Microbial fouling community analysis of the cooling water system of a nuclear test reactor with emphasis on sulphate reducing bacteria

Culture and molecular-based techniques were used to characterize bacterial diversity in the cooling water system of a fast breeder test reactor (FBTR). Techniques were selected for special emphasis on sulphate-reducing bacteria (SRB). Water samples from different locations of the FBTR cooling water system, in addition to biofilm scrapings from carbon steel coupons and a control SRB sample were characterized. Whole genome extraction of the water samples and SRB diversity by group specific primers were analysed using nested PCR and denaturing gradient gel electrophoresis (DGGE). The results of the bacterial assay in the cooling water showed that the total culturable bacteria (TCB) ranged from 10(3) to 10(5)?cfu?ml(-1); iron-reducing bacteria, 10(3) to 10(5)?cfu?ml(-1); iron oxidizing bacteria, 10(2) to 10(3)?cfu?ml(-1) and SRB, 2-29?cfu?ml(-1). However, the counts of the various bacterial types in the biofilm sample were 2-3 orders of magnitude higher. SRB diversity by the nested PCR-DGGE approach showed the presence of groups 1, 5 and 6 in the FBTR cooling water system; however, groups 2, 3 and 4 were not detected. The study demonstrated that the PCR protocol influenced the results of the diversity analysis. The paper further discusses the microbiota of the cooling water system and its relevance in biofouling.     

Investigation of a simple amperometric electrode system to rapidly quantify and detect bacteria in foods

A two electrode system mounted as a single probe was developed to measure electrochemically the rate of reduction of a redox mediator (thionine) by bacteria. The system gave a rapid (2 min) bacterial-dependent current above 2.5 x 10(5) cfu/ml with pure cultures of bacteria, but when applied to the measurement of the bacterial contamination in samples of meat and milk it was unable to detect or quantify the contamination reliably. Incubation of samples for a few hours before examination enabled the system to detect bacteria in excess of 10(6) cfu/ml.     

Post-processing microflora and the shelf stability of gari marketed in Port Harcourt

Gari was examined for its post-processing microbial content. Aerobic mesophilic bacteria and fungi were isolated from all samples. The total viable bacterial counts ranged from 2.0 X 10(2) to 8.0 X 10(4) cfu/g. Fungal counts ranged from 1.0 X 10(2) to 1.5 X 10(4) cfu/g. The total viable counts of fresh samples were much lower than those of market and packaged samples. Bacillus, Micrococcus and Proteus spp. were the bacteria isolated, Aspergillus niger, Aspergillus flavus and Penicillium spp. the fungi. Food borne parasites and pathogens such as Staph. aureus and Clostridium perfringens were not found. The gari samples were quite stable, having a shelf life of 3-6 months. The water activities of the samples ranged from 0.52 to 0.68. Based on the microbial counts of the samples, the critical upper limit for the safety of gari was set at 10(4) cfu/g dry sample.     

Optimization of a reusable hollow-fiber ultrafilter for simultaneous concentration of enteric bacteria,protozoa, and viruses from water

The detection and identification of pathogens from water samples remain challenging due to variations in recovery rates and the cost of procedures. Ultrafiltration offers the possibility to concentrate viral, bacterial, and protozoan organisms in a single process by using size-exclusion-based filtration. In this study, two hollow-fiber ultrafilters with 50,000-molecular-weight cutoffs were evaluated to concentrate microorganisms from 2- and 10-liter water samples. When known quantities (10(5) to 10(6) CFU/liter) of two species of enteric bacteria were introduced and concentrated from 2 liters of sterile water, the addition of 0.1% Tween 80 increased Escherichia coli strain K-12 recoveries from 70 to 84% and Salmonella enterica serovar Enteritidis recoveries from 36 to 72%. An E. coli antibiotic-resistant strain, XL1-Blue, was recovered at a level (87%) similar to that for strain K-12 (96%) from 10 liters of sterile water. When E. coli XL1-Blue was introduced into 10 liters of nonsterile Rio Grande water with higher turbidity levels (23 to 29 nephelometric turbidity units) at two inoculum levels (9 x 10(5) and 2.4 x 10(3) per liter), the recovery efficiencies were 89 and 92%, respectively. The simultaneous addition of E. coli XL1-Blue (9 x 10(5) CFU/liter), Cryptosporidium parvum oocysts (10 oocysts/liter), phage T1 (10(5) PFU/liter), and phage PP7 (10(5) PFU/liter) to 10 liters of Rio Grande surface water resulted in mean recoveries of 96, 54, 59, and 46%, respectively. Using a variety of surface waters from around the United States, we obtained recovery efficiencies for bacteria and viruses that were similar to those observed with the Rio Grande samples, but recovery of Cryptosporidium oocysts was decreased, averaging 32% (the site of collection of these samples had previously been identified as problematic for oocyst recovery). Results indicate that the use of ultrafiltration for simultaneous recovery of bacterial, viral, and protozoan pathogens from variable surface waters is ready for field deployment.     

