ABSTRACT Antibiotics used during food animal production account for approximately 77% of U.S. antimicrobial consumption by mass. Ground beef products labeled as raised without antibiotics (RWA) are perceived to harbor lower levels of antimicrobial-resistant bacteria than conventional (CONV) products with no label claims regarding antimicrobial use. Retail ground beef samples were obtained from six U.S. cities. Samples with an RWA or U.S. Department of Agriculture Organic claim ( n = 299) were assigned to the RWA production system. Samples lacking these claims ( n = 300) were assigned to the CONV production system. Each sample was cultured for the detection of five antimicrobial-resistant bacteria. Genomic DNA was isolated from each sample, and a quantitative PCR assay was used to determine the abundance of 10 antimicrobial resistance (AMR) genes. Prevalence of tetracycline-resistant Escherichia coli (CONV, 46.3%; RWA, 34.4%; P < 0.01) and erythromycin-resistant Enterococcus (CONV, 48.0%; RWA, 37.5%; P = 0.01) was higher in CONV ground beef. Salmonella was detected in 1.2% of samples. The AMR gene bla CTX-M (CONV, 4.1 log-normalized abundance; RWA, 3.8 log-normalized abundance; P < 0.01) was more abundant in CONV ground beef. The AMR genes mecA (CONV, 4.4 log-normalized abundance; RWA, 4.9 log-normalized abundance; P = 0.05), tet (A) (CONV, 3.9 log-normalized abundance; RWA, 4.5 log-normalized abundance; P < 0.01), tet (B) (CONV, 3.9 log-normalized abundance; RWA, 4.5 log-normalized abundance; P < 0.01), and tet (M) (CONV, 5.4 log-normalized abundance; RWA, 5.8 log-normalized abundance; P < 0.01) were more abundant in RWA ground beef. Although these results suggest that antimicrobial use during U.S. cattle production does not increase human exposure to antimicrobial-resistant bacteria via ground beef, quantitative microbiological risk assessments are required for authoritative determination of the human health impacts of the use of antimicrobial agents during beef production. HIGHLIGHTS Three antimicrobial resistances were higher in conventional products. Levels of four antimicrobial resistance genes were higher in RWA beef products. Vancomycin-resistant Enterococcus was not detected. Methicillin-resistant Staphylococcus aureus was detected in 1% of samples.

ABSTRACT Culled beef cows (cows that have reached the end of their productive life span in cow-calf operations) and culled dairy cows represent approximately 18% of the cattle harvested in the United States annually, but data on antimicrobial resistance (AMR) in these cull cattle are extremely limited. To address this data gap, colon contents were obtained from 180 culled conventional beef cows, 179 culled conventional dairy cows, and 176 culled organic dairy cows (produced without using antimicrobials). Sponge samples were also collected from 181 conventional beef, 173 conventional dairy, and 180 organic dairy cow carcasses. These samples were obtained on 6 days (3 days each at two beef harvest and processing establishments). At one establishment, 30 samples of beef manufacturing trimmings from conventional cows and 30 trim samples from organic dairy cows were acquired. All 1,129 samples were cultured for Escherichia coli, tetracycline-resistant (TET r ) E. coli, third-generation cephalosporin-resistant (3GC r ) E. coli, Salmonella, and 3GC r Salmonella . Metagenomic DNA was isolated from 535 colon content samples, and quantitative PCR assays were performed to assess the abundances of the following 10 antimicrobial resistance genes: aac(6′)-Ie-aph(2″)-Ia, aadA1, bla CMY-2 , bla CTX-M , bla KPC-2 , erm (B), mecA, tet (A), tet (B), and tet (M). For colon contents, only TET r E. coli ( P < 0.01), 3GC r E. coli ( P < 0.01), and erm (B) ( P = 0.03) levels were higher in conventional than in organic cows. Sampling day also significantly affected ( P < 0.01) these levels. Production system did not affect the levels of any measured AMR on carcasses or trim. The human health impact of the few significant AMR differences could not be determined due to the lack of standards for normal, background, safe, or basal values. Study results provide key heretofore unavailable data that may inform quantitative microbial risk assessments to address these gaps. HIGHLIGHTS Some AMR levels were higher in conventional than in organic cow colon contents. Carcass AMR levels did not differ between production systems. Trim AMR levels did not differ between production systems.

