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

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.

Enzootic pneumonia in pigs

This article reviews current knowledge concerning enzootic pneumonia. Enzootic pneumonia, caused by Mycoplasma hyopneumoniae and exacerbated by secondary invaders, occurs worldwide and has been known for many years. The organism, with its typical characteristics, invades the respiratory tract in several successive steps. Clinical symptoms and lesion development are the result of the pathogenic capacity of Mycoplasma hyopneumoniae and the defence reactions in the lung. The economic relevance of pneumonia is influenced to a large extent by common secondary infections which follow an initial M. hyopneumoniae infection. Different tests for the diagnosis of pneumonia in individual pigs and in groups are available. Treatment and control is not simple since enzootic pneumonia is a multi-factorial disease. Some epidemiological aspects and the most important measures for prevention of the disease are described.

Specific, nonradioactive detection of the NHP bacterium in Penaeus vannamei by in situ hybridization

Necrotizing hepatopancreatitis (NHP) is a disease of farm-raised Pacific white shrimp (Penaeus vannamei) caused by a pleomorphic intracellular bacterium. A DNA probe that is specific for the etiologic agent of necrotizing hepatopancreatitis was devised and tested in an in situ hybridization assay. A procedure was developed for labeling a single-stranded DNA probe with digoxigenin by the polymerase chain reaction. The DNA probe encompasses the V1 and V2 variable regions of the 16S ribosomal RNA (rRNA) gene and is designed to hybridize to complementary sequences of the 16S rRNA of the NHP bacterium. The probe was tested on fixed, paraffin-embedded specimens, and an intense, specific hybridization signal was localized to the cytoplasm of hepatopancreatic epithelial cells that were infected with the NHP bacterium, as demonstrated by serial sections stained with hematoxylin and eosin or the Steiner and Steiner method. Negative results were obtained from normal shrimp and from shrimp infected with Vibrio spp. The specificity of the probe was confirmed using either mammalian or avian tissues infected with other intracellular bacteria, including Ehrlichia canis, Salmonella enteritidis, Brucella abortus, and Chlymidia spp., and using another species of shrimp (P. monodon) infected with a different rickettisa-like intracellular bacterium.

Detection of Mycoplasma hyopneumoniae in nose swabs from pigs by in vitro amplification of the 16S rRNA gene

We report the use of PCR to detect DNA from Mycoplasma hyopneumoniae, the etiological agent of enzootic porcine pneumonia. A primer set was designed for the amplification of a 649-bp fragment of the 16S rRNA gene from M hyopneumoniae. The PCR product was identified by ethidium bromide staining after gel electrophoresis and by Southern hybridization with an M. hyopneumoniae-specific oligonucleotide probe. No amplification was observed from any other porcine bacteria tested, including several closely related mycoplasmas. It was also possible to demonstrate the presence of M. hyopneumoniae in bronchial lavage samples and lung tissue samples from experimentally infected pigs. Furthermore, the PCR system was used for analysis of nasal samples obtained from pigs in a fattening herd. By this method, we were able to detect M. hyopneumoniae in nose swabs from naturally infected pigs. However, our results suggest that M. hyopneumoniae can be detected in the nasal cavities only during a limited time period.

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.

An improved enzyme linked immunosorbent assay (ELISA) for the detection of porcine serum antibodies against Mycoplasma hyopneumoniae

An ELISA for the detection of serum antibodies to Mycoplasma hypopneumoniae in pigs and based on a 43 kDa purified protein derived from the cytoplasmic membrane of M. hyopneumoniae strain J is described. This ELISA (MHPP ELISA) was compared with another recently described (Auspharm ELISA, Sheldrake and Romalis 1992) that is based on column-purified sonicated proteins of strain J. Using sample to negative ELISA ratios of 3 and 4 as cutoffs for inconclusive and positive reactors respectively (compared to 2 and 3 for the Auspharm ELISA), the two tests had high specificity (MHPP 99.6%; Auspharm 100%) in 280 SPF pigs. In 176 pigs from commercial herds with endemic M. hyopneumoniae, the MHPP ELISA showed a higher sensitivity than the Auspharm ELISA in both high lung score (LS > or = 5) (85.5% vs. 69.9%) and low lung score (0 < LS < 5) (57.9% vs. 49%) pigs when the positive cutoff for each test was selected. The sensitivity when the inconclusive cutoff was selected was similar in both tests (85%; 85.7%) when low and high lung score pigs were pooled. Altough the MHPP also gave more positive reactors in 36 pigs from M. hyopneumoniae-infected herds with no lung pathology at slaughter than the Auspharm ELISA (11 vs. 4), the total number of inconclusive and positive reactors in these pigs was similar for both tests (18 vs. 14). The MHPP ELISA gave significantly higher ELISA ratios in infected pigs (up to 17.9) than the Auspharm ELISA (up to 9), and earlier seroconversion in naturally-infected (6-8 weeks vs. 9-10 weeks) and experimentally-infected pigs (2-4 weeks vs. 4-6 weeks post infection).

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.

Species-specific oligonucleotide probes complementary to 16S rRNA of Mycoplasma gallisepticum and Mycoplasma synoviae

Mycoplasma gallisepticum and M synoviae are important avian pathogens causing respiratory diseases which result in great economic losses in poultry farming. Two oligonucleotide probes, complementary to the variable region V8 of 16S rRNA from the avian mycoplasmas M gallisepticum and M synoviae have, therefore, been designed and used in direct filter hybridisation experiments. Both probes gave strong hybridisation signals with their homologous targets, whereas no cross-hybridisations were obtained with any of the other avian mycoplasmas tested. It was possible to detect 2-3 x 10(4) mycoplasma organisms by direct filter hybridisation experiments with radiolabelled probes. The probes were also used to analyse several laboratory strains and field isolates of M gallisepticum and M synoviae with complete agreement between the probe technique and the other methods used for species determination. Atypical M gallisepticum strains also gave strong hybridisation signals with the M gallisepticum specific probe.

Application of the polymerase chain reaction (PCR) in veterinary diagnostic virology

The polymerase chain reaction has become an important diagnostic tool for the veterinary virologist. Conventional methods for detecting viral diseases can be laborious or ineffective. In many cases PCR can provide a rapid and accurate test. In this article we explain the basic principles of PCR and supply a reference list of its uses in diagnostic veterinary virology.