The incidence of antimicrobial-resistant Salmonella spp on freshly processed poultry from US Midwestern processing plants

Assessing antimicrobial resistance occurrence in the Portuguese food system: Poultry, pigs and derived food, 2014-2018

Antimicrobial resistance (AMR) spread in the food system is a major threat to public and animal health. We describe AMR trends in zoonotic bacteria and identify risk factors associated with AMR occurrence in animals and derived food in Portugal. Data from the Portuguese AMR surveillance programme on food-producing animals, 2014-2018, were used. AMR frequencies were calculated for Escherichia coli, Campylobacter and Salmonella in broilers, turkeys, pig populations and their derived food products. AMR-associated factors were studied for Salmonella isolates: population, sampling stage (farm, slaughterhouse and processing plant), sample type (environmental, carcase and food), sampler (HACCP, industry, official and official and industry), sample context (control and eradication programmes and monitoring), year (2014-2018) and season. Logistic regression was applied to estimate crude odds ratio and adjusted odds ratio (aOR) with 95% confidence intervals (95% CI). The final models were obtained using a backward stepwise method. This study included 2,157 Escherichia coli, 561 Campylobacter and 1,071 Salmonella isolates. The highest prevalence estimates amongst tested antimicrobials for each bacterial species in 2014-2018 had the following ranges: (i) (fluoro)quinolones: E. coli: 84%-93%, Campylobacter: 94%-98%; (ii) tetracyclines: E. coli: 68%-91%, Campylobacter: 87%-91%, Salmonella: 72%; (iii) penicillins: E. coli: 82%-100%; (iv) sulphonamides: E. coli: 68%-82%. Compared with the reference categories for host (broiler), year (2014), season (winter) and sampler (HACCP own checks), resistance to at least one antimicrobial in Salmonella was significantly less likely in laying hens (aOR 0.28; 95% CI: 0.18-0.42), 2016 (aOR 0.56; 95% CI: 0.33-0.93), 2017 (aOR 0.29; 95% CI: 0.17-0.51) and 2018 (aOR 0.35; 95% CI: 0.20-0.61), autumn (aOR 0.63; 95% CI: 0.40-0.97) and more likely to occur in broiler products (aOR 5.14; 95% CI: 2.61-10.54), pork products (aOR 6.84; 95% CI: 3.74-12.98) and official and industry combined sampling (aOR 2.16; 95% CI: 1.06-4.47). This study reveals a high prevalence of Salmonella resistance, especially during the summer and in post-farm stages of the Portuguese food system to nearly all antimicrobials and in the summer in farms to (fluoro)quinolones. Measures to tackle resistance are required.

Prevalence and antimicrobial resistance phenotypes of Salmonella species recovered at various stages of broiler operations in Hathazari, Bangladesh

Background and Aim: Dissemination of multidrug-resistant (MDR) Salmonella through food chains has serious health implications, with higher rates of morbidity and mortality. Broiler meat remains a major reservoir of Salmonella contamination. The lack of proper hygiene in local broiler operations has, therefore, prompted this research into the assessment of Salmonella contamination in local shops and associated antimicrobial resistance (AMR) phenotypes. Materials and Methods: A total of 55 broiler samples including skin, meat, and swab samples from chopping and dressing sites were included in the study. The samples were collected from broiler shops in Hathazari, Bangladesh, and screened for the presence of Salmonella strains using culture-based methods. The isolates were biochemically characterized and further tested for AMR to eight common antibiotics using the disk diffusion technique. Results: Salmonella contaminations were identified in 29% (16/55) of the broiler samples. Swab samples collected from the chopping sites appeared to be contaminated in higher proportions (33%) than those collected from the dressing areas (25%). On the other hand, the skin samples (50%) were detected with a higher percentage of contamination than the meat samples (25%). All Salmonella isolates showed resistance toward at least one of the eight antibiotics used. Although none of the isolates was resistant to all antibiotics, 18.75% showed resistance to a maximum of seven antibiotics. Resistance to nalidixic acid was most prevalent (87.5%), followed by sulfamethoxazole-trimethoprim (81.25%), erythromycin (81.25%), tetracycline (75%), streptomycin (56.25%), ampicillin-clavulanic acid (50%), chloramphenicol (43.75%), and cefotaxime (18.75%). The resistance patterns of the isolates were found to be highly diverse. The most frequently observed pattern was the following: Ampicillin-clavulanic acid-sulfamethoxazole-trimethoprim-nalidixic acid-tetracycline-chloramphenicol-streptomycin-erythromycin. Conclusion: The relatively high prevalence of MDR strains in the samples underlies an urgent need for surveillance and control measures concerning hygiene and antibiotic use in local broiler operations.

Salmonella in Chicken Meat: Consumption, Outbreaks, Characteristics, Current Control Methods and the Potential of Bacteriophage Use

The control of Salmonella in chicken processing plants is an ongoing challenge for many factories around the globe, especially with the increasing demand for poultry escalating processing throughputs. Foodborne outbreaks due to Salmonella still pose a prominent risk to public health. As chicken meat is a good reservoir for Salmonella, it is important for chicken processing plants to continuously optimize methods to reduce the incidence of Salmonella on their products. Current methods include the use of chemical antimicrobials such as chlorine-containing compounds and organic acids. However, these current methods are decreasing in popularity due to the rising rate of Salmonella resistance, coupled with the challenge of preserving the sensory properties of the meat, along with the increasing stringency of antimicrobial use. Bacteriophages are becoming more appealing to integrate into the large-scale hurdle concept. A few factors need to be considered for successful implementation, such as legislation, and application volumes and concentrations. Overall, bacteriophages show great potential because of their host specificity, guaranteeing an alternative outcome to the selective pressure for resistant traits placed by chemicals on whole microbial communities.

Diversity, Antibiotic Resistance, and Biofilm-Forming Ability of Enterobacteria Isolated from Red Meat and Poultry Preparations

A total of 44 samples of beef, pork, and poultry preparations were tested. Average counts (log cfu/g) of enterobacteria were 1.99 ± 0.99 (beef preparations), 1.96 ± 1.44 (pork), 2.09 ± 0.92 (chicken), and 2.17 ± 1.06 (turkey) (p > 0.05). Two hundred enterobacterial strains were identified and 13 genera (21 species) were distinguished, including species that are a significant cause of infection. The most common genera were Escherichia (32.5% of strains), Serratia (17.0%), Hafnia (12.5%), and Salmonella (12.0%). Isolates were screened by disc diffusion for susceptibility to 15 antibiotics. A total of 126 strains (63% of the isolates) were multirresistant (having resistance to two or more antibiotics), 46 (23%) were resistant to one antibiotic, and 28 (14%) were sensitive to all antibiotics. The average number of resistances per strain was 2.53 ± 2.05. A higher (p < 0.05) average number of resistances was observed in strains from turkey (3.14 ± 2.55) than in strains from beef (2.15 ± 1.22), pork (2.16 ± 1.39), or chicken (2.44 ± 2.22). At least 50% of strains showed resistance or reduced susceptibility to ampicillin, cefotaxime, ceftazidime, or streptomycin, considered to be "critically important" antimicrobial agents in human medicine. Seventy-nine strains (39.5%), 60 strains (30.0%), and 46 strains (23.0%) were weak, moderate, and strong biofilm producers (crystal violet assay), respectively. This investigation provides evidence that bacteria from red meat and poultry preparations pose major potential risk to consumers.

