Comparison of T cell cytokines in resistant and susceptible mice infected with virulent Brucella abortus strain 2308

Abstract C57BL/10 and BALB/c mice differ in their abilities to clear infections with the intracellular bacterium Brucella abortus strain 2308. We have previously reported that in vivo neutralization of IL-10 in the susceptible BALB/c mice results in significantly fewer bacteria in their spleens 1 week after infection with 5 × 10³ colony forming units (CFU) of 2308. Here we extend those studies and report a similar effect when IL-4 is neutralized. In contrast, in the more resistant C57BL/10 mice infected with 5 × 10³ CFU, neither neutralization of IL-10 nor IL-4 significantly decreased the level of infection nor did it in either BALB/c or C57BL/10 mice infected with a 1000-fold higher dose of strain 2308. While splenocytes from the later mentioned groups of 1 produced IL-10 in response to stimulation with brucella antigen, they also produced higher levels of interferon (IFN)-γ than those from BALB/c mice infected with the low challenge dose of 5 × 10³ CFU. Results of in vivo neutralization of IFN-γ by monoclonal antibodies (MAb) reported here and elsewhere indicated that IFN-γ is important for control; thus, we postulate that the higher levels of IFN-γ may override the detrimental effects of Th2 cytokines. In vitro studies also showed that macrophages from the more resistant C57BL/10 mice were less susceptible to the ability of IL-10 to decrease anti-brucella activities than were BALB/c macrophages. CD4⁺ T cells were principally responsible for the production of IL-10 in BALB/c but not C57BL/10 splenocyte populations. C57BL/10 splenocytes produced more IFN-γ than those from BALB/c mice in response to stimulation with brucella antigens. These differences between BALB/c and C57BL/10 mice may contribute to the superior capacity of C57BL/10 mice to control infections with B. abortus strain 2308.     

Bacterivory by starved marine heterotrophic nanoflagellates of two species which feed differently, estimated by uptake of dual radioactive-labelled bacteria

Abstract: The rates of ingestion of bacteria and of accumulation of bacterial biomass by hungry Pteridomonas danica and Paraphysomonas imperforata were measured using dual radioactive-labelled bacteria in experiments lasting 4–8 h. Pteridomonas continuously consumed 4–5 bacteria h⁻¹ throughout experiments lasting 8 h, irrespective of bacterial concentration above a threshold of about 5 × 10⁵ bacteria ml⁻¹, and continued to catch bacteria even below this density. The clearance rate of about 1 nl cell⁻¹ h⁻¹ at higher bacterial concentrations increased three or four times as bacterial numbers fell. Paraphysomonas cells, with only half the biomass of Pteridomonas , ingested up to 10 bacteria h⁻¹ at high bacterial concentrations, and gradually reduced the feeding rate, effectively ceasing to feed at 10⁶ bacteria ml⁻¹; their initial clearance rate of 1–2.5 nl cell⁻¹ h⁻¹ subsequently fell as low as 0.1 nl cell⁻¹ h⁻¹. Estimation of feeding rate by extrapolation from short-term experiments on such flagellates requires extreme caution. These flagellates, starved to levels typical of the natural environment, accumulated ingested bacterial biomass at an efficiency of between 16 and 21%, indicating that in nature they would recycle 80% or more of the nutrients contained in their food.     

Bacterivory by the ciliate Euplotes in different states of hunger

Abstract: The feeding of the marine ciliate Euplotes mutabilis was studied using bacteria ( Vibrio natriegens ) doubly labelled with ³H-thymidine and ¹⁴C-leucine. In the presence of abundant bacteria (30 × 10⁶ bacteria ml⁻¹), an average Euplotes cell (initially without food vacuoles) with a protein content of 12 ng consumed 16 × 10³ bacteria in the first hour and 27 × 10³ bacteria over four hours, accumulating about 60% of the bacterial protein into ciliate macromolecules. Euplotes which had been starved or under-fed to reduce cell protein biomass to 7 or 9 ng consumed significantly fewer bacteria, but the gross growth efficiency for protein did not change. The rate of consumption of bacteria by large Euplotes of protein content 15 ng was initially less than that of 12 ng cells, and it decreased markedly before the end of a 4-hour experiment. Recently divided cells ingested bacteria rapidly, but showed a reduced gross growth efficiency of about 40%. At low bacterial concentrations (6 × 10⁶ bacteria ml⁻¹) the rates of ingestion were markedly reduced to between     and     of maximal levels; the smallest cells could not sustain feeding activity at the low prey concentration and gross growth efficiency fell from 43 to 20% during a 4-hour experiment. The strategy adopted by Euplotes in response to local fluctuations in food supply involves rapid consumption with high growth efficiency in times of plenty, but slow shrinkage without cell division to survive in times of shortage.     

