Antimicrobial Resistance Characteristics of Fecal Escherichia coli and Enterococcus Species in U.S. Goats: 2019 National Animal Health Monitoring System Enteric Study.

Escherichia coli and Enterococcus species are normal bacteria of the gastrointestinal tract and serve as indicator organisms for the epidemiology and emergence of antimicrobial resistance in their hosts and the environment. Some E. coli serovars, including E. coli O157:H7, are important human pathogens, although reservoir species such as goats remain asymptomatic. We describe the prevalence and antimicrobial resistance of generic E. coli, E. coli O157:H7, and Enterococcus species collected from a national surveillance study of goat feces as part of the National Animal Health Monitoring System (NAHMS) Goat 2019 study. Fecal samples were collected from 4918 goats on 332 operations across the United States. Expectedly, a high prevalence of E. coli (98.7%, 4850/4915) and Enterococcus species (94.8%, 4662/4918) was found. E. coli O157:H7 prevalence was low (0.2%; 10/4918). E. coli isolates, up to three per operation, were evaluated for antimicrobial susceptibility and 84.7% (571/674) were pansusceptible. Multidrug resistance (MDR; ≥3 classes) was uncommon among E. coli, occurring in 8.2% of isolates (55/674). Resistance toward seven antimicrobial classes was observed in a single isolate. Resistance to tetracycline alone (13.6%, 92/674) or to tetracycline, streptomycin, and sulfisoxazole (7.0% 47/674) was the most common pattern. All E. coli O157:H7 isolates were pansusceptible. Enterococcus isolates, up to four per operation, were prioritized by public health importance, including Enterococcus faecium and Enterococcus faecalis and evaluated. Resistance to lincomycin (93.8%, 1232/1313) was most common, with MDR detected in 29.5% (388/1313) of isolates. The combination of ciprofloxacin, lincomycin, and quinupristin resistance (27.1%, 105/388) was the most common pattern detected. Distribution and characteristics of antimicrobial resistance in E. coli and Enterococcus in the U.S. goat population from this study can inform stewardship considerations and public health efforts surrounding goats and their products.

Phenotypic and Genotypic Characterizations of Antimicrobial-Resistant Escherichia coli Isolates from Diverse Retail Meat Samples in North Carolina During 2018-2019.

Surveillance of antimicrobial-resistant pathogens in U.S. retail meats is conducted to identify potential risks of foodborne illness. In this study, we conducted a phenotypic and genotypic analysis of Escherichia coli recovered from a diverse range of retail meat types during 2018-2019 in North Carolina. The investigation was conducted as part of the National Antimicrobial Resistance Monitoring System (NARMS). Retail meat sampling and E. coli isolation were performed in accordance with NARMS retail meat isolation protocols. We used the Sensititre™ broth microdilution system to determine phenotypic resistance to 14 antimicrobial agents and the Illumina next-generation sequencing platform for genotypic resistance profiling. The highest prevalence of E. coli isolates was found in ground turkey (n = 57, 42.9%) and chicken (n = 27, 20.3%), followed by ground beef (n = 25, 18.9%) and pork (n = 24, 18%). The isolates were divided into seven different phylogroups using the Clermont typing tool, with B1 (n = 59, 44.4%) and A (n = 39, 29.3%) being the most dominant, followed by B2 (n = 14, 10.5%), D (n = 7, 5.3%), F (n = 6, 4.5%), E (n = 3, 2.3%), and C (n = 2, 1.5%). Using multilocus sequence typing (MLST), 128 Sequence types (STs) were identified indicating high diversity. Phenotypic and genotypic resistance was observed toward aminoglycosides, sulfonamides, beta-lactams, macrolides, tetracyclines, phenicols, and fluoroquinolones. Ground turkey samples were more resistant to the panel of tested antimicrobials than chicken, beef, or pork (p < 0.05). All isolates were found to be susceptible to meropenem. A high percentage of turkey isolates (n = 16, 28%) were multidrug-resistant (MDR) compared with 18.5% of chicken (n = 5), 8.4% of pork (n = 2), and 8% of beef isolates (n = 2). This study highlights the benefit of surveillance to identify MDR E. coli for epidemiologic tracking and is a comprehensive report of the phenotypic and genotypic characterization of E. coli isolated from retail meats in North Carolina.

