Detection of Mycoplasma bovis and Mycoplasma agalactiae by oligonucleotide probes complementary to 16S rRNA

Mycoplasma agalactiae, an Etiological Agent of Contagious Agalactia in Small Ruminants: A Review

Mycoplasma agalactiae is one of the causal agents of classical contagious agalactia (CA), a serious, economically important but neglected enzootic disease of small ruminants. It occurs in many parts of the world and most notably in the Mediterranean Basin. Following the infection common complications are septicaemia, mastitis, arthritis, pleurisy, pneumonia, and keratoconjunctivitis. Primary or tentative diagnosis of the organism is based upon clinical signs. Various serological tests, namely, growth precipitation, immunofluorescence, complement fixation test, haemagglutination inhibition, agglutination, immunodiffusion, enzyme immunoassays, immunoelectrophoresis, blotting techniques, and others, are available. Molecular tools seem to be much more sensitive, specific, and faster and help to differentiate various strains. The real-time PCR, multiplex PCR, quantitative PCR, PCR-RFLP, MLST, and gene probes, complementary to segments of chromosomal DNA or 16S ribosomal RNA (rRNA), have strengthened the diagnosis of M. agalactiae. Both live attenuated and adjuvant (alum precipitated or saponified) inactivated vaccines are available with greater use of inactivated ones due to lack of side effects. The present review discusses the etiology, epidemiology, pathogenesis, and clinical signs of contagious agalactia in small ruminants along with trends and advances in its diagnosis, treatment, vaccination, prevention, and control strategies that will help in countering this disease.

Detection and identification of Vibrio scophthalmi in the intestinal microbiota of fish and evaluation of host specificity

AIMS

To develop a species-specific probe (VSV3) for the detection of Vibrio scophthalmi in fish intestine and to apply this probe to study the host specificity of V. scophthalmi.

METHODS AND RESULTS

A specific probe (VSV3) based on the variable region V3 of the 16S rRNA gene (rDNA) was designed. Its specificity was tested by DNA-DNA hybridization and by colony hybridization. No cross-hybridization was found. The sensitivity of the probe was tested both by DNA-DNA hybridization and by colony hybridization. The detection limit of V. scophthalmi 16S rDNA was 150 pg or 10 cfu. Vibrio scophthalmi cells were detected in experimental samples constituted by mixed cultures when present in proportions of 1 : 10 and 1 : 100. The VSV3 probe also proved to be reliable for the detection of V. scophthalmi in samples of fish intestine.

CONCLUSIONS

The VSV3 probe can be used for the detection of V. scophthalmi in colony hybridization or DNA-DNA hybridization of amplified 16S rDNA. Preliminary results indicate that V. scophthalmi may present certain host specificity for turbot.

SIGNIFICANCE AND IMPACT OF THE STUDY

The VSV3 probe provides a useful tool for ecological studies.

Sequence, cloning, expression and characterisation of the 81-kDa surface membrane protein (P80) of Mycoplasma agalactiae

Mycoplasma agalactiae, the causative agent of contagious agalactia in small ruminants, produces a protein, named P80, that is detectable in all wild-type isolates examined to date and that appears expressed during the early phase of infection. We describe here the identification, cloning and expression of the gene encoding P80 (ma-mp81). The deduced amino acid sequence is consistent with a hydrophobic and basic protein that possesses a lipoprotein signal peptide. Sequence analysis of gene ma-mp81 suggests that P80 is a membrane lipoprotein that shows significant homology with other putative lipoproteins of M. pneumoniae. An internal 1-kb fragment of ma-mp81 was expressed in Escherichia coli as a 6xHis-tagged protein. The purified recombinant protein greatly reacted with polyclonal anti-P80 sera raised in lamb.