DIRECT DETECTION OF ESCHERICHIA COLI 0157:H7 IN UNPASTEURIZED APPLE JUICE WITH AN EVANESCENT WAVE BIOSENSOR

An evanescent wave biosensor was used to detect Escherichia coli O157:H7 in unpasteurized apple juice. Light is launched from a 635 nm laser diode into silica or polystyrene optical waveguides, generating an evanescent field which extends from the waveguide surface. Fluorescent molecules within the evanescent field are excited resulting in an emission signal that the biosensor then detects and quantifies. A sandwich immunoassay was performed on the waveguides using cyanine 5 dye-labeled anti-E. coli O157:H7 antibodies for generation of the specific fluorescent signal. The lower limit of detection was between 6.0 × 10² and 6.0 × 10⁴ CFU/mL with silica waveguides and between 3.2 × 10⁴ and 3.2 × 10⁴ CFU/mL using polystyrene waveguides. One-hundred percent correct identification of true positive samples occurred at 6.0 × 10⁴ and 3.2 × 10⁴ CFU/mL for silica and polystyrene waveguides, respectively. Signals from a variety of non-E. coli O157 bacteria, including closely related enterotoxigenic strains of E. coli at concentrations of ˜ 10⁶ CFU/mL, were below the limits of detection. Assays were conducted in near real-time with results obtained within 15 min of sample processing.     

Interaction between the effects of bacteria and dry storage on the opening and water relations of cut rose flowers

W.G. VAN DOORN AND K. D'HONT. 1994. Flowering stems of four rose cultivars (Sonia, Madelon, Jacaranda and Frisco) were placed in aqueous suspensions of bacteria at 10⁴ and 10⁸ colony-forming units (cfu) ml^-1 for 24 h at 5C, then stored dry or held in water for 24 h at 8C and subsequently placed in vase-water at 20C. The effects of these treatments on vase-water uptake were similar to the effects on flower opening. In Sonia and Madelon roses flower opening was negatively affected both by 10⁸ cfu ml^-1 of bacteria and by dry storage. No effect was found at 10⁴ cfu ml^-1, but this concentration had a detrimental effect on flower opening when combined with dry storage. Although flower development in Jacaranda roses was not affected by the bacteria treatments it was inhibited by dry storage. This inhibition was progressively greater when the stems had previously been pulse-treated with a larger number of bacteria. Flower opening in Frisco roses was not affected by even the highest concentration of bacteria, nor by the period of dry storage. It is concluded that placing flowers in water containing bacteria (up to 10⁸ cfu ml^-1) may not always have a negative effect on flower development in cut rose flowers but, together with the effects of dry storage, the presence of even a low number of exogenous bacteria (10⁴ cfu ml^-1) inhibits the development in several cultivars. Such bacterial counts are nearly always found in samples of water used for standing roses during distribution to the consumers.     

Effect of Lactobacillus gasseri BNR17 on blood glucose levels and body weight in a mouse model of type 2 diabetes

Aims:  To investigate the effect of Lactobacillus gasseri BNR17 isolated from human breast milk on blood glucose and body weight in type 2 diabetic animals.
Methods and results:  db/db mice were divided into one control group and five sample groups; the sample groups received BNR17 (10⁷, 10⁸, 10⁹ and 10¹⁰ CFU) or rosiglitazone (8 mg kg⁻¹) orally twice a day for 12 weeks. BNR17 groups had a dose-dependent reduction in food, water intake and amount of excrement. Body weight loss was not seen in the BNR17 groups. Fasting and postprandial 2 h blood glucose levels were significantly lower in the BNR17 (10¹⁰ CFU) group compared with the control group. HbA1c decreased in the BNR17 group, although it was not statistically significant. During the oral glucose tolerance test, the BNR17 groups exhibited dose-dependent improvement in glucose sensitivity.
Conclusions:  Lactobacillus gasseri BNR17 has a suppressing effect on blood glucose levels and improved diabetic symptoms in db/db mice.
Significance and Impact of the Study:  Blood glucose-lowering lactic acid bacteria are expected to be useful as a therapeutic for treating type 2 diabetes in humans.     

