

We have previously shown that Campylobacter jejuni strains do not produce a functional cholera toxin-like toxin (CTLT) detectable in a Chinese hamster ovary cell assay. Instead, the 53-kDa major outer membrane protein (OMP) of C. jejuni, PorA, reacts with cholera toxin (CT) antibody on immunoblots. Here, we have extended this observation to other species of Campylobacter, including C. coli, C. lari, C. fetus, C. hyointestinalis, and C. upsaliensis, the common 53-kDa OMP of which reacted with CT antibody in immunoblotting assays. There were additional reactive bands for C. fetus. As with C. jejuni, this finding may lead to the erroneous conclusion that these additional species produce a functional CTLT. However, this common cross-reactive OMP can be explored as a vaccine candidate to prevent campylobacteriosis.

Development of a multiplex PCR assay for identification of Campylobacter coli, Campylobacter fetus, Campylobacter hyointestinalis subsp. hyointestinalis, Campylobacter jejuni, Campylobacter lari and Campylobacter upsaliensis

A multiplex PCR assay has been developed for the identification of the six common Campylobacter taxa associated with human gastroenteritis and/or septicaemia, namely Campylobacter coli, Campylobacter fetus, Campylobacter hyointestinalis subsp. hyointestinalis, Campylobacter jejuni, Campylobacter lari and Campylobacter upsaliensis. The assay was developed using a combination of newly designed and published primers. It provided a specific PCR product for each of the five Campylobacter species and the one subspecies, and each of the PCR products was sufficiently distinguished by a difference in size by agarose gel electrophoresis. On evaluation of efficacy with 142 Campylobacter strains, the assay correctly identified all strains as 1 of the 6 Campylobacter taxa. This multiplex PCR assay is a rapid, simple and practical tool for identification of the six Campylobacter taxa commonly associated with gastroenteritis and/or septicaemia in humans, and offers an effective alternative to conventional biochemical-based assays.

Discovery of insertion element ISCfe1: a new tool for Campylobacter fetus subspecies differentiation

The species Campylobacter fetus is divided into the subspecies C. fetus subsp. venerealis (CFV) and C. fetus subsp. fetus (CFF). CFV is the causative agent of bovine genital campylobacteriosis, a highly contagious venereal disease that may lead to serious reproductive problems, including sterility and abortion. In contrast, CFF can be isolated from the gastrointestinal tract of a wide range of host species, is associated with abortion in sheep and cattle, and can also be isolated from local and systemic infections in humans. Despite differences in host and niche preferences, microbiological differentiation of the two subspecies of C. fetus is extremely difficult. This study describes the identification of a new insertion element, ISCfe1, which is present exclusively in CFV strains, with highly conserved specific ISCfe1 insertion sites. The results are useful for identification and differentiation of the two C. fetus subspecies and will help in understanding the evolution and pathogenesis of C. fetus.

Development of experimental genetic tools for Campylobacter fetus

Molecular analysis of the virulence mechanisms of the emerging pathogen Campylobacter fetus has been hampered by the lack of genetic tools. We report the development and functional analysis of Escherichia coli-Campylobacter shuttle vectors that are appropriate for C. fetus. Some vectors were constructed based on the known Campylobacter coli plasmid pIP1455 replicon, which confers a wide host range in Campylobacter spp. Versatility in directing gene expression was achieved by introducing a strong C. fetus promoter. The constructions carry features necessary and sufficient to detect the expression of phenotypic markers, including molecular reporter genes in both subspecies of C. fetus, while retaining function in C. jejuni. The capacity to express several gene products from different vectors in a single host can be advantageous but requires distinct plasmid replicons. To this end, replication features derived from a cryptic plasmid of C. fetus subsp. venerealis strain 4111/108, designated pCFV108, were adapted for a compatible series of constructions. The substitution of the C. coli replication elements reduced vector size while apparently limiting the host range to C. fetus. The complementation of a ciprofloxacin-resistant mutant phenotype via vector-driven gyrA expression was verified. Cocultivation demonstrated that shuttle vectors based on the pCFV108 replicon were compatible with pIP1455 replication functions, and the stable maintenance of two plasmids in a C. fetus subsp. venerealis host over several months was observed. The application of both vector types will facilitate the investigation of the genetics and cellular interactions of the emerging pathogen C. fetus.