Species identification of Mycoplasma bovis and Mycoplasma agalactiae based on the uvrC genes by PCR

The DNA repair genes uvrC from Mycoplasma bovis and Mycoplasma agalactiae type strains were cloned and their nucleotide sequences were established. These sequences were used to design polymerase chain reaction (PCR) primer pairs for M. bovis and M. agalactiae. Each primer pair amplified a 1-6 kb fragment of the uvrC gene in the respective species. The specificity of the primer pairs for the two species was demonstrated through the lack of cross-amplifications in heterologous PCR reactions and in reactions using DNA from other mycoplasma species. Subsequent restriction enzyme analysis of the amplified uvrC gene segments from type and field strains of M. bovis and M. agalactiae showed that the uvrC genes are well conserved in both species but differ significantly between the two species. The diagnostic PCR assay enabled unambiguous identification of M. bovis and M. agalactiae strains isolated from geographically diverse places, even in cases where 16S rRNA gene sequence analysis was unable to discriminate between the two species.

Characterization of membrane surface proteins of Mycoplasma agalactiae during natural infection

We have analyzed antigenic variation of seven M. agalactiae wild strains using different sera from naturally infected sheep. Only 30 day sera recognized all surface proteins and inhibited the growth of mycoplasmas. Furthermore, we have observed that two strongly immunogenic proteins: 55 and 35 kDa were digested using 500 micrograms/ml of trypsin. These two bands are immunoprecipitated together with four other proteins but only the 35 kDa protein is recognized by eluted antibodies.

Detection of Mycoplasma agalactiae in sheep milk samples by polymerase chain reaction

We developed a simple and rapid method for DNA extraction from sheep milk to use for polymerase chain reaction (PCR) diagnosis of Mycoplasma agalactiae. We tested 357 samples from 21 newly infected flocks (group 1) and 87 samples from 8 flocks infected in the past (group 2). PCR results were compared with those of conventional culture. By PCR we detected 175 positives in group 1, while by culture we detected only 153. Milk samples from group 2 were negative, both by PCR assay and by culture. Our PCR is much faster than culture and reduces the time required for diagnosis from several days to 5 h. The method could be used for the routine diagnosis of contagious agalactia caused by Mycoplasma agalactiae.

Genomic, protein homogeneity and antigenic variability of Mycoplasma agalactiae

Eleven strains of Mycoplasma agalactiae differing in pathogenicity, animal species origin and geographic localisation, showed similar chromosome restriction profiles with four endonucleases. However the international reference strain PG2 showed a unique profile. The protein and antigenic variabilities of 31 strains of M. agalactiae were investigated using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting performed with naturally infected animal sera and purified antibodies against the 29 kDa protein. Protein profiles were similar but antigenic profiles could be separated into two main groups according to geographic origin: (i) strains isolated in south-west France and (ii) strains from north-east France. Some differences also occurred from strain to strain within each group. The antigenic profile variability found in immunoblotting, originated in two different phenomena: (i) some epitopes were expressed only in strains of one profile type and (ii) some other epitopes were common to all strains but located on several proteins which differed in number and molecular mass from one strain to another. The presence of epitopes which undergo phase variation in the same lineage of clones from a single cell is discussed.

In vitro amplification of the 16S rRNA genes from Mycoplasma bovis and Mycoplasma agalactiae by PCR

Mycoplasma bovis and Mycoplasma agalactiae are two very closely related species which cause mastitis in cows and goats, respectively. M. bovis can also cause arthritis and respiratory disease in cattle. It has recently been shown that the 16S rRNA sequences differ only in 8 nucleotide positions between the two species [J.G. Mattsson, B. Guss and K.-E. Johansson (1994) FEMS Microbiol. Lett., 115: 325-328]. These nucleotide differences are distributed over the molecule in such a way that it is difficult to design specific identification systems, based on PCR only, for M. bovis and M. agalactiae. Two different PCR systems based on 16S rRNA sequence data have, however, been designed for these two species. The forward primers were identical in the two systems and complementary to a segment of the evolutionarily variable region V2. The reverse primers were complementary to the variable region V6, in which there are two nucleotide differences between M. bovis and M. agalactiae. The size of the PCR products, generated with these primers, was 360 bp. Cross-amplification was obtained with the two species in the heterologous PCR systems, but with approximately a 100-fold lower efficiency. Cross-amplification was not obtained with any other bovine or caprine mycoplasma except for Mycoplasma sp. strain A1343 of the caprine group 7. The detection limit of the PCR system for M. bovis with a reference culture was 4 x 10(2) CFU/ml and of the PCR system for M. agalactiae 2 x 10(2) CFU/ml. The M. bovis-PCR system was used to analyze nasal samples of calves from a herd where an outbreak of pneumonia had occured and it proved possible to detect M. bovis in these samples.

