Susceptibility of Campylobacter hyointestinalis subsp. hyointestinalis to antimicrobial agents and characterization of quinolone-resistant strains.

OBJECTIVES: To study the susceptibility of Campylobacter hyointestinalis subsp. hyointestinalis to several antimicrobial agents and to investigate the mechanisms of nalidixic acid and ciprofloxacin resistance. METHODS: The disc diffusion method was employed to study the susceptibility of 49 C. hyointestinalis subsp. hyointestinalis strains of reindeer and bovine origin to 12 different antimicrobial agents. In addition, the MICs of nalidixic acid and ciprofloxacin were determined. The nucleotide sequence of a 270 bp fragment of the gyrA gene was determined in ciprofloxacin-susceptible and -resistant strains. The effect of a multidrug efflux pump inhibitor Phe-Arg-beta-naphthylamide (PA beta N) on the MICs of ciprofloxacin and nalidixic acid was also studied. RESULTS: The only decreased susceptibility for antimicrobial agents of this study was observed for sulphonamide compound and streptomycin (24% and 32% of the strains, respectively), and this phenomenon was observed exclusively in the bovine strains. In sequence studies, a Thr-86-->Ile change was found in strains with MICs of ciprofloxacin of > or = 64 mg/L, but this mutation was absent in strains with lower resistance levels. The use of PA beta N did not affect the MIC of ciprofloxacin but decreased the MIC of nalidixic acid 2-4-fold. CONCLUSIONS: The Finnish C. hyointestinalis subsp. hyointestinalis strains are susceptible to a majority of the antimicrobials of veterinary importance. The mechanism of ciprofloxacin resistance at lower levels (< or = 32 mg/L) is not associated with a specific mutation in the quinolone resistance-determining region of the gyrA gene. Finally, there are distinct differences in the mechanisms of ciprofloxacin resistance compared with nalidixic acid resistance within the studied species.

Rhamnogalacturonate lyase RhiE is secreted by the out system in Erwinia chrysanthemi.

Supernatants of rhamnose-induced Erwinia chrysanthemi strain 3937 cultures contain a principal secreted protein named RhiE. A rhiE mutant has been found among a set of rhamnose-induced MudI1681 lacZ fusions. RhiE is a 62-kDa protein that has rhamnogalacturonate lyase activity on rhamnogalacturonan I (RG-I). It does not require a divalent cation for its activity and has an optimal pH of 6.0. rhiE expression is strongly induced in the presence of rhamnose but is also regulated by PecT and Crp, two regulators of the transcription of pectinolytic enzyme genes. RhiE is secreted through the type II Out secretion pathway. RhiE has no disulfide bond. The absence of RhiE secretion in a dsb mutant indicated that disulfide bond formation is required for the biogenesis of the secretion apparatus. RhiE was searched for in several E. chrysanthemi strains by using antibodies, and it was found to be present in one-third of the strains tested. However, the reduced virulence of the rhiE mutant indicates that degradation of the RG-I region of pectin is important for full virulence of E. chrysanthemi.