ABSTRACT The objective of this study was to assess the presence and characteristics of Salmonella enterica found in the synovial fluid of broiler carcasses. The synovial fluid of three individual joints from 500 broiler carcasses was individually sampled from five broiler processing facilities located in the Southeast and West regions of the United States (1,500 total samples). The external surface of broiler carcass was decontaminated before sampling of the shoulder, coxofemoral, and tibiofemoral joints. Individual samples were enriched, composited, and subjected to rapid PCR-based detection of Salmonella . Individual samples from any positive composites were also enriched before determination of Salmonella presence in the same manner. Positive individual samples were subjected to secondary enrichment before plating onto selective agar for isolation of Salmonella. Salmonella isolates were serotyped before determination of antimicrobial susceptibility. Overall, 1.00% (5 of 500 broiler carcasses) of composite samples and 0.47% (7 of 1,500 samples) of individual samples were positive for Salmonella . Five of the seven isolates were susceptible to all drugs tested and determined to be Salmonella Enteritidis. The remaining two isolates, identified as Salmonella Typhimurium, were resistant to streptomycin. To our knowledge, no previous assessments of Salmonella in the synovial fluid of broilers has been reported; however, results of the present study suggested that the synovial fluid may be a reservoir for Salmonella in broilers. Although the prevalence of Salmonella is low, this information provides valuable insight into potential poultry contamination pathways and warrants further exploration.

ABSTRACT Contamination of rendered products with Salmonella is a concern for the rendering industry, particularly when those products are intended for use in other foodstuffs, such as pet food. This study was conducted to understand the influence of compositional variation on the location and survivability of Salmonella in a poultry fat matrix. Specifically, this study aimed to (i) assess the influence of postinoculation time and moisture content on the distribution of Salmonella in rendered poultry fat and (ii) evaluate the impact of postinoculation time and physical parameters (i.e., impurity level and moisture content) on survival of three Salmonella strains in rendered poultry fat stored at two different temperatures. Three studies, designated as study I(a), I(b), and II, respectively, were conducted to address these objectives. In study I(a), a green fluorescent protein–expressing strain of Salmonella Typhimurium was used to map the organism within warmed (45°C) poultry fat containing various levels of moisture. In study I(b), the influence of storage temperature on the survivability of green fluorescent protein–expressing Salmonella was evaluated. In study II, the impacts of physical impurities, moisture content, and storage temperature on the survivability of three Salmonella strains (Enteritidis, Senftenberg, and Typhimurium) were assessed. The results of this study demonstrated that composition (i.e., moisture and impurity contents) influences the survivability of Salmonella in poultry fat; specifically, Salmonella is more persistent in poultry fat with a greater moisture content and water activity. Nonetheless, although composition impacts the distribution and survivability of Salmonella in poultry fat, Salmonella generally does not survive in poultry fat maintained at high temperatures (45°C and above).

ABSTRACT Validated surrogates are a useful tool for studying the response of pathogens to food safety interventions, but better surrogates are needed for studies using high pressure processing. Ground beef (85% lean, 15% fat) was inoculated separately with mixed cultures of Escherichia coli O157, non-O157 Shiga toxin–producing E. coli, nontyphoidal Salmonella, and nonpathogenic E. coli surrogate bacteria. The inoculated ground beef was subjected to high hydrostatic pressures of 200, 400, and 600 MPa for 4, 6, and 8 min at each pressure. High pressure processing at 200 MPa reduced the inoculated populations of the pathogenic bacteria by 0.9 to 1.8 log CFU/g, 400 MPa reduced the inoculated populations by 2.5 to 3.6 log CFU/g, and 600 MPa reduced the inoculated populations by 4.5 to 5.6 log CFU/g. The nonpathogenic E. coli surrogates were more resistant to the effects of high pressure processing than were the inoculated pathogen populations. This finding suggests that the nonpathogenic E. coli surrogates could be used as process control indicators for high pressure processing of ground beef to predict a specific level of pathogen reduction. The surviving populations of the potential surrogate bacteria were proportional to the surviving populations of the pathogenic bacteria. The models allow for an estimation of the potential surviving populations of the pathogenic bacteria based on quantitative results of the populations of the surrogate bacteria.

