Towards more virulent and antibiotic-resistantSalmonella?

Emerging Resistance and Virulence Patterns in Salmonella enterica: Insights into Silver Nanoparticles as an Antimicrobial Strategy

BACKGROUND/OBJECTIVES

This study aims to characterize antibiotic resistance (AR) and virulence markers in Salmonella spp. isolated from Romanian outpatients' stool samples.

METHODS

In 2019, community-acquired Salmonella strains were collected and identified using MALDI-TOF mass spectrometry, antibiotic susceptibility profiles have been determined with the MicroScan system, and soluble virulence factors were evaluated using specific culture media, while biofilm formation was quantified in 96-well plates. Molecular analysis targeted resistance genes for β-lactams (e.g., blaTEM and blaSHV); tetracyclines (e.g., tet(A)); sulphonamides; and quinolones, as well as virulence genes (e.g., invA, spvC, pldA, and held). Whole-genome sequencing (WGS) was performed on 19 selected isolates. A silver nanoparticles (AgNPsol) alternative to conventional antibiotics was tested for effectiveness against multidrug-resistant (MDR) isolates.

RESULTS

From the total of 309 Salmonella isolates (65.05% from children under 4 years of age) belonging to four subtypes and four serovars, 27.86% showed resistance to at least one antibiotic, most frequently to tetracycline, ampicillin, and piperacillin. The strains frequently expressed haemolysin (67%), aesculinase (65%), and gelatinase (62%). Resistance to trimethoprim-sulfamethoxazole was encoded by the sul1 gene in 44.83% of the strains and to tetracyclines by the tet(A) gene (59.52%). The ESBL genes blaTEM, blaSHV, and blaCTX-M were detected by PCR in 16.18%, 2.91%, and 0.65% of the strains, respectively. Additionally, 98.63% of the strains carried the invA marker, with notable positive associations between blaSHV, qnrB, and sul1 with spvC.

CONCLUSIONS

The present findings revealed significant patterns in Salmonella isolates, subtypes, serovars, AR, and virulence, emphasising the need for continuous surveillance of Salmonella infections. Additionally, the potential of AgNPs as an alternative treatment option was demonstrated, particularly for paediatric S. enterica infections.

Genomic Profiling of Antimicrobial Resistance Genes in Clinical Salmonella Isolates from Cattle in the Texas Panhandle, USA

Rising antimicrobial resistance (AMR) in Salmonella serotypes host-adapted to cattle is of increasing concern to the beef and dairy industry. The bulk of the existing literature focuses on AMR post-slaughter. In comparison, the understanding of AMR in Salmonella among pre-harvest cattle is still limited, particularly in Texas, which ranks top five in beef and dairy exports in the United States; inherently, the health of Texas cattle has nationwide implications for the health of the United States beef and dairy industry. In this study, long-read whole genome sequencing and bioinformatic methods were utilized to analyze antimicrobial resistance genes (ARGs) in 98 isolates from beef and dairy cattle in the Texas Panhandle. Fisher exact tests and elastic net models accounting for population structure were used to infer associations between genomic ARG profiles and antimicrobial phenotypic profiles and metadata. Gene mapping was also performed to assess the role of mobile genetic elements in harboring ARGs. Antimicrobial resistance genes were found to be statistically different between the type of cattle operation and Salmonella serotypes. Beef operations were statistically significantly associated with more ARGs compared to dairy operations. Salmonella Heidelberg, followed by Salmonella Dublin isolates, were associated with the most ARGs. Additionally, specific classes of ARGs were only present within mobile genetic elements.

Antibiotic resistance and virulence genes profile of Non typhodial Salmonella species isolated from poultry enteritis in India

Salmonella species (spp) is the most important gastrointestinal pathogen present ubiquitously. Non typhoidal Salmonella (NTS) is commonly associated with gastroenteritis in humans. Layer birds once get infection with NTS, can become persistently infected with Salmonella Typhimurium and intermittently shed the bacteria. It results in a high risk of potential exposure of eggs to the bacteria. The current study was conducted to determine the serotype diversity, presence of virulence genes, antibiotic resistance pattern, and genes of NTS from poultry enteritis. Out of 151 intestinal swabs from poultry total 118 NTS were isolated, which were characterized serologically as S. Typhimurium (51 strains), S. Weltevreden (57 strains) and untypable (10 strains). Most effective antibiotics were amikacin, gentamycin and ceftriaxone (33.05%) followed by ampicillin, azithromycin and ciprofloxacin (16.69%), co-trimoxazole (13.55%), and tetracycline (6.78%). Multidrug resistance recorded in 17.70% (N = 21/118) strains. Antimicrobial-resistant genes i.e. blaTEM, blaSHV, blaCTX-M, tet(A), tet(B), tet(C), sul1, sul2, sul3. blaTEM and tet(A) were present in 95% (20/21). Eleven virulence genes i.e. invA, hilA, sivH, tolC, agfA, lpfA, spaN, pagC, spiA, iroN and fliC 2 were present in all the 30 isolates. While, sopE was present in only 2 isolates, NTS strains with characteristics of pathogenicity and multidrug resistance from poultry enteritis were detected. Multidrug resistance showed the necessity of prudent use of antibiotics in the poultry industry.

Comparative assessment of medicinal plant extract efficacy against plaque and gingivitis: A case-control study

Background

In the last quarter of the 20th century, dedicated efforts have been made to use phytochemicals in the prevention of periodontal diseases, but the darker side of the coin is that we have hardly encountered studies with a scientific basis to prove the specific role of phytochemicals against dental plaque.

Objective

This study aimed to assess the antiplaque activity of Curcuma longa, Spilanthes acmella, and Quercus infectoria and to determine the antigingivitis activity of the extract, which shows high antiplaque potential.

Materials and Methods

Sixteen volunteers were selected as subjects in this biphasic study. In the first phase, 10 volunteers were subjected to topical application of aqueous ethanolic extract (1%) of C. longa, Q. infectoria, and S. acmella on the labial/buccal and lingual/palatal surfaces of 28 teeth. In the second phase, the extract showing the highest efficacy was selected to assess its antigingivitis activity on all the surfaces of six mandibular anterior teeth of six gingivitis patients. The percentage plaque reduction was calculated by dividing the difference of the base and end scores by the baseline scores.

Results

C. longa demonstrated superior results as it showed the maximum reduction in plaque formation. Antigingivitis activity of long-term topical application of 1% C. longa was depicted in independent clusters in different volunteers selected for the study. Only after 2 weeks, the treatment score was found to be statistically significant to depict optimal results.

Conclusion

C. longa can be considered the best at reducing plaque. The antigingivitis activity of C. longa ranked reasonably satisfactory and comparable to the existing data for commercially available drugs.

