Growth Media and Surface Conditioning Influence the Adherence of Pseudomonas fragi , Salmonella typhimurium , and Listeria monocytogenes Cells to Stainless Steel.

Microorganisms have been shown to adhere to food-contact surfaces and may provide a route for the contamination of processed food. To better understand this phenomenon, the effects of growth media and surface conditioning on the adherence of Pseudomonas fragi , Salmonella typhimurium and Listeria monocytogenes cells to stainless steel were studied. The microorganisms were grown in tryptic soy broth (TSB), 1% reconstituted skim milk (RSM) and RSM with 1% sucrose (RSM + S). Stainless-steel surfaces were conditioned by immersion in growth media for 1 h and then were rinsed in phosphate-buffered saline (PBS) prior to the adherence assay. After growing in each medium, cells were harvested, resuspended in PBS, and then allowed to contact the stainless steel for 30 min. Adherence was quantified by acridine orange-staining the cells and viewing under epifluorescence microscopy. Growth media had little influence on adherence to stainless steel that had not been preconditioned. P. fragi and L. monocytogenes cells adhered in the highest numbers when grown in RSM plus sucrose. S. typhimurium cells showed the highest level of adherence when grown in TSB. Analysis of variance yielded P values of less than 0.01, indicating that both growth media and surface conditioning were significant in the level of adherence observed.

Isolation and Identification of Adherent Gram-Negative Microorganisms from Four Meat-Processing Facilities.

Biofilms are described as a matrix of microorganisms which have adhered to and colonized a surface. Once formed, biofilms are difficult to remove and may be a source of contamination in food-processing environments. In this study, stainless-steel chips were fixed to surfaces adjacent to food-contact surfaces and cast-iron chips were suspended in the floor drains of four meat-processing plants. Biofilm formation was quantified by staining the attached cells and viewing them under epifluorescence microscopy. The stainless-steel and cast-iron chips removed from the plant environment showed some attached microorganisms. Floor drains appeared to provide an excellent environment for the formation of biofilms. Pseudomonas , Klebsiella , Aeromonas , and Hafnia species were identified as gram-negative microorganisms associated with the test surfaces.

Inhibition of Listeria monocytogenes , Escherichia coli O157:H7, and Micrococcus luteus by Linear Furanocoumarins in a Model Food System.

Lime peel, parsnip, lemon peel, dried parsley flakes, cold pressed lime oil, and distilled lime oil samples were analyzed for the presence and concentration of the linear furanocoumarins (LFs) psoralen, 5-methoxypsoralen (5- MOP), and 8-methoxypsoralen (8-MOP) by thin layer chromatography and gas chromatography mass spectrometry. Cold-pressed lime oil had the highest LF content (psoralen, 67 ± 29 µg/ml, 5-MOP, 1,634 ± 62 µg/ml, and 8-MOP, 44 ± 2 µg/ml). The antimicrobial effectiveness of LFs against Listeria monocytogenes , Escherichia coli O157:H7, and Micrococcus luteus was tested in a model food system consisting of a slurry of 25% commercial "garden vegetables" baby food in 0.1% peptone water. Inhibition required UV activation after the addition of the LFs to the model system. Lime peel extract, cold-pressed lime oil, and a 5-MOP standard inhibited the growth of L. monocytogenes , but not E. coli O157:H7. M. luteus was inhibited only by the cold-pressed lime oil. The minimum LF concentration that caused inhibition of the growth of L. monocytogenes was 32 µg/g and the minimum bactericidal concentration was 43 µg/g. Cold-pressed lime oil inhibited L. monocytogenes even at the lowest concentration added to the model system (10 µg/g), while the corresponding LF standard did not. This suggested the presence of other antimicrobial agents in the oil.

Inhibition of Listeria monocytogenes , Escherichia coli O157:H7, and Micrococcus luteus by Linear Furanocoumarins in Culture Media.

