Selenite Cystine Agar for Enumeration of Inoculated Salmonella Serovars Recovered from Stressful Conditions During Antimicrobial Validation Studies

Rapid Quantification of Salmonella Typhimurium in Ground Chicken Using Immunomagnetic Chemiluminescent Assay

Many countries have established regulatory frameworks to monitor and mitigate Salmonella contamination in poultry products. The ability to rapidly quantify Salmonella is critical for poultry processors to facilitate early detection, implement corrective measures, and enhance product safety. This study aimed to develop an Immunomagnetic Chemiluminescent Assay (IMCA) for the quantification of Salmonella Typhimurium in ground chicken. Immunomagnetic microbeads functionalized with monoclonal antibodies were employed to selectively capture and concentrate Salmonella from ground chicken samples. A biotin-labeled monoclonal antibody, followed by an avidin-horseradish peroxidase conjugate, was used to bind the captured bacteria and initiate a chemiluminescent reaction catalyzed by peroxidase. Light emission was quantified in relative light units (RLUs) using two luminometers. Ground chicken samples were inoculated with a four-strain S. Typhimurium cocktail ranging from 0 to 3.5 Log CFU/g. Bacterial concentrations were confirmed using the Most Probable Number (MPN) method. Samples underwent enrichment in Buffered Peptone Water (BPW) supplemented with BAX MP Supplement at 42 °C for 6 and 8 h before analysis via IMCA. A linear regression analysis demonstrated that the optimal quantification of Salmonella was achieved at the 8 h enrichment period (R2 ≥ 0.89), as compared to the 6 h enrichment. The limit of quantification (LOQ) was determined to be below 1 CFU/g. A strong positive correlation (R2 ≥ 0.88) was observed between IMCA and MPN results, indicating methodological consistency. These findings support the application of IMCA as a rapid and reliable method for the detection and quantification of Salmonella in ground chicken.

Efficacy of Copper Ion Treatment on Bacteria and Antibiotic Residues Contained in Bovine Waste Milk

Background/Objectives: Waste milk harbors many bacteria and antibiotic residues. Calves fed with untreated waste milk have a higher incidence of scours and an increased risk of developing antimicrobial-resistant bacteria. This study aimed to evaluate the efficacy of treatment with copper ions on bacteria and antibiotics contained in bovine waste milk. Methods: Waste milk samples were collected from a dairy farm for seven weeks and were subjected to treatment with copper ions. Total bacterial counts, coliforms, Streptococcus, and Staphylococcus were assessed before and after treatment. Additionally, metagenomic analysis was performed to determine microbial diversity. Results: Before treatment, the total bacterial count average was 4.0 × 106 CFU/mL, 1.7 × 104 CFU/mL for coliforms, 2.6 × 106 CFU/mL for Streptococcus, and 5.4 × 102 CFU/mL for Staphylococcus Copper treatment significantly reduced bacterial counts within 15 min. Total bacteria decreased from 4.0 × 106 CFU/mL to 1.1 × 102 CFU/mL after 30 min; meanwhile, other groups were not detected. The most abundant groups were Lactococcus (29.94%), Pseudomonas (28.89%), and Enterobacteriaceae (21.19%). Beta-lactams were detected in five-sevenths samples, and in one sample they were detected before and at 15 min of treatment but not after 30 min. Conclusions: The effect of treatment with copper ions on the different bacterial groups was significantly effective but showed limited effect on the detection of antibiotics.

Epidemiological and molecular investigations of Salmonella isolated from duck farms in southwest and around area of Shandong, China

Salmonella is a zoonotic pathogen posing a serious risk to the farming industry and public health due to food animals serving as reservoirs for future contamination and spread of Salmonella. The present study is designed to monitor the contamination status of Salmonella in duck farms and the main control points during breeding. 160 strains of duck-derived Salmonella were isolated from the 736 samples (cloacal swabs, feces, water, feed, soil, air and dead duck embryos) collected in southwest Shandong Province and the province's surrounding area. The percentage of Salmonella-positive samples collected was 21.74 % (160/736), and the greatest prevalence from duck embryo samples (40.00 %, 36/90). These Salmonella were classified into 23 serotypes depending on their O and H antigens, in which S. Typhimurium (30.15 %), S. Kottbus (13.97 %) and S. Enteritidis (10.29 %) were the prevailing serotypes. Subsequently, the molecular subtyping was done. Clustered regularly interspaced short palindromic repeats (CRISPR) analysis showed that 41 strains of S. Typhimurium and 14 strains of S. Enteritidis were classified into 13 and 3 genotypes, respectively. 19 S. Kottbus isolates from different sources featured ST1546, ST198, ST321, and ST1690 by multilocus sequence typing (MLST) analysis, among which ST1546 belongs to S. Kottbus was a new ST. The minimum spanning tree analysis based on the two CRISPR loci and seven MLST loci from all S. Typhimurium, S. Enteritidis and S. Kottbus isolates revealed that duck embryos, feed and water were key control points to the spread of Salmonella along the breeding chain. Meanwhile, the emergence of S. Kottbus in duck flocks was considered a potential public health hazard.

