Attachment of Salmonella on Modified Poultry Skin Surface

Poultry skin was treated with formalin, trisodium phosphate, lipase, and papain before attachment. No treatment affected ultimate attachment level. Attachment using different cell suspension concentrations showed that there was a limitation in attachment level for each cell suspension concentration. Total numbers of Salmonella cells on poultry skin including cells in the surface water film were compared with numbers of irreversibly attached cells that remained after washing. At 10⁷ CFU/mL inoculation, irreversibly attached cells accounted for 93% of the total surface cell population after 60 min exposure and at 10⁸ level, it was 38%.     

Effect of temperature and growth media on the attachment of Listeria monocytogenes to stainless steel

Listeria monocytogenes ATCC 19111 cultivated in nutrient-rich medium (brain heart infusion, BHI) or starved in minimal medium (10% filter sterilized pond water and 90% sterilized distilled water) were investigated for their initial attachment to austenitic stainless steel No. 4 with satin finish at 4 °C, 20 °C, 30 °C, 37 °C, or 42 °C. A droplet (10 μl) containing  10⁷ CFU/ml of L. monocytogenes suspended in BHI or minimal medium was placed on the stainless steel surface. After holding in saturated humidity for 3 h at the desired temperature the surface was washed and prepared for scanning electron microscopy (SEM). Using SEM, attachment of L. monocytogenes was determined by counting cells remaining on the surface. When L. monocytogenes cultivated in BHI were used, with the exception of the number of attached cells being lower at 42 °C than at 37 °C and 30 °C, the number of attached cells increased with increasing temperature (P < 0.05). When L. monocytogenes starved in minimal medium were used, the number of attached cells also increased with increasing attachment temperature (P < 0.05), but the number of attached cells at 42 °C was lower than that at the other temperatures. The attachment of L. monocytogenes to stainless steel surface was greater when cultivated in rich medium of BHI vs starved in the minimal medium.     

Use of Byproducts of Food Industry for Production of Antimicrobial Activity by Bacillus sp. P11

Production of antimicrobial activity by Bacillus sp. P11 was tested on different byproducts of food industry, like fish meal, grape waste, an industrial fibrous soybean residue, soybean meal, and cheese whey. Bacillus sp. P11 produced the higher amount of antimicrobial activity on soybean meal, followed by fish meal and fibrous soybean residue. Soybean meal was the selected medium to determine the effect of three variables (temperature, initial pH, and substrate concentration) on bacteriocin activity by response surface methodology, using a 2³ factorial design. Statistical analysis showed good adequacy to the model (R ² of 0.8268). In the range studied, temperature and initial pH of the medium have a significant effect on bacteriocin production, and substrate concentration has no significant effect. Response surface data showed maximum bacteriocin production at initial pH between 7.0 and 8.5 and temperature between 39 and 42 °C. In the optimum conditions (initial pH 7.0 and 42 °C), production of bacteriocin activity by Bacillus sp. P11 was compared using a commercial medium (BHI broth) and soybean meal. Maximum activity achieved with the soybean meal-based medium was similar to that obtained with BHI, indicating that soybean meal may be a cost-effective substrate for production of antimicrobial activity by Bacillus sp. P11.     

