Survival of Escherichia coli O157:H7 in ground beef jerky assessed on two plating media

Selection and Characterization of Staphylococcus hominis subsp. hominis WiKim0113 Isolated from Kimchi as a Starter Culture for the Production of Natural Pre-converted Nitrite

Synthetic nitrite is considered an undesirable preservative for meat products; thus, controlling synthetic nitrite concentrations is important from the standpoint of food safety. We investigated 1,000 species of microorganisms from various kimchi preparations for their potential use as a starter culture for the production of nitrites. We used 16S rRNA gene sequence analysis to select a starter culture with excellent nitrite and nitric oxide productivity, which we subsequently identified as Staphylococcus hominis subspecies hominis WiKim0113. That starter culture was grown in NaCl (up to 9%; w/v) at 10°C–40°C; its optimum growth was observed at 30°C at pH 4.0–10.0. It exhibited nonproteolytic activity and antibacterial activity against Clostridium perfringens, a bacterium that causes food poisoning symptoms. Analysis of Staphylococcus hominis subspecies hominis WiKim0113 with an API ZYM system did not reveal the presence of β-glucuronidase, and tests of the starter culture on 5% (v/v) sheep blood agar showed no hemolytic activity. Our results demonstrated the remarkable stability of coagulase-negative Staphylococcus hominis subspecies hominis WiKim0113, especially in strain negative for staphylococcal enterotoxins and sensitive to clinically relevant antibiotics. Moreover, Staphylococcus hominis subspecies hominis WiKim0113 exhibited a 45.5% conversion rate of nitrate to nitrite, with nitrate levels reduced to 25% after 36 h of culturing in the minimal medium supplemented with nitrate (200 ppm). The results clearly demonstrated the safety and utility of Staphylococcus hominis subspecies hominis WiKim0113, and therefore its suitability as a starter culture.

Microbiological safety of processed meat products formulated with low nitrite concentration - A review

Nitrite plays a major role in inhibiting the growth of foodborne pathogens, including Clostridium botulinum (C. botulinum) that causes botulism, a life-threatening disease. Nitrite serves as a color-fixing agent in processed meat products. However, N-nitroso compounds can be produced from nitrite, which are considered as carcinogens. Thus, consumers desire processed meat products that contain lower concentrations (below conventional concentrations of products) of nitrite or no nitrite at all, although the portion of nitrite intake by processed meat consumption in total nitrite intake is very low. However, lower nitrite levels might expose consumers to risk of botulism poisoning due to C. botulinum or illness caused by other foodborne pathogens. Hence, lower nitrite concentrations in combination with other factors such as low pH, high sodium chloride level, and others have been recommended to decrease the risk of food poisoning. In addition, natural compounds that can inhibit bacterial growth and function as color-fixing agents have been developed to replace nitrite in processed meat products. However, their antibotulinal effects have not been fully clarified. Therefore, to have processed meat products with lower nitrite concentrations, low pH, high sodium chloride concentration, and others should also be applied together. Before using natural compounds as replacement of nitrite, their antibotulinal activities should be examined.

Lethality of home-style dehydrator processes against Escherichia coli O157:H7 and salmonella serovars in the manufacture of ground-and-formed beef jerky and the potential for using a pathogen surrogate in process validation