Microbial load and antibiotic resistance in raw beef preparations from northwest Spain

Beef preparations (meatballs, minced meat, hamburgers, white sausages, and red sausages) from northwest Spain were tested. Microbial counts ranged from 0.70 ± 0.00 log10 cfu/g (enterococci) to 9.57 ± 0.37 log10 cfu/g (psychrotrophs). In 73.3% of cases, total aerobic counts were higher than the microbiological limits set for the end of the manufacturing process in the European Union (EU Regulation 2073/2005). Forty Escherichia coli isolates were tested against thirteen clinically important antibiotics (disk diffusion method; CLSI). Three of the strains (7.5%) were susceptible to all the antibiotics, four (10.0%) showed resistance or reduced susceptibility to one antibiotic, and 33 (82.5%) were multiresistant (with resistance or reduced susceptibility to between two and eight antibiotics), with an average of 1.85 resistances per strain. The highest rates of resistance were observed for two antimicrobials widely used on cattle farms (cefalotin and tetracycline). The findings in this research emphasize the need to correctly handle beef preparations with the aim of reducing risks to consumers.

Microbial Load and Antibiotic Resistance Patterns of Escherichia coli and Enterococcus faecalis Isolates from the Meat of Wild and Domestic Pigeons

An expansion in the consumption of pigeon meat has occurred in recent years. However, little is known about microbial load and antibiotic resistance of this foodstuff. The hygiene status and the antibiotic resistance patterns (disc diffusion; Clinical and Laboratory Standards Institute, CLSI) of Escherichia coli and Enterococcus faecalis isolates from wild and domestic pigeon carcasses were investigated. Average microbial loads (log10 cfu/cm2) ranged from 1.40 ± 1.17 (fecal coliforms) to 3.68 ± 1.40 (psychrotrophs). The highest (p < 0.05) microbial loads were observed in domestic pigeons. No substantial differences were found between isolates from domestic and wild pigeons with regard to the prevalence of antibiotic resistance. Of the E. coli strains, 20.00% were susceptible, 25.00% showed resistance or reduced susceptibility to one antimicrobial and 55.00% were multi-resistant. Among the E. faecalis isolates, 2.22% were susceptible and 97.78% were multi-resistant. The greatest prevalence of resistance or reduced susceptibility among E. coli was observed for amoxicillin-clavulanic acid (20.00% strains), ampicillin (26.67%), streptomycin (55.00%) and tobramycin (20.00%). The prevalence of resistance or reduced susceptibility among E. faecalis ranged from 31.11% (trimethoprim/sulfamethoxazole) to 97.78% (erythromycin). Meat from pigeons is a major reservoir of antibiotic-resistant bacteria. The need for the correct handling of this foodstuff in order to reduce risks to consumers is underlined.

Comparison of prevalence, phenotype, and antimicrobial resistance of Salmonella serovars isolated from turkeys in Taiwan

Salmonella spp. is a foodborne pathogen that causes zoonotic disease worldwide. The aim of this study was to investigate the prevalence of antimicrobial resistance of Salmonella isolated from turkey farms in Taiwan. During the past 2 yr, 243 strains of Salmonella were isolated from 2,040 samples (11.9%) from turkey farms, including 32.5% (52/160) from the intestines of 12-day-old turkey poults, 14.2% (119/840) from feces collected from the turkey growing periods, and 6.9% (72/1,040) from finishing periods. S. Albany (35.0%, 85/243), S. Schwarzengrund (23.0%, 56/243), and S. Hadar (19.3%, 47/243) were the most common serovars on turkey farms. For these strains, a high frequency of resistance was observed against florfenicol (97.5%), oxytetracycline (89.3%), doxycycline (78.6%), colistin (77.8%), ampicillin (75.7%), amoxicillin (75.3%), trimethoprim-sulfamethoxazole (73.7%), chloramphenicol (69.1%), and nalidixic acid (67.9%). floR (63.8%), tet (A) (60.5%), blaPSE (57.6%), blaTEM (42.0%), blaCTX-M (34.2%), cmlA (34.2%), and tet (D) (29.2%) were the most common resistance genes found in this study. The int1 gene was identified in 72.4% (176/243) of Salmonella isolates in which the conserved region 3' of class 1 integrons also was amplified, whereas none had the int2 gene. This study demonstrates that imported and fattening turkeys could be a reservoir for Salmonella isolates resistant to multiple antimicrobials. These results also reinforce the need to develop strategies and implement specific control procedures to reduce the development of antimicrobial resistance.

Microbial separation from a complex matrix by a hand-held microfluidic device

Through a simple chemical activation of biomolecules present in the outer structures of microbial cells, microorganisms can be rapidly isolated on gold-coated surfaces in a microfluidic device with over 99% capture efficiency. Bacterial and fungal cells can be selectively captured, concentrated and retrieved for further analysis.

An Attenuated Salmonella enterica Serovar Typhimurium Strain and Galacto-Oligosaccharides Accelerate Clearance of Salmonella Infections in Poultry through Modifications to the Gut Microbiome

Salmonella is estimated to cause one million foodborne illnesses in the United States every year. Salmonella-contaminated poultry products are one of the major sources of salmonellosis. Given the critical role of the gut microbiota in Salmonella transmission, a manipulation of the chicken intestinal microenvironment could prevent animal colonization by the pathogen. In Salmonella, the global regulator gene fnr (fumarate nitrate reduction) regulates anaerobic metabolism and is essential for adapting to the gut environment. This study tested the hypothesis that an attenuated Fnr mutant of Salmonella enterica serovar Typhimurium (attST) or prebiotic galacto-oligosaccharides (GOS) could improve resistance to wild-type Salmonella via modifications to the structure of the chicken gut microbiome. Intestinal samples from a total of 273 animals were collected weekly for 9 weeks to evaluate the impact of attST or prebiotic supplementation on microbial species of the cecum, duodenum, jejunum, and ileum. We next analyzed changes to the gut microbiome induced by challenging the animals with a wild-type Salmonella serovar 4,[5],12:r:- (Nal^r) strain and determined the clearance rate of the virulent strain in the treated and control groups. Both GOS and the attenuated Salmonella strain modified the gut microbiome but elicited alterations of different taxonomic groups. The attST produced significant increases of Alistipes and undefined Lactobacillus, while GOS increased Christensenellaceae and Lactobacillus reuteri The microbiome structural changes induced by both treatments resulted in a faster clearance after a Salmonella challenge.IMPORTANCE With an average annual incidence of 13.1 cases/100,000 individuals, salmonellosis has been deemed a nationally notifiable condition in the United States by the Centers for Disease Control and Prevention (CDC). Earlier studies demonstrated that Salmonella is transmitted by a subset of animals (supershedders). The supershedder phenotype can be induced by antibiotics, ascertaining an essential role for the gut microbiota in Salmonella transmission. Consequently, modulation of the gut microbiota and modification of the intestinal microenvironment could assist in preventing animal colonization by the pathogen. Our study demonstrated that a manipulation of the chicken gut microbiota by the administration of an attenuated Salmonella strain or prebiotic galacto-oligosaccharides (GOS) can promote resistance to Salmonella colonization via increases of beneficial microorganisms that translate into a less hospitable gut microenvironment.

