Potential Enteric Pathogens Research Articles

Antibacterial activities of lactic acid bacteria isolated from cow faeces against potential enteric pathogens.

The addition of sub therapeutic doses of antibiotics to cattle feed for growth promotion is a contributory factor to antibiotic resistance, thus an alternative to antibiotics is needed in animal feed additives. To determine the antimicrobial activity of cow's intestinal Lactic acid bacteria (LAB) against enteric commensals. Escherichia coli, Klebsiella species (spp) and LAB were isolated from thirty different cow faecal samples and the LAB identified by partial sequencing of 16S rRNA. The antimicrobial activity of the LAB was determined against the test Escherichia coli and Klebsiella spp. Five species of LAB were isolated from thirty cow faecal samples and identified as Enterococcus hirae (8), Enterococcus durans (6), Enterococcus faecium (1), Enterococcus faecalis (1) and Weissella confusa (1). Viable cells and cell free supernatant (CFS) of the LAB were able to inhibit the growth of the test organisms with the largest zone of inhibition by the viable cells being 26mm against Escherichia coli CB6 produced by Enterococcus hirae CO6A while Weissella confusa CO29M and Enterococcus hirae CO2A produced the largest zones of inhibition (26mm) against Klebsiella CB2. This study shows that LAB from cow faeces possess considerable antimicrobial activity against resistant Escherichia coli from the same environment.

Prevalence of Potential Enteric Pathogens in Treated and Untreated Water Sources around Eastern Cape Region

Background: Fecal contamination of water sources has always been a major safety concern and a factor in determining the need of a continuous treatment program. A routine monitoring program for drinking water sources would provide increased public health protection. The aim of this study was to determine the prevalent rates of potential enteric pathogens in water sources in Eastern Cape. Methods: Water samples (from water surfaces and undergrounds) were collected from treated and untreated water sources. The Colilert method (IDEXX Laboratories, Inc., Westbrook, Maine) was used to screen for fecal contamination and then selective culture media and Rapid 20E API Kit were used to identify different isolates. Results: of the 80 water sources (from Mthatha, Flagstaff, Tsolo, Mount frere, Libode,…. areas) sampled, there was a widespread contamination with coliforms ranging from…1..to.>2400……MPN/100ml. Whilst the contamination with E. coli remained relatively low in most of the sources, there were high contamination levels (>2400 MPN/ml) of E. coli in water sources from Ntabankulu, Ngqeleni, Libode and Flagstaff. Among the isolated enteric pathogens, Escherichia coli 1 was the most prevalent (41.2%) followed by Salmonella spp. (17.7%) and Enterobacter spp. (10%). Conclusion: The presence of pathogenic micro-organisms in drinking water may pose a serious health risk to consumers especially the young, elderly and the immune compromised. Therefore there is need for governing bodies to take extra steps in treatment and monitoring programs for safer and cleaner water sources.

Molecular survey of occurrence and quantity of Legionella spp., Mycobacterium spp., Pseudomonas aeruginosa and amoeba hosts in municipal drinking water storage tank sediments

To examine the occurrence and quantity of potential pathogens and an indicator of microbial contamination in the sediments of municipal drinking water storage tanks (MDWSTs), given the absence of such data across the United States. Sediment samples (87 MDWST) from eighteen locations across ten states of the United States were collected and assayed by qPCR for a range of potential enteric and opportunistic microbial pathogens and a sewage-associated Bacteroides marker. Potential opportunistic pathogens dominated, with the highest detection of occurrence (per cent positive detection; average cell equivalence (CE)) being Mycobacterium spp. (88·9%; 6·7 ± 8·5 × 10(4) CE g(-1) ), followed by Legionella spp. (66·7%; 5·2 ± 5·9 × 10(3) CE g(-1) ), Pseudomonas aeruginosa (22·2%; 250 ± 880 CE g(-1) ) and Acanthamoeba spp. (38·9%; 53 ± 70 CE g(-1) ), with no detected Naegleria fowleri. Most enteric pathogens (Campylobacter jejuni, Escherichia coli 0157:H7, Salmonella enterica, Cryptosporidium parvum and Giardia duodenalis) were not detected, except for a trace signal for Campylobacter spp. There was significant correlation between the qPCR signals of Legionella spp. and Acanthamoeba spp. (R(2) = 0·61, n = 87, P = 0·0001). Diverse Legionella spp. including Leg. pneumophila, Leg. pneumophila sg1 and Leg. anisa were identified, each of which might cause legionellosis. These results imply that potential opportunistic pathogens are common within MDWST sediments and could act as a source of microbial contamination, but need downstream growth to be of potential concern. The results imply that opportunistic pathogen risks may need to be managed by regular tank cleaning or other management practices.

