Genetic behavior of R factors in Vibrio cholerae

PVv3, a new shuttle vector for gene expression in Vibrio vulnificus

An efficient electroporation procedure for Vibrio vulnificus was designed using the new cloning vector pVv3 (3,107 bp). Transformation efficiencies up to 2 × 10(6) transformants per μg DNA were achieved. The vector stably replicated in both V. vulnificus and Escherichia coli and was also successfully introduced into Vibrio parahaemolyticus and Vibrio cholerae. To demonstrate the suitability of the vector for molecular cloning, the green fluorescent protein (GFP) gene and the vvhBA hemolysin operon were inserted into the vector and functionally expressed in Vibrio and E. coli.

Detection of R factors in naturally occurring Vibrio anguillarum strains

R factors were detected in Vibrio anguillarum strains from vibrio-diseased freshwater fish, ayu (Plecoglossus altivelis), in Japan. It was found that 65 out of the 68 random isolates from epidemics of vibrio disease in 1973 carried transferable drug resistance factors. The most common type determined resistance to sulfonamides, streptomycin, chloramphenicol, and tetracycline and belong to the fi(-) type. The high incidence of R factors in Vibrio anguillarum from cultured fish is assumed to be due to selective pressure exerted by chemotherapeutic agents used in fish culturing.

Antibiotic-resistant Vibrio cholerae in Parangipettai coastal environs, south east India

This study was undertaken to determine the comparative incidence of drug-resistant Vibrio cholerae non-01 in the environmental samples (water, sediment, and plankton) and in the seafood samples (finfish, shellfish, and crustacean) of estuarine, coastal, and mangrove communities. A total of 770 V. cholerae isolates were examined--all of the strains were sensitive to 100% against cephalothin (30 mcg), chloramphenical (30 mcg), and polymyxin-B (300 mcg). However, all of the strains isolated form environmental and seafood samples showed higher resistance (> 25%) to oxytetracycline, streptomycin, sulphadiazine, tetracycline, and to streptomycin, sulphadiazine, and tetracycline, respectively. The percentage of strains resistant to other antimicrobial substances depended on the antibiotic and on the isolation source. Among the isolates tested, a significantly higher number of drug-resistant bacteria was found to occur in water and finfish samples.

[The emergence of multiple antimicrobial resistance in Vibrio cholerae isolated from gastroenteritis patients in Ceará, Brazil]

Of 7058 Vibrio cholerae strains recovered from patients suspected of cholera in the State of Ceará between December 1991 and September 1993, two were resistant to antimicrobials (Ampicillin, erythromycin, trimethoprim-sulfamethoxazole, tetracycline) and to vibriostatic agent O/129 (2,4-diamino-6,7-diisopropylpteridine). From the bacteriological standpoint, one strain was identified as V. cholerae serogroup O:1, biotype El Tor, serovar Inaba, and another as V. cholerae serogroup O:22, biochemically classified as Heiberg type II. It was shown that only in the serogroup O:1 strain, multiple resistance was encoded by a plasmid transferrable by conjugation to Escherichia coli K12 and a sensitive strains of V. cholerae O1 and non-O1, with at a frequency between 8 x 10(-2) and 5 x 10(-6). The plasmid, with a molecular weight of 147 Kb, encoded both multiple resistance to antimicrobials and the vibriostatic compound (O/129), compatible with descriptions reported in other parts of world.

Biotype traits and antibiotic susceptibility of Vibrio cholerae serogroup O1 before, during and after the emergence of the O139 serogroup

Sixty-nine strains of Vibrio cholerae O1 isolated at different times were analysed to investigate if there were any differences among the O1 strains isolated before, during and after the advent of the O139 serogroup. Of the 69 O1 strains examined, 68 belonged to the Ogawa serotype while one belonged to the Inaba serotype. With the exception of one strain all other strains of V. cholerae O1 belonged to the eltor biotype. A single O1 strain isolated before the emergence of the O139 serogroup could not be classified as either eltor or classical biotype because it was resistant to both classical and eltor specific bacteriophages. Marked variations in the susceptibility to antibiotics of V. cholerae O1 isolated during the different periods were observed. In addition, strains of V. cholerae isolated after the epidemic of serogroup O139 in Calcutta showed an expanding R-type with resistance to a variety of drugs as compared to the O1 strains isolated before the advent of the O139 serogroup. From this study, it is clear that there is a substantial mobility in genetic elements of V. cholerae O1 which necessitates a continuous monitoring to keep abreast of the changing traits of the etiologic agent of cholera.

Transposon mutagenesis in Legionella pneumophila. I.--Persistence of suicide and broad host-range plasmids

Two of three highly virulent strains of Legionella pneumophila could act as recipients at high frequencies in conjugation experiments with Escherichia coli donor strains carrying broad host-range plasmids belonging to incompatibility groups N, P and W. All broad host-range and most transposon-delivery plasmids persisted within transconjugants with high stability. Only one (pSUP1021) of several vehicles designed for the delivery of transposons into the chromosome of Gram-negative bacteria was found to yield transposon mutants of Legionella at a detectable frequency.