The linear furanocoumarins psoralen, 5-methoxypsoralen (5-MOP), and 8-methoxypsoralen (8-MOP) were tested as antimicrobial agents against Listeria monocytogenes , Escherichia coli O157:H7 and Micrococcus luteus . The linear furanocoumarins were activated with UV light at 365 nm for 60 min. MICs of these furanocoumarins in tryptic soy broth supplemented with 0.6% yeast extract were determined at room temperature for 48 h. Psoralen was the most effective antimicrobial agent of the three studied. This compound inhibited the three test microorganisms at concentrations of 5 µg/ml or lower. Only L. monocytogenes was inhibited by 5-MOP.Concentrations of at least 10µg of 8-MOP per ml were required to inhibit the test microorganisms. Mixtures containing at least 7.5 µg of psoralen per ml inhibited the growth of the three microorganisms. In the absence of psoralen, mixtures of 5- MOP and 8-MOP were ineffective as growth inhibitors of M. luteus and E. coli O157:H7.

Biofilm Formation by Listeria monocytogenes Utilizes a Primary Colonizing Microorganism in Flowing Systems.

Listeria monocytogenes serotype 3a and Pseudomonas fragi ATCC 4973 were examined for attachment capability and biofilm development on glass coverslips under flowing systems. Tryptic soy broth supplemented with yeast extract was the growth medium. A continuous flow slide chamber was developed for in situ observations using phase-contrast microscopy. Glass coverslips were examined by epifluorescent and scanning electron microscopy for biofilm formation. The ultrastructure of attached test organisms was examined for the presence of exopolymers using transmission electron microscopy. In pure cultures, attachment of L. monocytogenes to glass coverslips was sparse, while P. fragi accumulated on glass coverslips as a confluent layer of cells. When L. monocytogenes was grown in mixed culture with P. fragi , an exopolymer-producing microorganism, attachment and microcolony formation by L. monocytogenes was enhanced. Results suggest that under flowing conditions the presence of an exopolymer-producing microorganism may be more important than hydrophobicity, surface charge, or flagellar movement in attachment of L. monocytogenes to inert surfaces.

Potential for the Low-Temperature Pasteurization of Dairy Fluids Using Membrane Processing.

Raw milk, reconstituted skim milk, skim milk, sweet whey, and acid whey were membrane processed on different units from several manufacturers using various membranes with pore sizes ranging from nanofiltration through microfiltration. The bulk fluids were inoculated with either Staphylococcus aureus 196E, Salmonella typhimurium var. Hillfarm, and/or Pseudomonas fragi 4973. In addition, indigenous microorganisms were present. The permeate and retentate streams were monitored for bacterial numbers. Percent total solids of the permeate streams was determined. Temperatures and pressures were controlled. In no cases were the bacteria completely retained while concomitantly allowing permeated solids to equal the solids in the original bulk fluid. Findings indicated different membranes of same molecular weight cut-off exhibited dissimilar bacterial retention characteristics. Unit design/configuration appeared to play a role in retention of bacteria. Spiral wound microfiltration and ultrafiltration membranes reduced bacterial loads in the permeate by 98.9 to 99.99% while allowing 5 to 6% of the solids in the bulk fluid to pass through the membrane. The bulk fluid does not appear to affect the bacterial retention. The different wheys, milks, and reconstituted skim milk showed similar reductions in bacterial numbers when microfiltered or ultrafiltered through the same type of membrane. All three test microbes demonstrated similar declines during membrane processing. It appeared that bacterial morphology and size did not affect the bacterial retention characteristics. Results indicated that low-temperature membrane processing will not eliminate all microorganisms in the permeate nor did all milk components pass through the membrane into the permeate.

Evaluation of Selected Sanitizers to Control Bacteria in a Simulated Sweet Water Coolant System 1.

