Antibiotic Susceptibility Profile and Tetracycline Resistance Genes Detection in Salmonella spp. Strains Isolated from Animals and Food

Oral vaccination of young broilers with a live Salmonella Typhimurium vaccine reduces caecal and internal organ colonization following a Salmonella Infantis challenge in a seeder-bird model

Poultry products are an important source of foodborne Salmonella infections in humans. Amongst these, the prevalence of S. Infantis is rising. In this study, the protection efficacy of an authorized live-attenuated S. Typhimurium vaccine against S. Infantis, was examined using a seeder-bird model in broilers. Vaccinated birds displayed a significantly lower colonization of S. Infantis bacteria in the caeca compared to the non-vaccinated counterparts (P = 0.017), with no significant differences observed in the spleen among the groups, three days post-infection. Thirty-two days post-infection, the disparity in average S. Infantis concentration between all-vaccinated and non-vaccinated birds was significant in both caeca (P = 0.0003) and spleen (P = 0.0002). Interestingly, a third group, consisting of seeder birds that were not vaccinated but housed with vaccinated penmates, exhibited significantly lower S. Infantis levels in both caeca (P = 0.0014) and spleen (P < 0.0001) compared to the non-vaccinated group. These findings underscore the potential of a live-attenuated S. Typhimurium vaccine administered to 2-day-old chicks in conferring protection against S. Infantis in broilers up to slaughter age.

Selection of starter lactic acid bacteria capable of forming biofilms on wooden vat prototypes for their future application in traditional Sicilian goat's milk cheese making

In this study, 327 presumptive lactic acid bacteria (LAB) were isolated from goats' milk acid curds produced at a Sicilian dairy farm with the aim to identify potential starter cultures for traditional cheeses. All isolates were first processed by randomly amplified polymorphic DNA (RAPD)-PCR analysis. This approach identified 63 distinct strains which were evaluated for their acidifying capacity. Only 15 strains specifically stood out for their acidification capacity and were identified through 16S rRNA gene sequencing as Lactococcus lactis (11 strains) Enterococcus faecalis (three strains), and Ligilactobacillus animalis (one strain). Notably, all 15 LAB isolates produced bacteriocin-like inhibitory substances and anti-biofilm compounds, against both planktonic and biofilm forms of Listeria monocytogenes, Salmonella Enteritidis, Escherichia coli, and Staphylococcus aureus, albeit at varying levels. Among these 15 LAB, En. faecalis RGM25 and Lc. lactis RGM55, susceptible to five antibiotics tested, were put in contact with wooden vat prototypes, because all equipment used in traditional cheese production in Sicily are made of wood. Scanning electron microscopy and bacterial plate counts of the wooden vat prototypes showed the development of biofilms at levels of approximately 6.0 log CFU/cm2. Overall, this study contributes to establishing a custom-made LAB starter cultures with bio-preservatives properties for Sicilian cheese productions.

Scolopax rusticola Carrying Enterobacterales Harboring Antibiotic Resistance Genes

The Eurasian woodcock (Scolopax rusticola) belongs to those bird species that make systematic migratory flights in spring and autumn in search of favorable breeding and wintering areas. These specimens arrive in the Mediterranean Area from northeastern European countries during the autumn season. The purpose of this study was to assess whether woodcocks can carry antibiotic resistance genes (ARGs) along their migratory routes. Although the role of migratory birds in the spread of some zoonotic diseases (of viral and bacterial etiology) has been elucidated, the role of these animals in the spread of antibiotic resistance has not yet been clarified. In this study, we analyzed the presence of beta-lactam antibiotic resistance genes. The study was conducted on 69 strains from 60 cloacal swabs belonging to an equal number of animals shot during the 2022-2023 hunting season in Sicily, Italy. An antibiogram was performed on all strains using the microdilution method (MIC) and beta-lactam resistance genes were investigated. The strains tested showed no phenotypic resistance to any of the 13 antibiotics tested; however, four isolates of Enterobacter cloacae and three of Klebsiella oxytoca were found to carry the blaIMP-70, blaVIM-35, blaNDM-5 and blaOXA-1 genes. Our results confirm the importance of monitoring antimicrobial resistance among migratory animals capable of long-distance bacteria spread.

