Direct detection of Vibrio cholerae and ctxA in Peruvian coastal water and plankton by PCR

Seawater and plankton samples were collected over a period of 17 months from November 1998 to March 2000 along the coast of Peru. Total DNA was extracted from water and from plankton grouped by size into two fractions (64 micro m to 202 micro m and >202 micro m). All samples were assayed for Vibrio cholerae, V. cholerae O1, V. cholerae O139, and ctxA by PCR. Of 50 samples collected and tested, 33 (66.0%) were positive for V. cholerae in at least one of the three fractions. Of these, 62.5% (n = 32) contained V. cholerae O1; ctxA was detected in 25% (n = 20) of the V. cholerae O1-positive samples. None were positive for V. cholerae O139. Thus, PCR was successfully employed in detecting toxigenic V. cholerae directly in seawater and plankton samples and provides evidence for an environmental reservoir for this pathogen in Peruvian coastal waters.     

Trophic regulation of Vibrio cholerae in coastal marine waters

Cholera disease, caused by the bacterium Vibrio cholerae, afflicts hundreds of thousands worldwide each year. Endemic to aquatic environments, V. cholerae's proliferation and dynamics in marine systems are not well understood. Here, we show that under a variety of coastal seawater conditions V. cholerae remained primarily in a free-living state as opposed to attaching to particles. Growth rates of free-living V. cholerae (micro: 0.6-2.9 day(-1)) were high (similar to reported values for the bacterial assemblages; 0.3-2.5 day(-1)) particularly in phytoplankton bloom waters. However, these populations were subject to heavy grazing-mortality by protozoan predators. Thus, grazing-mortality counterbalanced growth, keeping V. cholerae populations in check. Net population gains were observed under particularly intense bloom conditions when V. cholerae proliferated, overcoming grazing pressure terms in part via rapid growth (> 4 doublings day(-1)). Our results show V. cholerae is subject to protozoan control and capable of utilizing multiple proliferation pathways in the marine environment. These findings suggest food web effects play a significant role controlling this pathogen's proliferation in coastal waters and should be considered in predictive models of disease risk.     

Occurrence and distribution of Vibrio cholerae in the coastal environment of Peru

The occurrence and distribution of Vibrio cholerae in sea water and plankton along the coast of Peru were studied from October 1997 to June 2000, and included the 1997-98 El Ni?o event. Samples were collected at four sites in coastal waters off Peru at monthly intervals. Of 178 samples collected and tested, V. cholerae O1 was cultured from 10 (5.6%) samples, and V. cholerae O1 was detected by direct fluorescent antibody assay in 26 out of 159 samples tested (16.4%). Based on the number of cholera cases reported in Peru from 1997 to 2000, a significant correlation was observed between cholera incidence and elevated sea surface temperature (SST) along the coast of Peru (P < 0.001). From the results of this study, coastal sea water and zooplankton are concluded to be a reservoir for V. cholerae in Peru. The climate-cholera relationship observed for the 1997-98 El Ni?o year suggests that an early warning system for cholera risk can be established for Peru and neighbouring Latin American countries.     

Characterization of a clinical Vibrio cholerae O139 isolate from Mexico

Pathogenic strains of Vibrio cholerae O139 possess the cholera toxin A subunit (ctxA) gene as well as the gene for toxin co-regulated pili (tcpA). We report the isolation of a ctxA-negative, tcpA-negative V. cholerae O139 strain (INDREI) from a patient in Mexico diagnosed with gastrointestinal illness. Certain phenotypic characteristics of this strain were identical to those of V. cholerae O1 biotype El Tor. Unlike ctxA-positive V. cholerae O139 strains, this strain was sensitive to a wide panel of antibiotics, including ampicillin, chloramphenicol, ciprofloxacin, gentamicin, furazolidone, nalidixic acid, nitrofurantoin, tetracycline, trimethoprim-sulfamethoxazole, and streptomycin, but was resistant to polymyxin B. Ribotype and pulsed-field gel electrophoresis profiles of INDRE1 differed from those of ctxA-positive V. cholerae O139 and other V. cholerae strains. Phenotypic characteristics of the Mexico strain were similar to those reported for V. cholerae O139 isolates from Argentina and Sri Lanka.     

Vibrio cholerae (non-O1) isolated from California coastal waters.

Nineteen strains of Vibrio cholerae non-O1 were isolated from five separate marine sites along the Santa Cruz County coast. This environmental study was initiated after a human case of non-O1 cholera-like diarrhea was acquired endemically.     

Characterization of a Vibrio cholerae phage isolated from the coastal water of Peru

A Vibrio cholerae bacteriophage, family Myoviridae, was isolated from seawater collected from the coastal water of Lima, Peru. Genome size was estimated to be 29 kbp. The temperate phage was specific to V. cholerae and infected 12/13 V. cholerae O1 strains and half of the four non-O1/non-O139 strains tested in this study. Vibrio cholerae O139 strains were resistant to infection and highest infection rates were obtained in low nutrient media amended with NaCl or prepared using seawater as diluent.     