ABSTRACT A study was conducted to investigate the efficacy of a sulfuric acid–sodium sulfate blend (SSS) against Escherichia coli O157:H7, non-O157 Shiga toxin–producing E. coli (STEC), Salmonella, and nonpathogenic E. coli biotype I on prerigor beef surface tissue. The suitability of using the nonpathogenic E. coli as a surrogate for in-plant validation studies was also determined by comparing the data obtained for the nonpathogenic inoculum with those for the pathogenic inocula. Prerigor beef tissue samples (10 by 10 cm) were inoculated (ca. 6 log CFU/cm 2 ) on the adipose side in a laboratory-scale spray cabinet with multistrain mixtures of E. coli O157:H7 (5 strains), non-O157 STEC (12 strains), Salmonella (6 strains), or E. coli biotype I (5 strains). Treatment parameters evaluated were two SSS pH values (1.5 and 1.0) and two spray application pressures (13 and 22 lb/in 2 ). Untreated inoculated beef tissue samples served as controls for initial bacterial populations. Overall, the SSS treatments lowered inoculated (6.1 to 6.4 log CFU/cm 2 ) bacterial populations by 0.6 to 1.5 log CFU/cm 2 ( P < 0.05), depending on inoculum type and recovery medium. There were no main effects ( P ≥ 0.05) of solution pH or spray application pressure when SSS was applied to samples inoculated with any of the tested E. coli inocula; however, solution pH did have a significant effect ( P < 0.05) when SSS was applied to samples inoculated with Salmonella . Results indicated that the response of the nonpathogenic E. coli inoculum to the SSS treatments was similar ( P ≥ 0.05) to that of the pathogenic inocula tested, making the E. coli biotype I strains viable surrogate organisms for in-plant validation of SSS efficacy on beef. The application of SSS at the tested parameters to prerigor beef surface tissue may be an effective intervention for controlling pathogens in a commercial beef harvest process.

ABSTRACT A study was conducted to compare the efficacy of a commercially available sulfuric acid–sodium sulfate blend (SSS) and lactic acid (LA) in reducing inoculated Salmonella populations on beef. Sixty pieces of prerigor beef carcass surface brisket tissue, collected directly from the processing line of a commercial beef processing plant, were cut into two sections (10 by 10 cm each) and spot inoculated (6 to 7 log CFU/cm 2 ) on the adipose side with a six-strain mixture of Salmonella . One section per piece of brisket tissue was left untreated (control), while the second section was spray treated (5 s, 15 lb/in 2 , and 33 mL/s flow rate) with unheated (21°C) or heated (52°C) solutions of SSS (pH 1.1) or LA (4%). Unheated and heated SSS lowered ( P < 0.05) total bacterial counts from 6.3 to 4.6 and 4.3 log CFU/cm 2 , respectively. Likewise, unheated and heated LA reduced ( P < 0.05) total bacterial counts from 6.3 to 4.7 and 4.4 log CFU/cm 2 , respectively. Initial counts of inoculated Salmonella populations (6.1 to 6.2 log CFU/cm 2 ) were reduced ( P < 0.05) to 4.2 and 3.9 log CFU/cm 2 following treatment with unheated and heated SSS, respectively, and to 3.7 and 3.8 log CFU/cm 2 after treatment with unheated and heated LA, respectively. Overall, the temperature of the chemical solutions had a small (0.3 log CFU/cm 2 ), but significant ( P < 0.05), effect on total bacterial counts but not ( P > 0.05) on Salmonella counts. Regardless of solution temperature, Salmonella counts for LA-treated samples were 0.3 log CFU/cm 2 lower ( P < 0.05) than those of samples treated with SSS. These results indicate that both unheated and heated solutions of SSS and LA are effective interventions for reducing Salmonella contamination on prerigor beef carcass surface tissue.

Studies were conducted to (i) determine whether inoculants of nonpathogenic Escherichia coli biotype I effectively served as surrogates for E. coli O157:H7, non-O157 Shiga toxin–producing E. coli , and Salmonella when prerigor beef carcass tissue was treated with a commercially available blend of lactic acid and citric acid (LCA) at a range of industry conditions of concentration, temperature, and pressure; (ii) determine the antimicrobial efficacy of LCA; and (iii) investigate the use of surrogates to validate a hot water and LCA sequential treatment as a carcass spray intervention in a commercial beef harvest plant. In an initial laboratory study, beef brisket tissue samples were left uninoculated or were inoculated (~6 log CFU/cm 2 ) on the adipose side with E. coli O157:H7 (5-strain mixture), non-O157 Shiga toxin–producing E. coli (12-strain mixture), Salmonella (6-strain mixture), or nonpathogenic E. coli (5-strain mixture). Samples were left untreated (control) or were treated with LCA, in a spray cabinet, at one of eight combinations of solution concentration (1.9 and 2.5%), solution temperature (43 and 60°C), and application pressure (15 and 30 lb/in 2 ). In a second study, the E. coli surrogates were inoculated (~6 log CFU/cm 2 ) on beef carcasses in a commercial facility to validate the use of a hot water treatment (92.2 to 92.8°C, 13 to 15 lb/in 2 ) followed by an LCA treatment (1.9%, 50 to 51.7°C, 13 to 15 lb/in 2 , 10 s). In the in vitro study, surrogate and pathogen bacteria did not differ in their response to the tested LCA treatments. Treatment with LCA reduced ( P < 0.05) inoculated populations by 0.9 to 1.5 log CFU/cm 2 , irrespective of inoculum type. The hot water and LCA sequential treatments evaluated in the commercial facility reduced ( P < 0.05) the inoculated nonpathogenic E. coli surrogates on carcasses by 3.7 log CFU/cm 2 . This study therefore provides the meat industry with data for this sequential multiple hurdle system for the operation parameters described.