Microbial Profiling of Biltong Processing Using Culture-Dependent and Culture-Independent Microbiome Analysis

Biltong is a South African air-dried beef product that does not have a heat lethality step, but rather relies on marinade chemistry (low pH from vinegar, ~2% salt, spices/pepper) in combination with drying at ambient temperature and low humidity to achieve microbial reduction during processing. Culture-dependent and culture-independent microbiome methodologies were used to determine the changes in the microbial community at each step during biltong processing through 8 days of drying. Culture-dependent analysis was conducted using agar-based methods to recover viable bacteria from each step in the biltong process that were identified with 16S rRNA PCR, sequencing, and BLAST searching of the NCBI nucleotide database. DNA was extracted from samples taken from the laboratory meat processing environment, biltong marinade, and beef samples at three stages of processing (post-marinade, day 4, and day 8). In all, 87 samples collected from two biltong trials with beef obtained from each of three separate meat processors (n = six trials) were amplified, sequenced with Illumina HiSeq, and evaluated with bioinformatic analysis for a culture-independent approach. Both culture-dependent and independent methodologies show a more diverse population of bacteria present on the vacuum-packaged chilled raw beef that reduces in diversity during biltong processing. The main genera present after processing were identified as Latilactobacillus sp., Lactococcus sp., and Carnobacterium sp. The high prevalence of these organisms is consistent with extended cold-storage of vacuum-packaged beef (from packers, to wholesalers, to end users), growth of psychrotrophs at refrigeration temperatures (Latilactobacillus sp., Carnobacterium sp.), and survival during biltong processing (Latilactobacillus sakei). The presence of these organisms on raw beef and their growth during conditions of beef storage appears to 'front-load' the raw beef with non-pathogenic organisms that are present at high levels leading into biltong processing. As shown in our prior study on the use of surrogate organisms, L. sakei is resistant to the biltong process (i.e., 2-log reduction), whereas Carnobacterium sp. demonstrated a 5-log reduction in the process; the recovery of either psychrotroph after biltong processing may be dependent on which was more prevalent on the raw beef. This phenomenon of psychrotrophic bloom during refrigerated storage of raw beef may result in a natural microbial suppression of mesophilic foodborne pathogens that are further reduced during biltong processing and contributes to the safety of this type of air-dried beef.

Evaluation of Various Lactic Acid Bacteria and Generic E. coli as Potential Nonpathogenic Surrogates for In-Plant Validation of Biltong Dried Beef Processing

Validation studies conducted within a food processing facility using surrogate organisms could better represent the manufacturing process than controlled laboratory studies with pathogenic bacteria on precision equipment in a BSL-2 lab. The objectives of this project were to examine potential surrogate bacteria during biltong processing, conduct biltong surrogate validation lethality studies, and measure critical factors and intrinsic parameters during processing. Beef pieces (1.9 cm × 5.1 cm × 7.6 cm) were inoculated with four-strain mixtures of Carnobacterium divergens/C. gallinarum, Pediococcus acidilactici/P. pentosaceous, and Biotype 1 E. coli ATCC BAA (-1427, -1428, -1429, and -1430), as well as a two-strain mixture of Latilactobacillus sakei and other commercially available individual bacterial cultures (P. acidilactici Saga200/Kerry Foods; Enterococcus faecium 201224-016/Vivolac Cultures). Inoculated beef was vacuum-tumbled in marinade and dried in a humidity-controlled oven for 8−10 days (24.9 °C; 55% relative humidity). Microbial enumeration of surviving surrogate bacteria and evaluation of intrinsic factors (water activity, pH, and salt concentration) were performed post inoculation, post marination, and after 2, 4, 6, 8, and 10 days of drying. Trials were performed in duplicate replication with triplicate samples per sampling time and analyzed by one-way RM-ANOVA. Trials conducted with E. faecium, Pediococcus spp., and L. sakei never demonstrated more than 2 log reduction during the biltong process. However, Carnobacterium achieved a >5 log (5.85 log) reduction over a drying period of 8 days and aligned with the reductions observed in previous trials with pathogenic bacteria (Salmonella, E. coli O157:H7, L. monocytogenes, and S. aureus) in biltong validation studies. Studies comparing resuspended freeze-dried or frozen cells vs. freshly grown cells for beef inoculation showed no significant differences during biltong processing. Carnobacterium spp. would be an effective nonpathogenic in-plant surrogate to monitor microbial safety that mimics the response of pathogenic bacteria to validate biltong processing within a manufacturer’s own facility.

