Identification of nine sequence types of the 16S rRNA genes of Campylobacter jejuni subsp. jejuni isolated from broilers

<p>Abstract</p> <p>Background</p> <p>Campylobacter is the most commonly reported bacterial cause of enteritis in humans in the EU Member States and other industrialized countries. One significant source of infection is broilers and consumption of undercooked broiler meat. <it>Campylobacter jejuni </it>is the <it>Campylobacter </it>sp. predominantly found in infected humans and colonized broilers. Sequence analysis of the 16S rRNA gene is very useful for identification of bacteria to genus and species level. The objectives in this study were to determine the degree of intraspecific variation in the 16S rRNA genes of <it>C. jejuni </it>and <it>C. coli </it>and to determine whether the 16S rRNA sequence types correlated with genotypes generated by PFGE analysis of <it>Sma</it>I restricted genomic DNA of the strains.</p> <p>Methods</p> <p>The 16S rRNA genes of 45 strains of <it>C. jejuni </it>and two <it>C. coli </it>strains isolated from broilers were sequenced and compared with 16S rRNA sequences retrieved from the Ribosomal Database Project or GenBank. The strains were also genotyped by PFGE after digestion with <it>Sma</it>I.</p> <p>Results</p> <p>Sequence analyses of the 16S rRNA genes revealed nine sequence types of the <it>Campylobacter </it>strains and the similarities between the different sequence types were in the range 99.6–99.9%. The number of nucleotide substitutions varied between one and six among the nine 16S rRNA sequence types. One of the nine 16S rRNA sequence profiles was common to 12 of the strains from our study and two of these were identified as <it>Campylobacter coli </it>by PCR/REA. The other 10 strains were identified as <it>Campylobacter jejuni</it>. Five of the nine sequence types were also found among the <it>Campylobacter </it>sequences deposited in GenBank. The three 16S rRNA genes in the analysed strains were identical within each individual strain for all 47 strains.</p> <p>Conclusion</p> <p><it>C. jejuni </it>and <it>C. coli </it>seem to lack polymorphisms in their 16S rRNA gene, but phylogenetic analysis based on 16S rRNA sequences was not always sufficient for differentiation between <it>C. jejuni </it>and <it>C. coli</it>. The strains were grouped in two major clusters according to 16S rRNA, one cluster with only <it>C. jejuni </it>and the other with both <it>C. jejuni </it>and <it>C. coli</it>. Genotyping of the 47 strains by PFGE after digestion with <it>Sma</it>I resulted in 22 subtypes. A potential correlation was found between the <it>Sma</it>I profiles and the 16S rRNA sequences, as a certain <it>Sma</it>I type only appeared in one of the two major phylogenetic groups.</p

Transformational exchanges in the dihydropteroate synthase gene of Neisseria meningitidis: a novel mechanism for acquisition of sulfonamide resistance.

The nucleotide sequences of the chromosomal dihydropteroate synthase (dhps) genes in sulfonamide-susceptible and sulfonamide-resistant strains of Neisseria meningitidis of serogroups A, B and C were determined. The molecular weights and the amino acid sequences showed similarity to those of all other known dihydropteroate synthase polypeptides. Sequence comparison of the N. meningitidis dhps genes indicated horizontal transfer of DNA segments rather than point mutations as the cause for resistance in meningococci. The dhps genes in three of four sulfonamide-resistant meningococci contained identical central regions of 424 bp. Compared with the corresponding genes in susceptible strains, each central region included an insert of 6 bp. In one of the sulfonamide-resistant strains, the dhps gene was similar to the corresponding genes in the sensitive strains in its NH2-terminal and C-terminal parts. Its central region, however, was identical to the corresponding regions of two of the other resistant genes, and thus it could be seen as a hybrid dhps gene. Transformation experiments and mapping of transformed dhps genes indicated the existence of a novel mechanism for the dissemination of sulfonamide resistance in N. meningitidis. The origin of the resistance-mediating segment of the gene is unknown, but hybridization results showed the presence of homologous dhps genes in Neisseria gonorrhoeae and N. lactamica but not in N. subflava or Branhamella catarrhalis