Serovar distribution and antimicrobial susceptibility of swine Salmonella isolates from clinically ill pigs in diagnostic submissions from Indiana in the United States

Aims:  To determine serovar distribution and levels of antimicrobial susceptibility of Salmonella isolated from clinically ill pigs in diagnostic submissions.
Methods and Results:  A total of 197 Salmonella isolates were obtained by the Indiana Animal Disease Diagnostic Laboratory from 2003 to 2005. Minimal inhibitory concentrations (MICs) were determined using the standard microbroth dilution method. The top four serovars identified were Salm. enterica serovar Typhimurium variant Copenhagen, Salm . Derby, Salm . Choleraesuis var. Kunzendorf and Salm . Typhimurium. All isolates were susceptible to the fluoroquinolones tested except that eight isolates were intermediate to difloxacin. The isolates showed a low prevalence of resistance to trimethoprim/sulphadiazine (Sxt), gentamicin (G), ceftiofur (Cf) and cephalothin (Cp) with low MIC₅₀ value of ≤0·5, 0·5, 1 and 4  μ g ml⁻¹, respectively. They showed a high prevalence of resistance to tetracycline (T; 83·8%), and a moderate prevalence to ampicillin (55·8%), spectinomycin (42·6%), ticarcillin (41·6%) and florfenicol (41·1%). There were more isolates of Salm . Typhimurium, including var. Copenhagen and Salm . Agona, that possessed multiple antimicrobial resistance to amoxicillin/clavulanic acid, ampicillin, ceftiofur and cephalothin (AxApCfCp) than the other serovars.
Conclusions:  The swine Salmonella isolates were susceptible to the fluoroquinolones, Sxt, G, Cf and Cp, but resistant to T.
Significance and Impact of the Study:  These findings provided useful information regarding antimicrobial susceptibility and resistance in dealing with clinical salmonellosis in pig herds.     

The survival of Salmonella enterica serovar Typhimurium DT104 and total viable counts on beef surfaces at different relative humidities and temperatures

Aims:  The aim of this study was to investigate changes in Salmonella and total viable count (TVC) survival on beef carcass surfaces stored for 72 h under different combinations of relative humidity (i.e. RH 75% or 96%) and temperature (5°C or 10°C).
Methods and Results:  The influence of low water activity ( a _w) and temperature on the survival and growth of Salmonella enterica serovar Typhimurium DT104 and the aerobic mesophilic flora on meat pieces from different sites on beef carcasses was investigated, under controlled conditions (75% or 96% RH; 5 or 10°C) in an environmental cabinet. Salmonella counts declined during storage at low a _w (75% RH) conditions at 5°C or 10°C. Salmonella counts increased during storage at high a _w (96% RH) at 10°C only. At 5°C, TVCs increased during storage at high a _w, but not at low a _w. TVCs increased on all samples from carcasses stored at high or low a _w at 10°C, except those samples taken from areas of surface fat.
Conclusions:  This suggests that substrate composition dictates growth rates under low a _w conditions. The results are discussed in terms of the possible protective effects of substrate osmolyte accumulation in bacterial survival and/or growth.
Significance and Impact of the Study:  The data obtained in this study provides useful insights on the influence of a _w and temperature on pathogen survival on meat surfaces at chill temperature.     

Molecular characterization of antimicrobial resistance in Salmonella isolated from animals in Japan