Effect of Biltong Dried Beef Processing on the Reduction of Listeria monocytogenes, E. coli O157:H7, and Staphylococcus aureus, and the Contribution of the Major Marinade Components

Biltong is a dry beef product that is manufactured without a heat lethality step, raising concerns of whether effective microbial pathogen reduction can occur during biltong processing. Raw beef inoculated with 4-strain cocktails of either E. coli O157:H7, Listeria monocytogenes, or Staphylococcus aureus, and processed with a standard biltong process, were shown to incur a >5-log reduction in 6−8 days after marination by vacuum-tumbling for 30 min in vinegar, salt, spices (coriander, pepper) when dried at 23.9 °C (75 °F) at 55% relative humidity (RH). Pathogenic challenge strains were acid-adapted in media containing 1% glucose to ensure that the process was sufficiently robust to inhibit acid tolerant strains. Internal water activity (Aw) reached < 0.85 at 5-log reduction levels, ensuring that conditions were lower than that which would support bacterial growth, or toxin production by S. aureus should it be internalized during vacuum tumbling. This was further confirmed by ELISA testing for staphylococcal enterotoxins A and B (SEA, SEB) after marination and again after 10 days of drying whereby levels were lower than initial post-marination levels. Comparison of log reduction curves obtained for E. coli O157:H7, L. monocytogenes, S. aureus, and Salmonella (prior study) showed that microbial reduction was not significantly different (p < 0.05) demonstrating that even without a heat lethality step, the biltong process we examined produces a safe beef product according to USDA-FSIS guidelines.

Comparison of Sodium Nitrite and ‘Natural’ Nitrite on the Inhibition of Spore Germination and Outgrowth of Clostridium sporogenes in Low- and High-Fat Frankfurters

In the US, sodium and potassium nitrite are regulated food preservatives that prevent the germination of Clostridium spores in cured and processed meats. In recent years, the use of vegetable-derived nitrite (i.e., vegetable nitrate fermented to nitrite) has been designated as ‘natural nitrite’ to accommodate natural meats that cannot use artificial ingredients, and such meat products can be labelled as having ‘no added preservatives’. This new status and labelling allowance for microbially-modified nitrite provides for a ‘clean label’ application of nitrite against the stigma of chemical ingredients and has found increased use within the processed meat industry. The objectives of this study were to examine Clostridium sporogenes as a pathogen-surrogate challenge organism and the use of vegetable (celery) nitrite to prevent spore germination in cooked meat products. A three-strain spore crop of C. sporogenes ATCC 3584, ATCC 19404 and ATCC BAA-2695 was applied during ingredient formulation of low and high-fat hotdogs that were divided into three sub-batches (control without nitrite, hotdogs with sodium nitrite, hotdogs with celery nitrite). In both low and high-fat processes, sodium nitrite was compared to hotdogs made with comparable levels of celery nitrite (156 ppm). All treatments were performed with duplicate trial replication and triplicate sample testing within each trial. Comparisons were analyzed by repeated measures analysis of variance to determine significant difference (p < 0.05) of time course treatments. In shelf-life assays, growth was inhibited at both 5 °C and 15 °C, even if nitrite was absent; however, spore germination and growth readily occurred at 35 °C. Comparison of nitrite effects was best evaluated at 35 °C as a permissive condition to examine the effects of nitrite treatments. Celery nitrite showed no significant difference from sodium nitrite when used in both low and high-fat hotdogs, and spore outgrowth was only observed after 2–3 days at 35 °C compared to hotdogs without nitrite. Application of bacteriocin preparations in the formulation that were effective against Listeria monocytogenes, and moderately inhibitory towards the 3-strain spore mixture of C. sporogenes, were not effective in spore control in manufactured hotdogs. The nitrite validation hotdog trials described herein demonstrates that (celery or sodium) nitrite may prevent Clostridium spore germination for 24–48 h even under permissive conditions to help keep processed meat safe.

