Detection of florfenicol resistance genes in Escherichia coli isolated from sick chickens

Current examining methods and mathematical models of horizontal transfer of antibiotic resistance genes in the environment

The increasing prevalence of antibiotic resistance genes (ARGs) in the environment has garnered significant attention due to their health risk to human beings. Horizontal gene transfer (HGT) is considered as an important way for ARG dissemination. There are four general routes of HGT, including conjugation, transformation, transduction and vesiduction. Selection of appropriate examining methods is crucial for comprehensively understanding characteristics and mechanisms of different HGT ways. Moreover, combined with the results obtained from different experimental methods, mathematical models could be established and serve as a powerful tool for predicting ARG transfer dynamics and frequencies. However, current reviews of HGT for ARG spread mainly focus on its influencing factors and mechanisms, overlooking the important roles of examining methods and models. This review, therefore, delineated four pathways of HGT, summarized the strengths and limitations of current examining methods, and provided a comprehensive summing-up of mathematical models pertaining to three main HGT ways of conjugation, transformation and transduction. Finally, deficiencies in current studies were discussed, and proposed the future perspectives to better understand and assess the risks of ARG dissemination through HGT.

Antibiotic resistance in wildlife from Antarctic Peninsula

Although considered one of the most pristine ecosystems, Antarctica has been largely influenced by human activities during the last 50 years, affecting its unique biodiversity. One of the major global threats to health is the emergence of antibiotic-resistant bacteria that may be actively transferred to wildlife. We cultured and tested for antibiotic resistance in 137 cloacal and fresh fecal samples of several avian and marine mammal species from the Antarctic Peninsula, the most impacted area in Antarctica. Alarmingly, 80 % of the isolates showed antibiotic resistance, either phenotypically or genotypically. Most of the resistant bacteria, such as Enterobacteriaceae and Enterococcus species, are part of local gastrointestinal microbiota. Penguins and pinnipeds harbored a great diversity of antibiotic resistance and must be eligible as sentinels for future studies. These results show that antibiotic resistance has rapidly transferred to bacteria in Antarctic wildlife, which is a global matter of concern.

A review on the antibiotic florfenicol: Occurrence, environmental fate, effects, and health risks

Florfenicol, as a replacement for chloramphenicol, can tightly bind to the A site of the 23S rRNA in the 50S subunit of the 70S ribosome, thereby inhibiting protein synthesis and bacterial proliferation. Due to the widespread use in aquaculture and veterinary medicine, florfenicol has been detected in the aquatic environment worldwide. Concerns over the effects and health risks of florfenicol on target and non-target organisms have been raised in recent years. Although the ecotoxicity of florfenicol has been widely reported in different species, no attempt has been made to review the current research progress of florfenicol toxicity, hormesis, and its health risks posed to biota. In this study, a comprehensive literature review was conducted to summarize the effects of florfenicol on various organisms including bacteria, algae, invertebrates, fishes, birds, and mammals. The generation of antibiotic resistant bacteria and spread antibiotic resistant genes, closely associated with hormesis, are pressing environmental health issues stemming from overuse or misuse of antibiotics including florfenicol. Exposure to florfenicol at μg/L-mg/L induced hormetic effects in several algal species, and chromoplasts might serve as a target for florfenicol-induced effects; however, the underlying molecular mechanisms are completely lacking. Exposure to high levels (mg/L) of florfenicol modified the xenobiotic metabolism, antioxidant systems, and energy metabolism, resulting in hepatotoxicity, renal toxicity, immunotoxicity, developmental toxicity, reproductive toxicity, obesogenic effects, and hormesis in different animal species. Mitochondria and the associated energy metabolism are suggested to be the primary targets for florfenicol toxicity in animals, albeit further in-depth investigations are warranted for revealing the long-term effects (e.g., whole-life-cycle impacts, multigenerational effects) of florfenicol, especially at environmental levels, and the underlying mechanisms. This will facilitate the evaluation of potential hormetic effects and construction of adverse outcome pathways for environmental risk assessment and regulation of florfenicol.

Pharmacokinetics of florfenicol and its metabolite florfenicol amine in the plasma, urine, and feces of fattening male donkeys following single oral administration

Florfenicol (FF) is a commonly used antibacterial agent in animals. We investigated the pharmacokinetics of FF and its metabolite florfenicol amine (FFA) in donkeys. Donkeys were administered FF (30 mg/kg bodyweight, p.o.). Pharmacokinetic parameters were calculated using a non-compartmental model. The FF (FFA) pharmacokinetics parameters were characterized by along elimination half-life (t1/2 kz) of 5.92 h (15.95 h), plasma peak concentration (Cmax) of 0.13 μg/mL (0.08 μg/mL), and the time taken to reach Cmax (Tmax) of 0.68 h (0.72 h). The area under plasma concentration-time curve and mean residence time of FF (FFA) in plasma were 1.31 μg·mL-1·h (0.47 μg·mL-1·h) and 10.37 h (18.40 h), respectively. The t1/2 kz of FF and FFA in urine was 21.93 and 40.26 h, and the maximum excretion rate was 10.56 and 4.03 μg/h reached at 25.60 and 32.20 h, respectively. The respective values in feces were 0.02 and 0.01 μg·h-1 reached at 33.40 h. The amount of FF and FFA recovered in feces was 0.52 and 0.22 μg, respectively. In conclusion, FF (FFA) is rapidly absorbed and slowly eliminated after a single oral administration to donkeys. Compared to FF, FFA was more slowly eliminated. FF (FFA) is mostly excreted through urine.

Extended-spectrum β-lactamase-producing E. coli from retail meat and workers: genetic diversity, virulotyping, pathotyping and the antimicrobial effect of silver nanoparticles

BACKGROUND

The spread of extended-spectrum β-lactamases (ESBL) producing E. coli from food animals and the environment to humans has become a significant public health concern. The objectives of this study were to determine the occurrence, pathotypes, virulotypes, genotypes, and antimicrobial resistance patterns of ESBL-producing E. coli in retail meat samples and workers in retail meat shops in Egypt and to evaluate the bactericidal efficacy of silver nanoparticles (AgNPs-H2O2) against multidrug resistant (MDR) ESBL-producing E. coli.

RESULTS

A total of 250 retail meat samples and 100 human worker samples (hand swabs and stool) were examined for the presence of ESBL- producing E. coli. Duck meat and workers' hand swabs were the highest proportion of ESBL- producing E. coli isolates (81.1%), followed by camel meat (61.5%). Pathotyping revealed that the isolates belonged to groups A and B1. Virulotyping showed that the most prevalent virulence gene was Shiga toxin 2 (stx2) associated gene (36.9%), while none of the isolates harbored stx1 gene. Genotyping of the identified isolates from human and meat sources by REP-PCR showed 100% similarity within the same cluster between human and meat isolates. All isolates were classified as MDR with an average multiple antibiotic resistance (MAR) index of 0.7. AgNPs-H2O2 at concentrations of 0.625, 1.25, 2.5 and 5 μg/mL showed complete bacterial growth inhibition.

CONCLUSIONS

Virulent MDR ESBL-producing E. coli were identified in retail meat products in Egypt, posing significant public health threats. Regular monitoring of ESBL-producing E. coli frequency and antimicrobial resistance profile in retail meat products is crucial to enhance their safety. AgNPs-H2O2 is a promising alternative for treating MDR ESBL-producing E. coli infections and reducing antimicrobial resistance risks.

Longitudinal Study Detects the Co-Carriage of ESBL and mcr-1 and -4 Genes in Escherichia coli Strains in a Portuguese Farrow-to-Finish Swine Herd

Cephalosporins and polymyxins are employed in antimicrobial protocols to control and treat neonatal infections and post-weaning diarrhoea in swine operations. We conducted a longitudinal study to evaluate the colonization and transmission of antibiotic–resistant Escherichia coli in sows and their piglets in a farrow-to-finish operation, focusing on characterization of Extended Spectrum Beta-Lactamase (ESBL) and mcr genes, virulence traits and genetic relatedness. A total of 293 E. coli isolates were obtained from faecal samples collected in five time points. At birth blaCTX-M-1group cluster was detected in E. coli isolates from 9 sows and 49 piglets (73.41%), while in the following four’ piglets sampling moments it was detected in 91.8%, 57.6%, 71.4% and 97.4%. The gene mcr-1 was detected in E. coli from one sow and from three piglets from different litters at birth and increased in the first weeks of piglet life (68.85%, 100%, 90% and 8.1%). A new mcr-4 allele, mcr-4.7, was identified in 3.28%, 28.57%, 7.5% of E. coli isolates. Most mcr-positive E. coli isolates (96,7%) carried blaCTX-M-1Group genes and 93,33% carried both mcr-4 and mcr-1. CTX-M-1 and CTX-M-32 were the most predominant ESBLs. Plasmids belonged to IncI1, IncF and IncN groups. Most isolates belong to phylogenetic group B1; PAI IV536 marker was detected in nine isolates. The strains were kept in the different stages of the piglets’ life. The use of ceftiofur and colistin may explain the high prevalence and co-selection of blaCTX-M-1Group and mcr-1 and/or -4 genes, contributing to the maintenance of resistant and virulent isolates throughout the pig life cycle that may reach the food chain.