Enteropathogens associated with acute diarrhea in children from households with high socioeconomic level in uruguay.

Infectious diarrhea, a common disease of children, deserves permanent monitoring in all social groups. To know the etiology and clinical manifestations of acute diarrhea in children up to 5 years of age from high socioeconomic level households, we conducted a descriptive, microbiological, and clinical study. Stools from 59 children with acute community-acquired diarrhea were examined, and their parents were interviewed concerning symptoms and signs. Rotavirus, adenovirus, and norovirus were detected by commercially available qualitative immunochromatographic lateral flow rapid tests. Salmonella, Campylobacter, Yersinia, and Shigella were investigated by standard bacteriological methods and diarrheagenic E. coli by PCR assays. We identified a potential enteric pathogen in 30 children. The most frequent causes of diarrhea were enteropathogenic E. coli (EPEC), viruses, Campylobacter, Salmonella, and Shiga-toxin-producing E. coli (STEC). Only 2 patients showed mixed infections. Our data suggest that children with viral or Campylobacter diarrhea were taken to the hospital earlier than those infected with EPEC. One child infected with STEC O26 developed “complete” HUS. The microbiological results highlight the importance of zoonotic bacteria such as atypical EPEC, Campylobacter, STEC, and Salmonella as pathogens associated with acute diarrhea in these children. The findings also reinforce our previous communications about the regional importance of non-O157 STEC strains in severe infant food-borne diseases.

Prevalence of Blastocystis in Shelter-Resident and Client-Owned Companion Animals in the US Pacific Northwest

Domestic dogs and cats are commonly infected with a variety of protozoan enteric parasites, including Blastocystis spp. In addition, there is growing interest in Blastocystis as a potential enteric pathogen, and the possible role of domestic and in-contact animals as reservoirs for human infection. Domestic animals in shelter environments are commonly recognized to be at higher risk for carriage of enteropathogens. The purpose of this study was to determine the frequency of infection of shelter-resident and client-owned domestic dogs and cats with Blastocystis spp in the Pacific Northwest region of the USA. Fecal samples were collected from 103 shelter-resident dogs, 105 shelter-resident cats, 51 client-owned dogs and 52 client-owned cats. Blastocystis were detected and subtypes assigned using a nested PCR based on small subunit ribosomal DNA sequences. Shelter-resident animals were significantly more likely to test positive for Blastocystis (P<0.05 for dogs, P = 0.009 for cats). Sequence analysis indicated that shelter-resident animals were carrying a variety of Blastocystis subtypes. No relationship was seen between Blastocystis carriage and the presence of gastrointestinal disease signs in either dogs or cats. These data suggest that, as previously reported for other enteric pathogens, shelter-resident companion animals are a higher risk for carriage of Blastocystis spp. The lack of relationship between Blastocystis carriage and intestinal disease in shelter-resident animals suggests that this organism is unlikely to be a major enteric pathogen in these species.

Microbial quality and antibiotic resistant bacterial pathogens isolated from groundwater used by residents of Ongata Rongai, Kajiado North County, Kenya