Genetic relatedness within the genus Campylobacter inferred from rpoB sequences

The genus Campylobacter comprises 17 species, some of which are important animal and human pathogens. To gain more insight into the genetic relatedness of this genus and to improve the molecular tools available for diagnosis, a universal sequencing approach was established for the gene encoding the beta-subunit of RNA polymerase (rpoB) for the genus Campylobacter. A total of 59 strains, including the type strains of currently recognized species as well as field isolates, were investigated in the study. A primer set specific for Campylobacter species enabled straightforward amplification and sequencing of a 530 bp fragment of the rpoB gene. The 16S rRNA gene sequences of all of the strains were determined in parallel. A good congruence was obtained between 16S rRNA and rpoB gene sequence-based trees within the genus Campylobacter. The branching of the rpoB tree was similar to that of the 16S rRNA gene tree, even though a few discrepancies were observed for certain species. The resolution of the rpoB gene within the genus Campylobacter was generally much higher than that of the 16S rRNA gene sequence, resulting in a clear separation of most species and even some subspecies. The universally applicable amplification and sequencing approach for partial rpoB gene sequence determination provides a powerful tool for DNA sequence-based discrimination of Campylobacter species.

Identification of Campylobacter fetus subspecies by phenotypic differentiation and PCR

The species Campylobacter fetus is divided into the subspecies C. fetus subsp. venerealis and C. fetus subsp. fetus, which differ in their epidemiologies and clinical importance. The differences between these subspecies make accurate distinction between the two essential. First, the value of seven key tests for the traditional differentiation of C. fetus was investigated. Afterwards, the results of the phenotypic differentiation and PCR were compared to address the question of the reliability of this PCR assay. Altogether, 103 C. fetus isolates were investigated, including the type strains of C. fetus subsp. fetus and C. fetus subsp. venerealis. Depending on the result of the glycine tolerance test, the isolates could be separated into 81 C. fetus subsp. venerealis isolates (glycine intolerant) and 22 C. fetus subsp. fetus isolates (glycine tolerant). For all C. fetus subsp. venerealis strains tested, the results of the selenite reduction assay and sensitivity to metronidazole and cefoperazone completely agreed with the results of the glycine tolerance test (correspondence, 100%). Seventy-three C. fetus subsp. venerealis isolates did not grow at 42 degrees C (correspondence, 90.1%), but eight isolates showed a faintly discernible, flat, dark gray growth. For 22 C. fetus subsp. fetus isolates, the results of additional phenotypic tests only partly agreed with the results of the glycine tolerance test. For C. fetus subsp. fetus the results of the glycine tolerance test showed a relatively good correspondence with those of the selenite reduction assay (correspondence, 81.8%), assays for cefoperazone resistance (correspondence, 86.4%), and assays for growth at 42 degrees C (correspondence, 81.8%). The results of the glycine tolerance test and PCR completely agreed for the 103 C. fetus isolates tested. We conclude that at present the traditional phenotypic characterization of C. fetus subspecies under strongly defined conditions remains indispensable, but this PCR assay constitutes a valuable adjunctive technique for the confirmation of phenotypic results.

Comparison of culture and a novel 5' Taq nuclease assay for direct detection of Campylobacter fetus subsp. venerealis in clinical specimens from cattle

A Campylobacter fetus subsp. venerealis-specific 5' Taq nuclease PCR assay using a 3' minor groove binder-DNA probe (TaqMan MGB) was developed based on a subspecies-specific fragment of unknown identity (S. Hum, K. Quinn, J. Brunner, and S. L. On, Aust. Vet. J. 75:827-831, 1997). The assay specifically detected four C. fetus subsp. venerealis strains with no observed cross-reaction with C. fetus subsp. fetus-related Campylobacter species or other bovine venereal microflora. The 5' Taq nuclease assay detected approximately one single cell compared to 100 and 10 cells in the conventional PCR assay and 2,500 and 25,000 cells from selective culture from inoculated smegma and mucus, respectively. The respective detection limits following the enrichments from smegma and mucus were 5,000 and 50 cells/inoculum for the conventional PCR compared to 500 and 50 cells/inoculum for the 5' Taq nuclease assay. Field sampling confirmed the sensitivity and the specificity of the 5' Taq nuclease assay by detecting an additional 40 bulls that were not detected by culture. Urine-inoculated samples demonstrated comparable detection of C. fetus subsp. venerealis by both culture and the 5' Taq nuclease assay; however, urine was found to be less effective than smegma for bull sampling. Three infected bulls were tested repetitively to compare sampling tools, and the bull rasper proved to be the most suitable, as evidenced by the improved ease of specimen collection and the consistent detection of higher levels of C. fetus subsp. venerealis. The 5' Taq nuclease assay demonstrates a statistically significant association with culture (chi2 = 29.8; P < 0.001) and significant improvements for the detection of C. fetus subsp. venerealis-infected animals from crude clinical extracts following prolonged transport.