Characterization of Staphylococcus Species Isolates from Sheep Milk with Subclinical Mastitis: Antibiotic Resistance, Enterotoxins, and Biofilm Production

Subclinical mastitis represents one of the most contagious diseases affecting animals involved in dairy production systems. Although coagulase-negative staphylococci (CoNSs) have been considered minor pathogens for many years, they have recently emerged as opportunistic pathogens in mastitis disorders. The objectives of this work were to assess the antimicrobial resistance profile and the ability to produce a biofilm in comparison with a reference strain and to search for genes related to biofilm production, antimicrobial resistance, and enterotoxins in 18 isolates of Staphylococcus species from the milk of sheep with subclinical mastitis, collected from different Sicilian farms. This knowledge is essential to provide basic information on the pathogenicity and virulence of staphylococcal species and their impact on animal health. All isolates were resistant to ampicillin, 88.8% to streptomycin, 77.7% to gentamicin, 44.4% to chloramphenicol, 27.7% to erythromycin, and 11.1% to tetracycline, and two isolates were strong biofilm producers. Antibiotic resistance gene profiling showed that 16.6% of isolates possess the blaZ gene, whereas the search of biofilm-associated genes revealed the occurrence of the sasC gene in 33.3% of isolates, the ica gene in 27.7%, and bap and agr (accessory gene regulator) genes in 16.6% of isolates. Altogether, the results of this study indicate that CoNSs can acquire virulence genes and could have a role as pathogens in subclinical mastitis.

Antibiotic Resistance Genes Carried by Commensal Escherichia coli from Shelter Cats in Italy

Antimicrobial resistance is a widespread global health problem. The presence of resistant bacteria and antibiotic resistance genes has been demonstrated not only in humans but also in animals, including pets. Stray cats share the urban environment with people and pets. This may facilitate transmission of resistant bacteria and resistance genes between stray animals, people and domestic animals. Several studies have investigated the role of stray cats as a fecal carrier of ESBL-producing bacteria. However, there are many genes and resistance mechanisms that can be detected in commensal E. coli, which, because of its genetic plasticity, is considered an indicator for monitoring antibiotic resistance. In this study, rectal swabs were collected from stray cats from colonies and shelters in the city of Monza (Monza Brianza, Italy) to isolate commensal E. coli. Phenotypic tests, such as the minimum inhibitory concentration (MIC) and the double disc test (DDST), and molecular analyses to detect antimicrobial resistance genes (ARGs) were used to study the resistance of these isolates. The results obtained confirm that stray cats can carry ESBL-producing E. coli (6.7%) and genes conferring resistance to other important antibiotic classes such as tetracyclines and sulfonamides.

Prevalence of Salmonella infection in village chickens and determination of the tetracycline resistance genes in the Salmonella isolates in the Sistan region, Iran

Recently, an increasing number of multi drug resistant Salmonella species have been emerged due to overuse of antibiotics in veterinary and human medicine which has adverse consequences on public health. The present study was conducted with the aim of investigating the prevalence of Salmonella infection in village chickens in Sistan region and determining the prevalence of the antibiotic resistance genes in Salmonella isolated from these birds. In this study, 100 chickens were randomly selected from five counties of Sistan region. A cloacal swab sample was taken from each bird and also information about age, gender, breed, proximity with other birds, proximity with waterfowl, proximity with livestock, and receiving different antibiotics especially tetracycline were obtained using a questionnaire. Conventional culture methods used for Salmonella detection and isolation. Then, amplification of invA gene by PCR was used to confirm Salmonella colonies. Finally, 27 samples were confirmed to be infected with Salmonella by both culture and PCR methods. Disk diffusion method was used to determine the sensitivity to 4 antibiotics including; tetracycline, gentamicin, cefepime, and difloxacin. The results of the present study showed that proximity to waterfowl (OR = 0.273) significantly mitigates the risk of Salmonella infection. For the isolates, the highest resistance was recorded against cefepime and the highest susceptibility was to difloxacin. The presence proportion of tetA and tetB in tetracycline resistant isolates was higher than that in susceptible ones but this difference was not statistically significant.

