Effect of sodium chloride and chitosan on the inactivation of heat resistant or Shiga-toxin producing Escherichia coli during grilling of burger patties

Cattle are a reservoir for enterohemorrhagic Escherichia coli (EHEC), and ground beef is a major vehicle for human infection with EHEC. Heat resistance of E. coli, including EHEC, is impacted by NaCl and other additives. This study aimed to evaluate the effect of NaCl and other additives on the heat resistance of E. coli in beef patties. E. coli AW1.7ΔpHR1(pLHR) with the locus of heat resistance (LHR), E. coli AW1.7ΔpHR1(pRK767) without LHR, or a 5-strain cocktail of EHEC were inoculated (10⁷-10⁸ CFU/g) into ground beef (15% fat) with NaCl (0-3%), marinade, carvacrol (0.1%), potassium lactate (3%) or chitosan (0.1%) following different protocols. Patties were grilled immediately, or stored in sterile bags for two days at 4 °C prior to grilling to a core temperature of 71 °C. Cell counts of LHR-positive E. coli AW1.7ΔpHR1(pLHR) were higher than that of the isogenic LHR-negative E. coli AW1.7ΔpHR1(pRK767) by >3 log₁₀ (CFU/g) after cooking. Addition of 3% NaCl increased survival of E. coli AW1.7ΔpHR1(pRK767) and the EHEC cocktail while cell counts of the heat resistant strains were not changed. A protective effect of NaCl was not observed with E. coli AW1.7ΔpHR1(pRK767) or EHEC if cells of E. coli were cooled to 4 °C prior to mixing with cold meat and NaCl, indicating that the response of E. coli to osmotic shock contributes to this effect. Chitosan enhanced the thermal destruction of LHR-positive E. coli AW1.7ΔpHR1(pLHR) in ground beef stored at 4 °C for 2 days, while marinade, carvacrol, or potassium lactate had no such effect, indicating that chitosan can be characterized as an effective hurdle concept to reduce the potential risk of LHR-positive pathogen to meat safety.

Role of myofibers, perimysium and adipocytes in horse meat toughness

Horse meat is a good source of iron with low cholesterol but consumers consider tenderness most important when purchasing meat. Myofibers and intramuscular connective tissue, the main structural components of muscle, play major roles in meat toughness. The effects of myofibers and perimysium characteristics on Warner-Bratzler Shear Force (WBSF) values of horse semimembranosus were investigated on muscles previously assessed as tough (mean WBSF 68.87 ± 3.21 N, n = 8) or tender (mean WBSF 46.21 ± 2.27 N, n = 8). Mean Type IIA myofiber diameter was significantly greater in tender than in tough muscles. Secondary thick perimysium was thicker and collagen fibers more loosely arranged in tender muscles than in tough. A negative correlation was observed between WBSF values and perimysium thickness and a trend between WBSF and intramuscular fat. Adipocytes in perimysium of tender muscles may have contributed to thickening of perimysium and loosened collagen fibers thus contributing to tenderness of the meat.

Characterization of a highly potent antimicrobial peptide microcin N from uropathogenic Escherichia coli

Microcin N is a low-molecular weight, highly active antimicrobial peptide produced by uropathogenic Escherichia coli In this study, the native peptide was expressed and purified from pGOB18 plasmid carrying E. coli in low yield. The pure peptide was characterized using mass spectrometry, N-terminal sequencing by Edman degradation as well as trypsin digestion. We found that the peptide is 74-residue long, cationic (+2 total charge), highly hydrophobic and consists of glycine as the first N-terminal residue. The minimum inhibitory concentration of the peptide against Salmonella enteritidis was found to be 150 nM. Evaluation of the solution conformation of the peptide using circular dichroism spectroscopy showed that the peptide is well folded in 40% trifluoroethanol with helical structure whereas the folded structure is lost in aqueous solution. To increase the yield of this potent peptide, we overexpressed GST-tagged microcin N using E. coli BL21. Recombinant GST-tagged microcin N was successfully expressed in E. coli BL21; however, the cleaved mature microcin N did not show activity against the indicator strain (S. enterica) most likely due to the extreme hydrophobic nature of the peptide. Efforts to produce active microcin N in large scale are discussed as this peptide has huge potential to be the next generation antimicrobial agent.

