DNA‐DNA hybridization and analysis of restriction endonuclease and rRNA gene patterns of atypical (catalase‐weak/negative) Campylobacter jejuni from paediatric blood and faecal cultures

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Abstract
Sixteen strains of atypical (catalase‐weak or negative), hippurate‐hydrolysing campylobacters from paediatric blood and faecal cultures were identified by DNA–DNA slot hybridization. All were closely related ( 67%) to Campylobacter jejuni and representative strains had G + C contents of 30 ± 1 mol%. Numerical analysis of chromosomal DNA HaeIII digest patterns revealed two clusters of strains at the 55%S level corresponding to C. jejuni subsp. jejuni and C. jejuni subsp. doylei; most strains belonged to the latter subspecies. No two strains had identical patterns but within each subspecies two subgroups were identifiable, corresponding to Lior biotypes I and II. Southern blot hybridization analysis with a 16 + 23S rRNA cistron probe from Escherichia coli also showed differences between the various strains, and in a numerical analysis three groupings were formed at 70%S corresponding to C. jejuni subsp. jejuni Lior biotypes I and II, and C. jejuni subsp. doylei. Four of the subspecies doylei strains contained a 3·4‐MDa plasmid. These analyses showed that catalase‐negative C. jejuni subsp. jejuni were genomically distinguishable from C. jejuni subsp. doylei as were Lior biotypes within subsp. jejuni. Ability to produce catalase is not a feature common to all C. jejuni strains, and our results confirm that some strains of subspecies jejuni may be negative in that character although typical in other respects. DNA pattern heterogeneity was consistent with serological differences between strains.

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