Antibiotic resistance mechanism and diagnosis of common foodborne pathogens based on genotypic and phenotypic biomarkers

The emergence of antibiotic-resistant bacteria due to the overuse or inappropriate use of antibiotics has become a significant public health concern. The agri-food chain, which serves as a vital link between the environment, food, and human, contributes to the large-scale dissemination of antibiotic resistance, posing a concern to both food safety and human health. Identification and evaluation of antibiotic resistance of foodborne bacteria is a crucial priority to avoid antibiotic abuse and ensure food safety. However, the conventional approach for detecting antibiotic resistance heavily relies on culture-based methods, which are laborious and time-consuming. Therefore, there is an urgent need to develop accurate and rapid tools for diagnosing antibiotic resistance in foodborne pathogens. This review aims to provide an overview of the mechanisms of antibiotic resistance at both phenotypic and genetic levels, with a focus on identifying potential biomarkers for diagnosing antibiotic resistance in foodborne pathogens. Furthermore, an overview of advances in the strategies based on the potential biomarkers (antibiotic resistance genes, antibiotic resistance-associated mutations, antibiotic resistance phenotypes) for antibiotic resistance analysis of foodborne pathogens is systematically exhibited. This work aims to provide guidance for the advancement of efficient and accurate diagnostic techniques for antibiotic resistance analysis in the food industry.

Prevalence and antimicrobial resistance profiles of Salmonella spp. in poultry meat

The spread of multidrug resistant (MDR) Salmonella strains, along the poultry supply chain, can represent a relevant threat to human health. This study aimed to evaluate the prevalence and antimicrobial resistance of Salmonella spp. isolated from poultry meat for human consumption. Between 2019 and 2021, 145 samples were analyzed according to ISO 6579-1:2017. The strains isolated were identified by using biochemical-enzymatic assays and serotyping, according to the Kauffmann-White-Le Minor scheme. The antibiotic susceptibility tests were determined using the Kirby-Bauer method. Forty Salmonella spp. strains were isolated and serotyping showed Salmonella Infantis to be predominant. 80% of the isolated strains were MDR and identified as S. Infantis. This study confirms the circulation of MDR Salmonella isolated from poultry meat and highlights the predominance of the S. Infantis serovar, which represents an emerging risk factor under the One Health holistic approach.

Antimicrobial Susceptibility of Commensal E. coli Isolated from Wild Birds in Umbria (Central Italy)

The role of wildlife, including birds, in antimicrobial resistance is nowadays a speculative topic for the scientific community as they could be spreaders/sources of antimicrobial resistance genes. In this respect, we aimed to investigate the antimicrobial susceptibility of 100 commensal Escherichia coli strains, isolated from wild birds from an Umbrian rescue centre and admitted to the Veterinary Teaching Hospital of Perugia (Central Italy) mainly for traumatic injuries. The possible presence of Salmonella spp. and ESBL-producing E. coli was also estimated. The highest prevalence of resistance was observed for ampicillin (85%) and amoxicillin/clavulanic acid (47%), probably due to their extensive use in human and veterinary medicine. Seventeen out of the one hundred E. coli isolates (17%) displayed a multidrug-resistance profile, including the beta-lactam category, with the most common resistance patterns to three or four classes of antibiotics. Resistance to ciprofloxacin, cefotaxime and ceftazidime exhibited values of 18%, 17% and 15%, respectively. Eight out of the hundred E. coli isolates (8%) were ESBL and seven showed multidrug resistance profiles. Salmonella spp. was not isolated. Resistance to third-generation cephalosporins, also detected in long-distance migratory birds, suggests the need for monitoring studies to define the role of wild birds in antimicrobial resistance circuits.