Groundwater represents an important source of drinking water and its quality is currently threatened by a combination of over-abstraction and microbiological and chemical contamination. Nairobi, Kenya and its environs is plagued with un-planned dwelling residential settlements, with limited potable water sources which are often contaminated by bacterial pathogens. This coupled with increased incidences of antibiotic resistance among the pathogens is alarming. This study used the MPN technique to determine indicator organisms, and the agar diffusion method to determine resistance in isolated pathogenic bacteria. The total coliforms values recorded were as high as 1.12x102 (±8.8x101) MPN/100 ml, fecal coliform loads were 8.63(±7.01) MPN/100 ml for the shopping centre. Total bacterial counts values recorded were as high as 5.64x104 (±1.77x104) CFU/ml at the shopping centre. Numerous organisms that are potential enteric pathogens such as Vibrio sp, Salmonella sp., Shigella sp., P. aeruginosa and E. coli were isolated from the water samples. There was high resistance to many antibiotics particularly sulphamoxazole (98.5%), kanamycin (95.3%) and ampicillin (87.5%). The most active antibiotics were chloramphenicol with resistance level of 45.4% and streptomycin (59.4%). The study indicates that water from the studied boreholes was not suitable for human consumption and therefore calls for urgent intervention. There is a high likelihood that congestion and lack of proper waste and waste water management is responsible for contamination of aquifers in this region.Keywords: groundwater, contamination, coliforms, potable water, antibiotic resistance

Investigating turkey enteric coronavirus circulating in the Southeastern United States and Arkansas during 2012 and 2013.

Periodic monitoring of poultry flocks in the United States via molecular diagnostic methods has revealed a number of potential enteric viral pathogens in continuous circulation in turkeys and chickens. Recently turkey integrators in the Southeastern United States and Arkansas experienced an outbreak of moderate to severe enteritis associated with turkey enteric coronavirus (TCoV), and numerous enteric samples collected from turkey flocks in these areas tested positive for TCoV via real-time reverse-transcriptase PCR (RRT-PCR). This report details the subsequent sequence and phylogenetic analysis of the TCoV spike glycoprotein and the comparison of outbreak-associated isolates to sequences in the public database. TCoVs investigated during the present outbreak grouped geographically based upon state of origin, and the RRT-PCR assay was a good indicator of subsequent seroconversion by TCoV-positive turkey flocks.

An overview of calf diarrhea - infectious etiology, diagnosis, and intervention.

Calf diarrhea is a commonly reported disease in young animals, and still a major cause of productivity and economic loss to cattle producers worldwide. In the report of the 2007 National Animal Health Monitoring System for U.S. dairy, half of the deaths among unweaned calves was attributed to diarrhea. Multiple pathogens are known or postulated to cause or contribute to calf diarrhea development. Other factors including both the environment and management practices influence disease severity or outcomes. The multifactorial nature of calf diarrhea makes this disease hard to control effectively in modern cow-calf operations. The purpose of this review is to provide a better understanding of a) the ecology and pathogenesis of well-known and potential bovine enteric pathogens implicated in calf diarrhea, b) describe diagnostic tests used to detect various enteric pathogens along with their pros and cons, and c) propose improved intervention strategies for treating calf diarrhea.

Escherichia coli Contamination of Lettuce Grown in Soils Amended with Animal Slurry

A pilot study was conducted to assess the transfer of Escherichia coli from animal slurry fertilizer to lettuce, with E. coli serving as an indicator of fecal contamination and as an indicator for potential bacterial enteric pathogens. Animal slurry was applied as fertilizer to three Danish agricultural fields prior to the planting of lettuce seedlings. At harvest, leaves (25 g) of 10 lettuce heads were pooled into one sample unit (n = 147). Soil samples (100 g) were collected from one field before slurry application and four times during the growth period (n = 75). E. coli was enumerated in slurry, soil, and lettuce on 3M Petrifilm Select E. coli Count Plates containing 16 mg/liter streptomycin, 16 mg/liter ampicillin, or no antimicrobial agent. Selected E. coli isolates (n = 83) originating from the slurry, soil, and lettuce were genotyped by pulsed-field gel electrophoresis (PFGE) to determine the similarity of isolates. The slurry applied to the fields contained 3.0 to 4.5 log CFU/g E. coli. E. coli was found in 36 to 54% of the lettuce samples, streptomycin-resistant E. coli was found in 10.0 to 18.0% of the lettuce samples, and ampicillin-resistant E. coli in 0 to 2.0% of the lettuce samples (the detection limit was 1 log CFU/g). The concentration of E. coli exceeded 2 log CFU/g in 19.0% of the lettuce samples. No E. coli was detected in the soil before the slurry was applied, but after, E. coli was present until the last sampling day (harvest), when 10 of 15 soil samples contained E. coli. A relatively higher frequency of E. coli in lettuce compared with the soil samples at harvest suggests environmental sources of fecal contamination, e.g., wildlife. The higher frequency was supported by the finding of 21 different PFGE types among the E. coli isolates, with only a few common PFGE types between slurry, soil, and lettuce. The frequent finding of fecal-contaminated lettuce indicates that human pathogens such as Salmonella and Campylobacter can be present and represent food safety hazards.