Biofilm Formation, Antimicrobial Resistance, and Sanitizer Tolerance of Salmonella enterica Strains Isolated from Beef Trim

In the beef industry, product contamination by Salmonella enterica is a serious public health concern, which may result in human infection and cause significant financial loss due to product recalls. Currently, the precise mechanism and pathogen source responsible for Salmonella contamination in commercial establishments are not well understood. We characterized 89 S. enterica strains isolated from beef trim with respect to their biofilm-forming ability, antimicrobial resistance, and biofilm cell survival/recovery growth after sanitizer exposure. A total of 28 Salmonella serovars was identified within these strains. The most common serovars identified were Anatum, Dublin, Montevideo, and Typhimurium, with these accounting for nearly half of the total strains. The vast majority (86%) of the strains was able to develop strong biofilms, and the biofilm-forming ability was highly strain dependent and related to cell surface expression of extracellular polymeric structures. These strains also demonstrated strong tolerance to quaternary ammonium chloride (QAC) and chlorine dioxide (ClO₂), but were more sensitive to chlorine treatment. Sanitizer tolerance and bacterial postsanitization recovery growth were closely associated with strains' biofilm-forming ability. Thirty percent of the examined strains were found resistant to multiple antimicrobial agents and the resistance phenotypes were serovar associated, but not related to strains' biofilm-forming ability. Pulsed-field gel electrophoresis analysis tended to group strains by serovar rather than by biofilm-forming ability. Collectively, these data indicate that the strong biofilm formers of certain S. enterica strains/serovars possess significant potential for causing meat product contamination in meat processing environment.

Population dynamics and antimicrobial resistance of the most prevalent poultry-associated Salmonella serotypes

Salmonella spp. is the most predominant bacterial cause of foodborne gastroenteritis in humans. Due to the risk of human infection associated with poultry products and the prevalence of antimicrobial resistance, Salmonella also poses a significant challenge to commercial poultry production. During the last decade (2002 to 2012), the 12 most prevalent poultry-associated Salmonella serotypes (MPPSTs) were frequently and consistently isolated from poultry products in the United States. These MPPSTs and their percent prevalence in poultry products include Kentucky (4%), Enteritidis (2%) Heidelberg (2%), Typhimurium (2%), S. I 4,[5],12:i:- (0.31%), Montevideo (0.20%), Infantis (0.16%) Schwarzengrund (0.15%), Hadar (0.15%), Mbandaka (0.13%), Thompson (0.12%), and Senftenberg (0.04%). All MPPSTs except Kentucky are among the top 30 clinically significant serotypes that cause human illnesses in the United States. However with the exception of a few widely studied serotypes such as S. Enteritidis and Typhimurium, the ecology and epidemiology of the majority of MPPSTs still remain poorly investigated. Published data from the United States suggests that MPPSTs such as Heidelberg, Typhimurium, Kentucky, and Sentfenberg are more likely to be multi-drug resistant (MDR, ≥3 antimicobial classes) whereas Enteritidis, Montevideo, Schwarzengrund, Hadar, Infantis, Thompson, and Mbandaka are generally pan-susceptible or display resistance to fewer antimicobials. In contrast, the majority of MPPSTs isolated globally have been reported to display MDR phenotype. There also appears to be an international spread of a few MDR serotypes including Kentucky, Schwarzengrund, Hadar, Thomson, Sentfenberg, and Enteritidis, which may pose significant challenges to the public health. The current knowledge gaps on the ecology, epidemiology, and antimicrobial resistance of MPPSTs are discussed.

Pathogens of Food Animals: Sources, Characteristics, Human Risk, and Methods of Detection

Pathogens associated with food production (livestock) animals come in many forms causing a multitude of disease for humans. For the purpose of this review, these infectious agents can be divided into three broad categories: those that are associated with bacterial disease, those that are associated with viruses, and those that are parasitic in nature. The goal of this chapter is to provide the reader with an overview of the most common pathogens that cause disease in humans through exposure via the food chain and the consequence of this exposure as well as risk and detection methods. We have also included a collection of unusual pathogens that although rare have still caused disease, and their recognition is warranted in light of emerging and reemerging diseases. These provide the reader an understanding of where the next big outbreak could occur. The influence of the global economy, the movement of people, and food makes understanding production animal-associated disease paramount to being able to address new diseases as they arise.

Prevalence and molecular characterization of Salmonella enterica isolates throughout an integrated broiler supply chain in China

A total of 1145 samples were collected from chicken breeder farms, hatcheries, broiler farms, a slaughterhouse and retail refrigerated chicken stores in an integrated broiler supply chain in Guangdong Province, China, in 2013. One-hundred and two Salmonella enterica strains were isolated and subjected to serotyping, antimicrobial susceptibility testing, virulence profile determination and molecular subtyping by pulsed field gel electrophoresis (PFGE). The contamination rates in samples from breeder farms, hatcheries, broiler farms, the slaughterhouse and retail stores were 1·46%, 4·31%, 7·00%, 62·86% and 54·67%, respectively. The isolated strains of S. enterica belonged to 10 serotypes; most of them were S. Weltevreden (46·08%, 47/102) and S. Agona (18·63%, 19/102). Isolates were frequently resistant to streptomycin (38·2%), tetracycline (36·3%), sulfisoxazole (35·3%) and gentamicin (34·3%); 31·4% of isolates were multidrug resistant. The isolates were screened for 10 virulence factors. The Salmonella pathogenicity island genes avrA, ssaQ, mgtC, siiD, and sopB and the fimbrial gene bcfC were present in 100% of the strains. PFGE genotyping of the 102 S. enterica isolates yielded 24 PFGE types at an 85% similarity threshold. The PFGE patterns show that the genotypes of S. enterica in the production chain are very diverse, but some strains have 100% similarity in different parts of the production chain, which indicates that some S. enterica persist throughout the broiler supply chain.

SEROVARS AND ANTIMICROBIAL RESISTANCE OF Salmonella spp. ISOLATED FROM TURKEY AND BROILER CARCASSES IN SOUTHERN BRAZIL BETWEEN 2004 AND 2006

Salmonella spp. causes diseases in fowls, when species-specific serovars (Salmonella Pullorum and S.Gallinarum) are present in flocks, and public health problems, when non-typhoid serovars are isolated, as well as possible bacterial resistance induced by the preventive and therapeutic use of antimicrobials in animal production. This study describes the serovars and bacterial resistance of 280Salmonella spp. strains isolated from turkey and broiler carcasses in Southern Brazil between 2004 and 2006. SalmonellaEnteritidis was the most prevalent serovar (55.7%), followed by Heidelberg (5.0%), Agona (4.3%), Bredeney (3.9%), Hadar (3.2%), and Typhimurium (2.9%). Tennessee and S. Enterica subspecies enterica(O: 4.5) were isolated only in turkeys, and Hadar (18.6%) was the most prevalent serovar in this species. Antimicrobial susceptibility tests were performed in 178 isolates (43 from turkeys and 135 from broilers). All isolates were sensitive to amoxicillin + clavulanic acid, polymyxin B, ciprofloxacin, and norfloxacin, and were resistant to bacitracin and penicillin. Broiler carcass isolates showed resistance to nalidixic acid (48.9%), nitrofurantoin (34.3%), neomycin (9.6%), tetracycline (5.2%), and kanamycin (8.9%); and turkey carcass isolates were resistant to nalidixic acid (62.8%), tetracycline (34.9%), and neomycin (30.2%), with a significant difference in turkeys when compared to broiler carcass isolates. These results indicate the need for judicious use of antimicrobials in livestock production, given that the serovars identified are potential causes of food poisoning.

