Drug resistance, plasmids, biotypes and susceptibility to bacteriophages of Salmonella isolated from poultry in Canada

Recent Evolution and Genomic Profile of Salmonella enterica Serovar Heidelberg Isolates from Poultry Flocks in Brazil

Salmonella enterica serovar Heidelberg is isolated from poultry-producing regions around the world. In Brazil, S. Heidelberg has been frequently detected in poultry flocks, slaughterhouses, and chicken meat. The goal of the present study was to assess the population structure, recent temporal evolution, and some important genetic characteristics of S. Heidelberg isolated from Brazilian poultry farms. Phylogenetic analysis of 68 S. Heidelberg genomes sequenced here and additional whole-genome data from NCBI demonstrated that all isolates from the Brazilian poultry production chain clustered into a monophyletic group, here called S. Heidelberg Brazilian poultry lineage (SH-BPL). Bayesian analysis defined the time of the most recent common ancestor (tMRCA) as 2004, and the overall population size (N_e) was constant until 2008, when an ∼10-fold N_e increase was observed until circa 2013. SH-BPL presented at least two plasmids with replicons ColpVC (n = 68; 100%), IncX1 (n = 66; 97%), IncA/C2 (n = 65; 95.5%), ColRNAI (n = 43; 63.2%), IncI1 (n = 32; 47%), ColMG828, Col156, IncHI2A, IncHI2, IncQ1, IncX4, IncY, and TrfA (each with n < 4; <4% each). Antibiotic resistance genes were found, with high frequencies of fosA7 (n = 68; 100%), mdf(A) (n = 68; 100%), tet(34) (n = 68; 100%), sul2 (n = 64; 94.1%), and blaCMY-2 (n = 56; 82.3%), along with an overall multidrug resistance (MDR) profile. Ten Salmonella pathogenicity islands (SPI1 to SPI5, SPI9, and SPI11 to SPI14) and 139 virulence genes were also detected. The SH-BPL profile was like those of other previous S. Heidelberg isolates from poultry around the world in the 1990s. In conclusion, the present study demonstrates the recent introduction (2004) and high level of dissemination of an MDR S. Heidelberg lineage in Brazilian poultry operations. IMPORTANCE S. Heidelberg is the most frequent serovar in several broiler farms from the main Brazilian poultry-producing regions. Therefore, avian-source foods (mainly chicken carcasses) commercialized in the country and exported to other continents are contaminated with this foodborne pathogen, generating several national and international economic losses. In addition, isolates of this serovar are usually resistant to antibiotics and can cause human invasive and septicemic infection, representing a public health concern. This study demonstrates the use of whole-genome sequencing (WGS) to obtain epidemiological information for one S. Heidelberg lineage highly spread among Brazilian poultry farms. This information will help to define biosecurity measures to control this important Salmonella serovar in Brazilian and worldwide poultry operations.

Prevalence, Distribution, and Diversity of Salmonella Strains Isolated From a Subtropical Lake

This study investigated the prevalence, serovar distribution, antimicrobial resistance, and pulsed field gel electrophoresis (PFGE) typing of Salmonella enterica isolated from Lake Zapotlán, Jalisco, Mexico. Additionally, the association of the presence of Salmonella with physicochemical and environmental parameters was analyzed using Pearson correlation analysis and principal component analysis (PCA). Salmonella spp. were identified in 19 of 63 (30.15%) samples. The prevalence of Salmonella was positively correlated with air temperature, electrical conductivity, pH, and dissolved oxygen and negatively correlated with relative humidity, water temperature, turbidity, and precipitation. The predominant serotype identified was Agona (68.48%), followed by Weltevreden (5.26%), Typhimurium (5.26%), and serogroup B (21.05%). Overall, the highest detected antimicrobial resistance was toward colistin (73.68%), followed by sulfamethoxazole (63.15%), tetracycline (57.89%), nalidixic acid (52.63%), and trimethoprim (52.63%). All Salmonella strains were genetically diverse, with a total of 11 XbaI and four BlnI profiles on PFGE. The use of these two enzymes allowed differentiate strains of Salmonella of the same serotype. The results obtained in this study contribute to a better understanding of the Salmonella spp. ecology in an endorheic subtropical lake and provide information for decision makers to propose and implement effective strategies to control point and non-point sources of pathogen contamination.

Prevalence, Serovars, and Antimicrobial Resistance of Salmonella in Cecal Samples of Chickens Slaughtered in Pluck Shops in Trinidad

The aim of the study was to determine the prevalence and zonal distribution of Salmonella serotypes in poultry and to determine the antimicrobial resistance profile of Salmonella isolates. A total of 1,503 cecal samples of poultry were randomly collected from 33 pluck shops across Trinidad. Isolation and identification of Salmonella followed standard methods, and the disk diffusion method was used to determine resistance of isolates to 14 antimicrobial agents. Ninety-one (6.1%) of the 1,503 samples collected from four zones were positive for Salmonella. The frequency of isolation of Salmonella from chicken ceca (6.5%) was higher than that detected in duck ceca (5.1%), but the difference was not statistically significant (P > 0.05). Ten serotypes were detected, with Salmonella Molade, Salmonella enterica subsp. enterica I, and Salmonella Typhimurium the most prevalent at 56.0, 11.0, and 8.8%, respectively. The highest frequency of isolation of Salmonella was recorded in the northeast zone (59.3%). All 91 isolates exhibited resistance to at least 1 of the 14 antimicrobial agents. The highest frequency of resistance was exhibited to ampicillin (51.0%), kanamycin (49.5%), and streptomycin (37.4%). A total of 22 resistance patterns were exhibited by the 91 isolates of Salmonella, and 13 isolates (14.3%) exhibited multiple drug resistance. The results emphasize the need to implement hygienic practices to reduce the levels of contamination at poultry pluck shops and the need for prudent use of antimicrobial agents in the poultry production system in Trinidad.

