title: Genetic diversity and toxic activity of Aggregatibacter actinomycetemcomitans isolates.
abstract: BACKGROUND
  Very little is known of the diversity and expression of virulence factors of serotypes of Aggregatibacter actinomycetemcomitans. Toxic activity on Chinese hamster ovary (CHO) cells and cdt and ltx genotyping were evaluated in A. actinomycetemcomitans serotypes.
  
  
  METHODS
  Forty-one A. actinomycetemcomitans isolates were analysed for CHO cell growth inhibition. Genotyping was performed by polymerase chain reactions specific to the ltx promoter region, serotype-specific and cdt region and by sequencing of cdtB.
  
  
  RESULTS
  cdtABC was detected in 40 strains. Analysis of the cdtA upstream region revealed 10 cdt genotypes. Toxicity to CHO cells was detected for 92.7% of the isolates; however, no correlation between the toxic activity and the cdt genotype was detected. Serotype c was more prevalent among Brazilian samples (68.0%). Four serotype b isolates from subjects with aggressive periodontitis were associated with high leukotoxin production and exhibited moderate to strong toxic activity in CHO cells, but were classified in different cdt genotypes. High levels of toxicity in CHO cells were not associated with a particular serotype; 57.1% of serotype a isolates presented low toxicity to CHO cells whereas the highly toxic strains belonged to serotypes b and c. Sequencing of cdtB revealed a single nucleotide polymorphism of amino acid 281 but this was not related to the toxic activity in CHO cells.
  
  
  CONCLUSIONS
  Differences in prevalence of the low and highly cytotoxic strains among serotypes reinforce the hypothesis that serotype b and c isolates of A. actinomycetemcomitans are more virulent than serotype a strains.
authors.affiliation: Department of Microbiology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil.
authors.forename: D
authors.initials: D
authors.lastname: Kawamoto
authors.forename: E S
authors.initials: ES
authors.lastname: Ando
authors.forename: P L
authors.initials: PL
authors.lastname: Longo
authors.forename: A C R
authors.initials: AC
authors.lastname: Nunes
authors.forename: M
authors.initials: M
authors.lastname: Wikström
authors.forename: M P A
authors.initials: MP
authors.lastname: Mayer
mesh_terms: D016976:Aggregatibacter actinomycetemcomitans / Q000235:genetics* / Q000502:physiology*; D010520:Aggressive Periodontitis / Q000382:microbiology*; D000818:Animals; D001427:Bacterial Toxins / Q000235:genetics* / Q000633:toxicity; D016466:CHO Cells / Q000187:drug effects; D006224:Cricetinae; D003412:Cricetulus; D003603:Cytotoxins / Q000235:genetics*; D005098:Exotoxins / Q000096:biosynthesis / Q000235:genetics; D014644:Genetic Variation; D006801:Humans; D020641:Polymorphism, Single Nucleotide; D012703:Serotyping; D013045:Species Specificity; D014774:Virulence / Q000235:genetics
chemical_list: D001427:Bacterial Toxins; D003603:Cytotoxins; D005098:Exotoxins; C447141:cytolethal distending toxin, Actinobacillus actinomycetemcomitans; C018579:leukotoxin