Extensively drug-, ciprofloxacin-, cefotaxime-, and azithromycin-resistant Salmonella enterica serovars isolated from camel meat in Egypt

Given the great importance of Salmonella as a leading foodborne pathogen of global concern and the few available data regarding its prevalence in camel meat, the present study aimed to determine the prevalence, antimicrobial resistance (AMR) profile, virulence genes, β-lactamase genes of Salmonella enterica serovars isolated from camel meat marketed in Egypt. Forty-five (29.6 %) of the 152 camel meat samples examined were positive for Salmonella spp. Among the 432 Salmonella presumptive colonies isolated, 128 were molecularly verified as Salmonella after confirmation by PCR targeting the Salmonella marker (invA) gene. Virulence genes, encompassing stn, spvC, and hilA genes, were detected in 91.4 % (117/128), 20.3 % (26/128), and 80.5 % (103/128) of the isolates, respectively. S. Enteritidis, S. Typhimurium, S. Cerro, and S. Montevideo were the most prevalent serovars with incidences of 25 % (32/128), 15.6 % (20/128), 15.6 % (20/128), and 12.5 % (16/128), respectively. Interestingly, 56.3 %, 53.1 %, 37.5 %, 28.1 %, 21.9 %, 18.8 %, 12.5 %, and 3.1 % of the isolates tested showed resistance to cefepime, ciprofloxacin, levofloxacin, cefotaxime, gentamicin, colistin, meropenem, and azithromycin, respectively. Salmonella isolates showed resistance to at least one antibiotic, with a mean multiple antibiotic resistance (MAR) index of 0.472. Interestingly, 59.4 %, 15.6 %, and 3.1 % of the isolates were categorized into multidrug-resistant, extensively drug-resistant, and pan-drug-resistant, respectively. Only 23 (25 %) of the 92 ampicillin-resistant isolates were proven to be Extended Spectrum Beta-Lactamase (ESBL)-producing Salmonella, in which β-lactamase (bla) genes were detected. The blaOXA-2 was the most existing gene where it was detected lonely in 10 of the ampicillin-resistant isolates and coexisted with blaCMY-1 in 4 isolates and with blaCMY-2 in a single isolate. The blaCMY-1, however, existed in 11 isolates, whereas the blaCMY-2 gene was only detected in 3 isolates tested. The present findings affirm that camel meat could be a leading reservoir for multi- and extensively-drug-resistance β-lactamase-producing Salmonella, representing a global public health challenge. Therefore, further research is necessary to detect the prevalence and AMR of Salmonella serovars from camel meat in Egypt and other countries to put camel meat as a source of Salmonella in foods of animal origin.

Fowl Typhoid Outbreak on a Commercial Turkey Farm in Croatia

Fowl typhoid is a septicemic disease caused by Salmonella enterica subsp. enterica serovar Gallinarum biovar Gallinarum. It is a host-specific disease primarily affecting chickens and turkeys, although it has been reported in various animal species and sporadically in humans. Here, we present a case of a fowl typhoid outbreak on a turkey poult farm where the source of infection was the hatchery. The birds started showing symptoms of growth retardation at 21 days of age, after which the mortality rates gradually started to increase. Post mortem examination revealed that the main lesions were granulomatous proliferations in the small intestines. The results of the histopathological examination indicate that the severity of the infection was alleviated by the application of phytogenic mixtures and probiotics as a supportive treatment, even though the affected flock was eventually culled at 60 days of age. The farmer was advised to apply more strict biosecurity measures to prevent the spread of the disease on the farm and try to eradicate the pathogen from the barn. Since the outbreak, there have been no recurrent infections.

Drug Resistance, Characterization and Phylogenetic Discrepancy of Salmonella enterica Isolates from Distinct Sources

Salmonella enterica is one of the foodborne pathogens that can infect humans, spreading from one person to another by contaminated food and water. To identify the pathogenic S. enterica from the contaminated food product, culture-based and molecular identifications, drug resistance profiling, virulence and genetic traits of the strains have been used. Herein, different animal products was subjected to screen for S. enterica prevalence, pathogenic characterization and compared with clinical Salmonella isolates (human). A total of 173 isolates from animal products and 51 isolates from clinical samples were collected. S. Typhi, S. Agona and S. Ohio were predominant serovars in blood, stool and different animal products. Both, clinical [37% (n = 19/51)] and animal product-associated isolates [21% (n = 37/173)] expressed their highest resistance to nalidixic acid. Thirty-one percentage of (n = 16/51) clinical isolates and 12% (n = 21/173) animal food-associated isolates were resistant to multiple classes of antibiotics. Class 1 integrons encoded by S. Typhi, S. Infantis and S. Emek were screened for sequence analysis, the result revealed that the cassettes encoded-aminoglycoside acetyltransferase and dihydrofolate reductase enzymes. Salmonella pathogenicity island-1 encoded-hilA gene was detected most frequently in all the isolates. PFGE profile revealed the genetic traits of the isolates which were closely linked with antibiotic-resistant properties and virulent characteristics. Only S. Enteritidis, collected from different samples had clonal similarities. In summary, drug-resistant pathogenic Salmonella prevalence was observed in the animal product that could be an important alarm to consumers with the risk of enteric fever and it causes the potential risk to public health.

Assessment of multidrug-resistant profile, multi-locus sequence typing and efflux pump activity in Salmonella Typhimurium isolated from hospital sewage

Salmonella enterica serovar Typhimurium is becoming a leading cause of gastroenteritis and mortality. The use of antibiotics has increased natural resistance of S. Typhimurium to antibiotics. This study aims to isolate and characterize multi-drug-resistant (MDR) Salmonella strains from hospital sewage samples in Bhopal City, central India. The MDR isolates were characterized by molecular identification, antimicrobial resistance patterns, multi-locus sequence typing, and efflux pump activity. Specific genes (hilA, stn, invA, typh, and iroB) were used to confirm S. Typhimurium isolates. The Kirbey-Bauer method was employed to profile antimicrobial resistance using 20 antibiotics. Multi-locus sequence typing confirmed S. Typhimurium using seven housekeeping genes (aroC, dnaN, hemD, hisD, purE, sucA, and thr). Out of five strains, only four were confirmed as S. Typhimurium during MLST analysis. Efflux pump activity was determined using the ethidium bromide (EtBr) cartwheel test. Of the 160 isolates, 38 were presumptively confirmed as S. Typhimurium based on biochemical characterization, and only five MDR Salmonella strains were selected for their resistance against most antibiotics. Efflux pump activity revealed that five out of the four MDR isolates did not retain EtBr inside the cells, indicating pronounced efflux activity. Additionally, the isolated strains showed a specific correlation between the antimicrobial phenotypes and genotypes. The results of this study provide a better understanding of the characterization of S. Typhimurium serotype in Bhopal City. Future studies should focus on understanding changing antimicrobial resistance patterns, pathogenicity, and the genetic background of Salmonella serotypes. Further surveillance activities for antimicrobial-resistant Salmonella in different environmental sources should be prioritized.

Prevalence of Multidrug-Resistant Salmonella enterica Serovars in Buffalo Meat in Egypt

The current study aimed to investigate the presence of Salmonella spp. prevalence in buffalo meat in Egypt, along with studying the antimicrobial susceptibility of the recovered isolates. Salmonella spp. was detected in 25% of tested buffalo meat. A total of 53 (100%) isolates were genetically verified by PCR as Salmonella, based on the detection of the invA gene. The stn and hilA genes were detected in 71.7% (38/53), and 83.0% (44/53) of the recovered isolates, respectively. Salmonella Enteritidis (11/53; 20.7%) was the most commonly isolated serovar, followed by S. Typhimurium (9/53; 17%), S. Montevideo (6/53; 11.3%), meanwhile, S. Chester, S. Derby, S. Papuana, and S. Saintpaul were the least commonly identified serovars (a single strain for each; 1.9%). Among the 16 antimicrobials tested, amikacin, imipenem, gentamicin, cefotaxime, meropenem, ciprofloxacin, and enrofloxacin were the most effective drugs, with bacterial susceptibility percentages of 98.1%, 94.3%, 92.5%, 86.8%, 83.0%, 73.6%, and 69.8%, respectively. Meanwhile, the least effective ones were erythromycin, streptomycin, clindamycin, cefepime, and nalidixic acid, with bacterial resistance percentages of 100%, 98.1%, 88.7%, 77.4%, and 66%, respectively. Interestingly, the high contamination level of Egyptian buffalo meat with multidrug-resistant Salmonella (79.2%; 42/53) can constitute a problem for public health. Therefore, programs to control Salmonella contamination are needed in Egypt.

