Molecular characteristic of antimicrobial resistance of Salmonella Gallinarum isolates from chickens in Korea, 2014 to 2018

Insights into the global genomic features of Salmonella enterica serovar Gallinarum biovars Gallinarum and Pullorum

AIMS

Characterize global genomic features of 86 genomes of Salmonella Gallinarum (SG) and Pullorum (SP), which are important pathogens causing systemic infections in poultry.

METHODS AND RESULTS

All genomes harbored efflux pump encoding gene mdsA and gold tolerance genes golS and golT. Aminoglycoside (aac(6')-Ib, aadA5, aph(6)-Id, aph(3'')-Ib, ant(2'')-Ia), beta-lactam (blaTEM-1, blaTEM-135), efflux pump (mdsB), fosfomycin (fosA3), sulfonamide (sul1, sul2), tetracycline [tet(A)], trimethoprim (dfrA17), acid (asr), and disinfectant (qacEdelta1) resistance genes, gyrA, gyrB, and parC quinolone resistance point mutations, and mercury tolerance genes (mer) were found in different frequencies. Additionally, 310 virulence genes, pathogenicity islands (including SPI-1, 2, 3, 4, 5, 6, 9, 10, 12, 13, and 14), plasmids [IncFII(S), ColpVC, IncX1, IncN, IncX2, and IncC], and prophages (Fels-2, ST104, 500465-1, pro483, Gifsy-2, 103 203_sal5, Fels-1, RE-2010, vB_SenS-Ent2, and L-413C) were detected. MLST showed biovar-specific sequence types, and core genome MLST showed country-specific and global-related clusters.

CONCLUSION

SG and SP global strains carry many virulence factors and important antimicrobial resistance genes. The diverse plasmids and prophages suggest genetic variability. MLST and cgMLST differentiated biovars and showed profiles occurring locally or worldwide.

Salmonella enterica Serovar Gallinarum Biovars Pullorum and Gallinarum in Poultry: Review of Pathogenesis, Antibiotic Resistance, Diagnosis and Control in the Genomic Era

Salmonella enterica subsp. enterica serovar Gallinarum (SG) has two distinct biovars, Pullorum and Gallinarum. They are bacterial pathogens that exhibit host specificity for poultry and aquatic birds, causing severe systemic diseases known as fowl typhoid (FT) and Pullorum disease (PD), respectively. The virulence mechanisms of biovars Gallinarum and Pullorum are multifactorial, involving a variety of genes and pathways that contribute to their pathogenicity. In addition, these serovars have developed resistance to various antimicrobial agents, leading to the emergence of multidrug-resistant strains. Due to their economic and public health significance, rapid and accurate diagnosis is crucial for effective control and prevention of these diseases. Conventional methods, such as bacterial culture and serological tests, have been used for screening and diagnosis. However, molecular-based methods are becoming increasingly important due to their rapidity, high sensitivity, and specificity, opening new horizons for the development of innovative approaches to control FT and PD. The aim of this review is to highlight the current state of knowledge on biovars Gallinarum and Pullorum, emphasizing the importance of continued research into their pathogenesis, drug resistance and diagnosis to better understand and control these pathogens in poultry farms.

Prevalence and resistance to antibacterial agents in Salmonella enterica strains isolated from poultry products in Northern Kazakhstan