Characteristics of antimicrobial resistance in Escherichia coli isolated from retail meat products in North Carolina.

BACKGROUND: Escherichia coli is commonly used as an indicator for antimicrobial resistance (AMR) in food, animal, environment, and human surveillance systems. Our study aimed to characterize AMR in E. coli isolated from retail meat purchased from grocery stores in North Carolina, USA as part of the National Antimicrobial Resistance Monitoring System (NARMS). MATERIALS AND METHODS: Retail chicken (breast, n = 96; giblets, n = 24), turkey (n = 96), and pork (n = 96) products were purchased monthly from different counties in North Carolina during 2022. Label claims on packages regarding antibiotic use were recorded at collection. E. coli was isolated from meat samples using culture-based methods and isolates were characterized for antimicrobial resistance using whole genome sequencing. Multi-locus sequence typing, phylogroups, and a single nucleotide polymorphism (SNP)-based maximum-likelihood phylogenic tree was generated. Data were analyzed statistically to determine differences between antibiotic use claims and meat type. RESULTS: Of 312 retail meat samples, 138 (44.2%) were positive for E. coli, with turkey (78/138; 56.5%) demonstrating the highest prevalence. Prevalence was lower in chicken (41/138; 29.7%) and pork (19/138;13.8%). Quality sequence data was available from 84.8% (117/138) of the E. coli isolates, which included 72 (61.5%) from turkey, 27 (23.1%) from chicken breast, and 18 (15.4%) from pork. Genes associated with AMR were detected in 77.8% (91/117) of the isolates and 35.9% (42/117) were defined as multidrug resistant (MDR: being resistant to ≥3 distinct classes of antimicrobials). Commonly observed AMR genes included tetB (35%), tetA (24.8%), aph(3'')-lb (24.8%), and blaTEM-1 (20.5%), the majority of which originated from turkey isolates. Antibiotics use claims had no statistical effect on MDR E. coli isolates from the different meat types (X2 = 2.21, p = 0.33). MDR was observed in isolates from meat products with labels indicating "no claims" (n = 29; 69%), "no antibiotics ever" (n = 9; 21.4%), and "organic" (n = 4; 9.5%). Thirty-four different replicon types were observed. AMR genes were carried on plasmids in 17 E. coli isolates, of which 15 (88.2%) were from turkey and two (11.8%) from chicken. Known sequence types (STs) were described for 81 E. coli isolates, with ST117 (8.5%), ST297 (5.1%), and ST58 (3.4%) being the most prevalent across retail meat types. The most prevalent phylogroups were B1 (29.1%) and A (28.2%). Five clonal patterns were detected among isolates. CONCLUSIONS: E. coli prevalence and the presence of AMR and MDR were highest in turkey retail meat. The lack of an association between MDR E. coli in retail meat and antibiotic use claim, including those with no indication of antimicrobial use, suggests that additional research is required to understand the origin of resistance. The presence of ST117, an emerging human pathogen, warrants further surveillance. The isolates were distinctly diverse suggesting an instability in population dynamics.

Detection and molecular characterization of Salmonella species on U.S. goat operations.