Outbreak of Multidrug-Resistant Salmonella Heidelberg Infections Linked to Dairy Calf Exposure, United States, 2015-2018

In August 2016, the Wisconsin Department of Health Services notified the U.S. Centers for Disease Control and Prevention of multidrug-resistant (MDR) Salmonella enterica serovar Heidelberg infections in people who reported contact with dairy calves. Federal and state partners investigated this to identify the source and scope of the outbreak and to prevent further illnesses. Cases were defined as human Salmonella Heidelberg infection caused by a strain that had one of seven pulsed-field gel electrophoresis (PFGE) patterns or was related by whole genome sequencing (WGS), with illness onset from January 1, 2015, through July 2, 2018. Patient exposure and calf purchase information was collected and analyzed; calves were traced back from the point of purchase. Isolates obtained from animal and environmental samples collected on-farm were supplied by veterinary diagnostic laboratories and compared with patient isolates using PFGE and WGS. Antimicrobial susceptibility testing by standardized broth microdilution was performed. Sixty-eight patients from 17 states were identified. Forty (63%) of 64 patients noted cattle contact before illness. Thirteen (33%) of 40 patients with exposure to calves reported that calves were sick or had died. Seven individuals purchased calves from a single Wisconsin livestock market. One hundred forty cattle from 14 states were infected with the outbreak strain. WGS indicated that human, cattle, and environmental isolates from the livestock market were genetically closely related. Most isolates (88%) had resistance or reduced susceptibility to antibiotics of ≥5 antibiotic classes. This resistance profile included first-line antibiotic treatments for patients with severe salmonellosis, including ampicillin, ceftriaxone, and ciprofloxacin. In this outbreak, MDR Salmonella Heidelberg likely spread from sick calves to humans, emphasizing the importance of illness surveillance in animal populations to prevent future spillover of this zoonotic disease.

Anti-microbial resistance of Salmonella isolates from raw meat-based dog food in Japan

Background

Salmonella contamination of raw meat‐based diets (RMBDs) for pets poses a major public health concern but has not been investigated in Japan.

Objective

To investigate Salmonella contamination in RMBDs for dogs marketed in Japan and the anti‐microbial resistance profiles of the Salmonella isolates.

Methods

Sixty commercial RMBD samples were collected in the Okayama and Osaka Prefectures, Japan, between December 2016 and March 2017. The obtained Salmonella isolates were serotyped, their anti‐microbial resistance patterns were determined, and the anti‐microbial‐resistant isolates were screened for the presence of resistance genes by polymerase chain reaction.

Results

Salmonella enterica subsp. enterica was detected in seven of the 60 RMBD samples. Among them, five isolates were identified as S. Infantis (n = 3), S. Typhimurium (n = 1) and S. Schwarzengrund (n = 1), while the serotypes of two isolates were unable to be identified. All isolates were susceptible to ampicillin, cefazolin, cefotaxime and gentamycin. Two isolates were resistant to more than one anti‐microbial agent; one of the S. Infantis isolates was resistant to streptomycin, kanamycin, tetracycline and trimethoprim, while the S. Typhimurium isolate was resistant to nalidixic acid, ciprofloxacin and chloramphenicol. The S. Schwarzengrund isolate was resistant to tetracycline. Additionally, the S. Typhimurium isolate harboured the anti‐microbial resistance gene gyrA with a mutation corresponding to Ser‐83→Phe amino acid substitution.

Conclusion

The study findings suggest that RMBDs for dogs marketed in Japan can be a potential source of Salmonella infection for dogs and humans including infections caused by quinolone‐resistant isolates.

The current study's objective was to determine the prevalence of Salmonella contamination in RMBD for dogs and the antimicrobial resistance profiles of these isolates. Therefore, the incidence of Salmonella contamination in RMBD for dogs currently sold in Japan was surveyed. Salmonella was detected in seven of the 60 raw food samples.

Antimicrobial Resistance of Salmonella enteritidis and Salmonella typhimurium Isolated from Laying Hens, Table Eggs, and Humans with Respect to Antimicrobial Activity of Biosynthesized Silver Nanoparticles

Simple Summary

Salmonella enterica are common foodborne pathogens that cause gastrointestinal signs in a wide range of unrelated host species including poultry and humans. The overuse of antibiotics as therapeutic agents and growth promoters in the poultry industry has led to the emergence of multidrug-resistant (MDR) microorganisms. Thus, there is a need to find alternatives to conventional antibiotics. Recently, the biosynthesized silver nanoparticles (AgNPs) have shown an excellent antimicrobial activity. In this study, we investigated the antibacterial, antivirulent, and antiresistant activities of the biosynthesized AgNPs on the MDR and virulent S. enteritidis and S. typhimurium isolated from laying hens, table eggs, and humans. The obtained results indicated that AgNPs have the potential to be effective antimicrobial agents against MDR S. enteritidis and S. typhimurium and could be recommended for use in laying hen farms.

Abstract

Salmonella enterica is one of the most common causes of foodborne illness worldwide. Contaminated poultry products, especially meat and eggs are the main sources of human salmonellosis. Thus, the aim of the present study was to determine prevalence, antimicrobial resistance profiles, virulence, and resistance genes of Salmonella Enteritidis (S. enteritidis) and Salmonella Typhimurium (S. Typhimurium) isolated from laying hens, table eggs, and humans, in Sharkia Governorate, Egypt. The antimicrobial activity of Biosynthesized Silver Nanoparticles (AgNPs) was also evaluated. Salmonella spp. were found in 19.3% of tested samples with laying hens having the highest isolation rate (33.1%). S. Enteritidis) (5.8%), and S. Typhimurium (2.8%) were the dominant serotypes. All isolates were ampicillin resistant (100%); however, none of the isolates were meropenem resistant. Multidrug-resistant (MDR) was detected in 83.8% of the isolates with a multiple antibiotic resistance index of 0.21 to 0.57. Most isolates (81.1%) had at least three virulence genes (sopB, stn, and hilA) and none of the isolates harbored the pefA gene; four resistance genes (blaTEM, tetA, nfsA, and nfsB) were detected in 56.8% of the examined isolates. The AgNPs biosynthesized by Aspergillus niveus exhibit an absorption peak at 420 nm with an average size of 27 nm. AgNPs had a minimum inhibitory concentration of 5 µg/mL against S. enteritidis and S. typhimurium isolates and a minimum bactericidal concentration of 6 and 8 µg/mL against S. enteritidis and S. typhimurium isolates, respectively. The bacterial growth and gene expression of S. enteritidis and S. typhimurium isolates treated with AgNPs were gradually decreased as storage time was increased. In conclusion, this study indicates that S. enteritidis and S. typhimurium isolated from laying hens, table eggs, and humans exhibits resistance to multiple antimicrobial classes. The biosynthesized AgNPs showed potential antimicrobial activity against MDR S. enteritidis and S. typhimurium isolates. However, studies to assess the antimicrobial effectiveness of the biosynthesized AgNPs in laying hen farms are warranted.