Serological Variety and Antimicrobial Resistance in Salmonella Isolated from Reptiles

Salmonella enterica is one of the best adapted bacterial pathogens causing infections in a wide variety of vertebrate species. The aim of this study was to investigate the prevalence of Salmonella in different reptile species and to evaluate their serological variety and patterns of antimicrobial resistance. In total, 97 samples from 25 wild and domesticated reptile species were investigated in Lithuania. Serological variety, as well as phenotypical and genotypical resistance to antimicrobials, were investigated. Fifty isolates of Salmonella were obtained from the ninety-seven tested samples (51.5%; 95% CI 41.2−61.2). A significantly higher prevalence of Salmonella was detected in domesticated individuals (61.3%; 95% CI 50.0−71.5) compared with wild ones (18.2%; 95% CI 7.3−38.5). All isolates belonged to a single species, Salmonella enterica. Results demonstrated that reptiles carry a large variety of Salmonella serovars. Thirty-four isolates (68%) of Salmonella were resistant to at least one antimicrobial drug. The most frequent resistance of the isolates was to streptomycin (26%), cefoxitin, gentamicin, tetracycline and chloramphenicol (16%). Genes encoding resistance to tetracyclines, aminoglycosides, sulphonamides and trimethoprim were detected. No integrons that are associated with horizontal gene transfer were found. Data obtained provided knowledge about the adaptation of Salmonella in reptiles. Healthy individuals, irrespective of their origin, often carry Salmonella, including multi-resistant strains. Due to its large serological diversity, zoonotic potential and antimicrobial resistance, Salmonella in reptiles poses a risk to other animals and humans.

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

Background

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

Objective

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

Methods

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

Results

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

Conclusion

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

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

Bioactivity of Essential Oils for Mitigation of Listeria monocytogenes Isolated from Fresh Retail Chicken Meat

Listeria monocytogenes is one of the most severe foodborne pathogens found in several habitats. Therefore, this study aims to investigate the antilisterial activity of different essential oils (EOs) against multidrug-resistant (MDR) L. monocytogenes strains isolated from fresh chicken meat. Our results showed that the prevalence of L. monocytogenes in the examined samples was 48%. Seventy-eight isolates were identified as L. monocytogenes. Out of these, 64.1% were categorized as MDR and were categorized in 18 patterns with 50 MDR isolates. One isolate was selected randomly from each pattern to investigate their biofilm-forming ability, resistance, and virulence genes incidence. Out of 18 MDR isolates, 88.9% showed biofilm-forming ability. Moreover, the most prevalent resistance genes were ermB (72%), aadA (67%), penA (61%), and floR genes (61%). However, the most prevalent virulence genes were inlA (94.4%), prfA (88.9%), plcB (83.3%), and actaA (83.3%). The antilisterial activity of EOs showed that cinnamon bark oil (CBO) was the most effective antilisterial agent. CBO activity could be attributed to the bioactivity of cinnamaldehyde which effects cell viability by increasing the bacterial cell electrical conductivity, ion leakage, and salt tolerance capacity loss. Therefore, CBO could be an effective alternative natural agent for food safety applications.

Upraising a silent pollution: Antibiotic resistance at coastal environments and transference to long-distance migratory shorebirds

Large amounts of antibiotics from different sources have been released into coastal environments, especially in high human-populated areas, but comprehensive studies of antibiotic footprint in wildlife are scarce. Here we assess occurrence of antibiotic resistant bacteria (ARB) and antibiotic resistance gene (ARG) both in sediments and gut microbiota of a long-distance migratory shorebird species in two coastal wetlands at a sparsely-populated area in Pacific Patagonian coasts with contrasting potential antibiotic sources, especially from aquaculture. We found 62% of sediment samples showing ARB, and ARGs similarly occurring in sediments at both bays. However multi-resistant ARB were found only at sediments in the bay surrounding aquaculture operations. An 87% of cloacal bird samples showed at least one ARB, with 63% being multi-resistant and some of them with a high potential pathogenicity. ARGs were present in 46% of the samples from birds, with similar multi-resistant frequencies among bays. Besides specific differences mainly associated to antibiotics used in salmon aquaculture that boosted ARB in sediments, ARB and ARGs occurrence was overall similar at two bays with contrasting main human activities, in spite of being a comparatively low human-populated area. Therefore, our results reinforce the idea that the antibiotic footprint may be widespread at a global scale and can extend beyond the geographical influence of antibiotic sources, especially at coastal environments where migratory shorebirds act both as reservoirs and potential spreaders of antibiotic resistance.

First Isolation and Molecular Characterization of bla CTX-M-121 -Producing Escherichia coli O157:H7 From Cattle in Xinjiang, China

The bovine Escherichia coli O157:H7 is a major foodborne pathogen causing severe bloody diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome in humans. Cattle are recognized major reservoir and source of E. coli O157:H7. We investigated the antibiotic resistance, molecular profiles, and intrinsic relationship between 21 isolates of E. coli O157:H7 from cattle farms and slaughtering houses in Xinjiang. Using pulsed-field gel electrophoresis (PFGE) molecular typing, two types of PFGE were revealed through cluster analysis, including clusters I and II, with 66 and 100% similarity of PFGE spectra between 21 isolates. We also detected that 18 isolates (86%) carried at least one virulence gene, 16 isolates (76%) carried the eae gene, and 7 (33%) carried the stx1 + stx2 + eae + hly + tccp genes. Eighteen isolates were susceptible to antibiotics. Three isolates were resistant to antibiotics, and two were multidrug resistant. One of the two multidrug-resistant isolates detectably carried the bla CTX-M-121 gene. This is the first finding of the bla CTX-M-121 gene detected in E. coli O157:H7 isolated from cattle in Xinjiang. The bla CTX-M-121 gene is transferable between the bacterial strains via plasmid transmission. The results indicated that E. coli O157:H7 may have undergone clonal propagation in cattle population and cross-regional transmission in Xinjiang, China.

Occurrence of Antibiotic-Resistant Bacteria and Genes in Two Drinking Water Treatment and Distribution Systems in the North-West Province of South Africa

With the increasing spread of antimicrobial resistance, there is growing attention to the contribution made by drinking water systems. The potential health impact of two drinking water treatment and distribution systems (A and B) in the North-West Province of South Africa was determined by investigating the water quality and occurrence of antimicrobial-resistant heterotrophic bacteria and genes in the raw and treated water over four seasons. Most of the physicochemical parameters except for electrical conductivity were within permissible limits. Coliform bacteria reduced from raw to potable water except for counts higher than the threshold recorded in Summer and Winter. A total of 203 heterotrophic bacterial isolates were recovered on chromogenic R2A medium and subjected to susceptibility testing to twelve antibiotics. Most of the isolates were resistant to β-lactam antibiotics and Trimethoprim, whereas they were susceptible to Ciprofloxacin, Erythromycin, and Neomycin. The proportions of Cephalothin and Kanamycin-resistant isolates were significantly higher (p < 0.05) after treatment for site A, compared to significantly lower β-lactam, Oxytetracycline, and Trimethoprim-resistant isolates for B. Over 50% of isolates were of high risk, indicating their origin from high antibiotic-use sources. Seventy-one (35%) isolates were multidrug-resistant, out of which the majority (53.5%, n = 38) possessed the strA gene, followed by strB 21 (29.6%), dfrB 13 (18.3%), aadA 11 (15.5%), bla_CTX-M 5 (7.0%), and tetA 3 (4.2%). The 16S rRNA gene sequences of the isolates revealed strains belonging to eight bacterial families, some of which are clinically important.

