Scanning electron microscope observation of the swarming phenomenon of Vibrio parahaemolyticus.

Scanning electron microscopy was used to study the production of lateral flagella and the swarming phenomenon in Vibrio parahaemolyticus. Differences in the size and diameter of the sheathed, polar flagellum and lateral flagella were apparent in these preparations. Swarming of V. parahaemolyticus was found to be similar to the swarming of Proteus spp. in that swarm cells which are heavily flagellated and elongated are formed.     

ScrG, a GGDEF-EAL protein, participates in regulating swarming and sticking in Vibrio parahaemolyticus

In this work, we describe a new gene controlling lateral flagellar gene expression. The gene encodes ScrG, a protein containing GGDEF and EAL domains. This is the second GGDEF-EAL-encoding locus determined to be involved in the regulation of swarming: the first was previously characterized and named scrABC (for "swarming and capsular polysaccharide regulation"). GGDEF and EAL domain-containing proteins participate in the synthesis and degradation of the nucleotide signal cyclic di-GMP (c-di-GMP) in many bacteria. Overexpression of scrG was sufficient to induce lateral flagellar gene expression in liquid, decrease biofilm formation, decrease cps gene expression, and suppress the DeltascrABC phenotype. Removal of its EAL domain reversed ScrG activity, converting ScrG to an inhibitor of swarming and activator of cps expression. Overexpression of scrG decreased the intensity of a (32)P-labeled nucleotide spot comigrating with c-di-GMP standard, whereas overexpression of scrG(Delta)(EAL) enhanced the intensity of the spot. Mutants with defects in scrG showed altered swarming and lateral flagellin production and colony morphology (but not swimming motility); furthermore, mutation of two GGDEF-EAL-encoding loci (scrG and scrABC) produced cumulative effects on swarming, lateral flagellar gene expression, lateral flagellin production and colony morphology. Mutant analysis supports the assignment of the primary in vivo activity of ScrG to acting as a phosphodiesterase. The data are consistent with a model in which multiple GGDEF-EAL proteins can influence the cellular nucleotide pool: a low concentration of c-di-GMP favors surface mobility, whereas high levels of this nucleotide promote a more adhesive Vibrio parahaemolyticus cell type.     

副溶血弧菌的致病机制

副溶血性弧菌是引发微生物食源性疾病的首要病原菌,其在临床上主要引起3种疾病,即胃肠炎、伤口感染和败血症。经过多年的研究,人们对副溶血性弧菌的致病机制有了一定的认识。我们着重介绍副溶血性弧菌的主要毒力因子、毒力基因表达调控及常用的毒力表型研究方法。     

Serovars of Vibrio parahaemolyticus

Seashore water samples collected along the coastline in Bulgaria and Rumania contained in large numbers OK serovars of V. parahaemolyticus; some of these had been isolated repeatedly over an extended time period: 01 K32, 03 K30, 03 K48, 04 K37, 04 K53, 05 K17, 05 K30. The serovar 05 K17 was virtually present in all water samples and was also isolated from a case of purulent ear infection in a child from Burgas. In contrast, strains recovered from Asian and African coastal water had different K antigens and were never identified in Europe. Two strains of V. parahaemolyticus (serovars 05 K15 and 07 K10) had positive swarming growth resembling that of V. alginolyticus. The first of these was Kanagawa-positive and was isolated from a case of severe diarrhea in Brazzaville. Vibrio parahaemolyticus isolates came from marine or brackish water specimens collected on sand banks, 3 strains were recovered from marine or brackish water in Africa. Vibrio harveyi, a sucrose-negative species important from differential diagnostic aspects, has been isolated from seashore water samples collected on coarse-sand or pebbly beaches.     

The mechanism of swarming of Vibrio alginolyticus

Factors leading to swarming of Vibrio alginolyticus cells on solid media were studied. Polar flagellated rods from liquid medium develop into small colonies on solid medium. Byproducts, accumulating in the colony area, induce at certain critical concentrations, the formation of peritrichous flagella and development of long heavily flagellated filaments which swarm away form the high by-product concentrations. Several types of nonswarming mutants were isolated, among them, mutants which lack the capacity to form swarming-inducing pyproducts, but can be induced to swarm by byproducts of other mutants incapable of swarming. Different compounds could replace the natural metabolic byproducts; at very low concentration these compounds induce peritrichous flagella and swarming in some of the nonswarming mutants mentioned above. The natural metabolic byproducts accumulating in yeast-extract-peptone medium are suggested to be volatile acids belonging to the valine and isoleucine pathway. Wild-type V. alginolyticus cells cannot swarm on certain substrates but its mutants, able to swarm on many substrates in minimal media, are easily selected.     

Inactivation of Vibrio parahaemolyticus in Distilled Water

Vibrio parahaemolyticus cells are readily inactivated in distilled water. The time of exposure required to inactivate 90% of the cells was between 0.9 and 4.4 min.     

Isolation of a new drug-resistance plasmid from a strain of Vibrio parahaemolyticus

A new R plasmid, pSA55, with a molecular weight of 112 megadaltons (Md), was isolated from a strain of Vibrio parahaemolyticus with multiple drug resistance. The pSA55 plasmid conferred on its host resistance to chloramphenicol, tetracycline, streptomycin, kanamycin, ampicillin, trimethoprim and 2,4-diamino-6,7-diisopropyl pteridine, and belongs to incompatibility group C. The plasmid was transferable to Escherichia coli, V. parahaemolyticus, V. alginolyticus and NAG bivrio at a frequency of 10(-3) approximately -7, and was stably inherited by the transconjugants of these species. The conjugal transfer of pSA55 plasmid was significantly affected by the growth culture phase. The resistance pattern and resistance levels of transconjugants were the same as those of the donor strain. We did not observe fluctuations in minimal inhibitory concentrations with transfer, unlike the case of V. cholerae. The relationship between the pSA55 plasmid and the Kanagawa phenomenon was not clarified in the present study.