Ground-and-formed beef jerky can be made easily at home with ground beef and kits that include spice, cure, and jerky-forming equipment. Ground beef poses inherent risks of illness due to Escherichia coli O157:H7 and Salmonella contamination, making adequate pathogen lethality important in jerky manufacturing. We evaluated the effectiveness of drying regimes at eliminating E. coli O157:H7 and Salmonella in seasoned ground-and-formed beef jerky manufactured with three home-style dehydrators and one small commercial unit. Inoculated jerky strips were dried for up to 12 or 24 h in a home-style or the commercial unit, respectively, with target drying temperatures ranging from 51.7 degrees C (125 degrees F) to 71.1 degrees C (160 degrees F). Pathogen lethality varied with seasoning, temperature, and drying time (n = 288 samples). Lethality against E. coli O157:H7 ranged from 1.5 log CFU (Jerky Xpress, 57.2 degrees C [135 degrees F], 4 h) to 6.4 log CFU (Gardenmaster, 68.3 degrees C [155 degrees F], 12 h), and varied with seasoning. Lethality against Salmonella ranged from 1.7 log CFU (Jerky Xpress, 57.2 degrees C [135 degrees F], 4 h) to 6.0 log CFU (Gardenmaster, 68.3 degrees C [155 degrees F], 12 h), and also varied with seasoning. There was a > or =5-log CFU reduction in both pathogens in 0, 10, and 27 % of samples at 4, 8, and 12 h, respectively. Heating jerky for 10 min at 135 degrees C (275 degrees F) 4 or 6 h postdrying increased lethality, on average, 2.99 log CFU for Salmonella and 3.02 log CFU for E. coli O157:H7. The use of a lactic acid bacterium culture (Pediococcus spp.) as a pathogen surrogate accurately predicted safety in 28 % of samples containing E. coli O157:H7 and 78% of Salmonella-inoculated samples.

Validation of ground-and-formed beef jerky processes using commercial lactic acid bacteria starter cultures as pathogen surrogates

Beef jerky has been linked to multiple outbreaks of salmonellosis and Escherichia coli O157:H7 infection over the past 40 years. With increasing government scrutiny of jerky-making process lethality, a simple method by which processors can easily validate the lethality of their ground-and-formed beef jerky process against Salmonella' and E. coli O157:H7 is greatly needed. Previous research with whole-muscle beef jerky indicated that commercial lactic acid bacteria (LAB) may be more heat resistant than Salmonella and E. coli O157:H7, suggesting the potential use of LAB as pathogen surrogates. Of six commercial LAB-containing cultures evaluated for heat resistance in ground-and-formed beef jerky, Saga 200 (Pediococcus spp.) and Biosource (Pediococcus acidilactici) were identified as consistently more heat resistant than Salmonella and E. coli O157:H7. Six representative ground-and-formed beef jerky commercial processes, differing widely in lethality, were used to identify an appropriate level of LAB reduction that would consistently indicate a process sufficiently lethal (> or = 5.0-log reduction) for Salmonella and E. coli O157:H7. Both Saga 200 and Biosource consistently predicted adequate process lethality with a criterion of > or = 5.0-1og reduction of LAB. When either LAB decreased by > or = 5.0 log CFU, processes were sufficiently lethal against Salmonella and E. coli O157:H7 in 100% of samples (n=39 and 40, respectively). Use of LAB as pathogen surrogates for ground-and-formed beef jerky process validation was fieldtested by three small meat processors, who found this technique easy to use for process validation.

Validation of a commercial process for inactivation of Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes on the surface of whole muscle beef jerky

We validated the lethality of three time and temperature regimens for commercial processing of whole muscle beef jerky. A total of ca. 8.9 log CFU per strip of multiple-strain cocktails of Escherichia coli O157:H7, Salmonella Typhimurium, or Listeria monocytogenes were separately applied onto the surface of beef strips that were treated as follows: (i) inoculated but not marinated or (ii) inoculated and then marinated. A total of three beef strips for each treatment in each of three trials were separately inoculated with a cocktail of one of the three pathogens and placed on the top, middle, and bottom racks of a loading truck. The strips on the rack were loaded into a commercial smokehouse and cooked and dried for 1.5, 2.5, or 3.5 h at a target temperature of 180 degrees F (82.2 degrees C) with constant (natural hickory) smoking, but without the addition of humidity. Regardless of how the strips were treated or where the strips were placed on the loading rack, drying for 1.5, 2.5, or 3.5 h to a target temperature of 180 degrees F (average of 177.2 +/- 5.6 degrees F [80.7 +/- 3.1 degrees C]), with constant smoke at an initial average relative humidity of 63.1% to a final average relative humidity of 20.9% resulted in a decrease of > or = 7.3 log CFU per strip (> or = 6.9 log CFU/g) for each of the three pathogen cocktails. Of note, marinated strips that were cooked and dried for 2.5 and 3.5 h or nonmarinated strips cooked or dried for 3.5 h also satisfied the U.S. Food Safety and Inspection Service standard of identity (moisture-to-protein ratio < or = 0.75:1) and/or shelf-stability (water activity < or = 0.8) requirements for jerky.

