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543700.9365Analysis of antibiotics resistant genes in different strains of Staphylococcus aureus. The control of Staphylococcus aureus infection is being hampered by methicillin and other resistant strains. The identification of the unique antibiotic resistant genes from the genomes of various strains of S. aureus is of interest. We analyzed 11 S. aureus genomes sequences for Antibiotics Resistance Genes (ARGs) using CARD 2017 platform. We identified 32 ARGs across 11 S. aureus strains. Tet(38), norB, lmrB, mepA and mepR were present across genomes except for S. aureus strain UTSW MRSA 55. The mepA and mepR were found across 11 different genomes. However, FosB3, vgaALC, mphC and SAT-4 were found in UTSW MRSA 55, S.a. strain ISU935 and S.a. strain FDAARGOS_159. The prevalent mode of mechanism of antibiotics resistant was efflux pump complex or subunit conferring antibiotic resistance as well as protein(s). Analysis of norB, ImrB, norA, ImrB, tet (38), sav1866 and mecA have 12 to 14 TMHs. The results help in the understanding of Staphylococcus aureus pathogenesis in the context of antibiotic resistance.201829785070
523310.9305Antibiotic resistance pattern of the allochthonous bacteria isolated from commercially available spices. Spices are often used in dried form, sometimes with significant microbial contamination including pathogenic and food spoilage bacteria. The antibiotic resistance represents an additional risk for food industry, and it is worthy of special attention as spices are important food additives. During our work, we examined the microbiological quality of 50 different spices with cultivation methods on diverse selective media. The identification of the most representative bacteria was carried out using 16S rDNA gene sequence analysis. Antibiotic resistance profiling of twelve identified Bacillus species (B. subtilis subsp. stercoris BCFK, B. licheniformis BCLS, B. siamensis SZBC, B. zhangzhouensis BCTA, B. altitudinis SALKÖ, B. velezensis CVBC, B. cereus SALÖB isolate, B. tequilensis KOPS, B. filamentosus BMBC, B. subtilis subsp. subtilis PRBC2, B. safensis BMPS, and B. mojavensis BCFK2 isolate) was performed using the standard disk-diffusion method against 32 antibiotics. The study showed that the majority resistance was obtained against penicillin G (100%), oxacillin (91.67%), amoxyclav (91.67%), rifampicin (75%), and azithromycin (75%). Our findings suggest that spices harbor multidrug-resistant bacteria.202134401102
138120.9292Differences in antimicrobial resistance-related genes of Trueperella pyogenes between isolates detected from cattle and pigs. We investigated antimicrobial resistance-related genes in 109 isolates of Trueperella pyogenes that were isolated in cattle and pigs. All 89 tetracycline-resistant T. pyogenes isolates carried the resistance gene harbored either tetW, tetM, tetA(33), tetK, or tetL. The ermX or ermB were detected in 18 of 23 erythromycin-resistant isolates. Streptomycin-resistant aadA1, aadA9, aadA11, aadA24, strA, or strB were detected in 25 of 83 isolates. There were significant differences in the percentages of tetA(33), ermB, aadA1, aadA9, aadA11, or aadA24 carriage between cattle and pig isolates. In addition, the Class 1 gene cassette was detected only in 17 cattle isolates. This suggests that T. pyogenes isolates acquire resistance gene in each environment of cattle and pigs, and that the transmission of the bacteria between cattle and pigs is limited.202439293943
363330.9292Antimicrobial resistance of heterotrophic marine bacteria isolated from seawater and sands of recreational beaches with different organic pollution levels in southeastern Brazil: evidences of resistance dissemination. Antimicrobial resistance of marine heterotrophic bacteria to different antimicrobials agents were evaluated in seawater, dry and wet sands from three marine recreational beaches with different pollution levels. In all studied beaches, the greatest frequencies of resistance were found in relation to penicillin. On Gonzaguinha, the most polluted beach, 72.3% of all isolated strains showed simple