Detection of R factors in naturally occurring Vibrio anguillarum strains

Tetracycline Resistance Gene Profiles in Red Seabream (Pagrus major) Intestine and Rearing Water After Oxytetracycline Administration

Marine aquaculture fish and the environment are possible hot spots for the maintenance and spread of antibiotic resistance genes (ARGs). We here show the time courses of changes of six tetracycline resistance genes (tet) in fish rearing seawater and fish intestine in tank experiments. Experimental tanks were prepared as oxytetracycline (OTC) administration tanks and those without OTC. It was found that tet(B), tet(M), and tet(W) were dominant in seawater among the six tet genes. tet(B) and tet(M) abundances increased immediately after OTC administration, indicating that OTC served as a selective pressure to increase the proportion of tet-possessing bacteria. In contrast, the abundance of tet genes in the fish intestine did not differ between the with- and without-OTC administration groups, and clearly was not altered by OTC administration. Profile changing of tet in seawater and fish intestine did not synchronize. These observations suggested that the dynamics of intestinal tet-possessing bacteria do not directly reflect the environment, but reflect selection within the intestine.

Outer membrane vesicles from β-lactam-resistant Escherichia coli enable the survival of β-lactam-susceptible E. coli in the presence of β-lactam antibiotics

Outer membrane vesicles (OMVs) containing various bacterial compounds are released from mainly gram-negative bacteria. Secreted OMVs play important roles in the ability of a bacterium to defend itself, and thus contribute to the survival of bacteria in a community. In this study, we collected OMVs from β-lactam antibiotic-resistant Escherichia coli established by conjugation assay and the parental β-lactam antibiotic-susceptible strain, and performed comparative proteomic analysis to examine whether these OMVs carried β-lactam-resistant compounds. We also investigated whether both types of OMVs could protect susceptible cells from β-lactam-induced death and/or directly degrade β-lactam antibiotics. Several proteins that can be involved in degrading β-lactam antibiotics were more abundant in OMVs from β-lactam-resistant E. coli, and thus OMVs from β-lactam resistant E. coli could directly and dose-dependently degrade β-lactam antibiotics and fully rescue β-lactam-susceptible E. coli and other bacterial species from β-lactam antibiotic-induced growth inhibition. Taken together, present study demonstrate that OMVs from β-lactam-resistant E. coli play important roles in survival of antibiotic susceptible bacteria against β-lactam antibiotics. This finding may pave the way for new efforts to combat the current global spread of antibiotic resistances, which is considered to be a significant public health threat.

Diversity and characterization of oxytetracycline-resistant bacteria associated with non-native species, white-leg shrimp (Litopenaeus vannamei), and native species, black tiger shrimp (Penaeus monodon), intensively cultured in Thailand

AIMS

This study aimed at surveying prevalence of oxytetracycline (OTC)-resistant bacteria in the white-leg shrimp Litopenaeus vannamei, and the black tiger shrimp Penaeus monodon, intensively cultured in Thailand. We investigated the phylogenetic diversity of the bacterial isolates, as well as the minimum inhibitory concentration (MIC) of OTC, the occurrence of major OTC-resistant genes and multiple-antibiotic resistance in the isolates.

METHODS AND RESULTS

Shrimps were collected from culture ponds, and the homogenates of whole bodies were plated on tryptic soy agar supplemented with or without OTC. Percentages of OTC-resistant bacteria were 0·3-52·1% in white-leg samples and 0·008-22·3% in black tiger samples. Analyses of 16S rDNA sequences indicated that most OTC-resistant isolates were closely related to Aeromonas spp. and Lactococcus garvieae. MICs of OTC were 4-128 μg ml(-1) in the OTC-resistant aeromonads and 128-256 μg ml(-1) in OTC-resistant L. garvieae. OTC resistance was found to be conferred by the genes tet(A), tet(C), tet(D), tet(E), tet(M) and tet(S), detected either singly or in pairs. No resistance to ceftazidime, imipenem or chloramphenicol was observed in any isolate.