Pharmacokinetics of florfenicol and thiamphenicol after single oral and intravenous, as well as multiple oral administrations to geese

1. This study evaluated the pharmacokinetic profiles of florfenicol (FF) and thiamphenicol (TP), which are synthetic bacteriostatic antimicrobial drugs, in geese after a single intravenous or oral administration, as well as seven oral doses administered at 12 h intervals. For all treatments, the dose was 30 mg/kg. 2. After single IV administration, clearance and volume of distribution were low (0.23 ± 0.03 l/h/kg and 0.57 ± 0.08 l/kg for FF, and 0.23 ± 0.04 l/h/kg and 0.59 ± 0.08 l/kg for TP, respectively). The elimination half-life was similar between products and short (2.91 ± 0.41 and 2.84 ± 0.64 h for FF and TP, respectively). 3. The single oral administration resulted in efficient absorption (bioavailability of 83.15 ± 11.48 for FF and 75.21 ± 19.56% for TP) with high maximal concentrations of 30.47 ± 2.47 and 20.02 ± 3.87 μg/ml for FF and TP, respectively. The area under the curve was 108.36 ± 14.96 and 101.81 ± 26.48 mg×h/l for FF and TP, respectively. 4. For both drugs, the two latter parameters were found to be higher compared to earlier studies on terrestrial birds. This suggested that FF and TP may be efficient in treating infections in geese caused by certain bacteria sensitive to chloramphenicol. 5. Neither drug accumulated in tissues following the oral seven doses and no adverse effects were noted in any treated animals. Thus, the selected FF and TP dosage may be considered as a safe treatment for geese.

The Role of European Starlings (Sturnus vulgaris) in the Dissemination of Multidrug-Resistant Escherichia coli among Concentrated Animal Feeding Operations

Antimicrobial use in livestock production is a driver for the development and proliferation of antimicrobial resistance (AMR). Wildlife interactions with livestock, acquiring associated AMR bacteria and genes, and wildlife's subsequent dispersal across the landscape are hypothesized to play an important role in the ecology of AMR. Here, we examined priority AMR phenotypes and genotypes of Escherichia coli isolated from the gastrointestinal tracts of European starlings (Sturnus vulgaris) found on concentrated animal feeding operations (CAFOs). European starlings may be present in high numbers on CAFOs (>100,000 birds), interact with urban environments, and can migrate distances exceeding 1,500 km in North America. In this study, 1,477 European starlings from 31 feedlots in five U.S. states were sampled for E. coli resistant to third generation cephalosporins (3G-C) and fluoroquinolones. The prevalence of 3G-C and fluoroquinolone-resistant E. coli was 4% and 10%, respectively. Multidrug resistance in the E. coli isolates collected (n = 236) was common, with the majority of isolates displaying resistance to six or more classes of antibiotics. Genetic analyses of a subset of these isolates identified 94 genes putatively contributing to AMR, including seven class A and C β-lactamases as well as mutations in gyrA and parC recognized to confer resistance to quinolones. Phylogenetic and subtyping assessments showed that highly similar isolates (≥99.4% shared core genome, ≥99.6% shared coding sequence) with priority AMR were found in birds on feedlots separated by distances exceeding 150 km, suggesting that European starlings could be involved in the interstate dissemination of priority AMR bacteria.

Co-occurrence of mcr-1, mcr-3, mcr-7 and clinically relevant antimicrobial resistance genes in environmental and fecal samples

Multidrug-resistant bacteria harboring different antimicrobial resistance genes (ARGs) have been detected worldwide. The association of plasmid-mediated colistin resistance genes (mcr-like) and other ARGs in bacteria isolated from animals is a huge concern worldwide. Therefore, this study aimed to investigate the presence of mcr-like genes and clinically relevant ARGs as well as plasmids in samples from a zoo. Fecal and environmental (soil and water) samples were collected from a zoo and the DNA of cultivable aerobic bacteria was extracted. ARGs were screened by PCR and the plasmids were detected using the PCR-based replicon typing method. A total of 74 amplicons from 27 ARGs [mcr-1, mcr-3, mcr-7.1, bla_CTX-M-Gp1, bla_CTX-M-Gp2, bla_CTX-M-Gp9, bla_VEB, bla_PER, bla_CMY, tetA, tetB, tetC, aadA, aac(6')-Ib, aph(3')-Ia, ant(2'')-Ia, qnrA, qnrB, qnrS, oqxA, oqxB, sul1, sul2, sul3, cmlA, mefAE, ermB] and 21 amplicons from eight plasmid families (IncY, ColE-like, IncF_repB, IncFIA, IncFIB, IncHI1, IncFIC, IncP) were detected. These findings reinforce that the zoo acts as a reservoir of clinically relevant ARGs, including mcr-like, and call attention to the monitoring studies in the zoo. Therefore, to the best of our knowledge, this is the first report of the world of mcr-1, mcr-3 and mcr-7.1 in environmental samples from the zoo.

Genetic Diversity of Multidrug-Resistant CMY-Producing Escherichia coli from Feces and Soil in a Small-Scale Pig Farm

Diarrheagenic Escherichia coli cause diarrheal diseases, which are a public health concern and affect mainly developing countries. Multidrug-resistant (MDR) pathogens have been spreading in different sources, including animals and the environment. E. coli strains were obtained from a small-scale pig farm and 33 antimicrobials were tested. All strains were classified as MDR and harbored several antimicrobial resistance genes (ARGs) [bla_CMY, bla_OXA-1-like, bla_SHV, tet(A), tet(B), aadA, aac(6')-Ib, aph(3')-Ia, sul1, sul2, sul3, floR, and cmlA] and plasmids. Besides, mutations in quinolone resistance-determining region of GyrA (Ser83Leu and Asp87Asn) and ParC (Glu84Asp) were detected. Among the MDR E. coli, nine strains (52%) presented diarrheagenic virulence genes, including genes related to Shiga toxin-producing E. coli (STEC), enteroinvasive E. coli (EIEC), and enteroaggregative E. coli (EAEC). The pulsed-field gel electrophoresis results showed a high genetic diversity among the MDR E. coli strains. Multilocus sequence typing (MLST) analyses revealed different sequence types phylogenetically related to each other, including ST10 and ST56. Subtyping of MLST by fimH gene showed different fimH type. This study shows a high genetic diversity among MDR ARG-producing E. coli belonging to STEC, EIEC, and EAEC pathotypes obtained from a small-scale pig farm and contributes to the monitoring of antimicrobial-resistant pathogens worldwide, mainly in environmental samples, which are associated with One Health framework.

Characterisation of antibiotic resistance of Salmonella isolated from dog treats in Japan

Dog treats might be contaminated with Salmonella. In Canada and the USA, outbreaks of human salmonellosis related to exposure to animal-derived dog treats were reported. Consequently, surveillance data on Salmonella contamination of dog treats have been gathered in many countries, but not in Japan. In the current study, we investigated whether dog treats in Japan were contaminated with Salmonella. Overall, 303 dog treats (of which 255 were domestically produced) were randomly collected and the presence of Salmonella investigated. Seven samples were positive for Salmonella enterica subsp. enterica. Among these isolates, three were identified as serovar 4,5,12:i:–; two were serovar Rissen; and two were serovar Thompson. All serovar 4,5,12:i:– and Thompson isolates were resistant to one or more drugs. Two serovar Rissen isolates were fully susceptible to all tested antimicrobial agents. All Salmonella isolates were susceptible to cefotaxime, ciprofloxacin and nalidixic acid. The gene bla_TEM was detected in two serovar 4,5,12:i:– isolates. The bla_CTX−M and bla_CMY genes were not detected in any isolates. This study demonstrated that dog treats in Japan could constitute a potential source of dog and human Salmonella infections, including multidrug-resistant Salmonella isolates.

Domestic and game pigeons as reservoirs for Escherichia coli harbouring antimicrobial resistance genes

OBJECTIVES

In Iran, pigeons are kept and bred on the roofs of houses, which indicates the potential significance of pigeons in the dispersal of antimicrobial resistant Escherichia coli strains. Here we characterized antimicrobial resistance genotypes in relation to phenotypic presentations and phylogenetic backgrounds of the E. coli isolates from household pigeons in Kerman in southeast Iran.