resistance, whilst 8.33% had multiple resistance. The values found on Ilha Porchat beach, were 70.8% and 6.9% for simple and multiple resistances, respectively. On Guaraú, the less polluted beach, only 35.3% of isolated strains had simple resistance. Multiple resistance was not observed. While samples from Gonzaguinha and Ilha Porchat beach showed isolated strains resistant to seven and six different antimicrobial agents, respectively, samples from Guaraú beach were resistant only to penicillin and erytromicin. The positive correlations obtained between the degree of seawater contamination and frequency and variability of bacterial resistance indicate that polluted marine recreational waters and sands are sources of resistant bacteria contributing thus, to the dissemination of bacterial resistance.201019904625
588940.9289Monitoring of Virulence Genes, Drug-Resistance in Campylobacter coli Isolated from Golden Retrievers. The investigation was performed on 75 of Golden Retriever puppies. Faecal samples were collected on the 42 day of the puppies life (con-trol). Probiotic preparation was administered on 43 day of the puppies life and 10 days after the application of the probiotic, faecal samples were collected again (on 53 day of puppies life). All isolates of Campylobacter coli isolated prior to the administration of the probiotic were found to contain the cadF gene responsible for adhesion, as well as, the flaA gene influencing motility of the examined bacteria. Significant differences (P < 0.05) were recorded only in the case of enrofloxacin.201630015450
524050.9289Dynamics of Antimicrobial Resistance Carriage in Koalas (Phascolarctos Cinereus) and Pteropid Bats (Pteropus Poliocephalus) Before, During and After Wildfires. In the 2019-2020 summer, wildfires decimated the Australian bush environment and impacted wildlife species, including koalas (Phascolarctos cinereus) and grey headed flying fox pups (Pteropid bats, Pteropus poliocephalus). Consequently, hundreds of koalas and thousands of bat pups entered wildlife hospitals with fire-related injuries/illness, where some individuals received antimicrobial therapy. This study investigated the dynamics of antimicrobial resistance (AMR) in pre-fire, fire-affected and post-fire koalas and Pteropid bat pups. PCR and DNA sequencing were used to screen DNA samples extracted from faeces (koalas and bats) and cloacal swabs (koalas) for class 1 integrons, a genetic determinant of AMR, and to identify integron-associated antibiotic resistance genes. Class 1 integrons were detected in 25.5% of koalas (68 of 267) and 59.4% of bats (92 of 155). Integrons contained genes conferring resistance to aminoglycosides, trimethoprim and beta-lactams. Samples were also screened for blaTEM (beta-lactam) resistance genes, which were detected in 2.6% of koalas (7 of 267) and 25.2% of bats (39 of 155). Integron occurrence was significantly higher in fire-affected koalas in-care compared to wild pre-fire koalas (P < 0.0001). Integron and blaTEM occurrence were not significantly different in fire-affected bats compared to pre-fire bats (P > 0.05), however, their occurrence was significantly higher in fire-affected bats in-care compared to wild fire-affected bats (P < 0.0001 and P = 0.0488 respectively). The observed shifts of AMR dynamics in wildfire-impacted species flags the need for judicious antibiotic use when treating fire-affected wildlife to minimise unwanted selective pressure and negative treatment outcomes associated with carriage of resistance genes and antibiotic resistant bacteria.202438332161