The distribution of some freshwater planktonic bacteria in two stratified eutrophic lakes

SUMMARY. Changes in bacterial populations and certain physical and chemical variables in Esthwaite Water between June and September 1975 were studied and compared with results obtained from 1972 to 1974 in the hypolimnia of Blelham Tarn and the Lund tubes. The counts of total bacteria ranged between 1 and 7 × 10⁶ml⁻¹ and were highest in the anoxic hypolimnion. The bacterial genera examined in more detail constituted only a small percentage of this count and included Ochrobium (10⁴ml⁻¹), Naumanniella (10³ml⁻¹), Leptothrix (10²ml⁻¹), Planctomyces (10³ml⁻¹), and Metallogenium (10²ml⁻¹). The iron bacteria appear to grow best in the oxycline where there was not only sufficient oxygen for aerobic growth but also a plentiful supply of reduced iron. Planctomyces numbers increased as the thermocline became depressed in September. The results from Blelham Tarn might be interpreted as further evidence of growth by iron bacteria in the absence of dissolved oxygen, but other explanations are possible. Examination of the results by multiple regression analysis showed that it was possible to explain a significant proportion of the bacterial variation (with the notable exception of the Planctomyces counts) in spite of considerable intercorrelation of the regressor variables.     

Colonization of Vibrio pelagius and Aeromonas caviae in early developing turbot (Scophthalmus maximus L.) larvae

Polyclonal antisera made in rabbits against whole washed cells of Vibrio pelagius and Aeromonas caviae were used for detection of these bacterial species in the rearing water and gastrointestinal tract of healthy turbot ( Scophthalmus maximus ) larvae exposed to V. pelagius and/or Aer. caviae . The results demonstrated that this method is suitable for detection of V. pelagius and Aer. caviae in water samples and larvae at population levels higher than 10³ ml⁻¹ and 10³ larva⁻¹. Populations of aerobic heterotrophic bacteria present in the gastrointestinal tract of turbot larvae, estimated using the dilution plate technique, increased from approximately 4 × 10² bacteria larva⁻¹ on day 3 post-hatching to approximately 10⁵ bacteria fish⁻¹ 16 days post-hatching. Sixteen days after hatching, Vibrio spp. accounted for approximately 3 × 10⁴ cfu larva⁻¹ exposed to V. pelagius on days 2, 5 and 8 post-hatching. However, only 10³ of the Vibrio spp. belonged to V. pelagius . When larvae were exposed to Aer. caviae on day 2 post-hatching, the gut microbiota of 5-day old larvae was mainly colonized by Aeromonas spp. (10⁴ larva⁻¹), of which 9 × 10³ belonged to Aer. caviae . Later in the experiment, at the time when high mortality occurred, 9 × 10⁵ Aer. caviae were detected. Introduction of V. pelagius to the rearing water seemed to improve larval survival compared with fish exposed to Aer. caviae and with the control group. It was therefore concluded that it is beneficial with regard to larval survival to introduce bacteria ( V. pelagius ) to the rearing water.     

The planktonic and benthic bacterial populations of Lough Neagh

The planktonic and benthic bacterial populations of Lough Neagh, Northern Ireland, were studied over a one-year period. Direct counts of bacteria in the water column averaged 6 times 10⁷/ml with limited spatial or temporal variation; viable counts, however, showed a pronounced late spring maximum of 1.7 times 10⁶/ml and were consistently higher at a littoral sampling station. Direct counts of bacteria in the profundal sediments averaged 8 times 10⁹/ml whilst viable benthic counts rose steeply during spring to reach a June maximum of 1 times 10⁸/ml. Direct: viable count ratios were much greater in the more sandy littoral zone. The predominant benthic isolate was an Aeromonas sp. which was also common in samples from the water column. These results confirm the eutrophic status of Lough Neagh indicated by other biological and chemical surveys.     