Salmonella species are an important cause of gastrointestinal disease in animals, including goats. Additionally, Salmonella species are among the top five U.S. foodborne pathogens causing illness to humans. The goat industry is rapidly expanding in the U.S. yet estimates of Salmonella prevalence within these populations is lacking. The aim of this study was to investigate the fecal prevalence, antimicrobial resistance (AMR), biofilm potential, and virulence profile of Salmonella species isolated from goat feces as part of the United States Department of Agriculture (USDA) National Animal Health Monitoring System (NAHMS) Goat 2019 study, enteric microbe component. A total of 4917 fecal samples were collected from 332 operations, from September 2019-March 2020. Salmonella were isolated using standard enrichment and culture methods; antimicrobial susceptibility was determined by broth microdilution. Biofilm production was assessed using a crystal violet assay and normalized to a positive control strain, and PCR was used to detect virulence genes. Overall, we detected a low prevalence (0.7%, n = 35/4917) of Salmonella in goat feces and identified a broad range of serotypes including S. Bareilly (35%) and a single rare S. Sharon. All isolates were pansusceptible to 14 antimicrobials except one, which was resistant to only tetracycline (MIC ≥ 32 µg/mL). All strains were found to possess the majority of virulence determinants screened, and 40% (14 of 35) formed weak, moderate, or strong biofilm. We found a low prevalence of Salmonella, and characteristics of Salmonella in the U.S. goat population informs ongoing public health efforts to manage risk of animal food products and animal interactions.

Clustered Regularly Interspaced Short Palindromic Repeats Genotyping of Multidrug-Resistant Salmonella Heidelberg Strains Isolated From the Poultry Production Chain Across Brazil.

Salmonella enterica subsp. enterica serovar Heidelberg has been associated with a broad host range, such as poultry, dairy calves, swine, wild birds, environment, and humans. The continuous evolution of S. Heidelberg raises a public health concern since there is a global dispersal of lineages harboring a wide resistome and virulome on a global scale. Here, we characterized the resistome, phylogenetic structure and clustered regularly interspaced short palindromic repeats (CRISPR) array composition of 81 S. Heidelberg strains isolated from broiler farms (n = 16), transport and lairage (n = 5), slaughterhouse (n = 22), and retail market (n = 38) of the poultry production chain in Brazil, between 2015 and 2016 using high-resolution approaches including whole-genome sequencing (WGS) and WGS-derived CRISPR genotyping. More than 91% of the S. Heidelberg strains were multidrug-resistant. The total antimicrobial resistance (AMR) gene abundances did not vary significantly across regions and sources suggesting the widespread distribution of antibiotic-resistant strains from farm to market. The highest AMR gene abundance was observed for fosA7, aac(6')-Iaa, sul2, tet(A), gyrA, and parC for 100% of the isolates, followed by 88.8% for bla CMY-2. The ß-lactam resistance was essentially driven by the presence of the plasmid-mediated AmpC (pAmpC) bla CMY-2 gene, given the isolates which did not carry this gene were susceptible to cefoxitin (FOX). Most S. Heidelberg strains were classified within international lineages, which were phylogenetically nested with Salmonella strains from European countries; while CRISPR genotyping analysis revealed that the spacer content was overall highly conserved, but distributed into 13 distinct groups. In summary, our findings underscore the potential role of S. Heidelberg as a key pathogen disseminated from farm to fork in Brazil and reinforce the importance of CRISPR-based genotyping for salmonellae. Hence, we emphasized the need for continuous mitigation programs to monitor the dissemination of this high-priority pathogen.

Genomics of human and chicken Salmonella isolates in Senegal: Broilers as a source of antimicrobial resistance and potentially invasive nontyphoidal salmonellosis infections.

