Antimicrobial tolerance, biofilm formation, and molecular characterization of Salmonella isolates from poultry processing equipment

Evaluation of Commercially Available Sanitizers Efficacy to Control Salmonella (Sessile and Biofilm Forms) on Harvesting Bins and Picking Bags

This study evaluated the efficacy of five commercially available sanitizers to reduce Salmonella (sessile and biofilm forms) count on experimentally inoculated materials representative of harvesting bins and picking bags in the fresh produce industry. Sessile Salmonella cells were grown onto tryptic soy agar to create a bacterial lawn, while multistrain Salmonella biofilms were grown in a Centers for Disease Control and Prevention (CDC) reactor at 22 ± 2 °C for 96 h. Samples were exposed to 500 ppm free chlorine, 500 ppm peroxyacetic acid (PAA), 75 psi steam, and 5% silver dihydrogen citrate (SDC) for 30 sec, 1, or 2 min or 100 ppm chlorine dioxide gas for 24 h. Sanitizer, surface type, and application time significantly affected the viability of Salmonella in both sessile and biofilm forms (P < 0.05). All treatments resulted in a significant reduction of Salmonella when compared to the control (P < 0.05). Chlorine dioxide gas was the most effective treatment in both sessile and biofilm forms regardless of the type of surface, and it achieved a 5-log reduction. PAA at 500 ppm applied for 2 min was the only liquid sanitizer that resulted in a greater than 3-log reduction in all surfaces. Scanning electronic microscopy demonstrated the porous surface nature of nylon and wood, compared to HDPE, impacted sanitizer antimicrobial activity. Understanding the efficacy of sanitizers to control Salmonella on harvesting bins and picking bags may improve the safety of fresh produce by increasing available sanitizing treatment.

Virulence, multiple drug resistance, and biofilm-formation in Salmonella species isolated from layer, broiler, and dual-purpose indigenous chickens

Globally, the significant risk to food safety and public health posed by antimicrobial-resistant foodborne Salmonella pathogens is driven by the utilization of in-feed antibiotics, with variations in usage across poultry production systems. The current study investigated the occurrence of virulence, antimicrobial resistant profiles, and biofilm-forming potentials of Salmonella isolates sourced from different chicken types. A total of 75 cloacal faecal samples were collected using sterile swabs from layer, broiler, and indigenous chickens across 15 poultry farms (five farms per chicken type). The samples were analysed for the presence of Salmonella spp. using species-specific PCR analysis. Out of the 150 presumptive isolates, a large proportion (82; 55%) were confirmed as Salmonella species, comprising the serovars S. typhimurium (49%) and S. enteritidis (30%) while 21% were uncategorised. Based on phenotypic antibiotic susceptibility test, the Salmonella isolates were most often resistant to erythromycin (62%), tetracycline (59%), and trimethoprim (32%). The dominant multiple antibiotic resistance phenotypes were SXT-W-TE (16%), E-W-TE (10%), AML-E-TE (10%), E-SXT-W-TE (13%), and AMP-AML-E-SXT-W-TE (10%). Genotypic assessment of antibiotic resistance genes revealed that isolates harboured the ant (52%), tet (A) (46%), sui1 (13%), sui2 (14%), and tet (B) (9%) determinants. Major virulence genes comprising the invasion gene spiC, the SPI-3 encoded protein (misL) that is associated with the establishment of chronic infections and host specificity as well as the SPI-4 encoded orfL that facilitates adhesion, autotransportation and colonisation were detected in 26%, 16%, and 14% of the isolates respectively. There was no significant difference on the proportion of Salmonella species and the occurrence of virulence and antimicrobial resistance determinants among Salmonella isolates obtained from different chicken types. In addition, neither the chicken type nor incubation temperature influenced the potential of the Salmonella isolates to form biofilms, although a large proportion (62%) exhibited weak to strong biofilm-forming potentials. Moderate to high proportions of antimicrobial resistant pathogenic Salmonella serovars were detected in the study but these did not vary with poultry production systems.