Identification and antibiotic pattern analysis of bacillary dysentery causing bacteria isolated from stool samples of infected patients

Bacillary dysentery is a type of dysentery and a severe form of shigellosis. This dysentery is usually restricted to Shigella infection, but Salmonella enterica and enteroinvasive Escherichia coli strains are also known as this infection's causative agents. The emergence of drug-resistant, bacillary dysentery-causing pathogens is a global burden, especially for developing countries with poor hygienic environments. This study aimed to isolate, identify, and determine the drug-resistant pattern of bacillary dysentery-causing pathogens from the stool samples of the Kushtia region in Bangladesh. Hence, biochemical tests, serotyping, molecular identification, and antibiotic profiling were performed to characterize the pathogens. Among one hundred fifty (150) stool samples, 18 enteric bacterial pathogens were isolated and identified, where 12 were Shigella strains, 5 were S. enterica sub spp. enterica strains and one was the E.coli strain. Among 12 Shigella isolates, 8 were Shigella flexneri 2a serotypes, and 4 were Shigella sonnei Phage-II serotypes. Except for three Salmonella strains, all isolated strains were drug-resistant (83%), whereas 50% were multidrug-resistant (MDR), an alarming issue for public health. In antibiotic-wise analysis, the isolated pathogens showed the highest resistance against nalidixic acid (77.78%), followed by tetracycline (38.89%), kanamycin (38.89%), amoxicillin (27.78%), streptomycin (27.78%), cefepime (22.22%), ceftriaxone (22.22%), ampicillin (16.67%), ciprofloxacin (16.67%), and chloramphenicol (16.67%). The existence of MDR organisms that cause bacillary dysentery in the Kushtia area would warn the public to be more health conscious, and physicians would administer medications cautiously. The gradual growth of MDR pathogenic microorganisms needs immediate attention, and the discovery of effective medications must take precedence.

Supplementary information

The online version contains supplementary material available at 10.1007/s11756-022-01299-x.

Can Stray Cats Be Reservoirs of Antimicrobial Resistance?

The emergence and spread of antimicrobial resistance (AMR) is a global problem that requires a One Health approach. Despite several studies have reported the role of companion animals as reservoirs of AMR, limited information is available regarding the role of cats in the circulation of AMR. In this study, we evaluated the phenotypic and genotypic profile of 75 Escherichia coli isolated from rectal swabs and fecal samples of 75 stray cats (living in solitary or in a colony) sampled in Palermo (Sicily, Italy), to determine whether these animals may participate in the spread of AMR. Susceptibility to 8 antibiotics was tested using Minimum Inhibitory Concentration assays, while the presence of the common antibiotic resistance genes blaTEM, blaCTX-M, tet(A), and tet(B) was investigated by PCR. From the 75 E. coli isolates analyzed, 43% were resistant to at least one of the eight antibiotics tested, with 31% of the isolates resistant to ampicillin, 23% to cefotaxime, 21% to tetracycline, 20% to cefazolin, and 17% to amoxicillin/clavulanic acid. Most isolates harbored the blaTEM gene (29%), followed by blaCTX-M (23%), tet(A) (21%), and tet(B) (20%). Our results confirm the fecal carriage of antibiotic-resistant E. coli and clinically relevant resistance genes in stray cats. This study highlights the potential role of stray cats in the spread of AMR in urban environments, emphasising the need to better understand their role in AMR circulation when planning strategies to combat it.

