An Actinobacillus pleuropneumoniae PCR typing system based on the apx and omlA genes - evaluation of isolates from lungs and tonsils of pigs

The genetic variability of a gene coding for an outer membrane lipoprotein (omlA) was used to develop a PCR typing system for Actinobacillus pleuropne umoniae. Sequence differences in the middle region of the gene divided the A. pleuropneumoniae serotypes in five distinct groups. Group I included ser otypes 1, 9, 11 and 12 (omlA 1), Group II consisted of serotypes 2 and 8 (o mlA II), Group III included serotypes 3, 6 and 7 (omlA III), Group TV (omlA IV) consisted of serotype 4 and Group V of serotypes 5a, 5b and 10 (omlA V ). The sequence differences were utilized to construct PCR primers specific for each group, except of Group TV, as the amplicon of serotype 4 could be separated from Group III by size. Together with a PCR apr typing system, t he omlA PCR typing system could discriminate the majority of A. pleuropneum oniae serotypes of biovar 1 except of serotypes I, 9 and 11 and serotypes 2 and 8. The PCR typing system was tested on 102 field strains of A. pleurop neumoniae isolated from lungs of diseased pigs. The serotyping results of t he investigated field strains were in agreement with the apr and omlA gene patterns found in the reference strains of the bacteria, with the exception of the omlA gene of five strains of serotype 8. To examine the apx and oml A gene pattern of tonsil isolates, the PCR typing system was tested on a to tal of 280 A. pleuropneumoniae field strains isolated from tonsils of pigs. Agreement between serotyping and DNA typing was found in 96% of the isolat es using the apx gene patterns and in 89% of the isolates using the omlA ge ne. The same serotype specific apx/omlA gene pattern was thus found in the majority of the tonsil isolates and in isolates from diseased lungs. Most o f the differences in the omlA gene were found in 18 tonsil isolates of sero type 12. The omlA/apx PCR typing system described in the present study make s it possible to determine the type specificity of the majority of A. pleur opneumoniae isolates by simple PCR technique and enables phenotype independ ent characterization of isolates non-typable by serotyping. (C) 2000 Elsevi er Science B.V. All rights reserved.