EFFECT OF SOME MONOVALENT AND DIVALENT METAL IONS ON THE FLOCCULATION OF BREWERS YEAST STRAINS*

In agreement with previous reports, it has been found that both Mg⁺⁺ and Mn⁺⁺ ions can imitate Ca⁺⁺ as inducers of flocculation, though the intensity of the flocculation is considerably reduced. This reduction is not dependent upon the ionic concentration and a 10-fold increase in Mg⁺⁺ or Mn⁺⁺ from the normal concentration of 10 mg ion/litre fails to increase the flocculation intensity. Low concentrations (1–10 mg ion/litre) of Na⁺ or K⁺ induce flocculation in those strains displaying intense flocculation with Ca⁺⁺, but high concentrations of either Na⁺ or K⁺ (50–100 mg ion/litre) antagonize floc formation. It is suggested that divalent ions act by bridging cells through negative charges on the cell surface, whereas monovalent ions induce flocculation via a “counter ion” effect where the repellent forces of the negative charges on the cell surface are neutralized, thus allowing some floc formation due to hydrogen bonding or other types of non-ionic bonding between cells. The antagonism of high concentrations of monovalent ions towards flocculation may be due to the fact that all available cell surface charges are neutralized, resulting in insulation of the cells and thus preventing cell-to-cell hydrogen bonding.     

ADENOSINE TRIPHOSPHATE ENHANCES THE FLUORESCENCE OF 4′,6-DIAMIDINO-2-PHENYLINDOLE (DAPI)-LABELED ESCHERICHIA COLI O157:H71

Live cells of E. coli O157:H7 were labeled by 4′,6-diamidino-2-phenylindole (DAPI) in buffers of different pH. The extent of labeling was relatively insensitive to pH in the range of 6.5 to 9.5. The fluorescence intensity of ± 10⁴ DAPI-labeled bacteria per mL in optical cuvettes could be detected by a luminescence spectrometer. With a fluorescence microplate reader attachment, less than 10³ of labeled bacteria could be measured. DAPI-labeling inhibited the growth and respiratory activities of the bacteria. The addition of 0.5 to 6 mM concentrations of ATP induced a substantial increase in the fluorescence of labeled bacteria. Maximal enhancement by ATP was observed from bacteria still maintaining low levels of physiological activities. The enhancement favored more alkaline media with pH greater than 9. A replacement of ATP with ADP or AMP diminished the extent of enhancement. Other triphosphate nucleotides did not enhance fluorescence of DAPI-labeled bacteria. Comparable ATP enhancements were also observed with Pseudomonas alcaligenes and Shewanella putrefaciens. Solubilization/destruction of cell membranes of labeled bacteria by detergents essentially eliminated the ATP enhancement. Absorption and fluorescence spectroscopic measurements indicated that ATP could interact with free and bound DAPI. These results suggest that observed ATP enhancement in fluorescence intensity of DAPI labels in intact cells may be applied to increase the sensitivity of microorganism detection.     

FLOCCULATION—SOME OBSERVATIONS ON THE SURFACE CHARGES OF YEAST CELLS

Surface charges on flocculent and non-flocculent yeast cells have been measured by micro-electrophoresis. Yeasts were grown both in calcium deficient and in complete medium and particular attention was paid to changes as cells passed from a logarithimic to a stationary phase of growth. Many of the ionogenic groups contributing to surface charge are situated well within the cell wall; charges on cells from the calcium-deficient medium were higher than on cells from the complete medium. A pH-dependent rearrangement of an underlying surface protein layer is postulated for the flocculent yeast Saccharomyces cerevisiae Strain NCYC 1109. No evidence of a similar rearrangement was found with other flocculent strains examined. The results are discussed in relation to ‘calcium bridge’ formation.     

Development of a method to measure rheological properties of carrot cell and cell-wall materials

A method for measuring the rheological properties of carrot cells and cell-wall material during typical cooking conditions has been evaluated. A Bohlin controlled-stress rheometer with a rapid heating attachment was used. Because of potential slippage and sensitivity problems with cells and cell-wall material, different geometries (parallel plate, cone and plate, and concentric cylinder) were assessed. Initial experiments were designed to determine the linear viscoelastic regions for the cell and cell-wall materials at 25°C. Samples were subjected to varying shear stresses and oscillatory frequencies. For carrot cells, linearity was observed with cone and plate geometry and with concentric cylinder geometry over a fairly wide range of stresses and frequencies. Parallel plate geometry did not give linear results. Carrot cell-wall material behaved in a linear fashion with all three geometries over similar stress and frequency ranges as carrot cells. Using the appropriate conditions of geometry, frequency and stress, the influence of heat treatments on cell and cell-wall rheology was compared. A comparison of cone and plate and concentric cylinder geometry was performed using cells and cell-wall material heated from 25 to 90°C. Cone and plate geometry showed greater changes in rheological properties during heating than concentric cylinder geometry and also allowed a greater range of heating rates. Cone and plate geometry was used in further studies. Studies on the rheological behaviour of cells during heating showed that the complex shear modulus (G^*) increased in the range 25–75°C then decreased. For cell-wall material, G^* showed a steady increase from 25 to 90°C. Further experiments demonstrated that the increase in G^* was not due to water loss during heating. The amount of cell damage during heating was measured using a conductivity meter to establish if there was a correlation between changes in G^* and cell damage.     

