Bacterial Communities Associated with the Surfaces of Fresh Fruits and Vegetables

Fresh fruits and vegetables can harbor large and diverse populations of bacteria. However, most of the work on produce-associated bacteria has focused on a relatively small number of pathogenic bacteria and, as a result, we know far less about the overall diversity and composition of those bacterial communities found on produce and how the structure of these communities varies across produce types. Moreover, we lack a comprehensive view of the potential effects of differing farming practices on the bacterial communities to which consumers are exposed. We addressed these knowledge gaps by assessing bacterial community structure on conventional and organic analogs of eleven store-bought produce types using a culture-independent approach, 16 S rRNA gene pyrosequencing. Our results demonstrated that the fruits and vegetables harbored diverse bacterial communities, and the communities on each produce type were significantly distinct from one another. However, certain produce types (i.e., sprouts, spinach, lettuce, tomatoes, peppers, and strawberries) tended to share more similar communities as they all had high relative abundances of taxa belonging to the family Enterobacteriaceae when compared to the other produce types (i.e., apples, peaches, grapes, and mushrooms) which were dominated by taxa belonging to the Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria phyla. Although potentially driven by factors other than farming practice, we also observed significant differences in community composition between conventional and organic analogs within produce types. These differences were often attributable to distinctions in the relative abundances of Enterobacteriaceae taxa, which were generally less abundant in organically-grown produce. Taken together, our results suggest that humans are exposed to substantially different bacteria depending on the types of fresh produce they consume with differences between conventionally and organically farmed varieties contributing to this variation.     

铜绿丽金龟蛴螬肠道产消化酶细菌的分离与鉴定

目的 分离不同生态环境中铜绿丽金龟蛴螬肠道中产消化酶细菌,明确生态环境和食物对其肠道共生细菌产酶活性的影响。方法 2016年7月,自野外林间废弃的菜园和花生田分别采集蛴螬,鉴定出铜绿丽金龟蛴螬后,采用传统分离培养法对其肠道中的共生细菌进行分离鉴定,利用平板透明圈法分别进行淀粉酶、蛋白酶、脂肪酶和纤维素酶等的分泌能力测定。结果 自铜绿丽金龟蛴螬肠道中共分离出细菌24株,其中在野生铜绿丽金龟蛴螬体内分离出9株,花生田铜绿丽金龟蛴螬体内分离出15株。野生蛴螬体内分离的细菌中,产淀粉酶菌株1株,产蛋白酶菌株4株,产纤维素酶菌株1株,产脂肪酶菌株1株;花生田蛴螬体内分离的细菌中,产淀粉酶菌株1株,产蛋白酶菌株3株,产纤维素酶菌株9株,未分离到产脂肪酶的菌株。结论 野生铜绿丽金龟蛴螬肠道细菌中产蛋白酶种类较多,占44.4%;花生田铜绿丽金龟蛴螬肠道细菌中产纤维素酶菌株最多,所占比例可达60.0%,反映出生境和食性与昆虫肠道共生细菌产消化酶活性的相适应性。     

Sources and survival of Listeria monocytogenes on fresh,leafy produce

Listeria monocytogenes is an intracellular human pathogen which enters the body through contaminated food stuffs and is known to contaminate fresh leafy produce such as spinach, lettuce and rocket. Routinely, fresh leafy produce is grown and processed on a large scale before reaching the consumer through various products such as sandwiches and prepared salads. From farm to fork, the fresh leafy produce supply chain (FLPSC) is complex and contains a diverse range of environments where L. monocytogenes is sporadically detected during routine sampling of produce and processing areas. This review describes sources of the bacteria in the FLPSC and outlines the physiological and molecular mechanisms behind its survival in the different environments associated with growing and processing fresh produce. Finally, current methods of source tracking the bacteria in the context of the food supply chain are discussed with emphasis on how these methods can provide additional, valuable information on the risk that L. monocytogenes isolates pose to the consumer.     