Investigation of class 1 integrons and virulence genes in the emergent Salmonella serovar Infantis in Turkey

The emerging situation of Salmonella enterica subsp. enterica serovar Infantis (S. Infantis) in Turkey was investigated in terms of virulence genes and mobile genetic elements such as Salmonella genomic island 1 (SGI1) and class 1 (C1) integron to see whether increased multidrug resistance (MDR) and ability to cause human cases is a consequence of their possession. Screening of SGI1 (and its variants) and C1 integrons was done with conventional PCR, while screening of gene cassettes and virulence genes was conducted with real-time PCR for 70 S. Infantis isolates from poultry products. SGI1 or its variants were not detected in any of the isolates. Sixty-eight of 70 isolates were detected to carry one C1 integron of size 1.0 kb. These integrons were detected to carry ant(3″)-Ia gene cassette explaining the streptomycin/spectinomycin resistance. Sequence analysis of gene cassettes belongs to four representing isolates which showed that, although their difference in isolation date and place, genetically, they are 99.9% similar. Virulence gene screening was introduced as genotypic virulence profiles. The most dominant profile for S. Infantis isolates, among twelve genes, was gatC-tcfA, which are known to be related to colonization at specific hosts. This study revealed the high percentage of C1 integron possession in S. Infantis isolates from poultry products in Turkey. It also showed the potential of S. Infantis strains to be resistant to more antimicrobial drugs. Moreover, a dominant profile of virulence genes that are uncommon for non-typhoidal Salmonella (NTS) serovars was detected, which might explain the enhanced growth at specified hosts.

Antimicrobial and Antivirulence Impacts of Phenolics on Salmonella Enterica Serovar Typhimurium

Salmonella enterica serovar Typhimurium (ST) remains a major infectious agent in the USA, with an increasing antibiotic resistance pattern, which requires the development of novel antimicrobials capable of controlling ST. Polyphenolic compounds found in plant extracts are strong candidates as alternative antimicrobials, particularly phenolic acids such as gallic acid (GA), protocatechuic acid (PA) and vanillic acid (VA). This study evaluates the effectiveness of these compounds in inhibiting ST growth while determining changes to the outer membrane through fluorescent dye uptake and scanning electron microscopy (SEM), in addition to measuring alterations to virulence genes with qRT-PCR. Results showed antimicrobial potential for all compounds, significantly inhibiting the detectable growth of ST. Fluorescent spectrophotometry and microscopy detected an increase in relative fluorescent intensity (RFI) and red-colored bacteria over time, suggesting membrane permeabilization. SEM revealed severe morphological defects at the polar ends of bacteria treated with GA and PA, while VA-treated bacteria were found to be mid-division. Relative gene expression showed significant downregulation in master regulator hilA and invH after GA and PA treatments, while fliC was upregulated in VA. Results suggest that GA, PA and VA have antimicrobial potential that warrants further research into their mechanism of action and the interactions that lead to ST death.

Issues beyond resistance: inadequate antibiotic therapy and bacterial hypervirulence

The administration of antibiotics while critical for treatment, can be accompanied by potentially severe complications. These include toxicities associated with the drugs themselves, the selection of resistant organisms and depletion of endogenous host microbiota. In addition, antibiotics may be associated with less well-recognized complications arising through changes in the pathogens themselves. Growing evidence suggests that organisms exposed to antibiotics can respond by altering the expression of toxins, invasins and adhesins, as well as biofilm, resistance and persistence factors. The clinical significance of these changes continues to be explored; however, it is possible that treatment with antibiotics may inadvertently precipitate a worsening of the clinical course of disease. Efforts are needed to adjust or augment antibiotic therapy to prevent the transition of pathogens to hypervirulent states. Better understanding the role of antibiotic-microbe interactions and how these can influence disease course is critical given the implications on prescription guidelines and antimicrobial stewardship policies.

In vitro synergistic potentials of novel antibacterial combination therapies against Salmonella enterica serovar Typhimurium

Background

The antibiotics generally used in farm animals are rapidly losing their effectiveness all over the world as bacteria develop antibiotic resistance. Like some other pathogenic bacteria multidrug-resistant strains of Salmonella enterica serovar Typhimurium (S. Typhimurium) are also frequently found in animals and humans which poses a major public health concern. New strategies are needed to block the development of resistance and to prolong the life of traditional antibiotics. Thus, this study aimed to increase the efficacy of existing antibiotics against S. Typhimurium by combining them with opportunistic phenolic compounds gallic acid (GA), epicatechin, epicatechin gallate, epigallocatechin and hamamelitannin. Fractional inhibitory concentration indexes (FICI) of phenolic compound-antibiotic combinations against S. Typhimurium were determined. Based on the FICI and clinical importance, 1 combination (GA and ceftiofur) was selected for evaluating its effects on the virulence factors of this bacterium. Viability of Rattus norvegicus (IEC-6) cell in presence of this antibacterial combination was evaluated.

Results

Minimum inhibitory concentrations (MICs) of GA, epigallocatechin and hamamelitannin found against different strains of S. Typhimurium were 256, (512–1024), and (512–1024) μg/mL, respectively. Synergistic antibacterial effect was obtained from the combination of erythromycin-epicatechin gallate (FICI: 0.50) against S. Typhimurium. Moreover, additive effects (FICI: 0.502–0.750) were obtained from 16 combinations against this bacterium. The time-kill assay and ultrastructural morphology showed that GA-ceftiofur combination more efficiently inhibited the growth of S. Typhimurium compared to individual antimicrobials. Biofilm viability, and swimming and swarming motilities of S. Typhimurium in presence of GA-ceftiofur combination were more competently inhibited than individual antimicrobials. Viabilities of IEC-6 cells were more significantly enhanced by GA-ceftiofur combinations than these antibacterials alone.

Conclusions

This study suggests that GA-ceftiofur combination can be potential medication to treat S. Typhimurium-associated diarrhea and prevent S. Typhimurium-associated blood-stream infections (e.g.: fever) in farm animals, and ultimately its transmission from animal to human. Further in vivo study to confirm these effects and safety profiles in farm animal should be undertaken for establishing these combinations as medications.