Molecular characterization of antibiotic resistant Salmonella Typhimurium and Salmonella Kentucky isolated from pre- and post-chill whole broilers carcasses

There is conflicting data regarding whether commercial chilling has any effect on persistence of Salmonella serovars, including antibiotic resistant variants, on chicken carcasses. A total of 309 Salmonella Typhimurium and Salmonella Kentucky isolates recovered from pre- and post-chill whole broiler carcasses were characterized for genetic relatedness using Pulsed Field Gel Electrophoresis (PFGE) and for the presence of virulence factors (invA, pagC, spvC) by PCR and for aerobactin and colicin production by bioassays. A subset of these isolates (n = 218) displaying resistance to either sulfisoxazole and/or ceftiofur [S. Typhimurium (n = 66) and S. Kentucky (n = 152)] were further tested for the presence of associated antibiotic resistance elements (class-I integrons and blaCMY genes) by PCR. All 145 ceftiofur resistant S. Kentucky and S. Typhimurium isolates possessed blaCMY genes. Class-I integrons were only detected in 6.1% (n = 4/66) of sulfisoxazole resistant S. Typhimurium isolates. The PFGE analysis revealed the presence of genetically diverse populations within the recovered isolates but clusters were generally concordant with serotypes and antimicrobial resistance profiles. At a 100% pattern similarity index, thirty-six percent of the undistinguishable S. Typhimurium and 22% of the undistinguishable S. Kentucky isolates were recovered from the same chilling step. All isolates possessed the invA and pagC genes, but only 1.4%possessed spvC. Irrespective of the chilling step, there was a significant difference (P < 0.05) in the production of aerobactin and colicin between S. Typhimurium and S. Kentucky isolates. Taken together, these results indicate that chilling impacted the recovery of particular Salmonella clonal groups but had no effect on the presence of class-I integrons, blaCMY genes, and tested virulence factors.

Control of Salmonella enterica Typhimurium in chicken breast meat by irradiation combined with modified atmosphere packaging

Salmonella is one of the leading causes of human foodborne illnesses originating from meat and poultry products. Cross-contamination of Salmonella from raw to cooked products continues to be problematic in the food industry. Therefore, new intervention strategies are needed for meat and poultry products. Vacuum or modified atmosphere packaging (MAP) are common packaging techniques used to extend the shelf life of meat products. Irradiation has been well established as an antibacterial treatment to reduce pathogens on meat and poultry. Combining irradiation with high-CO(2)+CO MAP was investigated in this study for improving the control of Salmonella enterica Typhimurium on chicken breast meat. The radiation sensitivities (D10-values) of this pathogen in chicken breast meat were found to be similar in vacuum and in high-CO(2)+CO MAP (0.55 ± 0.03 kGy and 0.54 ± 0.03 kGy, respectively). Irradiation at 1.5 kGy reduced the Salmonella population by an average of 3 log. Some Salmonella cells survived in both vacuum and high-CO(2) + CO MAP through 6 weeks of refrigerated storage following irradiation. This pathogen also grew in both vacuum and MAP when the product was held at 25°C. This study demonstrated that irradiation is an effective means of reducing Salmonella on meat or poultry, but packaging in either vacuum or MAP had little impact during subsequent refrigerated storage.

Molecular and comparative analysis of Salmonella enterica Senftenberg from humans and animals using PFGE, MLST and NARMS

BACKGROUND

Salmonella species are recognized worldwide as a significant cause of human and animal disease. In this study the molecular profiles and characteristics of Salmonella enterica Senftenberg isolated from human cases of illness and those recovered from healthy or diagnostic cases in animals were assessed. Included in the study was a comparison with our own sequenced strain of S. Senfteberg recovered from production turkeys in North Dakota. Isolates examined in this study were subjected to antimicrobial susceptibility profiling using the National Antimicrobial Resistance Monitoring System (NARMS) panel which tested susceptibility to 15 different antimicrobial agents. The molecular profiles of all isolates were determined using Pulsed Field Gel Electrophoresis (PFGE) and the sequence types of the strains were obtained using Multi-Locus Sequence Type (MLST) analysis based on amplification and sequence interrogation of seven housekeeping genes (aroC, dnaN, hemD, hisD, purE, sucA, and thrA). PFGE data was input into BioNumerics analysis software to generate a dendrogram of relatedness among the strains.

RESULTS

The study found 93 profiles among 98 S. Senftenberg isolates tested and there were primarily two sequence types associated with humans and animals (ST185 and ST14) with overlap observed in all host types suggesting that the distribution of S. Senftenberg sequence types is not host dependent. Antimicrobial resistance was observed among the animal strains, however no resistance was detected in human isolates suggesting that animal husbandry has a significant influence on the selection and promotion of antimicrobial resistance.

CONCLUSION

The data demonstrates the circulation of at least two strain types in both animal and human health suggesting that S. Senftenberg is relatively homogeneous in its distribution. The data generated in this study could be used towards defining a pathotype for this serovar.

Comparison of Salmonella enterica serovar Heidelberg isolates from human patients with those from animal and food sources

Seventy-eight Salmonella enterica serovar Heidelberg isolates from humans were tested for antimicrobial susceptibility, resistance genes, and plasmids and genotyped by pulsed-field gel electrophoresis (PFGE). Most (88%) contained plasmids, and 47% were resistant to antimicrobials. The overall results were compared to those of previous S. Heidelberg studies of food- and animal-related sources, and multiple similarities were observed.

Qualitative map of Salmonella contamination on young chicken carcasses

Salmonella contamination of poultry is a global public health problem. The objective of this study was to map the distribution of Salmonella on the young chicken carcass, to improve poultry inspection and food safety. Young chickens (n = 70) in the Cornish game hen class were obtained at retail over a 3-year period. Carcasses were aseptically sectioned into 12 parts, and then Salmonella was isolated from whole-part incubations by conventional culture methods. Isolates were characterized for serotype and antibiotic resistance, and by pulsed-field gel electrophoresis (PFGE). Salmonella incidence was 21.5% (181 of 840) for parts and 57.1% (40 of 70) for carcasses. The number of contaminated parts per carcass ranged from 0 to 12, with a mean of 4.5 among contaminated carcasses. Chi-square analysis indicated that Salmonella incidence differed (P < 0.05) among parts, with rib back (38.6%) and sacral back (34.3%) being the most contaminated. Among the 40 contaminated carcasses, there were 37 different patterns of contamination among parts. Of the 33 carcasses with more than one contaminated part, 12.1% contained two serotypes, 33.3% contained two or more antibiotic resistance profiles, and 100% contained two or more PFGE patterns. The most common serotype was Typhimurium (94.5%), and most (97.2%) isolates were resistant to multiple antibiotics. These results indicated a diverse pattern of Salmonella contamination among carcasses and that multiple subtypes of Salmonella were often present on contaminated carcasses. Thus, whole-carcass incubation succeeded by characterization of multiple isolates per carcass is needed to properly assess and manage this risk to public health.

Repeated therapeutic dosing selects macrolide-resistant Campylobacter spp. in a turkey facility

AIMS

This study assessed the effects of the therapeutic use of Tylan® in a large-scale turkey production facility on the selection of macrolide-resistant Campylobacter.