CONCLUSIONS

Both species of shrimp are associated with OTC-resistant bacteria, occasionally at high densities exceeding 10(6) cfu g(-1). The associated bacteria, predominantly Lactococcus and Aeromonas genera, are potential pathogens and are reservoirs of a variety of OTC-resistant genes.

SIGNIFICANCE AND IMPACT OF THE STUDY

Cultured shrimps can be vehicle to carry OTC-resistant bacteria to domestic and foreign consumers via the food chain. Very low populations of OTC-resistant bacteria observed in the several ponds suggest that levels of the resistant bacteria are artificially high and should be reduced in farmed shrimps.

Viability during storage and stability of plasmids during storage and subculturing in strains of Vibrio anguillarum

The stability of plasmids, 3.3 kb - approximately 200 kb, in 8 strains of Vibrio anguillarum displaying different plasmid profiles and reactions with O-antisera was investigated over an 18 months period. All plasmid profiles proved to be resistant to storage at different temperatures but strains stored at 37 degrees C were only viable for a short period of maximum 2 months. Strains stored at 5 degrees C and 20 degrees C were viable for a longer period. Viable strains maintained their plasmid profile throughout the experiment, except in 2 cases where a 67 kb and a 200 kb plasmid were lost. Strains stored at -80 degrees C all remained viable and maintained their plasmid profile throughout the study. By subcultivating daily for up to 100 successive days, most strains maintained their plasmid profiles. Only 2 strains lost their plasmid. When picking 100 single colonies from agar plates, none of the colonies showed plasmid profiles deviating from the expected. The results suggest that plasmid profiles among V. anguillarium are very stable during subculturing, storage and laboratory handling using standard laboratory procedures, and thus, reliable for epidemiological investigations. In a second experiment, 2 pairs of 2 strains were grown together in mixed cultures. They were identical in all traits, except that one strain in each pair harboured the 67 kb pJM1-like virulence plasmid, whereas the other had lost this plasmid. The result showed that the growth rate was the same for strains with and without the plasmid, indicating that under laboratory conditions, this plasmid is neither a benefit nor the opposite for bacterial growth.

Viability during storage and stability of plasmids during storage and subculturing in strains of Vibrio anguillarum

The stability of plasmids, 3.3 kb - approximately 200 kb, in 8 strains of Vibrio anguillarum displaying different plasmid profiles and reactions with O-antisera was investigated over an 18 months period. All plasmid profiles proved to be resistant to storage at different temperatures but strains stored at 37 degrees C were only viable for a short period of maximum 2 months. Strains stored at 5 degrees C and 20 degrees C were viable for a longer period. Viable strains maintained their plasmid profile throughout the experiment, except in 2 cases where a 67 kb and a 200 kb plasmid were lost. Strains stored at -80 degrees C all remained viable and maintained their plasmid profile throughout the study. By subcultivating daily for up to 100 successive days, most strains maintained their plasmid profiles. Only 2 strains lost their plasmid. When picking 100 single colonies from agar plates, none of the colonies showed plasmid profiles deviating from the expected. The results suggest that plasmid profiles among V. anguillarium are very stable during subculturing, storage and laboratory handling using standard laboratory procedures, and thus, reliable for epidemiological investigations. In a second experiment, 2 pairs of 2 strains were grown together in mixed cultures. They were identical in all traits, except that one strain in each pair harboured the 67 kb pJM1-like virulence plasmid, whereas the other had lost this plasmid. The result showed that the growth rate was the same for strains with and without the plasmid, indicating that under laboratory conditions, this plasmid is neither a benefit nor the opposite for bacterial growth.