A surface epitope undergoing high-frequency phase variation is shared by Mycoplasma gallisepticum and Mycoplasma bovis

We have recently reported that three distinct size- and phase-variable surface lipoproteins (Vsps) of the bovine pathogen Mycoplasma bovis possess a common epitope recognized by monoclonal antibody 1E5. In the present study, we show that this epitope is also present on a size-variant protein (PvpA) of the avian pathogen Mycoplasma gallisepticum. Application of monoclonal antibody 1E5 in Western immunoblot analysis of Triton X-114 phase-fractionated proteins and in colony immunoblots, as well as in trypsin and carboxypeptidase digestion experiments, has demonstrated that (i) PvpA is an integral membrane protein with a free C terminus, (ii) the shared epitope is surface exposed, and (iii) PvpA is subjected to high-frequency phase variation in expression. By using serum antibodies from M. gallisepticum-infected chickens, we were able to demonstrate the immunogenic nature of PvpA and identify three additional highly immunogenic Triton X-114 phase proteins (p67, p72, and p75) also undergoing high-frequency phase variation spontaneously and independently. Metabolic labeling experiments with [14C]palmitate and [14C]oleate revealed that PvpA, in contrast to p67, p72, and p75, is not lipid modified. Southern blot hybridization with restriction fragments carrying the pvpA gene of M. gallisepticum or the vspA gene of M. bovis against digested genomic DNA of the two Mycoplasma species indicated the absence of genetic relatedness between the pvpA and vspA genes. The apparent complexity of the antigenic variation phenomenon in M. gallisepticum is discussed.

Genomic, protein and antigenic variability of mycoplasma bovis

Restriction endonuclease analysis (REA) with three enzymes SmaI, PstI, BamHI- was used to identify 13 different genomic groups among 37 Mycoplasma bovis strains. One genomic group was comprised of 14 strains. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) patterns for one strain chosen from each genomic group and an international reference strain PG45 were all similar. Antigenic variability in M. bovis species was investigated by immunoblotting, using serum from a calf that had been naturally infected with M. bovis and three M. bovis-specific monoclonal antibodies--mAbs N2, I2 and 5D7. Twenty M. bovis field strains were tested, comprising one from each genomic group, six from the same genomic group and the reference strain. Antigenic profiles obtained with calf serum differed markedly one from the other, the heterogeneity being equally great among the strains belonging to the same genomic group as those coming from different groups. A stable antigen common to 164 out of 168 strains was detected by mAb N2, whilst with mAbs I2 and 5D7, two different membrane antigenic systems were demonstrated that were strikingly variable. These variations in expression occurred not only from one strain to another, but also within the same lineage of clones from a single cell.