Distribution and Characterization of Quaternary Ammonium Biocides Resistant Bacteria in Different Soils, in South-Western China

Quaternary ammonium compounds (QACs) are active ingredients in hundreds of disinfectants for controlling the epidemic of infectious diseases like SARS-CoV-2 (COVID-19), and are also widely used in shale gas exploitation. The occurrence of QAC-resistant bacteria in the environment could enlarge the risk of sterilization failure, which is not fully understood. In this study, QAC-resistant bacteria were enumerated and characterized in 25 soils collected from shale gas exploitation areas. Total counts of QAC-resistant bacteria ranged from 6.81 × 103 to 4.48 × 105 cfu/g, accounting for 1.59% to 29.13% of the total bacteria. In total, 29 strains were further purified and identified as Lysinibacillus, Bacillus, and Klebsiella genus. There, bacteria covering many pathogenic bacteria showed different QACs tolerance with MIC (minimum inhibition concentration) varying from 4 mg/L to 64 mg/L and almost 58.6% of isolates have not previously been found to tolerate QACs. Meanwhile, the QAC-resistant strains in the produced water of shale gas were also identified. Phylogenetic trees showed that the resistant species in soil and produced water are distinctly different. That is the first time the distribution and characterization of QAC-resistant bacteria in the soil environment has been analyzed.

Phenotypic Characteristics That May Contribute to Persistence of Salmonella Strains in the Pistachio Supply Chain

Salmonella enterica subsp. enterica strain diversity in California pistachios is limited; some strains have persisted in the pistachio supply chain for ≥10 years. Representative isolates of six persistent strains and three sporadic strains isolated from California pistachios were selected to evaluate copper resistance, growth in pistachio hull slurry, biofilm formation, desiccation tolerance, and survival during subsequent storage. The presence of a copper homeostasis and silver-resistance island sequence in three of the persistent strains was associated with an increase in tolerance to CuSO4 from 7.5 mM to 15 mM under anaerobic but not aerobic conditions; all isolates were resistant to ≥120 mM Cu-EDTA under both anerobic and aerobic conditions. When inoculated into pistachio hull slurry at 2.75 ± 0.04 log CFU/mL and incubated at 30 °C, the populations of Salmonella Enteritidis strain A (sporadic) increased to significantly lower levels than the other strains at 16, 20, 24, and 28 h but not at 40 and 48 h. Maximum populations of 8.70-8.85 log CFU/mL were observed for all strains at ≥40 h of incubation. All nine Salmonella strains produced weak to strong biofilms after 4 days at 25 °C; seven strains, including two sporadic strains, produced moderate biofilms, and Salmonella Liverpool strain A (persistent) produced a strong biofilm. The rdar+ and rdar- morphotypes were observed in both persistent and sporadic Salmonella strains. Population declines of 5.03 log were observed for Salmonella Enteritidis strain A within 18 h of drying on filter paper whereas reductions of 0.50-1.25 log were observed for the other eight Salmonella strains. Population reductions (3.98-5.12 log) of these eight strains were not significantly different after storage at 25 ± 1 °C and 35% relative humidity for 50 days. The phenotypic characteristics evaluated here do not independently account for the persistence of a small number of Salmonella strains associated with the California pistachio production chain.

Antimicrobial Tolerance in Salmonella: Contributions to Survival and Persistence in Processing Environments

Salmonella remains a top bacterial pathogen implicated in several food-borne outbreaks, despite the use of antimicrobials and sanitizers during production and processing. While these chemicals have been effective, Salmonella has shown the ability to survive and persist in poultry processing environments. This can be credited to its microbial ability to adapt and develop/acquire tolerance and/or resistance to different antimicrobial agents including oxidizers, acids (organic and inorganic), phenols, and surfactants. Moreover, there are several factors in processing environments that can limit the efficacy of these antimicrobials, thus allowing survival and persistence. This mini-review examines the antimicrobial activity of common disinfectants/sanitizers used in poultry processing environments and the ability of Salmonella to respond with innate or acquired tolerance and survive exposure to persists in such environments. Instead of relying on a single antimicrobial agent, the right combination of different disinfectants needs to be developed to target multiple pathways within Salmonella.