EXPOSURE OF LISTERIA MONOCYTOGENES TO FOOD AND TEMPERATURE ABUSE USING A DIALYSIS TUBING CULTURE METHOD

Foodborne illnesses are often linked to foods that have been contaminated postprocessing and exposed to temperature abuse conditions prior to consumption. Limitations in methods to recover sufficient numbers of a target bacterium from an (inoculated) intentionally contaminated food can hinder genomic/proteomic analysis, and in conducting in vitro assays using the recovered cells. In this study, a dialysis tubing culture technique was developed to facilitate the recovery of high numbers of Listeria monocytogenes exposed to temperature abuse while in association with chocolate milk and frankfurter slurry. The impact of exposure to foods, followed by temperature abuse, on the virulence of L. monocytogenes was investigated using the Caco‐2 cell infection assay. The expression of groEL, associated with stress, was also determined. L. monocytogenes inoculated into brain–heart infusion (BHI) broth (control), chocolate milk or frankfurter slurry was held at 4C for 24 h to simulate short‐term exposure to each food. The L. monocytogenes‐contaminated food was then exposed to a series of temperature shifts to simulate temperature abuse. The final temperature of the abused BHI and chocolate milk was 30C, and the frankfurter slurry was 22C. The stress response gene, groEL, was only induced in the control cells (suspended in BHI) after they had been exposed to temperature abuse conditions. The expression of groEL was also evident in cells exposed to foods and temperature abuse conditions, suggesting that the foods used in this study were a stressful environment for the cells. This study showed that the exposure of L. monocytogenes to chocolate milk or frankfurter slurry, or temperature abuse has no impact on the virulence of L. monocytogenes as demonstrated using the Caco‐2 cell assay. However, the expression of groEL suggests that the foods evaluated can be stressful environments for L. monocytogenes despite its ability to grow or survive in those foods. The dialysis tubing culture technique developed is a simple and highly cost‐effective method for exposure of bacteria to food and the recovery of a large number of cells suitable for additional analysis.     

Growth Inhibition of Listeria monocytogenes by Sodium Polyphosphate as Affected by Polyvalent Metal Ions

Sodium polyphosphate (SPP, average chain length = 13) increased the lag time of L. monocytogenes Scott A (Lm) in brain-heart infusion broth (BHI). Polyvalent metal ions (1–10 mM) reversed inhibition of Lm growth by 0.5% SPP (nominal 3.6 mM). 10 mM Ca²⁺ or Mg²⁺, 5 mM Fe³⁺, 2 mM Mn²⁺ or 1 mM Zn²⁺ added to SPP-containing BHI, pH 6.0, at 19°C resulted in growth comparable to control cultures. Fe²⁺ partially restored growth; Ni²⁺, Co²⁺, Cu²⁺ or Al³⁺ were ineffective. SPP inhibited growth at 28°C in BHI, pH 5.0, and Lm grew upon addition of Ca²⁺, Mg²⁺ or Mn²⁺, but not Zn²⁺ or Fe³⁺. Addition of 0.5% SPP to mineral-rich foods, such as pureed beef, green beans or sweet potatoes, did not delay growth.     