Phenotypic and genotypic drug resistance profile of Salmonella serovars isolated from poultry farm and processing units located in and around Mumbai city, India

BACKGROUND AND AIM

The extensive use of antimicrobials in poultry has led to an increase in bacterial multidrug resistance, and the emergence of multidrug-resistant nontyphoidal Salmonella is a global problem. This study was performed to detect antibiotic-resistant Salmonella serovars in poultry farming and processing environment.

MATERIALS AND METHODS

A total of 956 various samples, comprising 432 farm origin, 324 poultry processing stage wise and environmental, and 154 product processing stages and environmental samples, were collected from poultry farms and processing units located in and around Mumbai city. Of a total of 71 recovered isolates, 42 randomly selected Salmonella isolates were subjected for antibiotic susceptibility testing by disk diffusion method and serotyping. A total of 31 serotypically confirmed isolates were characterized for the presence of tetA, tetB, bla TEM, and CTX-M gene.

RESULTS

Higher resistance was recorded against Doxycycline (100%), followed by Oxytetracycline (97.62%), Neomycin (88.10%), Erythromycin (83.33%), Tetracycline (78.57%), and Ceftizoxime (35.71%). Resistance from 0.00 to 26.19 percent was found to antimicrobials, namely Norfloxacin (26.19%), Ampicillin (21.43%), Azithromycin (21.43%), Ciprofloxacin (19.05%), Colistin (4.76%), Streptomycin (16.67%), Cefotaxime (14.19%), Enrofloxacin (14.29%), Amoxyclav (14.29%), Gentamicin (7.14%), Chloramphenicol (4.76%), Amikacin (4.76%), and Ceftazidime (0.0%). Results demonstrate that the Salmonella Virchow dominated and all serotypes were found to carry Tetracycline resistance gene tetA, 5 isolates were found to be positive for blaTEM , whereas none of the isolates were carrying tetB and CTX-M gene.

CONCLUSION

This study revealed that there is a significant rise of Tetracycline resistance with the presence of tetA gene in Salmonella spp. which indicates selective pressure for adopting resistance against tetracycline group of antibiotics.

Correlations among Resistances to Different Antimicrobial Compounds in Salmonella Strains from Hen Eggshells

Persistence of antibiotic-resistant Salmonella in the food chain may depend on strain tolerance to other antimicrobials and also on biofilm formation capacity. Yet, there is limited information on sensitivity of antibiotic-resistant Salmonella to other antimicrobials, such as phenolic compounds, chemical preservatives, or antimicrobial peptides. This study aimed at correlating antimicrobial resistance and biofilm formation capacity in antibiotic-resistant, biocide-tolerant Salmonella strains from hen eggshells. A collection of 21 strains previously selected according to their antibiotic resistance and biocide tolerance phenotypes were used for the present study. Strains were inspected for their biofilm formation capacity and for their sensitivity to (i) phenolic compounds (carvacrol, thymol), (ii) chemical preservatives (sodium lactate, trisodium phosphate), and (iii) cationic antimicrobials (polymyxin B, lysozyme-EDTA). Biofilm formation capacity was not correlated with antimicrobial resistances of the planktonic Salmonella. Polymyxin B and the lysozyme-EDTA combinations showed significant ( P < 0.05) positive correlations to each other and to sodium lactate. Significant ( P < 0.05) positive correlations were also observed for benzalkonium chloride and cetrimide with carvacrol, thymol, and trisodium phosphate, or between hexadecylpyridinium chloride and carvacrol. Antibiotic resistance also correlated positively with a higher tolerance to other antimicrobials (cefotaxime, ceftazidime, and ciprofloxacin with carvacrol, thymol, and trisodium phosphate; netilmicin with thymol and trisodium phosphate; tetracycline with carvacrol and thymol). These results must be taken into consideration to ensure a proper use of antimicrobials in the poultry industry, at concentrations that do not allow coselection of biocide-tolerant, antibiotic-resistant Salmonella.

Salmonella phages and prophages: genomics, taxonomy, and applied aspects

Since this book was originally published in 2007 there has been a significant increase in the number of Salmonella bacteriophages, particularly lytic virus, and Salmonella strains which have been fully sequenced. In addition, new insights into phage taxonomy have resulted in new phage genera, some of which have been recognized by the International Committee of Taxonomy of Viruses (ICTV). The properties of each of these genera are discussed, along with the role of phage as agents of genetic exchange, as therapeutic agents, and their involvement in phage typing.