Studies were conducted to evaluate the efficacy of a commercial blend of sulfuric acid and sodium sulfate (SSS) in reducing Salmonella on inoculated whole chilled chicken wings and to compare its efficacy to peroxyacetic acid (PAA) and cetylpyridinium chloride (CPC). Wings were spot inoculated (5 to 6 log CFU/ml of sample rinsate) with a five-strain mixture of novobiocin- and nalidixic acid–resistant Salmonella and then left untreated (control) or treated by immersing individual wings in 350 ml of antimicrobial solution. An initial study evaluated two treatment immersion times, 10 and 20 s, of SSS (pH 1.1) and compared cell recoveries following rinsing of treated samples with buffered peptone water or Dey/Engley neutralizing broth. In a second study, inoculated wings were treated with SSS (pH 1.1; 20 s), PAA (700 ppm, 20 s), or CPC (4,000 ppm, 10 s) and analyzed for survivors immediately after treatment (0 h) and after 24 h of aerobic storage at 4°C. Color and pH analyses were also conducted in the latter study. Recovery of Salmonella survivors following treatment with SSS (10 or 20 s) was not ( P ≥ 0.05) affected by the type of cell recovery rinse solution (buffered peptone water or Dey/Engley neutralizing broth), but there was an effect ( P < 0.05) of SSS treatment time. Immersion of samples for 10 or 20 s in SSS resulted in pathogen reductions of 0.8 to 0.9 and 1.1 to 1.2 log CFU/ml, respectively. Results of the second study showed that there was an interaction ( P < 0.05) between antimicrobial type and storage time. Efficacy against Salmonella at 0 h increased in the order CPC < SSS < PAA; however, after 24 h of aerobic storage, pathogen counts of SSS- and PAA-treated wings did not differ ( P ≥ 0.05). Overall, the results indicated that SSS applied at pH 1.1 for 20 s was an effective antimicrobial intervention to reduce Salmonella contamination on chicken wings.

Studies were conducted to compare the decontamination efficacy of six chemical treatments against Escherichia coli O157:H7 and multidrug-resistant and antibiotic-susceptible Salmonella inoculated on beef trimmings. The inocula, comprising four-strain mixtures of rifampin-resistant E. coli O157:H7 and antibiotic-susceptible or multidrug-resistant (MDR and/or MDR-AmpC) Salmonella Newport and Salmonella Typhimurium, were inoculated (3 log CFU/cm 2 ) separately onto samples (10 by 5 by 1 cm) derived from beef chuck rolls. Samples were left untreated (control), were immersed for 30 s in acidified sodium chlorite (0.1%, pH 2.5), peroxyacetic acid (0.02%, pH 3.8), sodium metasilicate (4%, pH 12.6), Bromitize Plus (0.0225% active bromine, pH 6.6), or AFTEC 3000 (pH 1.2), or were immersed for 5 s in SYNTRx 3300 (pH 1.0). Levels of surviving Salmonella on treated trimmings were not influenced by serotype or antibiotic resistance phenotype and were generally similar ( P > 0.05) or lower ( P < 0.05) than levels of surviving E. coli O157:H7 regardless of antimicrobial treatment. Overall, depending on chemical treatment (reductions within each chemical treatment were similar among all tested inocula), initial counts of E. coli O157:H7 (2.7 to 3.1 log CFU/cm 2 ) were reduced ( P < 0.05) by 0.2 to 1.4 log CFU/cm 2 . Similarly, initial counts of the tested Salmonella inocula (2.8 to 3.3 log CFU/cm 2 ) were reduced ( P < 0.05) by 0.4 to 1.4 ( Salmonella Newport, antibiotic susceptible), 0.3 to 1.4 ( Salmonella Newport, MDRAmpC), 0.2 to 1.5 ( Salmonella Typhimurium, antibiotic susceptible), 0.4 to 1.3 ( Salmonella Typhimurium, MDR), and 0.4 to 1.5 ( Salmonella Typhimurium, MDR-AmpC) log CFU/cm 2 , depending on antimicrobial treatment. Reductions obtained with sodium metasilicate were 1.3 to 1.5 log CFU/cm 2 , regardless of inoculum, and reductions obtained with the five remaining antimicrobial treatments were 0.2 to 0.7 log CFU/cm 2 (depending on treatment). Findings of this study should be useful to regulatory authorities and the meat industry as they consider Salmonella contamination on beef trimmings.