A multiplex polymerase chain reaction to detect and differentiate Campylobacter fetus subspecies fetus and Campylobacter fetus -species venerealis: use on UK isolates of C. fetus and other Campylobacter spp

AIMS

Subspeciation of Campylobacter fetus subsp. fetus (CFF) and Campylobacter fetus subsp. venerealis (CFV) is important for international animal import regulations. Phenotyping can be unreliable, and genotyping by techniques like pulsed field gel electrophoresis is difficult in routine diagnostic laboratories. A PCR subspeciation technique has been reported [Aust Vet J (1997) 75, 827]; we aimed to develop this PCR and investigate its use on UK C. fetus isolates.

METHODS AND RESULTS

We augmented the PCR with further primers, and tested 76 isolates of C. fetus and 16 isolates of other Campylobacter spp. PCR failed to correlate well with phenotyping, especially for CFV. We characterized the amplicon of the CFV-specific primers (reported as plasmid derived, but unavailable on the public databases); and predicted a parA gene sequence, anticipated to be plasmid-associated. However, although plasmid isolations from selected CFV isolates demonstrated the presence of several plasmids, there was no correlation between plasmid profile and PCR result. Further, the parA sequence was not detected by PCR in any of the plasmid bands.

CONCLUSIONS

This PCR is not suitable for subspeciation of C. fetus in the UK. The results suggest that this is a reflection of the presence of an unusual clone of CFV currently present in cattle in this country.

SIGNIFICANCE AND IMPACT OF THE STUDY

PCR cannot substitute for phenotyping of C. fetus isolates in the UK. The reasons for failure of PCR genotyping may reflect local strains and/or plasmid profiles. Further study is required to better elucidate molecular sub-speciation of C. fetus.

Clonal nature of Campylobacter fetus as defined by multilocus sequence typing

Campylobacter fetus can be divided into the subspecies C. fetus subsp. fetus and C. fetus subsp. venerealis. C. fetus subsp. fetus causes sporadic infections in humans and abortion in cattle and sheep and has been isolated from a variety of sites in different hosts. C. fetus subsp. venerealis is host restricted, being isolated mainly from the genital tracts of cattle, and is the causative agent of bovine genital campylobacteriosis. Despite differences in niche preference, microbiological subspecies differentiation has proven difficult. Different typing methods divided C. fetus isolates into different subgroups, depending on the methods used. The relative value of these methods can be assessed by the evolutionary relationship of isolates belonging to the genus; therefore, we developed a multilocus sequence typing (MLST) scheme for C. fetus. This scheme was applied to 140 C. fetus isolates previously typed by amplified fragment length polymorphism (AFLP) analysis. A total of 14 different sequence types (STs) were identified, and these exhibited low levels of inter-ST genetic diversity, with only 22 variable sites in 3,312 nucleotides. These MLST data indicate that C. fetus is genetically homogeneous compared to the homogeneity of other Campylobacter species. The two C. fetus subspecies were extremely closely related genetically, but ST-4 was associated only with C. fetus subsp. venerealis, which represents a "bovine" clone. The C. fetus subsp. fetus isolates studied were more diverse in terms of their STs, and the STs correlated with epidemiological relationships. Congruence was observed among C. fetus subspecies, sap type, and ST; therefore, MLST confirms that mammalian C. fetus is genetically stable, probably as result of the introduction of a single ancestral clone into a mammalian niche.