Aims:  To investigate the prevalence of integrons and antimicrobial resistance genes in Salmonella recovered from animals in Japan.
Methods and Results:  Forty-eight out of ninety-four (51·1%) Salmonella isolates showed multidrug resistance phenotypes and harboured at least one antimicrobial resistance gene. Twenty-two out of forty-seven (46·8%) Salmonella enterica serovar Typhimurium that were multidrug-resistant were of definitive phage type DT104. Class 1 integrons were identified in 34/94 isolates (36·2%): 21 isolates containing two gene cassettes, aadA2 and bla _PSE–1, and 13 containing one gene cassette, aadA1 , aadA2 or bla _PSE–1. Class 2 integrons containing estX - sat2 - aadA1 gene cassettes were only identified in Salmonella Enteritidis. The β-lactamase-encoding gene, bla _TEM, was only detected in S. Typhimurium. The plasmid-mediated quinolone resistance gene, qnrS1 , was identified in S. Typhimurium and Salmonella Thompson.
Conclusions:  Our results characterized integrons and antimicrobial resistance genes in Salmonella of animal origin. To the best of our knowledge, this is the first report of qnrS in Salmonella from Japan and also the first report of qnrS in S . Thompson.
Significance and Impact of the Study:  Little is known about the molecular basis of antimicrobial resistance in Salmonella isolated from animals. This study provides useful data on the incidence of integrons and resistance genes in Salmonella of animal origin.     

Comparative evaluation of methods for counting surviving biofilm cells adhering to a polyvinyl chloride surface exposed to chlorine or drying

Aim:  To compare techniques for assessing biofilm populations previously subjected, or not, to inimical treatment by chlorine or drying.
Methods and Results:  Four sonication treatments and swabbing were compared on Salmonella  Typhimurium or Pseudomonas fluorescens biofilms grown on polyvinyl chloride (PVC). The apparatuses emitting the highest ultrasound energy were the most efficient except on Salm. Typhimurium biofilms subjected to drying: a lethal effect, leading to an underestimation of at least 1·5 log (CFU cm^–2) was observed with the more aggressive treatment. The differences between the highest count and the swabbing counts ranged from 0·3 log (CFU cm^–2) (untreated Salm. Typhimurium) to 1·7 log (CFU cm^–2) (chlorine treated Ps. fluorescens ). Impedance measurements, used to assess populations without detaching any cells showed that the calibration curves that were built up from data obtained with suspended cells plus PVC slides were not appropriate.
Conclusions:  High energy ultrasound techniques designed either for in vitro or in situ studies proved efficient in assessing the number of attached CFU. However, the right treatment duration has to be carefully established before using high energy ultrasound techniques.
Significance and impact of the study:  The effectiveness of a cleaning and disinfection regime inferred from data obtained after swabbing may be greatly underestimated.     

Effect of temperature and water activity on in vitro germination of Monilinia spp.

Aims:  This study evaluated the effect of temperature (0–38°C) and water activity ( a _w: 0·87–0·99) on the lag phase prior to germination and the percentage of germination over time for Monilinia laxa , Monilinia fructicola and Monilinia fructigena .
Methods and Results:  More than 80% of viable conidia germinated at 25°C and 0·99 a _w within 2 h for M. fructicola and M. fructigena and 4 h for M. laxa . There was no germination at 38°C, and all three Monilinia spp. germinated at 0°C. At the lowest a _w (0·87), none of the Monilinia spp. was able to germinate at any of the incubation temperatures studied. Whereas at 0·90 a _w, conidia were only able to germinate at 15, 25 and 30°C for the three species studied, except for M. fructicola at 15°C. In contrast, at 0·95, 0·97 and 0·99 a _w, germination occurred at all studied temperatures less 38°C. Generally, the lag phase was longer at low levels of a _w (0·90–095), and differences were more evident as temperatures were far from the optimum (0–5°C).
Conclusions:  Germination and lag phase period were markedly influenced by temperature and a _w, and in general when conditions of temperature and a _w were suboptimal, the lag phase was longer and the percentage of germination was lower.
Significance and Impact of the Study:  Knowledge of the germination requirements of this fungus is important in order to understand their behaviour in natural situations and to provide baseline data required for the construction of new prediction models. Our study might be used to develop a predictive model to understand and control the disease caused by Monilinia spp.     

