Microbiological contamination in Three Large-Scale Pig Slaughterhouses in Northern Italy

Microbial contamination, antimicrobial resistance and biofilm formation of bacteria isolated from a high-throughput pig abattoir

The aim of this work was to assess the level of microbial contamination and resistance of bacteria isolated from a highthroughput heavy pig slaughterhouse (approx. 4600 pigs/day) towards antimicrobials considered as critical for human, veterinary or both chemotherapies. Samples, pre-operative and operative, were obtained in 4 different surveys. These comprised environmental sampling, i.e. air (n_total = 192) and surfaces (n_total = 32), in four different locations. Moreover, a total of 40 carcasses were sampled in two different moments of slaughtering following Reg. (CE) 2073/2005. Overall, 60 different colonies were randomly selected from VRBGA plates belonging to 20 species, 15 genera and 10 families being Enterobacteriaceae, Moraxellaceae and Pseudomonadaceae the most represented ones. Thirty-seven isolates presented resistance to at least one molecule and seventeen were classified as multi-drug resistant. Enterobacteriaceae, particularly E. coli, displayed high MIC values towards trimethoprim, ampicillin, tetracycline and sulphametoxazole with MIC_max of 16, 32, 32 and 512 mg/L, respectively. Moreover, isolated Pseudomonas spp. showed high MIC values in critical antibiotics such as ampicillin and azithromycin with MIC_max of 32 and 64 mg/L, respectively. Additionally, in vitro biofilm formation assays demonstrated that fifteen of these isolates can be classified as strong biofilm formers. Results demonstrated that a high diversity of bacteria containing antibiotic resistant and multiresistant species is present in the sampled abattoir. Considering these findings, it could be hypothesised that the processing environment could be a potential diffusion determinant of antibiotic resistant bacteria through the food chain and operators.

Prevalence and antimicrobial resistance profile in <em>Salmonella</em> spp. isolates from swine food chain

The aim of this survey was to examine the prevalence and the antimicrobial resistance (AMR) of Salmonella spp. isolated from swine food chain. A total of 435 samples were collected: 360 from slaughterhouse (150 carcasses, 30 cecal samples, 180 environmental samples) and 75 from Italian traditional pork dry sausages. Thirty-six Salmonella were isolated and identified by Polymerase Chain Reaction (PCR): 13,3% (4/30) in fecal samples, 5,5% (10/180) in environmental samples, 7,3% (11/150) in carcasses, and 14,6% (11/75) in Italian traditional dry sausages. Salmonella serotypes were: S. Typhimurium (44,4%), S. Typhimurium monophasic variant (8,3%), S. Typhi (2,8%), S. Enteritidis (22,2%), S. Rissen (16,6%) and S. Derby (5,5%). Phenotypic and genotypic characterization of AMR Salmonella spp. isolates was executed through automatic system (VITEK 2, bioMèrieux) and PCR assays. Salmonella spp. showed phonotypical and genotypical resistance to at least one or more classes of antibiotic. All Salmonella spp. were resistant to aminoglycoside (amikacin and tobramycin) and gentamicin, 86,1% strains were resistant to tetracycline, 55,5% strains were resistant to ampicillin and piperacillin, 25% strains to trimethoprim, 5,5% strains to chloramphenicol, 2,8% strains to amoxicillin/ clavulanic acid, and nitrofurantoin. Among Salmonella isolates, the most detected AMR genes were catA for chloramphenicol (94,4%), nitrofuran nfsA (77.7%), nfsB (86,1%) and, for fluoroquinolone par C (100%) and gyrA (94,4%). This study reported epidemiological data regarding Salmonella spp. and AMR’s circulation in the swine food chain. This phenomenon (AMR) has critical repercussions on the final consumer health; therefore, it represents a crucial One-Health issue.

Overcoming Multidrug Resistance in Salmonella spp. Isolates Obtained From the Swine Food Chain by Using Essential Oils: An in vitro Study