Background and Aim: Salmonella is one of the main causative agents of foodborne infections. The source of the pathogen, in most cases, is poultry products. The intensification of poultry farming and the constant and uncontrolled use of antimicrobials has led to an increase in the level of antibiotic resistance, especially in developing countries. This study aimed to determine the level of sensitivity to antimicrobial agents in Salmonella enterica strains isolated from poultry products in Northern Kazakhstan, as well as to determine the genetic mechanisms of resistance and the presence of integrons. Materials and Methods: In total, 398 samples of poultry products sold in Northern Kazakhstan were selected. Salmonella strains were isolated from product samples using microbiological methods. Salmonella was identified based on morphological, biochemical, and serological methods, as well as polymerase chain reaction (PCR). Sensitivity testing for antimicrobial agents was performed using the disk diffusion method. The detection of resistance genes was performed using PCR and gel electrophoresis. Results: Out of 398 samples of poultry products, a total of 46 Salmonella isolates were obtained. Most of the isolates belong to the serovar Salmonella Enteritidis (80.4%). The assessment of sensitivity to antibacterial agents showed that Salmonella was mainly resistant to nalidixic acid (63%), furadonin (60.9%), ofloxacin (45.6%), and tetracycline (39.1%). In 64.3% of cases, Salmonella was resistant to three or more groups of antibacterial agents. Resistance genes such as tetA, tetB, blaTEM, aadA, sul3, and catII, as well as integrons of two classes (teg1 and teg2), were identified. Conclusion: Poultry products contain antimicrobial-resistant strains of Salmonella, as well as genes encoding resistance mechanisms. The results emphasize the need for constant monitoring of not only pathogenic microorganisms but also their sensitivity to antimicrobial agents. The potential threat to human health requires a unified approach to the problem of antibiotic resistance from representatives of both public health and the agroindustrial complex. Keywords: antibiotic resistance, food safety, poultry, resistance genes, Salmonella.

Molecular Characterization and the Antimicrobial Resistance Profile of Salmonella spp. Isolated from Ready-to-Eat Foods in Ouagadougou, Burkina Faso

The emergence of antimicrobial-resistantfood-borne bacteria is a great challenge to public health. This study was conducted to characterize and determine the resistance profile of Salmonella strains isolated from foods including sesames, ready-to-eat (RTE) salads, mango juices, and lettuce in Burkina Faso. One hundred and forty-eight biochemically identified Salmonella isolates were characterized by molecular amplification of Salmonella marker invA and spiC, misL, orfL, and pipD virulence genes. After that, all confirmed strains were examined for susceptibility to sixteen antimicrobials, and PCR amplifications were used to identify the following resistance genes: bla_TEM, temA, temB, StrA, aadA, sul1, sul2, tet(A), and tet(B). One hundred and eight isolates were genetically confirmed as Salmonella spp. Virulence genes were observed in 57.4%, 55.6%, 49.1%, and 38% isolates for pipD, SpiC, misL, and orfL, respectively. Isolates have shown moderate resistance to gentamycin (26.8%), ampicillin (22.2%), cefoxitin (19.4%), and nalidixic acid (18.5%). All isolates were sensitive to six antibiotics, including cefotaxime, ceftazidime, aztreonam, imipenem, meropenem, and ciprofloxacin. Among the 66 isolates resistant to at least one antibiotic, 11 (16.7%) were multidrug resistant. The Multiple Antimicrobial Resistance (MAR) index of Salmonella serovars ranged from 0.06 to 0.53. PCR detected 7 resistance genes (tet(A), tet(B), bla_TEM, temB, sul1, sul2, and aadA) in drug-resistant isolates. These findings raise serious concerns because ready-to-eat food in Burkina Faso could serve as a reservoir for spreading antimicrobial resistance genes worldwide.

The targeted anti-Salmonella bacteriophage attenuated the inflammatory response of laying hens challenged with Salmonella Gallinarum