Characterization and evolution of antibiotic resistance of Salmonella in municipal wastewater treatment plants

The objective of this study was to investigate the evolution of antibiotic resistance phenotypes, antibiotic resistance genes (ARGs) and Class 1 integron of Salmonella in municipal wastewater treatment plants (WWTPs). A total of 221 Salmonella strains were isolated from different stages of three WWTPs. After the susceptibility testing, high frequency of resistance was observed for tetracycline (TET, 47.5% of isolates) and sulfamethoxazole (SMZ, 38.5%), followed by ampicillin (AMP, 25.3%), streptomycin (STP, 17.6%), chloramphenicol (CHL, 15.4%), and gentamicin (GEN, 11.3%). Low prevalence of resistance was detected for norfloxacin (0.45%), ciprofloxacin (0.9%), and cefotaxime (0.9%). The tetA and sul3 genes were most frequently detected among the Salmonella isolates. Statistically significant correlations among AMP, CHL, GEN, and STP resistances were observed. High detection frequencies of Class 1 integron were observed in double antibiotic-resistant and multiple-antibiotic-resistant (MAR) Salmonella, which were 94.3% and 85.7%, respectively. The proliferation of MAR Salmonella and transfer of ARGs occurred in WWTPs. Class 1 integron plays a crucial role in the evolution of MAR Salmonella during WWTPs.

Serotype, antimicrobial susceptibility and genotype profiles of Salmonella isolated from duck farms and a slaughterhouse in Shandong province, China

BACKGROUND

Salmonella has been considered as one of the most important foodborne pathogens that threatened breeding industry and public health. To investigate the prevalence and characterization of Salmonella isolated from duck farms and a slaughterhouse in Shandong province, a total of 49 Salmonella strains were isolated from 2342 samples from four duck farms and one duck slaughterhouse in Jinan and Tai'an, Shandong province, China.

RESULTS

Among the isolates, S. Enteritidis (20/49, 40.8%) and S. Anatum (10/49, 20.4%) were the most prevalent, and high resistance rates were detected for erythromycin (49/49, 100.0%) and nalidixic acid (47/49, 95.9%). Class I integrons were detected in 17 isolates (34.7%17/49), which contained gene cassettes aadA7 + aac3-Id(15/17) and aadA5 + dfrA17 (2/17). Eleven different kinds of resistance genes were detected while blaTEM(36/49, 73.5%) was the most prevalent, followed by sul2(14/49, 28.6%). Thirteen virulence genes were tested, and all of the strains carried invA, hilA and sipA. Multilocus sequence typing (MLST) results showed that seven sequence types (STs) were identified; ST11 was the most prevalent ST (20/49, 40.8%), followed by ST2441 (10/49, 20.4%). There was a strong correlation between STs and serovars. The results of pulsed field gel electrophoresis(PFGE) showed that 39 PFGE patterns were generated from 49 Salmonella strains. PFGE patterns were mostly diverse and revealed high similarity between the isolates from the same sampling sites.

CONCLUSIONS

The presence of Salmonella infections among duck farms revealed that ducks could also be potential reservoirs for Salmonella. The high resistance rates against commonly used antimicrobials suggested a need for more reasonable use of antimicrobials, as well as for investigating substitutes for antimicrobials.

Fecal Colonization of Extended-Spectrum Beta Lactamase-Producing Salmonella spp. in Broilers in Lorestan Province of Iran

Background: Poultry is considered as a major source of human contamination with nontyphoidal Salmonella species. Global concern regarding the emergence and dispersion of extended-spectrum beta-lactamase (ESBLs)-producing isolates in broilers has increased during recent years. Objective: This study was proposed to evaluate the prevalence of Salmonella and the associated ESBLs in broilers in Lorestan province of Iran. Materials and Methods: Five hundred fresh fecal samples of broilers were phenotypically screened for Salmonella. The isolates were confirmed molecularly using an invA-based polymerase chain reaction (PCR). Confirmatory combination disk method was applied for phenotypic detection of ESBLs among the isolates, followed by molecular identification of blaCTX-M, blaTEM, and blaSHV genes in 3 single PCR assays among positive isolates. Chi-square test in SPSS software was used for the assessment of statistical relationships. Results: Of the 95 Salmonella isolates detected using routine bacteriological methods, all were confirmed molecularly. They generated the expected 254-bp amplicon. Moreover, 13 isolates were phenotypically recognized as ESBL determinants, among which 9 and 4 harbored blaCTX-M and blaTEM, respectively. No blaSHV and co-existence of the genes were determined. Conclusion: The threat imposed by dissemination of ESBL-producing non-typhoidal Salmonella spp. isolated from broilers was confirmed in the studied region. Continuous monitoring programs, application of biosecurity measures, and prudent prescription of antibiotics are warranted in order to prevent the introduction or dispersion of the ESBL-producing Salmonella.

Drug Resistance and the Prevention Strategies in Food Borne Bacteria: An Update Review

Antibiotic therapy is among the most important treatments against infectious diseases and has tremendously improved effects on public health. Nowadays, development in using this treatment has led us to the emergence and enhancement of drug-resistant pathogens which can result in some problems including treatment failure, increased mortality as well as treatment costs, reduced infection control efficiency, and spread of resistant pathogens from hospital to community. Therefore, many researches have tried to find new alternative approaches to control and prevent this problem. This study, has been revealed some possible and effective approaches such as using farming practice, natural antibiotics, nano-antibiotics, lactic acid bacteria, bacteriocin, cyclopeptid, bacteriophage, synthetic biology and predatory bacteria as alternatives for traditional antibiotics to prevent or reduce the emergence of drug resistant bacteria.

Characterization of the emerging multidrug-resistant Salmonella enterica serovar Indiana strains in China

Emergence of multidrug-resistant (MDR) Salmonella enterica serovar Indiana (S. Indiana), a dominant Salmonella serovar in China, has raised global awareness because the MDR S. Indiana also was rapidly emerged in other countries recently. To improve our understanding of underlying MDR mechanism and evolution of this emerging zoonotic pathogen, here we examined the standard ATCC51959 strain together with 19 diverse and representative Chinese S. Indiana strains by performing comprehensive microbiological, molecular, and comparative genomics analyses. The findings from S1-PFGE, plasmid origin analysis and Southern blotting suggested the MDR phenotype in the majority of isolates was associated with large integron-carrying plasmids. Interestingly, further in-depth analyses of two recently isolated, plasmid-free MDR S. Indiana revealed a long chromosomal class I integron (7.8 kb) that is not linked to the Salmonella Genome Island 1 (SGI1), which is rare. This unique chromosomal integron shares extremely high similarity to that identified in a MDR E. coli plasmid pLM6771 with respect to both genomic organization and sequence identity. Taken together, both plasmid and chromosomal integron I exist in the examined MDR S. Indiana strains. This timely study represents a significant step toward the understanding of molecular basis of the emerging MDR S. Indiana.

Carriage of Class 1 integrons and molecular characterization of intI1 gene in multidrug-resistant Salmonella spp. isolates from broilers

Aim:

The present study was conducted with the following aims: (i) To screen the Salmonella spp. isolates recovered from suspected cases of fowl typhoid for carriage of Class 1 integrons and analyze their association with antimicrobial resistance and (ii) to carry out molecular characterization and phylogenetic analysis of Class 1 integron-integrase (intI1) gene.

Materials and Methods:

A total of 43 Salmonella isolates were subjected to polymerase chain reaction (PCR) assay to determine the presence of Class1 intI1. Differences between different serotypes in relation to their carriage of integrons and the differences between strains containing or not containing an integron and being resistant to different antimicrobials were analyzed by Fisher exact test using STATA™ (StataCorp, College Station, TX). Phylogenetic analysis was carried out using MEGA6 software.