543560.9289Distribution of fibronectin-binding protein genes (prtF1 and prtF2) and streptococcal pyrogenic exotoxin genes (spe) among Streptococcus pyogenes in Japan. Two hundred and seventy-two strains of Streptococcus pyogenes isolated from patients with invasive and noninvasive infections in Japan were evaluated for the prevalence of fibronectin-binding protein genes (prtF1 and prtF2). The possible associations of the genes with streptococcal pyrogenic exotoxin genes, macrolide resistance genes, and emm types were also evaluated. Overall, about 50% of S. pyogenes isolates carried fibronectin-binding protein genes. The prevalence of the prtF1 gene was significantly higher among isolates from noninvasive infections (71.4%) than among isolates from invasive infections (30.8%; P = 0.0037). Strains possessing both the prtF1 and prtF2 genes were more likely to be isolates from noninvasive infections than isolates from invasive infections (50.6% vs 15.4%; P = 0.019). S. pyogenes isolates with streptococcus pyrogenic exotoxin genes (speA and speZ) were more common among isolates without fibronectin-binding protein genes. The speC gene was more frequently identified among isolates with fibronectin-binding protein genes (P = 0.05). Strains belonging to emm75 or emm12 types more frequently harbored macrolide resistance genes than other emm types (P = 0.0094 and P = 0.043, respectively). Strains carrying more than one repeat at the RD2 region of the prtF1 gene and the FBRD region of the prtF2 gene were more prevalent among strains with macrolide resistance genes than among strains negative for macrolide resistance genes. These genes (i.e., the prtF1, prtF2, and spe genes) may enable host-bacteria interaction, and internalization in the host cell, but may not enable infection complications such as invasive diseases.200920012726
538270.9285Characterization of Streptococcus pyogenes from Animal Clinical Specimens, Spain. Streptococcus pyogenes appears to be almost exclusively restricted to humans, with few reports on isolation from animals. We provide a detailed characterization (emm typing, pulsed-field gel electrophoresis [PFGE], and multilocus sequence typing [MLST]) of 15 S. pyogenes isolates from animals associated with different clinical backgrounds. We also investigated erythromycin resistance mechanisms and phenotypes and virulence genes. We observed 2 emm types: emm12 (11 isolates) and emm77 (4 isolates). Similarly, we observed 2 genetic linages, sequence type (ST) 26 and ST63. Most isolates exhibited the M macrolide resistance phenotype and the mefA/ermB genotype. Isolates were grouped into 2 clones on the basis of emm-MLST-PFGE-virulence gene profile combinations: clone 1, characterized by the combined genotype emm12-ST36-pulsotype A-speG; and clone 2, characterized by the genotype emm77-ST63-pulsotype B-speC. Our results do not show conclusively that animals may represent a new reservoir of S. pyogenes but indicate the ability of human-derived S. pyogenes isolates to colonize and infect animals.201729148379
40780.9285Molecular cloning and characterization of two lincomycin-resistance genes, lmrA and lmrB, from Streptomyces lincolnensis 78-11. Two different lincomycin-resistance determinants (lmrA and lmrB) from Streptomyces lincolnensis 78-11 were cloned in Streptomyces lividans 66 TK23. The gene lmrA was localized on a 2.16 kb fragment, the determined nucleotide sequence of which encoded a single open reading frame 1446 bp long. Analysis of the deduced amino acid sequence suggested the presence of 12 membrane-spanning domains and showed significant similarities to the methylenomycin-resistance protein (Mmr) from Streptomyces coelicolor, the QacA protein from Staphylococcus aureus, and several tetracycline-resistance proteins from both Gram-positive and Gram-negative bacteria, as well as to some sugar-transport proteins from Escherichia coli. The lmrB gene was actively expressed from a 2.7 kb fragment. An open reading frame of 837 bp could be localized which encoded a protein that was significantly similar to 23S rRNA adenine(2058)-N-methyltransferases conferring macrolide-lincosamide-streptogramin resistance. LmrB also had putative rRNA methyltransferase activity since lincomycin resistance of ribosomes was induced in lmrB-containing strains. Surprisingly, both enzymes, LmrA and LmrB, had a substrate specificity restricted to lincomycin and did not cause resistance to other lincosamides such as celesticetin and clindamycin, or to macrolides.19921328813