Genetic divergence of Campylobacter fetus strains of mammal and reptile origins

Campylobacter fetus is a gram-negative bacterial pathogen of both humans and animals. Two subspecies have been identified, Campylobacter fetus subsp. fetus and Campylobacter fetus subsp. venerealis, and there are two serotypes, A and B. To further investigate the genetic diversity among C. fetus strains of different origins, subspecies, and serotypes, we performed multiple genetic analyses by utilizing random amplification of polymorphic DNA (RAPD), pulsed-field gel electrophoresis (PFGE), and DNA-DNA hybridization. All 10 primers used for the RAPD analyses can distinguish C. fetus strains of reptile and mammal origin, five can differentiate between C. fetus subsp. fetus and C. fetus subsp. venerealis strains, and four showed differences between type A and type B isolates from mammals. PFGE with SmaI and SalI digestion showed varied genome patterns among different C. fetus strains, but for mammalian C. fetus isolates, genome size was well conserved (mean, 1.52 +/- 0.06 Mb for SmaI and 1.52 +/- 0.05 Mb for SalI). DNA-DNA hybridization demonstrated substantial genomic-homology differences between strains of mammal and reptile origin. In total, these data suggest that C. fetus subsp fetus strains of reptile and mammal origin have genetic divergence more extensive than that between the two subspecies and that between the type A and type B strains. Combining these studies with sequence data, we conclude that there has been substantial genetic divergence between Campylobacter fetus of reptile and mammal origin. Diagnostic tools have been developed to differentiate among C. fetus isolates for taxonomic and epidemiologic uses.

Immunohistochemical identification of Campylobacter fetus in natural cases of bovine and ovine abortions

An immunohistochemistry (IHC) procedure for the detection of Campylobacter fetus antigens using an avidin-biotin complex technique was performed on formalin fixed bovine and ovine fetal tissues from 26 natural cases of Campylobacter spp. abortion (four ovine and 22 bovine). The species of Campylobacter isolated included C. fetus ssp. venerealis from 13 bovine fetuses, C. fetus ssp. fetus from two ovine and one bovine fetus, Campylobacter jejuni from seven bovine fetuses, Campylobacter lari from two ovine fetuses and an unspeciated Campylobacter species in one bovine fetus. Histologic lesions identified in the aborted fetuses included placentitis, serositis, pneumonia, gastroenteritis, hepatitis and encephalitis. Campylobacter fetus antigens were identified by IHC in 13 of 13 bovine fetuses from which C. fetus ssp. venerealis was isolated and in two of two ovine fetuses from which C. fetus ssp. fetus was isolated. The IHC stains were negative in tissues from seven bovine fetuses from which C. jejuni was isolated, one bovine fetus infected with C. fetus ssp. fetus, one bovine fetus infected with the unspeciated Campylobacter and two ovine fetuses infected with C. lari. In positive cases, the IHC stain most frequently identified bacteria in the lung and gastrointestinal tract. The C. fetus IHC procedure performed on formalin fixed tissues is a practical tool for the diagnosis of natural cases of ovine and bovine abortion caused by C. fetus.

Investigation of bovine venereal campyloacteriosis in beef cow herds in New Zealand

AIMS

To determine regional prevalences of beef cow herds in New Zealand positive for Campylobacter fetus subsp venerealis antibodies in samples of vaginal mucus tested using an immunoglobulin (Ig) A enzyme-linked immunosorbent assay (ELISA), and to examine the suitability of the IgA ELISA for detecting infection with C. fetus subsp venerealis under field conditions in New Zealand.

METHODS

Vaginal mucus samples (n=1,230) collected from beef cow herds (n=125) throughout New Zealand (approximately 10 samples/herd) were tested for antibodies to C. fetus subsp venerealis using an IgA ELISA. Test results were compared between herds classified as having low, medium and high fertility based on pregnancy test results interpreted in relation to the duration of the mating period used. In addition, a small number of samples were collected from dairy cows that were mated using artificial insemination (AI) and had no contact with breeding bulls. The influence of putative risk factors for the spread of venereal disease and the effect of sample quality on the status of herds according to test results was assessed using multivariate logistical regression. Preputial washings from 54 bulls from nine herds classified as low fertility in which mucus samples from > or =3 cows were IgA antibody-positive were cultured for the presence of Campylobacter spp, and isolates of C. fetus subspecies were characterised using a polymerase chain reaction (PCR) test.