Studies were performed to determine whether lactic acid treatments used to reduce Escherichia coli O157:H7 on beef trimmings are also effective in controlling non-O157 Shiga toxin–producing E. coli (nSTEC), and multidrug-resistant and antibiotic-susceptible Salmonella . Beef trimming pieces (10 by 5 by 1 cm) were inoculated (3 log CFU/cm 2 ) separately with four-strain mixtures of rifampin-resistant E. coli O157:H7, O26, O45, O103, O111, O121, and O145. Similarly, in a second study, trimmings were separately inoculated with rifampin-resistant E. coli O157:H7, and antibiotic-susceptible or multidrug-resistant (MDR and/or MDR-AmpC) Salmonella Newport and Salmonella Typhimurium. Inoculated trimmings were left untreated (control) or were immersed for 30 s in 5% lactic acid solutions (25 or 55°C). No differences ( P ≥ 0.05) were obtained among surviving counts of E. coli O157:H7 and those of the tested nSTEC serogroups on lactic acid–treated (25 or 55°C) samples. Counts (3.1 to 3.3 log CFU/cm 2 ) of E. coli O157:H7 and nSTEC were reduced ( P < 0.05) by 0.5 to 0.9 (25°C lactic acid) and 1.0 to 1.4 (55°C lactic acid) log CFU/cm 2 . Surviving counts of Salmonella on treated trimmings were not influenced by serotype or antibiotic resistance phenotype and were similar ( P ≥ 0.05) or lower ( P < 0.05) than surviving counts of E. coli O157:H7. Counts (3.0 to 3.3 log CFU/cm 2 ) were reduced ( P < 0.05) by 0.5 to 0.8 ( E. coli O157:H7) and 1.3 to 1.5 ( Salmonella ) log CFU/cm 2 after treatment of samples with 25°C lactic acid. Corresponding reductions following treatment with lactic acid at 55°C were 1.2 to 1.5 ( E. coli O157:H7) and 1.6 to 1.9 ( Salmonella ) log CFU/cm 2 . Overall, the results indicated that lactic acid treatments used against E. coli O157:H7 on beef trimmings should be similarly or more effective against the six nSTEC serogroups and against multidrug-resistant and antibiotic-susceptible Salmonella Newport and Salmonella Typhimurium.

Surface-browned but uncooked frozen breaded chicken products have been associated with salmonellosis outbreaks due to inadequate or no cooking of the products before consumption. This study was conducted to evaluate the effect of three antimicrobials against Salmonella during manufacture of a surface-browned, uncooked frozen breaded chicken meat product. Fresh chicken breast meat portions (5 by 5 by 5 cm) were inoculated (4 to 5 log CFU/g) with Salmonella and mixed with caprylic acid (CAA; 0.5 and 1.0%), carvacrol (CAR; 0.3 and 0.5%), ɛ-polylysine (POL; 0.125 and 0.25%), or distilled water (control). Sodium chloride (1.2%) and sodium tripolyphosphate (0.3%) were added to all treatments, and the mixtures were ground (5%total moisture enhancement level) and formed into portions (9 by 5 by 3 cm). The products were breaded and surface browned by baking in an oven (208°C for 15 min) or deep frying in vegetable oil (190°C for 15 s), packaged in polyethylene bags, and stored at −20°C for 7 days. Total reductions of inoculated Salmonella in untreated control oven- or fryer-browned products after frozen storage were 1.2 and 0.8 log CFU/g, respectively. In comparison, treatment with CAA, CAR, or POL reduced initial pathogen counts by 3.3 to >4.5, 4.1 to >4.7, and 1.1 to 1.6 log CFU/g, respectively, regardless of the antimicrobial concentration and browning method. Treatment with 1.0%CAA (oven browned) or 0.5%CAR (oven or fryer browned) reduced Salmonella to nondetectable levels (<0.3 log CFU/g) in stored frozen products. These data may be useful for development of suitable antimicrobial treatments to reduce the risk of Salmonella contamination in surface-browned, uncooked frozen breaded chicken products.

