Influence of fluorescence of bacteria stained with acridine orange on the enumeration of microorganisms in raw milk

Biofilms Comprise a Component of the Annual Cycle of Vibrio cholerae in the Bay of Bengal Estuary

Vibrio cholerae, an estuarine bacterium, is the causative agent of cholera, a severe diarrheal disease that demonstrates seasonal incidence in Bangladesh. In an extensive study of V. cholerae occurrence in a natural aquatic environment, water and plankton samples were collected biweekly between December 2005 and November 2006 from Mathbaria, an estuarine village of Bangladesh near the mangrove forests of the Sundarbans. Toxigenic V. cholerae exhibited two seasonal growth peaks, one in spring (March to May) and another in autumn (September to November), corresponding to the two annual seasonal outbreaks of cholera in this region. The total numbers of bacteria determined by heterotrophic plate count (HPC), representing culturable bacteria, accounted for 1% to 2.7% of the total numbers obtained using acridine orange direct counting (AODC). The highest bacterial culture counts, including toxigenic V. cholerae, were recorded in the spring. The direct fluorescent antibody (DFA) assay was used to detect V. cholerae O1 cells throughout the year, as free-living cells, within clusters, or in association with plankton. V. cholerae O1 varied significantly in morphology, appearing as distinctly rod-shaped cells in the spring months, while small coccoid cells within thick clusters of biofilm were observed during interepidemic periods of the year, notably during the winter months. Toxigenic V. cholerae O1 was culturable in natural water during the spring when the temperature rose sharply. The results of this study confirmed biofilms to be a means of persistence for bacteria and an integral component of the annual life cycle of toxigenic V. cholerae in the estuarine environment of Bangladesh.

Vibrio cholerae, the causative agent of cholera, is autochthonous in the estuarine aquatic environment. This study describes morphological changes in naturally occurring V. cholerae O1 in the estuarine environment of Mathbaria, where the bacterium is culturable when the water temperature rises and is observable predominantly as distinct rods and dividing cells. In the spring and fall, these morphological changes coincide with the two seasonal peaks of endemic cholera in Bangladesh. V. cholerae O1 cells are predominantly coccoid within biofilms but are rod shaped as free-living cells and when attached to plankton or to particulate matter in interepidemic periods of the year. It is concluded that biofilms represent a stage of the annual life cycle of V. cholerae O1, the causative agent of cholera in Bangladesh.

New applications of the acridine orange fluorescence staining method: Screening for circulating tumor cells

The aim of the present study was to explore use of the acridine orange fluorescence (AO-F) staining method for screening of circulating tumor cells (CTCs) in renal cell carcinoma (RCC) patients. The AO-F positive staining rate of live and dead tumor cells was calculated. The positive staining rate in the live group was 93.4±3.0%, while the dead group failed to emit specific fluorescence. A known number of tumor cells were added to peripheral blood, and the detection sensitivity of the four groups (50, 100, 200 and 500 cells/tube) was 10.2±3.8, 9.2±2.3, 10.8±2.6 and 10.5±1.9%, respectively. The average detection sensitivity of the four groups was 10.16±2.73%. There was a positive correlation between the number of cells that was positively stained with AO-F and the total number cells in the system (χ²=0.959; P<0.001). Subsequently, the AO-F staining method was used to detect positive staining cells in 8 healthy volunteers (control group), and 112 non-metastatic and 27 metastatic RCC patients. The positive staining rate was 13.67% (19/139) in RCC patients, while none of the control group was positive. The AO-F positive staining rate was not significantly different between the metastatic and non-metastatic patients according to age, gender, the pathological pattern, T2/3 (according to the Tumor-Node-Metastasis classification) or Fuhrman grade, while there was a significant difference according to T1. The positive staining rate was 8.93% (10/112) for non-metastatic patients and 33.33% (9/27) for metastatic patients, which showed a significant difference (P<0.05). In 112 non-metastatic and 27 metastatic patients, the positive staining rate was not significantly associated with gender, age, tumor size, the pathological pattern, T classification, Fuhrman grade, the presence of a lesion or metastasis to the lungs. The present study demonstrated that the method of CTC staining with AO-F, which has high reproducibility and specificity, was feasible for identifying CTCs and warrants further study.