Fowl typhoid is a severe disease caused by Salmonella Gallinarum with considerable mortality and morbidity in laying hen farms. The current study has focused on controlling the infection in laying hens using anti-Salmonella spp. bacteriophage. The treatments included, PC, without challenge; NC, S. Gallinarum challenged (SGC); B5, 5 mg bacteriophage/kg + SGC; B10, 10 mg bacteriophage/kg + SGC. The Salmonella shedding, inflammatory responses, and gene expression of pro-inflammatory cytokines, toll-like receptor (TLR), and heat shock protein (HSP) in the jejunum, liver, and thigh muscle were tested in laying hens. Supplementation of bacteriophage reduced the abundance of S. Gallinarum in the excreta at d 3, 7, and 14. The abundance of S. Gallinarum was lower in the B10 than the B5 at d 7. Supplementation of bacteriophage decreased the abundance of S. Gallinarum in the oviduct, spleen, and cecum at d 14. The laying hens in the NC group showed an increased relative spleen weight compared with the PC and B10 treatments. Among the SGC treatments, the NC treatment showed higher gene expressions of IL-4 compared with the B5, higher gene expressions of interferon (IFNγ), TLR4, and tumor necrosis factor-α (TNF-α) compared with the B5 and B10, and higher gene expressions of HSP27 compared with the B10 in the jejunum. Dietary supplementation of B10 decreased the mRNA expressions of TLR4 and TNF-α compared with the B5 treatment in the jejunum. The NC treatment showed the highest gene expressions of HSP27, TLR4, and TNF-α in the liver. Dietary supplementation of B10 showed lower mRNA expressions of HSP27 compared with the B5 treatment in the liver. Moreover, the IFNγ and HSP27 were upregulated in the NC treatment compared with the B5 and B10 in the muscle. In conclusion, it can be suggested that bacteriophage is an effective supplement to control S. Gallinarum infection in laying hens and possibly lower horizontal contaminations in laying hen flocks.

Emergence, Dissemination and Antimicrobial Resistance of the Main Poultry-Associated Salmonella Serovars in Brazil

Salmonella infects poultry, and it is also a human foodborne pathogen. This bacterial genus is classified into several serovars/lineages, some of them showing high antimicrobial resistance (AMR). The ease of Salmonella transmission in farms, slaughterhouses, and eggs industries has made controlling it a real challenge in the poultry-production chains. This review describes the emergence, dissemination, and AMR of the main Salmonella serovars and lineages detected in Brazilian poultry. It is reported that few serovars emerged and have been more widely disseminated in breeders, broilers, and layers in the last 70 years. Salmonella Gallinarum was the first to spread on the farms, remaining as a concerning poultry pathogen. Salmonella Typhimurium and Enteritidis were also largely detected in poultry and foods (eggs, chicken, turkey), being associated with several human foodborne outbreaks. Salmonella Heidelberg and Minnesota have been more widely spread in recent years, resulting in frequent chicken/turkey meat contamination. A few more serovars (Infantis, Newport, Hadar, Senftenberg, Schwarzengrund, and Mbandaka, among others) were also detected, but less frequently and usually in specific poultry-production regions. AMR has been identified in most isolates, highlighting multi-drug resistance in specific poultry lineages from the serovars Typhimurium, Heidelberg, and Minnesota. Epidemiological studies are necessary to trace and control this pathogen in Brazilian commercial poultry production chains.

Isolation and Partial Characterization of Salmonella Gallinarum Bacteriophage

Infections caused by Salmonella remain a major public health problem worldwide. Animal food products, including poultry meat and eggs, are considered essential components in the individual’s daily nutrition. However, chicken continues to be the main reservoir for Salmonella spp.

Poultry farmers use several types of antibiotics to treat pathogens. This can pose a health risk as pathogens can build antibiotic resistance in addition to the possibility of accumulation of these antibiotics in food products. The use of phages in treating poultry pathogens is increasing worldwide due to its potential use as an effective alternative to antibiotics. Phages have several advantages over antibiotics; phages are very specific to target bacteria, less chances of developing secondary infections, and they only replicate at the site of infection.

Here we report the isolation of a bacteriophage from chicken feces. The isolated bacteriophage hosts on Salmonella Gallinarum, a common zoonotic infection that causes fowl typhoid, known to cause major losses to poultry sector. The isolated bacteriophage was partially characterized as a DNA virus resistant to RNase digestion with approximately 20 Kb genome. SDS-PAGE analysis of total viral proteins showed at least five major bands (21, 28, 42, 55 and 68 kDa), indicating that this virus is relatively small compared to other known poultry phages. The isolated bacteriophage has the potential to be an alternative to antibiotics and possibly reducing antibiotic resistance in poultry farms.