Results:

Out of 43 isolates, 40 (93.02%) were found positive for Class 1 integrons. 35/40 (87.5%) intI1-positive isolates were multidrug resistance (MDR) (resistant to ≥4 antibiotics), which support the hypothesis of an association between the presence of Class 1 integrons and emerging MDR in Salmonella. There was no significant difference among isolates resistant to different antimicrobials in Class 1 integron carrying isolates and the Class 1 integron negative isolates (p<0.05). Further, there was no significant difference among different serotypes in respect of their carriage of Class 1 integrons.

Conclusion:

It can be concluded that the high prevalence of Class 1 integrons indicates a high potential of Salmonella isolates for horizontal transmission of antimicrobial genes, especially among Gram-negative organisms.

Phenotypic and genotypic antimicrobial resistance and virulence genes of Salmonella enterica isolated from pet dogs and cats

Salmonella enterica isolates (n = 122), including 32 serotypes from 113 dogs and 9 cats, were obtained from household dogs (n = 250) and cats (n = 50) during 2012-2015. The isolates were characterized by serotyping, antimicrobial resistance phenotyping and genotyping, and virulence gene screening. Serovars Weltevreden (15.6%) and Typhimurium (13.9%) were the most common. The majority (43%) of the isolates were multidrug resistant. The dog isolates (12.3%) harbored class 1 integrons, of which the dfrA12-aadA2 cassette was most frequent (66.7%). The only class integron in serovar Albany was located on a conjugative plasmid. Two ESBL-producing isolates (i.e., a serovar Krefeld and a serovar Enteritridis) carried bla_TEM and bla_CTX-M, and the bla_TEM gene in both was horizontally transferred. Of the plasmid-mediated quinolone resistance genes tested, only qnrS (4.9%) was detected. Most Salmonella isolates harbored invA (100%), prgH (91.8%), and sipB (91%). Positive associations between resistance and virulence genes were observed for bla_PSE-1/orgA, cmlA/span, tolC, and sul1/tolC (p ＜ 0.05). The results suggest that companion dogs and cats are potential sources of S. enterica strains that carry resistance and virulence genes and that antimicrobial use in companion animals may select for the examined Salmonella virulence factors.

Characterization of Salmonella enterica isolates causing bacteremia in Lima, Peru, using multiple typing methods

In this study, different molecular typing tools were applied to characterize 95 Salmonella enterica blood isolates collected between 2008 and 2013 from patients at nine public hospitals in Lima, Peru. Combined results of multiplex PCR serotyping, two- and seven-loci multilocus sequence typing (MLST) schemes, serotyping, IS200 amplification and RAPD fingerprints, showed that these infections were caused by eight different serovars: Enteritidis, Typhimurium, Typhi, Choleraesuis, Dublin, Paratyphi A, Paratyphi B and Infantis. Among these, Enteritidis, Typhimurium and Typhi were the most prevalent, representing 45, 36 and 11% of the isolates, respectively. Most isolates (74%) were not resistant to ten primarily used antimicrobial drugs; however, 37% of the strains showed intermediate susceptibility to ciprofloxacin (ISC). Antimicrobial resistance integrons were carried by one Dublin (dfra1 and aadA1) and two Infantis (aadA1) isolates. The two Infantis isolates were multidrug resistant and harbored a large megaplasmid. Amplification of spvC and spvRA regions showed that all Enteritidis (n = 42), Typhimurium (n = 34), Choleraesuis (n = 3) and Dublin (n = 1) isolates carried the Salmonella virulence plasmid (pSV). We conclude that the classic serotyping method can be substituted by the multiplex PCR and, when necessary, sequencing of only one or two loci of the MLST scheme is a valuable tool to confirm the results. The effectiveness and feasibility of different typing tools is discussed.

Salmonella Typhimurium, the major causative agent of foodborne illness inactivated by a phage lysis system provides effective protection against lethal challenge by induction of robust cell-mediated immune responses and activation of dendritic cells

Salmonella Typhimurium infection via foodborne transmission remains a major public health threat even in developed countries. Vaccines have been developed to reduce the disease burden at the pre-harvest stage, but the cell-mediated immune response against intracellular invasion of the pathogen is not sufficiently elicited by conventional killed Salmonella vaccines, which are safer than live vaccines. In this study, we developed a genetically inactivated vaccine candidate by introducing lysis plasmid pJHL454 harboring the λ phage holin-endolysin system into S. Typhimurium; we designated this vaccine JOL1950. In vitro expression of endolysin was validated by immunoblotting, and complete inactivation of JOL1950 cells was observed following 36 h of the lysis. Electron microscopic examinations by scanning electron microscopy and immunogold labeling transmission EM revealed conserved surface antigenic traits of the JOL1950 cells after lysis. An in vivo immunogenicity study in mice immunized with lysed cells showed significantly increased serum IgG, IgG1, and IgG2a levels. Further, we observed markedly increased in vitro cell proliferation and upregulation of Th1, Th2, and Th17 cytokines in the repulsed splenic T-cells of immunized mice. In dendritic cells (DCs) treated with lysed JOL1950, we observed a significant increase in dendritic cell activation, co-stimulatory molecule production, and levels of immunomodulatory cytokines. In addition, Th1 and Th17 cytokines were also released by naïve CD4⁺ T-cells pulsed with primed DCs. Lysed JOL1950 also protected against lethal challenge in immunized mice. Together, these results indicate that our vaccine candidate has great potential to induce cell-mediated immunity against S. Typhimurium by facilitating the activation of DCs.

Salmonella virulence plasmid: pathogenesis and ecology

A current view on the role of the Salmonella virulence plasmid in the pathogenesis of animal and human hosts is discussed; including the possible relevance in secondary ecological niches. Various strategies towards further studies in this respect are proposed within the One Health Concept.

Characterization of Virulence-Associated Genes, Antimicrobial Resistance Genes, and Class 1 Integrons in Salmonella enterica serovar Typhimurium Isolates from Chicken Meat and Humans in Egypt

Foodborne pathogens are leading causes of illness especially in developing countries. The current study aimed to characterize virulence-associated genes and antimicrobial resistance in 30 Salmonella Typhimurium isolates of chicken and human origin at Mansoura, Egypt. The results showed that invA, avrA, mgtC, stn, and bcfC genes were identified in all the examined isolates, while 96.7% and 6.7% were positive for sopB and pef genes, respectively. The highest resistance frequencies of the isolates were to chloramphenicol and trimethoprim-sulfamethoxazole (73.3%, each), followed by streptomycin (56.7%), tetracycline and ampicillin (53.3%, each), and gentamicin (30%). However, only 2.7% of the isolates were resistant to cefotaxime and ceftriaxone each. Different resistance-associated genes, including blaTEM, aadB, aadC, aadA1, aadA2, floR, tetA(A), tetA(B), and sul1, were identified in Salmonella Typhimurium isolates with the respective frequencies of 53.3%, 6.7%, 23.3%, 46.7%, 63.3%, 73.3%, 60%, 20%, and 96.7%. None of the isolates was positive for blaSHV, blaOXA, and blaCMY genes. The results showed that the intI1 gene was detected in 24 (80%) of the examined Salmonella Typhimurium isolates. Class 1 integrons were found in 19 (79.2%) isolates that were intI1 positive. Seven integron profiles (namely: P-I to P-VII) were identified with P-V (gene cassette dfrA15, aadA2), the most prevalent profile. To the best of our knowledge, this is the first study to characterize the unusual gene cassette array dfrA12-OrfF-aadA27 from Salmonella Typhimurium isolates in Egypt.