Biofilm formation in food processing plants and novel control strategies to combat resistant biofilms: the case of Salmonella spp

Salmonella is one of the pathogens that cause many foodborne outbreaks throughout the world, representing an important global public health problem. Salmonella strains with biofilm-forming abilities have been frequently isolated from different food processing plants, especially in poultry industry. Biofilm formation of Salmonella on various surfaces can increase their viability, contributing to their persistence in food processing environments and cross-contamination of food products. In recent years, increasing concerns arise about the antimicrobial resistant and disinfectant tolerant Salmonella, while adaptation of Salmonella in biofilms to disinfectants exacerbate this problem. Facing difficulties to inhibit or remove Salmonella biofilms in food industry, eco-friendly and effective strategies based on chemical, biotechnological and physical methods are in urgent need. This review discusses biofilm formation of Salmonella in food industries, with emphasis on the current available knowledge related to antimicrobial resistance, together with an overview of promising antibiofilm strategies for controlling Salmonella in food production environments.

Association of resistance to quaternary ammonium compounds and organic acids with genetic markers and their relationship to Escherichia coli serogroup

Sanitizer resistance is being extensively investigated due to the potential for bacterial survival and cross-resistance with other antimicrobials. Similarly, organic acids are being used due to their microbial inactivation potential as well as being generally recognized as safe (GRAS). However, little is known about associations of genetic and phenotypic factors in Escherichia coli related to resistance to sanitizers and organic acids as well as differences between "Top 7" serogroups. Therefore, we investigated 746 E. coli isolates for resistance to lactic acid and two commercial sanitizers based on quaternary ammonium and peracetic acid. Furthermore, we correlated resistance to several genetic markers and investigated 44 isolates using Whole Genome Sequencing. Results indicate that factors related to motility, biofilm formation, and Locus of Heat Resistance played a role in resistance to sanitizers and lactic acid. In addition, Top 7 serogroups significantly differed in sanitizer and acid resistance, with O157 being the most consistently resistant to all treatments. Finally, mutations in rpoA, rpoC, and rpoS genes were observed, in addition to presence of a Gad gene with alpha-toxin formation in all O121 and O145 isolates, which may be related to increased resistance of these serogroups to the acids used in the present study.

Salmonella Biofilm Formation under Fluidic Shear Stress on Different Surface Materials

This study characterized biofilm formation of various Salmonella strains on common processing plant surface materials (stainless steel, concrete, rubber, polyethylene) under static and fluidic shear stress conditions. Surface-coupons were immersed in well-plates containing 1 mL of Salmonella (6 log CFU/mL) and incubated aerobically for 48 h at 37 °C in static or shear stress conditions. Biofilm density was determined using crystal violet assay, and biofilm cells were enumerated by plating on tryptic soy agar plates. Biofilms were visualized using scanning electron microscopy. Data were analyzed by SAS 9.4 at a significance level of 0.05. A surface-incubation condition interaction was observed for biofilm density (p < 0.001). On stainless steel, the OD₆₀₀ was higher under shear stress than static incubation; whereas, on polyethylene, the OD₆₀₀ was higher under static condition. Enumeration revealed surface-incubation condition (p = 0.024) and surface-strain (p < 0.001) interactions. Among all surface-incubation condition combinations, the biofilm cells were highest on polyethylene under fluidic shear stress (6.4 log/coupon; p < 0.001). Biofilms of S. Kentucky on polyethylene had the highest number of cells (7.80 log/coupon) compared to all other strain-surface combinations (p < 0.001). Electron microscopy revealed morphological and extracellular matrix differences between surfaces. Results indicate that Salmonella biofilm formation is influenced by serotype, surface, and fluidic shear stress.

Mobile genetic elements drive the multidrug resistance and spread of Salmonella serotypes along a poultry meat production line

The presence of mobile genetic elements in Salmonella isolated from a chicken farm constitutes a potential risk for the appearance of emerging bacteria present in the food industry. These elements contribute to increased pathogenicity and antimicrobial resistance through genes that are related to the formation of biofilms and resistance genes contained in plasmids, integrons, and transposons. One hundred and thirty-three Salmonella isolates from different stages of the production line, such as feed manufacturing, hatchery, broiler farm, poultry farm, and slaughterhouse, were identified, serotyped and sequenced. The most predominant serotype was Salmonella Infantis. Phylogenetic analyses demonstrated that the diversity and spread of strains in the pipeline are serotype-independent, and that isolates belonging to the same serotype are very closely related genetically. On the other hand, Salmonella Infantis isolates carried the pESI IncFIB plasmid harboring a wide variety of resistance genes, all linked to mobile genetic elements, and among carriers of these plasmids, the antibiograms showed differences in resistance profiles and this linked to a variety in plasmid structure, similarly observed in the diversity of Salmonella Heidelberg isolates carrying the IncI1-Iα plasmid. Mobile genetic elements encoding resistance and virulence genes also contributed to the differences in gene content. Antibiotic resistance genotypes were matched closely by the resistance phenotypes, with high frequency of tetracycline, aminoglycosides, and cephalosporins resistance. In conclusion, the contamination in the poultry industry is described throughout the entire production line, with mobile genetic elements leading to multi-drug resistant bacteria, thus promoting survival when challenged with various antimicrobial compounds.