This study was conducted to compare thermal inactivation of stress-adapted and nonadapted Escherichia coli O157:H7 in nonintact beef moisture enhanced with different brine formulations and cooked to 65°C. Coarsely ground beef was mixed with acid, cold, heat, starvation, or desiccation stress–adapted or nonadapted rifampin-resistant E. coli O157:H7 (eight-strain mixture, 5 to 6 log CFU/g) and a brine solution for a total moisture enhancement level of 10%. The brine treatments included distilled water (control), sodium chloride (0.5% NaCl) plus sodium tripolyphosphate (0.25% STP), or NaCl+STP combined with cetylpyridinium chloride (0.2% CPC), lactic acid (0.3% LA), or sodium metasilicate (0.2% SM). The treated meat was extruded into bags (15 cm diameter), semifrozen (−20°C for 4.5 h), and cut into 2.54-cm (1-in.)-thick portions. Samples were individually vacuum packaged, frozen (−20°C for 42 h), and tempered at 4°C for 2.5 h before cooking. Partially thawed (−1.8 ± 0.4°C) samples were pan broiled to an internal temperature of 65°C. Pathogen counts of partially thawed (before cooking) samples moisture enhanced with brines containing CPC, LA, or SM were 0.7 to 1.1, 0.0 to 0.4, and 0.2 to 0.4 log CFU/g, respectively, lower than those of the control. Compared with microbial count reductions obtained after pan broiling of beef inoculated with nonadapted E. coli O157:H7 cells, count reductions during cooking of meat inoculated with cold and desiccation stress–adapted, acid stress–adapted, and heat and starvation stress–adapted cells indicated sensitization, cross protection, and no effect, respectively, of these stresses on the pathogen during subsequent exposure to heat. Among all stressed cultures, CPC-treated samples (0.8 to 3.6 log CFU/g) and LA-treated samples (0.8 to 3.5 log CFU/g) had the lowest numbers of E. coli O157:H7 survivors after cooking.

This study compared thermal inactivation of Escherichia coli O157:H7 in nonintact beefsteaks of different thicknesses by different cooking methods and appliances. Coarsely ground beef was inoculated with rifampin-resistant E. coli O157:H7 (eight-strain composite, 6 to 7 log CFU/g) and then mixed with sodium chloride (0.45%) plus sodium tripolyphosphate (0.23%); the total water added was 10%. The meat was stuffed into bags (10-cm diameter), semifrozen (−20°C, 6 h), and cut into 1.5-, 2.5-, and 4.0-cm-thick steaks. Samples were then individually vacuum packaged, frozen (−20°C, 42 h), and tempered (4°C, 2.5 h) before cooking. Partially thawed (−2 ± 1°C) steaks were pan broiled (Presto electric skillet and Sanyo grill), double pan broiled (George Foreman grill), or roasted (Oster toaster oven and Magic Chef standard kitchen oven) to a geometric center temperature of 65°C. Extent of pathogen inactivation decreased in order of roasting (2.0 to 4.2 log CFU/g) > pan broiling (1.6 to 2.8 log CFU/g) ≥ double pan broiling (1.1 to 2.3 log CFU/g). Cooking of 4.0-cm-thick steaks required a longer time (19.8 to 65.0 min; variation was due to different cooking appliances), and caused greater reductions in counts (2.3 to 4.2 log CFU/g) than it did in thinner samples (1.1 to 2.9 log CFU/g). The time to reach the target temperature increased in order of George Foreman grill (3.9 to 19.8 min) < Oster toaster oven (11.3 to 45.0 min) < Presto electric skillet (16.3 to 55.0 min) < Sanyo grill (14.3 to 65.0 min) < standard kitchen oven (20.0 to 63.0 min); variation was due to steak thickness. Results indicated that increased steak thickness allowed greater inactivation of E. coli O157:H7, as time to reach the target internal temperature increased. Roasting in a kitchen oven was most effective for pathogen inactivation.

This study involved a comparison of the antimicrobial efficacy of several beef hide decontamination interventions to identify those that more effectively reduced levels of Escherichia coli O157:H7 and Salmonella . Whole beef hides were inoculated with E. coli O157:H7 and Salmonella and decontaminated with sprays of solutions of acetic acid (AA; 10%, 55°C), lactic acid (LA; 10%, 55°C), sodium hydroxide (SH; 3%, 23°C), sodium metasilicate (SM; 4%, 23°C), or sodium hydroxide (1.5%), followed by high-pressure washing with chlorinated (0.02%) water (SHC; both applied at 23°C) or water (W; 23°C) or by deluging with solutions of potassium cyanate (PC; 2.4%, 30°C) or sodium sulfide (SS; 6.2%, 30°C). All spraying treatments (AA, LA, SH, SM, and SHC) resulted in removal of visual organic material, whereas the dehairing treatments (PC and SS) successfully removed hair along with visual organic material. The PC, SS, and SHC treatments resulted in the greatest reductions of E. coli O157:H7 ( P < 0.05), by 5.1, 4.8, and 5.0 log CFU/cm 2 , respectively. The SS and SHC treatments decreased Salmonella by 4.2 and 4.4 log CFU/cm 2 , respectively, compared with the water treatment, which reduced levels by 1.7 log CFU/cm 2 ( P < 0.05). The SH, AA, and LA treatments also lowered both E. coli O157:H7 and Salmonella by at least 2.0 log CFU/cm 2 . The treatments that were effective in this study deserve further consideration for commercial implementation as hide decontamination interventions.