Salmonella enterica is the most common foodborne pathogen worldwide. It causes two types of diseases, a self-limiting gastroenteritis and an invasive, more threatening, infection. Salmonella gastroenteritis is caused by several serotypes and is common worldwide. In contrast, invasive salmonellosis is rare in high-income countries (HIC) while frequent in low- and middle-income countries (LMIC), especially in sub-Saharan Africa (sSA). Invasive Nontyphoidal Salmonella (iNTS), corresponding to serotypes other than Typhi and Paratyphi, have emerged in sSA and pose a significant risk to public health. We conducted a whole-genome sequence (WGS) analysis of 72 strains of Salmonella isolated from diarrheic human patients and chicken meat sold in multipurpose markets in Dakar, Senegal. Antimicrobial susceptibility testing combined with WGS data analysis revealed frequent resistance to fluoroquinolones and the sulfamethoxazole-trimethoprim combination that are among the most used treatments for invasive Salmonella. In contrast, resistance to the historical first-line drugs chloramphenicol and ampicillin, and to cephalosporins was rare. Antimicrobial resistance (AMR) was lower in clinical isolates compared to chicken strains pointing to the concern posed by the excessive use of antimicrobials in farming. Phylogenetic analysis suggested possible transmission of the emerging multidrug resistant (MDR) Kentucky ST198 and serotype Schwarzengrund from chicken to human. These results stress the need for active surveillance of Salmonella and AMR in order to address invasive salmonellosis caused by nontyphoidal Salmonella strains and other important bacterial diseases in sSA.

Correction: Class 1 integron-borne cassettes harboring blaCARB-2 gene in multidrug-resistant and virulent Salmonella Typhimurium ST19 strains recovered from clinical human stool samples, United States.

[This corrects the article DOI: 10.1371/journal.pone.0240978.].

Whole-genome sequencing analysis and CRISPR genotyping of rare antibiotic-resistant Salmonella enterica serovars isolated from food and related sources.

For decades, Salmonella Typhimurium and Salmonella Enteritidis have prevailed in several countries as agents of salmonellosis outbreaks. In Brazil, the largest exporter of poultry meat, relatively little attention has been paid to infrequent serovars. Here, we report the emergence and characterization of rare serovars isolated from food and related sources collected between 2014 and 2016 in Brazil. Twenty-two Salmonella enterica isolates were analyzed through the use of whole-genome sequencing (WGS) and clustered regularly interspaced short palindromic repeats (CRISPR) genotyping. These isolates were classified into 10 infrequent serovars, including S. Abony, S. Isangi, S. Rochdale, S. Saphra, S. Orion, S. Ouakam, S. Grumpensis, S. Carrau, S. Abaetetuba, and S. Idikan. The presence of six antimicrobial resistance (AMR) genes, qnrB19, blaCMY-2, tetA, aac(6')-Iaa, sul2 and fosA7, which encode resistance to quinolones, third-generation cephalosporin, tetracycline, aminoglycoside, sulfonamide and fosfomycin, respectively, were confirmed by WGS. All S. Isangi harbored qnrB19 with conserved genomic context across strains, while S. Abony harbored blaCMY-2. Twelve (54.5%) strains displayed chromosomal mutations in parC (Thr57→Ser). Most serovars were classified as independent lineages, except S. Abony and S. Abaetetuba, which phylogenetically nested with Salmonella strains from different countries. CRISPR analysis revealed that the spacer content was strongly correlated with serovar and multi-locus sequence type for all strains, independently confirming the observed phylogenetic patterns, and highlighting the value of CRISPR-based genotyping for Salmonella. These findings add valuable information to the epidemiology of S. enterica in Brazil, where the emergency of antibiotic-resistant Salmonella continues to evolve.

Class 1 integron-borne cassettes harboring blaCARB-2 gene in multidrug-resistant and virulent Salmonella Typhimurium ST19 strains recovered from clinical human stool samples, United States.