Dissemination of antimicrobial-resistant isolates of Salmonella spp. in wild boars and its relationship with management practices

Antimicrobial resistance (AMR) is a global concern and controlling its spread is critical for the effectiveness of antibiotics. Members of the genus Salmonella are broadly distributed, and wild boar may play an important role in its circulation between peri-urban areas and the environment, due to its frequent interactions both with livestock or human garbage. As the population of these animals is rising due to management on certain hunting estates or the absence of natural predators, the aim of the present work is to identify the mechanisms of AMR present and/or expressed in Salmonella spp. from wild boar populations and to determine the possible role of management-related factors applied to different game estates located in central Spain. The detection of Salmonella spp. was carried out in 121 dead wild boar from 24 game estates, and antimicrobial resistance traits were determined by antibiotic susceptibility testing and screening for their genetic determinants. The effects of feeding supplementation, the proximity of livestock, the existence of a surrounding fence and the density of wild boar on the AMR of the isolates were evaluated. The predominant subspecies and serovar found were S. enterica subsp. enterica (n = 69) and S. choleraesuis (n = 33), respectively. The other subspecies found were S. enterica subsp. diarizonae, S. enterica subsp. salamae and S. enterica subsp. houtenae. AMR was common among isolates (75.2%) and 15.7% showed multi drug resistance (MDR). Resistance to sulphonamides was the most frequent (85.7%), as well as sul1 which was the AMR determinant most commonly found. Plasmids appeared in 38.8% of the isolates, with IncHI1 being the replicon detected with the highest prevalence. The AMR of the isolates increased when the animals were raised with feeding supplementation and enclosed by fences around the estates.

Prevalence, Antibiotic-Resistance, and Replicon-Typing of Salmonella Strains among Serovars Mainly Isolated from Food Chain in Marche Region, Italy

Nontyphoidal salmonellosis (NTS) is the second most commonly reported gastrointestinal infection in humans and an important cause of food-borne outbreaks in Europe. The use of antimicrobial agents for animals, plants, and food production contributes to the development of antibiotic-resistant Salmonella strains that are transmissible to humans through food. The aim of this study was to investigate the presence and the potential dissemination of multidrug-resistant (MDR) Salmonella strains isolated in the Marche Region (Central Italy) via the food chain. Strains were isolated from different sources: food, human, food animal/livestock, and the food-processing environment. Among them, we selected MDR strains to perform their further characterization in terms of resistance to tetracycline agent, carriage of tet genes, and plasmid profiles. Tetracycline resistance genes were detected by PCR and plasmid replicons by PCR-based replicon typing (PBRT). A total of 102 MDR Salmonella strains were selected among the most prevalent serovars: S. Infantis (n = 36/102), S. Derby (n = 20/102), S. Typhimurium (n = 18/102), and a monophasic variant of S. Typhimurium (MVST, n = 28/102). Resistance to sulfisoxazole (86%) and tetracycline (81%) were the most common, followed by ampicillin (76%). FIIS was the most predominant replicon (17%), followed by FII (11%) and FIB (11%) belonging to the IncF incompatibility group. Concerning the characterization of tet genes, tetB was the most frequently detected (27/89), followed by tetA (10/89), tetG (5/89), and tetM (1/89). This study showed the potential risk associated with the MDR Salmonella strains circulating along the food chain. Hence, epidemiological surveillance supported by molecular typing could be a very useful tool to prevent transmission of resistant Salmonella from food to humans, in line with the One Health approach.

Prevalence and Genomic Investigation of Multidrug-Resistant Salmonella Isolates from Companion Animals in Hangzhou, China