RESULTS

One or more mucus samples was positive to the IgA ELISA in 70% of all herds tested. The prevalence of IgA antibody- positive individuals was >20% in most regions of New Zealand and did not differ significantly for cows from herds classified as high, medium or low fertility (28%, 26% and 23%, respectively; p=0.39). No relationship was found between mucus antibody status and age of breeding group, herd size, herd fertility, number of herds that female replacements or breeding bulls were sourced from, whether a serving ability test (SAT) was used to assess bulls, or the quality of samples submitted to the laboratory. Campylobacter fetus subsp venerealis was not cultured from any of the 54 bulls sampled. Four other species of Campylobacter and related organisms were cultured, viz Arcobacter cryaerophilus, Campylobacter jejuni, Campylobacter fetus subsp fetus and Helicobacter cinaedi.

CONCLUSIONS

The specificity of the IgA ELISA as a diagnostic test for C. fetus subsp venerealis was found to be unsatisfactory under New Zealand conditions. It is possible that an immunological response by cows to Campylobacter species other than C. fetus subsp venerealis caused cross-reactivity in the IgA ELISA. The results do not support the hypothesis that C. fetus subsp venerealis is widespread in New Zealand.

Species-specific identification of campylobacters by partial 16S rRNA gene sequencing

Species-specific identification of campylobacters is problematic, primarily due to the absence of suitable biochemical assays and the existence of atypical strains. 16S rRNA gene (16S rDNA)-based identification of bacteria offers a possible alternative when phenotypic tests fail. Therefore, we evaluated the reliability of 16S rDNA sequencing for the species-specific identification of campylobacters. Sequence analyses were performed by using almost 94% of the complete 16S rRNA genes of 135 phenotypically characterized Campylobacter strains, including all known taxa of this genus. It was shown that 16S rDNA analysis enables specific identification of most Campylobacter species. The exception was a lack of discrimination among the taxa Campylobacter jejuni and C. coli and atypical C. lari strains, which shared identical or nearly identical 16S rDNA sequences. Subsequently, it was investigated whether partial 16S rDNA sequences are sufficient to determine species identity. Sequence alignments led to the identification of four 16S rDNA regions with high degrees of interspecies variation but with highly conserved sequence patterns within the respective species. A simple protocol based on the analysis of these sequence patterns was developed, which enabled the unambiguous identification of the majority of Campylobacter species. We recommend 16S rDNA sequence analysis as an effective, rapid procedure for the specific identification of campylobacters.

Phenotypic and molecular characterization of bovine Campylobacter fetus strains isolated in Brazil

The objective of the present study was to characterize the phenotypic and molecular aspects of Campylobacter fetus strains isolated from bovine herds with reproductive problems. Thirty-one Brazilian field isolates, together with one reference strain of each subspecies of C. fetus, were analyzed. The strains were submitted to phenotypic identification followed by subspecies characterization using the polymerase chain reaction (PCR) and numeric evaluation of restriction fragment length polymorphism (RFLP) separated by pulsed-field gel electrophoresis (PFGE). Phenotypically, 4 isolates (12.1%) were classified as C. fetus subsp. fetus, and 29 isolates (87.9%) were classified as C. fetus subsp. venerealis. However, according to molecular analysis, only 1 isolate (3.0%) was classified as C. fetus subsp. fetus (the reference strain), whereas 32 isolates (97.0%) were considered C. fetus subsp. venerealis. SalI digestion of C. fetus genomic DNA, obtained from the 33 strains, yielded 7-10 DNA fragments ranging in size from 40 to 373kb, with 12 distinct patterns. Furthermore, the numeric analysis by neighbor-joining of the DNA from the 33 strains resulted in a dendrogram in which 2 distinct groups were identified. It was concluded that phenotypic characterization of C. fetus subspecies might lead to erroneous classification of field isolates. Although RFLP-PFGE is a powerful and reliable technique to characterize C. fetus, it has the inconvenience of being time consuming and laborious. Whereas PCR, besides providing rapid results, was found to be reliable and convenient for the characterization of field isolates of C. fetus.

Isolation of Campylobacter fetus subsp. fetus from a patient with cellulitis

Campylobacter fetus subsp. fetus is a gram-negative, slender, spirally curved bacterial pathogen. It has been isolated from human blood, spinal fluid, and abscesses, but cellulitis associated with bacteremia is rare. We report its isolation from a blood culture of a human patient with cellulitis as well as difficulties encountered in determining the identity of the subspecies of C. fetus.