International lineages, such as Salmonella Typhimurium sequence type (ST) 19, are most often associated with foodborne diseases and deaths in humans. In this study, we compared the whole-genome sequences of five S. Typhimurium strains belonging to ST19 recovered from clinical human stool samples in North Carolina, United States. Overall, S. Typhimurium strains displayed multidrug-resistant profile, being resistance to critically and highly important antimicrobials including ampicillin, ticarcillin/clavulanic acid, streptomycin and sulfisoxazole, chloramphenicol, tetracycline, respectively. Interestingly, all S. Typhimurium strains carried class 1 integron (intl1) and we were able to describe two genomic regions surrounding blaCARB-2 gene, size 4,062 bp and 4,422 bp for S. Typhimurium strains (HS5344, HS5437, and HS5478) and (HS5302 and HS5368), respectively. Genomic analysis for antimicrobial resistome confirmed the presence of clinically important genes, including blaCARB-2, aac(6')-Iaa, aadA2b, sul1, tetG, floR, and biocide resistance genes (qacEΔ1). S. Typhimurium strains harbored IncFIB plasmid containing spvRABCD operon, as well as rck and pef virulence genes, which constitute an important apparatus for spreading the virulence plasmid. In addition, we identified several virulence genes, chromosomally located, while the phylogenetic analysis revealed clonal relatedness among these strains with S. enterica isolated from human and non-human sources obtained in European and Asian countries. Our results provide new insights into this unusual class 1 integron in virulent S. Typhimurium strains that harbors a pool of genes acting as potential hotspots for horizontal gene transfer providing readily adaptation to new surrounds, as well as being crucially required for virulence in vivo. Therefore, continuous genomic surveillance is an important tool for safeguarding human health.

Optimizing a Screening Protocol for Potential Extended-Spectrum ß-Lactamase Escherichia coli on MacConkey Agar for Use in a Global Surveillance Program.

The increasing prevalence of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli is worrisome. Coordinated efforts to better understand global prevalence and risk factors are needed. Developing lower- and middle-income countries need reliable, readily available, and cost-effective solutions for detecting ESBL E. coli to contribute to global surveillance. We evaluated MacConkey agar supplemented with ceftriaxone or cefotaxime as a screening method for accurately detecting and quantifying potential ESBL E. coli MacConkey agar from eight manufacturers, representing seven countries, was prepared with 2 or 4 µg/ml ceftriaxone or cefotaxime. Four E. coli strains (NC11, ATCC 25922, CM-13457, and CM-10455) and one Klebsiella pneumoniae strain (CM-11073) were grown overnight, serially diluted, and plated in triplicate for enumeration on all medium combinations. After recovery was assessed, US-1 MacConkey agar with cefotaxime was used to further evaluate the reproducibility and detection of potential ESBL E. coli from poultry cecal (n = 30) and water (n = 30) samples. Results indicated the recovery of E. coli 13457 from four MacConkey agar manufacturers was reduced by up to 4 log CFU/ml, and phenotypic differences in colony size and color were apparent for each manufacturer for control E. coli strains. A true ESBL, NC11, was not reduced with 4 µg/ml cefotaxime. From ceca and water, potential ESBL E. coli isolates were only confirmed from MacConkey agar with 4 µg/ml cefotaxime, where 45% and 16.6% of E. coli isolates phenotypically expressed ESBL production. The quality and reproducibility of MacConkey agar varied by manufacturer, which suggests that a single manufacturer and medium type should be selected for global monitoring efforts so that training and interpretation can be standardized.

Genomic Features of High-Priority Salmonella enterica Serovars Circulating in the Food Production Chain, Brazil, 2000-2016.

Multidrug-resistant (MDR) Salmonella enterica has been deemed a high-priority pathogen by the World Health Organization. Two hundred and sixty-four Salmonella enterica isolates recovered over a 16-year period (2000 to 2016) from the poultry and swine production chains, in Brazil, were investigated by whole-genome sequencing (WGS). Most international lineages belonging to 28 serovars, including, S. enterica serovars S. Schwarzengrund ST96, S. Typhimurium ST19, S. Minnesota ST548, S. Infantis ST32, S. Heidelberg ST15, S. Newport ST45, S. Brandenburg ST65 and S. Kentucky ST198 displayed MDR and virulent genetic backgrounds. In this regard, resistome analysis revealed presence of qnrE1 (identified for the first time in S. Typhimurium from food chain), qnrB19, qnrS1, blaCTX-M-8, blaCTX-M-2 and blaCMY-2 genes, as well as gyrA mutations; whereas ColpVC, IncHI2A, IncHI2, IncFIA, Incl1, IncA/C2, IncR, IncX1 and po111 plasmids were detected. In addition, phylogenetic analysis revealed multiple independent lineages such as S. enterica serovars S. Infantis, S. Schwarzengrund, S. Minnesota, S. Kentucky and S. Brandenburg. In brief, ocurrence and persistence of international lineages of S. enterica serovars in food production chain is supported by conserved genomes and wide virulome and resistome.

