Salmonella typhimurium survival and viability is unaltered by suspended particles in freshwater

Insights into effects of algae on decay and distribution of bacterial pathogens in recreational water: Implications for microbial risk management

The decay and distribution of bacterial pathogens in water is an important information for the health risk assessment to guide water safety management, and suspended algae might affect bacterial pathogens in water. This study established microcosms to investigate the effects of algae-related factors on the representative indicators and opportunistic pathogen species in water. We found that suspended algae increased the persistence of targeted species by 1-2 orders of magnitude of concentrations compared to microcosms without algae; and the effect of algae on microbial survival was affected by water nutrient levels (i.e., carbon, nitrogen and phosphorus), as the increased microbial persistence were correlated to the increased algae concentrations with more nutrient supplies. Moreover, decay and distribution profiles of representative species were determined. The three opportunistic pathogen species (Pseudomonas aeruginosa, Aeromonas hydrophila and Staphylococcus aureus) showed lower decay rates (0.82-0.98/day, 0.76-0.98/day, 0.63-0.87/day) largely affected by algae-related factors, while the enteric species (Escherichia coli and Enterococcus faecalis) had higher decay rates (0.94-1.31/day, 0.89-1.21/day) with little association with algae, indicating the propensity for attachment to algae is an important parameter in microbial fate. Together results suggest suspended algae played an evident role in the decay and distribution of bacterial pathogens, providing important implications regarding microbial safety in recreational water.

Fate of Salmonella in Central Florida Surface Waters and Evaluation of EPA Worst Case Water as a Standard Medium

HIGHLIGHTS

Survival of Salmonella was studied in surface waters. Salmonella stayed alive in nonsterile microcosms for 168 days. Limited decline was seen in sterile surface, deionized, and EPA Worst Case water. EPA Worst Case water offers potential as a standardized medium.

Frequency and correlation of some enteric indicator bacteria and Salmonella in ready-to-eat raw vegetable salads from Mexican restaurants

Data about Salmonella presence in ready-to-eat raw vegetable salads (REVS) consumed in restaurants or sold as REVS in México is not available. The objective of the study was to measure the frequency of coliform bacteria (CB), fecal coliform (FC), Escherichia coli, and Salmonella in REVS from different types of restaurants and determine the correlations of CB, FC, and E. coli versus Salmonella from frequencies and concentration data. The REVS were purchased from 3 types of restaurants: national chain restaurants (A1 , A2 ); local restaurants (B1 , B2 ); and small restaurants in local markets (C1 , C2 , C3 ). Two restaurants for each A and B, and 3 for C, were included. Forty REVS were purchased at each A and B restaurant, and 20 at each C restaurant. CB were tested by plate count using violet red bile agar, FC and E. coli were detected by the most probable number method and E. coli confirmed using IMViC test; conventional method of culture was used for Salmonella. Of 220 analyzed samples, 100% had CB, 95.5% had FC, 83.2% had E. coli, and 6.8% had Salmonella. E. coli frequency was equal to or exceeded 75% in all the cases: 75% (A1 , C1 , C2 ), 80% (B2 ), 85% (B1 , C3 ), and 100% (A2 ). Salmonella frequency was equal to or exceeded 2.5% in all cases: 2.5% (A1 ), 5% (B2 , C2 ), 7.5% (B1 ), and 10% (A2 , C1 , C3 ). No correlation was observed between FC or E. coli versus Salmonella in the analyzed salads. All the tested salads were of poor quality microbiologically, and microbiological quality did not differ between the restaurants types.