Resistance to antimicrobial agents among Salmonella isolates recovered from layer farms and eggs in the Caribbean region

This investigation determined the frequency of resistance of 84 isolates of Salmonella comprising 14 serotypes recovered from layer farms in three Caribbean countries (Trinidad and Tobago, Grenada, and St. Lucia) to eight antimicrobial agents, using the disc diffusion method. Resistance among isolates of Salmonella was related to the country of recovery, type of sample, size of layer farms, and isolate serotype. Overall, all (100.0%) of the isolates exhibited resistance to one or more of seven antimicrobial agents tested, and all were susceptible to chloramphenicol. The resistance detected ranged from 11.9% to sulphamethoxazole-trimethoprim (SXT) to 100.0% to erythromycin. The difference was, however, not statistically significant (P = 0.23). Across countries, for types of samples that yielded Salmonella, significant differences in frequency of resistance were detected only to SXT (P = 0.002) in Trinidad and Tobago and to gentamycin (P = 0.027) in St. Lucia. For the three countries, the frequency of resistance to antimicrobial agents was significantly different for ampicillin (P = 0.001) and SXT (P = 0.032). A total of 83 (98.8%) of the 84 isolates exhibited 39 multidrug resistance patterns. Farm size significantly (P = 0.032) affected the frequency of resistance to kanamycin across the countries. Overall, among the 14 serotypes of Salmonella tested, significant (P < 0.05) differences in frequency of resistance were detected to kanamycin, ampicillin, and SXT. Results suggest that the relatively high frequency of resistance to six of the antimicrobial agents (erythromycin, streptomycin, gentamycin, kanamycin, ampicillin, and tetracycline) tested and the multidrug resistance detected may pose prophylactic and therapeutic concerns for chicken layer farms in the three countries studied.

Salmonella pathogenicity and host adaptation in chicken-associated serovars

Enteric pathogens such as Salmonella enterica cause significant morbidity and mortality. S. enterica serovars are a diverse group of pathogens that have evolved to survive in a wide range of environments and across multiple hosts. S. enterica serovars such as S. Typhi, S. Dublin, and S. Gallinarum have a restricted host range, in which they are typically associated with one or a few host species, while S. Enteritidis and S. Typhimurium have broad host ranges. This review examines how S. enterica has evolved through adaptation to different host environments, especially as related to the chicken host, and continues to be an important human pathogen. Several factors impact host range, and these include the acquisition of genes via horizontal gene transfer with plasmids, transposons, and phages, which can potentially expand host range, and the loss of genes or their function, which would reduce the range of hosts that the organism can infect. S. Gallinarum, with a limited host range, has a large number of pseudogenes in its genome compared to broader-host-range serovars. S. enterica serovars such as S. Kentucky and S. Heidelberg also often have plasmids that may help them colonize poultry more efficiently. The ability to colonize different hosts also involves interactions with the host's immune system and commensal organisms that are present. Thus, the factors that impact the ability of Salmonella to colonize a particular host species, such as chickens, are complex and multifactorial, involving the host, the pathogen, and extrinsic pressures. It is the interplay of these factors which leads to the differences in host ranges that we observe today.

Avian colibacillosis and salmonellosis: a closer look at epidemiology, pathogenesis, diagnosis, control and public health concerns

Avian colibacillosis and salmonellosis are considered to be the major bacterial diseases in the poultry industry world-wide. Colibacillosis and salmonellosis are the most common avian diseases that are communicable to humans. This article provides the vital information on the epidemiology, pathogenesis, diagnosis, control and public health concerns of avian colibacillosis and salmonellosis. A better understanding of the information addressed in this review article will assist the poultry researchers and the poultry industry in continuing to make progress in reducing and eliminating avian colibacillosis and salmonellosis from the poultry flocks, thereby reducing potential hazards to the public health posed by these bacterial diseases.

Characteristics of non-typhoidal Salmonella isolates from human and broiler-chickens in southwestern Seoul, Korea

Non-typhoidal Salmonella (NTS) is an important commensal microorganism. The purpose of this study was to determine the epidemiological relation between NTS isolates from livestock and NTS isolates from human by analyzing antimicrobial susceptibilities and performing molecular typing. We determined the serotypes of 36 human clinical isolates and 64 livestock isolates, performed antimicrobial susceptibility testing against 8 antibiotics, and determined the molecular types of isolated NTS spp. by pulsed field gel electrophoresis (PFGE). In human isolates, S. enteritidis was the most common serotype (17 isolates; 47.2%) and S. typhimurium the second most (8 isolates; 22.2%). In livestock isolates, S. typhimurium was the most common serotype (15 isolates; 23.44%), and S. enteritidis was the second most (14 isolates; 21.88%). Ampicillin and tetracycline resistance were 50% (32/64 isolates) each among broiler-chicken NTS isolates. No human or livestock NTS isolates showed resistance to ciprofloxacin, TMP-SMX, or ceftriaxone. However, 19.4% (7/36) and 46.8% (30/64) of the human and livestock NTS isolates were resistant to nalidixic acid (MIC > or = 16 mg/mL), respectively. The presence of the three identical PFGE molecular types from human and broiler-chicken NTS isolates suggests the possibility of transmission from livestock to humans.