Multidrug- and colistin-resistant Salmonella enterica 4,[5],12:i:- sequence type 34 carrying the mcr-3.1 gene on the IncHI2 plasmid recovered from a human.

A colistin-resistant Salmonella enterica 4, [5],12:i:- sequence type (ST) 34 harbouring mcr-3.1 was recovered from a patient who travelled to China 2 weeks prior to diarrhoea onset. Genomic analysis revealed the presence of the mcr-3.1 gene located in the globally disseminated IncHI2 plasmid, highlighting the intercontinental dissemination of the colistin-resistant S. enterica 4, [5],12:i:- ST34 pandemic clone.

Phenotypic and Genotypic Characterization of Escherichia coli and Salmonella enterica from Dairy Cattle Farms in the Wakiso District, Uganda: A Cross-Sectional Study.

Enterobacteriaceae producing ß-lactamases have spread rapidly worldwide and pose a serious threat to human-animal-environment interface. In this study, we present the presence of Salmonella enterica (1.3%) and commensal Escherichia coli (96.3%) isolated from 400 environmental fecal dairy cattle samples over 20 farms in Uganda. Among E. coli isolates, 21% were resistant to at least one antimicrobial tested and 7% exhibited multidrug resistance. Four E. coli isolates displayed extended-spectrum beta-lactamase (ESBL)-producing genes, including blaCTX-M-15 (n = 2/4), blaCTX-M-27 (n = 1/4), blaSHV-12 (n = 1/4), and blaTEM-1B (n = 2/4). Whole genome sequencing confirmed the presence of the plasmid-mediated quinolone resistance qnrS1 gene among three ESBL isolates. No statistically significant differences in seasonal prevalence for E. coli and S. enterica among dairy cattle sampling periods were observed. Furthermore, to our knowledge, this is the first report of E. coli carrying blaCTX-M-15, blaCTX-M-27, blaSHV-12, or qnrS1 isolated from dairy cattle in Uganda. We conclude that the presence of globally disseminated blaCTX-M-15 and blaCTX-M-27 warrants further study to prevent further spread. In addition, the presence of fluoroquinolone resistant ESBL-producing E. coli on dairy farms highlights the potential risk among the human-livestock-environment interaction. This study can be used as a baseline for implementation of a more robust national integrated surveillance system throughout Uganda.

Ceftriaxone-Resistant Nontyphoidal Salmonella from Humans, Retail Meats, and Food Animals in the United States, 1996-2013.