Antimicrobial Resistance and PFGE Molecular Typing of Salmonella enterica serovar Gallinarum Isolates from Chickens in South Korea from 2013 to 2018

Simple Summary

Salmonella enterica serovar Gallinarum (S. enterica ser. Gallinarum) is a host-specific agent of fowl typhoid (FT). This is one of the most important bacterial infections in the poultry industry in both developing and developed countries, including South Korea. The use of antimicrobial drugs is the first choice for disease control. Antimicrobials, such as β-lactams, aminoglycosides, and fluoroquinolones, are frequently used to treat FT. However, the continuous use of antimicrobial drugs has led to the emergence and persistence of antimicrobial-resistant S. enterica ser. Gallinarum. In this study, we analyzed the antimicrobial susceptibility and epidemiological relationship of thirty isolates of S. enterica ser. Gallinarum isolated from poultry farms with an FT outbreak from 2013 to 2018 in South Korea. All the isolates showed a multi-drug resistant (MDR) phenotype. This study confirmed horizontal transmission and cross-contamination between farms within the same integrated poultry company or between farms belonging to different companies. The characterization of these isolates would be helpful to develop prevention and control strategies for the MDR S. enterica ser. Gallinarum infection in South Korea.

Abstract

Antimicrobial resistance and pulsed-field gel electrophoresis (PFGE) genotypes of collected S. enterica ser. Gallinarum isolates were investigated to examine the epidemiological relationship between field outbreak isolates of S. enterica ser. Gallinarum. Thirty S. enterica ser. Gallinarum isolates collected from poultry farms with FT outbreaks from 2013 to 2018 in South Korea were analyzed. All isolates were resistant to at least 3 of the 18 antimicrobials tested and exhibited an MDR phenotype. All isolates showed resistance to streptomycin, sulfisoxazole, and colistin. One isolate was resistant to 9 antimicrobials. The antimicrobial resistance profile, streptomycin-sulfisoxazole-colistin-nalidixic acid-ciprofloxacin-gentamicin (18/30, 60.0%), was the most prevalent. PFGE types were classified into 10 groups with a 100% correlation cutoff in dendrograms for 30 field isolates. The dominant PFGE types were 1 (8/30, 26.7%), 4 (7/30, 23.3%), and 9 (5/30, 16.7%). Interestingly some isolates collected from the same and different companies had the same PFGE type. We reported a high MDR rate in S. enterica ser. Gallinarum isolates. The present study highlights the occurrence of horizontal spread and cyclic contamination of MDR S. enterica ser. Gallinarum within the same company. Furthermore, we showed cross-contamination between different companies. The characterization of these isolates would be helpful in the development of prevention and control strategies for MDR S. enterica ser. Gallinarum infection in South Korea.

Prevalence and Multidrug Resistance of Salmonella in Swine Production Chain in a Central Province, Thailand