Hydrogen sulfide downregulates the aortic L-arginine/nitric oxide pathway in rats

The aim of the present study was to investigate the effect of hydrogen sulfide (H(2)S) signaling by nitric oxide (NO) in isolated rat aortas and cultured human umbilical vein endothelial cells (HUVECs). Both administration of H(2)S and NaHS, as well as endogenous H(2)S, reduced NO formation, endothelial nitric oxide synthase (eNOS) activity, eNOS transcript abundance, and l-arginine (l-Arg) transport (all P < 0.01). The kinetics analysis of eNOS activity and l-Arg transport showed that H(2)S reduced V(max) values (all P < 0.01) without modifying K(m) parameters. Use of selective NOS inhibitors verified that eNOS [vs. inducible NOS (iNOS) and neuronal NOS (nNOS)] was the specific target of H(2)S regulation. H(2)S treatment (100 micromol/l) reduced Akt phosphorylation and decreased eNOS phosphorylation at Ser1177. H(2)S reduced l-Arg uptake by inhibition of a system y+ transporter and decreased the CAT-1 transcript. H(2)S treatment reduced protein expression of eNOS but not of nNOS and iNOS. Pinacidil (K(ATP) channel opener) exhibited the similar inhibitory effects on the l-Arg/NOS/NO pathway. Glibenclamide (K(ATP) channel inhibitor) partly blocked the inhibitory effect of H(2)S and pinacidil. An in vivo experiment revealed that H(2)S downregulated the vascular l-Arg/eNOS/NO pathway after intraperitoneal injection of NaHS (14 micromol/kg) in rats. Taken together, our findings suggest that H(2)S downregulates the vascular l-Arg/NOS/NO pathway in vitro and in vivo, and the K(ATP) channel could be involved in the regulatory mechanism of H(2)S.

Salmonella phages and prophages--genomics and practical aspects

Numerous bacteriophages specific to Salmonella have been isolated or identified as part of host genome sequencing projects. Phylogenetic analysis of the sequenced phages, based on related protein content using CoreGenes, reveals that these viruses fall into five groupings (P27-like, P2-like, lambdoid, P22-like, and T7-like) and three outliers (epsilon15, KS7, and Felix O1). The P27 group is only represented by ST64B; the P2 group contains Fels-2, SopEphi, and PSP3; the lambdoid Salmonella phages include Gifsy-1, Gifsy-2, and Fels-1. The P22-like viruses include epsilon34, ES18, P22, ST104, and ST64T. The only member of the T7-like group is SP6. The properties of each of these phages are discussed, along with their role as agents of genetic exchange and as therapeutic agents and their involvement in phage typing.

Acquisition of resistance to extended-spectrum cephalosporins by Salmonella enterica subsp. enterica serovar Newport and Escherichia coli in the turkey poult intestinal tract

Salmonella enterica subsp. enterica serovar Newport resistant to the extended-spectrum cephalosporins (ESCs) and other antimicrobials causes septicemic salmonellosis in humans and animals and is increasingly isolated from humans, animals, foods, and environmental sources. Mechanisms whereby serovar Newport bacteria become resistant to ESCs and other classes of antimicrobials while inhabiting the intestinal tract are not well understood. The present study shows that 25.3% of serovar Newport strains isolated from the turkey poult intestinal tract after the animals were dosed with Escherichia coli harboring a large conjugative plasmid encoding the CMY-2 beta-lactamase and other drug resistance determinants acquired the plasmid and its associated drug resistance genes. The conjugative plasmid containing the cmy-2 gene was transferred not only from the donor E. coli to Salmonella serovar Newport but also to another E. coli serotype present in the intestinal tract. Laboratory studies showed that the plasmid could be readily transferred between serovar Newport and E. coli intestinal isolates. Administration of a single dose of ceftiofur, used to prevent septicemic colibacillosis, to 1-day-old turkeys did not result in the isolation of ceftiofur-resistant E. coli or Salmonella serovar Newport. There was a remarkable association between serotype, drug resistance, and plasmid profile among the E. coli strains isolated from the poults. This study shows that Salmonella serovar Newport can become resistant to ESCs and other antibiotics by acquiring a conjugative drug resistance plasmid from E. coli in the intestines.

Antimicrobial resistance in Salmonella enteritidis strains isolated from broiler carcasses, food, human and poultry-related samples

Antimicrobial resistance was investigated in 91 Salmonella enteritidis isolates from broiler carcasses, food, human and poultry-related samples originated from South of Brazil. A great proportion of resistant strains was found, 90.1% showing resistance to at least one antimicrobial drug. There was a high resistance to sulfonamides (75.8%) and nitrofurantoin (52.8%). Lower levels of resistance were found for tetracycline (15.4%), streptomycin (7.7%), nalidixic acid (7.7%), gentamicin (5.5%), norfloxacin (3.3%), trimethoprim (3.3%), cefalotin (2.2%), ampicillin (1.1%), and chloramphenicol (1.1%). Resistance to ciprofloxacin was not detected. A total of 51.6% of S. enteritidis strains were multiresistant (resistance to two or more antimicrobial agents) and 18 resistance patterns were found. The highest resistance was found in strains isolated from poultry-related samples, where all strains were resistant to at least one antimicrobial agent. No predominant resistance pattern was related to phage type in our isolates. The high number of antimicrobial resistant S. enteritidis found in Southern Brazil indicates the need for the prudent drugs uses to diminish the development and spread of antimicrobial resistance.