METHODS AND RESULTS

A flock of production turkeys (c. 30,000 birds) was followed from brooding to slaughter, and the effects of macrolide application was assessed in one half of the flock from finishing stage to final product and compared against the control barn where no macrolide was used. Overall, Campylobacter prevalence in turkeys was almost 100% by 4 weeks of age. When Campylobacter prevalence was assessed in relation to treatment, high levels of macrolide resistance were evident in this group following treatment, with Campylobacter coli becoming the dominant strain type. Over time, and in the absence of a selection agent, the population of resistant strains decreased suggesting that there was a fitness cost associated with macrolide resistance carriage and persistence. Macrolide resistance was detected in the control barn at a very low level (four isolates recovered during the study), suggesting that the creation or selection of macrolide-resistant Campylobacter was correlated with the treatment regime used. Molecular analysis of a selection of macrolide-resistant Campylobacter recovered was assessed using PCR, RFLP and sequence analysis of the 23S rRNA. The majority of isolates displaying high-level macrolide resistance (>256 μg ml(-1)) possessed an A2075G transition mutation in the 23S rRNA and the CmeABC efflux pump.

CONCLUSIONS

These studies suggest that macrolide resistance can be promoted through the application of treatment during the grow-out phase and once established in a production facility has the potential to persist and be transferred to final product.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study highlights the prudent use of antimicrobials in treatment of disease in poultry. Of significance is the presence of macrolide-resistant Campylobacter in poultry production and finished product as a consequence of macrolide usage.

A predominant multidrug-resistant Salmonella enterica serovar Saintpaul clonal line in German turkey and related food products

Recently, Salmonella enterica subsp. enterica serovar Saintpaul has increasingly been observed in several countries, including Germany. However, the pathogenic potential and epidemiology of this serovar are not very well known. This study describes biological attributes of S. Saintpaul isolates obtained from turkeys in Germany based on characterization of their pheno- and genotypic properties. Fifty-five S. Saintpaul isolates from German turkeys and turkey-derived food products isolated from 2000 to 2007 were analyzed by using antimicrobial agent, organic solvent, and disinfectant susceptibility tests, isoelectric focusing, detection of resistance determinants, plasmid profiling, pulsed-field gel electrophoresis (PFGE), and hybridization experiments. These isolates were compared to an outgroup consisting of 24 S. Saintpaul isolates obtained from humans and chickens in Germany and from poultry and poultry products (including turkeys) in Netherlands. A common core resistance pattern was detected for 27 German turkey and turkey product isolates. This pattern included resistance (full or intermediate) to ampicillin, amoxicillin-clavulanic acid, gentamicin, kanamycin, nalidixic acid, streptomycin, spectinomycin, and sulfamethoxazole and intermediate resistance or decreased susceptibility to ciprofloxacin (MIC, 2 or 1 mug/ml, respectively) and several third-generation cephalosporins (including ceftiofur and cefoxitin [MIC, 4 to 2 and 16 to 2 mug/ml, respectively]). These isolates had the same core resistance genotype, with bla(TEM-1), aadB, aadA2, sul1, a Ser83-->Glu83 mutation in the gyrA gene, and a chromosomal class 1 integron carrying the aadB-aadA2 gene cassette. Their XbaI, BlnI, and combined XbaI-BlnI PFGE patterns revealed levels of genetic similarity of 93, 75, and 90%, respectively. This study revealed that a multiresistant S. Saintpaul clonal line is widespread in turkeys and turkey products in Germany and was also detected among German human fecal and Dutch poultry isolates.

Prevalence, serotype, and antimicrobial resistance of Salmonella on broiler carcasses postpick and postchill in 20 U.S. processing plants

The objective of this study was to measure the effect of broiler processing on the prevalence, serotype, and antimicrobial resistance profiles of salmonellae. Twenty U.S. commercial processing plants representing eight integrators in 13 states were included in the survey. In each of four replications, 10 carcasses from one flock were collected at rehang and 10 more carcasses were collected at postchill; each carcass was sampled by whole-carcass rinse. Salmonella organisms were isolated from carcass rinses by standard cultural techniques, serotypes were determined, and the resistance to 15 antimicrobials was measured. Overall, Salmonella was detected on 72% of carcasses at rehang (ranging from 35 to 97%) and on 20% of carcasses postchill (ranging from 2.5 to 60%). In every instance, a significant (P < 0.05) decrease in Salmonella prevalence was noted between rehang and postchill. The four most common serotypes, accounting for 64% of all Salmonella isolates, were Kentucky, Heidelberg, Typhimurium, and Typhimurium var. 5-; most isolates of Kentucky (52%), Heidelberg (79%), and Typhimurium (54%) serotypes were susceptible to all antimicrobial drugs tested. However, only 15% of the Typhimurium var. 5- isolates were pansusceptible; more than one-half of the isolates of this serotype were resistant to three or more drugs. No isolate of any serotype exhibited resistance to amikacin, ceftriaxone, ciprofloxacin, or trimethoprim-sulfamethoxazole. These data demonstrate that although processing lessens carcass contamination with Salmonella, antimicrobial-resistant isolates may still be present.

Antimicrobial drug resistance and molecular characterization of Salmonella isolated from domestic animals, humans, and meat products

OBJECTIVES

1) To characterize and determine genotypic relatedness of Salmonella serovars commonly isolated from domestic animals and humans in North Dakota, and 2) to assess their role in transferring antimicrobial resistance (AMR) to humans.

MATERIALS AND METHODS

A total of 434 Salmonella isolates obtained from 1) feces of apparently healthy feedlot, range, and dairy cattle in North Dakota; 2) clinical samples from sick or dead animals submitted to North Dakota State University-Veterinary Diagnostic Laboratory (2000-2005); 3) previous meat product surveillance studies in North Dakota; and 4) 179 samples from human patients in North Dakota (2000-2005) by the North Dakota Department of Health were studied. The isolates were initially serotyped and later genotyped by pulsed-field gel electrophoresis (PFGE) to investigate their relatedness. The National Antimicrobial Resistance Monitoring Systems panel was used to compare AMR profiles of animal and human isolates to assess a possible role of domestic animals in transfer of AMR to humans.

RESULTS

Salmonella Typhimurium was the predominant serotype in both humans (13.4%) and domestic animals (34.3%), followed by Newport in animals (2.6%) and human (3.9%). Salmonella Arizona (0.7%), Salmonella Give (0.9%), and Salmonella Muenster (3.5%) were isolated from sick or dead animals. PFGE results confirmed occurrence of similar Salmonella genotypes in both domestic animals and humans. AMR profiles showed that most animal strains were multidrug resistant. A single human isolate had PFGE and multidrug resistance profiles similar to a major cattle genotype, suggesting a possible AMR transmission from cattle to humans. CONCLUSION AND APPLICATION: Similar Salmonella genotypes were infecting domestic animals and humans in North Dakota. The AMR levels were higher in domestic animal isolates than in humans, implying that the occurrence of AMR in animal isolates may not translate directly into AMR in human isolates in North Dakota. This is helpful in determining future policies regarding antimicrobial drug use in domestic animals and humans.

Baseline Campylobacter prevalence at a new turkey production facility in North Dakota

Campylobacter jejuni isolates (n = 340) were collected from nine turkey flocks in three rotations (A, B, and C) at a newly established turkey production facility in North Dakota and at processing. Samples were collected at weeks 1, 4, 9, and 18, as well as at two stages on the processing line at the processing plant. Campylobacter was not isolated from the first flocks in the rotations (A1, B1, and C1), but was detected at week 18 in the second flock groupings and at week 9 in the third flock groupings. The cumulative increase in Campylobacter prevalence observed in each subsequent rotation was attributed to flock rotation through the brooder barn, in which each flock was housed for 4 weeks before moving to a finishing barn; the brooder was the only common building shared by all flocks in each grouping (A, B, and C). C. jejuni isolates recovered were analyzed for the presence of selected virulence genes; 100% of the isolates tested were positive for the flaA, pldA, and cadF genes; 99.7% of the isolates were positive for the cdtB, cdtC, and ciaB genes. The prevalence of the cdtA and cjp05 genes was much lower at 11.2 and 67.5%, respectively. Results of this study indicate flock rotation may increase Campylobacter prevalence; molecular characterization provided information about Campylobacter from a new turkey production facility.

