Occurrence and antimicrobial resistance of Salmonella strains from food of animal origin in southern Italy

Monitoring of Antimicrobial Resistance of Salmonella Serotypes Isolated from Humans in Northwest Italy, 2012-2021

Salmonella enterica is among the most common causes of foodborne outbreaks in humans in Europe. The global emergence of resistance to antimicrobials calls for close monitoring of the spread and prevalence of resistant Salmonella strains. In this study, we investigated the occurrence of antimicrobial resistance of Salmonella serotypes isolated from humans between 2012 and 2021 in Piedmont, northwest Italy. A total of 4814 Salmonella strains (168 serotypes) were tested against six classes of antimicrobials. Many strains (83.3%) showed resistance to at least one antibiotic: tetracycline (85.1%), ampicillin (79.2%), quinolones (47.4%), and gentamicin (28.4%). Between the first (2012-2016) and the second study period (2017-2021), a decrease in antimicrobial resistance was noted for tetracycline (from 92.4% to 75.3%), ampicillin (from 85.3% to 71.3%), quinolones (from 49.4% to 44.6%), and cefotaxime (from 34.8% to 4.0%). Many multidrug resistant Salmonella strains (43.6%) belonged to S. ser. Typhimurium, S. ser. Infantis, and S. ser. Typhimurium 1,4,[5],12:i:-. Overall, multidrug resistance decreased from 60.7% to 26.4%, indicating a reduction in the antimicrobial resistance of Salmonella strains in Piedmont and in Europe and demonstrating the effectiveness of the measures that were put in place to reduce antimicrobial resistance.

Antimicrobial Resistance of Salmonella Strains Isolated from Human, Wild Boar, and Environmental Samples in 2018-2020 in the Northwest of Italy

Antimicrobial resistance is one of the most challenging public health problems worldwide, and integrated surveillance is a key aspect in a One Health control strategy. Additionally, Salmonella is the second most common zoonosis in Europe. We aimed to investigate the circulation of Salmonella strains and their related antimicrobial resistance in human, environmental, and wild boar samples from the northwest of Italy, from 2018 to 2020, to obtain a more comprehensive epidemiological picture. Salmonella Typhimurium 1,4,[5],12:i:-, S. Veneziana and S. Newport were the most common serotypes occurring in humans, the environment, and wild boar, respectively. Antimicrobial resistance was rather common in Salmonella isolates, with those from human displaying the highest degree of resistance against sulfadiazine−sulfamerazine−sulfamethazine (>90% of resistance). Moreover, resistance against azithromycin were exclusively observed in environmental samples, while only 7.7% (95% CI = 1.6−20.8) of wild boar isolates experienced resistance against trimethoprim−sulfamethoxazole. Multidrug resistance concurrently involved up to seven antimicrobial classes in human isolates, including third-generation cephalosporins and fluoroquinolones. Salmonella Typhimurium in humans and serotypes Goldcoast and Rissen from environmental sources showed the highest levels of resistance. This study shows diverse antimicrobial resistance patterns in Salmonella strains isolated from different sources and gives a broad picture of antimicrobial resistance spread in wild animals, humans, and the environment.

A Ternary Copper (II) Complex with 4-Fluorophenoxyacetic Acid Hydrazide in Combination with Antibiotics Exhibits Positive Synergistic Effect against Salmonella Typhimurium

Salmonella spp. continues to figure prominently in world epidemiological registries as one of the leading causes of bacterial foodborne disease. We characterised 43 Brazilian lineages of Salmonella Typhimurium (ST) strains, characterized drug resistance patterns, tested copper (II) complex as control options, and proposed effective antimicrobial measures. The minimum inhibitory concentration was evaluated for seven antimicrobials, isolated and combined with the copper (II) complex [Cu(4-FH)(phen)(ClO4)2] (4-FH = 4-fluorophenoxyacetic acid hydrazide and phen = 1,10-phenanthroline), known as DRI-12, in planktonic and sessile ST. In parallel, 42 resistance genes were screened (PCR/microarray). All strains were multidrug resistant (MDR). Resistance to carbapenems and polymyxins (86 and 88%, respectively) have drawn attention to the emergence of the problem in Brazil, and resistance is observed also to CIP and CFT (42 and 67%, respectively), the drugs of choice in treatment. Resistance to beta-lactams was associated with the genes blaTEM/blaCTX-M in 39% of the strains. Lower concentrations of DRI-12 (62.7 mg/L, or 100 μM) controlled planktonic and sessile ST in relation to AMP/SUL/TET and AMP/SUL/TET/COL, respectively. The synergistic effect provided by DRI-12 was significant for COL/CFT and COL/AMP in planktonic and sessile ST, respectively, and represents promising alternatives for the control of MDR ST.