High prevalence of multiple resistance to antibiotics in Salmonella serovars isolated from a poultry slaughterhouse in Spain

Salmonellosis is a major foodborne infection in Spain, and strains that are resistant to a great variety of antibiotics have become a major public health concern. The aim of this study was to determine the level of antibiotic resistance in 133 Salmonella isolates obtained from a poultry slaughterhouse in Zaragoza (NE Spain). Antimicrobial resistance testing was performed by disk diffusion method using 19 antibiotics. Results were interpreted following the NCCLS criteria. Overall, the highest percentage of resistance was found to the following antimicrobial agents: sulfadiazine (96.2%), neomycin (53.4%), tetracycline (21.8%), and streptomycin (11.3%). All isolates were found to be resistant to one or more of the antibiotics tested. Multiple resistance was observed in 87 strains (65.4%). We found 23 different patterns of resistance in Salmonella Enteritidis. Resistance to sulfadiazine was the most common single resistance. The most frequent patterns of multiresistant strains were neomycin+sulfadiazine and neomycin+tetracycline+sulfadiazine. S. 4,5,12:b: showed the highest percentages of resistance to the tested drugs, with five different resistance patterns found. Ampicillin+chloramphenicol+streptomycin+sulphonamides+tetracycline (ACSSuT) resistance pattern, commonly associated with S. Typhimurium DT 104, was not detected in strains of the same phage type from broilers. The appearance of substantial multiresistance in foodborne Salmonella isolates suggests the need for more prudent use of antibiotics by farmers, veterinarians, and physicians.

Analysis of integrons in human isolates ofSalmonella entericaserovar typhimurium isolated in the Slovak Republic

About 110 sporadic, epidemiologically unrelated Salmonella enterica serovar typhimurium strains isolated in the Slovak Republic were analyzed for the presence of integrons. Of these 110 examined strains, 47 were of definitive phage type DT104 and 63 were strains of various phage type, RDNC and untypeable, designated here as non-DT104 strains. All isolates were also tested for antimicrobial resistance to 10 antibiotics as well as for the presence of virulence plasmid. Of 63 non-DT104 strains, 15 isolates were multiple-resistant, independently from phage type, other strains were resistant to one, two or three drugs. Resistance to ampicillin, streptomycin, tetracycline and sulfisoxazole was most frequently observed. Among the DT104 isolates up 65.9% exhibited characteristic pentaresistance--ACSSuT phenotype. The integron content was studied in PCR experiments using a 5'-CS/3'-CS primer pair. Fourteen non-DT104 strains, independently from phage type, were found to carry integrons with amplicons 650-1900 bp in size. Thirty-six DT104 strains contained integrons of 1000 and 1200 bp and 31 of they exhibited the ACSSuT phenotype. No integron was found in 10 DT104 strains, which included strains mostly resistant only to streptomycin, tetracycline and sulfisoxazole. The majority of non-DT104 strains did not possess any integrons. Our findings show the widespread existence of both resistant and multiple-resistant epidemiologically unrelated Salmonella typhimurium strains and suggest that integrons contribute to this antimicrobial resistance. The presence of 90-kb virulence plasmid in the 54 non-DT104 and in the all DT104 strains was found.

Salmonella enterica subsp. enterica serovar Enteritidis harbours ColE1, ColE2, and rolling-circle-like replicating plasmids

Using DNA hybridization, at least three distinct groups of low molecular mass plasmids were identified in Salmonella enterica subsp. enterica serovar Enteritidis. After sequencing representative plasmids from each group, we concluded that they belonged to ColE1, ColE2, and rolling-circle-like replicating plasmids. Plasmid pK (4245 bp) is a representative of widely distributed ColE1 plasmids. Plasmid pP (4301 bp) is homologous to ColE2 plasmids and was present predominantly in single-stranded DNA form. The smallest plasmids pJ (2096 bp) and pB (1983 bp) were classified as rolling-circle-like replicating plasmids. Both encoded only a single protein essential for their own replication, and they must have existed in an unusual molecular structure, as (i) they were capable of hybridization without denaturation, (ii) their DNA could be linearized with S1 nuclease, and (iii) even after such treatment, the ability to hybridize without denaturation did not disappear.

Incidence of Salmonella from poultry products and their susceptibility to antimicrobial agents

The incidence of Salmonella in 60 samples of poultry products of national origin available for consumers obtained from two local butcher shops and one canteen of the city of Porto and the susceptibility to antimicrobial agents allowed for human or animal therapy were evaluated. The results show that poultry samples are frequently contaminated with Salmonella (60%), belonging to 10 different serotypes. Salmonella enteritidis and S. hadar were the most prevalent serotypes. In addition, a high number (75%) of the Salmonella isolates was resistant to one or more antimicrobial agents and eight different resistance profiles were recorded. Resistance to nalidixic acid and enrofloxacin was demonstrated for 50% of the isolates and the occurrence of resistant and multiresistant S. enteritidis isolates were less frequent than for S. hadar. This study suggests a high incidence of Salmonella on Portuguese poultry products and shows that they could be a potential vehicle of resistant Salmonella foodborne infections.