Sources and fate of Salmonella and fecal indicator bacteria in an urban creek

This research aimed to understand the sources and fate of Salmonella and fecal bacteria in urban surface waters. An urban creek (San Pedro Creek, California, USA) that had unusually high levels of Salmonella and fecal bacteria relative to other nearby waterbodies was chosen as a model field site. State of the art microbiological methods were used in concert with modeling to investigate Salmonella and fecal bacteria sources, and determine field-relevant dark inactivation and photoinactivation rates. Three along-creek surveys that spanned reaches adjacent to both urban and forested land covers were conducted to measure Salmonella, enterococci, Escherichia coli, and horse- and human-specific Bacteroidales. Salmonella were detected adjacent to and downstream of urban land cover, but not adjacent to forested land cover. No human or horse-specific Bacteroidales fecal markers were detected implicating other urban animal sources of bacteria. Two locations along the creek where Salmonella was consistently detected were sampled hourly for 25 hours and a mass-balance model was applied to determine field-relevant light and dark inactivation rates for Salmonella, enterococci, and E. coli. Sunlight inactivation did not appear to be important in modulating concentrations of Salmonella, but was important in modulating both enterococci and E. coli concentrations. Dark inactivation was important for all three organisms. This is the first study to quantitatively examine the fate of Salmonella within an urban surface water. Although the work is carried out at a single site, the methodologies are extendable to source tracking in other waterbodies. Additionally, the rate constants determined through the modeling will be useful for modeling these organisms in other surface waters, and represent useful benchmarks for comparison to laboratory-derived inactivation rates.

Evaluation of low-copy genetic targets for waterborne bacterial pathogen detection via qPCR

Recent developments in water quality research have highlighted difficulties in accurately predicting the incidence of pathogens within freshwater based on the viability, culturability and metabolic activity of indicator organisms. QPCR-driven assays are candidates to replace standard culture-based methods, however, protocols suitable for routine use have yet to be sufficiently validated. The objective of this study was to evaluate five oligonucleotide primers sets (ETIR, SINV, exoT, VS1 and ipaH2) for their potential applicability in qPCR assays to detect contamination from five waterborne bacterial pathogens (Escherichia coli O157:H7, Salmonella Typhimurium, Campylobacter jejuni, Pseudomonas aeruginosa, and Shigella flexneri). An enrichment-free qPCR protocol was also tested using S. Typhimurium-seeded source water, combining membrane filtration and mechanical, chemical and enzymatic lysis techniques to recover the bacterial cells. All five primer sets were found to have high specificity and sensitivity for the tested organisms. Four of the primers were able to detect pathogen loads as low as 10 cells/mL while 200 cells/mL of C. jejuni were detectable in pure culture. Although sensitivity decreased in an artificially contaminated environmental matrix, it was still possible to detect as few as 10 S. Typhimurium cells without enrichment. The primers and protocols evaluated in this study have demonstrated potential for further validation for possible application alongside traditional indicator techniques.

Salmonella rarely detected in Mississippi coastal waters and sediment

AIMS

Standards for the rapid detection of individual pathogens from environmental samples have not been developed, but in their absence, the use of molecular-based detection methods coupled with traditional microbiology techniques allows for rapid and accurate pathogen detection from environmental waters and sediment. The aim of this research was to combine the use of enrichment with PCR for detection of Salmonella in Mississippi coastal waters and sediment and observe if that presence correlated with levels of enterococci and climatological variables.

METHODS AND RESULTS

Salmonella were primarily found in samples that underwent nutrient enrichment and were present more frequently in freshwater than marine waters. Salmonella were detected infrequently in marine and freshwater sediments. There was a significant positive correlation between the presence of detectable Salmonella and the average enterococcal count. An inverse relationship, however, was observed between the frequency of detection and the levels of salinity, turbidity and sunlight exposure.

CONCLUSIONS

Results from this study indicated the presence of Salmonella in Mississippi coastal waters, and sediments are very low with significant differences between freshwater and marine environments.

SIGNIFICANCE AND IMPACT OF THE STUDY

Using pathogenic and novel nonpathogenic molecular markers, Salmonella do not appear to be a significant pathogenic genus along the Mississippi Coast.

