Identification of volatile organic compounds produced by fluorescent pseudomonads on chicken breast muscle

Probabilistic Models to Predict the Growth Initiation Time for Pseudomonas spp. in Processed Meats Formulated with NaCl and NaNO2

This study developed probabilistic models to determine the initiation time of growth of Pseudomonas spp. in combinations with NaNO2 and NaCl concentrations during storage at different temperatures. The combination of 8 NaCl concentrations (0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, and 1.75%) and 9 NaNO2 concentrations (0, 15, 30, 45, 60, 75, 90, 105, and 120 ppm) were prepared in a nutrient broth. The medium was placed in the wells of 96-well microtiter plates, followed by inoculation of a five-strain mixture of Pseudomonas in each well. All microtiter plates were incubated at 4, 7, 10, 12, and 15℃ for 528, 504, 504, 360 and 144 h, respectively. Growth (growth initiation; GI) or no growth was then determined by turbidity every 24 h. These growth response data were analyzed by a logistic regression to produce growth/no growth interface of Pseudomonas spp. and to calculate GI time. NaCl and NaNO2 were significantly effective (p<0.05) on inhibiting Pseudomonas spp. growth when stored at 4-12℃. The developed model showed that at lower NaCl concentration, higher NaNO2 level was required to inhibit Pseudomonas growth at 4-12℃. However, at 15℃, there was no significant effect of NaCl and NaNO2. The model overestimated GI times by 58.2±17.5 to 79.4±11%. These results indicate that the probabilistic models developed in this study should be useful in calculating the GI times of Pseudomonas spp. in combination with NaCl and NaNO2 concentrations, considering the over-prediction percentage.

Production of bioactive volatiles by different Burkholderia ambifaria strains

Increasing evidence indicates that volatile compounds emitted by bacteria can influence the growth of other organisms. In this study, the volatiles produced by three different strains of Burkholderia ambifaria were analysed and their effects on the growth of plants and fungi, as well as on the antibiotic resistance of target bacteria, were assessed. Burkholderia ambifaria emitted highly bioactive volatiles independently of the strain origin (clinical environment, rhizosphere of pea, roots of maize). These volatile blends induced significant biomass increase in the model plant Arabidopsis thaliana as well as growth inhibition of two phytopathogenic fungi (Rhizoctonia solani and Alternaria alternata). In Escherichia coli exposed to the volatiles of B. ambifaria, resistance to the aminoglycoside antibiotics gentamicin and kanamycin was found to be increased. The volatile blends of the three strains were similar, and dimethyl disulfide was the most abundant compound. Sulfur compounds, ketones, and aromatic compounds were major groups in all three volatile profiles. When applied as pure substance, dimethyl disulfide led to increased plant biomass, as did acetophenone and 3-hexanone. Significant fungal growth reduction was observed with high concentrations of dimethyl di- and trisulfide, 4-octanone, S-methyl methanethiosulphonate, 1-phenylpropan-1-one, and 2-undecanone, while dimethyl trisulfide, 1-methylthio-3-pentanone, and o-aminoacetophenone increased resistance of E. coli to aminoglycosides. Comparison of the volatile profile produced by an engineered mutant impaired in quorum-sensing (QS) signalling with the corresponding wild-type led to the conclusion that QS is not involved in the regulation of volatile production in B. ambifaria LMG strain 19182.

Volatile mediated interactions between bacteria and fungi in the soil

Soil is one of the major habitats of bacteria and fungi. In this arena their interactions are part of a communication network that keeps microhabitats in balance. Prominent mediator molecules of these inter- and intraorganismic relationships are inorganic and organic microbial volatile compounds (mVOCs). In this review the state of the art regarding the wealth of mVOC emission is presented. To date, ca. 300 bacteria and fungi were described as VOC producers and approximately 800 mVOCs were compiled in DOVE-MO (database of volatiles emitted by microorganisms). Furthermore, this paper summarizes morphological and phenotypical alterations and reactions that occur in the organisms due to the presence of mVOCs. These effects might provide clues for elucidating the biological and ecological significance of mVOC emissions and will help to unravel the entirety of belowground' volatile-wired' interactions.

Volatile metabolites from some gram-negative bacteria

A survey of volatile organic compounds (VOCs) excreted from various Gram-negative bacteria (Pseudomonas spp., Serratia spp. and Enterobacter spp.) was carried out. Compounds were identified by gas chromatography-mass spectrometry. VOCs identified included dimethyl disulphide, dimethyl trisulphide and isoprene.

Microbial and biochemical spoilage of foods: an overview

During harvesting, processing and handling operations food may become contaminated with a wide range of microorganisms. Subsequently, during distribution and storage only a small fraction of these will develop and cause serious deteriorations. Which microorganisms will develop or what (bio)chemical reactions occur is dependent upon food derived or environmental factors. This paper will describe the main mechanisms involved in the loss of food quality for the most important food commodities. Food spoilage may be caused by a wide range of reactions including some that are mainly physical or chemical, others due to action of enzymes or microorganisms. The primary factors associated with food spoilage are associated with intrinsic food properties (e.g., endogenous enzymes, substrates, sensitivity for light, oxygen) and (cross)contamination during harvesting, slaughter and processing in combination with temperature abuse. For fresh foods the primary quality changes may be categorized as (i) bacterial growth and metabolism resulting in possible pH-changes and formation of toxic compounds, off-odours, gas and slime-formation, (ii) oxidation of lipids and pigments in fat-containing foods resulting in undesirable flavours, formation of compounds with adverse biological effects or discoloration. Although interrelated with the microbial spoilage, the last category is 'purely' chemical in nature and will, all other things being equal, increase in importance with decreasing temperature. Little is known about the relationship between microbial activity and (bio)chemical spoilage parameters under different packaging and storage conditions. Although there is much progress in the characterisation of the total microflora and metabolites developing during spoilage, not much is known about the identification of specific microorganisms in relation to food composition. Despite the fact that food spoilage is a huge economical problem world wide, it is obvious that the mechanisms and interaction leading to food spoilage are very poorly understood.