Survival of enteric bacteria and coliphage MS2 in pure human urine

Aims:  The survival of Escherichia coli , Salmonella enterica serovar Typhimurium, Enterococcus faecalis and coliphage MS2 was studied in stored, fresh and diluted (1 : 1) human urine at 15 and 30°C.
Methods and Results:  Survival rate was studied by the plate count method. All the organisms showed rapid inactivation in stored urine, but they survived better in diluted and fresh urine. The high pH level and temperature were the major factors found to influence the survival of the micro-organisms with the survival rate being higher at 15°C than at 30°C.
Conclusions:  The destruction of all micro-organisms in stored urine required <1 week at 30°C. Thus, the storage of urine is a useful way to reduce the risk of contamination while using urine as a fertilizer.
Significance and Impact of the Study:  The urine fertilization is aimed for the developing countries and the high temperatures in these countries may hasten the destruction of micro-organisms in urine. On the contrary, a higher survival rate of these organisms in fresh and diluted urine is a public health concern because the dilution of urine with water is likely to happen during flushing.     

Resistance of Escherichia coli grown at different temperatures to various environmental stresses

Aims:  To study the influence of growth temperature on the resistance of Escherichia coli to three agents of different nature: heat, pulsed electric field (PEF) and hydrogen peroxide.
Methods and Results:  Escherichia coli cells were grown to stationary phase at 10°C, 20°C, 30°C, 37°C and 42°C. Survival curves to a heat treatment at 57·5°C, to a PEF treatment at 22 kV cm⁻¹ and to 40 mmol l⁻¹ hydrogen peroxide were obtained and fitted to a model based on the Weibull distribution to describe and compare the inactivation. Time to inactivate the first log cycle of the population at 57·5°C of cells grown at 42°C was sixfold higher than that corresponding to cells grown at 10°C. On the contrary, cells grown at 10°C and 20°C were more resistant to PEF and hydrogen peroxide treatments.
Conclusions:  The influence of growth temperature on bacterial resistance depends on the stress applied. Cells grown at higher temperatures were more heat resistant, but more sensitive to PEF and hydrogen peroxide.
Significance and Impact of the Study:  Results obtained in this investigation help in understanding the physiology of bacterial resistance and the inactivation mechanisms of different technologies.     

Effects of yeast probiotic formulation on viability, revival and protection against infection with Salmonella enterica ssp. enterica serovar Typhimurium in mice

Aims:  To compare the effects of five yeast probiotic formulations on viability, revival and washout kinetic in the digestive tract of mice, and the protection against an experimental infection with Salmonella enterica serovar Typhimurium.
Methods and Results:  The number of viable cells in five commercial probiotic products codified as A, B, C and D ( Saccharomyces boulardii – lyophilized) and E ( Saccharomyces cerevisiae – aqueous suspension) was determined, as well as revival and washout kinetic in mouse intestine. Protective capacity was evaluated by survival rate and histopathology of liver and intestine of mice treated with each product and then challenged with Salm . Typhimurium.
Conclusions:  Product A contained the highest number of viable cells and, fed to mice, gave the highest counts of viable yeasts and the longest persistence in faeces. Probably as a consequence, the highest survival and protection of intestinal and hepatic tissues were observed when product A was used for mouse treatment. Product E showed low counts in the formulation and was not recovered from mouse intestine.
Significance and Impact of the Study:  Formulation (lyophilization or aqueous suspension) is an important factor for revival and survival of a probiotic product in vivo and consequently for its protective properties.     

Effect of heat treatment on Cronobacter spp. in reconstituted, dried infant formula: preparation guidelines for manufacturers

Aim:  To explore safe guidelines for manufacturers and consumers to prepare, handle and store dry infant formula (DIF) to protect infants against Cronobacter spp.
Methods and Results:  Selected strains (2.45, FSM 293, ATCC-12868, FSM-271) screened from 68 strains of Cronobacter spp . were used to study growth and survival in commercial DIF. Prototype growth patterns in Enterobacteriaceae enrichment broth (EEB) containing a cocktail comprised of ATCC 12868, ATCC 29004, ATCC 29544 and ATCC 51329 showed a rapid increase in cell count (2·0 log₁₀ to 6·2 log₁₀ CFU ml⁻¹). Infant formula provided a better protective environment for the cells of Cronobacter strains than did buffered peptone water . Experiments on survival in inoculated (10⁴–10⁶ CFU ml⁻¹) reconstituted infant formula (RIF), preparation temperature, the effect of preparation volume (one-serving or two-serving) and effect of storage at room temperature for up to 10 h provided information to develop consumer guidelines for DIF preparation and handling.
Conclusions:  Reconstituted DIF in water at >70°C in larger volumes, minimizing storage time before feeding and storing unused reconstituted formulate at <4°C, may reduce the risk of Cronobacter infection in infants.
Significance and Impact of the Study:  Meningitis, necrotizing enterocolitis and bacteremia in premature babies has been linked to contaminated milk powder and DIF; better handling practices may improve the safety of these foods for neonates.     