Prevalence of Antibiotic Resistance in Salmonella Serotypes Concurrently Isolated from the Environment, Animals, and Humans in South Africa: A Systematic Review and Meta-Analysis

One of the main global concerns is the usage and spread of antibiotic resistant Salmonella serovars. The animals, humans, and environmental components interact and contribute to the rapid emergence and spread of antimicrobial resistance, directly or indirectly. Therefore, this study aimed to determine antibiotic resistance (AR) profiles of Salmonella serotypes isolated from the environment, animals, and humans in South Africa by a systematic review and meta-analysis. The preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines were followed to search four databases for studies published from 1980 to 2021, that reported the antibiotic resistance profiles of Salmonella serotypes isolated in South Africa. The AR was screened from 2930 Salmonella serotypes which were isolated from 6842 samples. The Western Cape province had high pooled prevalence estimates (PPE) of Salmonella isolates with AR profiles followed by North West, Gauteng, and Eastern Cape with 94.3%, 75.4%, 59.4%, and 46.2%, respectively. The high PPE and heterogeneity were observed from environmental samples [69.6 (95% CI: 41.7−88.3), Q = 303.643, I² = 98.353, Q-P = 0.045], animals [41.9 (95% CI: 18.5–69.5), Q = 637.355, I² = 98.745, Q-P = 0.577], as well as animals/environment [95.9 (95% CI: 5.4−100), Q = 55.253, I² = 96.380, Q-P = 0.300]. The majority of the salmonella isolates were resistant to sulphonamides (92.0%), enrofloxacin and erythromycin (89.3%), oxytetracycline (77.4%), imipenem (72.6%), tetracycline (67.4%), as well as trimethoprim (52.2%), among the environment, animals, and humans. The level of multidrug-resistance recorded for Salmonella isolates was 28.5% in this review. This study has highlighted the occurrence of AR by Salmonella isolates from animals, humans, and environmental samples in South Africa and this calls for a consolidated “One Health” approach for antimicrobial resistance epidemiological research, as well as the formulation of necessary intervention measures to prevent further spread.

Serotyping and Evaluation of Antimicrobial Resistance of Salmonella Strains Detected in Wildlife and Natural Environments in Southern Italy

Wild animals are potential vectors of antibiotic-resistant bacteria in the environment. The present study aimed to investigate the occurrence of antimicrobial resistance among Salmonella serovars isolated from wildlife and the environment in Italy. A total of 164 Salmonella isolates were analyzed, and six different subspecies and 64 serovars were detected. High proportions of Salmonella isolates proved resistant to streptomycin (34.1%), followed by trimethoprim-sulfamethoxazole (23.2%), tetracycline (17.7%), ciprofloxacin (14.63%) and ampicillin (11.59%). By source, the lowest level of resistance was observed in Salmonella serovars isolated from a water environment, while antimicrobial resistance was frequent in strains collected from shellfish, reptiles and birds. Multidrug-resistant strains were recovered from seafood (n = 11), mammals (n = 3) and water (n = 1). Three S. Typhimurium monophasic variant strains showed asimultaneous resistance to ampicillin, streptomycin, tetracycline and trimethoprim-sulfamethoxazole, which represents a recognized alert resistance profile for this serovar. These data indicate the environmental dissemination of resistant strains due to anthropogenic activities, which, in southern Italy, probably have a higher impact on marine ecosystems than on terrestrial ones. Moreover, as most of the animals considered in the present study are usually consumed by humans, the presence of resistant bacteria in them is a matter of great concern.

Antimicrobial Susceptibility Testing for Salmonella Serovars Isolated from Food Samples: Five-Year Monitoring (2015-2019)

The continuous collection and analysis of updated data on the antimicrobic resistance among bacterial strains represent the essential core for the surveillance of this problem. The present work aimed to investigate the occurrence of antimicrobial resistance among Salmonella serovars isolated in foods in 2015-2019. A total of 178 Salmonella strains belonging to 39 serovars were tested against 10 antimicrobials. High proportions of Salmonella isolates were resistant to tetracycline (n = 53.9%), ciprofloxacin (n = 47.2%), ampicillin (n = 44.4%), nalidixic acid (n = 42.7%), and trimethoprim-sulfamethoxazole (n = 38.8%). Different resistance rates were recorded among the different serotypes of Salmonella, and S. Infantis, exhibited the highest resistance to antibiotics. A high percentage of strains isolated from poultry, pork, and bovine were resistant to at least one or two antimicrobials. Resistant and multidrug-resistant (MDR) strains were also recorded among the isolates from molluscan shellfish; however, the occurrence of resistant Salmonella strains isolated from this source was significantly lower compared with those reported for poultry, pork, and bovine. The high levels of resistance reported in the present study indicate a potential public health risk. Consequently, additional hygiene and antibiotic stewardship practices should be considered for the food industry to prevent the prevalence of Salmonella in foods.