Effects of preparation methods on the microbiological safety of home-dried meat jerky

Historically, drying meats to produce jerky was conisidered to be a safe preservation process and the convenience and flavor of jerky has made it a popular food product for home food preservers. Recent outbreaks of foodborne illness related to both home-dried and commercially manufactured jerky have raised concerns about the safety of the product. Some traditional home recipes and drying processes were shown to be inadequate to destroy Escherichia coli O157, Salmonella, Staphylococcus aureus, and Listeria monocytogenes in both whole-muscle and ground-meat jerky. Several research studies have identified processes such as precooking meats before drying, usingacidic marinades, cooking meats after drying, or some combination of these treatments that can destroy pathogens of concern to produce microbiologically safe and palatable meat jerky at home.

Effect of acid adaptation on inactivation of Salmonella during drying and storage of beef jerky treated with marinades

This study evaluated the influence of pre-drying marinade treatments on inactivation of acid-adapted or nonadapted Salmonella on beef jerky during preparation, drying and storage. The inoculated (five-strain composite, 6.0 log CFU/cm2) slices were subjected to the following marinades (24 h, 4 degrees C) prior to drying at 60 degrees C for 10 h and aerobic storage at 25 degrees C for 60 days: (1) no marinade, control (C), (2) traditional marinade (TM), (3) double amount of TM modified with added 1.2% sodium lactate, 9% acetic acid, and 68% soy sauce with 5% ethanol (MM), (4) dipping into 5% acetic acid and then TM (AATM), and (5) dipping into 1% Tween 20 and then into 5% acetic acid, followed by TM (TWTM). Bacterial survivors were determined on tryptic soy agar with 0.1% pyruvate and xylose-lysine-tergitol 4 (XLT4) agar. Results indicated that drying reduced bacterial populations in the order of pre-drying treatments TWTM (4.8-6.0 log CFU/cm2)> or =AATM> or =MM>TM> or =C (2.6-5.0 log CFU/cm2). Nonadapted Salmonella were significantly (P<0.05) more resistant to inactivation during drying than acid-adapted Salmonella in all treatments. Bacterial populations decreased below the detection limit (-0.4 log CFU/cm2) as early as 7 h during drying or remained detectable even after 60 days of storage, depending on acid adaptation, pre-drying treatment, and agar media. The results indicated that acid adaptation may not cause increased resistance of Salmonella to the microbial hurdles involved in jerky processing and that use of modified marinades in manufacturing jerky may improve the effectiveness of drying in inactivating Salmonella.

Inactivation of acid-adapted and nonadapted Escherichia coli O157:H7 during drying and storage of beef jerky treated with different marinades

The inactivation of both acid-adapted and unadapted Escherichia coli O157:H7 during the processing of beef jerky was studied. Following inoculation with the pathogen, beef slices were subjected to different predrying marinade treatments, dried at 60 degrees C for 10 h, and stored at 25 degrees C for 60 d. The predrying treatments evaluated were as follows: (i) no treatment (C), (ii) traditional marinade (TM), (iii) double-strength TM modified with added 1.2% sodium lactate, 9% acetic acid, and 68% soy sauce with 5% ethanol (MM), (iv) dipping into 5% acetic acid for 10 min followed by application of TM (AATM), and (v) dipping into 1% Tween 20 for 15 min and then into 5% acetic acid for 10 min followed by TM (TWTM). Bacterial survivors were determined during drying and storage using tryptic soy agar with 0.1% pyruvate, modified eosin methylene blue agar, and sorbitol MacConkey agar. Results indicated that bacterial populations decreased during drying in the order of TWTM (4.9 to 6.7 log) > AATM > MM > C > or = TM (2.8 to 4.9 log) predrying treatments. Populations of acid-adapted E. coli O157:H7 decreased faster (P < 0.05) in AATM and TWTM than nonadapted cells during drying, whereas no significant difference was found in inactivation of acid-adapted and nonadapted inocula in C and TM samples. MM was more effective in inactivating the nonadapted than the adapted inoculum. Bacterial populations continued to decline during storage and dropped below the detection limit (-0.4 log10 CFU/cm2) as early as day 0 (after drying) or as late as day 60, depending on acid adaptation, predrying treatment, and agar medium. The results indicated that acid adaptation may not increase resistance to the hurdles involved in jerky processing and that use of additional antimicrobial chemicals or preservatives in jerky marination may improve the effectiveness of drying in inactivating E. coli O157:H7.