Studies were conducted to identify effective antimicrobials and application parameters that could be used as decontamination interventions to reduce microbial loads on cattle hides before removal from carcasses. In study I, hide swatches inoculated with Escherichia coli O157:H7 were sprayed with 10% acetic acid (at 23 and 55°C), 10% lactic acid (at 23 and 55°C), 3% sodium hydroxide (at 23°C) or 4 and 5% sodium metasilicate (at 23°C). All antimicrobials were evaluated independently after being applied alone, being applied after a water rinse, or being followed by a water rinse. Antimicrobial treatments followed by a water rinse lowered E. coli O157:H7 populations by 0.6 to 2.4 log CFU/cm 2 and resulted in hides with a surface pH of 6.3 to 9.2. Treatments in which a water rinse was followed by antimicrobial application lowered E. coli O157:H7 populations by 1.5 to 5.1 log CFU/cm 2 but resulted in hides with a surface pH of 3.9 to 10.5. In study II, whole hides were treated with one of four antimicrobials (acetic acid, lactic acid, sodium hydroxide, or sodium metasilicate) followed by a water rinse. Hides were evaluated for aerobic bacterial counts, total coliform counts, and E. coli counts. Generally, all antimicrobials resulted in greater reductions ( P < 0.05) of E. coli counts when compared with the control; however, only acetic and lactic acids resulted in greater reductions ( P < 0.05) of aerobic bacterial counts and total coliform counts compared with the controls. These antimicrobials could be used to reduce microbial contamination on hides, potentially reducing micro-biological contamination transferred to carcasses or to the plant environment.

Internalization of Escherichia coli O157:H7 in nonintact beef products during mechanical tenderization or during injection of marination and tenderization ingredients is of concern if such products are undercooked. This study tested organic acids (0.2% citric acid and 0.3% acetic acid), potassium and calcium salts (1.8% potassium lactate, 0.63% calcium lactate, 0.86% calcium ascorbate, and 0.23% calcium chloride), and sodium chloride (2.5%) for their influence on thermal destruction of E. coli O157:H7 in ground beef serving as a model system. Ground beef batches (700 g; 5% fat) were mixed with equal volumes (22 ml) of each treatment solution or distilled water and portions (30 g) of treated ground beef were extruded in test tubes (2.5 by 10 cm). A five-strain mixture of E. coli O157:H7 (0.3 ml; 7 log CFU/g) was introduced at the center of the sample with a pipette. After overnight storage (4°C), simulating product marination, samples were heated to 60 or 65°C internal temperature, simulating rare and medium rare doneness of beef, in a circulating water bath. At 65°C, treatments with citric and acetic acid showed greater ( P < 0.05) reduction (4 to 5 log CFU/g) of E. coli O157:H7 than all the other ingredients and the control (3 to 4 log CFU/g). Sodium chloride reduced weight losses (16 to 18% compared with 20 to 27% by citric or acetic acid) and resulted in a 4-log reduction in counts during cooking to 65°C. Ingredients such as citric or acetic acid may improve thermal inactivation of E. coli O157:H7 internalized in nonintact beef products, while sodium chloride may reduce cooking losses in such products.

U.S. regulations require that processors employ lethal or inhibitory antimicrobial alternatives in production of ready-toeat meat and poultry products that support growth of Listeria monocytogenes and may be exposed to the processing environment after a lethality treatment. In this study, lactic acid (LA; 5%, vol/vol) and sodium lauryl sulfate (SLS; 0.5%, wt/vol) were evaluated individually or as a mixture (LASLS) for control of L. monocytogenes on frankfurters. Frankfurters were inoculated with a 10-strain mixture of L. monocytogenes , sprayed for 10 s (20 bar, 23 ± 2°C) with antimicrobials or distilled water (DW) before (LASLS or DW) or after (LA, SLS, LASLS, or DW) inoculation (4.8 ± 0.1 log CFU/cm 2 ), vacuum packaged, and stored at 4°C for 90 days. Samples were analyzed for numbers of the pathogen (on PALCAM agar) and for total microbial counts (on tryptic soy agar with yeast extract) during storage. Spraying with DW, LA, or SLS after inoculation reduced numbers of L. monocytogenes by 1.3 ± 0.2, 1.8 ± 0.5, and 2.0 ± 0.4 log CFU/cm 2 , respectively. The LASLS mixture applied before or after inoculation reduced pathogen populations by 1.8 ± 0.4 and 2.8 ± 0.2 log CFU/cm 2 , respectively. No further reduction by any treatment was observed during storage. The bacterial growth curves (fitted by the model of Baranyi and Roberts) indicated that the lag-phase duration of the bacterium on control samples (13.85 to 15.18 days) was extended by spraying with all solutions containing LA. For example, LA suppressed growth of L. monocytogenes for 39.14 to 41.01 days. Pathogen growth rates also were lower on frankfurters sprayed after inoculation with LA or LASLS compared to those sprayed with DW. Therefore, spraying frankfurters with a mixture of LA and SLS may be a useful antilisterial alternative treatment for ready-to-eat meat and poultry products.