Responses of the sheep blowflies Lucilia sericata and L. cuprina to odour and the development of semiochemical baits

The literature relating to the attraction of the sheep blowflies Lucilia sericata and Lucilia cuprina to their ovine hosts is reviewed. The responses of the two species are similar and different components of the behaviour leading to host location and oviposition appear to involve at least two distinct sets of semiochemical cues. Activation, upwind orientation and landing appear to occur in response to putrefactive sulphur-rich volatiles, originating from bacterial decomposition products. Oviposition is elicited primarily by the presence of decomposition products. Oviposition is elicited primarily by the presence of ammonia-rich compounds; moisture, pheromones and tactile stimuli may also act as oviposition stimuli. There is a pronounced sex difference in the response of Lucilia to semiochemicals with a higher proportion of females attracted than males and a higher proportion of gravid than non-gravid females. While the mechanisms of host location by Lucilia are of intrinsic interest, understanding the responses to semiochemicals is important in the attempt to develop powerful synthetic baits for deployment with the traps or targets used for population sampling or suppression. The literature is discussed with respect to the development of synthetic semiochemical baits.

Inhibitory effect against pathogenic and spoilage bacteria of Pseudomonas strains isolated from spoiled and fresh fish

The antibacterial effects of 209 Pseudomonas strains isolated from spoiled iced fish and newly caught fish were assessed by screening target organisms in agar diffusion assays. One-third (67 strains) inhibited the growth of one or several of six target organisms (Escherichia coli, Shewanella putrefaciens, Aeromonas sobria, Pseudomonas fluorescens, Listeria monocytogenes, and Staphylococcus aureus), of which S. aureus and A. sobria were the most sensitive. The inhibitory action was most pronounced among the strains producing siderophores, and the presence of iron eliminated the antibacterial effect of two-thirds of the inhibitory strains. Siderophore-mediated competition for iron may explain the inhibitory activity of these strains. All but nine of the inhibiting strains were found to inhibit the growth of 38 psychrotrophic S. putrefaciens strains isolated from spoiling fish and fish products. Siderophore-containing Pseudomonas culture supernatants inhibited growth of S. putrefaciens, as did the addition of iron chelators (ethylenediamine dihydroxyphenylacetic acid [EDDHA]). In particular, Pseudomonas strains isolated from newly caught and spoiled Nile perch (Lates niloticus) inhibited S. putrefaciens. This suggests that microbial interaction (e.g., competition or antagonism) may influence the selection of a microflora for some chilled food products.

Characterization of pathogenic bacteria by automated headspace concentration-gas chromatography

Automated headspace concentration-gas chromatography (AHC-GC) was used to profile the volatile metabolites produced by Proteus mirabilis, Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus. Bacterial cultures were incubated in trypticase soy broth and examined at 24 h. The profiles were consistent for each genus examined and variation observed among the different strains of each species was chiefly quantitative. The volatiles were identified by concurrent headspace concentration-gas chromatography-mass spectrometry and consisted mainly of isobutanol, isopentanol, isopentyl acetate, 1-undecene and methyl ketones. There were sufficient differences in the profiles in the 4-6 min elution period to distinguish P. aeruginosa and S. aureus from each other and from the other two bacteria. P. mirabilis and K. pneumoniae typically showed three intense peaks which corresponded to isobutanol, isopentyl acetate and isopentanol. The determination of volatiles by AHC-GC is sensitive, rapid and offers a possible alternative for automatic detection and characterization of pathogenic bacteria.

Time course of volatile compound formation during refrigerated storage of naturally contaminated beef in air

The microbial flora of naturally contaminated beef stored in air was similar to that frequently recorded for meat stored under gas permeable films. Compounds produced as a result of microbial growth were acetoin, diacetyl, 3-methyl-1-butanol, 2-methyl-1-propanol, ethyl esters of acetic, propionic, butyric, isovaleric and hexanoic acids, methane thiol, dimethylsulphide, dimethyl disulphide, 1-undecene and 1,4-undecadiene. The first four compounds, which are known end-products of Brochothrix thermosphacta metabolism, were consistently detected at earlier stages of storage than the others, all of which have been shown to be produced by Pseudomonas spp. A pattern of odour development consistent with the chemical changes was also observed.

Volatile compounds associated with the aerobic growth of some Pseudomonas species on beef

Five strains representing four clusters of meat spoilage pseudomonads were grown on sterile beef at 5 degrees C. After 7 days incubation sensory assessments were made and the chemical composition of the headspace gases determined by gas chromatography-mass spectrometry. There was good correlation between odour descriptions and chemical data for three of the strains. The most numerous types of product were esters and sulphur-containing compounds. Of 45 compounds identified only 1-undecene was common to all the tested strains.