Post-processing microflora and the shelf stability of gari marketed in Port Harcourt

Gari was examined for its post-processing microbial content. Aerobic mesophilic bacteria and fungi were isolated from all samples. The total viable bacterial counts ranged from 2.0 × 10² to 8.0 × 10⁴ cfu/g. Fungal counts ranged from 1.0 × 10² to 1.5 × 10⁴ cfu/g. The total viable counts of fresh samples were much lower than those of market and packaged samples. Bacillus, Micrococcus and Proteus spp. were the bacteria isolated, Aspergillus niger, Aspergillus flavus and Penicillium spp. the fungi. Food borne parasites and pathogens such as Staph. aureus and Clostridium perfringens were not found. The gari samples were quite stable, having a shelf life of 3–6 months. The water activities of the samples ranged from 0.52 to 0.68. Based on the microbial counts of the samples, the critical upper limit for the safety of gari was set at 10⁴ cfu/g dry sample.     

Evaluation of a Modified Cefsulodin-Irgasan-Novobiocin Agar for Isolation of Yersinia spp

Y. enterocolitica and Y. pseudotuberculosis are important food borne pathogens. However, the presence of competitive microbiota makes the isolation of Y. enterocolitica and Y. pseudotuberculosis from naturally contaminated foods difficult. We attempted to evaluate the performance of a modified Cefsulodin-Irgasan-Novobiocin (CIN) agar in the differentiation of Y. enterocolitica from non-Yersinia species, particularly the natural intestinal microbiota. The modified CIN enabled the growth of Y. enterocolitica colonies with the same efficiency as CIN and Luria-Bertani agar. The detection limits of the modified CIN for Y. enterocolitica in culture medium (10 cfu/ml) and in artificially contaminated pork (10⁴ cfu/ml) were also comparable to those of CIN. However, the modified CIN provided a better discrimination of Yersinia colonies from other bacteria exhibiting Yersinia-like colonies on CIN (H₂S-producing Citrobacter freundii, C. braakii, Enterobacter cloacae, Aeromonas hydrophila, Providencia rettgeri, and Morganella morganii). The modified CIN exhibited a higher recovery rate of Y. enterocolitica from artificially prepared bacterial cultures and naturally contaminated samples compared with CIN. Our results thus demonstrated that the use of modified CIN may be a valuable means to increase the recovery rate of food borne Yersinia from natural samples, which are usually contaminated by multiple types of bacteria.     

Numérations bactériennes dans le lagon du grand Cul-de-Sac marin et sa zone côtière (guadeloupe)

Sixty sea-water and marine sediment samples have been collected in the clear and dredged coral waters of a lagoon in Guadeloupe. Total counts of 10 to 100 living bacteria were obtained by counting colonies on membranes after filtration and pour plate count techniques in the clear water coral zones. Living bacterial populations ranging from 2 × 10³ to 20 × 10³/ml of water were detected in the dredged coral zone. Suspended sandy particulate matter resulting from dredging seems to be the direct cause of the abnormal increase in bacteria. The mean values were ≈ 10³ living bacteria/ml for the coastal sea water and 10⁴ for the brackish waters of channels in the mangrove swamp. It seems that the bacterial sediment population has been under-estimated.     