Antimicrobial and antibiofilm activity of silver nanoparticles against Salmonella Enteritidis

Salmonella enterica serotype Enteritidis is one of the main pathogens associated with foodborne illnesses worldwide. Biofilm formation plays a significant role in the persistence of pathogens in food production environments. Owing to an increase in antimicrobial resistance, there is a growing need to identify alternative methods to control pathogenic microorganisms in poultry environments. Thus, this study aimed to synthesize silver nanoparticles (AgNPs) and evaluate their antibiofilm activity against poultry-origin Salmonella Enteritidis in comparison to a chemical disinfectant. AgNPs were synthesized, characterized, and tested for their minimum inhibitory concentration, minimum bactericidal concentration, and antibiofilm activity against S. Enteritidis strains on polyethylene surfaces. The synthesized AgNPs, dispersed in a liquid medium, were spherical in shape with a mean diameter of 6.2 nm. AgNPs exhibited concentration-dependent bactericidal action. The bacterial reduction was significantly higher with AgNPs (3.91 log10 CFU [Formula: see text] cm-2) than that with sanitizer (2.57 log10 CFU ∙ cm-2). Regarding the time of contact, the bacterial count after a contact time of 30 min was significantly lower than that after 10 min. The AgNPs exhibited antimicrobial and antibiofilm activity for the removal of biofilms produced by S. Enteritidis, demonstrating its potential as an alternative antimicrobial agent. The bactericidal mechanisms of AgNPs are complex; hence, the risk of bacterial resistance is minimal, making nanoparticles a potential alternative for microbial control in the poultry chain.

Identification and characterization of MDR virulent Salmonella spp isolated from smallholder poultry production environment in Edo and Delta States, Nigeria

Salmonella is responsible for some foodborne disease cases worldwide. It is mainly transmitted to humans through foods of animal origin through the consumption of poultry products. The increased international trade and the ease of transboundary movement could propel outbreaks of local origin to translate into severe global threats. The present study aimed to characterize Salmonella serovars isolated from poultry farms in Edo and Delta States, Nigeria. A total of 150 samples (faecal, water and feed) were collected from ten poultry farms between January and August 2020 and analyzed for Salmonella characterization using standard bacteriological and molecular methods. Salmonella serovars identified include: Salmonella Enteritidis [n = 17 (39.5%)], Salmonella Typhimurium [n = 13 (30.2%)] and other Salmonella serovars [n = 13 (30.2%)]. All Salmonella serovars were cefotaxime and ampicillin resistant. The presence of the invA gene ranged from 9(69.2%) to 15(88.2%). The spvC gene ranged from 2(14.4%) to 10(58.8%). All Salmonella serovars had sdiA gene. The Salmonella isolates produced some extracellular virulence factors (such as protease, lipase, β-hemolytic activity, and gelatinase), while 13(30.2%) of the overall isolates formed strong biofilms. In conclusion, the detection of multiple antibiotic-resistant Salmonella serovars in faecal sources, which also exhibited virulence determinants, constituted a public health risk as these faecal samples have the potential as manure in the growing of crops. These pathogens can be transmitted to humans nearby and through poultry products, resulting in difficult-to-treat infections and economic loss.