Assessing multiple foodborne, waterborne and environmental exposures of healthy people to potential enteric pathogen sources: effect of age, gender, season, and recall period.

Information is lacking in Canada on the frequency of exposures of healthy people to enteric pathogen sources (i.e. water, food, animal contact) at the community level. This information is critical to develop more robust risk assessments and prioritize control measures. A 12-month-long cross-sectional telephone survey of 1200 healthy individuals in a sentinel community was performed. Survey respondents were divided into three recall period groups (3, 7, 14 days). The occurrence of 46 exposures (including water, animal contact, environmental contact and high-risk foods) was assessed per recall period. Effect of age, gender, and season on exposures was modelled and frequencies of exposure were extrapolated. Thirty-five exposures had similar occurrences across recall periods. Age was significant for 23 exposures, season for 18, and gender for three. Exposures that vary by age and season (i.e. bottled water, swimming, etc.) warrant consideration when investigating and analysing cases of enteric illness.

Risks Associated with High-Dose Lactobacillus rhamnosus in an Escherichia coli Model of Piglet Diarrhoea: Intestinal Microbiota and Immune Imbalances

Probiotic could be a promising alternative to antibiotics for the prevention of enteric infections; however, further information on the dose effects is required. In this study, weanling piglets were orally administered low- or high-dose Lactobacillus rhamnosus ACTT 7469 (1010 CFU/d or 1012 CFU/d) for 1 week before F4 (K88)-positive Escherichia coli challenge. The compositions of faecal and gastrointestinal microbiota were recorded; gene expression in the intestines was assessed by real-time PCR; serum tumour necrosis factor-α (TNF-α) concentrations and intestinal Toll-like receptor 4 (TLR4) were detected by ELISA and immunohistochemistry, respectively. Unexpectedly, high-dose administration increased the incidence of diarrhoea before F4+ETEC challenge, despite the fact that both doses ameliorated F4+ETEC-induced diarrhoea with increased Lactobacillus and Bifidobacterium counts accompanied by reduced coliform shedding in faeces. Interestingly, L. rhamnosus administration reduced Lactobacillus and Bifidobacterium counts in the colonic contents, and the high-dose piglets also had lower Lactobacillius and Bacteroides counts in the ileal contents. An increase in the concentration of serum TNF-α induced by F4+ETEC was observed, but the increase was delayed by L. rhamnosus. In piglets exposed to F4+ETEC, jejunal TLR4 expression increased at the mRNA and protein levels, while jejunal interleukin (IL)-8 and ileal porcine β-defensins 2 (pBD2) mRNA expression increased; however, these increases were attenuated by administration of L. rhamnosus. Notably, expression of jejunal TLR2, ileal TLR9, Nod-like receptor NOD1 and TNF-α mRNA was upregulated in the low-dose piglets after F4+ETEC challenge, but not in the high-dose piglets. These findings indicate that pretreatment with a low dose of L. rhamnosus might be more effective than a high dose at ameliorating diarrhoea. There is a risk that high-dose L. rhamnosus pretreatment may negate the preventative effects, thus decreasing the prophylactic benefits against potential enteric pathogens. Our data suggest a safe threshold for preventative use of probiotics in clinical practice.