Effect of Various Agents Upon the Attachment of Pseudomonas fragi to Stainless Steel

Epifluorescent microscopy was used to assay for the effect of selected chemicals and enzymes upon physical attachment of Pseudomonas fragi to stainless steel. The assays were conducted after the pretreatment of cells with the agents, in the presence of agents, and in the removal of attached cells with test agents. Compared to the controls, sodium periodate, cetyltrimethylammonium bromide (Cetavlon), NaOH, and Concanavalin A inhibited the attachment process in the pretreatment and presence assays. Trypsin, sodium dodecyl sulfate (SDS), NaOH and sodium periodate were effective in removing attached cells, while Cetavlon and Triton X-100 stabilized the attachment of cells to the stainless steel surface and prevented their removal. Neither EDTA nor mechanical removal of flagella had a significant effect upon attachment. These results suggested that attachment of P. fragi to stainless steel involved a polysaccharide and protein matrix surrounding the cells.     

Inactivation kinetics of a piezotolerant Staphylococcus aureus isolated from high-pressure-treated sliced ham by high pressure in buffer and in a ham model system: Evaluation in selective and non-selective medium

The kinetics of inactivation by high pressure of a pressure-resistant strain of Staphylococcus aureus isolated from pressure-treated packaged sliced ham, in buffer and in a ham model system was studied. Selective (BP agar) and enrichment media (BHI agar) were used for enumeration in order to count healthy and sublethally injured cells of the pathogen. A first-order kinetic inactivation was observed in both suspension media, and a very significant increase in D values was apparent when the microorganism was suspended and pressurized in the model food system compared to buffer. In the case of phosphate buffer as suspension medium, the z_p values obtained were 107.5 and 113.6 MPa for the two recovery media, i.e. BP and BHI agars, respectively. In contrast, in the case of the food model system, a two-phase linear relation was apparent and the PDT (Pressure Death Time) curve can be divided into two linear sections, so that two z_p values could be defined, one for each section. Z_p values of 100 and 79.4 MPa correspond to pressures < 500 MPa for the BP and BHI counts, respectively, while z_p values of 416.7 and 333.3 MPa correspond to higher pressures > 500 MPa for the selective and non-selective medium, respectively. When S. aureus had been pressurized in phosphate buffer, the BHI agar was slightly better in cell recovery, while in the case of the ham model system, the BP agar proved superior and gave significantly higher colony counts.

Industrial relevance

The paper provides significant information for the food processing industry as it deals with the effect of high-pressure technology on a piezotolerant pathogen that may survive in sliced ham. This technology is already applied in ham products and this paper supports the need for the use of real food in pressure studies in order to avoid underestimation of the effect and hence the processing times. It is also shown that different recovery media, i.e. selective and non-selective, should be used to avoid underestimation of the surviving cells.     

Growth of a tropical marine yeast Yarrowia lipolytica NCIM 3589 on bromoalkanes: relevance of cell size and cell surface properties

Yarrowia lipolytica 3589, a tropical marine yeast, grew aerobically on a broad range of bromoalkanes varying in carbon chain length and differing in degree and position of bromide group. Amongst the bromoalkanes studied, viz. 2‐bromopropane (2‐BP), 1‐bromobutane (1‐BB), 1,5‐dibromopentane (1,5‐DBP) and 1‐bromodecane (1‐BD), the best utilized was 1‐BD, with a maximal growth rate (μ_max) of 0.055 h^?1 and an affinity ratio (μ_max/K_s) of 0.022. Utilization of these bromoalkanes as growth substrates was associated with a concomitant release of bromide (8202.9 µm ) and cell mass (36 × 10⁹ cells/ml), occurring maximally on 1‐BD. Adherence of yeast cells to these hydrophobic bromoalkanes was observed microscopically, with an increase in cell size and surface hydrophobicity. The maximal cell diameter was for 1‐BD (4.66 µm), resulting in an increase in the calculated cell surface area (68.19 µm²) and sedimentation velocity (1.31 µm/s). Cell surface hydrophobicity values by microbial adhesion to solvents (MATS) analysis for yeasts grown on bromoalkanes and glucose were significantly high, i.e. >80%. Similarly, water contact angles also indicate that the cell surface of yeast cells grown in glucose possess a relatively more hydrophilic cell surface (θ = 49.1°), whereas cells grown in 1‐BD possess a more hydrophobic cell surface (θ = 90.7°). No significant change in emulsification activity or surface tension was detected in the cell‐free supernatant. Thus adherence to the bromoalkane droplets by an increase in cell size and surface hydrophobicity leading to debromination of the substrate might be the strategy employed in bromoalkane utilization and growth by Y. lipolytica 3589. Copyright © 2011 John Wiley & Sons, Ltd.     