Multidrug-Resistant Biofilms (MDR): Main Mechanisms of Tolerance and Resistance in the Food Supply Chain

Biofilms are mono- or multispecies microbial communities enclosed in an extracellular matrix (EPS). They have high potential for dissemination and are difficult to remove. In addition, biofilms formed by multidrug-resistant strains (MDRs) are even more aggravated if we consider antimicrobial resistance (AMR) as an important public health issue. Quorum sensing (QS) and horizontal gene transfer (HGT) are mechanisms that significantly contribute to the recalcitrance (resistance and tolerance) of biofilms, making them more robust and resistant to conventional sanitation methods. These mechanisms coordinate different strategies involved in AMR, such as activation of a quiescent state of the cells, moderate increase in the expression of the efflux pump, decrease in the membrane potential, antimicrobial inactivation, and modification of the antimicrobial target and the architecture of the EPS matrix itself. There are few studies investigating the impact of the use of inhibitors on the mechanisms of recalcitrance and its impact on the microbiome. Therefore, more studies to elucidate the effect and applications of these methods in the food production chain and the possible combination with antimicrobials to establish new strategies to control MDR biofilms are needed.

Electrochemical Control of Biofilm Formation and Approaches to Biofilm Removal

This review deals with microbial adhesion to metal-based surfaces and the subsequent biofilm formation, showing that both processes are a serious problem in the food industry, where pathogenic microorganisms released from the biofilm structure may pollute food and related material during their production. Biofilm exhibits an increased resistance toward sanitizers and disinfectants, which complicates the removal or inactivation of microorganisms in these products. In the existing traditional techniques and modern approaches for clean-in-place, electrochemical biofilm control offers promising technology, where surface properties or the reactions taking place on the surface are controlled to delay or prevent cell attachment or to remove microbial cells from the surface. In this overview, biofilm characterization, the classification of bacteria-forming biofilms, the influence of environmental conditions for bacterial attachment to material surfaces, and the evaluation of the role of biofilm morphology are described in detail. Health aspects, biofilm control methods in the food industry, and conventional approaches to biofilm removal are included as well, in order to consider the possibilities and limitations of various electrochemical approaches to biofilm control with respect to potential applications in the food industry.

Biocides as Biomedicines against Foodborne Pathogenic Bacteria

Biocides are currently considered the first line of defense against foodborne pathogens in hospitals or food processing facilities due to the versatility and efficiency of their chemical active ingredients. Understanding the biological mechanisms responsible for their increased efficiency, especially when used against foodborne pathogens on contaminated surfaces and materials, represents an essential first step in the implementation of efficient strategies for disinfection as choosing an unsuitable product can lead to antibiocide resistance or antibiotic–biocide cross-resistance. This review describes these biological mechanisms for the most common foodborne pathogens and focuses mainly on the antipathogen effect, highlighting the latest developments based on in vitro and in vivo studies. We focus on biocides with inhibitory effects against foodborne bacteria (e.g., Escherichia spp., Klebsiella spp., Staphylococcus spp., Listeria spp., Campylobacter spp.), aiming to understand their biological mechanisms of action by looking at the most recent scientific evidence in the field.

Differences in biofilm formation of Salmonella serovars on two surfaces under two temperature conditions

AIMS

Salmonella is extremely diverse, with >2500 serovars that are genetically and phenotypically diverse. The aim of this study was to build a collection of Salmonella isolates that are genetically diverse and to evaluate their ability to form biofilm under different conditions relevant to a processing environment.

METHODS AND RESULTS

Twenty Salmonella isolates representative of 10 serovars were subtyped using Clustered regularly interspaced short palindromic repeats (CRISPR)-typing to assess the genetic diversity between isolates of each serovar. Biofilm formation of the isolates on both plastic and stainless-steel surfaces at 25 and 15°C was assessed. At 25°C, 8/20 isolates each produced strong and moderate biofilm on plastic surface compared to stainless-steel (3/20 and 13/20 respectively). At 15°C, 5/20 produced strong biofilm on plastic surface and none on stainless-steel. Several isolates produced weak biofilm on plastic (11/20) and stainless-steel (16/20) surfaces. Serovar Schwarzengrund consistently produced strong biofilm while serovars Heidelberg and Newport produced weak biofilm.

CONCLUSION

These results suggest that Salmonellae differ in their attachment depending on the surface and temperature conditions encountered, which may influence persistence in the processing environment.

SIGNIFICANCE AND IMPACT OF STUDY

These differences in biofilm formation could provide useful information for mitigation of Salmonella in processing environments.