Characterization of Salmonella enterica serovar Heidelberg from turkey-associated sources

Salmonella enterica serovar Heidelberg strains are frequently associated with food-borne illness, with recent isolates showing higher rates of resistance to multiple antimicrobial agents. One hundred eighty S. enterica serovar Heidelberg isolates, collected from turkey-associated production and processing sources, were tested for antimicrobial susceptibility and compared by pulsed-field gel electrophoresis (PFGE) and plasmid profile analysis. The potential for the transfer of resistance between strains was studied by conjugation experiments. PFGE analysis using XbaI digestion identified eight clusters (based on 90% similarity), with the largest containing 71% of the isolates. Forty-two percent of the isolates were resistant to at least 1 of the 15 antimicrobial agents tested, and 4% of the isolates were resistant to 8 or more antimicrobial agents. Resistances to streptomycin (32%), tetracycline (30%), and kanamycin (24%) were most commonly detected. Interestingly, the XbaI PFGE profiles of selective multidrug-resistant strains (n = 22) of S. enterica serovar Heidelberg from turkey-associated sources were indistinguishable from the predominant profile (JF6X01.0022) detected in isolates associated with human infections. These isolates were further differentiated into seven distinct profiles following digestion with the BlnI enzyme, with the largest cluster comprising 15 isolates from veterinary diagnostic and turkey processing environments. Conjugation experiments indicated that resistance to multiple antimicrobial agents was transferable among strains with diverse PFGE profiles.

Characterization of antimicrobial susceptibility and virulence genes of Salmonella serovars collected at a commercial turkey processing plant

AIMS

To determine the antimicrobial susceptibility profiles, distribution of class 1 integrons, virulence genes and genes encoding resistance to tetracycline (tetA, tetC, tetD and tetE) and streptomycin (strA, strB and aadA1) in Salmonella recovered from turkeys.

METHODS AND RESULTS

The antimicrobial susceptibility of 80 isolates was determined using National Antimicrobial Resistance Monitoring System. The distribution of resistance genes, class 1 integrons and virulence genes was determined using PCR. Resistances to tetracycline (76 x 3%) and streptomycin (40%) were common. Sixty-two (77 x 5%) isolates displayed resistance against one or more antimicrobials and 33 were multi-drug resistant. tetA was detected in 72 x 5% of the isolates, while tetC, tetD and tetE were not detected. The strA and strB genes were detected in 73 x 8% of the isolates. Two isolates possessed class 1 integrons of 1 kb in size, containing the aadA1 gene conferring resistance to streptomycin and spectinomycin. Fourteen of the virulence genes were detected in over 80% of the isolates.

CONCLUSIONS

This study shows that continuous use of tetracycline and streptomycin in poultry production selects for resistant strains. The Salmonella isolates recovered possess significant ability to cause human illness.

SIGNIFICANCE AND IMPACT OF THE STUDY

Information from this study can be employed in guiding future strategies for the use of antimicrobials in poultry production.

Evaluation of Salmonella occurrence in domestic animals and humans in North Dakota (2000-2005)

OBJECTIVES

To evaluate the occurrence, serotypes, and antimicrobial susceptibility of Salmonellae from domestic animals and humans in North Dakota.

MATERIALS AND METHODS

Salmonellosis data (2000-2005) in humans (n = 286) and animals (n = 258) were extracted from the North Dakota Department of Health (NDDoH) and North Dakota State University Veterinary Diagnostic Laboratory (NDSU-VDL), and analyzed for temporal and spatial trends, and for other associations. Additionally, random samples of 35, 30, and 15 Salmonella isolates from NDSU-VDL, NDDoH, and North Dakota healthy cattle, respectively, were tested for antimicrobial susceptibility.

RESULTS

Most animal salmonellosis occurred in cattle (64.7%) sheep (12%), pigs (10.9%), and bison (0.4%) with Salmonella Typhimurium (45.7%) as the predominant serotype; Salmonella Arizona (10.9%) and Dublin (10.5%) were host specific in sheep and cattle respectively. In humans, Salmonella Typhimurium (32.5%) and Salmonella Newport (11.2%) were predominant. Season influenced human (p = 0.027) and animal (p = 0.014) salmonellosis with cases peaking in the spring and summer for animals and humans, respectively. Salmonella Typhimurium case reports in humans were not seasonally related to domestic animals (p = 0.001) nor cattle (p = 0.001). Over time, case reports increased in humans but decreased in domestic animals. Most serotypes from domestic animals were multidrug resistant compared to human isolates. CONCLUSIONS AND APPLICATIONS: Many Salmonella serotypes (17) were involved in North Dakota human and animal salmonellosis with case reports closely related in fall and winter, but not during warmer months. Spatial clustering of human and animal cases was similar. Antimicrobial resistance was widespread but lower in human isolates. These data are helpful in determining future policy, research, and control strategies for salmonellosis in humans and domestic animals.

Occurrence of antimicrobial-resistant salmonella species in raw and ready to eat turkey meat products from retail outlets in the midwestern United States

OBJECTIVES

To investigate occurrence of Salmonella in raw and ready to eat (RTE) turkey from retail outlets, determine factors associated with its occurrence and antimicrobial-resistance patterns.

MATERIALS AND METHODS

A total of 959 turkey products (raw, n = 345; and RTE, n = 614) were purchased in 3 months from four stores in one city in the midwestern United States. Chi-square and logistic regression analyses were used to test for associations of microbial contamination with product type and brand, expiration date, sampling time, and retail store. Antimicrobial resistance of Salmonellae was determined using a National Antimicrobial Resistance Monitoring System (NARMS) panel of antimicrobials.

RESULTS

Overall, 2.2% (21/959) of the samples (4.1% [14/345] raw and 1.1% [7/614] RTE) were contaminated with Salmonella. A significant difference in Salmonella occurrence (p < 0.05), between meat type (raw vs. RTE; OR = 4.2, 95% CI = 1.6, 10.8); and sampling month (p < 0.05) was reported, but not between retail stores and product brands. Salmonellae belonged to 6 serotypes: Hadar, Heidelberg, Typhimurium var. Copenhagen, Newport, Saintpaul, and Agona. Salmonellae from raw turkey exhibited higher antimicrobial resistance (53%) compared to those from RTE products (33%). Multidrug resistance was exhibited by 62% of Salmonellae (86% RTE, 50% raw meats). CONCLUSION AND CLINICAL APPLICATIONS: Turkey (both raw and RTE) may occasionally be contaminated with antimicrobial-resistant Salmonellae whose occurrence was influenced by sampling month and meat type. Continued surveillance of Salmonella occurrence in meat products, in particular RTE ones, is warranted in order to ensure a safe food supply.