环腺苷酸在灰盖鬼伞子实体发育中的效用研究

通过测试ｃＡＭＰ,子实体浸提液对灰盖鬼伞（Ｃｏｐｒｉｎｕｓ　ｃｉｎｅｒｅｕｓ）双核体菌丝的子实体诱导测试研究及通过用腺苷分别抑制ｃＡＭＰ在子实体发育各阶段的合成,对ｃＡＭＰ在灰盖克伞子实体发育中的影响进行了研究。结果表明：ｃＡＭＰ及子实体浸提液对灰盖鬼伞双核体菌丝的子实体形成并无诱导信号作用,阻止ｃＡＭＰ的合成延缓了子实体原基的发生,菌盖的形成,担孢子梗的形成,也延缓了质配和担孢子的发生,但菌柄的延长,子实体的成熟,担孢子的着色与释放则不受ｃＡＭＰ合成受阻的影响。     

Survival of viruses on fresh produce, using MS2 as a surrogate for norovirus

AIMS: To study the survival and removal of viruses from fresh fruit and vegetables using the bacteriophage MS2 as a potential surrogate for noroviruses. METHOD AND RESULTS: Survival of MS2 in buffer and on fresh produce was studied at 4, 8 and 22 degrees C. At 4 and 8 degrees C a reduction of <1 log10 was observed after 50 days in buffer; however a reduction in excess of 1 log10 occurred within 9 days at 22 degrees C. Similar results were obtained with fresh produce with virus survival times exceeding the shelf life of the produce. In washing experiments, using a chlorine wash (100 ppm), in all but one case <1.5 log10 MS2 bacteriophage was removed from fruit and vegetables. The mean across all produce types was 0.89 log10. With potable water, reduction was lower (0.3 log mean across all produce types). CONCLUSIONS: MS2 survived for prolonged periods, both in buffer and on fresh produce, at temperatures relevant to chilled foods. It was not removed effectively by chlorine washing. SIGNIFICANCE AND IMPACT OF THE STUDY: Bacteriophage MS2 has been evaluated as a potential surrogate for noroviruses on fresh produce. Experimental results together with current knowledge of norovirus resistance and survival indicate that MS2 could be used as an effective surrogate in future evaluations.     

Inactivation of a human norovirus surrogate by high-pressure processing: effectiveness, mechanism, and potential application in the fresh produce industry

Fresh produce is often a high-risk food for norovirus contamination because it can become contaminated at both preharvest and postharvest stages and it undergoes minimal or no processing. Currently, there is no effective method to eliminate the viruses from fresh produce. This study systematically investigated the effectiveness of high-pressure processing (HPP) on inactivating murine norovirus (MNV-1), a surrogate for human norovirus, in aqueous medium and fresh produce. We demonstrated that MNV-1 was effectively inactivated by HPP. More than a 5-log-PFU/g reduction was achieved in all tested fresh produce when it was pressurized at 400 MPa for 2 min at 4°C. We found that pressure, pH, temperature, and food matrix affected the virus survival in foods. MNV-1 was more effectively inactivated at 4°C than at 20°C in both medium and fresh produce. MNV-1 was also more sensitive to HPP at neutral pH than at acidic pH. We further demonstrated that disruption of viral capsid structure, but not degradation of viral genomic RNA, is the primary mechanism of virus inactivation by HPP. However, HPP does not degrade viral capsid protein, and the pressurized capsid protein was still antigenic. Overall, HPP had a variable effect on the sensorial quality of fresh produce, depending on the pressure level and type of product. Taken together, HPP effectively inactivated a human norovirus surrogate in fresh produce with a minimal impact on food quality and thus can provide a novel intervention for processing fruits intended for frozen storage and related products such as purees, sauces, and juices.     

Wolbachia requirement for oogenesis: occurrence within the genus Asobara (Hymenoptera, Braconidae) and evidence for intraspecific variation in A. tabida

Wolbachia are symbiotic bacteria that induce a diversity of phenotypes on their numerous invertebrate host species. In the wasp Asobara tabida (Braconidae), each individual harbours three Wolbachia strains: wAtab3, which is required for host oogenesis, and wAtab1 and wAtab2, that do not have this function but induce cytoplasmic incompatibility. In this study, we surveyed and identified Wolbachia strains in four additional Asobara species. We detected Wolbachia in one of these species, but both the identity (based on wsp gene) and prevalence of the Wolbachia detected in natural population indicate that this host species is not dependent on Wolbachia for oogenesis. We also compared A. tabida lines of different geographical origin for their dependence on Wolbachia. All individuals from 16 A. tabida lines proved to be infected by the three Wolbachia strains wAtab1, wAtab2 and wAtab3, but, interestingly, we found variation among lines in the degree to which females were dependent on Wolbachia to produce their oocytes. In three lines, aposymbiotic females (cured from the three Wolbachia strains by antibiotics) can produce some oocytes. However, these aposymbiotic females produce fewer and smaller oocytes than symbiotic ones, and the larvae they produce die before full development. Thus, depending on which nuclear genotype they have, A. tabida females depend on Wolbachia either because they fail to produce any oocyte or because the few oocytes they do produce generate unviable offspring. We discuss the implications of these findings for the understanding of the physiological and genetic deficiency of aposymbiotic females.     