Epidemiology of <i>Salmonella</i> and <i>Salmonellosis</i>

The prevalence of enteritis and its accompanying diarrheal and other health challenges linked to infections with Salmonella has continuously plagued sub Saharan Africa. In Nigeria, typhoid fever is among the major widespread diseases affecting both young and old as a result of many interrelated factors such as inadequate sanitaion, indiscriminate use of antibiotics and fecal contamination of water sources. Morbidity associated with illness due to Salmonella continues to increase with untold fatal consequences, often resulting in death. An accurate figure of cases is difficult to arrive at because only large outbreaks are mostly investigated whereas sporadic cases are under-reported. A vast majority of rural dwellers in Africa often resort to self-medication or seek no treatment at all, hence serving as carries of this disease. Non typhoidal cases of salmonellosis account for about 1.3 billion cases with 3 million deaths annually. Given the magnitude of the economic losses incurred by African nations in the battle against salmonella and salmonellosis, this article takes a critical look at the genus Salmonella, its morphology, isolation, physiological and biochemical characteristics, typing methods, methods of detection, virulence factor, epidemiology and methods of spread within the environment.

Genetic characterisation of multidrug-resistant Salmonella enterica serotypes isolated from poultry in Cairo, Egypt

Background

Food-borne diseases pose serious health problems, affecting public health and economic development worldwide.

Methods

Salmonella was isolated from samples of chicken parts, skin samples of whole chicken carcasses, raw egg yolks, eggshells and chicken faeces. Resulting isolates were characterised by serogrouping, serotyping, antimicrobial susceptibility testing and detection of extended-spectrum β-lactamase (ESBL) production. Antibiotic resistance genes and integrons were identified by polymerase chain reaction (PCR).

Results

The detection rates of Salmonella were 60%, 64% and 62% in chicken parts, skin, and faeces, respectively, whereas the egg yolks and eggshells were uniformly negative. Salmonella Kentucky and S. Enteritidis serotypes comprised 43.6% and 2.6% of the isolates, respectively, whilst S. Typhimurium was absent. Variable resistance rates were observed against 16 antibiotics; 97% were resistant to sulfamethoxazole, 96% to nalidixic acid and tetracycline and 76% to ampicillin. Multidrug resistance was detected in 82% (64/78) of the isolates and ESBL production was detected in 8% (6/78). The β-lactamase blaTEM-1 gene was detected in 57.6% and blaSHV-1 in 6.8% of the isolates, whilst the blaOXA gene was absent. The sul1 gene was detected in 97.3% and the sul2 gene in 5.3% of the isolates. Sixty-four of the 78 isolates (82%) were positive for the integrase gene (int I) from class 1 integrons, whilst int II was absent.

Conclusion

This study reveals the presence of an alarming number of multidrug-resistant Salmonella isolates in the local poultry markets in Cairo. The high levels of drug resistance suggest an emerging problem that could impact negatively on efforts to prevent and treat poultry and poultry-transmitted human diseases in Egypt.

Prevalence of drug resistance and virulence features in Salmonella spp. isolated from foods associated or not with salmonellosis in Brazil

Salmonella is the most common etiological agent of cases and outbreaks of foodborne diarrheal illnesses. The emergence and spread of Salmonella spp., which has become multi-drug resistant and potentially more pathogenic, have increased the concern with this pathogen. In this study, 237 Salmonella spp., associated or not with foodborne salmonellosis in Brazil, belonging mainly to serotype Enteritidis, were tested for antimicrobial susceptibility and the presence of the virulence genes spvC, invA, sefA and pefA. Of the isolates, 46.8% were sensitive to all antimicrobials and 51.9% were resistant to at least one antimicrobial agent. Resistance to more than one antimicrobial agent was observed in 10.5% of the strains. The highest rates of resistance were observed for streptomycin (35.9%) and nalidixic acid (16.9%). No strain was resistant to cefoxitin, cephalothin, cefotaxime, amikacin, ciprofloxacin and imipenem. The invA gene was detected in all strains. Genes spvC and pefA were found in 48.1% and 44.3% of strains, respectively. The gene sefA was detected in 31.6% of the strains and only among S. Enteritidis. Resistance and virulence determinants were detected in Salmonella strains belonging to several serotypes. The high rates of antibiotic-resistance in strains isolated from poultry products demonstrate the potential risk associated with the consumption of these products and the need to ensure good food hygiene practices from farm to table to reduce the spread of pathogens relevant to public health.

Agriculture and food animals as a source of antimicrobial-resistant bacteria

One of the major breakthroughs in the history of medicine is undoubtedly the discovery of antibiotics. Their use in animal husbandry and veterinary medicine has resulted in healthier and more productive farm animals, ensuring the welfare and health of both animals and humans. Unfortunately, from the first use of penicillin, the resistance countdown started to tick. Nowadays, the infections caused by antibiotic-resistant bacteria are increasing, and resistance to antibiotics is probably the major public health problem. Antibiotic use in farm animals has been criticized for contributing to the emergence of resistance. The use and misuse of antibiotics in farm animal settings as growth promoters or as nonspecific means of infection prevention and treatment has boosted antibiotic consumption and resistance among bacteria in the animal habitat. This reservoir of resistance can be transmitted directly or indirectly to humans through food consumption and direct or indirect contact. Resistant bacteria can cause serious health effects directly or via the transmission of the antibiotic resistance traits to pathogens, causing illnesses that are difficult to treat and that therefore have higher morbidity and mortality rates. In addition, the selection and proliferation of antibiotic-resistant strains can be disseminated to the environment via animal waste, enhancing the resistance reservoir that exists in the environmental microbiome. In this review, an effort is made to highlight the various factors that contribute to the emergence of antibiotic resistance in farm animals and to provide some insights into possible solutions to this major health issue.

Antimicrobial susceptibility and virulence characteristics of Salmonella enterica Typhimurium isolates from healthy and diseased pigs in Korea

This study compared the antimicrobial susceptibility and prevalence of virulence genes in Salmonella enterica Typhimurium isolated from healthy and diseased pigs in Korea. A total of 456 Salmonella Typhimurium isolated from healthy (n = 238) and diseased (n = 218) pigs between 1998 and 2011 were investigated. In total, 93.4% of the Salmonella Typhimurium isolates were resistant to at least one antimicrobial agent tested. The isolates were most often resistant to tetracycline (85.7%), followed by streptomycin (83.6%), nalidixic acid (67.3%), ampicillin (49.3%), chloramphenicol (42.8%), and gentamicin (37.1%). Moreover, multidrug resistance phenotype and resistance to ampicillin, florfenicol, gentamicin, nalidixic acid, neomycin, streptomycin, and tetracycline were significantly higher (P < 0.01) among Salmonella Typhimurium isolates from the diseased pigs compared with those from the healthy pigs. The most common resistance pattern observed in both groups of isolates was streptomycin-tetracycline. Overall, more than 96% of the isolates tested possessed invA, spiA, msgA, sipB, prgH, spaN, tolC, lpfC, sifA, sitC, and sopB virulence genes. The prevalence of orgA, pagC, and iroN were 50.2, 74.1, and 91.0%, respectively, whereas isolates carrying cdtB (1.5%), pefA (7.0%), and spvB (14.9%) were identified much less frequently. Furthermore, the prevalence of invA, lpfC, orgA, pagC, and iroN was significantly higher (P < 0.01) among the isolates from the diseased pigs than in isolates from the healthy pigs. Our results demonstrated that, among diseased pigs, there was significantly higher resistance to some antimicrobials and greater prevalence of some virulence genes than in healthy pigs, indicating the role these factors play in pathogenesis. Multidrug-resistant Salmonella isolates that carry virulence-associated genes are potentially more dangerous and constitute a public health concern. Thus, continuous surveillance of antimicrobial resistance and virulence characteristics in Salmonella is essential.