ABSTRACT

Salmonella causes foodborne disease outbreaks worldwide and raises concerns about public health and economic losses. To determine prevalence, serovar, antimicrobial resistance patterns, and the presence of extended-spectrum β-lactamase (ESBL) genes in a cross-sectional study, 418 total samples from feces and carcasses (from three slaughterhouses) and pork and cutting boards (from four markets) were collected in a central Thailand province in 2017 and 2018. Of the 418 samples, 272 (65.1%) were positive for Salmonella. The prevalence of Salmonella-positive samples from markets (158 of 178; 88.8%) was significantly higher than that among samples from slaughterhouses (114 of 240; 47.5%) (P < 0.05). A total of 1,030 isolates were identified; 409 were assigned to 45 serovars, with Salmonella Rissen the most common (82 of 409; 20%). Two serovars, Salmonella Cannstatt and Salmonella Braubach, were identified for the first time in Thailand in market and slaughterhouse samples, respectively. Among 180 isolates representing 19 serovars, 133 (73.9%) exhibited multidrug resistance. Screening for ESBL production revealed that 41 (10.3%) of 399 isolates were ESBL positive. The prevalence of ESBL-producing Salmonella isolates was significantly higher among the market isolates (31 of 41; 75.6%) than among the slaughterhouse isolates in (10 of 41; 24.4%) (P < 0.05). In market samples, 24 (77.4%) of 31 isolates were recovered from pork and 7 (22.6%) were recovered from cutting boards. Nine ESBL-producing isolates carried single ESBL genes, either blaTEM (4 of 41 isolates; 9.8%) or blaCTX-M (5 of 41 isolates; 12.2%), whereas 11 (26.8%) carried both blaTEM and blaCTX-M. No ESBL-producing Salmonella isolate carried the blaSHV gene. These results suggest that pigs, their flesh, and cutting boards used for processing pork could be reservoirs for widespread ESBL-producing Salmonella isolates with multidrug resistance and outbreak potential across the food chain.

HIGHLIGHTS

Global colistin use: A review of the emergence of resistant Enterobacterales and the impact on their genetic basis

The dramatic global rise of MDR and XDR Enterobacterales in human medicine forced clinicians to the reintroduction of colistin as last-resort drug. Meanwhile, colistin is used in the veterinary medicine since its discovery, leading to a steadily increasing prevalence of resistant isolates in the livestock and meat-based food sector. Consequently, transmission of resistant isolates from animals to humans, acquisition via food and exposure to colistin in the clinic are reasons for the increased prevalence of colistin-resistant Enterobacterales in humans in the last decades. Initially, resistance mechanisms were caused by mutations in chromosomal genes. However, since the discovery in 2015, the focus has shifted exclusively to mobile colistin resistances (mcr). This review will advance the understanding of chromosomal-mediated resistance mechanisms in Enterobacterales. We provide an overview about genes involved in colistin resistance and the current global situation of colistin-resistant Enterobacterales. A comparison of the global colistin use in veterinary and human medicine highlights the effort to reduce colistin sales in veterinary medicine under the One Health approach. In contrast, it uncovers the alarming rise in colistin consumption in human medicine due to the emergence of MDR Enterobacterales, which might be an important driver for the increasing emergence of chromosome-mediated colistin resistance.

Occurrence and antimicrobial resistance of Salmonella isolated from retail meats in Anhui, China

Salmonella is considered one of the major foodborne pathogens associated with severe infections. Little attempt has been focused on the distribution of Salmonella in retail meats and the analysis of its phenotypic characteristics in Anhui Province. The aim of this study was to characterize the prevalence of Salmonella serovars, antimicrobial susceptibility, antimicrobial resistance genes, and virulence genes in Salmonella recovered from retail meats in Anhui, China. Out of the 120 samples collected from supermarket chains and open-air markets, 16 samples (13.3%) were positive for Salmonella, of which Salmonella enterica serovars Enteritidis and Typhimurium were the common serotypes. Significant differences in incidence were found between supermarket chains and open-air markets (p < 0.05). Overall, all 16 isolates were resistant to at least two tested antimicrobials, while 12 isolates showed multiple antimicrobial resistant phenotypes. High resistance was observed for ampicillin (87.5%), doxycycline (75.0%), and tetracycline (62.5%). The sul2 was detected in all isolates, and the aac(6')-Ib-cr (93.8%) and the tetA (81.3%) were predominant in 10 resistance genes conferring five classes of antimicrobials. In addition, the correlation between resistance phenotypes and genes of tetracyclines and aminoglycosides was more than 80%. Interestingly, all the Salmonella isolates contained the genes mogA, mgtC, sopB, and spvB, whereas the siiE was variably represented. The findings in this study showed high prevalence, antimicrobial resistance, and the existence of virulence genes, suggesting that effective measures are required to ensure microbial safety from retail meats.