Characterization of the 16S rRNA genes from Mycoplasma sp. strain F38 and development of an identification system based on PCR

Mycoplasma sp. (strain F38) is the causative agent of contagious caprine pleuropneumonia, which is a goat disease of great global concern. Strain F38 belongs to the so-called "Mycoplasma mycoides cluster," and the members of this cluster have many biochemical and serological properties in common, which makes it difficult to differentiate between them by conventional methods. Their phylogenetic interrelationship are thus uncertain. The 16S rRNA gene of the rrnB operon from strain F38 was cloned and sequenced. The sequence was compared with the 16S rRNA sequences of related mycoplasmas, and phylogenetic trees were constructed by parsimony analysis. A three-way ambiguity among strain F38, Mycoplasma capricolum, and Mycoplasma sp. strain PG50 was observed in the trees. This observation is in agreement with a recent proposal to reclassify strain F38 and M. capricolum. A primer set was designed for in vitro amplification by PCR of a fragment of the 16S rRNA genes from the M. mycoides cluster. The amplimers of strain F38 could be distinguished easily from the corresponding amplimers from other members of the M. mycoides cluster by restriction enzyme analysis with PstI. This observation was utilized to design an identification system for strain F38. Part of the 16S rRNA gene of the rrnA operon from strain F38 was also cloned, and several sequence differences between the two rRNA operons were discovered, revealing microheterogeneity between the two 16S rRNA genes of this organism.

Cloning and characterization of the RNase P RNA genes from two porcine mycoplasmas

We report the cloning of the RNase P RNA genes from the primary aetiological agent of porcine pneumonia, Mycoplasma hyopneumoniae, and the closely related commensal, Mycoplasma flocculare. The monocistronic genes each have promoters with AT-rich -35 regions and Rho-independent-like transcription terminators which are retained in the RNase P RNA. Both of these RNase P RNA variants are shown to be catalytically active in vitro in spite of a low overall GC content (30%). Our results suggest a new example of a stable mini-helix in the conserved core of the mycoplasmal RNase P RNAs. Deletion of the corresponding structural element in Escherichia coli RNase P RNA (M1 RNA) generated an RNase P RNA with an impaired substrate interaction. Displacement of this structural element with the mycoplasmal mini-helix resulted in an enzyme with a phenotype similar to that of wild-type M1 RNA. In addition, this structural element is important for lead ion-induced cleavage at specific sites in M1 RNA.

The phylogeny of Mycoplasma bovis as determined by sequence analysis of the 16S rRNA gene

The nucleotide sequence of the 16S rRNA gene of Mycoplasma bovis has been determined. Comparisons with other 16S rRNA sequences of mycoplasmas showed that Mycoplasma agalactiae is phylogenetically the closest relative. In total, only eight nucleotides differed between the M. bovis and M. agalactiae 16S rRNA sequences. The phylogenetic position of M. bovis with respect to other mycoplasmas was determined by sequence comparisons and from features in the secondary structure of 16S rRNA.

Identification and classification of different isolates of Francisella tularensis

The causative agent of tularemia, Francisella tularensis, occurs in two main biovars, the highly virulent F. t. biovar tularensis, found in North America; and the less virulent biovar palaearctica, found all over the northern hemisphere. Two other biovars have been proposed, F. t. biovar mediaasiatica and F. t. biovar palaearctica var. japonica. In Sweden tularemia is most frequently observed in man and varying hares (Lepus timidus), and occasionally in other species. Tularemia in hares is normally an acute fatal disease, although less fatal infections have been reported. The diagnosis of tularemia is routinely based on immunological reactions. We studied 10 different isolates of F. tularensis from varying hares, one isolate from an Ural owl (Strix uralensis), one vaccine strain, one strain of F. t. biovar japonica, and six isolates from a virulence study of F. tularensis, by biochemical tests and by hybridization experiments with probes complementary to 16S rRNA. All isolates, except the isolate F. t. biovar japonica, were characterized as F. t. biovar palaearctica by biochemical tests. In the 16S rRNA analysis all isolates were positive to the probe for Francisella tularensis and the probe for F. t. biovar palaearctica with the exception that F. t. biovar japonica reacted with the probe specific to F. t. biovar tularensis. To further confirm that the strains used belonged to F. t. biovar palaearctica virulence tests in rabbits were performed which disclosed this phenotype. The results presented in this work show that the isolated strains from the western part of Europe were F. t. biovar palaearctica, irrespective of animal origin or virulence.