Plasmid-mediated changes in virulence of Vibrio cholerae

The effects of several plasmids, including cloning vectors and R factors, on the virulence of Vibrio cholerae CA401R were determined by measuring the dose-related diarrheal response in orally challenged infant mice. The plasmids were also examined for their effects on the colonization ability of strain CA401R by joint infection experiments with a spectinomycin-resistant CA401 strain as an internal standard. One V. cholerae R factor, pVH2, enhanced the diarrheal response, while R factors Rts1 and pVH1 reduced it; plasmids RP4, pRK290, Sa, pSJ8, pSJ5, and pBR328 had no effect. The ability of the plasmids to affect in vitro toxin production by CA401R was variable. Cells containing large plasmids all showed a modest decrease in colonization ability. These results showed that some plasmids affected V. cholerae virulence, but that the cloning vectors pBR328, RP4, and pRK290 did not.

Epidemiological differences between cholera due to multiple antibiotic resistant and multiple antibiotic sensitive Vibrio cholerae infection

The appearance of cholera caused by multiply antibiotic resistant Vibrio cholerae in Bangladesh provided an opportunity to compare epidemiological features of infection caused by resistant and by sensitive V. cholerae. A prospective study was carried out using 46 families of hospital in-patient cholera cases due to resistant V. cholerae and 11 families of hospital cases due to sensitive V. cholerae and nine cases of cholera due to resistant and six cases due to sensitive V. cholerae detected in the neighbourhoods of hospital patients. All families were visited daily during ten days for cultures of rectal swabs, samples of domestic water and for history of diarrhoea. The results showed no significant difference in secondary infection and case rates in contacts of hospital cholera cases due to resistant and sensitive V. cholerae. However, the secondary infection rate (57%) in contacts of cases due to resistant V. cholerae detected from the neighbourhoods of hospital cases was significantly higher (p less than 0.05), than in the neighbourhood case-contacts (29%) of cases due to sensitive V. cholerae. The mean duration of diarrhoea in untreated resistant V. cholerae cases who were contacts of hospital cases (3.3 days) was significantly longer (p less than 0.05) than that of untreated sensitive V. cholerae (2.2 days). Higher isolation rates of V. cholerae were obtained from water sources used by cholera cases due to resistant V. cholerae, than from sources used by cases due to sensitive V. cholerae, but the differences were not statistically significant (p greater than 0.05). The study suggests that resistant V. cholerae poses an additional threat through a higher secondary infection rate and by causing illnesses of longer duration.

Cloning of extracellular DNase and construction of a DNase-negative strain of Vibrio cholerae

The structural gene xds for extracellular DNase of Vibrio cholerae was cloned and inactivated by insertion of the transposon Tn5. The inactivated gene was introduced into the chromosome of V. cholerae by recombination to construct an extracellular DNase-negative strain. Tn5-mediated transposon-facilitated recombination was used to establish the position of xds between the pro-1 and ile-201 markers on the genetic map of V. cholerae. The extracellular DNase-negative strain described here should be useful for investigating the role of the xds-encoded DNase in the physiology of V. cholerae and its plasmids as well as for characterizing other DNases in this organism.

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.

Conjugation of drug-resistance plasmids from vibrio anguillarum to Vibrio parahaemolyticus

Drug-resistant strains of Vibrio anguillarum, a fish pathogen, were isolated from diseased fish in culture ponds. In investigations of these strains, the transfer of resistance to chloramphenicol, tetracycline, and sulfanilamide from multiple resistant organisms to laboratory recipients was observed. The plasmid from V. anguillarum was stably maintained in both recipient strains of Vibrio parahaemolyticus and Escherichia coli. The plasmids isolated from Vibrio anguillarum belong to incompatibility group C. The molecular weight of these plasmids determined by electron microscopic observation was about 103 to 113 megadaltons.

Effect of UV light disinfection on antibiotic-resistant coliforms in wastewater effluents

Total coliforms and total coliforms resistant to streptomycin, tetracycline, or chloramphenicol were isolated from filtered activated sludge effluents before and after UV light irradiation. Although the UV irradiation effectively disinfected the wastewater effluent, the percentage of the total surviving coliform population resistant to tetracycline or chloramphenicol was significantly higher than the percentage of the total coliform population resistant to those antibiotics before UV irradiation. This finding was attributed to the mechanism of R-factor-mediated resistance to tetracycline. No significant difference was noted for the percentage of the surviving total coliform population resistant to streptomycin before or after UV irradiation. Multiple drug resistance patterns of 300 total coliform isolates revealed that 82% were resistant to two or more antibiotics. Furthermore, 46% of these isolates were capable of transferring antibiotic resistance to a sensitive strain of Escherichia coli.