Influence of cell surface hydrophobicity on attachment of Campylobacter to abiotic surfaces

This work aimed to investigate the influence of physicochemical properties and prior mode of growth (planktonic or sessile culture) on attachment of 13 Campylobacter jejuni strains and 5 Campylobacter coli strains isolated from chicken samples to three abiotic surfaces: stainless steel, glass and polyurethane. Water contact angle and zeta potential measurements indicated that the strains varied with respect to surface hydrophobicity (17.6 ± 1.5 to 53.0 ± 2.3°) and surface charge (−3.3 ± 0.4 to −15.1 ± 0.5 mV). Individual strains had different attachment abilities to stainless steel and glass (3.79 ± 0.16 to 5.45 ± 0.08 log cell cm⁻²) but did not attach to polyurethane, with one exception. Attachment of Campylobacter to abiotic surfaces significantly correlated with cell surface hydrophobicity (P ≤ 0.007), but not with surface charge (P ≥ 0.507). Cells grown as planktonic and sessile culture generally differed significantly from each other with respect to hydrophobicity and attachment (P < 0.05), but not with respect to surface charge (P > 0.05). Principal component analysis (PCA) clustered strains into three groups (planktonic culture) and two groups (sessile culture) representing those with similar hydrophobicity and attachment. Of the four highly hydrophobic and adherent strains, three were C. coli suggesting that isolates with greater hydrophobicity and adherence may occur more frequently among C. coli than C. jejuni strains although this requires further investigation using a larger number of strains. Assignment of pulsed-field gel electrophoresis profiles to PCA groups using Jackknife analysis revealed no overall relationship between bacterial genotypes and bacterial attachment. No relationship between serotype distribution and bacterial attachment was apparent in this study.     

The use of various live animal measurements to predict carcass and meat quality in two divergent lamb breeds

Live weight, subjective scores of condition and conformation, live animal video image analysis (LVIA), ultrasound and X-ray computed tomography (CT) scanning were used to investigate the best method or combination of methods for predicting carcass and meat quality traits in live Texel and Scottish Blackface lambs. Predictors derived from CT alone accounted for a high proportion of the variance in dissected fat and muscle weight in Texel lambs (adjusted R² = 0.8), as well as intra-muscular fat content in the loin (0.6), but lower proportions in Blackface lambs (0.7 for fat, 0.4–0.5 for muscle and intra-muscular fat), after adjusting for sire and fixed effects. Adding traits measured by other in vivo methods increased prediction accuracies (adjusted R²) by up to 0.26, depending on trait and data set. Shear force and ultimate pH could not be accurately predicted using the traits considered here (adjusted R² < 0.4). Although the same methods tended to be best for predicting product quality traits between breeds, prediction accuracies differed.     