Antimicrobial effect and shelf-life extension by combined thermal and pulsed electric field treatment of milk

Aims:  The impact of a combined hurdle treatment of heat and pulsed electric fields (PEF) was studied on native microbiota used for the inoculation of low-fat ultra-high temperature (UHT) milk and whole raw milk. Microbiological shelf-life of the latter following hurdle treatment or thermal pasteurization was also investigated.
Methods and Results:  UHT milk was preheated to 30°C, 40°C or 50°C over a 60-s period, pulsed for 50  μ s or 60  μ s at a field strength of 40 kV cm⁻¹ or for 33  μ s at 50 kV cm⁻¹. Heat and PEF reduced the microbial count by a maximum of 6·4 log in UHT milk (50°C; 50 kV cm⁻¹, 33  μ s) compared to 6·0 log ( P  ≥ 0·05) obtained by thermal pasteurization (26 s, 72°C). When raw milk was treated with a combination of hurdles (50°C; 40 kV cm⁻¹, 60  μ s) a 6·0 log inactivation of microbiota was achieved and microbiological milk shelf-life was extended to 21 days under refrigeration (4°C) vs 14 days in thermally pasteurized milk. Native microbiota was decreased by 6·7 log following conventional pasteurization.
Conclusions:  The findings suggest that heat and PEF achieved similar inactivation of native microbiota in milk and longer stabilization of microbiological shelf-life than thermal pasteurization.
Significance and Impact of the Study:  A hurdle approach of heat and PEF could represent a valid milk processing alternative to conventional pasteurization. Hurdle treatment might also preserve native milk quality better due to less thermal exposure.     

Novel approach to control Salmonella enterica by modern biophotonic technology: photosensitization

Aims:  Salmonellosis is one of the most common foodborne diseases in the world. The aim of this study was to evaluate the antibacterial efficiency of 5-aminolevulinic acid (ALA) based photosensitization against one of food pathogens Salmonella enterica .
Methods and Results:  Salmonella enterica was incubated with ALA (7·5 mmol l⁻¹) for 1–4 h and afterwards illuminated with visible light. The light source used for illumination of S. enterica emitted light λ  = 400 nm with energy density 20 mW cm⁻². The illumination time varied from 0 to 20 min and subsequently a total energy dose reached 0–24 J cm⁻². The data obtained indicate that S. enterica is able to produce endogenous photosensitizer PpIX when incubated with ALA. Remarkable inactivation of micro-organisms can be achieved (6 log) after photosensitization. It is obvious that photosensitization-based inactivation of S. enterica depends on illumination as well as incubation with ALA time.
Conclusion:  ALA-based photosensitization can be an effective tool against multi-drug resistant Gram-negative bacteria S. enterica serovar Typhimurium.
Significance and Impact of the Study:  Experimental data and mathematical evaluations support the idea that ALA-based photosensitization can be a useful tool for the development of nonthermal food preservation technology in future.     