Salmonella Gallinarum in Small-Scale Commercial Layer Flocks: Occurrence, Molecular Diversity and Antibiogram

Salmonella Gallinarum is one of the most important bacterial pathogens associated with diminished egg production in poultry. The aim of this study was to understand the occurrence, molecular traits and antimicrobial resistance patterns of Salmonella Gallinarum strains isolated from small-scale commercial layer flocks with low level biosecurity standards in Bangladesh. A total of 765 samples, including cloacal swabs (535), visceral organs (50), and droppings (180), were collected from chickens of 12 layer flocks in 11 districts. Salmonella Gallinarum was isolated and characterized through culture-based method, followed by biochemical tests, sero-grouping, PCR assays, sequencing, and antibiogram. The identity of biochemically detected isolates of Salmonella Gallinarum was confirmed via genus-specific 16S rRNA gene based PCR, followed by invA and spvC genes based PCR assays. Occurrence of Salmonella Gallinarum was detected in overall 25.75% (197/765) samples, with a significantly (p < 0.05) higher incidence in visceral organs (42%) in comparison to cloacal swab (24%) and droppings (26%). Sequencing and subsequent phylogenetic analysis of invA and spvC genes in representative strains of Salmonella Gallinarum revealed a close genetic lineage, with a sequence similarity of 98.05–99.21% and 97.51–99.45%, respectively, to previously published sequences of the corresponding genes from the same serogroup strains. Remarkably, 66.5% (131/197) of the isolated strains of Salmonella Gallinarum were found to be resistant to 3 to 6 antimicrobial agents, and interpreted as multidrug resistant (MDR). The findings of this study underscore an inherent need of appropriate control measures to curb the widespread incidence of MDR Salmonella Gallinarum in small-scale commercial layer flocks, thereby, facilitating enhanced egg production and further support to the food security and safety in low resource settings.

Virulence Variation of Salmonella Gallinarum Isolates through SpvB by CRISPR Sequence Subtyping, 2014 to 2018

Simple Summary

Salmonella Gallinarum causes fowl typhoid in all ages of chickens, which results in economic loss of commercial chicken farms. The disease has been eradicated in many developed countries, but is still prevalent in Korea. In this study, we investigated virulence and genetic variation of S. Gallinarum from Korea, between 2014 and 2018. The results indicated that virulence was increased, which was associated with genetic change over time. Therefore, surveillance of genetic change associated with virulence increase is necessary for monitoring of S. Gallinarum isolates for dissemination.

Abstract

Salmonella Gallinarum is a Gram-negative bacteria that causes fowl typhoid, a septicemic disease with high morbidity and mortality that affects all ages of chickens. Although vaccines and antimicrobials have been used nationwide to eradicate the disease, the malady is still prevalent in Korea. In this study, we investigated the virulence and genetic variation of 116 S. Gallinarum isolates from laying hens between 2014 and 2018. A total of 116 isolates were divided into five Gallinarum Sequence Types (GST) through clustered regularly interspaced short palindromic repeats (CRISPR) subtyping method. The GSTs displayed changes over time. The 116 isolates showed no difference in virulence gene distribution, but the polyproline linker (PPL) length of the SpvB, one of the virulence factors of Salmonella spp., served as an indicator of S. Gallinarum pathogenicity. The most prevalent PPL length was 22 prolines (37.9%). The shortest PPL length (19 prolines) was found only in isolates from 2014 and 2015. However, the longest PPL length of 24 prolines appeared in 2018. This study indicates that PPLs of S. Gallinarum in Korea tend to lengthen over time, so the pathogenic potency of the bacteria is increasing. Moreover, the transition of GST was associated with PPL length extension over time. These results indicate that surveillance of changing GST and PPL length are necessary in the monitoring of S. Gallinarum isolates.