METHODS

Totally, 152 faecal E. coli isolates from domestic and household pigeons were screened for 13 antimicrobial resistance genes, bla_TEM, bla_SHV, bla_CTX-M, sulI, sulII, dhfrI, dhfrV, aadA, aac(3)-I, tetA, tetB, floR and qnrA, by conventional polymerase chain reaction (PCR) technique. Clermont phylogenetic background of E. coli strains was studied and antibiotic resistance of all strains was assessed for seven antibiotics.

RESULTS

The antimicrobial resistance genes bla_TEM, tetA, tetB and aadA were detected in 52.6%, 6.5%, 6.5% and 5.9% of the isolates, respectively. PCR phylotyping revealed that a significant number of isolates within A₀ (54%), A₁ (70%), B1 (57.6%), B2₂ (75%) and D1 (87.5%) phylogroups were positive for the studied resistance genes. One phenotypic resistance pattern (trimethoprim-sulfamethoxazole) was associated with the presence of the corresponding gene sul2.

CONCLUSIONS

An alarming rate of phenotypic resistance was observed in this study. Many isolates were positive for the screened resistance genes. According to the phylogenetic background, most resistant isolates belonged to the commensal phylotypes, representing significant role of commensal strains as a source of resistance genes. These findings highlight the role of the pigeon as disseminator of resistant E. coli strains.

Molecular characterization of multidrug-resistant Shiga toxin-producing Escherichia coli harboring antimicrobial resistance genes obtained from a farmhouse

Shiga toxin-producing Escherichia coli (STEC) colonize the gastrointestinal tract of animals; however, STEC may also cause severe diarrheal diseases. Food-producing animals have been acting as reservoirs and disseminators of multidrug-resistant (MDR) bacteria and antimicrobial resistance genes (ARGs); however, there are few studies characterizing molecularly bacterial isolates from sheep. Therefore, this study aimed to characterize E. coli isolates obtained from feces of sheep in a Brazilian farmhouse. A total of 14 MDR E. coli isolates were obtained from 100 feces samples, six of which were classified as non-O157 STEC (stx1, stx2 and ehxA). MDR E. coli isolates presented different ARGs [bla_CTX-M-Gp9, bla_CMY, bla_SHV, qnrS, oqxB, aac(6')-Ib, tet(A), tet(B), tet(C), sul1, sul2, and cmlA] and plasmids (IncI1, IncF_repB, IncFIB, IncFIA, IncHI1, IncK, and ColE-like). In addition, mutations in the quinolone-resistance determining region of GyrA (Ser83Leu; Asp87Asn) and ParC (Glu84Asp) were detected. PFGE showed a high genetic diversity (30.9 to 83.9%) and thirteen STs were detected (ST25, ST48, ST155, ST162, ST642, ST1247, ST1518, ST1725, ST2107, ST2522, ST3270, ST5036, and ST7100). Subtyping of the fimH gene showed seven fimH-type (25, 32, 38, 41, 54, 61, and 366). The results found in the present study showed high genetic diversity among MDR ARGs-producing E. coli obtained from a farmhouse. This study reports for the first time, the presence of MDR STEC and non-STEC belonging to ST25, ST162, ST642, ST1247, ST1518, ST1725, ST2107, ST3270, ST5036, and ST7100 in sheep, and contributes to the surveillance studies associated with One Health concept.

Antimicrobial resistance of Escherichia coli isolates from cattle in Eastern Algeria

Background and Aim

Lack of information about the antibiotic resistance in commensal Escherichia coli from Algerian livestock prompted us to do this study to determine the different levels of antimicrobial susceptibility, antibiotic multidrug resistance (MDR) rates, and phenotypical patterns of E. coli strains isolated from healthy cattle to control the spread of animal-resistant strains to humans and the environment.

Materials and Methods

A total of 198 cattle were sampled (swabbed in the rectum), reared in the farms of Souk Ahras, Tebessa, and Oum el Bouaghi governorates of Eastern Algeria. Isolation of E. coli strains was performed on MacConkey agar and then the different strains were identified to the species level using an API 20E identification kit. Antimicrobial susceptibility was determined using a panel of 13 antibiotic disks by disk diffusion method on Mueller-Hinton agar. The double-disk synergy test with cefotaxime and amoxicillin-clavulanate disks was used for the screening of extended-spectrum beta-lactamase phenotypes. For colistin susceptibility, the minimum inhibitory concentration was examined using broth microdilutions technique.

Results

The results showed that among the 198 E. coli isolates, elevated resistance rates were observed for ampicillin (59.09%) and tetracycline (43.43%), and moderate resistance rates for cephalothin (16.16%), trimethoprim/sulfamethoxazole (15.15%), and amoxicillin/clavulanate (11.62%); however, low resistance rates were found for nalidixic acid (8.08%), ciprofloxacin (7.07%), kanamycin (6.56%), cefotaxime (4.54%), chloramphenicol (4.04%), nitrofurantoin (2.52%), cefoxitin (2.02%), gentamycin (1.01%), and no resistance to colistin. However, nine extended-spectrum ß-lactamases producing E. coli strains were identified. Forty-four different patterns were determined, indicating a wide variety of resistance, ranging from one antimicrobial to a combination of 10. Analysis of coresistances revealed that 63 isolates (31.82%) were susceptible to all antibiotics used in the study, 42 isolates (21.21%) were resistant to one antibiotic, 43 isolates (21.72%) were resistant to two antibiotics, 24 isolates (12.12%) resistant to three antibiotics, 26 isolates (13.13%) were resistant for more than three agents, and 45 isolates (22.73%) were MDR (which means resistant to three or more families of antibiotics).

Conclusion

This study demonstrates that commensal E. coli remains a potential source of antibiotic resistance in view of the high prevalence of antimicrobial resistance. The vast range of MDR phenotypes, especially extended-spectrum ß-lactamases producing strains, emphasizes the urgent requirement to adopt measures to control the use of antimicrobials, in particular, by private veterinarians, as well as the strengthening of veterinary surveillance networks for antimicrobial resistance to control the spread of MDR bacteria from animals to humans and the environment.

Antimicrobial Resistance in Escherichia coli

Multidrug resistance in Escherichia coli has become a worrying issue that is increasingly observed in human but also in veterinary medicine worldwide. E. coli is intrinsically susceptible to almost all clinically relevant antimicrobial agents, but this bacterial species has a great capacity to accumulate resistance genes, mostly through horizontal gene transfer. The most problematic mechanisms in E. coli correspond to the acquisition of genes coding for extended-spectrum β-lactamases (conferring resistance to broad-spectrum cephalosporins), carbapenemases (conferring resistance to carbapenems), 16S rRNA methylases (conferring pan-resistance to aminoglycosides), plasmid-mediated quinolone resistance (PMQR) genes (conferring resistance to [fluoro]quinolones), and mcr genes (conferring resistance to polymyxins). Although the spread of carbapenemase genes has been mainly recognized in the human sector but poorly recognized in animals, colistin resistance in E. coli seems rather to be related to the use of colistin in veterinary medicine on a global scale. For the other resistance traits, their cross-transfer between the human and animal sectors still remains controversial even though genomic investigations indicate that extended-spectrum β-lactamase producers encountered in animals are distinct from those affecting humans. In addition, E. coli of animal origin often also show resistances to other-mostly older-antimicrobial agents, including tetracyclines, phenicols, sulfonamides, trimethoprim, and fosfomycin. Plasmids, especially multiresistance plasmids, but also other mobile genetic elements, such as transposons and gene cassettes in class 1 and class 2 integrons, seem to play a major role in the dissemination of resistance genes. Of note, coselection and persistence of resistances to critically important antimicrobial agents in human medicine also occurs through the massive use of antimicrobial agents in veterinary medicine, such as tetracyclines or sulfonamides, as long as all those determinants are located on the same genetic elements.

Mechanisms of Bacterial Resistance to Antimicrobial Agents

During the past decades resistance to virtually all antimicrobial agents has been observed in bacteria of animal origin. This chapter describes in detail the mechanisms so far encountered for the various classes of antimicrobial agents. The main mechanisms include enzymatic inactivation by either disintegration or chemical modification of antimicrobial agents, reduced intracellular accumulation by either decreased influx or increased efflux of antimicrobial agents, and modifications at the cellular target sites (i.e., mutational changes, chemical modification, protection, or even replacement of the target sites). Often several mechanisms interact to enhance bacterial resistance to antimicrobial agents. This is a completely revised version of the corresponding chapter in the book Antimicrobial Resistance in Bacteria of Animal Origin published in 2006. New sections have been added for oxazolidinones, polypeptides, mupirocin, ansamycins, fosfomycin, fusidic acid, and streptomycins, and the chapters for the remaining classes of antimicrobial agents have been completely updated to cover the advances in knowledge gained since 2006.