High Prevalence of Hyper-Aerotolerant Campylobacter jejuni in Retail Poultry with Potential Implication in Human Infection

Campylobacter jejuni is a leading cause of foodborne illnesses around the world. Since C. jejuni is microaerophilic and sensitive to oxygen, aerotolerance is important in the transmission of C. jejuni to humans via foods under aerobic conditions. In this study, 70 C. jejuni strains were isolated from retail raw chicken meats and were subject to multilocus sequence typing (MLST) analysis. In the aerotolerance testing by aerobic shaking at 200 rpm, 50 (71.4%) isolates survived after 12 h (i.e., aerotolerant), whereas 20 (28.6%) isolates did not (i.e., aerosensitive). Interestingly, further aerobic cultivation showed that 25 (35.7%) isolates still survived even after 24 h of vigorous aerobic shaking (i.e., hyper-aerotolerant). Compared to aerosensitive strains, the hyper-aerotolerant strains exhibited increased resistance to oxidative stress, both peroxide and superoxide. A mutation of ahpC in hyper-aerotolerant strains significantly impaired aerotolerance, indicating oxidative stress defense plays an important role in hyper-aerotolerance. The aerotolerant and hyper-aerotolerant strains were primarily classified into MLST clonal complexes (CCs)-21 and -45, which are known to be the major CCs implicated in human gastroenteritis. Compared to the aerosensitive strains, CC-21 was more dominant than CC-45 in aerotolerant and hyper-aerotolerant strains. The findings in this study revealed that hyper-aerotolerant C. jejuni is highly prevalent in raw chicken meats. The enhanced aerotolerance in C. jejuni would impact human infection by increasing possibilities of the foodborne transmission of C. jejuni under aerobic conditions.

Impact of oxidative stress defense on bacterial survival and morphological change in Campylobacter jejuni under aerobic conditions

Campylobacter jejuni, a microaerophilic foodborne pathogen, inescapably faces high oxygen tension during its transmission to humans. Thus, the ability of C. jejuni to survive under oxygen-rich conditions may significantly impact C. jejuni viability in food and food safety as well. In this study, we investigated the impact of oxidative stress resistance on the survival of C. jejuni under aerobic conditions by examining three mutants defective in key antioxidant genes, including ahpC, katA, and sodB. All the three mutants exhibited growth reduction under aerobic conditions compared to the wild-type (WT), and the ahpC mutant showed the most significant growth defect. The CFU reduction in the mutants was recovered to the WT level by complementation. Higher levels of reactive oxygen species were accumulated in C. jejuni under aerobic conditions than microaerobic conditions, and supplementation of culture media with an antioxidant recovered the growth of C. jejuni. The levels of lipid peroxidation and protein oxidation were significantly increased in the mutants compared to WT. Additionally, the mutants exhibited different morphological changes under aerobic conditions. The ahpC and katA mutants developed coccoid morphology by aeration, whereas the sodB mutant established elongated cellular morphology. Compared to microaerobic conditions, interestingly, aerobic culture conditions substantially induced the formation of coccoidal cells, and antioxidant treatment reduced the emergence of coccoid forms under aerobic conditions. The ATP concentrations and PMA–qPCR analysis supported that oxidative stress is a factor that induces the development of a viable-but-non-culturable state in C. jejuni. The findings in this study clearly demonstrated that oxidative stress resistance plays an important role in the survival and morphological changes of C. jejuni under aerobic conditions.

Development and validation of a surrogate strain cocktail to evaluate bactericidal effects of pressure on verotoxigenic Escherichia coli

Many strains of verotoxigenic Escherichia coli (VTEC) are highly resistant to pressure. To facilitate future studies to improve the elimination of VTEC by pressure processing of food, this study developed and validated a cocktail of non-pathogenic strains of E. coli with equal or higher resistance to pressure when compared to pressure resistant strains of VTEC. Strains of E. coli obtained from a beef processing plant were screened for their resistance to heat and pressure. Treatments were carried out in LB broth. Cell counts of 3 out of 16 strains were reduced by 5-6 log (cfu/mL) after 30 min at 60 °C, and cell counts of 10 out of 16 strains were reduced by 5-6 log (cfu/mL) after 30 min at 40 °C and 400 MPa. All highly heat resistant strains were also pressure resistant but not all pressure resistant strains were also heat resistant. Pressure resistant and -sensitive strains of E. coli were treated in presence of 0 or 2% NaCl and at 3, 20, or 40 °C. The effect of these parameters on the lethality of pressure treatments was comparable for all strains. The addition of 2% NaCl did not increase pressure resistance. The bactericidal effect of treatments at 3 and 20 °C and 600 MPa was comparable but inactivation of E. coli was faster at 40 °C and 600 MPa. The resistance to treatment with 600 MPa at 20 °C of a cocktail of 5 non-pathogenic strains of E. coli was compared to a 5 strain cocktail of pressure resistant VTEC. Treatments were performed in ground beef containing 15% fat. Survival and sublethal injury of the two cocktails was comparable; cell counts of beef inoculated with either cocktail were reduced by about 4 log (cfu/mL) after 30 min of treatment. In conclusion, this study validated a cocktail of non-pathogenic strains of E. coli for use as surrogate organisms in studies on the elimination of E. coli by pressure.