Evaluation of the bacteriological and physicochemical quality of water supplies in Nsukka, Southeast, Nigeria

The bacteriological and physicochemical quality of various water samples from bore hole, dug well and spring, collected from ten different locations within Nsukka were determined. Total viable and coliform counts were evaluated using the standard plate count method and the most probable number (MPN) technique, respectively. The physicochemical parameters were analyzed using standard methods. The mean total bacteria count of the water samples ranged as follows: bore hole (0.92 × 10 4 to 1.41 × 10 4 ) cfu/ml, well water (1.80 × 10 4 to 2.40 × 10 4 ) cfu/ml and spring water (0.78 × 10, 4 to 1.06 × 10 4 ) cfu/ml. The mean total coliform count of the samples in (MPN/100 ml) ranged as follows: bore hole (10 to 15), well water (14 to 18) and spring water (8 to 10). The isolated and identified bacteria were Enterobacter spp., Alcaligenes spp., Escherichia coli , Proteus spp., Klebsiella spp., Pseudomonas aeruginosa , Acinetobacter spp., Staphylococcus aureus and Bacillus sp. The physicochemical values of the water samples ranged as follows: pH (5.6 to 6.4), dissolved oxygen (DO) (5.4 to 6.4), biochemical oxygen demand (BOD) (10.0 to 20.4), chloride (1.6 to 2.3) mg L -1 , total hardness (48.6 to 68.0) mg L -1 , total dissolved solids (6.3 to 9.7) mg L -1 , sulphate (2.0 to 3.4) mg L -1 and nitrate (1.2 to 4.1) mg L -1 . The water supply sources in the present study have good physicochemical attributes for human consumption but the presence of E. coli and other potential enteric pathogens indicated faecal matter contamination of the water implying that they are not suitable for human consumption. Keywords: Drinking water, bacteriological and physicochemical quality, coliforms

Evaluation of the bacteriological and physicochemical quality of water supplies in Nsukka, Southeast, Nigeria

The bacteriological and physicochemical quality of various water samples from bore hole, dug well and spring, collected from ten different locations within Nsukka were determined. Total viable and coliform counts were evaluated using the standard plate count method and the most probable number (MPN) technique, respectively. The physicochemical parameters were analyzed using standard methods. The mean total bacteria count of the water samples ranged as follows: bore hole (0.92 × 104 to 1.41 × 104) cfu/ml, well water (1.80 × 104 to 2.40 × 104) cfu/ml and spring water (0.78 × 104to 1.06 × 104) cfu/ml. The mean total coliform count of the samples in (MPN/100 ml) ranged as follows: bore hole (10 to 15), well water (14 to 18) and spring water (8 to 10). The isolated and identified bacteria were Enterobacter spp., Alcaligenes spp.,Escherichia coli, Proteus spp., Klebsiella spp., Pseudomonas aeruginosa,Acinetobacter spp., Staphylococcus aureus and Bacillus sp. The physicochemical values of the water samples ranged as follows: pH (5.6 to 6.4), dissolved oxygen (DO)(5.4 to 6.4), biochemical oxygen demand (BOD) (10.0 to 20.4), chloride (1.6 to 2.3) mg L-1, total hardness (48.6 to 68.0) mg L-1, total dissolved solids (6.3 to 9.7) mg L-1, sulphate (2.0 to 3.4) mg L-1 and nitrate (1.2 to 4.1) mg L-1. The water supply sources in the present study have good physicochemical attributes for human consumption but the presence of E. coli and other potential enteric pathogens indicated faecal matter contamination of the water implying that they are not suitable for human consumption. Key words: Drinking water, bacteriological and physicochemical quality, coliforms.

Gene-centric metagenomics analysis of feline intestinal microbiome using 454 junior pyrosequencing

The feline gastrointestinal microbiota have direct influence on feline health and also human health as a reservoir for potential zoonotic pathogens and antibiotic resistant bacterial strains. In order to describe the feline gastrointestinal microbial diversity, fecal samples from cats have been characterized using both culture-dependent and culture-independent methods. However, data correlating total microbial composition and their functions are lacking. Present descriptive study evaluated both phylogenetic and metabolic diversity of the feline intestinal microbiota using GS Junior titanium shotgun pyrosequencing. A total of 152,494 pyrosequencing reads (5405 assembled contigs) were generated and classified into both phylogenetic and metabolic profiles of the feline intestinal microbiota. The Bacteroides/Chlorobi group was the most predominant bacterial phylum comprising ~68% of total classified diversity, followed by Firmicutes (~13%) and Proteobacteria (~6%) respectively. Archaea, fungi and viruses made up the minor communities in the overall microbial diversity. Interestingly, this study also identified a range of potential enteric zoonotic pathogens (0.02–1.25%) and genes involved in antimicrobial resistance (0.02–0.7%) in feline fecal materials. Based on clustering among nine gastrointestinal metagenomes from five different monogastric hosts (dog, human, mice, cat and chicken), the cat metagenome clustered closely together with chicken in both phylogenetic and metabolic level (>80%). Future studies are required to provide deeper understandings on both intrinsic and extrinsic effects such as impact of age, genetics and dietary interventions on the composition of the feline gastrointestinal microbiome.