Modulation of antimicrobial resistance in clinical isolates of Enterobacter aerogenes: A strategy combining antibiotics and chemosensitisers

OBJECTIVE

The main focus of this study was to evaluate the antimicrobial susceptibility profiles of a number of human clinical isolates of Enterobacter aerogenes isolates and to explore the effects of selected chemosensitisers on reversal of the resistant phenotype of these isolates.

METHODS

This study design was accomplished by: (i) characterising several multidrug-resistant (MDR) E. aerogenes clinical isolates; (ii) evaluating the contribution of target gene mutations to the resistance phenotype, focusing on fluoroquinolones and chloramphenicol only; (iii) evaluating the contribution of membrane permeability and efflux to the MDR phenotype; (iv) assessing the combined action of selected antimicrobials and chemosensitisers in order to identify combinations with synergistic effects able to reduce the minimum inhibitory concentration (MIC); and (v) understanding how these combinations can modulate the permeability or efflux of these isolates.

RESULTS

Resistance to ciprofloxacin could not be totally reversed owing to pre-existing mutations in target genes. Chloramphenicol susceptibility was efficiently restored by the addition of the selected chemosensitisers. From the modulation kinetics it was clear that phenothiazines were able to increase the accumulation of Hoechst dye.

CONCLUSIONS

Modulation of permeability and efflux in the presence of chemosensitisers can help us to propose more appropriate chemotherapeutic combinations that can set the model to be used in the treatment of these and other MDR infections.

Prevalence and molecular characteristics of multi-resistant Escherichia coli in wild birds

Humans and animals share the same bacterial species including the resistant ones. For that reason, epidemiological studies in domestic and wild animals should be performed on a regular basis. Wild, particularly migratory birds, should be investigated as potential carriers of antimicrobial resistant bacteria that can be spread globally in a short time. The aim of this study was to investigate the prevalence and to characterize multi-resistant Escherichia coli in wild birds. Three hundred and ninety two samples were obtained from different bird species including gulls (Larus spp.), mallards (Anas platyrhynchos), mute swans (Cygnus olor), as well as other species of birds. Phenotypical and genotypical resistance of E. coli was investigated. In total 60 isolates from 179 tested were resistant to three or more antimicrobial classes and treated as multi-resistant (33.5%; 95% CI 21.56–45.44); the isolates were obtained from gulls, mallards, swans, and rooks. All of the strains demonstrated resistance to aztreonam and cefpodoxime. The most frequent resistance prevalence of the above-mentioned isolates in vitro was also demonstrated to ampicillin (82%), ampicillin/sulbactam (68%), cefazolin (66%), ceftriaxone (55%), and ciprofloxacin (47%). All E. coli isolates were susceptible to amikacin. The results of polymerase chain reaction confirmed the presence of the genes encoding resistance to beta-lactams, aminoglycosides, tetracycline, amphenicols, trimethoprim, and sulphonamides. Consequently, wild birds might constitute a potential hazard to human and animal health by transmitting multi-resistant E. coli strains to waterways and other environmental sources via bird faeces.

Characterization of Resistance Patterns and Detection of Apramycin Resistance Genes in Escherichia coli Isolated from Chicken Feces and Houseflies after Apramycin Administration

The aim of this study was to evaluate the influence of apramycin administration on the development of antibiotic resistance in Escherichia coli (E. coli) strains isolated from chicken feces and houseflies under field conditions. Chickens in the medicated group (n = 25,000) were given successive prophylactic doses (0.5 mg/l) of apramycin in their drinking water from Days 1 to 5, while no antibiotics were added to the un-medicated groups drinking water (n = 25,000). Over 40 days, a total of 1170 E. coli strains were isolated from fecal samples obtained from medicated and un-medicated chickens and houseflies from the same chicken farm. Apramycin MIC90 values for E. coli strains obtained from the medicated group increased 32-128 times from Days 2 to 6 (256-1024 μg/ml) when compared to those on Day 0 (8 μg/ml). Strains isolated from un-medicated chickens and houseflies had consistently low MIC90 values (8-16 μg/ml) during the first week, but showed a dramatic increase from Days 8 to 10 (128-1024 μg/ml). The apramycin resistance gene aac(3)-IV was detected in E. coli strains from medicated (n = 71), un-medicated (n = 32), and housefly groups (n = 42). All strains positive for aac(3)-IV were classified into 12 pulsed-field gel electrophoresis (PFGE) types. PFGE types A, E, and G were the predominant types in both the medicated and housefly groups, suggesting houseflies play an important role in spreading E. coli-resistant strains. Taken together, our study revealed that apramycin administration could facilitate the occurrence of apramycin-resistant E. coli and the apramycin resistance gene acc(3)-IV. In turn, these strains could be transmitted by houseflies, thus increasing the potential risk of spreading multi-drug-resistant E. coli to the public.

Detection of floR gene and active efflux mechanism of Escherichia coli in Ningxia, China

Florfenicol is an antibiotic, a fluorinated structural analogue of thiamphenicol and chloramphenicol, approved exclusively for use in Asia for aquaculture since the 1980's. Our study examined the prevalence of florfenicol resistance in bovine mastitis Escherichia coli isolates. A total of 245 E. coli isolates were collected from bovine mastitis in Ningxia Province, China between May 2016 to July 2017 and screened for florfenicol resistance gene, floR gene by PCR analysis. About 7.35% (15/245) of the isolates were positive for floR gene. Minimal inhibitory concentration (MIC) results showed that 9 isolates were susceptible strains and 6 isolates were highly resistant to florfenicol. HPLC (high performance liquid chromatography) results showed that the amounts of florfenicol was significantly improved in the presence of carbonyl cyanide 3-chlorophenylhydrazone (CCCP) as an efflux pump inhibitor. This, therefore, indicates that the employment of florfenicol in conjunction with CCCP in future drug formulations should be considered.

Antibiotic resistant Pseudomonas spp. in the aquatic environment: A prevalence study under tropical and temperate climate conditions

Microbial populations which are resistant to antibiotics are an emerging environmental concern with potentially serious implications for public health. Thus, there is a growing concern in exploring the occurrence of antibiotic resistance in the environment with no limitations to the factors that contribute to their emergence. The aquatic environment is considered to be a hot-spot for the acquisition and spread of antibiotic resistance due to pollution with emerging contaminants derived from anthropogenic activities. In this study, we report on the isolation and characterization of 141 Pseudomonas spp. from aquatic sediments receiving partially (un)treated hospital and communal effluents from three distinct geographical locations: Democratic Republic of the Congo (DRC), India (IN), and Switzerland (CH). P. putida (42%) and P. aeruginosa (39%) were the dominant Pseudomonas species. The highest frequency of antibiotic resistance against eight anti-pseudomonas agents was found among IN isolates (35-60%), followed by DRC (18-50%) and CH (12-54%). CTX-M was the most frequent β-lactamase found in CH (47% of isolates), while VIM-1 was dominant in isolates from DRC (61%) and IN (29%). NDM-1 was found in 29% of the total IN isolates and surprisingly also in 6% of CH isolates. Chromosomally-encoded efflux mechanisms were overexpressed in P. aeruginosa isolates from all three geographic locations. In vitro conjugative transfers of antibiotic resistance plasmids occurred more frequently under tropical temperatures (30 and 37 °C) than under temperate conditions (10 °C). The presence of Extended Spectrum β-lactamases (ESBLs) and Metallo β-lactamases (MBLs) in the isolates from environmental samples has important implications for humans who depend on public water supply and sanitation facilities. To our knowledge, this is the first study to demonstrate a comparison between treated/untreated effluents from urban and hospital settings as a source of microbial resistance by evaluating the aquatic ecosystems sediments from tropical and temperate climate conditions. Taken together, our findings demonstrate a widespread occurrence of antibiotic resistance in aquatic ecosystems sediments receiving untreated/treated wastewater and how these contemporary sources of contamination, contribute to the spread of microbial resistance in the aquatic environment. This research presents also useful tools to evaluate sediment quality in the receiving river/reservoir systems which can be applied to similar environments.

