A Comparative Study on Antimicrobial Resistance in Escherichia coli Isolated from Channel Catfish and Related Freshwater Fish Species

Antimicrobial resistance (AMR) trends in 114 generic Escherichia coli isolated from channel catfish and related fish species were investigated in this study. Of these, 45 isolates were from commercial-sized channel catfish harvested from fishponds in Alabama, while 69 isolates were from Siluriformes products, accessed from the U.S. Department of Agriculture Food Safety and Inspection Service' (FSIS) National Antimicrobial Resistance Monitoring System (NARMS) program. Antibiotic susceptibility testing and whole genome sequencing were performed using the GenomeTrakr protocol. Upon analysis, the fishpond isolates showed resistance to ampicillin (44%), meropenem (7%) and azithromycin (4%). The FSIS NARMS isolates showed resistance to tetracycline (31.9%), chloramphenicol (20.3%), sulfisoxazole (17.4%), ampicillin (5.8%) and trimethoprim-sulfamethoxazole, nalidixic acid, amoxicillin-clavulanic acid, azithromycin and cefoxitin below 5% each. There was no correlation between genotypic and phenotypic resistance in the fishpond isolates, however, there was in NARMS isolates for folate pathway antagonists: Sulfisoxazole vs. sul1 and sul2 (p = 0.0042 and p < 0.0001, respectively) and trimethoprim-sulfamethoxazole vs. dfrA16 and sul1 (p = 0.0290 and p = 0.013, respectively). Furthermore, correlations were found for tetracyclines: Tetracycline vs. tet(A) and tet(B) (p < 0.0001 each), macrolides: Azithromycin vs. mph(E) and msr(E) (p = 0.0145 each), phenicols: Chloramphenicol vs. mdtM (p < 0.0001), quinolones: Nalidixic acid vs. gyrA_S83L=POINT (p = 0.0004), and β-lactams: Ampicillin vs. blaTEM-1 (p < 0.0001). Overall, we recorded differences in antimicrobial susceptibility testing profiles, phenotypic-genotypic concordance, and resistance to critically important antimicrobials, which may be a public health concern.

Prevalence and Types of Extended-Spectrum β-Lactamase-Producing Bacteria in Retail Seafood

Objectives: To assess prevalence and types of extended-spectrum β-lactamase (ESBL)-producing bacteria in retail seafood. Methods: A literature review was completed according to international guidelines for systematic reviews, except for being performed by a single reviewer. Kruskal-Wallis and Dunn tests were used to determine statistical differences between continents or seafood types. Results: Among 12,277 hits, 42 publications from 2011 to 2023 were deemed relevant to the review's objectives. The median prevalence of ESBL-contaminated products was 19.4%. A significantly lower prevalence was observed in Europe (p = 0.006) and Africa (p = 0.004) compared to Asia. Amongst the 2053 isolates analyzed in the selected studies, 44.8% were ESBL-positive. The predominant type was CTX-M (93.6%), followed by TEM (6.7%) and SHV (5.0%). Only 32.6% and 18.5% of the CTX-M-positive isolates were typed to group and gene level, respectively. While group 1 (60.2%) was prevalent over group 9 (39.8%) among Enterobacterales, the opposite trend was observed in Vibrio spp. (60.0% vs. 40.0%). Information at gene level was limited to Enterobacterales, where CTX-M-15 was the most prevalent (79.2%). Conclusions: On average, one in five seafood products sold at retail globally is contaminated with ESBL-producing Enterobacterales of clinical relevance. Our findings highlight a potential risk for consumers of raw seafood, especially in Asia.

Characterization of Antibiotic Resistant Coliform Bacteria and Resistance Genes Isolated from Samples of Smoothie Drinks and Raw Milk

Raw foodstuffs have been marked as a healthier alternative in the context of nutrient content and are becoming more popular with consumers. Thermally untreated foods may represent a microbiological risk connected with the possible presence of antimicrobial resistance. The aim of this study was to prove that popular raw food beverages such as smoothies and raw milk may be a source of antibiotic-resistant coliform bacteria and resistant genes. The majority of antibiotic-resistant isolates (110) were identified as Enterobacter spp., Escherichia coli, and species of Klebsiella spp., predominantly β-lactam and chloramphenicol resistant. Multidrug resistance has been registered in one-third of resistants. Overproduction of efflux pumps was clarified in 8 different bacteria. The majority of resistant isolates were strong biofilm producers. Antibiotic resistance gene blaOXA was detected in 25% of isolates, especially in E. coli. Resistance genes blaTEM and blaSHV were detected in 19% and 14%, respectively. This is the first study to point out that popular raw drinks such as smoothies or raw milk, besides their nutrient benefits, could represent a reservoir of antibiotic-resistant bacteria as well as antibiotic resistance genes. According to this, raw drinks could contribute to the dissemination of antibiotic resistance in the human gastrointestinal tract and environment.