Connective tissues: signalling by tenascins

Different connective tissue cells secrete different types of tenascins. These glycoproteins contribute to extracellular matrix (ECM) structure and influence the physiology of the cells in contact with the tenascin containing environment. Tenascin-C expression is regulated by mechanical stress. It shows highest expression in connective tissue surrounding tumors, in wounds and in inflamed tissues where it may regulate cell morphology, growth, and migration by activating diverse intracellular signalling pathways. Thus, integrin and syndecan signalling is influenced by tenascin-C and the levels and/or activies of several proteins involved in intracellular signalling pathways are regulated by its presence. Tenascin-X is important for the proper deposition of collagen fibers in dermis and patients with a tenascin-X deficiency suffer from Ehlers Danlos syndrome. Tenascin-R (and -C) is prominent in the nervous system and has an impact on neurite outgrowth and synaptic functions, and tenascin-W is found in the extracellular matrix of bone, muscle, and kidney. Cell facts:bone: osteoblasts produce tenascin-C, -W cartilage: perichondrial cells produce tenascin-C tendon: fibroblasts produce tenascin-C smooth muscle cells produce tenascin-W, -C skeletal muscle: endo-, peri-, and epimysial fibroblasts produce tenascin-X dermal fibroblasts produce tenascin-X tumors: stromal fibroblasts produce tenascin-C wounds: fibroblasts produce tenascin-C nervous system: glial cells produce tenascin-R, -C, -X.     

温度对甲烷产生和氧化的影响

综述了温度对土壤产甲烷和氧化甲烷的影响及其机制．温度主要通过土壤中产甲烷菌的优势菌发生更替来改变土壤的产甲烷能力．较高温条件下产甲烷菌以乙酸和H2／CO2都能利用的甲烷八叠球菌(Methanosarcinaceae)为主,使得土壤处于较高的产甲烷状态．较低温条件下产甲烷菌以只能利用乙酸的甲烷毛菌(Methanosaetaceae)为主,土壤形成甲烷的能力相对较弱．温度提高可以显著地增加甲烷的产生,Q10为1．5-28,平均4．1,但是温度效应明显受控于底物浓度,提高底物浓度降低了产甲烷菌对底物的亲和力,相应地增加了度效应,因此在较低温条件下提高底物浓度可以促进甲烷的产生．温度对大气甲烷氧化的影响弱于产甲烷,甲烷氧化菌较少受温度变化的影响,即便在较低温条件下,土壤也具有一定的氧化大气甲烷能力,原因尚不清楚,可能与甲烷氧化菌对大气甲烷具有较高的亲和力有关,有待进一步研究．     

Effects of caerulein + haloperidol on amphetamine-induced locomotor stereotypy in rats

The combination of haloperidol + caerulein has been reported to produce a long-lasting reduction of amphetamine-induced hyperlocomotions in rats. This study was designed to replicate those findings and to determine whether haloperidol + caerulein produce any unique effect on amphetamine-induced locomotor stereotypy. In two experiments, haloperidol + caerulein failed to produce a long-lasting reduction in amphetamine-induced hyperlocomotions. Although haloperidol reduced the locomotor stereotypy produced by higher doses of amphetamine, caerulein had no effect, either alone or combined with haloperidol.     

Variation in the abillties of different strains of Drosophila melanogaster to utilize diverse carbon sources

In several experiments, flies of different geographic origins have been tested for their abilities to produce adult progeny on culture media containing primarily one or the other of several sugars. Flies of different origins differ in their abilities to produce progeny on a given sugar; flies of a single origin differ on different sugars. The data reveal a strong strain-sugar interaction as well. Strains of flies maintained for two or more years by mass transfer on culture media containing one or the other of several sugars, including xylose and lactose, adapt to that culture medium. Hybrid flies-either between lines within localities or between localities-are best able to produce offspring on xylose-containing medium.     

Male field crickets that provide reproductive benefits to females incur higher costs

Abstract.  1. Females often select mates based on signals correlated with the quality of the direct benefits that males will provide to them. A male's quality as a mate and the structure of his mating signals may covary because both traits are energetically expensive for males to produce and because both traits are affected by short-term changes in nutritional condition.
2. In the variable field cricket, Gryllus lineaticeps , previous work has shown that females receive reproductive benefits from males that produce higher chirp rates and lifespan benefits from males that produce longer chirp durations, even when they only receive the sperm and seminal fluid contained in male spermatophores. Higher chirp rates are energetically expensive for males to produce, and chirp rate is strongly affected by diet quality, whereas longer chirp durations do not appear to be expensive for males to produce, and chirp duration does not appear to be affected by male diet quality. In this study two hypotheses were tested about the energetic costs of spermatophore production: (1) that spermatophores are expensive for males to produce and (2) that males providing greater direct benefits to females incur higher costs of spermatophore production.
3. Males that were provided with a lower quality diet took longer to produce a new spermatophore. This result suggests that spermatophores are costly for males to produce.
4. Males that produced higher chirp rates took longer to produce a new spermatophore. This result suggests that male chirp rate and female reproductive benefits may covary because both traits are energetically expensive for males to produce and thus are affected by male nutritional condition. There was no association, however, between male chirp duration and spermatophore production time.     