Prevalence, virulence potential, and pulsed-field gel electrophoresis profiling of Shiga toxin-producing Escherichia coli strains from cattle

BACKGROUND

As a primary source of Shiga-toxin-producing Escherichia coli (STEC) infection, cattle are often targeted to develop strategies for reducing STEC contamination. Monitoring the virulence potentials of STEC isolates from cattle is important for tracing contamination sources, managing outbreaks or sporadic cases, and reducing the risks for human infection. This study aimed to investigate the prevalence of STEC in cattle farm samples in South Korea and to assess their virulence potentials.

RESULTS

In total, 63 STEC were isolated from 496 cattle farm samples, and temperature and rainfall affected STEC prevalence (p < 0.001). The O157 serogroup was most prevalent, followed by O108, O8, O84, O15, and O119. In the stx variant test, high prevalence of stx2a and stx2c (known to be associated with high STEC virulence) were observed, and stx2g, a bovine STEC variant, was detected in STEC O15 and O109. Additionally, stx1c was detected in eae-positive STEC, suggesting genetic dynamics among the virulence genes in the STEC isolates. STEC non-O157 strains were resistant to tetracycline (17.9%), ampicillin (14.3%), and cefotaxime (3.6%), while STEC O157 was susceptible to all tested antimicrobials, except cefotaxime. The antimicrobial resistance genes, bla_TEM (17.5%), tetB (6.3%), and tetC (4.8%), were only detected in STEC non-O157, whereas tetE (54.0%) was detected in STEC O157. AmpC was detected in all STEC isolates. Clustering was performed based on the virulence gene profiles, which grouped STEC O84, O108, O111, and O157 together as potentially pathogenic STEC strains. Finally, PFGE suggested the presence of a prototype STEC that continues to evolve by genetic mutation and causes within- and between-farm transmission within the Gyeonggi province.

CONCLUSIONS

Considerable numbers of STEC non-O157 were isolated from cattle farms, and the virulence and antimicrobial resistance features were different between the STEC O157 and non-O157 strains. STEC from cattle with virulence or antimicrobial resistance genes might represent a threat to public health and therefore, continual surveillance of both STEC O157 and non-O157 would be beneficial for controlling and preventing STEC-related illness.

Antimicrobial Susceptibility of Bordetella bronchiseptica Isolates from Swine and Companion Animals and Detection of Resistance Genes

Bordetella bronchiseptica causes infections of the respiratory tract in swine and other mammals and is a precursor for secondary infections with Pasteurella multocida. Treatment of B. bronchiseptica infections is conducted primarily with antimicrobial agents. Therefore it is essential to get an overview of the susceptibility status of these bacteria. The aim of this study was to comparatively analyse broth microdilution susceptibility testing according to CLSI recommendations with an incubation time of 16 to 20 hours and a longer incubation time of 24 hours, as recently proposed to obtain more homogenous MICs. Susceptibility testing against a panel of 22 antimicrobial agents and two fixed combinations was performed with 107 porcine isolates from different farms and regions in Germany and 43 isolates obtained from companion animals in Germany and other European countries. Isolates with increased MICs were investigated by PCR assays for the presence of resistance genes. For ampicillin, all 107 porcine isolates were classified as resistant, whereas only a single isolate was resistant to florfenicol. All isolates obtained from companion animals showed elevated MICs for β-lactam antibiotics and demonstrated an overall low susceptibility to cephalosporines. Extension of the incubation time resulted in 1-2 dilution steps higher MIC50 values of porcine isolates for seven antimicrobial agents tested, while isolates from companion animals exhibited twofold higher MIC50/90 values only for tetracycline and cefotaxime. For three antimicrobial agents, lower MIC50 and MIC90 values were detected for both, porcine and companion animal isolates. Among the 150 isolates tested, the resistance genes blaBOR-1 (n = 147), blaOXA-2, (n = 4), strA and strB (n = 17), sul1 (n = 10), sul2 (n = 73), dfrA7 (n = 3) and tet(A) (n = 8) were detected and a plasmid localisation was identified for several of the resistance genes.

Prevalence, antimicrobial susceptibility and virulotyping of Listeria species and Listeria monocytogenes isolated from open-air fish markets

BACKGROUND

The aim of this study was to investigate the prevalence and characterization of Listeria species and Listeria monocytogenes isolated from raw fish and open-air fish market environments. Eight hundred and sixty two samples including raw fish and fish market environments (samples from workers' hands, workers' knives, containers and work surface) were collected from the open-air fish markets in the Northern region of Iran.

RESULTS

Listeria spp. was isolated from 104/488 (21.3%) raw fish and 29/374 (7.8%) of samples from open-air fish market environment. The isolates of Listeria spp. included L. innocua (35.3%), L. monocytogenes (32.3%), L. seeligeri (18%), and L. ivanovii (14.3%). Of the 43 L. monocytogenes isolates, 31 (72.1%), 10 (23.3%) and 2 (4.7%) belonged to serovars 1/2a, 4b, and 1/2b, respectively. The inlA, inlB, inlC, inlJ, actA, hlyA, iap, plcA, and prfA virulence-associated genes were detected in almost all of the L. monocytogenes isolates. The Listeria spp. isolates showed high resistance against tetracycline (23.3%), penicillin G, and cephalothin (each 16.5%). Besides, we observed significant resistance level to tetracycline (27.9%), ampicillin (20.9%), cephalothin, penicillin G, and streptomycin (each 16.3%) in the L. monocytogenes isolates. All of the isolates were susceptible to cefotaxime, gentamicin, kanamycin, and pefloxacin. We found that tetM (25.6%), tetA (23.3%), ampC (14%), and penA (11.6%) were the most prevalent antibiotic resistance genes in the L. monocytogenes isolates.

CONCLUSIONS

Recovery of potentially pathogenic L. monocytogenes from raw fish and environment of open-air fish market samples in this study is a convincing evidence for the zoonotic potential of listeriosis.

Prevalence, antimicrobial susceptibility and virulotyping of Listeria species and Listeria monocytogenes isolated from open-air fish markets

BACKGROUND

The aim of this study was to investigate the prevalence and characterization of Listeria species and Listeria monocytogenes isolated from raw fish and open-air fish market environments. Eight hundred and sixty two samples including raw fish and fish market environments (samples from workers' hands, workers' knives, containers and work surface) were collected from the open-air fish markets in the Northern region of Iran.

RESULTS

Listeria spp. was isolated from 104/488 (21.3%) raw fish and 29/374 (7.8%) of samples from open-air fish market environment. The isolates of Listeria spp. included L. innocua (35.3%), L. monocytogenes (32.3%), L. seeligeri (18%), and L. ivanovii (14.3%). Of the 43 L. monocytogenes isolates, 31 (72.1%), 10 (23.3%) and 2 (4.7%) belonged to serovars 1/2a, 4b, and 1/2b, respectively. The inlA, inlB, inlC, inlJ, actA, hlyA, iap, plcA, and prfA virulence-associated genes were detected in almost all of the L. monocytogenes isolates. The Listeria spp. isolates showed high resistance against tetracycline (23.3%), penicillin G, and cephalothin (each 16.5%). Besides, we observed significant resistance level to tetracycline (27.9%), ampicillin (20.9%), cephalothin, penicillin G, and streptomycin (each 16.3%) in the L. monocytogenes isolates. All of the isolates were susceptible to cefotaxime, gentamicin, kanamycin, and pefloxacin. We found that tetM (25.6%), tetA (23.3%), ampC (14%), and penA (11.6%) were the most prevalent antibiotic resistance genes in the L. monocytogenes isolates.

CONCLUSIONS

Recovery of potentially pathogenic L. monocytogenes from raw fish and environment of open-air fish market samples in this study is a convincing evidence for the zoonotic potential of listeriosis.

Scallop larvae hatcheries as source of bacteria carrying genes encoding for non-enzymatic phenicol resistance

The main aim of the study was to evaluate the role of scallop hatcheries as source of the floR and cmlA genes. A number of 133 and 121 florfenicol-resistant strains were isolated from scallop larval cultures prior to their transfer to seawater and from effluent samples from 2 commercial hatcheries and identified by 16S rRNA gene sequence analysis, observing a predominance of the Pseudomonas, Pseudoalteromonas and Halomonas genera and exhibiting an important incidence of co-resistance to streptomycin, oxytetracycline and co-trimoxazole. A high percentage of strains from both hatcheries carried the floR gene (68.4% and 89.3% of strains), whereas a lower carriage of the cmlA gene was detected (27.1% and 54.5% of strains). The high prevalence of floR-carrying bacteria in reared scallop larvae and hatchery effluents contributes to enrich the marine resistome in marine environments, prompting the need of a continuous surveillance of these genes in the mariculture environments.