Requirement of cyclic adenosine 3',5'-monophosphate for the thermosensitive effects of Rts1 in a cyclic adenosine 3',5'-monophosphate-less mutant of Escherichia coli

Previous publications showed that a covalently closed circular (CCC) Rts1 plasmid deoxyribonucleic acid (DNA) that confers kanamycin resistance upon the host bacteria inhibits host growth at 42 degrees C but not at 32 degrees C. At 42 degrees C, the CCC Rts1 DNA is not formed, and cells without plasmids emerge. To investigate the possible role of cyclic adenosine 3',5'-monophosphate (cAMP) in the action of Rts1 on host bacteria, Rts1 was placed in an Escherichia coli mutant (CA7902) that lacks adenylate cyclase or in E. coli PP47 (a mutant lacking cAMP receptor protein). Rts1 did not exert the thermosensitive effect on these cells, and CCC Rts1 DNA was formed even at 42 degrees C. Upon addition of cAMP to E. coli CA7902(Rts1), cell growth and formation of CCC Rts1 DNA were inhibited at 42 degrees C. The addition of cAMP to E. coli PP47(Rts1) did not cause inhibitory effects on either cell growth or CCC Rts1 DNA formation at 42 degrees C. The inhibitory effect of cAMP on E. coli CA7902(Rts1) is specific to this cyclic nucleotide, and other cyclic nucleotides such as cyclic guanosine 3',5'-monophosphate did not have the effect. For this inhibitory effect, cells have to be preincubated with cAMP; the presence of cAMP at the time of CCC Rts1 DNA formation is not enough for the inhibitory effect. If the cells are preincubated with cAMP, one can remove cAMP during the [(3)H]thymidine pulse and still observe its inhibitory effect on the formation of CCC Rts1 DNA. The presence of chloramphenicol during this preincubation period abolished the inhibitory effect of cAMP. These observations suggest that cAMP is necessary to induce synthesis of a protein that inhibits CCC Rts1 DNA formation and cell growth at 42 degrees C.

Incidence and elimination of R plasmids in Vibrio cholerae

Of 124 strains of Vibrio cholerae, 32 were multiply resistant to antibiotics. This resistance appeared to be determined by R plasmids on the basis of their effective elimination by sodium dodecyl sulfate, acridine orange, ethidium bromide, and ultraviolet radiation.

R plasmids from Asian strains of Vibrio cholerae

Five R plasmids transferred from Asian strains of Vibrio cholerae all proved to be members of compatibility group C. A non-self-transmissible plasmid, stable in V. cholerae, was mobilized for transfer to Escherichia coli K-12 and found to be unstably inherited in that host. Plasmids of group C and P transferred to a wild V. cholerae strain were stably inherited.

Temperature-sensitive R plasmid obtained from naturally isolated drug-resistant Vibrio cholerae (biotype El Tor)

A temperature-sensitive fi(-) R plasmid, pJY1, which confers resistance to chloramphenicol, streptomycin, and sulfonamide, was found in a drug-resistant strain of Vibrio cholerae (biotype El Tor) isolated in the Philippines in 1973. The R plasmid is temperature sensitive for transferability but not for stability in the hosts. pJY1 is stably maintained either in V. cholerae or in Escherichia coli at a range of culture temperatures from 27 to 42 degrees C. Compatibility tests with reference R plasmids revealed that pJY1 belongs to the J group. Growth of V. cholerae carrying pJY1 is poor on TCBS (thiosulfate-citrate-bile-sucrose) selective plates when the microbe is subcultured in nutrient broth at temperatures higher than 37 degrees C.

Global surveillance of antibiotic sensitivity of Vibrio cholerae

Strains of Vibrio cholerae-1156 from various parts of the world-were examined by standardized antibiotic sensitivity tests in one centre, to determine the global incidence of antibiotic resistance in this organism and to assess the extent to which differences in methods of sensitivity testing might be responsible for discrepancies in the reported incidence of resistant strains. Of the strains examined, 1127 were fully sensitive to ampicillin, chloramphenicol, tetracycline, furazolidone, and three different sulphonamides, 27 showed stable and reproducible resistance to one or more of these agents, and 2 proved to contain a minority of cells with unstable, presumably plasmid-borne, resistance to chloram-phenicol. Unstable resistance to antibiotics may be common in V. cholerae but rarely recognized, and may account for some of the discrepancies in the reported incidence of resistant strains.

Plasmid mutations affecting self-maintenance and host growth in Escherichia coli

As reported in the accompanying paper, a number of mutants of the ColVBtrp plasmid that can not be maintained stably in the host cell of Escherichia coli have been isolated. Each of the mutated plasmids has been transferred to an isogenic Col minus strain, and the resulting Col+ strains were studied to examine the effects of plasmid mutations on some properties of the host bacteria. Many of the strains harboring a mutated plasmid were thus found to be temperature sensitive; they failed to grow and divide normally at high temperatures. Some of them formed "filaments" under these conditions. These abnormal growth characteristics were accompanied by an increased susceptibility to sodium deoxycholate and methylene blue, suggesting that the cytoplasmic membrane has been altered. Moreover, studies of temperature-independent revertants obtained from two of these temperature-sensitive Col+ strains suggested that a single mutation on the plasmid is responsible for the pleiotropic effects exerted on the host cell. The bearing of these findings on the mode of replication and segregated of stringent-type plasmids such as ColVBtrp in the host bacteria is discussed.