Nationwide surveillance on serotype distribution and antimicrobial resistance profiles of non-typhoidal Salmonella serovars isolated from food-producing animals in South Korea

Food-producing animals are considered a leading source of human Salmonella infections in Korea. However, there is a lack of comprehensive and up-to-date data regarding the diversity and resistance profiles of Salmonella serotypes in these animals. Therefore, this study aimed to determine the distribution and antimicrobial resistance profiles of Salmonella serotypes isolated from cattle, pigs, and chickens in Korea between 2010 and 2018. A total of 3018 Salmonella isolates were obtained from 16 laboratories/centers participating in the Korean Veterinary Antimicrobial Resistance Monitoring System. Salmonella serotypes were identified from the following isolates: 179 cattle (17 serotypes), 959 pig (45 serotypes), and 1880 chicken (64 serotypes). The most frequent serotypes in cattle (Typhimurium, Salmonella 4,[5],12:i:-, and Schwarzengrund), pigs (Typhimurium, Rissen, and S. 4,[5],12:i:-), and chickens (Enteritidis, Albany, Virchow, and Montevideo) accounted for more than 50% of the total serotypes in the respective animal species. To the best of our knowledge, Salmonella 4,[5],12:i:- has not been identified in cattle in Korea to date. More than 80% of the isolates demonstrated resistance to at least one antimicrobial agent. Multidrug-resistance was found in almost half of the serotypes; the highest proportion in cattle (59.2%), followed by pigs (53.4%), and chickens (45.7%). Significant proportions of the serotypes were resistant to ampicillin, streptomycin, and tetracycline. Ceftiofur and ciprofloxacin resistance rates were the highest in Salmonella isolated from chickens (17.1% and 4.1%, respectively) and cattle (10.1% and 3.9%, respectively) compared to that in pigs. Among the frequent serotypes, Albany demonstrated the highest resistance rate (>90%) to five different antimicrobials. Alarmingly, some Salmonella serotypes that are frequently associated with human infections demonstrated a trend of increasing resistance to critically important antibiotics, including 3rd generation cephalosporins and quinolones. Collectively, the presence of antibiotic-resistant Salmonella in food-producing animals poses a potential risk to public health.

Effect of two lytic bacteriophages against multidrug-resistant and biofilm-forming Salmonella Gallinarum from poultry

1. Salmonella Gallinarum (SG) infections cause fowl typhoid, which leads to important economic losses. Multidrug resistance (MDR) and the capacity for bacteria to form biofilms could play an important role in the persistence of SG in poultry flocks resulting in intermittent disease outbreaks. The aim of the following study was to assess the lytic activity of two new bacteriophages (Salmonella phages UPF_BP1 and UPF_BP2) against MDR and biofilm-forming SG. 2. Forty-six strains of SG, isolated in 2015, were characterised by antimicrobial resistance, biofilm formation profiles and susceptibility to two new bacteriophages. 3. Of these strains, 24% were multidrug resistant and more than 80% formed biofilm, with no statistical difference between incubation temperatures (42°C or 22°C). With regard to the lytic activity of the phages, 85% of strains were susceptible to at least one phage. Of these, 74% were lysed by both phages, including MDR and biofilm producing strains. 4. The use of salmonella phages UPF_BP1 and UPF_BP2 were shown to be promising alternatives for the biological control of fowl typhoid.