An analysis of water flow in tube-living animals

Water flow has been studied in six tube-dwelling animals that have different pumping mechanisms and layout of their tube systems. The characteristics of the pumping mechanisms and the resistance of the tube systems have been found. Cilia act as impeller pumps and can produce large rates of flow when arranged in parallel, but may produce sufficient flow for small, long thin bodied animals when arranged in series. Larger vermiform animals must use piston mechanism to produce sufficient rates of flow and the high pressures they can produce do not seem to be of use to the animals during normal pumping. Animals with rigid limbs can use these to impel water and produce high rates of flow. Echinocardium, which has a globular body, must match the flow at the inflow and outflow points on the test to the flow over the circumference and has special ciliated spines at these sites to boost flow.     

Production of branches from unsuccessful primary germ tubes of conidia of Erysiphe graminis f. sp. tritici on wheat leaves

Confusion exists regarding nomenclature and possible significance of outgrowths produced by conidial primary germ tubes (PGT) of Erysiphe graminis f. sp. tritici Em. Marchai on wheat leaves. Production of these outgrowths has been taken as a criterion of successful host-parasite relationship. However, such outgrowths have been observed to have developed from 12.3 % of the unsuccessful PGT on a resistant wheat and 9.2 % of the unsuccessful PGT on a susceptible wheat.It is proposed that these outgrowths may be called PGT branches which may develop whether the penetration by PGT is successful or not. In case the PGT penetration is successful, then such a PGT branch may be called a secondary hypha. These branches from unsuccessful PGT may also produce host responses in the form of halos in the host cell-walls or may also penetrate the host cells successfully and produce apparently healthy (normal) haustoria. Both PGT branches and the secondary hyphae may be called functional when they produce either host responses in the form of halos or penetrate successfully and produce haustoria, or produce both halos and haustoria.     

phzO, a gene for biosynthesis of 2-hydroxylated phenazine compounds in Pseudomonas aureofaciens 30-84

Certain strains of root-colonizing fluorescent Pseudomonas spp. produce phenazines, a class of antifungal metabolites that can provide protection against various soilborne root pathogens. Despite the fact that the phenazine biosynthetic locus is highly conserved among fluorescent Pseudomonas spp., individual strains differ in the range of phenazine compounds they produce. This study focuses on the ability of Pseudomonas aureofaciens 30-84 to produce 2-hydroxyphenazine-1-carboxylic acid (2-OH-PCA) and 2-hydroxyphenazine from the common phenazine metabolite phenazine-1-carboxylic acid (PCA). P. aureofaciens 30-84 contains a novel gene located downstream from the core phenazine operon that encodes a 55-kDa aromatic monooxygenase responsible for the hydroxylation of PCA to produce 2-OH-PCA. Knowledge of the genes responsible for phenazine product specificity could ultimately reveal ways to manipulate organisms to produce multiple phenazines or novel phenazines not previously described.     

Effect of curli expression and hydrophobicity of Escherichia coli O157:H7 on attachment to fresh produce surfaces

Aim: To investigate the effect of curli expression on cell hydrophobicity, biofilm formation and attachment to cut and intact fresh produce surfaces. Methods and Results: Five Escherichia coli O157:H7 strains were evaluated for curli expression, hydrophobicity, biofilm formation and attachment to intact and cut fresh produce (cabbage, iceberg lettuce and Romaine lettuce) leaves. Biofilm formation was stronger when E. coli O157:H7 were grown in diluted tryptic soy broth (1 : 10). In general, strong curli‐expressing E. coli O157:H7 strains 4406 and 4407 were more hydrophobic and attached to cabbage and iceberg lettuce surfaces at significantly higher numbers than other weak curli‐expressing strains. Overall, E. coli O157:H7 populations attached to cabbage and lettuce (iceberg and Romaine) surfaces were similar (P > 0·05), indicating produce surfaces did not affect (P < 0·05) bacterial attachment. All E. coli O157:H7 strains attached rapidly on intact and cut produce surfaces. Escherichia coli O157:H7 attached preferentially to cut surfaces of all produce types; however, the difference between E. coli O157:H7 populations attached to intact and cut surfaces was not significant (P > 0·05) in most cases. Escherichia coli O157:H7 attachment and attachment strength (S_R) to intact and cut produce surfaces increased with time. Conclusions: Curli‐producing E. coli O157:H7 strains attach at higher numbers to produce surfaces. Increased attachment of E. coli O157:H7 on cut surfaces emphasizes the need for an effective produce wash to kill E. coli O157:H7 on produce. Significance and Impact of the Study: Understanding the attachment mechanisms of E. coli O157:H7 to produce surfaces will aid in developing new intervention strategies to prevent produce outbreaks.     