Survival and Metabolic Activity of Microencapsulated Bifidobacterium longum in Stirred Yogurt

ABSTRACT: Live cells of Bifidobacterium longum, microencapsulated in K‐carrageenan, were added to stirred yogurt after fermentation (pH 4.6) and stored at 4.4 °C for 30 d. Cell enumeration indicated no decline of encapsulated cell number in yogurt samples, while there was significant reduction in nonencapsulated cell population (89.3% for B. longum B6 and 91.8% for B. longum ATCC 15708). Ion‐exchange high‐performance liquid chromatography showed comparable amounts of lactic and acetic acids in all samples, indicating little metabolic activity by bifidobacteria in experimental yogurts. Consumer sensory analysis of blackberry‐flavored yogurts revealed that samples containing encapsulated bifidobacteria had a grainy texture. Results suggested that microencapsulation protected bifidobacteria from the low pH of yogurt.     

Phenolic constituents of cell wall types of normal and brown midrib mutants of pearl millet (Pennisetum glaucum (L) R Br) in relation to wall biodegradability

The cell walls of parenchyma, rind and vascular bundle fractions of pearl millet (Pennisetum glaucum (L) R Br) were isolated from two brown midrib mutants (bmr) 5753 and 5778 and from their normal (N) near-isogenic line. The cell wall content of parenchyma was lower than that of vascular bundle which, in turn, was lower than that of rind. The amounts of ferulic and p-coumaric acids released by NaOH treatment of the cell walls were in the ranges 3-7 mg g^?1 and 2-26 mg g^?1, respectively. Parenchyma cell walls of the N line had the highest content of p-coumaric acid (26 mg g^?1). This content of p-coumaric acid in the N line contrasts with that of bmr 5753 parenchyma (2 mg acid g^?1 walls) and bmr 5778 (7 mg acid g^?1 walls). The concentration of p-coumaric acid was highest in parenchyma cell walls that had been found to be the least digested. Parenchyma, rind and vascular bundle cells walls of the N line had much higher ratios of p-coumaric acid to ferulic acid than the mutants; rind and vascular bundle walls were less digestible than parenchyma. Small amounts of truxillic acid dimers were released by NaOH from the parenchyma walls of bmr 5778. Treatment of parenchyma, rind and vascular bundle cells walls with purified ‘driselase’ (containing xylanases and cellulases) released p-coumaroyl and feruloyl trisaccharides. Between 25 and 53% of the ferulic acid that was released by the NaOH treatment could be accounted for as feruloyl trisaccharide, but only 1-19% of the p-coumaric acid was accounted for as p-coumaroyl trisaccharide.     

Modification of Food-Contacting Surfaces by Plasma Polymerization Technique: Reducing the Biofouling of Microorganisms on Stainless Steel Surface

In this study, the prevention of the attachment of test microorganism Enterobacter sakazakii onto stainless steel (SS 316) surfaces by radio frequency (RF) plasma polymerization (PlzP) technique using several hydrophilic monomers as precursors was reported. Different plasma conditions (RF discharge power of 20–80 W with exposure time of 10 min) were employed during the modifications. PlzP-modified surfaces were characterized in detail by static contact angle measurements in order to state the change of surface hydrophilicity. The surface topology of unmodified and PlzP [ethylenediamine (EDA)]-modified SS 316 plates was characterized by atomic force microscopy. The attachment of the model microorganism on the SS 316 surface modified by plasma using EDA at 45 W and 10 min was reduced by 99.74% in comparison to the unmodified control surface. For equilibrium adsorption behavior, Freundlich and Langmuir models were attempted and model parameters for Freundlich (K _F and 1/n) and for Langmuir (a and b) were obtained. The values of the K _F and 1/n were 5.6 and 0.58 and 0.9 and 0.39, respectively; the values of a and b were 25 × 10⁴ and 1.82 × 10⁻⁸ and 0.3 × 10⁴ and 7.96 × 10^-8, for bare and PlzP-EDA-modified SS 316 surfaces, respectively. As a result, PlzP technique was found to be an alternative simple method to decrease the microbial attachment and create bacterial anti-fouling surfaces.     