Survival and persistence of human and ruminant-specific faecal Bacteroidales in freshwater microcosms

Amplification of host-specific markers from Bacteroidales faecal anaerobes can rapidly identify the source of faecal pollution. It is necessary to understand persistence and survival of these markers and marker cells, both to interpret quantitative source-tracking data, and to use such data to predict pathogen occurrence. We measured marker persistence and cell survival of two human (HF134, HF183) and two ruminant (CF128, CF193) faecal Bacteroidales markers, compared with Escherichia coli and enterococci. Freshwater microcosms were inoculated with fresh cattle or human faeces and incubated at 13 degrees C in natural light or darkness. Marker persistence was measured by polymerase chain reaction (PCR) and quantitative PCR. Survival of marker cells was measured by real-time quantitative PCR. There was no difference in persistence between the two human-specific Bacteroidales DNA markers in the light and dark microcosms. Cell survival profiles of the two human markers were also similar; both were significantly affected by light. Ruminant markers persisted and survived longer than human markers (14 versus 6 days respectively). CF193 decreased more rapidly than CF128, and light significantly affected CF128 but not CF193. These results support use of host-specific faecal Bacteroidales markers as indicators of recent faecal pollution, but suggest that caution is needed in interpreting quantitative results to indicate proportional contribution of different sources, as individual markers differ in their survival, persistence and response to environmental variables. The survival and persistence profiles for Bacteroidales markers are consistent with survival profiles for several faecal pathogens.

Animal and environmental impact on the presence and distribution of Salmonella and Escherichia coli in hydroponic tomato greenhouses

From 2003 to 2004, we studied the impact of environmental influences on the microbiological quality of a hydroponic tomato farm. The presence of Salmonella was investigated on 906 samples of tomatoes and 714 environmental samples. The farm comprised 14 greenhouses and a technologically advanced packinghouse, and operated under a sanitary agricultural practices plan. The objective of the present study was to determine the operating sources of contamination. During the course of the study, two independent natural events affected the farm. In 2003, water runoff entered some of the greenhouses. A year later, wild animals (opossums, mice, and sparrows) gained entry into several of the greenhouses. Salmonella and Escherichia coli were found in samples of tomatoes, water puddles, soil, shoes, and the feces of local wild and farm animals. Salmonella Montevideo, Salmonella Newport, and strains of the F serogroup were isolated from tomatoes. Almost all of the Salmonella Newport strains were isolated from samples collected during or immediately after the flood. Analysis by pulsed-field gel electrophoresis revealed that some Salmonella Montevideo isolates from tomatoes, opossums, and mice displayed identical XbaI or AvrII patterns, suggesting that these wild animals represented one source of contamination. F serogroup strains were found mostly on samples of goat feces and personnel shoes when standard working practices were in place. Shoes were found to be an important vehicle for dissemination of Salmonella into the greenhouses. The level of protection provided by hydroponic greenhouses does not exclude the eventuality that enteric pathogenic bacteria can gain access through various avenues.

Microbiological profile of greenhouses in a farm producing hydroponic tomatoes

Produce, including tomatoes, has been implicated in several outbreaks of foodborne illness. A number of the sources of contamination for produce grown in open fields are known. However, as an alternative agricultural system, hydroponic greenhouses are reasonably expected to reduce some of these sources. The objective of the present study was to determine the microbiological profile of tomatoes grown in greenhouses at a Mexican hydroponic farm with a high technological level and sanitary agricultural practices (SAPs) in place. Tomatoes and other materials associated with the farm were analyzed for the presence of Salmonella enterica and populations of Escherichia coli, coliforms, and Enterobacteriaceae. Tomatoes showed median levels of 0.8 log CFU per tomato for Enterobacteriaceae, < 0.5 log CFU per tomato for coliforms, and 0.5 most probable number per tomato for E. coli. Despite the physical barriers that the facilities provide and the implemented SAPs, we found that 2.8% of tomatoes were contaminated with Salmonella and 0.7% with E. coli. Other Salmonella-positive materials were puddles, soil, cleaning cloths, and sponges. Samples from the nursery and greenhouses were positive for E. coli, whereas Salmonella was found only in the latter. Although hydroponic greenhouses provide physical barriers against some sources of enteric bacterial contamination, these results show that sporadic evidence of fecal contamination and the presence of Salmonella can occur at the studied greenhouse farm.