Quantification of Process Lethality (5-Log Reduction) of Salmonella and Salt Concentration during Sodium Replacement in Biltong Marinade

Salt (sodium chloride, NaCl) is commonly used in ready-to-eat (RTE) meat products such as biltong, a South African style dried beef product for flavor, enhanced moisture loss, and reduction of microbial growth. However, increased consumption of high sodium content foods is commonly associated with high blood pressure and heart disease. This study evaluated the use of alternative salts, potassium chloride (KCl) and calcium chloride (CaCl₂) in the biltong marinade to achieve a ≥ 5-log reduction of Salmonella, a pathogen of concern in beef products. Beef pieces (1.9 cm × 5.1 cm × 7.6 cm) were inoculated with a five-serovar mixture of Salmonella (Salmonella Thompson 120, Salmonella Enteritidis H3527, Salmonella Typhimurium H3380, Salmonella Heidelberg F5038BG1, and Salmonella Hadar MF60404), vacuum-tumbled in a traditional biltong marinade of salt, spices, and vinegar containing either NaCl, KCl or CaCl₂ (2.2% concentration) followed by an 8-10 day drying period at 23.9 °C (75 °F) and 55% relative humidity. Microbial enumeration of Salmonella was conducted following inoculation, after marination, and after 2, 4, 6, 8, and 10 days of drying in a humidity/temperature chamber. Biltong produced with CaCl₂, NaCl, or KCl achieved a > 5-log reduction of Salmonella after 6, 7, and 8 days, respectively. The Salmonella reduction trends with biltong made with NaCl or CaCl₂ were not significantly different (p < 0.05) while both were significantly different from that made with KCl (p > 0.05). Sodium, calcium, and potassium ion concentrations were measured using ion-specific electrode meters following biltong processing and drying. As expected, the biltong made with the corresponding salt had the most abundant ion in the sample. Regardless of the salt used in the marinade, the potassium ion levels were moderately elevated in all samples. This was determined to be from potassium levels naturally present in beef rather than from other ingredients. Sampling of several commercial brands of biltong for sodium content showed that some were significantly above the allowable level of claims made on package ingredient statements. The substitution of NaCl with KCl or CaCl₂ during biltong processing can also provide a 5-log reduction of Salmonella to produce a safe product that can be marketed as a more healthy low-sodium food alternative that may appeal to consumers who need to reduce their blood pressure and are conscientious of sodium levels in their diet.

Processing of Biltong (Dried Beef) to Achieve USDA-FSIS 5-log Reduction of Salmonella without a Heat Lethality Step

In the US, dried beef products (beef jerky) are a popular snack product in which the manufacture often requires the use of a heat lethality step to provide adequate reduction of pathogens of concern (i.e., 5-log reduction of Salmonella as recommended by the United States Department of Agriculture Food Safety and Inspection Service (USDA-FSIS)). Biltong, a South African-style dried beef product, is manufactured with low heat and humidity. Our objectives were to examine processes for the manufacture of biltong that achieves a 5-log reduction of Salmonella without a heat lethality step and with, or without, the use of additional antimicrobials. Beef pieces (1.9 cm × 5.1 cm × 7.6 cm) were inoculated with a 5-serovar mixture of Salmonella (Salmonella Thompson 120, Salmonella Heidelberg F5038BG1, Salmonella Hadar MF60404, Salmonella Enteritidis H3527, and Salmonella Typhimurium H3380), dipped in antimicrobial solutions (lactic acid, acidified calcium sulfate, sodium acid sulfate) or water (no additional antimicrobial), and marinaded while vacuum tumbling and/or while held overnight at 5 °C. After marination, beef pieces were hung in an oven set at 22.2 °C (72 °F), 23.9 °C (75 °F), or 25 °C (77 °F) depending on the process, and maintained at 55% relative humidity. Beef samples were enumerated for Salmonella after inoculation, after dip treatment, after marination, and after 2, 4, 6, and 8 days of drying. Water activity was generally <0.85 by the end of 6–8 days of drying and weight loss was as high as 60%. Trials also examined salt concentration (1.7%, 2.2%, 2.7%) and marinade vinegar composition (2%, 3%, 4%) in the raw formulation. Nearly all approaches achieved 5-log₁₀ reduction of Salmonella and was attributed to the manner of microbial enumeration eliminating the effects of microbial concentration on dried beef due to moisture loss. All trials were run as multiple replications and statistical analysis of treatments were determined by repeated measures analysis of variance (RM-ANOVA) to determine significant differences (p < 0.05). We believe this is the first published report of a biltong process achieving >5.0 log₁₀ reduction of Salmonella which is a process validation requirement of USDA-FSIS for the sale of dried beef in the USA.