Plasmid profiles, restriction fragment length polymorphisms and O-serotypes among Vibrio anguillarum isolates

A total of 279 Vibrio anguillarum strains were serotyped and examined for plasmid content. Plasmids were subjected to digestion with restriction enzymes. Most strains belonged to serogroup O1 (39%) and O2 (16%). In total 164 strains (53%) carried plasmids. Of the O1 and O2 isolates, 92% and 30%, respectively, carried one or more plasmids. Restriction fragment length polymorphism (RFLP) analysis of plasmid DNA indicated that plasmids belonged to several groups. Each group seemed to be restricted to a single O-serovar. The largest group was the pJM1-like plasmids among most serovar O1 strains. Most of these plasmids were about 67 kb like the pJM1 plasmid, but various derivatives ranged from 26-77 kb. RFLP studies of the 67 kb plasmids revealed 17 different restriction patterns. Some patterns were dominant among European strains whereas others were dominant among North American strains. The results confirmed the applicability of O-serotyping together with plasmid profile and restriction analysis of plasmids for typing of V. anguillarum. They also indicated that plasmids among strains which belonged to the traditional fish pathogenic serogroups, O1 and O2, showed more homology than did strains from most other serogroups, that were usually non-pathogenic, environmental bacteria.

Antibiotic resistance of Vibrio anguillarum, in relation to serovar and plasmid contents

A total of 520 Vibrio anguillarum strains, isolated from fish and the environment, were tested for their sensitivity to 20 different antibiotics. Most isolates were of European origin. The results were compared with data on the O-serogroup and plasmid contents. All strains were sensitive to neomycin, spectinomycin, nitrofurantoin, flumequine and oxolinic acid, while most strains were sensitive to streptomycin, oxytetracycline, chloramphenicol, sulphonamides, trimethoprim, sulphonamides with trimethoprim, nalidixan, rifampicin, novobiocin and O/129. A major part of the strains were resistant to the macrolides, spiramycin and lincomycin. For ampicillin, cephalothin, and colistin marked differences were recorded with respect to O-serogroup. Most O1 strains were resistant to colistin and sensitive to ampicillin and cephalothin, while most O2 strains were sensitive to colistin but resistant to ampicillin and cephalothin. Some antibiotic resistant strains carried plasmids but no conjugation experiments were carried out to detect possible R factors.

Evidence for the existence of distinct populations of Vibrio anguillarum serogroup O1 based on plasmid contents and ribotypes

A total of 103 Vibrio anguillarum serogroup O1 strains displaying 15 different plasmid profiles were characterized with respect to biochemical properties and ribotypes. The results confirmed that V. anguillarum O1 is a biochemically homogeneous group. The 103 strains could be allocated to three main clusters with high similarity coefficients. None of the biochemical properties were connected with the presence of plasmids. In total, 12 different ribotypes were demonstrated, with HindIII being used as the restriction enzyme. Forty of the strains were isolated from the same Danish fish farm, some from the kidneys of diseased fish and some from the environment, and some strains were isolated from the mucus, gills, and feces of healthy fish. Nineteen of these isolates possessed the 67-kb virulence plasmid alone or in combination with other plasmids, while 21 had no plasmids. All strains isolated from the kidneys of diseased fish on this farm had plasmids. Irrespective of their origin (kidneys, gills, or mucus), all 19 strains carrying the 67-kb virulence plasmid had the same ribotype, profile 1, while isolates without plasmids belonged to five different profiles, all different from profile 1. These results suggest that pathogenic V. anguillarum O1 strains possessing a virulence plasmid and nonpathogenic strains without plasmids from a small geographical area and even from the same fish may constitute two essentially distinct populations. Thus, it may be suggested that an exchange of virulence plasmids among strains is unlikely to occur in vivo.

Antibiotic resistance of Vibrio anguillarum, in relation to serovar and plasmid contents

A total of 520 Vibrio anguillarum strains, isolated from fish and the environment, were tested for their sensitivity to 20 different antibiotics. Most isolates were of European origin. The results were compared with data on the O-serogroup and plasmid contents. All strains were sensitive to neomycin, spectinomycin, nitrofurantoin, flumequine and oxolinic acid, while most strains were sensitive to streptomycin, oxytetracycline, chloramphenicol, sulphonamides, trimethoprim, sulphonamides with trimethoprim, nalidixan, rifampicin, novobiocin and O/129. A major part of the strains were resistant to the macrolides, spiramycin and lincomycin. For ampicillin, cephalothin, and colistin marked differences were recorded with respect to O-serogroup. Most O1 strains were resistant to colistin and sensitive to ampicillin and cephalothin, while most O2 strains were sensitive to colistin but resistant to ampicillin and cephalothin. Some antibiotic resistant strains carried plasmids but no conjugation experiments were carried out to detect possible R factors.