Investigation of a simple amperometric electrode system to rapidly quantify and detect bacteria in foods

A two electrode system mounted as a single probe was developed to measure electrochemically the rate of reduction of a redox mediator (thionine) by bacteria. The system gave a rapid (2 min) bacterial-dependent current above 2.5×10⁵ cfu/ml with pure cultures of bacteria, but when applied to the measurement of the bacterial contamination in samples of meat and milk it was unable to detect or quantify the contamination reliably. Incubation of samples for a few hours before examination enabled the system to detect bacteria in excess of 10⁶ cfu/ml.     

Characterization of lactic acid bacteria isolated from the one humped camel milk produced in Morocco

One hundred and twenty (120) strains of lactic acid bacteria (LAB) were enumerated and isolated from raw dromedary milk in Morocco using various cultured media. Strains isolated were characterized by phenotypic, physiological and biochemical properties. Results showed that high counts of LAB were found. Presumptive lactobacilli counts ranged from 2.5x10(2) to 6x10(7)cfu/ml, presumptive lactococci levels varied from 5x10(2) to 6x10(7)cfu/ml, presumptive streptococci counts varied from 4.2x10(2) to 8x10(7)cfu/ml, presumptive leuconostoc levels ranged from 5.4x10(2) to 5.4x10(7)cfu/ml. Results showed also that Lactobacillus and Lactococcus were the predominant genera with 37.5% and 25.8%, respectively. The dominated species found were Lactococcus lactis subsp. lactis (17.5%), Lactobacillus helveticus (10%), Streptococcus salivarius subsp. thermophilus (9.20%), Lactobacillus casei subsp. casei (5.80%) and Lactobacillus plantarum (5%). This is the first report on the characterization of LAB strains isolated from the one humped camel milk produced in Morocco.     

Bacterial infection of mudfish Clarias gariepinus (Siluriformes: Clariidae) fingerlings in tropical nursery ponds

Bacterial infection among the most common cultured mudfish Clarias gariepinus in Africa, has become a cause of concern, because it constitutes the largest economic loss in fish farms. In order to provide useful biological data of the pathogens for good management practices, samples were collected monthly between January 2008 and December 2009 in three monoculture nursery ponds, located in three different positions: upriver (A, grassland), mid-river (B, mixed forest and grassland) and downriver (C, rainforest) along 200 km length of Cross River floodplains, Nigeria. A total of 720 fingerlings between 15.1 and 20.7 g were analyzed to determine the degree of infection. The bacterial pathogens were taken from their external surfaces, and were isolated and identified by standard methods. The caudal fins of fingerlings from pond A had the highest bacterial load (5.8 x 10(3) cfu/g), while the least counts (1.2 x 103 cfu/g) were identified on the head of fish from pond C, with Flexibacter columnaris as the major etiological agent. Pseudomonas fluorescens, Aeromonas hydrophila, Escherichia coli, Staphylococcus aureus and Micrococcus luteus were identified as co-isolates with P. fluorescens as dominant (0.7 x 10(2) cfu/mL) co-isolates in pond water. Clinical signs of five white spots with red periphery appeared on the external surface of infected fish. All the fish sampled, died after 4 to 9 days. There was no significant difference in the bacterial counts between different ponds, but the difference between fish organs/parts examined was significant. Fish from these ponds are therefore potentially dangerous to consumers and highly devalued, with the economic impact to producers. Preventive methods to avoid these infections are recommended.     