Three types of sanitizers commonly used in dairy processing plants were evaluated at varying concentrations and at 25 and 4°C for their ability to control potential spoilage and pathogenic bacteria in water. Test organisms included Pseudomonas fluorescens , Staphylococcus haemolyticus , and Bacillus spp. These had been isolated from samples of sweet water coolants collected in a previous national survey in grade A dairy plants. S. haemolyticus required 10 ppm chlorine, 12.5 ppm iodine, or 10 ppm quaternary ammonium compound (QAC) to reduce the population >99% at 25°C. At 4°C, however, only 93% of the population of S. haemolyticus was reduced with the 10 ppm QAC. Concentrations of 25 ppm chlorine, 2.5 ppm iodine, or 20 ppm QAC reduced the P. fluorescens population >99% at both 25 and 4°C. The Bacillus spp. was reduced >99% at concentrations of 10 ppm chlorine at 25 and 4°C, 2.5 ppm iodine at 25°C, and 10 ppm QAC at both temperatures. At 4°C, 2.5 ppm iodine reduced the Bacillus population to only 93%. All three organisms were reduced >90% at both test temperatures with concentrations of 25 ppm chlorine, 12.5 ppm iodine, or 20 ppm QAC.

Scanning Electron Microscopic Examination of Yersinia enterocolitica Attached to Stainless Steel at Selected Temperatures and pH values 1.

Attachment of Yersinia enterocolitica to stainless steel surfaces at 35, 21, and 10°C was investigated using scanning electron microscopy (SEM). Cells adhered at all three temperatures, but, in general, the greatest number of adhered cells were observed at pH 8 and 21°C. Multi-flagellated cells were noted under these growth conditions. When grown at pH 9.5 and 21°C, fibrils were observed between cells and extending to the stainless steel surface. Fewer cells with flagella were seen at this pH. Adherence may be related to the flagella and any exopolymer surrounding the cells.

Survival of Salmonellae in Refrigerated, Agitated Water and Water/Glycol Mixtures 1.

Survival of Salmonella typhimurium in refrigerated water and a 30:70 mixture of ethylene glycol and water was studied. Survival was determined with an MPN procedure using 333 ml of the cooling medium. Initial populations were determined by spread plating 1 ml of sample on 3 plates of XLD. With water as the suspending medium, the temperature of the circulating water was 1°C. When the cooling medium was the glycol/water mixture, the temperature was -1°C. Low numbers of S. typhimurium were recovered from the cold water for 9 d and from the glycol/water mixture for 14 d. The initial population in the water was 310 CFU/ml and 630 CFU/ml in the glycol/water system. A preliminary survey of the pressure relationships in the cooling sections of HTST pasteurizers in 8 fluid milk plants showed that 3 had higher pressures on the coolant side than on the pasteurized side. Such a pressure relationship could result in the contamination of pasteurized milk with the cooling medium.

Scanning Electron Microscopic Study on Some Effects of Sodium Hypochlorite on Attachment of Bacteria to Stainless Steel 1.

Scanning Electron Microscopy (SEM) was used to demonstrate the effects of rinsing with water and various concentrations of sodium hypochlorite (NaOCl) on extracellular attachment fibers of Pseudomonas fragi (ATCC 4793), Salmonella montevideo , and Bacillus cereus (F4165/75) attached to stainless steel chips. Results indicated that use of a water rinse before sanitization with NaOCl was not sufficient to eliminate attached microorganisms and debris.

Composition and Microbiology of Some Native Alaskan Preserved Foods.

Ten samples of native Alaskan processed or partially processed fish and fermenled whale meat were obtained from three of five native Alaskan villages visited in three different geographical areas of the state. Native Alaskan methods of processing/preserving the fish were observed. Samples were analyzed for composition and microbiologically for anaerobic bacteria. Compositional analysis suggested that the major preservation effect was through the reduction of aw.

Recipe Hazard Analysis - RHAS - A Systematic Approach to Analyzing Potential Hazards in a Recipe for Food Preparation/Preservation 1.

A systematic approach to analyzing food preservation - food preparation recipes for potential hazards is presented. The method is based on the Hazard Analysis Critical Control Point (HACCP) concept developed by the food processing industry for identifying potential hazards in processing. The Recipe Hazard Analysis System (RHAS) is used to identify potential hazards in several recipes. Worksheets and the method of analysis are given.