Commercial cured ham formulated with or without potassium lactate and sodium diacetate was inoculated with Listeria monocytogenes and stored to simulate conditions of processing, retail, and home storage. The ham was sliced, inoculated with a 10-strain composite of L. monocytogenes (1 to 2 log CFU/cm 2 ), vacuum packaged, and stored at 4°C to simulate contamination following lethality treatment at processing (first shelf life). After 10, 20, 35, and 60 days of storage, packages were opened, samples were tested, and bags with remaining slices were reclosed with rubber bands. At the same times, portions of original product (stored at 4°C in original processing bags) were sliced, inoculated, and packaged in delicatessen bags to simulate contamination during slicing at retail (second shelf life). Aerobic storage of both sets of packages at 7°C for 12 days was used to reflect domestic storage conditions (home storage). L. monocytogenes populations were lower ( P < 0.05) during storage in ham formulated with lactate-diacetate than in product without antimicrobials under both contamination scenarios. Inoculation of ham without lactate-diacetate allowed prolific growth of L. monocytogenes in vacuum packages during the first shelf life and was the worst case contamination scenario with respect to pathogen numbers encountered during home storage. Under the second shelf life contamination scenario, mean growth rates of the organism during home storage ranged from 0.32 to 0.45 and from 0.18 to 0.25 log CFU/cm 2 /day for ham without and with lactate-diacetate, respectively, and significant increases in pathogen numbers ( P < 0.05) were generally observed after 4 and 8 days of storage, respectively. Regardless of contamination scenario, 12-day home storage of product without lactate-diacetate resulted in similar pathogen populations (6.0 to 6.9 log CFU/cm 2 )( P ≥ 0.05). In ham containing lactate-diacetate, similar counts were found during the home storage experiment under both contamination scenarios, and only in 60-day-old product did samples from the first shelf life have higher ( P < 0.05) pathogen numbers than those found in samples from the second shelf life. These results should be useful in risk assessments and for the establishment of “sell by” and “consume by” date labels for refrigerated ready-to-eat meat products.

The fate of acid-adapted and nonadapted Listeria monocytogenes inoculated onto bologna slices (formulated with or without antimicrobials) was examined during storage and after exposure to in vitro gastric challenge. Bologna slices formulated with no antimicrobials (control), 3% sodium lactate (SL), or 1.8% SL plus 0.25% sodium diacetate (SD) were inoculated (2 log CFU/cm 2 ) with a 10-strain composite of acid-adapted or nonadapted L. monocytogenes strains. Growth or survival of the two inocula on bologna was evaluated during vacuum-packaged storage (10°C) for up to 36 days. Survival of previously acid-adapted or nonadapted L. monocytogenes on stored bologna exposed to simulated gastric fluid (adjusted to pH 1.0 with HCl) for 20, 40, and 60 min also was determined. As expected, inclusion of antimicrobials in the product formulation inhibited growth of L. monocytogenes during storage of vacuum-packaged bologna compared with growth on control samples. Acid adaptation of L. monocytogenes prior to product inoculation did not affect subsequent survival or growth on bologna or resistance to simulated gastric fluid ( P > 0.05). Survival of L. monocytogenes exposed to simulated gastric fluid during storage increased with product age, growth phase of the cells, and possibly age of the cells, particularly for control samples (no antimicrobials), in which the pathogen grew uninhibited to approximately 6 log CFU/cm 2 by day 8 of storage. Inhibition of L. monocytogenes growth on product formulated with antimicrobials was associated with only sporadic and small numbers of survivors following exposure of these samples to simulated gastric fluid, especially in samples stored longer. However, cell numbers in these treatment groups before the gastric challenge did not exceed 3.8 log CFU/cm 2 . Inhibition of growth on product with antimicrobials precluded detection of survivors resistant to the effects of simulated gastric fluid.