Modelling the effect of the redox potential and pH of heating media on Listeria monocytogenes heat resistance

Aims:  Study the effect of redox potential and pH of the heating media on Listeria monocytogenes heat resistance and model its action at fixed temperature.
Methods and Results:  The heat resistance of Listeria monocytogenes at 58°C was studied in Brain Heart Infusion broth as a function of pH (from 5·0 to 7·0) and redox potential ( E _h7). The media redox was adjusted with nitrogen gas, potassium ferricyanide and dithiothreitol. A Weibull model was used to fit survival curves. The heat resistance parameter (δ_58°C) was estimated from each inactivation curve. A major effect of pH was observed. Bigelow model was used to describe the effect of redox potential on the apparent L. monocytogenes heat resistance. The highest δ_58°C values have been obtained at pH 7·0 and oxidizing conditions.
Conclusions:  The developed model indicates that the E _h7 has a significant effect and varied depending on the pH of the heating media. The z _redox values, calculated from δ_58°C allowed quantifying the influence of heating media redox potential on L. monocytogenes thermal inactivation.
Significance and Impact of the Study:  The obtained model shows the action of redox potential on L. monocytogenes thermal destruction and might be useful to take into account in food thermal processes.     

Changes in Escherichia coli O157:H7 numbers during holding on excised lean, fascia and fat beef surfaces at different temperatures

Aim:  To investigate changes in Escherichia coli O157:H7 numbers on excised beef carcass surfaces over 72 h at different temperatures.
Methods and Results:  Excised lean meat, fascia and fat were inoculated with E. coli O157:H7 and held in an environmental chamber for 72 h, at air speed 0·5 m s⁻¹, relative humidity (RH) 90%, and temperatures 4, 8 and 12°C. On lean, pathogen counts increased significantly at 12°C. On fascia, significant reductions in counts occurred at 4 and 8°C. Pathogen numbers were significantly reduced on fat at 4, 8 and 12°C (64 h). Counts on fat were significantly less at all temperatures, compared to lean or fascia and surface water activity, a_w, decreased significantly over time on fat at 4°C. Significant decreases in surface pH values were recorded on all meat substrates.
Conclusions:  The survival of E. coli O157:H7 varied in relation to the meat substrate and the holding temperature. Reductions in counts on fat surfaces appeared to be related to low surface a_w values. No relationship between pathogen survival and surface pH was established.
Significance and Impact of the Study:  The use of excised meat pieces in an environmental cabinet offers a more flexible approach to determining the use of different chilling regimes in the production of safe meat.     

Inactivation of Salmonella during anaerobic digestion of sewage sludge

The inactivation of Salmonella duesseldorf in sewage sludge during anaerobic digestion was investigated at 35 and 48°C with mean retention periods of between 10 and 20 days. Digesters were fed daily with raw sludge containing added Salm. duesseldorf after removal of digested sludge. During steady operation, the levels of Salm. duesseldorf in the digested and the feed sludge were determined and their specific rates of decay were estimated. The latter were: (i) greater at 48°C than at 35°C for the same retention time; (ii) similar for retention periods greater than 15 d, but lower for 10 d; (iii) greater when the level of salmonellas in the feed was lower. Gas production, a measure of steady state, was gradually lost when the mean retention period was reduced to 6.7 d. In experiments in which a single dose of Salm. duesseldorf was added to digesting sludge, the inactivation appeared to follow first-order kinetics at 35°C and the decimal decay rate, 1.6/d, was similar to that in the daily feeding experiments (1.4/d) with larger and similar inocula of Salm. duesseldorf. At 48°C, however, the rate of inactivation declined with decreasing time from inoculation suggesting that the culture contained cells differing in thermal resistance. The degrees and rates of inactivation of salmonellas in those experiments were greater than in full-scale digesters, because the latter seldom operated under conditions ideal for inactivation or because indigenous salmonellas are more resistant.     

Nonisothermal heat resistance determinations with the thermoresistometer Mastia

Aims:  To design and build a thermoresistometer, named Mastia, which could perform isothermal and nonisothermal experiments.
Methods and Results:  In order to evaluate the thermoresistometer, the heat resistance of Escherichia coli vegetative cells and Alicyclobacillus acidoterrestris spores was explored. Isothermal heat resistance of E. coli was characterized by D _60°C = 0·38 min and z =  4·7°C in pH 7 buffer. When the vegetative cells were exposed to nonisothermal conditions, their heat resistance was largely increased at slow heating and fast cooling rates. Isothermal heat resistance of A. acidoterrestris was characterized by D _95°C = 7·4 min and z =  9·5°C in orange juice. Under nonisothermal conditions, inactivation was reasonably well predicted from isothermal data.
Conclusions:  The thermoresistometer Mastia is a very suitable instrument to get heat resistance data of micro-organisms under isothermal and nonisothermal treatments.
Significance and Impact of the Study:  The thermoresistometer Mastia can be a helpful tool for food processors in order to estimate the level of safety of the treatments they apply.     