Epidemiological characteristics of uropatogenic isolates of Escherichia coli in hospitals

The aim of the study was to evaluate the genetic affinity of uropathogenic E. coli cultures (UPEC) and to identify the major types of extended spectrum beta-lactamases (ESBL) found among nosocomial isolates. A molecular typing of UPEC (n=93) isolated from patients with urinary tract infections (UTI) who were hospitalised in nine medical facilities (MO) in Perm was performed. It was found that 69.89% of the cultures had individual RAPD/ERIC profiles, the remaining 30.10% were distributed among 13 genome groups. Most frequently blaCTX-M-1 was detected individually or in combination with other beta-lactamase genes (n=23, 79.31% of ESBL phenotype-positive isolates), genes were detected in seventeen cases (58.62%) blaTEM and/or blaOXA, the blaCMY fragment was found in only three isolates (10.34%), blaSHV was missing in this isolates. It was shown that in two thirds of the cases the pathogens of the infection process are representatives of the endogenous intestinal microbiota of the patients, in other cases an exogenous infection occurs. The proportion of "circulating" (possibly hospital) isolates in the spectrum of UTI increased in the series: therapy departments - surgery departments - intensive care units. In addition, in multidisciplinary hospitals there are conditions for cross-infections of patients, but the epidemiological chains of episodes of UTI are short and concise. It has been shown that the probability of infection with E. coli producing CTX-M or OXA enzymes is significantly higher in the intensive care unit than in surgery or therapy departments. The data obtained complement the understanding of the epidemiology of UTI caused by E. coli and can be used as an aid in the planning and implementation of methods for the prevention and control of nosocomial UTI.

Prevalence and Genetic Characterization of mcr-1-Positive Escherichia coli Isolated from Retail Meats in South Korea

The spread of plasmid-mediated colistin resistance has posed a serious threat to public health owing to its effects on the emergence of pandrug-resistant bacteria. In this study, we investigated the prevalence and characteristics of mcr-1-positive Escherichia coli isolated from retail meat samples in Korea. In total, 1,205 E. coli strains were isolated from 3,234 retail meat samples in Korea. All E. coli strains were subjected to antimicrobial susceptibility testing and were examined for the presence of mcr-1 gene. All mcr-1-positive E. coli (n = 10, 0.8%) from retail meat were subjected to pulse-field gel electrophoresis (PFGE) and whole-genome sequencing (WGS). The transferability of mcr-1 gene was determined by conjugation assays. The mcr-1-positive strains exhibited diverse clonal types. Our mcr-1 genes were located in plasmids belonged to the IncI2 (n = 1) and IncX4 (n = 8) types, which were reported to be prevalent in Asia and worldwide, respectively. Most mcr-1 genes from mcr-1-positive strains (9/10) were transferable to the recipient strain and the transfer frequencies ranged from 2.4 × 10^-3 to 9.8 × 10^-6. Our data suggest that the specific types of plasmid may play an important role in spreading plasmid-mediated colistin resistance in Korea. Furthermore, our findings suggest that the retail meat may be an important tool for disseminating plasmid-mediated colistin resistance.