133790.9284Biofilm formation, antimicrobial assay, and toxin-genotypes of Clostridium perfringens type C isolates cultured from a neonatal Yangtze finless porpoise. This is a culture-dependent study with the objective of pure culturing and characterizing pathogenic bacteria from the blowhole, lung, stomach and fecal samples of a neonatal crucially endangered Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) that died 27 days after birth. Bacteria were inoculated using a swab onto blood and MacConkey agar plates and representative isolates were identified through 16S rRNA gene sequence analysis. A total of three Clostridium perfringens type C strains from the fecal samples were isolated. Toxin genes, including cpa, cpb and cpb2, were detected by PCR amplification, whereas the etx, iap and cpe genes were not detected. Biofilm formation of the three strains was then examined. Only one strain was capable of biofilm formation. In addition, isolates showed strong resistance against the antibiotics amikacin (3/3), erythromycin (1/3), gentamicin (3/3), streptomycin (3/3), and trimethoprim (3/3), while sensitivity to ampicillin (3/3), bacitracin (3/3), erythromycin (2/3), penicillin G (3/3), and tetracycline (3/3). The results suggested C. perfringens type C could have contributed to the death of this neonatal porpoise.202235662380
2995100.9280Antibiotic resistance in bacteria from magpies (Pica pica) and rabbits (Oryctolagus cuniculus) from west Wales. The prevalence of antibiotic-resistant bacteria in wild animal and bird populations is largely unknown, with little consistency among the few published reports. We therefore examined intestinal bacteria from magpies (Pica pica) and rabbits (Oryctolagus cuniculus) collected in rural west Wales. Escherichia coli isolates resistant to multiple antibiotics were grown from eight of 20 magpies trapped in spring, 1999 and one of 17 in spring, 2000; the most prevalent resistance trait among these isolates was to tetracycline, but resistances to ampicillin, chloramphenicol, kanamycin, sulphonamide, tetracycline and trimethoprim were also found. Tetracycline-resistant Enterococcus spp. were found in one of 20 magpies in 1999 and three of 17 in 2000. Only one resistant E. coli isolate was detected among gut bacteria from 13 rabbits, and this strain was resistant only to tetracycline. Differences in the prevalence of resistance between bacteria from rabbits and magpies may reflect differences in diet: rabbits graze field edges, whereas magpies are omnivorous and opportunistic. The resistance genes found in E. coli isolates from magpies mostly corresponded to those common among human isolates, but those conferring tetracycline resistance were unique.200111722546
1254110.9280Genetic diversity and antimicrobial resistance of Staphylococcus aureus from recurrent tonsillitis in children. The aim of this study was to analyze the prevalence of Staphylococcus aureus in the tonsils of children subjected tonsillectomy due to recurrent tonsilitis and to determine the spa types of the pathogens, carriage of virulence genes and antimicrobial resistance profiles. The study included 73 tonsillectomized children. Bacteria, including S. aureus were isolated from tonsillar surface prior to tonsillectomy, recovered from tonsillar core at the time of the surgery, and from posterior pharynx 2-4 weeks after the procedure. Staphylococcus aureus isolates were compared by spa typing, tested for antimicrobial susceptibility and for the presence of superantigenic toxin genes (sea-seu, eta, etb, tst, lukS/lukF-PV) by multiplex polymerase chain reaction. Seventy-three patients (mean 7.1 ± 4.1 years, 61.6% male) were assessed. The most commonly isolated bacteria were S. aureus. The largest proportion of staphylococcal isolates originated from tonsillar core (63%), followed by tonsillar surface (45.1%) and posterior pharynx in tonsillectomized children (18.2%, p = 0.007). Five (6.3%) isolates were identified as MRSA (mecA-positive). Up to 67.5% of the isolates synthesized penicillinases (blaZ-positive isolates), and 8.8% displayed MLS(B) resistance. The superantigenic toxin genes were detected in more than half of examined isolates (56.3%). spa types t091, t084, and t002, and clonal complexes (CCs) CC7, CC45, and CC30 turned out to be most common. Staphylococcus aureus associated with RT in children showed pathogenicity potential and considerable genetic diversity, and no clones were found to be specific for this condition although further studies are needed.202031692060