Quantification of Desulfovibrio vulgaris dissimilatory sulfite reductase gene expression during electron donor- and electron acceptor-limited growth

Previous studies have suggested that levels of transcripts for dsrA, a gene encoding a subunit of the dissimilatory sulfite reductase, are not directly related to the rates of sulfate reduction in sediments under all conditions. This phenomenon was further investigated with chemostat-grown Desulfovibrio vulgaris. Under sulfate-limiting conditions, dsrA transcript levels increased as the bulk rates of sulfate reduction in the chemostat increased, but transcript levels were similar at all sulfate reduction rates under electron donor-limiting conditions. When both electron donor- and electron acceptor-limiting conditions were considered, there was a direct correspondence between dsrA transcript levels and the rates of sulfate reduction per cell. These results suggest that dsrA transcript levels may provide important information on the metabolic state of sulfate reducers.

Two putative c-type multiheme cytochromes required for the expression of OmcB, an outer membrane protein essential for optimal Fe(III) reduction in Geobacter sulfurreducens

Deletion of two homologous Geobacter sulfurreducens c-type cytochrome genes, omcG and omcH, decreased the rate of Fe(III) reduction and decreased the level of an outer membrane cytochrome critical for Fe(III) reduction, OmcB, without affecting its transcription. Expression of either gene restored Fe(III) reduction and OmcB expression, suggesting functional similarity.

OmcF, a putative c-Type monoheme outer membrane cytochrome required for the expression of other outer membrane cytochromes in Geobacter sulfurreducens

Outer membrane cytochromes are often proposed as likely agents for electron transfer to extracellular electron acceptors, such as Fe(III). The omcF gene in the dissimilatory Fe(III)-reducing microorganism Geobacter sulfurreducens is predicted to code for a small outer membrane monoheme c-type cytochrome. An OmcF-deficient strain was constructed, and its ability to reduce and grow on Fe(III) citrate was found to be impaired. Following a prolonged lag phase (150 h), the OmcF-deficient strain developed the ability to grow in Fe(III) citrate medium with doubling times and yields that were ca. 145% and 70% of those of the wild type, respectively. Comparison of the c-type cytochrome contents of outer membrane-enriched fractions prepared from wild-type and OmcF-deficient cultures confirmed the outer membrane association of OmcF and revealed multiple changes in the cytochrome content of the OmcF-deficient strain. These changes included loss of expression of two previously characterized outer membrane cytochromes, OmcB and OmcC, and overexpression of a third previously characterized outer membrane cytochrome, OmcS, during growth on Fe(III) citrate. The omcB and omcC transcripts could not be detected in the OmcF-deficient mutant by either reverse transcriptase PCR or Northern blot analyses. Expression of the omcF gene in trans restored both the capacity of the OmcF-deficient mutant to reduce Fe(III) and wild-type levels of omcB and omcC mRNA and protein. Thus, elimination of OmcF may impair Fe(III) reduction by influencing expression of OmcB, which has previously been demonstrated to play a critical role in Fe(III) reduction.

A flow cytometric technique for quantification and differentiation of bacteria in bulk tank milk

AIMS

The present study describes a flow cytometric technique for quantification and differentiation of bacteria in bulk tank milk according to the main cause of elevated counts.

METHODS AND RESULTS

A total of 75 Danish bulk tank milk samples exceeding the grading level of 3.0 x 10(4) CFU ml(-1) were examined by both flow cytometry and traditional microbiological analyses. The correlation coefficient (r) between the two methods was 0.71. For the differential analyses of the dominant bacterial populations four different parameters were used to give a species-characteristic pattern. The four parameters were as follows: staining with Oregon Green conjugated wheat germ agglutinin that binds to the cell wall of bacteria, staining with hexidium iodide that binds to all bacterial DNA, the flow cytometric forward scatter and the flow cytometric side scatter. Three regions in the flow cytometric plot were defined: region 1 includes bacteria mainly associated with poor hygiene, region 2 includes psychrotrophic hygiene bacteria and region 3 includes bacteria mainly related to mastitis. The ability of the flow cytometric technique to predict the main cause of elevated bacterial counts on routine samples was examined. Comparing these results with results obtained by traditional microbiological analyses for identification showed that for 81% of the samples the two techniques agreed on the main cause of an elevated bacterial count.

CONCLUSIONS

The ability of the presented flow cytometric technique to enumerate and differentiate bacteria in bulk tank milk according to the main cause of elevated counts was demonstrated.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study described the first step in development of a technique suitable for routine analyses of bulk tank milk samples. A technique indicating the main cause of an elevated count will enable the farmer to eliminate the contamination source within a short time limit.