Characterization of Extended-Spectrum β-Lactamase-Producing Escherichia coli Isolated from Fresh Produce and Agricultural Environments in Korea

ABSTRACT

This study was conducted to characterize Escherichia coli strains and evaluate the spread of antimicrobial resistance among these strains from fresh produce and farm environments in Korea. We then conducted phenotypic and genetic studies on antimicrobial-resistant isolates. We determined the genetic epidemiological characteristics of isolates that produced extended-spectrum β-lactamase (ESBL) and confirmed plasmid transfer in isolates that carried blaCTX-M-type genes. E. coli strains were isolated from 8 samples of fresh produce and 152 samples from the farm environment collected from May 2014 to June 2016. Cephalosporin resistance was the most prevalent (61.8%) type of resistance among the isolates. Five ESBL-producing strains with high genetic homology with E. coli of human or livestock origin were identified. Lateral transfer of plasmids harboring blaCTX-M-type genes to transconjugants was successful. Two isolates from Chinese cabbage and from water samples collected from a nearby stream harbored the ISEcp1-blaCTX-M-55-orf477 operon and were confirmed as sequence type 1196 and the same type of plasmid replicon, suggesting that cross-contamination was highly likely. A high-risk clone of sequence type 69 (clonal complex 69) isolates was also recovered from the farm environment. This study provides genetic evidence that antimicrobial resistance factors in E. coli from farm environments originate in the clinic or in livestock, highlighting the fact that good agricultural practices in farming are important to inhibit the spread of antimicrobial resistance to bacteria on fresh produce.

HIGHLIGHTS

Escherichia coli Isolated from Cases of Colibacillosis in Russian Poultry Farms (Perm Krai): Sensitivity to Antibiotics and Bacteriocins

Escherichia coli strains isolated from case of colibacillosis in Russian poultry farms in the region of Perm Krai were analyzed for their sensitivity to main antibiotics and bacteriocins. Sensitivity profiles for 9 antibiotics and 20 bacteriocins were determined with the disc diffusion method and the overlay test, respectively. Further, with the PCR the presence of several bla and integron 1 genes was revealed and the phylogenetic group for each strain determined. Among the 28 studied E. coli strains 85.7% were resistant to at least three antibiotics, 53.6% to five or more drugs, and 10.7% to eight antibiotics. PCR revealed that the bla_TEM gene was harbored by 71.4% of strains and the bla_CTX-M gene by 53.6% of strains. The class 1 integrons were found in 28.6% of strains. All of the studied strains were insensitive to ten or more bacteriocins. More than 90% of the studied strains were insensitive to pore-forming colicins of group A and B colicins, while 60.7% were insensitive to colicins with DNase and RNase activity. All of the analyzed strains were insensitive to at least two of the tested microcins. Neither the antibiotic resistance profile nor the bacteriocin resistance profile correlated with phylogenetic group of the strains. Thus, the studied strains were shown to possess high levels of multiple resistance to antibiotics and insensitivity to bacteriocins.

Prevalence and Antimicrobial Characteristics of Shiga Toxin-Producing Escherichia coli Isolates from Pork in Korea

Shiga toxin-producing Escherichia coli (STEC) strains are important food-borne pathogens that can be transmitted through the consumption of food products derived from pigs. Moreover, antimicrobial resistance in STEC has been a matter of increasing concern. The aim of this study was to investigate the prevalence and antimicrobial characteristics of STEC isolates from pork in Korea. We isolated 131 isolates of E. coli from 334 pork samples collected from slaughterhouses and retail markets from 2008 to 2009. Among the 131 isolates, 6 (4.58%) were confirmed to belong to 6 different serotypes of STEC. All six STEC isolates contained stx1 and eaeA virulence genes, and four of them additionally carried the hly gene. The minimum inhibitory concentration (MIC) of 15 antibiotics (amoxicillin/clavulanic acid, ampicillin, cephalothin, cefoxitin, ceftiofur, gentamicin, neomycin, streptomycin, nalidixic acid, ciprofloxacin, colistin, chloramphenicol, florfenicol, tetracycline and sulfamethoxazole/trimethoprim) toward the STEC isolates was determined. As a result, three strains were associated with high MICs for florfenicol and chloramphenicol (64 μg/mL). Furthermore, all three strains were found to contain the florfenicol-resistant gene (floR) but not the chloramphenicol-resistant gene (cat). Sequence alignment and BLAST analysis of the polymerase chain reaction products of the floR gene indicated that they contained sequences with homology to the floR gene of E. coli or Salmonella enterica serovar, Heidelberg. This is the first report on the detection of floR in STEC isolated from pork obtained from retail markets in Korea.