An evaluation of conventional culture, invA PCR, and the real-time PCR iQ-Check kit as detection tools for Salmonella in naturally contaminated premarket and retail turkey

This study was aimed at comparing the ability of conventional culture, the iQ-Check real-time PCR kit, and invA PCR to detect Salmonella in naturally contaminated premarket and retail turkey parts. Premarket (n = 120) turkey parts collected from a commercial turkey processing plant, and retail turkey parts (n = 138) were examined. Both PCR methods detected a significantly greater (P < 0.05) number of positive samples when compared with the conventional culture method for the premarket turkey parts. The indices of total agreement between the conventional culture method and the iQ-Check kit for the premarket and retail parts were 79.2% (95% CI: 70.8, 86) and 90.6% (95% CI: 84.4, 94.9), respectively. When the conventional culture method was compared with invA PCR for Salmonella detection in the premarket and retail parts, the indices of total agreement were 75.8% (95% CI: 67.2, 83.2) and 84.1% (95% CI: 76.9, 89.7), respectively. The rates of false positives (premarket: 31.9%, retail: 9.7%) and false negatives (premarket: 5.9%, retail: 9.7%) were determined between the culture method and the iQ-Check kit. When invA PCR was compared with the culture method, the rates of false positives (premarket: 37.7%, retail: 11.1%) and false negatives (premarket: 5.9%, retail: 18.3%) were obtained. The higher total agreement and the lower rates of both false positives and false negatives for the iQ-Check kit compared with invA PCR for both premarket and retail turkey parts corroborates the use of the iQ-Check kit as a screening tool for Salmonella in poultry meat.

Prevalence and antimicrobial resistance of Salmonella recovered from processed poultry

This study was conducted to determine the prevalence and antimicrobial resistance of Salmonella isolates recovered from processed poultry. Four hundred eighty pre- and postchill whole broiler chicken carcasses were collected from a poultry processing plant between July 2004 and June 2005. Water samples also were collected at the entrance and exit of the chiller. After preenrichment, carcass and water samples were analyzed for the presence of Salmonella using the automated BAX system followed by traditional culture methods. The proportions of pre- and postchill carcasses that were positive for Salmonella were 88.4 and 84.1%, respectively. Ninety-two percent of water samples collected at the entrance of the chiller were positive for Salmonella, but all exit samples were negative. There was no significant difference in the prevalence of Salmonella between pre- and postchill carcasses (P > 0.05). Salmonella isolates recovered were serotyped and tested for susceptibility to antimicrobials. Thirteen serotypes were identified; the most common were Salmonella Kentucky (59.5%) and Salmonella Typhimurium (17.8%). Three hundred thirty-nine (79.8%) of the isolates were resistant to at least one antimicrobial, and 53.4% were resistant to three or more antimicrobials. Resistance was most often observed to tetracycline (73.4% of isolates), ampicillin (52.9%), amoxicillin-clavulanic acid (52%), ceftiofur (51.7%), streptomycin (35.2%), and sulfisoxazole (21.8%). These results indicate the high prevalence of Salmonella contamination in whole broiler carcasses, and a large number of these Salmonella isolates were resistant to commonly used antimicrobials.

Salmonella challenges: prevalence in swine and poultry and potential pathogenicity of such isolates

Salmonellosis is the second leading cause of bacterial foodborne illness in the United States, and the great majority of these infections are associated with the consumption of products such as meat, poultry, eggs, milk, seafood, and fresh produce contaminated with Salmonella. The per capita consumption of meat and poultry in United States has increased significantly over the past century. This increase is especially evident with poultry products, where there has been a nearly 6-fold increase in chicken consumption and 17-fold increase in turkey consumption since 1909. The per capita consumption of pork has also increased over this time from 18.7 to 21.7 kg/yr. With this increase in meat and poultry consumption, the dynamics of animal production and consumer exposure have changed leading to new challenges in limiting salmonellosis. To meet the demands of consumers, more intensive agricultural practices have been adopted, which has likely changed the population characteristics of Salmonella present among poultry flocks and swine populations. In Salmonella isolated from swine in the United States, S. Typhimurium has replaced S. Choleraesuis as the predominant serovar in recent years. Among isolates from turkeys collected in 2004, serovars S. Senftenberg and S. Hadar were most common overall; however, S. Heidelberg was most common from clinical diagnostic sources, potentially indicating increased virulence. Salmonella Heidelberg was also the most commonly detected serovar among chicken isolates from clinically ill birds and Salmonella surveillance samples. Overall among the 10 serovars most commonly associated with human infections, 6 are also found in the top serovars of swine and poultry. These include S. Typhimurium, S. Enteritidis, S. Heidelberg, S. Montevideo, S. Saintpaul, and S. I 4,[5],12:i:-.

Comparison of Salmonella enterica serovar Heidelberg susceptibility testing results

OBJECTIVE

Disk diffusion and broth dilution assays are conventionally used for antimicrobial susceptibility testing (AST) of bacteria. The goal of this study was to determine the correlation of results from different AST methods for the Salmonella enterica serovar Heidelberg.

DESIGN

S. enterica serovar Heidelberg (n=105) strains were tested using 4 different AST methods: agar disk diffusion, broth microdilution using Sensititre with the NARMS (CMV1AGNF) panel, manual broth microdilution and Vitek with GNS-207 cards.

METHODS

AST was performed using standardized methods and Clinical and Laboratory Standards Institute recommended quality control organisms. Eight drugs were common to all testing methods including amikacin, amoxicillin/clavulanic acid, ampicillin, chloramphenicol, ciprofloxacin, gentamicin, tetracycline and trimethoprim/sulfamethoxazole.

RESULTS

No resistance to amikacin and ciprofloxacin was detected. Overall, the agreement of the AST results among all four methods for the drugs tested was: amikacin (100%), amoxicillin/clavulanic acid (96.1%), ampicillin (97.1%), chloramphenicol (96.2%), ciprofloxacin (100%), gentamicin (80.0%), tetracycline (80.0%) and trimethoprim/sulfamethoxazole (94.3%). There was 97.1%, 95.5% and 98.0% overall agreement between the reference diffusion method and the manual broth microdilution, Sensititre microdilution and Vitek methods, respectively.

CONCLUSION

The study indicated that AST methods correlated with one another when testing S. enterica serovar Heidelberg isolates, with a few exceptions. In general, discrepancies among the methods were due to isolates being interpreted as intermediately susceptible or due to an increased number of resistances detected with Sensititre and a lower number with Vitek.

Molecular characterization and antibiotic resistance profiling of Salmonella isolated from retail Turkey meat products

Contaminated poultry meat has been identified as one of the principal foodborne sources of Salmonella. Molecular characterization of Salmonella is important in addressing methods to control this pathogen. Seventy-four retail turkey meat samples were collected from various stores in Fargo, North Dakota in the fall of 2003. Salmonella was recovered from 30 samples using the standard conventional culture method (FSIS, USDA). Isolated Salmonella were characterized by serotyping, pulsed-field gel electrophoresis (PFGE) analysis, plasmid analysis, and antibiotic resistance profiling. Five serotypes were identified among the isolates: Newport (n = 12), Hadar (n = 8), Heidelberg (n = 7), 4,12:nonmotile (n = 2), and Reading (n = 1). XbaI PFGE analysis revealed 13 PFGE types and succeeded in grouping the isolates according to their serotypes. Plasmid profiling identified 5 plasmid types (with 1 or 2 plasmids) among eleven isolates that harbored plasmids. Seventeen isolates were resistant to antibiotics. The Heidelberg serotype showed resistance to multiple antibiotics: 1 isolate had resistance to gentamicin, sulfamethoxazole, and streptomycin, and 6 isolates had resistance to tetracycline, gentamycin, sulfamethoxazole, kanamycin, and streptomycin. The Hadar serotype isolates were resistant to 2 or 3 antibiotics: tetracycline and streptomycin (1 isolate); tetracycline and kanamycin (1 isolate); and tetracycline, kanamycin, and streptomycin (6 isolates). The 4,12:nonmotile serotype isolates showed resistance to tetracycline only. The Newport and the Reading serotypes were susceptible to all 16 of the antimicrobials tested.