Comparison of adhesion characteristics of common dairy sporeformers and their spores on unmodified and modified stainless steel contact surfaces

The attachment of aerobic spore-forming bacteria and their spores to the surfaces of dairy processing equipment leads to biofilm formation. Although sporeformers may differ in the degree of attachment, various surface modifications are being studied in order to develop a surface that is least vulnerable to attachment. This study was conducted to compare the extent of adhesion of spores and vegetative cells of the thermotolerant sporeformer Bacillus licheniformis and the high-heat-resistant sporeformers Geobacillus stearothermophilus and Bacillus sporothermodurans on both native and modified stainless steel surfaces. We studied the effect of contact surface and cell surface properties (including surface energy, surface hydrophobicity, cell surface hydrophobicity, and zeta potential) on the adhesion tendency of both types of sporeformers and their spores. Attachment to native and modified (Ni-P-polytetrafluoroethylene, Ni-P-PTFE) stainless steel surfaces was determined by allowing interaction between the respective contact surface and vegetative cells or spores for 1 h at ambient temperature. The hydrophobicity of vegetative cells and spores of aerobic spore-forming bacteria was determined using the hexadecane assay, and zeta potential was determined using the Zeta sizer Nano series instrument (Malvern Panalytical, Malvern, UK). The results indicated a higher adhesion tendency of spores over vegetative cells for both thermotolerant and high-heat-resistant sporeformers. On comparing the sporeformers, B. sporothermodurans demonstrated the highest adhesion tendency followed by G. stearothermophilus; B. licheniformis exhibited minimal attachment on both surfaces. The tendency to adhere varied with cell surface properties, decreasing with lower cell surface hydrophobicity and higher cell surface charge. On the other hand, modifying contact surface properties for higher surface hydrophobicity and lower surface energy decreased attachment.     

Growth of Salmonella enterica Serovar Enteritidis PT4 in media containing glucose results in enhanced RpoS-independent heat and acid tolerance but does not affect the ability to survive air-drying on surfaces

The heat and acid tolerance of isolates of Salmonella enterica serovar Enteritidis PT4 was markedly higher if cells were grown to stationary phase in either commercially produced Tryptone Soya (TSBG) or brain–heart infusion (BHI) broth containing glucose than when cells were grown in either nutrient or Tryptone Soya broth without glucose. Differences between the populations were found to be related to the production of acid in either TSBG or BHI which caused the culture media pH values to fall to pH 5·8–4·7 during overnight incubation. This led to habituation, which increased both heat- and acid-tolerance, although there was no effect on the abilities of cells to survive air-drying on surfaces. The acid tolerance mechanisms, induced by fermentative growth in complex media, responsible for survival at pH 2·8, were RpoS-independent. In addition, although growth rates as measured by cfu were essentially the same in all media, optical density measurements were very different, with those of cells in media containing glucose being much higher. This was found to be due to the formation of larger cells by the Salmonella in these media.     

Association of micro-organisms with the inner surfaces of bottles of non-carbonated mineral waters

Three brands of non-carbonated mineral water were tested using rinsing techniques and electron microscopy for attachment of bacteria to the inner surface of the bottle. Rinse solutions used were distilled water (DW), DW+0.1% Tween 80, DW+0.1% salt, DW+0.1% SDS. The microbial population attached to the inner surface of the bottles varied between 5-;44% depending upon the brand and the batch of water examined. Most of the attached bacteria (80-;90%) were removed during the first two rinses. Species (Burkholderia cepacia, Methylobacterium mesophilicum, Acidovorax delafieldii, Brevundimonas vesicularis, Xanthomonas campestris) attached to the bottle surface were found to be the same as those in the mineral water. Measurement of the cell surface hydrophobicity of these species failed to prove this as the only factor for attachment to bottle surfaces. Scanning electron micrographs of inner surfaces of bottles showed bacterial attachment of densities of 10⁷cells cm^-;2, with evidence of microcolony but no visible biofilm formation.