Isolation and characterization of turbot (Scophtalmus maximus)-associated bacteria with inhibitory effects against Vibrio anguillarum

More than 400 isolates from the intestine and the external surface of farmed Scophtalmus maximus as well as from fish food and hatchery water were screened for inhibitory effects against the fish pathogen Vibrio anguillarum HI 11345 and seven other fish pathogens. The bacteria with inhibitory effects were then characterized with regard to their sites of colonization, especially the intestinal regions and sites within each region. Of the total number of bacterial isolates from the intestine, 28% were inhibitory against V. anguillarum HI 11345. A marine biochemical assay was used to order the inhibitory strains into different phena. Most inhibitory bacteria were found in the rinse and mucus fractions of the gastrointestinal tract. No correlations among the different phena, site of colonization, and inhibitory effect could be found; however, a biochemical diversity was noted in the strains with an inhibitory effect. Of the isolates with an inhibitory effect against V. anguillarum HI 11345, 60% had an inhibitory effect on five other fish-pathogenic serotypes of V. anguillarum. Inhibitory effects of the isolates were also shown against Aeromonas salmonicida and Aeromonas hydrophila.

New tetracycline resistance determinant on R plasmids from Vibrio anguillarum

Two classes of tetracycline resistance determinants on R plasmids were detected in Vibrio anguillarum strains isolated from ayu (sweat fish; Plecoglossus altivelis) farms in Japan. Tetracycline resistance genes categorized as class B were prevalent from 1973 to 1977; however, a new tetracycline resistance gene, which was not classified into tetracycline resistance determinant class A, B, C, or D, has been prevalent since 1981.

Phylogenetic relationships among Vibrio anguillarum plasmids

Results of restriction endonuclease analysis and Southern blot hybridization suggest that the R-plasmids from Vibrio anguillarum strains isolated in Japan can be divided into at least four groups of homology depending on the time of their isolation and geographical source. Molecular cloning experiments allowed identification of specific restriction endonuclease fragments carrying the genes for either Cmr or Tcr as the common sequences between some of these groups of R-plasmids. The Cmr region from the V. anguillarum R-plasmids was homologous to the Cmr sequences of an R-plasmid isolated from another fish pathogen, Aeromonas salmonicida. The plasmid pJM1 from V. anguillarum strains isolated in the Pacific Northwest region of the United States, which encodes an iron transport system associated with the high-virulence phenotype of these strains, showed homology with two of the Japanese R-plasmids.

Drug resistance and R plasmids in Vibrio anguillarum isolated in cultured ayu (Plecoglossus altivelis)

Two hundred twenty-six strains of Vibrio anguillarum collected from cultured ayu ( Plecoglossus altivelis ) between 1978 and 1980 were studied for their sensitivities to 10 chemotherapeutics. In order to determine whether the drug-resistant strains possessed transferable R plasmids, they were conjugated with Escherichia coli. Almost all the strains isolated during the 3 years showed resistance to nalidixic acid (NA) and/or furazolidone (NF). NA and NF resistance were not transferred to Escherichia coli from any of the strains. Chloramphenicol-resistant strains were isolated in every year and almost all of them carried transferable R plasmids. Only one strain with tetracycline resistance was found among the strains tested. Strains resistant to sulfonamides, streptomycin, ampicillin (ABP), and trimethoprim (TMP) increased rapidly in 1980, and a large number of them carried transferable R plasmids. Transferable R plasmids encoded with resistance to ABP and TMP were detected for the first time in V. anguillarum strains. The R plasmids detected in the strains isolated in 1980 were classified into incompatibility groups E, A, and an untypable group. The R plasmid DNAs were cleaved by EcoRI to yield 11 to 13 fragments. The estimated molecular weights of the R plasmids from the five strains ranged from 97 to 104 M daltons.