Variation in heat and pressure resistance of verotoxigenic and nontoxigenic Escherichia coli

This study evaluated the heat and pressure resistance of 112 strains of Escherichia coli, including 102 strains of verotoxigenic E. coli (VTEC) representing 23 serotypes and four phylogenetic groups. In an initial screening, the heat and pressure resistance of 100 strains, including 94 VTEC strains, were tested in phosphate-buffered saline (PBS). Treatment at 60°C for 5 min reduced cell counts by 2.0 to 5.5 log CFU/ml; treatment at 600 MPa for 3 min at 25°C reduced the cell counts by 1.1 to 5.5 log CFU/ml. Heat or pressure resistance did not correlate to the phylogenetic group or the serotype. A smaller group of E. coli strains was evaluated for heat and pressure resistance in Luria-Bertani (LB) broth. Generally, the levels of heat resistance of E. coli strains in LB and PBS were similar; however, the levels of pressure resistance observed for treatments in LB broth or PBS were variable. The cell counts of pressure-resistant strains of VTEC were reduced by less than 1.5 log CFU/ml after treatment at 600 MPa for 3 min. E. coli strains were also treated with 600 MPa for 3 min in ground beef or inoculated into beef patties and grilled to 63 or 71°C. The cell counts of the VTEC E. coli O26:H11 strain 05-6544 were reduced by 2 log CFU/g by pressure treatment in ground beef. The cell counts of the heat-resistant E. coli strain AW1.7 were reduced by 1.4 and 3.4 log CFU/g in beef patties grilled to internal temperatures of 63 and 71°C, respectively. The cell counts of E. coli 05-6544 were reduced by less than 3 and 6 log CFU/g in beef patties grilled to internal temperatures of 63 and 71°C, respectively. To study whether the composition of the beef patties influenced heat resistance, E. coli strains AW1.7, AW1.7 Δ pHR1, MG1655, and LMM1030 were mixed into beef patties containing 15 or 35% fat and 0 or 2% NaCl, and the patties were grilled to an internal temperature of 63°C. The highest heat resistance of E. coli was observed in patties containing 15% fat and 2% NaCl.

Origin of contamination and genetic diversity of Escherichia coli in beef cattle

The possible origin of beef contamination and genetic diversity of Escherichia coli populations in beef cattle, on carcasses and ground beef, was examined by using random amplification of polymorphic DNA (RAPD) and PCR-restriction fragment length polymorphism (PCR-RFLP) analysis of the fliC gene. E. coli was recovered from the feces of 10 beef cattle during pasture grazing and feedlot finishing and from hides, carcasses, and ground beef after slaughter. The 1,403 E. coli isolates (855 fecal, 320 hide, 153 carcass, and 75 ground beef) were grouped into 121 genetic subtypes by using the RAPD method. Some of the genetic subtypes in cattle feces were also recovered from hides, prechilled carcasses, chilled carcasses, and ground beef. E. coli genetic subtypes were shared among cattle at all sample times, but a number of transient types were unique to individual animals. The genetic diversity of the E. coli population changed over time within individual animals grazing on pasture and in the feedlot. Isolates from one animal (59 fecal, 30 hide, 19 carcass, and 12 ground beef) were characterized by the PCR-RFLP analysis of the fliC gene and were grouped into eight genotypes. There was good agreement between the results obtained with the RAPD and PCR-RFLP techniques. In conclusion, the E. coli contaminating meat can originate from cattle feces, and the E. coli population in beef cattle was highly diverse. Also, genetic subtypes can be shared among animals or can be unique to an animal, and they are constantly changing.

Painful bladder syndrome--a clinical and immunopathological study

Painful bladder syndrome is a clinical diagnosis in patients with symptoms of varying severity which always include frequency and suprapubic pain and occasionally include dysuria, nocturia and urgency persisting for more than 3 months with no loss of bladder capacity and no overt infection. Immunofluorescence studies of biopsy specimens in 38 female patients were assessed and correlated with the duration and severity of symptoms, and also with routine histology (including mast cell infiltration and integrity of the glycosaminoglycans layer), in order to assess the role of immunological mechanisms in this distressing condition. The results indicated that submucosal angiogenesis and persistence of antigen-antibody complex in vessel walls could be responsible for this syndrome.

Histological identification of Campylobacter using Gimenez technique in gastric antral mucosa

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Pain, control over treatment, and compliance in dialysis and transplant patients

Pain was surveyed via structured interview and the McGill Pain Questionnaire in 53 dialysis and 27 transplant patients. Increased patient control over the dialysis procedure was not associated with a reduction in pain though perceived control may have been. Compliance with the dialysis regimen did not predict pain and the validity of the category "dialysis headache" was questioned. Overall, transplant recipients did not report significantly less pain than dialysis patients. Self-reported depression was correlated positively with pain. The clinical implications of these findings are discussed.