Salmonella is a group of bacteria that constitutes the leading cause of diarrheal diseases, posing a great disease burden worldwide. There are numerous pathways for zoonotic Salmonella transmission to humans; however, the role of companion animals in spreading these bacteria is largely underestimated in China. We aimed to investigate the prevalence of Salmonella in pet dogs and cats in Hangzhou, China, and characterize the antimicrobial resistance profile and genetic features of these pet-derived pathogens. In total, 137 fecal samples of pets were collected from an animal hospital in Hangzhou in 2018. The prevalence of Salmonella was 5.8% (8/137) in pets, with 9.3% (5/54) of cats and 3.6% (3/83) of dogs being Salmonella positive. By whole-genome sequencing (WGS), in silico serotyping, and multilocus sequence typing (MLST), 26 pet-derived Salmonella isolates were identified as Salmonella Dublin (ST10, n = 22) and Salmonella Typhimurium (ST19, n = 4). All of the isolates were identified as being multidrug-resistant (MDR), by conducting antimicrobial susceptibility testing under both aerobic and anaerobic conditions. The antibiotics of the most prevalent resistance were streptomycin (100%), cotrimoxazole (100%), tetracycline (96.20%), and ceftriaxone (92.30%). Versatile antimicrobial-resistant genes were identified, including floR (phenicol-resistant gene), blaCTX-M-15, and blaCTX-M-55 (extended-spectrum beta-lactamase genes). A total of 11 incompatible (Inc) plasmids were identified, with IncA/C2, IncFII(S), and IncX1 being the most predominant among Salmonella Dublin, and IncFIB(S), IncFII(S), IncI1, and IncQ1 being the most prevailing among Salmonella Typhimurium. Our study applied WGS to characterize pet-derived Salmonella in China, showing the presence of MDR Salmonella in pet dogs and cats with a high diversity of ARGs and plasmids. These data indicate a necessity for the regular surveillance of pet-derived pathogens to mitigate zoonotic diseases.

Evaluation of Antimicrobial Resistance in Salmonella Strains Isolated from Food, Animal and Human Samples between 2017 and 2021 in Southern Italy

Salmonella enterica is one of the most common causes of foodborne infection in the world, and the most common one in Italy. Italy collaborates with the other EU member states to survey the antimicrobial resistance of Salmonella on a large scale. This study on the situation in Apulia and Basilicata provides a more focused point of view on the territory, and anticipates the data reported in future Italian reports. Antimicrobial resistance was detected using the MIC detection method, with EUVSEC® plates, on the strains collected between 2017 and 2021. The results of serotyping showed that Salmonella Infantis is the serovar that has increased the most over time in veterinary samples, while Salmonella Tyhimurium and its monophasic variant are the most isolated in human samples. The results of the antimicrobial resistance study comply with European data, showing high resistance to quinolones, tetracyclines, ampicillin and trimethoprim, and low resistance to colistin and cephems. The significant exception was that all strains were resistant to sulphametoxazole. The presence of MDRs, which was 85% in veterinary and 77.4% in human strains, often included critically important antibiotics, which is a sign that more study and action is needed to manage the use of antibiotics.

Food Is Reservoir of MDR Salmonella: Prevalence of ESBLs Profiles and Resistance Genes in Strains Isolated from Food

Salmonella spp. are among the most frequent causes of foodborne diseases, and the increasing occurrence of MDR strains is an additional cause for concern. In the three-year period 2019-2021, we collected Salmonella spp. strains isolated from different food categories analysed in the context of Regulation (EC) No 2073/2005 in order to assess their antibiotic susceptibility profiles and ESBL production. To determine the susceptibility profiles and identify MDR strains, we used the Kirby-Bauer method to test 17 antibiotics. Double-disc and PCR testing then allowed us to assess the production of ESBLs and the presence of beta-lactamase resistance genes. Phenotypic tests showed that 36 out of 67 strains were MDR and 52.7% of these were ESBL producers. Finally, molecular investigations conducted on ESBL-producing strains revealed the presence of blaSHV, blaCTX-M and blaTEM genes. Our results confirmed the prevalence of S. Infantis, an MDR strain and ESBL producer, in chicken meat. This suggests that further research on the prevalence of antibiotic resistance genes (ARGs) in foodborne strains is needed, especially from a One Health perspective.