Plasmids in Vibrio parahemolyticus strains isolated in Japan and Bangladesh with special reference to different distributions

We surveyed plasmids in naturally occurring Vibrio parahemolyticus strains isolated in Japan and Bangladesh. Among the strains isolated in Japan, about half of the strains isolated from stools of patients of domestic diarrhea outbreaks as well as of travelers returning from East Asia were found to have plasmids, but no strains from foods had plasmids. In contrast, among the strains isolated in Bangladesh, none of the four strains isolated from patients had plasmids, but two out of eight strains isolated from water had plasmids, suggesting that plasmids are common in strains from the water in Bangladesh. All plasmids so far reported in V. parahemolyticus were detected in strains isolated from stools of patients. Incidences of plasmids in this organism were not so high in either area. In Japan, all plasmids were detected in strains from human intestines at 37 C, but in Bangladesh, where the temperature is around 30-40 C, the plasmids were detected in strains from the natural environment. These results suggested the possibility that these plasmids can come from different bacteria under rather high temperatures and that incidences of plasmids are influenced by the incidences of plasmids in bacteria present in the vicinity of V. parahemolyticus strains. None of these plasmids were found to have any relation to the biological characters tested.

Characterization of plasmids in bacterial fish pathogen

Plasmid profiles of representative fish pathogens, Aeromonas salmonicida, Aeromonas hydrophila, Vibrio anguillarum, Pasteurella piscicida, Yersinia ruckeri, Edwardsiella tarda, and Renibacterium salmoninarum, were determined by agarose gel electrophoresis with four different plasmid detection methods. A combination of two methods was required to detect the plasmids present in these strains and to calculate precisely the molecular weights of the plasmids. Of 38 strains, 28 harbored one or more plasmids, with the majority of strains demonstrating multiplasmid banding. Similarity in plasmid banding between strains was noted and related to geographic source. Five strains of A. salmonicida possessed six plasmid bands having molecular weights of 8.6 X 10(6), 8.4 X 10(6), 8.1 X 10(6), 3.6 X 10(6), 3.5 X 10(6), and 3.4 X 10(6). Four P. piscicida isolates shared three plasmid bands having molecular weights of 37 X 10(6), 15 X 10(6), and 5 X 10(6), and five A. hydrophila strains harbored a common plasmid having a molecular weight of ca. 20 X 10(6) to 30 X 10(6). The highest-molecular-weight plasmids (145 X 10(6) and 130 X 10(6) were detected in V. anguillarum. From curing experiments, it was found that in A. hydrophila strain 79-62, a loss of resistance to tetracycline was associated with loss of plasmid content in all susceptible derivatives, suggesting plasmid-mediated tetracycline resistance. Cell surface characteristics and metabolic properties were also modified in cured derivatives of A. hydrophila strain 79-62.

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.

Evidence for plasmid contribution to the virulence of fish pathogen Vibrio anguillarum

Analysis of the plasmid deoxyribonucleic acid complement of high- and low- virulent strains of the fish pathogen Vibrio anguillarum showed a correlation between enhanced virulence and the presence of a 50-megadalton plasmid class. All 50-megadalton plasmids isolated from different high-virulent V. anguillarum strains were homologous as judged by the analysis of plasmid deoxyribonucleic acid-deoxyribonucleic acid hybridization. The 50-megadalton plasmid class did not have polynucleotide sequences in common with plasmids of different incompatibility groups.

New R plasmid-mediated restriction-modification system of deoxyribonucleic acid conferred by group E R plasmids

A new R plasmid-mediated restriction-modification system of deoxyribonucleic acid was identified. This system is specific for group E plasmids which have been detected in unidentified marine Vibrio fish pathogens.

Detection of R plasmids in naturally occurring fish-pathogenic bacteria, Edwardsiella tarda

The conjugative R plasmids were detected from fish-pathogenic Edwardsiella tarda isolated from cultured eels. These R plasmids were resistant to sulfonamide and tetracycline, or sulfonamide, streptomycin, chloramphenicol, tetracycline and kanamycin. There were no inhibitions in growth of phages W-31, P1, T1, T3, T7, and lambda. They were classified into incompatibility group A.