Antimicrobial resistance (AMR) is a global concern, and new approaches are needed to circumvent animal and food-borne resistant pathogens. Among the new strategies, the combination of antibiotics with natural compounds such as essential oils (EOs) could be an alternative to challenge bacterial resistance. The present study evaluates the phenotypic and genotypic antibiotic resistance of 36 Salmonella enterica (16 S. Typhimurium, 3 monophasic variant S. Typhimurium, 8 S. Enteritidis, 6 S. Rissen, 1 S. Typhi, and 2 S. Derby) strains, isolated from the swine production chain. The isolates displayed phenotypic resistance to gentamicin, amikacin, tobramycin, and tetracycline, while the resistance genes most commonly detected were parC, catA, nfsB, nfsA, blaTEM, tetA, and tetB. Then 31/36 Salmonella isolates were chosen to evaluate resistance to tetracycline and Thymus vulgaris, Eugenia caryophyllata, and Corydothymus capitatus EOs by determining minimum inhibitory concentrations (MICs). Finally, the synergistic effect between tetracycline and each EOs was evaluated by the checkerboard method, calculating the fractional inhibitory concentration (FIC) index. Among the EOs, C. capitatus displayed the best bioactivity in terms of MICs, with the lowest values (0.31 and 0.625 μl/ml). On the contrary, the strains showed the ability to grow in the presence of the maximum concentration of tetracycline employed (256 μg/ml). While not displaying a real synergism according to the FIC index, the combination of tetracycline compounds and the three EOs resulted in a significant reduction in the MIC values to tetracycline (4 μg/ml), suggesting a restoration of the susceptibility to the antibiotic in Salmonella spp.

Impact of cleaning and disinfection procedures on microbial ecology and Salmonella antimicrobial resistance in a pig slaughterhouse

To guarantee food safety, a better deciphering of ecology and adaptation strategies of bacterial pathogens such as Salmonella in food environments is crucial. The role of food processing conditions such as cleaning and disinfection procedures on antimicrobial resistance emergence should especially be investigated. In this work, the prevalence and antimicrobial resistance of Salmonella and the microbial ecology of associated surfaces communities were investigated in a pig slaughterhouse before and after cleaning and disinfection procedures. Salmonella were detected in 67% of samples and isolates characterization revealed the presence of 15 PFGE-patterns belonging to five serotypes: S.4,5,12:i:-, Rissen, Typhimurium, Infantis and Derby. Resistance to ampicillin, sulfamethoxazole, tetracycline and/or chloramphenicol was detected depending on serotypes. 16S rRNA-based bacterial diversity analyses showed that Salmonella surface associated communities were highly dominated by the Moraxellaceae family with a clear site-specific composition suggesting a persistent colonization of the pig slaughterhouse. Cleaning and disinfection procedures did not lead to a modification of Salmonella susceptibility to antimicrobials in this short-term study but they tended to significantly reduce bacterial diversity and favored some genera such as Rothia and Psychrobacter. Such data participate to the construction of a comprehensive view of Salmonella ecology and antimicrobial resistance emergence in food environments in relation with cleaning and disinfection procedures.

Deciphering Resistome and Virulome Diversity in a Porcine Slaughterhouse and Pork Products Through Its Production Chain

We aimed to better understand resistome and virulome patterns on animal and process-area surfaces through a pig slaughterhouse to track possible contamination within the food production chain. Culture-dependent methods revealed high levels of microbial contamination, corresponding to mesophilic and pathogenic bacteria on both the animal and process-area surfaces mainly in the anesthesia (AA and AS) zone followed by “scorching and whip” (FA and FS) zone and also in the end products. To evaluate the potential risk of antibiotic resistance and virulence determinants, shotgun metagenomic DNA-sequencing of isolates from selected areas/products uncovered a high diversity and richness of antibiotic resistance genes (ARGs): 55–62 genes in the anesthesia area (AA and AS) and 35–40 in “animal-arrival zone” (MA and MS). The “scorching and whip” (FA and FS) area, however, exhibited lowered abundance of ARGs (1–6), indicating that the scalding and depilating process (an intermediate zone between “anesthesia” and “scorching and whip”) significantly decreased bacterial load by 1–3 log₁₀ but also diminished the resistome. The high prevalence of antibiotic-inactivating enzyme genes in the “animal-arrival zone” (60–65%) and “anesthesia” area (56%) were mainly represented by those for aminoglycoside (46–51%) and lincosamide (14–19%) resistance, which did not reflect selective pressures by antibiotics most commonly used in pig therapy—tetracyclines and beta-lactams. Contrary to ARGs, greater number of virulence resistance genes were detected after evisceration in some products such as kidney, which reflected the poor hygienic practices. More than 19 general virulence features—mainly adherence, secretion system, chemotaxis and motility, invasion and motility were detected in some products. However, immune evasion determinants were detected in almost all samples analyzed from the beginning of the process, with highest amounts found from the anesthesia area. We conclude that there are two main sources of contamination in a pig slaughterhouse: the microorganisms carried on the animals’ hide, and those from the evisceration step. As such, focussing control measures, e.g., enhanced disinfection procedures, on these contamination-source areas may reduce risks to food safety and consumer health, since the antibiotic and virulence determinants may spread to end products and the environment; further, ARG and virulence traits can exacerbate pathogen treatments.