BACKGROUND: Ceftriaxone resistance in Salmonella is a serious public health threat. Ceftriaxone is commonly used to treat severe Salmonella infections, especially in children. Identifying the sources and drivers of ceftriaxone resistance among nontyphoidal Salmonella is crucial. MATERIALS AND METHODS: The National Antimicrobial Resistance Monitoring System (NARMS) tracks antimicrobial resistance in foodborne and other enteric bacteria from humans, retail meats, and food animals. We examined NARMS data reported during 1996-2013 to characterize ceftriaxone-resistant Salmonella infections in humans. We used Spearman rank correlation to examine the relationships between the annual percentage of ceftriaxone resistance among Salmonella isolates from humans with isolates from retail meats and food animals. RESULTS: A total of 978 (2.9%) of 34,100 nontyphoidal Salmonella isolates from humans were resistant to ceftriaxone. Many (40%) ceftriaxone-resistant isolates were from children younger than 18 years. Most ceftriaxone-resistant isolates were one of three serotypes: Newport (40%), Typhimurium (26%), or Heidelberg (12%). All were resistant to other antimicrobials, and resistance varied by serotype. We found statistically significant correlations in ceftriaxone resistance between human and ground beef Newport isolates (r = 0.83), between human and cattle Typhimurium isolates (r = 0.57), between human and chicken Heidelberg isolates (r = 0.65), and between human and turkey Heidelberg isolates (r = 0.67). CONCLUSIONS: Ceftriaxone resistance among Salmonella Newport, Typhimurium, and Heidelberg isolates from humans strongly correlates with ceftriaxone resistance in isolates from ground beef, cattle, and poultry, respectively. These findings support other lines of evidence that food animals are important reservoirs of ceftriaxone-resistant Salmonella that cause human illness in the United States.

Prevalence and Antimicrobial Resistance of Salmonella Isolated from Cattle Feces in United States Feedlots in 2011.

The objective of this study was to determine the prevalence and characteristics of Salmonella spp. isolated from feces of cattle in feedlots in the United States. Fecal samples were collected from up to three pens of cattle in each of 68 feedlots in 12 states. Samples included up to 25 individual fecal pats from the pen floors and up to five composite samples from the floors of the same pens. The prevalence of Salmonella-positive samples was 9.1% (460/5050) and 11.3% (114/1009) for individual and composite samples, respectively. The prevalences of Salmonella at the pen level were 35.6% (72/202) and 22.8% (46/202) for individual and composite samples, respectively. Dietary factors, including inclusion of cottonseed hulls, coccidiostats, and antimicrobial drugs, were associated with differences in prevalence of Salmonella isolation. Overall, 32 serotypes of Salmonella were identified, but six serotypes accounted for 69.1% (495/716) of the isolates. Nearly two-thirds (64.7%, 44/68) of feedlots had at least one positive sample. All isolates were evaluated for susceptibility to a panel of 15 antimicrobial drugs. Most isolates (74.4%, 533/716) were susceptible to all antimicrobial drugs in the panel. When resistance was detected, it was most commonly to tetracycline (21.7%, 155/716 of isolates) or sulfisoxazole (12.4%, 89/716 of isolates). Less than 10% of the isolates were resistant to any other antimicrobials in the panel. The results of this study indicate that the prevalence of Salmonella in individual fecal samples was less than 10%, but that Salmonella is widely distributed among feedlot cattle. Furthermore, when Salmonella is present in feedlot cattle, there is a low occurrence of antimicrobial resistance with the exception of tetracycline and sulfisoxazole. More research is indicated to understand the ecology of Salmonella and antimicrobial resistance, when present, in cattle-feeding operations.

Antimicrobial Susceptibility and Plasmid Replicon Typing of Salmonella enterica Serovar Kentucky Isolates Recovered from Broilers.