Characterization of Salmonella Typhimurium and its monophasic variant 1,4, [5],12:i:- isolated from different sources

In order to characterize the most commonly detected Salmonella serotypes, we tested 124 isolates of S. Typhimurium and 89 isolates of the monophasic variant of S. Typhimurium (S. 1,4, [5],12:i:-) for their antimicrobial susceptibility by means of the Kirby-Bauer disk-diffusion method, and for the detection of 19 genes (four Phage Markers (g13, Sieb, eat, g8), ten prophage-related virulence genes (gipA, gtgB, nanH, gogB, grvA, sopE, sspH1, sspH2, sodC1, gtgE), and five plasmid-borne virulence genes (spvC, pefA, mig5, rcK, srgA)) by means of PCR-based assays. A total of 213 strains were analyzed from, humans (n = 122), animals (n = 25), food (n = 46), and irrigation water (n = 20). S. Typhimurium isolates showed higher variability, in both their resistance profiles and molecular typing, than S. 1,4, [5],12:i:-. Strains from irrigation water displayed significantly higher susceptibility to antibiotics than those from the other sources. Resistance to ampicillin, streptomycin, sulfonamide, and tetracycline was the most commonly detected resistance profile (R-type), being in serovar S. 1,4, [5],12:i:-, frequently associated to resistance to other antimicrobials. Significant differences in genetic profiles in the two abovementioned Salmonella serotypes were found. None of the plasmid-borne virulence genes investigated were detected in S. 1,4, [5],12:i:- isolates, while those genes, characterized 37.9% of the S. Typhimurium strains. Differences in the prevalence of some molecular targets between the two Salmonella serotypes deserve further study. Importantly, the grvA gene was found exclusively in S. Typhimurium strains, whereas sopE, sodC, gtgB, and gipA were mainly detected, with a statistically significant difference, in S. 1,4, [5],12:i:- isolates.

Characterization of non-typhoidal Salmonella enterica strains of human origin in central and southern Italy

Non-typhoidal Salmonella enterica infection is a significant public health problem worldwide. The aim of this study was to characterize Salmonella enterica strains isolated from human specimens in central and southern Italy, for epidemiological studies. One hundred and fifty S. enterica strains were serotyped. Isolates were tested for their antimicrobial susceptibility, by disk diffusion method. The molecular characterizations, based on PCR, were carried out for the detection of invA gene and other virulence elements and phage marker genes. Eighteen different Salmonella serotypes were identified. The most common serotypes detected were S. Typhimurium, S. Enteritidis, the monophasic variant of S. Typhimurium (S. 4,[5],12:i:-), and S. Napoli. High resistance rates were recorded for tetracycline (64%), streptomycin (62%), sulphonamide (57%), and ampicillin (56%). The ASSuT R-type, also associated to resistance to other antibiotics, was highly prevalent in S. 4,[5],12:i:- (97%) and S. Typhimurium (55%), while the ACSSuT R-type, also associated to other antibiotics, was observed prevalently in S. Typhimurium (20.4%). The genes of more common detection were invA (100%), sspH2 (86.6%), gtgB (84.6%), g8 (80%), sodC1 (77.3%), gipA (52.6%), sspH1 (52.6%).

Prevalence, molecular and antimicrobial resistance of Salmonella isolated from sausages in Meknes, Morocco

Salmonella is among the most important food borne pathogens worldwide contaminating a wide range of animal products including meat products. The aims of this study go through two steps: The first step is to estimate the proportion of sausages products contaminated with Salmonella in Meknes city (Morocco), which were collected from various shopping sites: butchery, street vendors, supermarket and souk (Weekly market combines the population of the small villages around Meknes city). The second one is to identify serovars, to determine the antimicrobials resistance patterns of isolates and to detect the invA and spvC genes. 34 (21.79%) Salmonella were isolated, recovered 4 serogroups and 12 serotypes. The most prevalent serotypes were Salmonella Corvallis (23.53%) and Salmonella Kentucky (17.65%). All Salmonella isolates were tested for their susceptibility to 18 selected antimicrobials agents, of which 100% were resistant to at least one antimicrobial, 85.30% (29/34) were resistant to two or more antimicrobials and 44.12% (15/34) were resistant to at least three antimicrobials. All Salmonella are resistant to ampicillin, 76.47% to streptomycin, 20.59% to sulfonamides, 17.65% to Tetracycline and 11.77% to Ofloxacin. The "ACSSuT" penta-resistance pattern was observed in tow of the Salmonella Typhimurium strains. In addition, this study showed that all Salmonella strains (34) were positive for invasion gene invA and negative for the virulence gene spvC.