A CHEMILUMINESCENCE BIOSENSOR COUPLED WITH IMMUNOMAGNETIC SEPARATION FOR RAPID DETECTION OF SALMONELLA TYPHIMURIUM

A chemiluminescence biosensor, using a fiber-optic-linked photometer and a data acquisition unit connected to a PC, was developed in conjunction with immunomagnetic separation for rapid detection of Salmonella Typhimurium. Magnetic microbeads coated with Anti-Salmonella antibodies and anti-Salmonella antibodies conjugated with horseradish peroxidase (HRP) were added to artificially-inoculated samples, and the immuno-reaction was completed in 60 min resulting in a sandwich complex. A magnetic field was applied to collect magnetic beads and the addition of luminol to HRP-conjugated antibodies resulted in a chemiluminescence reaction. The signal was collected through a fiber optic light guide, measured with a photometer, and recorded in the data acquisition unit. The minimum detection limit of the chemiluminescence biosensor for S. Typhimurium was 1.97 × 10³ CFU/mL and the range of the detectable signal was from 8.6 to 350 mV for cell numbers from 1.97 × 10³ to 1.97 × 10⁶ CFU/mL. Signal values for 10⁶ CFU/mL of S. Typhimurium were at least 97 and 394% higher than the corresponding values for S. enteritidis and four times the signal values for others including S. montevideo, S. california, S. heidlberg, and S. seftenberg, respectively. The biosensor response showed a significant difference (P < 0.05) between 10³ CFU/mL S. Typhimurium and 10⁶ CFU/mL of commonly-occurring bacteria in foods including Listeria monocytogenes, Pseudomonas aeruginosa, Citrobacter freundii, Campylobacter jejuni, Escherichia coli O157, and generic Escherichia coli. A regression equation, V = 0.0262 N ^5.7713, with R²= 0.9713 was obtained for the calibration curve over the detection range for S. Typhimurium. The whole procedure could be completed within 90 min.     

Effect of Saccharomyces boulardii against experimental oral infection with Salmonella typhimurium and Shigella flexneri in conventional and gnotobiotic mice

A.C.P. RODRIGUES, R.M. NARDI, E.A. BAMBIRRA, E.C. VIEIRA AND J.R. NICOLI. 1996. Saccharomyces boulardii was shown to be capable of inhibiting multiplication of enteropathogenic bacteria in vitro and is currently used for its anti-diarrhoea properties. We studied the capacity of this yeast to antagonize Salmonella typhimurium and Shigella flexneri in the intestinal tract of conventional or gnotobiotic NMRI mice. Conventional animals were given daily 10 mg doses of S. boulardii , whereas germ-free animals were given a single 10 mg dose. Both groups were challenged orally 5 d later with the pathogenic bacteria (10⁸ or 10² viable cells, respectively). Control groups were treated with saline instead of S. boulardii. Mortality and/or histopathological data showed a protective effect against the pathogenic bacteria in yeast-treated mice. Saccharomyces boulardii colonized the digestive tract of gnotobiotic mice and the number of viable cells ranged around 10¹⁰ g^-1 of faeces. In experimental and control gnotobiotic animals, Salm. typhimurium and Sh. flexneri became rapidly established at a level of about 10¹⁰ viable cells g^-1 of faeces and remained at high levels until the animals died or were sacrificed. The protection against Salm. typhimurium and Sh. flexneri obtained in conventional and/or gnotobiotic mice previously associated with S. boulardii is not due to the reduction of the bacterial populations in the intestines.     

The role of ice nucleation active bacteria in supercooling of citrus tissues

The frost sensitivity of Citrus sinensis in relation to the presence of biogenic ice nuclei was studied. In commercially managed citrus groves the ice nucleation active (INA) bacterium Pseudomonas syringae reached 6 × 10⁴ colony forming units (CFU) leaf⁻¹, a population sufficiently high to catalyze ice formation. However, a transient loss of bacterial nucleation activity was noticeable at subzero field temperatures, followed by resumption as temperatures rose. This loss was apparently due to a temporary transition of INA to ice nucleation inactive (INI) bacteria. Field application of Bordeaux mixture, copper hydroxide, streptomycin, and 2-hydroxypropylmethanethiolsulfonate (HPMTS), resulted in reduction of INA bacterial populations to detectability (≤ 10² CFU leaf⁻¹) limits. However, the corresponding reduction in ice nucleation events in treated samples as compared to controls at nucleation temperature ≥−3°C was not as dramatic. It ranged from approximately 7% in samples treated with the bactericide HPMTS, to 35% in samples treated with chemicals possessing combined bactericidal - fungicidal action (coppers). Since a quantitative relationship exists between ice nucleation events on individual leaves and the INA bacterial populations harbored by these leaves, these results suggest the co-existence of a bacterial and a proteinaceous, yet non-bacterial ice nucleating source in citrus, both active at ≥−3°C.     