Salmonella Kentucky has become the predominant serovar recovered from broilers slaughtered in the United States, and the prevalence of antimicrobial resistance (AMR) has increased dramatically in this serovar. Relationships between AMR, genotype, and plasmid replicon types were characterized for 600 Salmonella Kentucky isolates recovered from chicken carcasses from 2004 to 2013. Pulsed-field gel electrophoresis cluster analysis revealed 112 unique types sharing 79% similarity. Over half of the isolates studies were assigned to two large clusters (unique restriction patterns) consisting of 190 (A) and 151 (B) isolates. The remaining (n = 259) more diverse isolates (110 unique patterns) shall be designated cluster C for discussion. Clusters A had significantly more (p < 0.05) isolates resistant to streptomycin (68.4%) and tetracycline (91.6%) compared to cluster C (50.6% and 40.9% to streptomycin and tetracycline, respectively) or cluster B, which had the least (p < 0.05) resistance (11.9% and 13.2% to streptomycin and tetracycline, respectively). In addition, there was segregation of plasmid replicon types among clusters. Cluster A had significantly more (p < 0.05) replicon type FIB (90.5%) compared to cluster C (37.1%), which had significantly more compared to cluster B (10.6%). Cluster B had significantly more (p < 0.05) replicon type I1 (87.4%) compared to cluster C (68.7%), which had significantly more (p < 0.05) compared to cluster A (32.6%). Cluster C harbored significantly more (p < 0.05) HI2 replicon type (18.1%) compared to clonal clusters A (1.6%) or B (1.3%). The prevalence of plasmid replicon type A/C did not differ among clusters (A, 0.5%; B, 2.0%; C, 0.4%). Both streptomycin and tetracycline resistance were significantly linked (p < 0.05) to plasmid replicon type FIB. In addition, replicon type HI2 was also significantly linked (p < 0.05) to streptomycin resistance. We conclude that the dramatic increase in streptomycin and tetracycline resistance among Salmonella Kentucky isolated from poultry is due to the expansion of strains harboring plasmid replicon types FIB and HI2.

Salmonella Prevalence and Antimicrobial Susceptibility from the National Animal Health Monitoring System Sheep 2011 Study.

Salmonella is a major cause of foodborne illness and can cause clinical disease in animals. Understanding the on-farm ecology of Salmonella will be helpful in decreasing the risk of foodborne transmission. An objective of this study was to determine the prevalence of Salmonella among fecal samples collected on sheep operations in the United States. Another objective was to compare the use of composite fecal samples with fecal samples collected from individual sheep as a tool for screening sheep flocks for Salmonella. Sheep fecal samples (individual and composite) were collected on operations in 22 states. Salmonella isolates were characterized with regard to species, serotype, and antimicrobial susceptibility profile. Most operations (72.1%) had at least one positive sample and overall 26.9% of samples were positive. The percentage of positive samples varied by animal age class. Composite and individual samples gave similar results. The majority of the isolates (94%) were Salmonella enterica subspecies diarizonae serotype 61:-:1,5,7. Nearly all of the isolates (91.2%) tested for antimicrobial susceptibility were susceptible to all antimicrobials in the panel. The findings suggest that salmonellae typically associated with foodborne disease transmission are infrequently found on sheep operations in the United States.

Identification and characterization of multidrug-resistant Salmonella enterica serotype Albert isolates in the United States.

Salmonella enterica is one of the most common causes of bacterial foodborne illness in the United States. Although most Salmonella infections are self-limiting, antimicrobial treatment of invasive salmonellosis is critical. The primary antimicrobial treatment options include fluoroquinolones or extended-spectrum cephalosporins, and resistance to these antimicrobial drugs may complicate treatment. At present, S. enterica is composed of more than 2,600 unique serotypes, which vary greatly in geographic prevalence, ecological niche, and the ability to cause human disease, and it is important to understand and mitigate the source of human infection, particularly when antimicrobial resistance is found. In this study, we identified and characterized 19 S. enterica serotype Albert isolates collected from food animals, retail meat, and humans in the United States during 2005 to 2013. All five isolates from nonhuman sources were obtained from turkeys or ground turkey, and epidemiologic data suggest poultry consumption or live-poultry exposure as the probable source of infection. S. enterica serotype Albert also appears to be geographically localized to the midwestern United States. All 19 isolates displayed multidrug resistance, including decreased susceptibility to fluoroquinolones and resistance to extended-spectrum cephalosporins. Turkeys are a likely source of multidrug-resistant S. enterica serotype Albert, and circulation of resistance plasmids, as opposed to the expansion of a single resistant strain, is playing a role. More work is needed to understand why these resistance plasmids spread and how their presence and the serotype they reside in contribute to human disease.