The complete plasmid sequences of Salmonella enterica serovar Typhimurium U288

Salmonella enterica Serovar Typhimurium U288 is an emerging pathogen of pigs. The strain contains three plasmids of diverse origin that encode traits that are of concern for food security and safety, these include antibiotic resistant determinants, an array of functions that can modify cell physiology and permit genetic mobility. At 148,711 bp, pSTU288-1 appears to be a hybrid plasmid containing a conglomerate of genes found in pSLT of S. Typhimurium LT2, coupled with a mosaic of horizontally-acquired elements. Class I integron containing gene cassettes conferring resistance against clinically important antibiotics and compounds are present in pSTU288-1. A curious feature of the plasmid involves the deletion of two genes encoded in the Salmonella plasmid virulence operon (spvR and spvA) following the insertion of a tnpA IS26-like element coupled to a blaTEM gene. The spv operon is considered to be a major plasmid-encoded Salmonella virulence factor that is essential for the intracellular lifecycle. The loss of the positive regulator SpvR may impact on the pathogenesis of S. Typhimurium U288. A second 11,067 bp plasmid designated pSTU288-2 contains further antibiotic resistance determinants, as well as replication and mobilization genes. Finally, a small 4675 bp plasmid pSTU288-3 was identified containing mobilization genes and a pleD-like G-G-D/E-E-F conserved domain protein that modulate intracellular levels of cyclic di-GMP, and are associated with motile to sessile transitions in growth.

Characterization of extended-spectrum beta-lactamases-producing Salmonella strains isolated from retail foods in Shaanxi and Henan Province, China

Extended-spectrum beta-lactamases (ESBL)-producing Salmonella enterica have been reported worldwide. However, research on foodborne ESBL-producing Salmonella has been rarely conducted. One hundred and thirty eight ceftriaxone or/and cefoperazone-resistant Salmonella strains recovered from retail foods in Shaanxi and Henan Province, China, were screened for ESBL. The ESBL-producing strains were further characterized for antimicrobial resistance, pulse field gel electrophoresis (PFGE) profiles, and the presence of blaTEM, blaSHV, blaOXA, blaCTX-M, and blaPSE. The transferability of ESBL encoding genes to a susceptible Escherichia coli strain was also investigated. Thirty (21.7%) isolates were identified as ESBL positive and belonged to S. enterica serovars Indiana, Shubra, Typhimurium, and Enteritidis. S. Indiana and S. Shubra isolates were firstly identified in ESBL-producing strains. Great genetic diversity was seen among these ESBL-producing strains. Nucleotide sequence analysis revealed that blaTEM-1B was the only ESBL-encoding gene among the genes tested and was detected in 26 of 30 strains and was carried in the conjugative plasmids. The blaTEM-1B gene was transferable through conjugation at rates ranging from 4.71 × 10(-7) to 7.55 × 10(-6) transconjugant per recipient cell. This study provides the evidence of foodborne ESBL-producing Salmonella, and the transferability of plasmid harboring ESBL-encoding genes could possibly contribute to the dissemination of ESBL.

Fine-mapping and phenotypic analysis of the Ity3 Salmonella susceptibility locus identify a complex genetic structure

Experimental animal models of Salmonella infections have been widely used to identify genes important in the host immune response to infection. Using an F2 cross between the classical inbred strain C57BL/6J and the wild derived strain MOLF/Ei, we have previously identified Ity3 (Immunity to Typhimurium locus 3) as a locus contributing to the early susceptibility of MOLF/Ei mice to infection with Salmonella Typhimurium. We have also established a congenic strain (B6.MOLF-Ity/Ity3) with the MOLF/Ei Ity3 donor segment on a C57BL/6J background. The current study was designed to fine map and characterize functionally the Ity3 locus. We generated 12 recombinant sub-congenic strains that were characterized for susceptibility to infection, bacterial load in target organs, cytokine profile and anti-microbial mechanisms. These analyses showed that the impact of the Ity3 locus on survival and bacterial burden was stronger in male mice compared to female mice. Fine mapping of Ity3 indicated that two subloci contribute collectively to the susceptibility of B6.MOLF-Ity/Ity3 congenic mice to Salmonella infection. The Ity3.1 sublocus controls NADPH oxidase activity and is characterized by decreased ROS production, reduced inflammatory cytokine response and increased bacterial burden, thereby supporting a role for Ncf2 (neutrophil cytosolic factor 2 a subunit of NADPH oxidase) as the gene underlying this sublocus. The Ity3.2 sub-locus is characterized by a hyperresponsive inflammatory cytokine phenotype after exposure to Salmonella. Overall, this research provides support to the combined action of hormonal influences and complex genetic factors within the Ity3 locus in the innate immune response to Salmonella infection in wild-derived MOLF/Ei mice.

Survival of Salmonella enterica in poultry feed is strain dependent

Feed components have low water activity, making bacterial survival difficult. The mechanisms of Salmonella survival in feed and subsequent colonization of poultry are unknown. The purpose of this research was to compare the ability of Salmonella serovars and strains to survive in broiler feed and to evaluate molecular mechanisms associated with survival and colonization by measuring the expression of genes associated with colonization (hilA, invA) and survival via fatty acid synthesis (cfa, fabA, fabB, fabD). Feed was inoculated with 1 of 15 strains of Salmonella enterica consisting of 11 serovars (Typhimurium, Enteriditis, Kentucky, Seftenburg, Heidelberg, Mbandanka, Newport, Bairely, Javiana, Montevideo, and Infantis). To inoculate feed, cultures were suspended in PBS and survival was evaluated by plating samples onto XLT4 agar plates at specific time points (0 h, 4 h, 8 h, 24 h, 4 d, and 7 d). To evaluate gene expression, RNA was extracted from the samples at the specific time points (0, 4, 8, and 24 h) and gene expression measured with real-time PCR. The largest reduction in Salmonella occurred at the first and third sampling time points (4 h and 4 d) with the average reductions being 1.9 and 1.6 log cfu per g, respectively. For the remaining time points (8 h, 24 h, and 7 d), the average reduction was less than 1 log cfu per g (0.6, 0.4, and 0.6, respectively). Most strains upregulated cfa (cyclopropane fatty acid synthesis) within 8 h, which would modify the fluidity of the cell wall to aid in survival. There was a weak negative correlation between survival and virulence gene expression indicating downregulation to focus energy on other gene expression efforts such as survival-related genes. These data indicate the ability of strains to survive over time in poultry feed was strain dependent and that upregulation of cyclopropane fatty acid synthesis and downregulation of virulence genes were associated with a response to desiccation stress.