Effects of storage and the presence of a beef microflora on the thermal resistance of Salmonella Typhimurium DT104 in beef and broth systems

AIMS: To investigate the effects of storage and the presence of a beef microflora on the thermal resistance of Salmonella serotype Typhimurium DT104 on beef surfaces and in a broth system during subsequent heat treatments after extended low-temperature storage (4 degrees C for 14 days) or mild temperature abuse (10 degrees C for 7 days). METHODS AND RESULTS: Surviving Salm. Typhimurium DT104 cells were estimated after heating in a water bath (55 degrees C) by plating beef and broth samples on tryptone soya agar and overlaying with xylose-lysine-deoxycholate agar. In beef and broth systems, D(55) values for Salm. Typhimurium DT104 stored at 4 degrees C or 10 degrees C in the presence or absence of a beef microflora were significantly lower (P < 0.01) than the D values for this organism heat-treated immediately after inoculation. In beef systems, the D(55) values were significantly lower (P < 0.05) in the presence of a beef microflora than the D(55) values obtained in 'pure' culture under all temperature/storage combinations. However, in broth systems, there was no significant difference between the D(55) values obtained in 'pure' culture and the D(55) values obtained from systems containing beef microflora. CONCLUSIONS: Storage of Salm. Typhimurium DT104 significantly reduced the thermal resistance of the pathogen in beef and broth systems. In the presence of high numbers of a Gram-negative beef microflora, the heat sensitivity of the pathogen was further increased on beef surfaces but not in broth. SIGNIFICANCE AND IMPACT OF THE STUDY: Studies investigating the survival of Salm. Typhimurium DT104 in different food systems will help define safe food preservation processes and will aid in the elimination this pathogen from the food production environments.     

The combined effects of high pressure and nisin on germination and inactivation of Bacillus spores in milk

Aims:  The aim of this work was to investigate the germination and inactivation of spores of Bacillus species in buffer and milk subjected to high pressure (HP) and nisin.
Methods and Results:  Spores of Bacillus subtilis and Bacillus cereus suspended in milk or buffer were treated at 100 or 500 MPa at 40°C with or without 500 IU ml⁻¹ of nisin. Treatment at 500 MPa resulted in high levels of germination (4 log units) of B. subtilis spores in both milk and buffer; this increased to >6 logs by applying a second cycle of pressure. Viability of B. subtilis spores in milk and buffer was reduced by 2·5 logs by cycled HP, while the addition of nisin (500 IU ml⁻¹) prior to HP treatment resulted in log reductions of 5·7 and 5·9 in phosphate buffered saline and milk, respectively. Physical damage of spores of B. subtilis following HP was apparent using scanning electron microscopy. Treating four strains of B. cereus at 500 MPa for 5 min twice at 40°C in the presence of 500 IU ml⁻¹ nisin proved less effective at inactivating the spores of these isolates compared with B. subtilis and some strain-to-strain variability was observed.
Conclusions:  Although high levels of germination of Bacillus spores could be achieved by combining HP and nisin, complete inactivation was not achieved using the aforementioned treatments.
Significance and Impact of the Study:  Combinations of HP treatment and nisin may be an appealing alternative to heat pasteurization of milk.     