Diversity in antimicrobial resistance and other characteristics among Salmonella typhimurium DT104 isolates

Multiresistant Salmonella enterica subspecies enterica serovar Typhimurium definitive type 104 (S. Typhimurium DT104 or DT104) bacteria are important pathogens in animals and humans. DT104 isolates are often called pentaresistant strains that spread clonally. The purpose of this study was to determine phenotypic, genotypic, and epidemiologic characteristics of 175 S. Typhimurium DT104 strains isolated from food-producing animals in Canada. More than 90% of the isolates were resistant to ampicillin (Amp), chloramphenicol (Chl), florfenicol (Flo), sulfisoxazole (Sul), and tetracycline (Tet), 53% of the isolates were additionally resistant to spectinomycin (Spc) and streptomycin (Str), and 28% to kanamycin (Kan) and neomycin (Neo). Sixty-one percent of the strains harbored a single 60-MDa plasmid, 21% contained 60- and 2.0-MDa plasmids, and 4% had 60, 4.6- and 2.0-MDa plasmids. Resistance to Kan and Neo was encoded by the aminoglycoside aphA-1 gene on 2.0-MDa plasmids, whereas resistance to trimethoprim (Tmp) and Sul was encoded by the dhfrIb gene on 4.6-MDa plasmids. Polymerase chain reactions (PCR) showed the presence of integrons with the ant (3")-Ia aminoglycoside adenyltransferase and the bla(PSE-1) beta-lactamase gene cassettes, and the presence of the flost gene in all but one strain resistant to Spc and Str, Amp, and Chl and Flo, respectively. DT104 isolates from cattle at six feedlots represented a separate clone; they were sensitive to Str and Spc and lacked the ant (3")-Ia gene. Pulsed-field gel electrophoresis (PFGE) using Bln I, Spe I, and Xba I resulted in 15, 12, and 8 PFGE patterns, respectively. In summary, we observed considerable diversity in phenotypic, genotypic, and epidemiological characteristics among the DT104 isolates.

Screening of Salmonella isolates from a turkey production facility for antibiotic resistance

An ecological survey was conducted from April 1997 to June 1999 on four turkey flocks (F1 to F4). Turkey cecal contents, litter, waterers, feed, feeders, and environmental swabs were analyzed. Presence of Salmonella was determined using conventional microbiological screening techniques and confirmed by serology. Positive isolates were serotyped and screened for antibiotic resistance. From a total of 69 Salmonella isolates 25% were resistant to one or more antibiotics including gentamicin (G), spectinomycin (SP), streptomycin (S), tetracycline (T), tobramycin (TO), and trimethoprim/sulfamethoxazole. Isolates included 45 S. heidelberg, 13 S. senftenberg, 7 S. muenster, 2 S. anatum, and 2 S. worthington. Resistance to antibiotic(s) was highest among waterer isolates (55%) followed by environmental swabs (43%), feeder content samples (33%), turkey cecal contents (26%), and litter samples (5%). Frequencies of antibiotic-resistant Salmonella in F1, F2, and F4 were 27, 13, and 40%, respectively. Salmonella was undetected in F3. In F1, S. heidelberg from cecal content and waterer samples was resistant to G, SP, S, and T, whereas S. anatum from waterer samples was resistant to T and S. In F2, S. worthington from litter and feeder content samples was resistant to T, and in F4, S. muenster from environmental swabs was resistant to TO, S, SP, and G. Identifying preharvest sources and characterizing serotype and antibiotic-resistance profile can assist poultry producers and integrators in tracking movement of Salmonella on turkey farms.

Antimicrobial-resistant Salmonella enterica serovars isolated from chickens in Spain

In order to analyze the antibiotic resistance of Salmonella enterica serovars, a total of 112 Salmonella strains were tested (54 S. enteritidis, 32 S. typhimurium, 11 S. heidelberg, 7 S. infantis, 4 S. virchow and 4 S. hadar). The bacteria were isolated from 691 samples of frozen and fresh chicken meat. Identification of microorganisms and antimicrobial sensitivity testing were undertaken by means of the automated MicroScan AutoScan 4 method (Baxter in Spain). 45.5% of 112 strains tested were susceptible to all antibiotics. The highest percentage of resistance was found to: chloramphenicol (44.6%), ampicillin (34.8%) and tetracycline (33.9%). Multiple resistance was observed in 49 strains (43.7%), whereas single resistance was seen in 12 isolates (10.7%). We found 12 different patterns of resistance in Salmonella enterica serovar enteriditis. Resistance to chloramphenicol was the most common single resistance. The most frequent patterns of multiresistant strains were ampicillin + amoxicillin/clavulanate + cefazolin + imipenem and chloramphenicol + impipenem. In this serotype, 49 isolates belonged to phagetype 4. Salmonella typhimurium showed the highest percentages of resistance to the tested drugs, with six different resistance patterns found. 25 strains out of 32 S. typhimurium isolates belonged to phagotype 120 and 13 of these showed the same resistance pattern: chloramphenicol + tetracycline + ampicillin. The high incidence of antibiotic resistant salmonellae found in chickens in our study suggests the need for public health interventions to decrease selective pressure on bacterial strains by antimicrobial agents.