U.S. Food Safety and Inspection Service testing for Salmonella in selected raw meat and poultry products in the United States, 1998 through 2003: analysis of set results

The U.S. Food Safety and Inspection Service (FSIS) tests sets of samples of selected raw meat and poultry products for Salmonella to ensure that federally inspected establishments meet performance standards defined in the pathogen reduction-hazard analysis and critical control point system (PR-HACCP) final rule. In the present report, sample set results are described and associations between set failure and set and establishment characteristics are identified for 4,607 sample sets collected from 1998 through 2003. Sample sets were obtained from seven product classes: broiler chicken carcasses (n = 1,010), cow and bull carcasses (n = 240), market hog carcasses (n = 560), steer and heifer carcasses (n = 123), ground beef (n = 2,527), ground chicken (n = 31), and ground turkey (n = 116). Of these 4,607 sample sets, 92% (4,255) were collected as part of random testing efforts (A sets), and 93% (4,166) passed. However, the percentage of positive samples relative to the maximum number of positive results allowable in a set increased over time for broilers but decreased or stayed the same for the other product classes. Three factors associated with set failure were identified: establishment size, product class, and year. Set failures were more likely early in the testing program (relative to 2003). Small and very small establishments were more likely to fail than large ones. Set failure was less likely in ground beef than in other product classes. Despite an overall decline in set failures through 2003, these results highlight the need for continued vigilance to reduce Salmonella contamination in broiler chicken and continued implementation of programs designed to assist small and very small establishments with PR-HACCP compliance issues.

Effect of preslaughter events on the prevalence of Salmonella in market-weight turkeys

The goal of this study was to determine if preslaughter events, such as transport to and holding at the slaughterhouse, affect Salmonella prevalence in turkeys. Floors of transport crates were swabbed after loading and prior to transport at the farm (time 1, n = 100 swabs per trial) and after transport to and holding at the abattoir (time 2, n = 100 swabs per trial). In addition, environmental samples were taken at each of the six premises (n = 25 per premises) as well as in the holding shed at the abattoir (n = 25 samples per trial). At slaughter, the crops, ceca, and spleens were cultured (n = 50 each per flock). As shown from the culture of the crate floor swabs collected pre- and posttransport, when individual farms were analyzed, samples from only one premises exhibited a statistically significant change, as seen by the decline in Salmonella prevalence posttransport (P < 0.01). When the data from all farms were combined, Salmonella was recovered more frequently from swabs collected pretransport at loading on-farm (time 1, 47.6%) than from swabs collected after transport (time 2, 39.7%, P < 0.01). This suggests that transport to and holding at the abattoir do not increase the prevalence of Salmonella in turkeys. This observation contrasts with the increase in Salmonella prevalence reported for hogs and some broilers.

Prevalence and molecular profiles of Salmonella collected at a commercial turkey processing plant

In this study, whole carcasses were sampled at eight stages on a turkey-processing line and Salmonella prevalence was determined using enrichment techniques. Recovered Salmonella was further characterized using serotyping and the molecular profiles were determined using pulsed-field gel electrophoresis (PFGE). Prevalence data showed that contamination rates varied along the line and were greatest after defeathering and after chilling. Analysis of contamination in relation to serotypes and PFGE profiles found that on some visits the same serotype was present all along the processing line while on other days, additional serotypes were recovered that were not detected earlier on the line, suggesting that the birds harbored more than one serotype of Salmonella or there was cross-contamination occurring during processing. Overall, this study found fluctuations in Salmonella prevalence along a turkey-processing line. Following washing, Salmonella prevalence was significantly reduced, suggesting that washing is critical for Salmonella control in turkey processing and has significant application for controlling Salmonella at the postdefeathering and prechill stages where prevalence increased.

Antibiotic resistance profiles and cell surface components of Salmonellae

Salmonellae were isolated from raw chilled retail poultry meats (n=100) using the procedures outlined in the Bacteriological Analytical Manual and Microbiology Laboratory Guidebook. These isolates and 36 Salmonella strains from our laboratory culture collection were tested for their resistance to 12 different antibiotics and for their ability to produce thin aggregative fimbriae and/or cellulose, two of the most important surface components influencing the ability of cells to attach to surfaces and form biofilms. The sensitivity of the salmonellae to the antibiotics was determined with a disc diffusion assay. Of 52 Salmonella isolates, 25 (48.0%) were resistant to one antibiotic, 5 (9.6%) were resistant to two, 4 (7.7%) were resistant to three, 6 (11.5%) were resistant to four, and 5 (9.6%) were resistant to five antibiotics. Two (3.8%) of the isolates were resistant to up to nine of the antibiotics tested. Fifty-one (98%) of the isolates were resistant to novobiocin, 18 (34.6%) were resistant to streptomycin, 14 (26.9%) were resistant to tetracycline, and 14 (26.9%) were resistant to oxytetracycline. In separate experiments, the isolates were grown on Luria-Bertani no-salt agar supplemented with Congo red (40 microg/ml) and Coomassie brilliant blue (20 microg/ml) or Calcofluor (200 microg/ml) to determine whether they produced thin aggregative fimbriae and/or cellulose. Of the total 52 Salmonella isolates, 25 expressed only thin aggregative fimbriae, and 1 synthesized only cellulose. Ten isolates produced both thin aggregative fimbriae and cellulose, and the remaining 16 isolates expressed neither surface structure. The findings of this study reveal a prevalence of Salmonella on raw retail poultry products in central Georgia and suggest that salmonellae have the ability to develop resistance to multiple antibiotics and to synthesize cell surface components that help them survive in hostile or suboptimal environments.

Comparison of antibiotic susceptibility profiles and molecular typing patterns of clinical and environmental Salmonella enterica serotype Newport

The genus Salmonella is composed of more than 2,400 serotypes, many of which cause enteric diseases in humans and animals. Several Salmonella serotypes are multidrug resistant, and there is evidence of the clonal spread of these strains from animals to humans. Salmonella enterica serotype Newport is one of the serotypes that increasingly present a multidrug-resistant phenotype. Source tracking and antibiotic resistance testing are important considerations for identifying the outbreak strain. The first goal of this study was to examine the antibiotic susceptibility patterns of clinical and environmental Salmonella Newport isolates from various geographic locations and to compare the discriminatory ability of two DNA fingerprinting techniques. The second goal was to determine whether the antibiotic resistance profiles and typing patterns correlated. Thirty Salmonella Newport isolates, including environmental and human clinical strains, were subjected to pulsed-field gel electrophoresis (PFGE), ribotyping, and antibiotic susceptibility testing. Eighty percent of the isolates showed total or intermediate resistance to one or more drugs; 75% of the isolates were multidrug resistant. Ribotyping with the EcoRI enzyme and PFGE with the XbaI enzyme each divided the isolates into 14 groups. Cluster analysis based on antibiotic susceptibility patterns generated 23 profiles. The susceptible and resistant isolates were not differentiated on the basis of either of the molecular typing techniques. Hence, no correlation was observed between the antibiotic resistance profiles and the DNA subtyping patterns. In conclusion, ribotyping is as discriminatory as PFGE and, when used in combination with antibiotic resistance profiles, provides a powerful tool for the source tracking of Salmonella Newport.