Comparison of epidemiologically linked Campylobacter jejuni isolated from human and poultry sources

Campylobacter jejuni is responsible for most foodborne bacterial infections worldwide including Australia. The aim of this study was to investigate a combination of typing methods in the characterization of C. jejuni isolated from clinical diarrhoeal samples (n = 20) and chicken meat (n = 26) in order to identify the source of infection and rank isolates based on their relative risk to humans. Sequencing of the flaA short variable region demonstrated that 86% of clinical isolates had genotypes that were also found in chicken meat. A polymerase chain reaction binary typing system identified 27 different codes based on the presence or absence of genes that have been reported to be associated with various aspects of C. jejuni pathogenicity, indicating that not all isolates may be of equal risk to human health. The lipooligosaccharide (LOS) of the C. jejuni isolates was classified into six classes (A, B, C, E, F, H) with 10·4% remaining unclassified. The majority (72·7%) of clinical isolates possessed sialylated LOS classes. Sialylated LOS classes were also detected in chicken isolates (80·7%). Antimicrobial tests indicated a low level of resistance, with no phenotypic resistance found to most antibiotics tested. A combination of typing approaches was useful to assign isolates to a source of infection and assess their risk to humans.

Resistance phenotypes and genotypes among multiple-antimicrobial-resistant Salmonella enterica subspecies enterica serovar Choleraesuis strains isolated between 2008 and 2012 from slaughter pigs in Okinawa Prefecture, Japan

A total of 349 Salmonella enterica subspecies enterica serovar Choleraesuis (S. Choleraesuis) strains, which were isolated between 2008 and 2012 from 349 pigs at two slaughterhouses in Okinawa Prefecture, Japan, were investigated for antimicrobial susceptibility and the presence of antimicrobial resistance genes. All isolates were resistant to at least four antimicrobial agents. The antimicrobial agents for which isolates showed a high incidence of resistance were as follows: ampicillin (100%) and streptomycin (100%), followed by gentamicin (99.7%), oxytetracycline (99.7%), sulfamethoxazole/trimethoprim (99.4%), nalidixic acid (40.1%) and oxolinic acid (40.1%). All isolates were sensitive to cefuroxime, ceftiofur, colistin, fosfomycin, enrofloxacin, orbifloxacin and danofloxacin. The predominant resistance phenotypes and genotypes were: resistance to ampicillin, streptomycin, gentamicin, oxytetracycline and sulfamethoxazole/trimethoprim (58.5%, 204/349) and blaTEM-strA-strB-aadA1-aadA2-aacC2-tet (B)-sul1-sul2-dhfrXII-dhfrXIII (36.1%, 126/349). The quinolone resistance-determining regions (QRDRs) of gyrA, gyrB, parC and parE of the quinolone-resistant isolates (n=12) showed amino acid substitutions of Ser-83→Phe or Asp-87→Tyr in GyrA and Ser-107→Ala in ParC. To our knowledge, this is the first report on the molecular characterization of antimicrobial resistance among S. Choleraesuis strains in Japan.

Antimicrobial resistance of Escherichia coli isolates from canine urinary tract infections

This study determined the antimicrobial resistance profiles of Escherichia coli isolates from dogs with a presumptive diagnosis of urinary tract infection (UTI). Urine samples from 201 dogs with UTI diagnosed through clinical examination and urinalysis were processed for isolation of Escherichia coli. Colonies from pure cultures were identified by biochemical reactions (n=114) and were tested for susceptibility to 18 antimicrobials. The two most frequent antimicrobials showing resistance in Urinary E. coli isolates were oxytetracycline and ampicillin. Among the resistant isolates, 17 resistance patterns were observed, with 12 patterns involving multidrug resistance (MDR). Of the 69 tetracycline-resistant E. coli isolates, tet(B) was the predominant resistance determinant and was detected in 50.9% of the isolates, whereas the remaining 25.5% isolates carried the tet(A) determinant. Most ampicillin and/or amoxicillin-resistant E. coli isolates carried bla_TEM-1 genes. Class 1 integrons were prevalent (28.9%) and contained previously described gene cassettes that are implicated primarily in resistance to aminoglycosides and trimethoprim (dfrA1, dfrA17-aadA5). Of the 44 quinolone-resistant E. coli isolates, 38 were resistant to nalidixic acid, and 6 were resistant to nalidixic acid, ciprofloxacin and enrofloxacin. Chromosomal point mutations were found in the GyrA (Ser83Leu) and ParC (Ser80Ile) genes. Furthermore, the aminoglycoside resistance gene aacC2, the chloramphenicol resistant gene cmlA and the florfenicol resistant gene floR were also identified. This study revealed an alarming rate of antimicrobial resistance among E. coli isolates from dogs with UTIs.

Antimicrobial resistance, virulence genes and PFGE-profiling of Escherichia coli isolates from South Korean cattle farms

To estimate the prevalence of Escherichia coli with potential pathogenicity in cattle farm in South Korea, a total of 290 E. coli isolates were isolated from cattle farms over a period of 2 years in South Korea. These were examined for phenotypic and genotypic characteristics including antimicrobial susceptibility, serotype, and gene profiles of virulence and antimicrobial resistance. The most dominant virulence gene was f17 (26.2%), followed by stx2 (15.9%), ehxA (11.0%), stx1 (8.3%), eae (5.2%), and sta (4.1%). Some shiga-toxin producing E. coli isolates possessed eae (15.9%). All isolates except for one showed resistance to one or more antimicrobials, with 152 isolates exhibiting multidrug-resistance. The most prevalent resistance phenotype detected was streptomycin (63.1%), followed by tetracycline (54.5%), neomycin (40.3%), cephalothin (32.8%), amoxicillin (30.0%), ampicillin (29.7%), and sulphamethoxazole/trimethoprim (16.6%). The associated resistance determinants detected were strA-strB (39.0%), tet(E) (80.0%), tet(A) (27.6%), aac(3)-IV (33.1%), aphA1 (21.4%), bla TEM (23.8%), and sul2 (22.1%). When investigated by O serotyping and PFGE molecular subtyping, the high degree of diversity was exhibited in E. coli isolates. These results suggest that E. coli isolates from South Korean cattle farms are significantly diverse in terms of virulence and antimicrobial resistance. In conclusion, the gastroinstestinal flora of cattle could be a significant reservoir of diverse virulence and antimicrobial resistance determinants, which is potentially hazardous to public health.

Prevalence and molecular characterization of fluoroquinolone resistance in Escherichia coli isolates from dairy cattle with endometritis in China

Fluoroquinolones are frequently used to treat infectious disease that is caused by Escherichia coli in dairy cattle. However, fluoroquinolone resistance occurs and is due either to chromosomal mutations in the bacterial topoisomerase genes and/or to plasmid-mediated resistance genes. The purpose of this study was to determine the prevalence and molecular characteristics of fluoroquinolone resistance determinants in E. coli strains (n=148) isolated from dairy cattle with bovine endometritis in Inner Mongolia (China). Analysis of the mutations in the quinolone resistance-determining regions of resistant E. coli isolates confirmed previously reported substitutions in the GyrA and ParE. However, we identified additional substitutions in the ParC and GyrB that have not been reported earlier. No plasmid-mediated quinolone resistance genes in any of the isolates were found. The number of point mutations found per isolate correlated with an increase in the minimum inhibitory concentration of ciprofloxacin. Overall, 45.5% of the isolates were positive for the class I integrase gene along with four gene cassettes that were responsible for resistance to trimethoprim (dfr1 and dfrA17) and aminoglycosides (aadA1 and aadA5), respectively. The prevalence of extended-spectrum β-lactamases (ESBLs) was 100%, and the blaTEM gene was predominant in all of the isolates. In conclusion, our results identify the mechanism of quinolone resistance for the first time and reveal the prevalence of integron and ESBLs in E. coli isolates from dairy cattle with bovine endometritis in China after 20 years of quinolone usage in cattle.