Isolation of halophilic and halotolerant bacteria from a Japanese salt field and comparison of the partial 16S rRNA gene sequence of an extremely halophilic isolate with those of other extreme halophiles

Halophilic and halotolerant bacteria were isolated from soil samples of a Japanese salt field, an environment where salt concentrations vary annually. From 1 g of each of the five samples collected, over 1×10³ bacterial colonies (colony forming units (cfu)g^-1) grew on agar medium containing 2M Na⁺. In contrast, 0–4 bacterial colonies (cfu g^-1) were observed on agar medium containing 4M Na⁺. Two of the five samples contained numerous bacteria (10²–10³ cfu g^-1) capable of growth on a 2M Na⁺ alkaline (pH=9.5) medium, while few bacterial colonies were observed from the other three samples. Only one of the five samples was shown to contain bacteria capable of growth on a 4M Na⁺ alkaline medium. Most of the bacteria isolated on 4M Na⁺ agar were eubacteria, but one extreme halophile (TR-1, already described as Haloarcula japonica JCM7785) was also isolated. The 16S rRNA sequence of TR-1 was determined and shows high homology (94.4–98.5%) to Ha. marismortui and Ha. sinaiiensis. These results suggested that: 1) environments with seasonally varying salinity can harbour halotolerants as well as halophiles and, 2) closely related halophiles can be isolated from geographically distant habitats.     

长江口低氧区异养细菌及氮磷细菌分布

2009年8月15-28日,对长江口低氧高发海域的异养细菌、无机磷细菌、有机磷细菌、反硝化细菌和氨化细菌的空间分布特征进行初步研究.结果表明:氨化细菌数量最高,表层水、底层水和表层沉积物的数量均值分别为307.52×104个·L-1、184.50×104个·L-1和199.97×102个·g-1;其次为异养细菌,数量均值分别为87.35×104 cfu·L-1、86.85×104cfu·L-1和64.26×102cfu·g-1;再次为有机磷细菌,数量均值分别为19.26×104 cfu·L-1、18.82×104cfu·L-1和19.56×102cfu·g-1;无机磷细菌只分布在长江口内和河口南槽至舟山海域,数量均值分别为18.50×104cfu·L-1、31.00×104cfu·L-1和7.17×102cfu·g-1;反硝化细菌分布广,但数量较低,均值分别为3.94×104个·L-1、23.08×104个·L-1和6.22×102个·g-1.相关性分析结果说明:盐度、硝酸盐、磷酸盐、硅酸盐和pH是影响水体和表层沉积物异养细菌、磷细菌和反硝化细菌分布的主要因子;底层水和表层沉积物异养细菌、磷细菌与水温呈显著正相关;底层水异养细菌和有机磷细菌与溶解氧(DO)呈显著正相关;表层沉积物无机磷细菌与DO呈显著正相关,氨化细菌与DO呈显著负相关.聚类分析结果说明:低氧对表层沉积物的细菌群落结构产生影响.     

Effects of ozone treatment on cell growth and ultrastructural changes in bacteria

Ozone appeared to inhibit growth and caused the death of gram negative and gram positive tested bacteria: Escherichia coli, Salmonella sp., Staphylococcus aureus and Bacillus subtilis. Bacterial cultures at 10(3), 10(4), 10(5), 10(6), and 10(7) cfu/ml dilution were exposed to 0.167/mg/min/L of ozone at different time intervals (0, 5, 10, 15, 30, 60, 90, 120, and 150 min). Cell viability was observed in all types of tested bacteria at 10(3), 10(4), 10(3) cfu/ml within 30 min after ozone exposure. However, cell inactivation was not significantly observed at concentrations of 10(6), 10(7) cfu/ml even after an exposure of 150 min. Ultrastructural changes of treated bacteria showed deformation, rough damage and surface destruction revealed by scanning electron microscopy. Some bacterial cells showed collapsed and shrunken patterns within 60 min and severe rupture and cellular lysis after 90 min of ozone treatment. This study supports the proposed mechanism of the bacteria inactivation by ozone that caused cell membrane destruction and finally lysis reaction. Thus, the precaution of using ozone as a biocide should be used to address appropriate concentrations of bacterial contamination in water.     