Emergence of Transferable mcr-9 Gene-Carrying Colistin-Resistant Salmonella enterica Dessau ST14 Isolated from Retail Chicken Meat in Korea

Colistin is an important antibiotic currently used to manage infections caused by multidrug-resistant pathogens in both humans and livestock animals. A new mobile colistin-resistance (mcr-9) gene was recently discovered; this discovery highlighted the need for rigorous monitoring of bacterial resistance against colistin. Salmonella is one of the major pathogens responsible for foodborne illnesses; however, there is minimal information regarding the presence of mcr genes in foodborne Salmonella strains. The aim of this study was to investigate the presence of mcr genes among 178 Salmonella strains isolated from chicken meat in Korea. Antimicrobial susceptibility was measured using the broth microdilution method. Bioinformatics characterization of colistin-resistant strains and genetic environment of the mcr-9 gene were analyzed using next-generation sequencing. Transferability of the mcr-9 carrying colistin-resistant Salmonella strain was tested using broth-mating conjugation. Thirteen of the 178 Salmonella isolates showed colistin resistance, but only one strain, Salmonella Dessau ST14 (KUFSE-SAL043) from a traditional chicken market in Korea, carried an mcr family gene, mcr-9. This strain also carried other acquired antimicrobial resistance genes such as bla_TEM-1B, qnrS1, and aac(6')-Iaa. Only the IncX1 plasmid replicon type was detected in this strain. In the strain KUFSE-SAL043, the mcr-9 gene was located between two insertion sequences, IS903B and IS26, followed by the downstream regulatory genes qseB-like and qseC-like, which were located between IS1R and ΔIS1R. Conjugation tests revealed that the mcr-9 gene was successfully transferred to Escherichia coli J53 at a mean frequency of 2.03 × 10^-7. This is the first report of a transferable mcr-9 gene in Salmonella isolated from chicken meat in Korea, highlighting the possibility of transfer of colistin resistance. Therefore, the wide use of colistin should be reconsidered, and a One Health perspective should be adopted to monitor the antimicrobial resistance of Enterobacteriaceae strains in humans, livestock, and the environment.

Genetic Characterization of Fluoroquinolone Resistance in Salmonella enterica Serovar Gallinarum Isolates from Chicken in Korea

Salmonella enterica serovar Gallinarum is a nonmotile host-adapted Salmonella that causes fowl typhoid (FT), and an outbreak of FT is characterized by anorexia, greenish-yellow diarrhea, paleness, and sudden death with high mortality in poultry. To control and treat FT in commercial chickens, fluoroquinolones are widely used in Korea. This study aimed to investigate the genetic characteristics of fluoroquinolone-resistant Salmonella Gallinarum isolates from 2014-18 from chicken in Korea. A total of 35 ciprofloxacin (CIP)-resistant Salmonella Gallinarum was tested, and 22 (62.9%) isolates were observed to have multidrug resistance. All isolates had a mutation at the Ser83 or Asp87 codon in the gyrA gene, whereas three isolates had only double mutations at Ser83 → Phe and Asp87 → Asn or Ser83 → Phe and Asp87 → Gly. Minimum inhibitory concentrations of isolates with double mutations were relatively higher (≥8 mg/L for CIP and ≥16 mg/L for enrofloxacin) than those of other isolates with a single mutation in gyrA. Among 35 CIP-resistant Salmonella Gallinarum, plasmid-mediated quinolone resistance genes were detected in six (17.1%) isolates, and qnrB and qnrS were detected in four and two isolates, respectively. In the distribution of antimicrobial resistance genes in 35 CIP-resistant Salmonella Gallinarum, ant(2″)-I (54.3%) was the most prevalent gene, followed by TEM-1 (14.3%), sul1 (11.4%), and cmlA (5.7%). Fifteen (42.9%) of the 35 CIP-resistant Salmonella Gallinarum also carried class 1 integrons, which showed five types of resistance gene cassettes: aadA2 (7 isolates), aadA2 + dfrA12 (5 isolates), and aadA1 + aad A2 (3 isolates). Among plasmid replicons, 23 isolates (65.7%) carried five different plasmid replicons: Frep (9 isolates), FIB (7 isolates), FIIA (6 isolates), B/O (4 isolates), and I1 (3 isolates). These results suggest that continued monitoring of fluoroquinolone resistance is necessary to preserve the effectiveness of fluoroquinolones in poultry and to surveil the transmission to humans through the food chain.