Toxins of Vibrio cholerae

Surveyed in the paper are published data on properties, biological activity, genetic determinants and action mechanisms of recently known toxins produced by different strains of Vibrio cholerae irrespectively of their capacity for the synthesis of choleric toxin--the main virulence factor. Their possible importance both for the general clinical pattern of cholera provoked by cholerogenic agents and as independent virulence factors causing diarrhea without cholera is elucidated. The sets and levels of expression of additional toxins can differ for different pathogenic clones and they can correspondingly condition degrees of their epidemic and etiological safety.     

The Zymovars of Vibrio cholerae: multilocus enzyme electrophoresis of Vibrio cholerae

Zymovars analysis also known as multilocus enzyme electrophoresis is applied here to investigate the genetic variation of Vibrio cholerae strains and characterise strains or group of strains of medical and epidemiological interest. Fourteen loci were analyzed in 171 strains of non-O1 non-O139, 32 classical and 61 El Tor from America, Africa, Europe and Asia. The mean genetic diversity was 0.339. It is shown that the same O antigen (both O1 and non-O1) may be present in several genetically diverse (different zymovars) strains. Conversely the same zymovar may contain more than one serogroup. It is confirmed that the South American epidemic strain differs from the 7th pandemic El Tor strain in locus LAP (leucyl leucyl aminopeptidase). Here it is shown that this rare allele is present in 1 V. mimicus and 4 non-O1 V. cholerae. Non toxigenic O1 strains from South India epidemic share zymovar 14A with the epidemic El Tor from the 7th pandemic, while another group have diverse zymovars. The sucrose negative epidemic strains isolated in French Guiana and Brazil have the same zymovar of the current American epidemic V. cholerae.     

Progressive Changes of Vibrio Serotypes in Germ-free Mice Infected with Vibrio cholerae

Germ-free mice inoculated with Vibrio cholerae became colonized with vibrios throughout the gastrointestinal tract, but they did not become ill. High vibrio concentrations in the feces were observed throughout the 3 months of observation in spite of the presence of serum antibody. Reciprocal conversions of both Inaba and Ogawa serotypes occurred regularly after inoculation and could be correlated temporally with the appearance of serum-agglutinating antibody. Both of these smooth serotype were later progressively replaced by rough vibrios. Rough to smooth serotype reversions were also found in mice inoculated with a rough vibrio strain. Studies employing immunosuppression and selective vaccination suggested that such serotypic changes were a result of the selective effect of antibody within the intestinal lumen.     

Iron acquisition in Vibrio cholerae

Vibrio cholerae, the causative agent of cholera, has an absolute requirement for iron and must obtain this element in the human host as well as in its varied environmental niches. It has multiple systems for iron acquisition, including the TonB-dependent transport of heme, the endogenous siderophore vibriobactin and several siderophores that are produced by other microorganisms. There is also a Feo system for the transport of ferrous iron and an ABC transporter, Fbp, which transports ferric iron. There appears to be at least one additional high affinity iron transport system that has not yet been identified. In iron replete conditions, iron acquisition genes are repressed by Fur. Fur also represses the synthesis of a small, regulatory RNA, RyhB, which negatively regulates genes for iron-containing proteins involved in the tricarboxylic acid cycle and respiration as well as genes for motility and chemotaxis. The redundancy in iron transport systems has made it more difficult to determine the role of individual systems in vivo and in vitro, but it may reflect the overall importance of iron in the growth and survival of V. cholerae.     

Genomic and phenotypic diversity of coastal Vibrio cholerae strains is linked to environmental factors

Studies of Vibrio cholerae diversity have focused primarily on pathogenic isolates of the O1 and O139 serotypes. However, autochthonous environmental isolates of this species routinely display more extensive genetic diversity than the primarily clonal pathogenic strains. In this study, genomic and metabolic profiles of 41 non-O1/O139 environmental isolates from central California coastal waters and four clinical strains are used to characterize the core genome and metabolome of V. cholerae. Comparative genome hybridization using microarrays constructed from the fully sequenced V. cholerae O1 El Tor N16961 genome identified 2,787 core genes that approximated the projected species core genome within 1.6%. Core genes are almost universally present in strains with widely different niches, suggesting that these genes are essential for persistence in diverse aquatic environments. In contrast, the dispensable genes and phenotypic traits identified in this study should provide increased fitness for certain niche environments. Environmental parameters, measured in situ during sample collection, are correlated to the presence of specific dispensable genes and metabolic capabilities, including utilization of mannose, sialic acid, citrate, and chitosan oligosaccharides. These results identify gene content and metabolic pathways that are likely selected for in certain coastal environments and may influence V. cholerae population structure in aquatic environments.     

Aspects of Vibrio cholerae lipopolysaccharide

In this review information on the chemical structure, biosynthesis, antigenic and biological properties of V. cholerae lipopolysaccharide (LPS) is presented. The specific structural feature of this LPS is a small size of the polysaccharide chain of O-antigen. In vibrios of serogroup O 139 it is oligosaccharide. The modification of the O-chain (methylation of individual sugars, shortened chain, etc.) plays an essential role in the antigenic specificity of V. cholerae LPS. All these factors affect of endotoxin function, the microbial resistance to external influences. V. cholerae LPS takes part in the formation of microcapsules and biofilms. The evolutional development of V. cholerae in this direction determines, to some extent, their increased resistance in the environment. In human body the heterogeneity of the LPS composition permits the preservation of vibrios and ensures, together with cholerogen, their pathogenetic action.