title: Rapid determination of vapA/vapB genotype in Rhodococcus equi using a differential polymerase chain reaction method.
abstract: Rhodococcus equi is a facultative pathogen of foals. Infection causes an often fatal pulmonary pneumonia. The organism has also been isolated from pigs, cattle, humans and the environment. Equine virulence has a high positive correlation with the expression of a 17.4 kD polypeptide of unknown function, VapA, the product of the plasmid-encoded vapA gene. More recently an isogene of vapA, referred to as vapB and encoding an 18.2 kDa polypeptide, has been identified among pig and human isolates. The two genes share > 80% sequence identity, yet their host strains apparently exhibit different pathogenicity profiles (for example by reference to virulence in mouse model system and host specificity). In this study, a polymerase chain reaction (PCR) technique was developed that permits the selective amplification of vapA and vapB. Using this technique the distribution of the two genes among 35 randomly selected isolates of Rhodococcus equi from various animal and environmental sources was determined. Using this technique the genotype of each isolate could be unambiguously assigned as vapA+, vapB+ or vap- (i.e., scoring negative for both vapA and vapB). No isolate scored positive for both vapA and vapB. 100% of equine isolates scored vapA+, confirming the status of vapA as a reliable marker of equine virulence. All three genotypes were found among human isolates; porcine isolates scored either vapB+ or vap- and no vapA+ isolates were present in this sample. Rigorous statistical analysis using the Fisher Exact test confirmed that the high frequency of vapA+ among equine isolates is significant; however the sample size was too small to draw statistically significant conclusions regarding the distribution of genotypes among within other animal groups.
authors.affiliation: Molecular Biology Research Group, MicroScience Technologies Ltd, Pentlands Science Park, Edinburgh EH26 0PZ, UK.
authors.forename: Christopher
authors.initials: C
authors.lastname: Oldfield
authors.forename: Hal
authors.initials: H
authors.lastname: Bonella
authors.forename: Lynne
authors.initials: L
authors.lastname: Renwick
authors.forename: Hilary I
authors.initials: HI
authors.lastname: Dodson
authors.forename: Grace
authors.initials: G
authors.lastname: Alderson
authors.forename: Michael
authors.initials: M
authors.lastname: Goodfellow
mesh_terms: D000193:Actinomycetales Infections / Q000662:veterinary; D000818:Animals; D000942:Antigens, Bacterial / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D004268:DNA-Binding Proteins / Q000235:genetics*; D004783:Environmental Microbiology; D005838:Genotype; D006734:Horse Diseases / Q000382:microbiology; D006736:Horses; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics*; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction / Q000379:methods*; D016929:Rhodococcus equi / Q000235:genetics*; D016415:Sequence Alignment; D037521:Virulence Factors / Q000235:genetics*
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D008562:Membrane Glycoproteins; D037521:Virulence Factors; C077517:VapB protein, Bacteria