Antigen capture ELISA using a monoclonal antibody for the detection of Mycoplasma bovis in milk

An enzyme-linked immunosorbent assay (ELISA) using a monoclonal antibody (mAb) was developed to detect Mycoplasma (M.) bovis in milk samples from cattle. With this procedure, 1 x 10(5) colony forming units per ml (cfu/ml) milk were routinely detectable. No cross-reactions to other bovine mycoplasma species were observed. Both the sensitivity of 80.6% and the specificity of 94.9% are sufficient for its use in diagnosis of clinical mastitis. The sensitivity could be increased by 10% after introduction of 48-hour pre-incubation of samples. This allowed recognition of cows shedding M. bovis amounts of 10(3) cfu/ml in their milk, which is typical for subclinical cases. Screening of milk samples by means of this antigen capture ELISA has advantages over culture methods in terms of speed and potential to monitor large herds, thereby permitting early culling of infected animals to reduce transmission of the pathogen to non-infected animals.

Oligonucleotide probes complementary to 16S rRNA for rapid detection of mycoplasma contamination in cell cultures

Mycoplasma contamination of cell cultures is a menace to diagnostic and research procedures. Rapid and reliable detection methods are, therefore, sorely needed. After comparing 16S rRNA sequences from those mycoplasmas that contaminate cell cultures, three different oligonucleotide probes were constructed. Two of these probes were designed to be group-specific and one to be species-specific. The three oligonucleotide probes were designed to cover all mycoplasmas commonly isolated from cell cultures. Contaminated cell lines could easily be detected by a direct filter hybridization assay in which the probes were incubated jointly. The assay proved to be rapid and sensitive with the possibility to perform and evaluate the mycoplasma testing within one working day.

Detection and identification of Mobiluncus species by direct filter hybridization with an oligonucleotide probe complementary to rRNA

A hybridization assay for direct detection and identification of Mobiluncus species has been developed and tested. A [32P]-labelled synthetic oligonucleotide probe, complementary to a nucleotide sequence in the variable region V8 of Mobiluncus 16S ribosomal RNA, was utilized. One of the advantages of using rRNA as target molecule for the hybridization assays is the copy number of rRNA, which can be as high as 10(4), and that additionally three to six sites on the minus strand of the DNA gene can be utilized. This probe was found to be sensitive and to react with 62 of 68 tested typical or atypical Mobiluncus isolates. It was also specific, and was shown not to react with 96 tested unrelated bacterial species and isolates, including taxonomically closely related species like Actinomyces or Bifidobacterium spp., or with bacteria isolated from the vagina of both healthy persons with an undisturbed flora, as well as from patients suffering from the bacterial vaginosis syndrome (BV).

Specificity of oligonucleotide probes complementary to evolutionarily variable regions of 16S rRNA from Mycoplasma hyopneumoniae and Mycoplasma hyorhinis

Mycoplasma is the common name for the smallest free-living microorganisms, the Mollicutes. Mycoplasma hyopneumoniae is of great importance in veterinary medicine, causing enzootic pneumonia in pigs. M hyorhinis can cause polyserositis and may cause pneumonia in piglets. Oligonucleotides complementary to variable regions of 16S rRNA from these mycoplasmas were designed and used as probes for detection and identification of these mycoplasmas. The probe complementary to 16S rRNA of M hyorhinis gave a very weak cross-hybridisation with M hyosynoviae in filter hybridisation experiments, but not with any of the other porcine mycoplasmas tested. Three oligonucleotide probes complementary to M hyopneumoniae 16S rRNA were tested. One of the probes (Mhp6/30) was found to be specific to M hyopneumoniae, but the other two gave cross-hybridisation with M flocculare. Using the Mhp6/30 probe in direct filter hybridisation experiments, it proved possible to detect M hyopneumoniae in lung biopsies from experimentally infected pigs.