Escherichia coli, enterococci, and Bacteroides thetaiotaomicron qPCR signals through wastewater and septage treatment

Fecal indicators such as Escherichia coli and enterococci are used as regulatory tools to monitor water with 24 h cultivation techniques for possible input of sewage or feces and presence of potential enteric pathogens yet their source (human or animal) cannot be determined with routine methods. This critical uncertainty has furthered water pollution science toward new molecular approaches. Members of Bacteroides genus, such as Bacteroides thetaiotaomicron are found to have features that allow their use as alternative fecal indicators and for Microbial Source Tracking (MST). The overall aim of this study was to evaluate the concentration and fate of B. thetaiotaomicron, throughout a wastewater treatment facility and septage treatment facility. A large number of samples were collected and tested for E. coli and enterococci by both cultivation and qPCR assays. B. thetaiotaomicron qPCR equivalent cells (mean: 1.8 × 10 7/100 mL) were present in significantly higher concentrations than E. coli or enterococci in raw sewage and at the same levels in raw septage. The removal of B. thetaiotaomicron target qPCR signals was similar to E. coli and enterococci DNA during the treatment of these wastes and ranged from 3 to 5 log 10 for wastewater and was 7 log 10 for the septage. A significant correlation was found between B. thetaiotaomicron marker and each of the conventional indicators throughout the waste treatment process for both raw sewage and septage. A greater variability was found with enterococci when compared to E. coli, and CFU and equivalent cells could be contrasted by various treatment processes to examine removal and inactivation via septage and wastewater treatment. These results are compared and contrasted with other qPCR studies and other targets in wastewater samples providing a view of DNA targets in such environments.

Microbial quality, diversity and antibiotic susceptibility profiles of bacterial isolates from borehole water used by schools in Greater Giyani Municipality, Mopani District, South Africa

In the present study, the microbial quality of several boreholes, used by rural schools in Greater Giyani Municipality, was assessed over a six months period to determine their safety for human consumption and to highlight the potential occurrence of water-borne diseases. The microbiological quality of the water sources was performed using the membrane filtration technique, while standard culture methods were used for bacteria isolation. The MicroScan was used for identification and antibiotic susceptibility profiles of isolated potentially pathogenic bacteria. The results obtained indicated that the water quality of the boreholes was poor over the study period (June to October, 2009). Indicator organisms were higher than the acceptable maximum limits prescribed by the South African Department of Water Affairs and Forestry (DWAF) and the World Health Organisation. Numerous organisms that are potential enteric pathogens such as Vibriospp., Shigella species and Klebsiella spp, were isolated throughout the study period. There was high resistance to many antibiotics particularly ampicillin (92%), cefazolin (95.9%), cefuroxime (91.7%) and cefoxitin (92.6%). The most active antibiotics were tobramycin with resistance level of 8.7% and levofloxacin (23.0%). The study indicates that water from the studied boreholes was not suitable for human consumption and may pose a serious threat to the health of consumers and therefore calls for urgent intervention. High level of antibiotic resistance is of concern in the management of infections caused by these organisms. Further studies are needed to identify the sources of contamination in order to curb the negative effect of contaminated water particularly in children. Key words: Antibiotic resistance, bacterial indicators, children, water quality, borehole, schools, South Africa.