Survival of Salmonella hadar after washing disinfection of minimally processed spinach

Washing disinfection with chlorine is widely used to reduce the initial microbiological load during the preparation of minimally processed vegetables. The effects of initial concentration of chlorine, time and the liquid volume:produce weight ratio on the reduction of Salmonella counts on inoculated spinach were evaluated using response surface methodology. Initial chlorine concentration, time and the interaction between them had a significant effect on reduction of Salmonella populations. However, the liquid volume:produce weight ratio did not have significant effects. The highest Salmonella reduction was around 1.2-1.4 log at 125 ppm during 8 min regardless of the water:produce ratio. According to the results, chlorination reduced Salmonella hadar population, but the complete elimination from the produce was not achieved.     

Untangling metabolic and communication networks: interactions of enterics with phytobacteria and their implications in produce safety

Recent outbreaks of vegetable-borne gastrointestinal illnesses across the globe demonstrate that human enteric pathogens can contaminate produce at any stage of production. Interactions of enterics with native plant-associated microbiota influence the microbiological safety of produce by affecting the attachment, persistence and proliferation of human pathogens on plants. Supermarket surveys have revealed that bacteria, but not fungi or mechanical damage, promote the growth of Salmonella enterica on produce. Field and laboratory studies have indicated that some plant pathogenic bacteria and fungi facilitate the entry and internalization of human pathogens in plants. Conversely, some phytobacteria, including those involved in biocontrol of plant diseases, significantly inhibit attachment and plant colonization by non-typhoidal Salmonella and enterovirulent Escherichia coli by producing antibiotics or competing for nutrients in the phyllosphere. In this review, we attempt to elucidate the mechanisms of interactions between human enteric pathogens and plant-associated microbiota, and describe how these interactions affect produce safety.     

A Farm to Fork Risk Assessment for the Use of Wastewater in Agriculture in Accra,Ghana

The need to minimise consumer risk, especially for food that can be consumed uncooked, is a continuing public health concern, particularly in places where safe sanitation and hygienic practices are absent. The use of wastewater in agriculture has been associated with disease risks, though its relative significance in disease transmission remains unclear. This study aimed at identifying key risk factors for produce contamination at different entry points of the food chain. Over 500 produce and ready-to-eat salad samples were collected from fields, markets, and kitchens during the dry and wet seasons in Accra, Ghana, and over 300 soil and irrigation water samples were collected. All samples were analysed for E. coli, human adenovirus and norovirus using standard microbiological procedures, and real time RT-PCR. Finally, critical exposures associated with microbial quality of produce were assessed through observations and interviews. The study found that over 80% of produce samples were contaminated with E. coli, with median concentrations ranging from 0.64 to 3.84 Log E. coli/g produce. Prepared salad from street food vendors was found to be the most contaminated (4.23 Log E. coli/g), and that consumption of salad exceeded acceptable health limits. Key risk factors identified for produce contamination were irrigation water and soil at the farm level. Storage duration and temperature of produce had a significant influence on the quality of produce sold at markets, while observations revealed that the washed water used to rinse produce before sale was dirty. The source of produce and operating with a hygiene permit were found to influence salad microbial quality at kitchens. This study argues for a need to manage produce risk factors at all domains along the food chain, though it would be more effective to prioritise at markets and kitchens due to cost, ease of implementation and public health significance.     

The use of a novel plate assay in a search for yeast mutants defective in deoxyribonucleases.

Methods by which the intracellular enzymes deoxyribonuclease, ribonuclease and protease can be assayed in whole colonies of Saccharomyces cerevisiae on agar plates are described. A search for mutants deficient in deoxyribonuclease has been carried out. Two types of mutant are described. One apparently fails to produce deoxyribonuclease, ribonuclease or protease on agar plates and the other apparently fails to produce deoxyribonuclease and ribonuclease.