Differentiation of Campylobacter species by AFLP fingerprinting

The fluorescent amplified fragment length polymorphism (AFLP) fingerprinting method was tested for its ability to identify and subtype the most important Campylobacter species found in veterinary infections. Sixty-nine reference strains and 19 clinical isolates of Campylobacter jejuni subsp. jejuni, Campylobacter jejuni subsp. doylei, Campylobacter upsaliensis, Campylobacter coli, Campylobacter lari, Campylobacter fetus subsp. fetus, C. fetus subsp. venerealis, Campylobacter hyointestinalis subsp. hyointestinalis, C. hyointestinalis subsp. lawsonii, Campylobacter mucosalis, Campylobacter helveticus and Campylobacter sputorum were subjected to analysis. The topology of the dendrogram obtained by numerical analysis of the AFLP profiles did not reflect the phylogenetic relationships as derived from 16S rDNA sequence comparison. However, except for C. lari, AFLP analysis grouped the strains that belonged to the same genomic species into distinct clusters. C. lari strains were separated into two distinct AFLP groups, which corresponded with nalidixic-acid-sensitive and -resistant variants of C. lari. These results correlated with data from whole-cell protein profiling. Within C. jejuni, C. hyointestinalis and C. fetus, strains could be identified at the subspecies level. AFLP analysis also allowed the subtyping of most species at the strain level. It is concluded that AFLP analysis is a valuable tool for concurrent identification of campylobacters at the species, subspecies and strain levels. In addition, the data confirm and extend previous reports showing that C. lari is a heterogeneous species that may comprise multiple taxa.

Comparative study using amplified fragment length polymorphism fingerprinting, PCR genotyping, and phenotyping to differentiate Campylobacter fetus strains isolated from animals

A collection of Campylobacter fetus strains, including both C. fetus subsp. fetus and C. fetus subsp. venerealis, were phenotypically identified to the subspecies level and genotypically typed by PCR and amplified fragment length polymorphism (AFLP) analysis. Phenotypic subspecies determination methods were unreliable. Genotyping of the strains by PCR and AFLP showed a clear discrimination between the two subspecies.

Evaluation of numerical analysis of PFGE-DNA profiles for differentiating Campylobacter fetus subspecies by comparison with phenotypic, PCR and 16S rDNA sequencing methods

AIMS

To assess the efficacy of numerical analysis of PFGE-DNA profiles for identification and differentiation of Campylobacter fetus subspecies.

METHODS AND RESULTS

31 Camp. fetus strains were examined by phenotypic, PCR- and PFGE-based methods, and the 16S rDNA sequences of 18 strains compared. Numerical analysis of PFGE-DNA profiles divided strains into two clusters at the 86% similarity level. One cluster contained 19 strains clearly identified as Camp. fetus subsp. venerealis. The other cluster comprised 12 strains, of which 10 were unambiguously identified as Camp. fetus subsp. fetus. The remaining two strains were identified as Camp. fetus subsp. venerealis by either phenotypic or PCR methods, but not both. At higher similarity levels, clusters containing isolates from each of two countries were identified, suggesting that certain clones predominate in certain geographical regions.

CONCLUSION

Numerical analysis of PFGE-DNA profiles is an effective method for differentiating Camp. fetus subspecies.

SIGNIFICANCE AND IMPACT OF THE STUDY

Critical comparison of PFGE, PCR, 16S rDNA sequencing and phenotypic methods for differentiation of Camp. fetus subspecies was attained. Novel phenotypic markers for distinguishing subspecies were identified. Evidence for dominant clones of each subspecies in certain countries was provided.

Identification of taxonomic and epidemiological relationships among Campylobacter species by numerical analysis of AFLP profiles

Amplified fragment length polymorphism (AFLP)-based profiling was performed on 138 strains representing all named Campylobacter species and subspecies. Profiles of 15/16 species comprised 6 to greater than 100 fragments and were subjected to numerical analysis. The mean similarity of 48 duplicate, outbreak and/or 'identical' strain profiles exceeded 94%. Species were clearly distinguished at the 17.90% similarity (S-) level in the dendrogram. Subspecies of Campylobacter jejuni and Campylobacter hyointestinalis, and biovars of Campylobacter lari and Campylobacter sputorum were distinguished at higher S-levels. All outbreak or 'genetically identical' strains of C. jejuni subsp. jejuni, Campylobacter coli, C. hyointestinalis and C. sputorum clustered at S-levels >92% and were distinguished from unrelated strains. Numerical analysis of AFLP profiles is useful for concurrent identification of taxonomic and epidemiological relationships among most Campylobacter species.