Trends in antimicrobial resistance of Salmonella isolated from animals, foods of animal origin, and the environment of animal production in Canada, 1994-1997

The purpose of our study was to determine the occurrence, magnitude, trends, and relationships regarding antibiotic resistance of Salmonella isolated from animals, animal food products, and the environment of animals. We examined 621 strains of 67 different serovars isolated in 1994, 721 strains of 75 different serovars isolated in 1995, 1,219 strains of 83 different serovars isolated in 1996, and 1,336 Salmonella strains of 92 different serovars isolated in 1997, for resistance to 17 antibiotics at one to three different concentrations with the agar dilution method. The overall resistance magnitude regressed from 9.2% in 1994 to 8.1% in 1997. Resistance to streptomycin (30.4% of 3,897 isolates), tetracycline (27.3%), and sulfisoxazole (23.7%) was highest. Resistance to streptomycin, tetracycline, kanamycin, and gentamicin declined during the 4-year period. Notable increases in resistance to ampicillin, chloramphenicol, and neomycin occurred during the 1994-1997 years. None of the isolates was resistant to amikacin. None of the isolates was resistant to ciprofloxacin at 1, 2, and 4 microg/ml. Salmonella bredeney isolates from turkeys showed a decreased sensitivity to ciprofloxacin and were resistant at the low level of 0.125 microg/ml, but none of these isolates was resistant at 1 microg/ml. Resistance to nalidixic acid correlated significantly with decreased sensitivity to ciprofloxacin; 122 of 127 (96%) isolates resistant to nalidixic acid at 32 microg/ml were resistant to ciprofloxacin at 0.125 microg/ml but sensitive at 1 microg/ml. Resistance to S. typhimurium to each of the seven antibiotics ampicillin, chloramphenicol, kanamycin, neomycin, streptomycin, sulfisoxazole, and tetracycline increased persistently during each of the years 1994-1997, but none of the S. typhimurium isolates showed decreased sensitivity to ciprofloxacin. Clinical isolates of Salmonella were twice as frequently resistant to the antimicrobials in the test panel than isolates obtained during surveys. Salmonella isolates from turkeys were more frequently resistant than isolates from pigs, cattle, and chickens.

Virulence in the chick model and stress tolerance of Salmonella enterica serovar Orion var. 15+

Three Salmonella enterica serovar Orion var. 15+ isolates of distinct provenance were tested for survival in various stress assays. All were less able to survive desiccation than a virulent S. Enteritidis strain, with levels of survival similar to a rpoS mutant of the S. Enteritidis strain, whereas one isolate (F3720) was significantly more acid tolerant. The S. Orion var. 15+ isolates were motile by flagellae and elaborated type-1 and curli-like fimbriae; surface organelles that are considered virulence determinants in Salmonella pathogenesis. Each adhered and invaded HEp-2 tissue culture cells with similar proficiency to the S. Enteritidis control but were significantly less virulent than S. Enteritidis in the one-day-old and seven-day-old chick model. Given an oral dose of 1 x 10(3) cfu to one-day-old chicken, S. Orion var. 15+ isolates colonised 25% of liver and spleens examined at 24 h whereas S. Enteritidis colonised 100% of organs by the same with the same dose. Given an oral dose of 1 x 10(7) cfu at seven-day old, S. Orion var. 15+ failed to colonise livers and spleens in any bird examined at 24 h whereas S. Enteritidis colonised 50% of organs by the same with the same dose. Based on the number of internal organs colonised, one of the three S. Orion var. 15+ isolates tested (strain F3720) was significantly more invasive than the other two (B1 and B7). Also, strain F3720 was shed less than either B1 or B7 supporting the concept that there may be an inverse relationship between the ability to colonise deep tissues and to persist in the gut. These data are discussed in the light that S. Orion var. 15+ is associated with sporadic outbreaks of human infection rather than epidemics.

Characterization of Salmonella isolates from beef cattle, broiler chickens and human sources on Prince Edward Island

Non-typhoid Salmonella serovars remain a potential threat to human health, and beef cattle and broiler chickens are possible sources of these organisms on Prince Edward Island (PEI). In this study, the ceca of beef cattle belonging to fasted and non-fasted groups, and broiler chickens were examined for Salmonella at the time of slaughter. The characteristics of the isolates, including antimicrobial resistance patterns and virulence genes, were studied along with the isolates obtained from cases of human salmonellosis on PEI during the study period (1996-97). The prevalence of Salmonella in beef cattle was 4.6% (11/240). The rate was significantly higher in fasted cattle (7.46%), than in non-fasted cattle (0.94%). The prevalence rate in chickens was 32.5% (39/120). In beef cattle, Salmonella typhimurium phage type (PT) or definitive type (DT) 104 which was resistant to ampicillin, chloramphenicol, streptomycin, sulfisoxazole and tetracycline, was the most predominant type (64%). In chickens, S. heidelberg, with resistance to gentamicin, streptomycin and sulfisoxazole, predominated. Of 26 isolates from humans, the most common serovar was S. typhimurium, including a multidrug-resistant strain of DT104. Examination by PCR revealed presence of the virulence gene invA in all serovars, and the spvC gene in all S. typhimurium isolates, of both beef cattle and human origin. Among the other serovars the latter gene was found in 7 human isolates, but in none of the chicken or beef isolates. All but 3 of the spvC-positive isolates possessed a 90 kilobasepair (kbp) plasmid suggesting that the 3 isolates had the spvC gene on their chromosome. These findings were confirmed by plasmid DNA isolation using 3 different protocols and by sequence analysis of the spvC-PCR product.