Bacterial microflora in the gastro-intestinal tract of Dover sole (Solea solea L.), with emphasis on the possible role of bacteria in the nutrition of the host

Abstract There was a progressive increase in the size of the aerobic heterotrophic bacterial populations along the gastro-intestinal tract of farmed Dover sole. Moreover, higher counts were recorded in juvenile than in adult animals. Thus, in juvenile fish, 5.2 × 10⁵, 8.0 × 10⁵ and 9.8 × 10⁶ aerobic heterotrophs/g were recovered from the stomach/foregut, midgut and hindgut/rectum, respectively. In adult fish, comparative samples revealed the presence of only 3.0 × 10⁴, 7.0 × 10⁴ and 2.3 × 10⁵ bacteria/g, respectively. There bacteria were equated with Acinetobacter, Alcaligenes , Enterobacteriaceae representatives, Flavobacterium, Micrococcus, Photobacterium, Staphylococcus and Vibrio . Of the compounds tested, many isolates, particularly those recovered from the hindgut/rectum, degraded p -nitrophenyl- β - N -acetylglucosaminide, chitin and collagen. Consequently, it is likely that such organisms may contribute to nutritional processes within Dover sole.     

EVALUATION OF ADENOSINE TRIPHOSPHATE (ATP) BIOLUMINESCENCE FOR ESTIMATING BACTERIA ON SURFACES OF BEEF CARCASSES

A rapid (<15 min), inexpensive and simple method has been developed to estimate the concentration of bacteria on surfaces of beef carcasses using adenosine triphosphate (ATP) bioluminescence. Surfaces (5x5 cm²) of beef carcasses (n= 159) were collected by excision. An ATP assay and aerobic plate count were performed on each sample. A significant (p < 0.001) positive linear relationship (r = 0.83) between plate count and ATP assay was obtained for 159 beef carcass samples. When thresholds levels were set at 1 × 10⁴, 1 × 10⁵ and 1 × 10⁶ CFU/cm², there was moderate to good agreement between the ATP bioluminescence assay and the aerobic plate count as determined by the k-statistic. The application of this ATP bioluminescence test to HACCP systems for beef slaughter processes is discussed.     

Association of bacteria with the fungal fermentation of soybean tempe

Bacteria grew to viable populations of 10⁸–10⁹ cfu/g during the fermentation of soybeans into tempe with the fungus, Rhizopus oligosporus. Bacillus pumilus and B. brevis were the predominant bacterial species, reaching populations of approximately 10⁸ cfu/g during the 48 h fermentation. Species of Streptococcus faecium, Lactobacillus casei, Klebsiella pneumoniae and Enterobacter cloacae also contributed to the fermentation and achieved populations of 10⁶–10⁷ cfu/g. and accepted 25 May 1989     

Monitoring the fate of genetically engineered bacteria sprayed on the phylloplane of bush beans and grass

Abstract The fate of a Bacillus amyloliquefaciens with the recombinant plasmid pSB20 sprayed on the phyllosphere of grass, and of a Tn 5 marked Pseudomonas syringae sprayed on the phyllosphere of bush beans was studied in planted soil microcosms. B. amyloliquefaciens showed a decline from 1.5×10⁸ to 3.1×10² cfu g⁻¹ on the phylloplane of grass in the course of the experiment. B. amyloliquefaciens was easy to follow by selective cultivation due to the complete absence of bacterial background growth. Southern blot hybridization of Hin dIII digested genomic DNA showed plasmid restriction patterns identical with pSB20 indicating high plasmid stability. In total DNA extracts from phyllosphere bacteria the recombinant plasmid was detectable by Southern blot hybridization up to 6×10⁴ cfu g⁻¹ (wet weight). Counts of hybridizing colonies showed that P. syringae established on the phyllosphere of bush beans at between 5×10³ and 4×10⁶ cfu g⁻¹ fresh weight. During senescence of the bean plants the strain was no longer detectable by selective cultivation and subsequent colony hybridization. In contrast, Tn5 marked DNA was detected after PCR amplification over the whole period of the experiment.     