The Dynamics of the Antimicrobial Resistance Mobilome of Salmonella enterica and Related Enteric Bacteria

The foodborne pathogen Salmonella enterica is considered a global public health risk. Salmonella enterica isolates can develop resistance to several antimicrobial drugs due to the rapid spread of antimicrobial resistance (AMR) genes, thus increasing the impact on hospitalization and treatment costs, as well as the healthcare system. Mobile genetic elements (MGEs) play key roles in the dissemination of AMR genes in S. enterica isolates. Multiple phenotypic and molecular techniques have been utilized to better understand the biology and epidemiology of plasmids including DNA sequence analyses, whole genome sequencing (WGS), incompatibility typing, and conjugation studies of plasmids from S. enterica and related species. Focusing on the dynamics of AMR genes is critical for identification and verification of emerging multidrug resistance. The aim of this review is to highlight the updated knowledge of AMR genes in the mobilome of Salmonella and related enteric bacteria. The mobilome is a term defined as all MGEs, including plasmids, transposons, insertion sequences (ISs), gene cassettes, integrons, and resistance islands, that contribute to the potential spread of genes in an organism, including S. enterica isolates and related species, which are the focus of this review.

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.

Molecular Detection of Integrons, Colistin and β-lactamase Resistant Genes in Salmonella enterica Serovars Enteritidis and Typhimurium Isolated from Chickens and Rats Inhabiting Poultry Farms

The rapid growth of multidrug-resistant Salmonella is a global public health concern. The aim of this study was to detect integrons, colistin and β-lactamase resistance genes in Salmonella enteritidis and typhimurium. A total of 63 isolates of S. enteritidis (n = 18) and S. typhimurium (n = 45) from fecal samples of layers and rats at chicken farms were screened for antibiotic resistant genes. Conventional PCR was performed for the detection of integrons (classes 1, 2, and 3), colistin (mcr-1-5) and β-lactamase (bla_CTX-M, bla_CTX-M-1, bla_CTX-M-2, bla_CTX-M-9, bla_CTX-M-15, bla_TEM, bla_SHV, and bla_OXA) resistant genes. Of these isolates, 77% and 27% of S. typhimurium and S. enteritidis harboured the mcr-4 encoded gene for colistin, respectively. The prevalence of class 1 integrons for S. typhimurium and S. enteritidis was 100% for each serovar, while for class 2 integrons of S. typhimurium and S. enteritidis it was 49% and 33% respectively, while class 3 integron genes was not detected. Our study also detected high levels of β-lactamase encoding genes (bla gene), namely bla_CTX-M, bla_CTX-M-1, bla_CTX-M-9 and bla_TEM from both S. typhimurium and S. enteritidis. This, to our knowledge, is the first report of mcr-4 resistance gene detection in Salmonella serovars in South Africa. This study also highlights the importance of controlling rats at poultry farms in order to reduce the risk of transmission of antibiotic resistance to chickens and eventually to humans.

Preliminary Results on the Prevalence of Salmonella spp. in Marine Animals Stranded in Sicilian Coasts: Antibiotic Susceptibility Profile and ARGs Detection in the Isolated Strains

The presence of Salmonella spp. in marine animals is a consequence of contamination from terrestrial sources (human activities and animals). Bacteria present in marine environments, including Salmonella spp., can be antibiotic resistant or harbor resistance genes. In this study, Salmonella spp. detection was performed on 176 marine animals stranded in the Sicilian coasts (south Italy). Antibiotic susceptibility, by disk diffusion method and MIC determination, and antibiotic resistance genes, by molecular methods (PCR) of the Salmonella spp. strains, were evaluated. We isolated Salmonella spp. in three animals, though no pathological signs were detected. Our results showed a low prevalence of Salmonella spp. (1.7%) and a low incidence of phenotypic resistance in three Salmonella spp. strains isolated. Indeed, of the three strains, only Salmonella subsp. enterica serovar Typhimurium from S. coeruleoalba and M. mobular showed phenotypic resistance: the first to ampicillin, tetracycline, and sulphamethoxazole, while the latter only to sulphamethoxazole. However, all strains harbored resistance genes (blaTEM, blaOXA, tet(A), tet(D), tet(E), sulI, and sulII). Although the low prevalence of Salmonella spp. found in this study does not represent a relevant health issue, our data contribute to the collection of information on the spread of ARGs, elements involved in antibiotic resistance, now considered a zoonosis in a One Health approach.