Measuring the spermosphere colonizing capacity (spermosphere competence) of bacterial inoculants

Spermosphere establishment by bacteria which were coated onto seeds was studied using soybean seeds treated with four bacterial strains at levels of log10 1 to 4 colony-forming units (cfu) per seed planted in a field soil mix, and incubated 48 h. Each strain at every inoculum level developed spermosphere population densities of log10 4 to 8 cfu/seed, demonstrating an average multiplication of log10 3 cfu/seed. An alternative method was developed to differentially rank bacteria for spermosphere colonizing capacity, based upon incorporation of bacteria into a soil and monitoring the resulting spermosphere population densities around noninoculated seeds after 4 days at 14 degrees C. Fifty-seven bacterial strains which were isolated from soybean roots or from water samples, including Pseudomonas putida, P. putida biovar B, P. fluorescens, Serratia liquefaciens, Enterobacter aerogenes, and Bacillus spp. were tested in the spermosphere colonization assay. Average spermosphere population densities for the 57 strains ranged from 0 to log10 7.0 cfu/seed. Strains of a given taxon demonstrated marked diversity with ranges from 0 to log10 6.0 cfu/seed for Bacillus spp. and from log10 1.4 to 7.0 cfu/seed for Pseudomonas putida. The relative ranking of representative strains was consistent in repeating experiments. The potential usefulness of the assay for efforts to develop competitive bacterial inoculants for crop seeds is discussed.     

Microbiological quality of bottled water sold in retail outlets in Nigeria

M.T. OGAN. 1992. The microbiological quality of four brands of bottled water sold in retail outlets in Nigeria were assessed by routine methods in 90 samples. Samples of two brands were acidic in the pH range 3.5–5.9. Faecal coliforms and streptococci were not recovered from any sample. Heterotrophic plate counts (HPC) numbered 50–800 cfu/ml in two brands, A and B, and 100–87000 cfu/ml in C and D. Component colony types among the HPC bacteria in brands C and D produced water-soluble, fluorescent pigments on colony count and other agar media, and occurred in 11 of 16 batches: their numbers varied from 60 to 82000 cfu/ml. Presumptive antibiotic-resistant proportions of the HPC bacteria were also recovered from brands C and D on agar amended with ampicillin, penicillin or streptomycin. Five isolates from the green pigmented colonies, representing five batches of brands C and D were satisfactorily identified as strains of Pseudomonas aeruginosa. These strains resisted between four and nine of 14 antibiotics tested. Resistance to tetracycline was eliminated in one isolate when it was cured by incubation at 42C for 100 h, but gel electrophoretic resolution of the DNA did not reveal presence of a plasmid. Strains of Bacillus were the second most commonly isolated bacteria; they were the only colony types in most samples with low HPC counts.     

Microbiological quality of bottled water sold in retail outlets in Nigeria.

The microbiological quality of four brands of bottled water sold in retail outlets in Nigeria were assessed by routine methods in 90 samples. Samples of two brands were acidic in the pH range 3.5-5.9. Faecal coliforms and streptococci were not recovered from any sample. Heterotrophic plate counts (HPC) numbered 50-800 cfu/ml in two brands, A and B, and 100-87,000 cfu/ml in C and D. Component colony types among the HPC bacteria in brands C and D produced water-soluble, fluorescent pigments on colony count and other agar media, and occurred in 11 of 16 batches: their numbers varied from 60 to 82,000 cfu/ml. Presumptive antibiotic-resistant proportions of the HPC bacteria were also recovered from brands C and D on agar amended with ampicillin, penicillin or streptomycin. Five isolates from the green pigmented colonies, representing five batches of brands C and D were satisfactorily identified as strains of Pseudomonas aeruginosa. These strains resisted between four and nine of 14 antibiotics tested. Resistance to tetracycline was eliminated in one isolate when it was cured by incubation at 42 degrees C for 100 h, but gel electrophoretic resolution of the DNA did not reveal presence of a plasmid. Strains of Bacillus were the second most commonly isolated bacteria; they were the only colony types in most samples with low HPC counts.     