Characterization of Salmonella enterica serovar typhimurium DT104 isolated from Denmark and comparison with isolates from Europe and the United States

A total of 136 isolates of Salmonella enterica serovar Typhimurium DT104 from Denmark (n = 93), Germany (n = 10), Italy (n = 4), Spain (n = 5), and the United Kingdom (n = 9) were characterized by antimicrobial resistance analysis, plasmid profiling, pulsed-field gel electrophoresis (PFGE) with the restriction enzymes XbaI and BlnI, and analysis for the presence of integrons and antibiotic resistance genes. The isolates from Denmark were from nine pig herds, while the isolates from other countries were both of animal and of human origin. All but 10 isolates were resistant to ampicillin, chloramphenicol, spectinomycin, streptomycin, sulfonamides, and tetracycline. Five isolates from the United Kingdom and Spain were sensitive to all antibiotics examined, whereas four isolates from the United Kingdom and the United States were also resistant to one or more of the antibiotics, namely, gentamicin, neomycin, and trimethoprim. All but two strains had the same PFGE profiles when the XbaI restriction enzyme was used, while seven different profiles were observed when the BlnI restriction enzyme was used. Different dominating BlnI types were observed among European isolates compared with the types observed among those from the United States. All the isolates harbored common 95-kb plasmids either alone or in combination with smaller plasmids, and a total of 11 different plasmid profiles were observed. Furthermore, all but one of the multidrug-resistant isolates contained two integrons, ant (3")-Ia and pse-1. Sensitive isolates contained no integrons, and isolates that were resistant to spectinomycin, streptomycin, and sulfonamides had only one integron containing ant (3")-Ia. When restriction enzyme BlnI was used, the 14 isolates from one of the nine herds in Denmark showed unique profiles, whereas isolates from the remaining herds were homogeneous. Among isolates from seven of nine herds, the same plasmid profile (95 kb) was observed, but isolates from two herds had different profiles. Thus, either PFGE (with BlnI) or plasmid profiling could distinguish isolates from three of nine pig herds in Denmark. The epidemiological markers (antimicrobial susceptibility testing, plasmid profiling, and PFGE) applied demonstrated high in vivo stability in the Danish herds. This may indicate that some different strains of multidrug-resistant S. enterica serovar Typhimurium DT104 have been introduced into Danish food animal herds. The presence of isolates from six different countries with similar profiles by PFGE with XbaI and highly homogeneous profiles by PFGE with BlnI indicate that multidrug-resistant S. enterica serovar Typhimurium DT104 has probably been spread clonally in these countries. However, some minor variation could be observed by using plasmid profiling and profiling by PFGE with BlnI. Thus, a more sensitive technique for subtyping of strains of DT104 and a broader investigation may help in elucidating the epidemiological spread of DT104 in different parts of the world.

Resistance to antimicrobial agents used for animal therapy in pathogenic-, zoonotic- and indicator bacteria isolated from different food animals in Denmark: a baseline study for the Danish Integrated Antimicrobial Resistance Monitoring Programme (DANMAP)

This study describes the establishment and first results of a continuous surveillance system of antimicrobial resistance among bacteria isolated from pigs, cattle and broilers in Denmark. The three categories of bacteria tested were: 1) indicator bacteria (Escherichia coli, Enterococcus faecalis, Enterococcus faecium), 2) zoonotic bacteria (Campylobacter coli/jejuni, Salmonella enterica, Yersinia enterocolitica), and 3) animal pathogens (E. coli, Staphylococcus aureus, coagulase-negative staphylococci (CNS), Staphylococcus hyicus, Actinobacillus pleuropneumoniae). A total of 3304 bacterial isolates collected from October 1995 through December 1996 were tested for susceptibility to all major classes of antimicrobial agents used for therapy in Denmark. Bacterial species intrinsically resistant to an antimicrobial were not tested towards that antimicrobial. Acquired resistance to all antimicrobials was found. The occurrence of resistance varied by animal origin and bacterial species. In general, resistance was observed more frequently among isolates from pigs than from cattle and broilers. The association between the occurrence of resistance and the consumption of the antimicrobial is discussed, as is the occurrence of resistance in other countries. The results of this study show the present level of resistance to antimicrobial agents among a number of bacterial species isolated from food animals in Denmark. Thus, the baseline for comparison with future prospective studies has been established, enabling the determination of trends over time.