Novel activator of mannose-specific phosphotransferase system permease expression in Listeria innocua, identified by screening for pediocin AcH resistance.

To identify genes that are important for class IIa bacteriocin interaction and resistance in Listeria species, transposon Tn917 knockout libraries were constructed for Listeria innocua strain Lin11 and screened for mutants that are resistant to pediocin AcH. A highly resistant mutant (G7) (MIC > 20 microg/ml; 1,000-fold less susceptible than the wild type), in which the transposon integrated into the putative promoter of the lin0142 gene, was isolated. lin0142 is located immediately upstream of the mpt operon (mptA/mptC/mptD) that encodes the mannose-specific phosphoenolpyruvate-dependent phosphotransferase system permease EIItMan, which serves as a docking protein for class IIa bacteriocins.

Prevalence and Biological Control of Bacteriocin-Producing Psychrotrophic Leuconostocs Associated with Spoilage of Vacuum-Packaged Processed Meats.

Low heat-processed vacuum-packaged commercial meat products are expected to have a relatively long shelf life at refrigerated temperature. However, temperature abuse often occurs and spoilage of these products is not uncommon. One common lype of spoilage is characterized by accumulation of gas and purge in the package wilh products having sour lo off odor.

Bacteriocins of Lactic Acid Bacteria in Combination Have Greater Antibacterial Activity.

Antibacterial efficiency of two bacteriocins from lactic acid bacteria, pediocin AcH, and nisin was tested individually and in combination against several gram-positive bacterial strains including some involved in food spoilage and foodborne diseases. Pediocin AcH and nisin were more antibacterial in combination than when they were used alone. The principles of this greater antibacterial spectrum have been proposed.

Viability Loss of Foodborne Pathogens by Starter Culture Metabolites.

Antibacterial metabolites produced by starter culture bacteria were tested for inhibitory properties against foodborne pathogens capable of growing in foods at refrigeration temperature. Three culture preparations containing the bacteriocins pediocin AcH, nisin, and sakacin A produced by Pediococcus acidilactici H, Lactococcus lactis ssp. lactis DL 16, and Lactobacillus sake 706, respectively, were studied in addition to four commercial preparations: Nisaplin (similar to nisin), Na-lactate, diacetyl and Microgard.

Spoilage of Vacuum-Packaged Refrigerated Beef by Clostridium.

A motile, gram-positive, spore forming, anaerobic, psychrotrophic bacterial species, probably from the genus Clostridium , was involved in spoilage of vacuum-packaged refrigerated fresh beef. The spoilage was associated with accumulation of large quantities of foul smelling gas and purge in the bag and loss of color and texture of the meat. Attempts to grow the organism in several laboratory media were not yet successful; however, inoculation of purge from a spoiled sample into a fresh beef, vacuum-packaging and refrigeration storage facilitated growth of this species and produced characteristic spoilage of beef.

Impact of Bacterial Injury and Repair in Food Microbiology: its Past, Present and Future.

Studies done during the past 25 years revealed that microorganisms present in semipreserved foods can be injured by sublethal treatments. The injured cells, irrespective of differences in sublethal treatments, have similarities in their manifestation of injury and their repair. A simple resuscitation step incorporated into currently recommended isolation procedures would enable detection of these cells.

Cellular Damage in Dried Lactobacillus acidophilus.

Lactobacillus acidophilus cells surviving freeze drying and vacuum drying became sensitive to oxgall and lysozyme probably from damage to the cell wall. The dried cells also became sensitive to NaCl and permeable to orthonitrophenol β-galactoside from damage to the cytoplasmic membrane. Scanning electron microscopy indicated loss of some surface material from the damaged cells.

Growth of Indicator, Pathogenic and Psychrotrophic Bacteria in Mechanically Separated Beef, Lean Ground Beef and Beef Bone Marrow .

Growth of Escherichia coli , Salmonella anatum , Staphylococcus aureus , Clostridium perfringens and naturally occurring psychrotrophs in mechanically separated beef (MSB), lean ground beef (LGB) and beef bone marrow (BBM) was studied. Six good grade steers were slaughtered and samples of MSB, LGB and BBM were prepared under proper sanitary care. Six hundred grams of each sample were collected; 100 g were used for chemical analysis.

Cryoprotectants Protect Lipopolysaccharide Molecules of the Outer Membrane of Escherichia coli B from Freeze-Damage.

Lipopolysaccharide (LPS) molecules of the outer membrane (OM) of Escherichia coli B were damaged by freezing and thawing as evidenced by lysozyme lysis of cells frozen in water and their inability to adsorb LPS-specific phages. Permeating cryoprotectants, i.e.

Prevalence of Viable Lactobacillus acidophilus in Dried Commercial Products.

Samples of 27 dried acidophilus products used as dietary adjuncts for Lactobacillus acidophilus in humans, were enumerated for viable cells on plate count agar (PCA), MRS broth plus 1.5% agar (MRSA) and MRSA plus 0.15 % oxgall (MRSOA).

Bacteriology of Restructured Lamb Roasts Made with Mechanically Deboned Meat .

Composite samples of restructured lamb roast containing 10 or 30% mechanically deboned meat (MDM) were analyzed for bacteriological quality before and after cooking to 62.8°C (145°F). Uncooked samples had less than 3.

Occurrence of Enteric Bacteria and Viruses in Oysters.

Enteric bacteria and virus levels were determined in oysters from paired stations that were opened or closed for commercial shellfishing on the basis of total coliform levels in the water. Six pairs of stations were sampled quarterly over a 1-year period. Enteric viruses were found in 3 of 24 50-g oyster samples from closed areas and in none of 23 samples from open areas.

Methods to Detect Stressed Microorganisms .

A population of surviving bacteria, after a sublethal physical or chemical treatment, is composed of the stressed or injured and the uninjured or normal cells. Injured cells develop sensitivity to many chemical compounds due to damage to their permeability barriers in the cell wall and the cell membrane. They also fail to repair this damage in the presence of selective compounds and consequently fail to multiply.