2423120.9279Toxin gene detection and antibiotic resistance of Clostridium perfringens from aquatic sources. Clostridium perfringens is a zoonotic opportunistic pathogen that produces toxins that can cause necrotic enteritis and even "sudden death disease". This bacterium is widely distributed in the intestines of livestock and human, but there are few reports of distribution in aquatic animals (Hafeez et al., 2022). In order to explore the isolation rate of C. perfringens and the toxin genes they carry, 141 aquatic samples, including clams (Ruditapes philippinarum), oysters (Ostreidae), and mud snails (Bullacta exerata Philippi), were collected from the coastal areas of Shandong Province, China. C. perfringens strains were tested for cpa, cpb, etx, iap, cpb2, cpe, netB, and tpeL genes. 45 clam samples were boiled at 100 °C for 5 min before bacteria isolation. 80 strains were isolated from 141 samples with the positive rate being 57 %.And the positive rates of cooked clams was 87 % which was higher than the average. In detection of 8 toxin genes, all strains tested cpa positive, 3 strains netB positive, and 2 cpb and cpe, respectively. 64 strains were selected to analyze the antibiotic resistance phenotype of 10 antibiotics. The average antibiotic resistance rates of the strains to tetracycline, clindamycin, and ampicillin were 45 %, 20 %, and 16 % respectively, and the MIC of 4 strains to clindamycin was ≥128 μg/mL. A high isolation rate of C. perfringens from aquatic animals was shown, and it was isolated from boiled clams for the first time, in which cpe and netB toxin genes were detected for the first time too. The toxin encoded by cpe gene can cause food poisoning of human, thus the discoveries of this study have certain guiding significance for food safety. Antibiotics resistant C. perfringens of aquatic origin may arise from transmission in the terrestrial environment or from antibiotic contamination of the aquaculture environment and is of public health significance.202438428166
1352130.9277Bacterial Diversity and Antimicrobial Resistance of Microorganisms Isolated from Teat Cup Liners in Dairy Farms in Shandong Province, China. Global milk consumption exceeds 800 million tons a year and is still growing. Milk quality and its products are critical to human health. A teat cup makes direct contact with the cow's teats during milking and its cleanliness is very important for the quality of raw milk. In this study, the microorganism from post-milking teat cup liners were collected from six dairy farms in Shandong Province of China, the bacterial species were identified using microbial mass spectrometry, the minimum inhibitory concentrations of the isolated strains against ten antimicrobial agents were determined using the broth microdilution method, and the antimicrobial resistance genes were detected by PCR. The results indicated that the most frequently isolated bacteria in this study were Bacillus licheniformis (39/276, 14.13%), followed by Bacillus pumilus (20/276, 7.25%), Bacillus cereus (17/276, 6.16%), and Bacillus subtili (16/276, 5.80%). The isolates exhibited the highest average resistance to lincomycin (87.37%), followed by sulfadiazine (61.05%) and streptomycin (42.63%); the highest detection rate of resistance genes was Sul1 (55.43%), followed by ant(4') (51.09%), tet(M) (25.36%), bla(KPC) (3.62%) and qnrS (3.62%). These findings imply the necessity for enhanced measures in disinfecting cow udders and milking equipment, highlighting the persistently challenging issue of antimicrobial resistance in Shandong Province.202439123692
5383140.9277Draft genome sequence of Acinetobacter haemolyticus strain MUWRP1017 isolated from the pus of a female inpatient at Bwera General Hospital in Uganda. The bacterium Acinetobacter haemolyticus, with a genome size of 3.4 Mb, was isolated from a pus swab of a wound on the left lower limb above the ankle joint of a female patient. This strain carries the antimicrobial resistance genes cephalosporinase blaADC-25, oxallinase blaOXA-264, floR, and sul2 and other resistance and virulence genes.202439162454