Survival of Campylobacter spp. in bovine faeces on pasture

Aims:  To determine the survival on pasture of Campylobacter spp. naturally present in bovine faeces and compare this with a previously published study using laboratory-cultured Campylobacter spp.
Methods and Results:  Ten freshly collected cow pats were deposited on pasture during summer, and Campylobacter spp. were enumerated by enrichment broth culture. The counts in three pats were below detection limits. Counts of Campylobacter spp. in the other seven pats fell below detection limits within 14 days. The geometric means of the counts up to 7 days produced a T ₉₀ of 2·2 days. Characterization of Campylobacter spp. by PCR and pulsed field gel electrophoresis indicated the presence of at least six genotypes of Campylobacter jejuni , Campylobacter coli and Campylobacter lari .
Conclusions:  Campylobacter spp. naturally present in cow faeces exhibited a similar survival rate to that previously determined using laboratory-cultured strains. The highly variable counts of naturally occurring Campylobacter spp., and the predominance of lower counts, also support the earlier decision to use laboratory-cultured strains in survival experiments.
Significance and Impact of the Study:  This study reaffirms the short survival of Campylobacter spp. in cow faeces deposited on pasture. This information will be incorporated into a 'reservoir model' for Campylobacter spp. in cow pats on New Zealand pastures.     

Surfactin reduces the adhesion of food-borne pathogenic bacteria to solid surfaces

Aims:  To investigate the effect of the biosurfactants surfactin and rhamnolipids on the adhesion of the food pathogens Listeria monocytogenes , Enterobacter sakazakii and Salmonella Enteritidis to stainless steel and polypropylene surfaces.
Methods and Results:  Quantification of bacterial adhesion was performed using the crystal violet staining technique. Preconditioning of surfaces with surfactin caused a reduction on the number of adhered cells of Ent. sakazakii and L. monocytogenes on stainless steel. The most significant result was obtained with L. monocytogenes where number of adhered cells was reduced by 10² CFU cm⁻². On polypropylene, surfactin showed a significant decrease on the adhesion of all strains. The adsorption of surfactin on polystyrene also reduces the adhesion of L. monocytogenes and Salm. Enteritidis growing cells. For short contact periods using nongrowing cells or longer contact periods with growing cells, surfactin was able to delay bacterial adhesion.
Conclusions:  The prior adsorption of surfactin to solid surfaces contributes on reducing colonization of the pathogenic bacteria.
Significance and Impact of the Study:  This is the first work investigating the effect of surfactin on the adhesion of the food pathogens L. monocytogenes , Ent. sakazakii and Salm. Enteritidis to polypropylene and stainless steel surfaces.     

Optimization and biochemical characterization of a bacteriocin from a newly isolated Bacillus subtilis strain 14B for biocontrol of Agrobacterium spp. strains

Aims:  The identification of a new compound active against Agrobacterium tumefaciens .
Methods and Results:  The culture conditions of a newly isolated Bacillus subtilis strain, designed 14B, were optimized, as a first step, to produce its bacteriocin (termed Bac 14B) for the biocontrol of Agrobacterium spp., the causal agents of the crown gall disease. Bac 14B was then partially purified and biochemically characterized. Bacillus subtilis 14B was observed to produce an antibacterial compound having a protinaceous nature. As estimated by sodium dodecyl sulfate-polyacrilamide gel electrophoresis (SDS-PAGE), the semi-purified bacteriocin substance was found to be a monomeric protein with a molecular weight of 21 kDa. While the latter's antimicrobial activity was completely stable during exposure to a temperature range of up to 100°C for 2 h, its initial activity was totally lost at 121°C for 20 min. The maximum bacteriocin production (4096 AU ml⁻¹) was recorded after 96 h-incubation in an optimized Luria Bertani medium supplemented with 10 g l⁻¹ glucose, 15 g l⁻¹ K₂HPO₄ and 5 g l⁻¹ MgSO₄ 7H₂O at 30°C in a shaking flask culture. Interestingly, the B. subtilis 14B culture supernatant that contained the bacteriocin under study was proved efficient in reducing both the percentage of galled plants and the number of galls in tomato.
Conclusion:  The findings revealed that B. subtilis 14B and its bacteriocin are efficient in reducing the percentage of infections in plants caused by Ag. tumefaciens .
Significance and Impact of the Study:  The results could be useful for the nurserymen who are particularly interested in the biocontrol of the crown gall disease.