Methods for the detection and isolation of Shiga toxin-producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) are an important cause of haemorrhagic colitis and the diarrhoea-associated form of the haemolytic uraemic syndrome. Of the numerous serotypes of E. coli that have been shown to produce Shiga toxin (Stx), E. coli O157:H7 and E. coli O157:NM (non-motile) are most frequently implicated in human disease. Early recognition of STEC infections is critical for effective treatment of patients. Furthermore, rapid microbiological diagnosis of individual patients enables the prompt notification of outbreaks and implementation of control measures to prevent more cases. Most human infections caused by STEC have been acquired by the consumption of contaminated foods, especially those of bovine origin such as undercooked ground beef and unpasteurized cows' milk, and by person-to-person contacts. To identify the reservoirs of STEC and the routes of transmission to man, sensitive methods are needed as these pathogens may only be present in food, environmental and faecal samples in small numbers. In addition, sensitive and rapid detection methods are necessary for the food industry to ensure a safe supply of foods. Sensitive methods are also needed for surveillance programmes in risk assessment studies, and for studies on survival and growth of STEC strains. Cultural methods for the enrichment, isolation and confirmation of O157 STEC are still evolving. Several selective enrichment media have been described, of which modified tryptone soy broth with novobiocin and modified E. coli broth with novobiocin, seem to be the most appropriate. These media are minimally-selective broths that give a somewhat limited differential specificity favouring isolation of O157 STEC, as opposed to other Gram-negative bacteria, in the sample. An incubation temperature of 41-42 degrees C further enhances selectivity. The occurrence of heat-, freeze-, acid- or salt-stressed STEC in foods means that it is important to be able to detect cells that are in a stressed state, as STEC generally have a very low infectious dose, and injured cells mostly retain their pathogenic properties. For the isolation of stressed O157 STEC, pre-enrichment in a non-selective broth is necessary. The most widely used plating medium for the isolation of typical sorbitol-non-fermenting strains of STEC of serogroup O157 is sorbitol MacConkey agar with cefixime and tellurite (CT-SMAC). As some STEC strains are sensitive for tellurite and/or are sorbitol-fermenting, the use of a second isolation medium, such as one of the newer chromogenic media, is recommended. Immunomagnetic separation (IMS) following selective enrichment, and subsequent spread-plating of the concentrated target cells onto CT-SMAC agar, appears to be the most sensitive and cost-effective method for the isolation of E. coli O157 from raw foods. IMS increases sensitivity by concentrating E. coli O157 relative to background microflora, which may overgrow or mimic O157 STEC cells on selective agars. While cultural isolation of O157 STEC from foods and faeces is time-consuming, labour-intensive and hence, costly, rapid immunological detection systems have been developed which significantly reduce the analysis time. These methods include enzyme-linked immunosorbent assays (ELISAs), colony immunoblot assays, direct immunofluorescent filter techniques, and several immunocapture techniques. Both polyclonal and monoclonal antibodies specific for the O and H antigens are used for these methods. Many of these test systems are able to detect less than one O157 STEC cell g(-1) of raw meat after overnight enrichment. Presumptive results are available after just one day, but need to be completed with the isolation of the organisms. The primary use of these procedures is therefore to identify food and faecal samples that possibly contain O157 STEC.