Automated concentration and recovery of micro-organisms from drinking water using dead-end ultrafiltration

Aims:  Concentration of pathogens diluted in large volumes of water is necessary for their detection. An automated concentration system placed online in drinking water distribution systems would facilitate detection and mitigate the risk to public health.
Methods and Results:  A prototype concentrator based on dead-end hollow fibre ultrafiltration was used to concentrate Bacillus atrophaeus spores directly from tap water. Backflush was used to recover accumulated particulates for analysis. In field tests conducted on a water utility distribution system, 3·2 × 10⁴–1·4 × 10⁶ CFU ml⁻¹ (6·1 × 10⁶–3·0 × 10⁸ CFU) were recovered from the filter when 2·9 × 10⁷–1·0 × 10⁹ CFU were spiked into the system. Per cent recovery ranged from 21% to 68% for flow volumes of 15–21 l. Tests using spore influent levels <10 CFU l⁻¹ (spike < 1000 CFU) yielded 23–40% recovery for volumes >100 l.
Conclusions:  B. atrophaeus spores at levels <10 CFU l⁻¹ were concentrated directly from tap water using an automated dead-end hollow-fibre ultrafiltration system.
Significance and Impact of the Study:  The prototype concentrator represents a critical step towards an autonomous system that could be installed in drinking water distribution lines or other critical water lines to facilitate monitoring. Recovered samples can be analysed using standard or rapid biosensor methods.     

Increased ELISA sensitivity using a modified extraction buffer for detection of Xanthomonas campestris pv. vesicatoria in leaf tissue

In vitro and in planta sensitivity of an indirect enzyme-linked immunoassaytechnique, using a monoclonal antibody specific for the lipopolysaccharide (LPS) of Xanthomonas campestris pv. vesicatoria , was increased 10-foldby using a newextraction buffer (gl of : KH₂PO₄, 2; NaHPO₄, 11·5; EDTAdisodium, 0·14; thimerosal, 0·02; and lysozyme, 0·2). The procedure improvedsensitivity without increasing background levels. In vitro , the limit of detection wasbetween 1×10⁷ and 1×10⁸ cells ml⁻¹ with the conventionalextraction buffer phosphate-buffered saline (PBS) and less than 1×10⁶ cells ml⁻¹ when lysozyme extraction buffer was substituted for PBS. In comparing 22 X. c.vesicatoria strains, absorbance readings were increased close to three-fold with the lysozymeextraction buffer as opposed to PBS. When leaf tissue extract was spiked with the bacterium, thelimit of detection was 1×10⁷ cfu ml⁻¹ and 1×10⁸ cfu ml⁻¹ with the lysozyme solution and PBS, respectively, as the extraction buffers. Whenusing the lysozyme extraction buffer in combination with a commercial amplification system, thelimit of detection was decreased to less than 1×10⁵ cfu ml⁻¹ in leaftissue. The addition of the lysozyme and EDTA to the phosphate buffer resulted in release of asignificant quantity of LPS and concomitant dramatic increase in sensitivity. The new procedure,termed lysozyme ELISA (L-ELISA), should increase sensitivity of ELISA reactions where LPS isthe reacting epitope.     

Sulphate-reducing bacteria in bovine faeces

Sulphate-reducing bacteria (SRB) were found in all of 200 bovine faeces examined. The number of SRB in bovine faeces ranged from 5 times 10² to 6 times 10⁸ bacteria g^-1. Of 50 isolates identified, all were assigned to the genus Desulfovibrio .     

Survival of Ralstonia solanacearum in Soil under Irrigated Rice Culture and Aquatic Weeds

The survival of Ralstonia solanacearum in naturally infested sandy loam soil under irrigated rice culture was investigated in Sankhu village (1400 m above sea level) in central Nepal. The experimental plot had a previous history of bacterial wilt and a range of 1.5 × 10⁴–3 × 10⁴ colony-forming units (CFU) per g soil was present. The survival of R. solanacearum was monitored in roots of naturally growing aquatic weeds in the rice plot and in soil before and after rice harvest. The incidence of the bacterial infection in the weeds, Dopatrium sp. and Monochoria vaginalis , were 57.5 and 10%, respectively. The bacterial population detected in soil before rice harvest was 1.5 × 10⁴ CFU per g soil whereas a range of 7.5 × 10²–1.5 × 10³ CFU per g was detected after the rice harvest. Biovar typing of R. solanacearum isolated from potato plants, potato tubers, aquatic weeds, and the soil from the experimental plot yielded the diverse biovars 2 A, 3 and 4. This is the first report of the survival of these biovars in soil, which was under continuous flow of irrigation water for 3 months during rice culture.