Genetic mechanisms of antimicrobial resistance identified in Salmonella enterica, Escherichia coli, and Enteroccocus spp. isolated from U.S. food animals

The prevalence of antimicrobial resistance (AR) in bacteria isolated from U.S. food animals has increased over the last several decades as have concerns of AR foodborne zoonotic human infections. Resistance mechanisms identified in U.S. animal isolates of Salmonella enterica included resistance to aminoglycosides (e.g., alleles of aacC, aadA, aadB, ant, aphA, and StrAB), β-lactams (e.g., bla_{CMY−2, TEM−1, PSE−1}), chloramphenicol (e.g., floR, cmlA, cat1, cat2), folate pathway inhibitors (e.g., alleles of sul and dfr), and tetracycline [e.g., alleles of tet(A), (B), (C), (D), (G), and tetR]. In the U.S., multi-drug resistance (MDR) mechanisms in Salmonella animal isolates were associated with integrons, or mobile genetic elements (MGEs) such as IncA/C plasmids which can be transferred among bacteria. It is thought that AR Salmonella originates in food animals and is transmitted through food to humans. However, some AR Salmonella isolated from humans in the U.S. have different AR elements than those isolated from food animals, suggesting a different etiology for some AR human infections. The AR mechanisms identified in isolates from outside the U.S. are also predominantly different. For example the extended spectrum β-lactamases (ESBLs) are found in human and animal isolates globally; however, in the U.S., ESBLs thus far have only been found in human and not food animal isolates. Commensal bacteria in animals including Escherichia coli and Enterococcus spp. may be reservoirs for AR mechanisms. Many of the AR genes and MGEs found in E. coli isolated from U.S. animals are similar to those found in Salmonella. Enterococcus spp. isolated from animals frequently carry MGEs with AR genes, including resistances to aminoglycosides (e.g., alleles of aac, ant, and aph), macrolides [e.g., erm(A), erm(B), and msrC], and tetracyclines [e.g., tet(K), (L), (M), (O), (S)]. Continuing investigations are required to help understand and mitigate the impact of AR bacteria on human and animal health.

Multiresistant Enterobacteriaceae with class 1 and class 2 integrons in a municipal wastewater treatment plant

In this study, 1832 strains of the family Enterobacteriaceae were isolated from different stages of a municipal wastewater treatment plant, of which 221 (12.1%) were intI-positive. Among them 61.5% originated from raw sewage, 12.7% from aeration tank and 25.8% from the final effluent. All of the intI-positive strains were multiresistant, i.e. resistant to at least three unrelated antimicrobials. Although there were no significant differences in resistance range, defined as the number of antimicrobial classes to which an isolate was resistant, between strains isolated from different stages of wastewater treatment, for five β-lactams the percentage of resistant isolates was the highest in final effluent, which may reflect a selective pressure the bacteria are exposed to, and the possible route of dissemination of β-lactam resistant strains to the corresponding river. The sizes of the variable part of integrons ranged from 0.18 to 3.0 kbp and contained up to four incorporated gene cassettes. Sequence analysis identified over 30 different gene cassettes, including 24 conferring resistance to antibiotics. The highest number of different gene cassettes was found in bacteria isolated from the final effluent. The gene cassettes were arranged in 26 different resistance cassette arrays; the most often were dfrA1-aadA1, aadA1, dfrA17-aadA5 and dfrA12-orfF-aadA2. Regarding the diversity of resistance genes and the number of multiresistant bacteria in the final effluent, we concluded that municipal sewage may serve as a reservoir of integron-embedded antibiotic resistance genes.

Comparison of the prevalences and antimicrobial resistances of Escherichia coli isolates from different retail meats in the United States, 2002 to 2008

Escherichia coli isolates were recovered from the National Antimicrobial Resistance Monitoring System retail meat program and examined for antimicrobial susceptibility. Retail meat samples (n = 11,921) from four U.S. states collected during 2002 to 2008, consisting of 2,988 chicken breast, 2,942 ground turkey, 2,991 ground beef, and 3,000 pork chop samples, were analyzed. A total of 8,286 E. coli isolates were recovered. The greatest numbers of samples contaminated with the organism were chicken (83.5%) and turkey (82.0%), followed by beef (68.9%) and pork (44.0%). Resistance was most common to tetracycline (50.3%), followed by streptomycin (34.6%), sulfamethoxazole-sulfisoxazole (31.6%), ampicillin (22.5%), gentamicin (18.6%), kanamycin (8.4%), amoxicillin-clavulanic acid (6.4%), and cefoxitin (5.2%). Less than 5% of the isolates had resistance to trimethoprim, ceftriaxone, ceftiofur, nalidixic acid, chloramphenicol, and ciprofloxacin. All isolates were susceptible to amikacin. Compared to beef and pork isolates, the poultry meat isolates had a greater percentage of resistance to all tested drugs, with the exception of chloramphenicol, to which pork isolates had the most resistance. More than half of the turkey isolates (56%) were resistant to multidrugs (≥3 classes) compared to 38.9% of chicken, 17.3% of pork, and 9.3% of beef isolates. The bla(CMY) gene was present in all ceftriaxone- and ceftiofur-resistant isolates. The cmlA, flo, and catI genes were present in 45%, 43%, and 40% of chloramphenicol-resistant isolates, respectively. Most nalidixic acid-resistant isolates (98.5%) had a gyrA mutation in S83 or D87 or both, whereas only 6.7% had a parC mutation in either S80 or E84. The results showed that E. coli was commonly present in the retail meats, and antimicrobial resistance profiles differed according to the animal origin of the isolates.

Characterization of multidrug-resistant Escherichia coli isolates from animals presenting at a university veterinary hospital

In this study, we examined molecular mechanisms associated with multidrug resistance (MDR) in a collection of Escherichia coli isolates recovered from hospitalized animals in Ireland. PCR and DNA sequencing were used to identify genes associated with resistance. Class 1 integrons were prevalent (94.6%) and contained gene cassettes recognized previously and implicated mainly in resistance to aminoglycosides, β-lactams, and trimethoprim (aadA1, dfrA1-aadA1, dfrA17-aadA5, dfrA12-orfF-aadA2, bla(OXA-30)-aadA1, aacC1-orf1-orf2-aadA1, dfr7). Class 2 integrons (13.5%) contained the dfrA1-sat1-aadA1 gene array. The most frequently occurring phenotypes included resistance to ampicillin (97.3%), chloramphenicol (75.4%), florfenicol (40.5%), gentamicin (54%), neomycin (43.2%), streptomycin (97.3%), sulfonamide (98.6%), and tetracycline (100%). The associated resistance determinants detected included bla(TEM), cat, floR, aadB, aphA1, strA-strB, sul2, and tet(B), respectively. The bla(CTX-M-2) gene, encoding an extended-spectrum β-lactamase (ESβL), and bla(CMY-2), encoding an AmpC-like enzyme, were identified in 8 and 18 isolates, respectively. The mobility of the resistance genes was demonstrated using conjugation assays with a representative selection of isolates. High-molecular-weight plasmids were found to be responsible for resistance to multiple antimicrobial compounds. The study demonstrated that animal-associated commensal E. coli isolates possess a diverse repertoire of transferable genetic determinants. Emergence of ESβLs and AmpC-like enzymes is particularly significant. To our knowledge, the bla(CTX-M-2) gene has not previously been reported in Ireland.

Detection of florfenicol resistance genes in Riemerella anatipestifer isolated from ducks and geese

The cat gene, coding for chloramphenicol acetyltransferase has been reported for conferring the chloramphenicol resistance for Riemerella anatipestifer. Chloramphenicol acetyltransferases, however, are unable to inactivate florfenicol. In this study, 66 R. anatipestifer isolates were investigated for their susceptibility to chloramphenicol and florfenicol and the presence of floR gene. Results showed nine florfenicol intermediate or resistant R. anatipestifer isolates were all floR positive. The expression of floR gene in E. coli and inhibition studies with PAβN indicated that the floR gene was as an efflux pump conferring resistance to both chloramphenicol and florfenicol. Southern hybridization revealed the floR was located in the plasmid DNA of five isolates and in the chromosomal DNA of four isolates. Furthermore, two novel floR-carrying plasmids designated pRA0726 and pRA0846 were sequenced completely. pRA0726 was 11,704 bp in size with 10 putative open reading frames which included the floR, catB and bla(OXA-209) resistance genes. The most differences between sequences of pRA0846 and pRA0726 were the absence of a bla(OXA-209) gene and the deletion of 321 nucleotides of orf1 in pRA0846. Plasmid curing tests demonstrated that pRA0726 carried functional coding proteins for resistance to phenicol and β-lactam antimicrobials. To the best of our knowledge, this is the first report of presence of the floR and bla(OXA-209) resistance genes in R. anatipestifer.