Prevalence of mycobacteria in a swimming pool environment

A study was performed to evaluate the prevalence of non-tubercular mycobacteria in swimming pool environments. The bacteria in question were found in 88.2% of pool water samples. The most frequent species were Mycobacterium gordonae (73.5% of samples; range 1-840 cfu 100 ml - 1), M. chelonei (38.2% 2-360 cfu 100 ml - 1) and M. fortuitum (35.3% 2-250 cfu 100 ml - 1). The same species were also recovered from the water at the different phases of the treatment cycle, with relative percentages similar to those of the pool water. Shower floors and pool edges also presented high concentrations of the mycobacteria (100% of samples) and M. marinum was isolated from the surfaces of pool edges on two occasions (4.5% of samples). The swimming pool environment provides a suitable habitat for the survival and reproduction of mycobacteria. Although mycobacteria are common in swimming pools, human mycobacterial disease associated with their use is rare. Apart from superficial infections with M. marinum, the risk of more serious diseases in subjects with weakened immune systems should not be underestimated, given the widespread presence of mycobacteria that are possible opportunistic pathogens and the direct contact bathers have with the water and aerosol.     

Slow rehydration improves the recovery of dried bacterial populations.

Slow rehydration of bacteria from dried inoculant formulations provided higher viable counts than did rapid rehydration. Estimates were higher when clay and peat powder formulations of Rhizobium meliloti, Rhizobium leguminosarum biovar trifolii, and Pseudomonas putida, with water activities between 0.280 and 0.650, were slowly rehydrated to water activities of approximately 0.992 before continuing the dilution plating sequence. Rhizobium meliloti populations averaged 6.8 x 10(8) cfu/g and 1328 cfu/alfalfa seed greater when slowly rehydrated from bulk powder and preinoculated seeds, respectively. Bulk powder samples were slowly rehydrated to 0.992 water activity by the gradual addition of diluent, followed by a 10-min period for moisture equilibration. Preinoculated seed samples were placed in an environmental chamber at 24 degrees C with relative humidity greater than 80% for 1 h to allow moisture absorption. "Upshock," osmotic cellular stresses that occur during rehydration, was reduced when dried microbial formulations were slowly rehydrated and equilibrated before becoming fully hydrated in the dilution plating sequence. These procedures may also be applicable when estimating total viable bacterial populations from dried soil or other dry formulations.     

Rapid and sensitive magnetoelastic biosensors for the detection of Salmonella typhimurium in a mixed microbial population

In this article, we report the results of an investigation into the performance of a wireless, magnetoelastic biosensor designed to selectively detect Salmonella typhimurium in a mixed microbial population. The Langmuir-Blodgett (LB) monolayer technique was employed for antibody (specific to Salmonella sp.) immobilization on rectangular shaped strip magnetoelastic sensors (2 x 0.4 x 0.015 mm). Bacterial binding to the antibody on the sensor surface changes the resonance parameters, and these changes were quantified as a shift in the sensor's resonance frequency. Response of the sensors to increasing concentrations (5 x 10(1) to 5 x 10(8) cfu/ml) of S. typhimurium in a mixture of extraneous foodborne pathogens (Escherichia coli O157:H7 and Listeria monocytogenes) was studied. A detection limit of 5 x 10(3) cfu/ml and a sensitivity of 139 Hz/decade were observed for the 2 x 0.4 x 0.015 mm sensors. Binding kinetics studies have shown that the dissociation constant (K(d)) and the binding valencies for water samples spiked with S. typhimurium was 435 cfu/ml and 2.33 respectively. The presence of extraneous microorganisms in the mixture did not produce an appreciable change in the biosensor's dose response behavior.     

Bacterial colonization of domestic reverse-osmosis water filtration units

We have analyzed the bacterial content of water from the reservoirs of 300 reverse-osmosis units installed in households. The heterotrophic plate counts on R2A medium (20 and 35 degrees C) ranged from 0 to 10(7) colony forming units per millilitre (cfu/mL). Most reservoirs contained water with bacterial counts between 10(4) and 10(5) cfu/mL. The bacteria identified were Pseudomonas (not aeruginosa), Alcaligenes or Moraxella, Acinetobacter, Flavobacterium, and Chromobacterium. This report emphasizes the importance of bacterial colonization by heterotrophic bacteria in water reservoirs from domestic reverse-osmosis units.