Recognition and prevention of hospital-associated enteric infections in the intensive care unit

The objectives of this article were to review the causes and extent of hospital-associated infectious diarrhea and associated risks in the general hospital ward and intensive care unit (ICU), to compare microorganisms with similar symptoms to aid in recognition that will lead to timely and appropriate treatment and control measures, and to propose infection prevention protocols that could decrease human process errors in the ICU. This literature review describes epidemiology, comparison of microbial characteristics for potential hospital-associated enteric pathogens, diagnosis, and prevention, especially if important in the ICU, and particularly in regard to Clostridium difficile. Enteric organisms that most commonly cause hospital-associated infectious diarrhea in acute care settings and the ICU are C. difficile, rotavirus, and norovirus, although others may also be important, particularly in developing countries. To recognize and control infectious diarrhea successfully in the ICU, intensivists should be aware that epidemiology, risks, and prevention measures may differ between these microorganisms. In addition, intensivists should be ready to implement systems changes related to notification, isolation precautions and prevention, and environmental cleaning in the ICU.

Impact of organic and conventional management on the phyllosphere microbial ecology of an apple crop.

Bacterial communities associated with the phyllosphere of apple trees (Malus domestica cv. Enterprise) grown under organic and conventional management were assessed to determine if increased biological food safety risks might be linked with the bacterial communities associated with either treatment. Libraries of 16S rRNA genes were generated from phyllosphere DNA extracted from a wash made from the surfaces of leaves and apples from replicated organic and conventional treatments. 16S rRNA gene libraries were analyzed with software designed to identify statistically significant differences between bacterial communities as well as shared and unique phylotypes. The identified diversity spanned eight bacterial phyla and 14 classes in the pooled organic and conventional libraries. Significant differences between organic and conventional communities were observed at four of six time points (P < 0.05). Despite the identification of significantly diverse microfloras associated with organic and conventional treatments, no detectable differences in the presence of potential enteric pathogens could be associated with either organic or conventional management. Neither of the bacterial genera most commonly associated with produce-related illness outbreaks (Salmonella and Escherichia) was observed in any of the libraries. The impressive bacterial diversity that was documented in this study provides a valuable contribution to our developing understanding of the total microbial ecology associated with the preharvest phyllospheres of food crops. The fact that organic and conventional phyllosphere bacterial communities were significantly different at numerous time points suggests that crop management methods may influence the bacterial consortia associated with the surfaces of fruits and vegetables.

Role of RNA polymerase sigma-factor (RpoS) in induction of glutamate-dependent acid-resistance of Escherichia albertii under anaerobic conditions

Escherichia albertii is a potential enteric food-borne pathogen with poorly defined genetic and biochemical properties. Acid resistance is perceived to be an important property of enteric pathogens, enabling them to survive passage through stomach acidity so that they may colonize the mammalian gastrointestinal tract. We analyzed glutamate-dependent acid-resistance pathway (GDAR) in five E. albertii strains that have been identified so far. We observed that the strains were unable to induce GDAR under aerobic growth conditions. Mobilization of the rpoS gene restored aerobic induction of this acid-resistance pathway, indicating that all five strains may have a dysfunctional sigma-factor. On the other hand, under anaerobic growth conditions where GDAR is induced in an RpoS-independent manner (i.e. in Shigella spp. and Escherichia coli O157:H7 strains), only three out of five E. albertii strains successfully induced GDAR. The remainder of the two strains exhibited dependence on functional RpoS even under anaerobic conditions to express GDAR, a regulatory function previously considered to be redundant. The data indicate that certain E. albertii strains may have an alternate RpoS-dependent pathway for acid-resistance under anaerobic growth conditions.

Ecological Characterization of the Colonic Microbiota of Normal and Diarrheic Dogs

We used terminal restriction fragment polymorphism (T-RFLP) analysis to assess (1) stability of the fecal microbiota in dogs living in environments characterized by varying degrees of exposure to factors that might alter the microbiota and (2) changes in the microbiota associated with acute episodes of diarrhea. Results showed that the healthy canine GI tract harbors potential enteric pathogens. Dogs living in an environment providing minimal exposure to factors that might alter the microbiota had similar microbiotas; the microbiotas of dogs kept in more variable environments were more variable. Substantial changes in the microbiota occurred during diarrheic episodes, including increased levels of Clostridium perfringens, Enterococcus faecalis, and Enterococcus faecium. When diet and medications of a dog having a previously stable microbiota were changed repeatedly, the microbiota also changed repeatedly. Temporal trend analysis showed directional changes in the microbiota after perturbation, a return to the starting condition, and then fluctuating changes over time.