5216150.9277Unraveling the draft genome and phylogenomic analysis of a multidrug-resistant Planococcus sp. NCCP-2050(T): a promising novel bacteria from Pakistan. Planococcus is a genus of Gram-positive bacteria known for potential industrial and agricultural applications. Here, we report the first draft genome sequence and phylogenomic analysis of a CRISPR-carrying, multidrug-resistant, novel candidate Planococcus sp. NCCP-2050(T) isolated from agricultural soil in Pakistan. The strain NCCP-2050(T) exhibited significant resistance to various classes of antibiotics, including fluoroquinolones (i.e., ciprofloxacin, levofloxacin, ofloxacin, moxifloxacin, and bacitracin), cephalosporins (cefotaxime, ceftazidime, cefoperazone), rifamycins (rifampicin), macrolides (erythromycin), and glycopeptides (vancomycin). Planococcus sp. NCCP-2050(T) consists of genome size of 3,463,905 bp, comprised of 3639 annotated genes, including 82 carbohydrate-active enzyme genes and 39 secondary metabolite genes. The genome also contained 80 antibiotic resistance, 162 virulence, and 305 pathogen-host interaction genes along with two CRISPR arrays. Based on phylogenomic analysis, digital DNA-DNA hybridization, and average nucleotide identity values (i.e., 35.4 and 88.5%, respectively) it was suggested that strain NCCP-2050(T) might represent a potential new species within the genus Planococcus. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13205-023-03748-z.202337663752
5376160.9277In vitro Activity of Contezolid Against Methicillin-Resistant Staphylococcus aureus, Vancomycin-Resistant Enterococcus, and Strains With Linezolid Resistance Genes From China. Contezolid is a novel oxazolidinone, which exhibits potent activity against gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), and penicillin-resistant Streptococcus pneumoniae (PRSP). In this study, the in vitro activity of contezolid was compared with linezolid (LZD), tigecycline (TGC), teicoplanin (TEC), vancomycin (VA), daptomycin (DAP), and florfenicol (FFC) against MRSA and VRE strains isolated from China. Contezolid revealed considerable activity against MRSA and VRE isolates with MIC(90) values of 0.5 and 1.0 μg/mL, respectively. For VRE strains with different resistance genotypes, including vanA- and vanM-type strains, contezolid did not exhibit significantly differential antibacterial activity. Furthermore, the antimicrobial activity of contezolid is similar to or slightly better than that of linezolid against MRSA and VRE strains. Subsequently, the activity of contezolid was tested against strains carrying linezolid resistance genes, including Staphylococcus capitis carrying cfr gene and Enterococcus faecalis carrying optrA gene. The results showed that contezolid exhibited similar antimicrobial efficacy to linezolid against strains with linezolid resistance genes. In general, contezolid may have potential benefits to treat the infections caused by MRSA and VRE pathogens.202134489919
1299170.9276Prevalence, Drug Resistance, and Virulence Genes of Potential Pathogenic Bacteria in Pasteurized Milk of Chinese Fresh Milk Bar. Fresh Milk Bar (FMB), an emerging dairy retail franchise, is used to instantly produce and sell pasteurized milk and other dairy products in China. However, the quality and safety of pasteurized milk in FMB have received little attention. The objective of this study was to investigate the prevalence, antimicrobial resistance, and virulence genes of Escherichia coli, Staphylococcus aureus, and Streptococcus in 205 pasteurized milk samples collected from FMBs in China. Four (2.0%) isolates of E. coli, seven (3.4%) isolates of S. aureus, and three (1.5%) isolates of Streptococcus agalactiae were isolated and identified. The E. coli isolates were resistant to amikacin (100%), streptomycin (50%), and tetracycline (50%). Their detected resistance genes include aac(3)-III (75%), blaTEM (25%), aadA (25%), aac(3)-II (25%), catI (25%), and qnrB (25%). The S. aureus isolates were mainly resistant to penicillin G (71.4%), trimethoprim-sulfamethoxazole (71.4%), kanamycin (57.1%), gentamicin (57.1%), amikacin (57.1%), and clindamycin (57.1%). blaZ (42.9%), mecA (28.6%), ermB (14.3%), and ermC (14.3%) were detected as their resistance genes. The Streptococcus strains were mainly resistant to tetracycline (66.7%) and contained the resistance genes pbp2b (33.3%) and tetM (33.3%). The virulence genes eae and stx2 were only found in one E. coli strain (25%), sec was detected in two S. aureus strains (28.6%), and bca was detected in one S. agalactiae strain (33.3%). The results of this study indicate that bacteria with drug resistance and virulence genes isolated from the pasteurized milk of FMB are a potential risk to consumers' health.202134129676
3628180.9276Antibiotic resistance patterns of gram-negative bacteria isolated from environmental sources. A total of 2,445 gram-negative bacteria belonging to fecal coliform, Pseudomonas, Moraxella, Acinetobacter, and Flavobacterium-Cytophaga groups were isolated from the rivers and bay of Tillamook, Oregon, and their resistances to chloramphenicol (25 microgram/ml), streptomycin (10 microgram/ml), ampicillin (10 microgram/ml), tetracycline (25 microgram/ml), chlortetracycline (25 microgram/ml), oxytetracycline (25 microgram/ml), neomycin (50 microgram/ml), nitrofurazone (12.5 microgram/ml), nalidixic acid (25 microgram/ml), kanamycin (25 microgram/ml), and penicillin G (10 IU/ml) were determined. Among fecal coliforms the bay isolates showed greater resistance to antibiotics than those from tributaries or surface runoff. No such well-defined difference was found among other bacterial groups. The antibiotic resistance patterns of gram-negative bacteria from different sources correlated well, perhaps indicating their common origin. The antibiotic resistance patterns of gram-negative bacteria of different general also correlated well, perhaps indicating that bacteria which share a common environment also share a common mode for developing antibiotic resistance.1978727777
5245190.9275Antimicrobial Resistance in U.S. Retail Ground Beef with and without Label Claims Regarding Antibiotic Use. ABSTRACT: Antibiotics used during food animal production account for approximately 77% of U.S. antimicrobial consumption by mass. Ground beef products labeled as raised without antibiotics (RWA) are perceived to harbor lower levels of antimicrobial-resistant bacteria than conventional (CONV) products with no label claims regarding antimicrobial use. Retail ground beef samples were obtained from six U.S. cities. Samples with an RWA or U.S. Department of Agriculture Organic claim (n = 299) were assigned to the RWA production system. Samples lacking these claims (n = 300) were assigned to the CONV production system. Each sample was cultured for the detection of five antimicrobial-resistant bacteria. Genomic DNA was isolated from each sample, and a quantitative PCR assay was used to determine the abundance of 10 antimicrobial resistance (AMR) genes. Prevalence of tetracycline-resistant Escherichia coli (CONV, 46.3%; RWA, 34.4%; P < 0.01) and erythromycin-resistant Enterococcus (CONV, 48.0%; RWA, 37.5%; P = 0.01) was higher in CONV ground beef. Salmonella was detected in 1.2% of samples. The AMR gene blaCTX-M (CONV, 4.1 log-normalized abundance; RWA, 3.8 log-normalized abundance; P < 0.01) was more abundant in CONV ground beef. The AMR genes mecA (CONV, 4.4 log-normalized abundance; RWA, 4.9 log-normalized abundance; P = 0.05), tet(A) (CONV, 3.9 log-normalized abundance; RWA, 4.5 log-normalized abundance; P < 0.01), tet(B) (CONV, 3.9 log-normalized abundance; RWA, 4.5 log-normalized abundance; P < 0.01), and tet(M) (CONV, 5.4 log-normalized abundance; RWA, 5.8 log-normalized abundance; P < 0.01) were more abundant in RWA ground beef. Although these results suggest that antimicrobial use during U.S. cattle production does not increase human exposure to antimicrobial-resistant bacteria via ground beef, quantitative microbiological risk assessments are required for authoritative determination of the human health impacts of the use of antimicrobial agents during beef production.202133302298