Molecular Characterization of Multidrug-Resistant Escherichia coli Isolates from Edible Offal in Korea

HIGHLIGHTS

Edible offal is significantly contaminated by antimicrobial-resistant Escherichia coli. E. coli from edible offal is harboring various antimicrobial resistance and virulence genes. Improvements in hygienic conditions of edible offal production is required.

Antibiotic resistance of Escherichia coli isolated from broilers sold at live bird markets in Chattogram, Bangladesh

Objective

The present study was carried out to appraise the antibiotic resistance and to detect some of the target resistant genes in Escherichia coli (E. coli) isolated from apparently healthy broilers.

Materials and Methods

Cloacal swab samples (n = 60) were collected from apparently healthy broilers (n = 60) sold at two different live bird markets (LBMs) of Chattogram, Bangladesh. Isolation and identification of the Escherichia coli was done by the following standard bacteriological techniques followed by biochemical tests. The antibiotic susceptibility of E. coli isolates was determined by the disk diffusion method. The antibiotic resistant genes were detected by polymerase chain reaction (PCR) using specific primers.

Results

The overall prevalence of E. coli in broilers was 61.67% (n = 37/60) (95% CI = 49-72.93). The antibiogram study showed that the isolates were 100% resistant to ampicillin and tetracycline followed by sulfomethoxazole-trimethoprim (94.59%, n = 35/37) and nalidixic acid (91.89%, n = 34/37). To the contrary, 56.76% (n = 21/37) isolates were sensitive to both ceftriaxone and gentamicin followed by colistin (48.65%, n = 18/37). All of E. coli isolates were multidrug resistant (MDR) and carried bla _TEM, tetA, and Sul2 genes.

Conclusion

The presence of MDR genes in E. coli isolates in broilers could pose a serious public health threat.

Prevalence and Characterization of β-Lactamases Genes and Class 1 Integrons in Multidrug-Resistant Escherichia coli Isolates from Chicken Meat in Korea

Antimicrobial resistance has become a serious public health threat throughout the world, and therapeutic options for several infectious diseases are currently limited by the presence of multidrug-resistant (MDR) bacteria. This study was designed to examine the drug resistance patterns, the prevalence of the β-lactamases, and class 1 integrons in MDR Escherichia coli isolates from chicken meat in Korea. Among 200 chicken meat samples, 101 isolates were observed to be positive for E. coli, of which 57 were identified as MDR E. coli. Among 57 MDR E. coli isolates, the prevalence of bla gene, bla_CTX-M-1, bla_CTX-M-14, and bla_TEM-1, were identified in 2, 4, and 16 E. coli strains, respectively; only 1 E. coli strain had both, bla_TEM-1 and bla_CTX-M-1 genes. Twenty-one of the 57 MDR E. coli isolates also carried class 1 integrons, and 5 different gene cassette arrangements were found in 14 of the 21 class 1 integron-positive isolates. The β-lactamase-producing E. coli and integron-positive E. coli had significantly higher resistance to 16 antimicrobial drugs than the non-β-lactamase-producing E. coli and the integron-negative E. coli (p < 0.05). Our findings suggest that β-lactamase and class 1 integrons are widely distributed in E. coli isolates from chicken meat, and directly contribute to resistance to diverse antimicrobial agents. Therefore, continuous investigation of integron gene cassette arrays will provide useful information regarding antimicrobial resistance mechanisms.

Characterization and Horizontal Transfer of Antimicrobial Resistance Genes and Integrons in Bacteria Isolated from Cooked Meat Products in China

The aim of this study was to investigate antimicrobial resistance and the presence and transferability of corresponding resistance genes and integrons in bacteria isolated from cooked meat samples in the People's Republic of China. A total of 150 isolates (22 species belonging to 15 genera) were isolated from 49 samples. Resistance of these isolates to antimicrobials was commonly observed; 42.7, 36.0, and 25.3% of the isolates were resistant to tetracycline, streptomycin, and ampicillin, respectively. Multidrug resistance was observed in 41 (27.3%) of the isolates. Sixteen resistance genes, i.e., bla_TEM-1 and bla_CTX-M-14 (β-lactams), aac(3)-IIa (gentamicin), strA and strB (streptomycin), qnrB and qnrS (fluoroquinolone), sul1, sul2, and sul3 (sulfamethoxazole), cat1 and cat2 (chloramphenicol), and tetM, tetA, tetS, and tetB (tetracycline), were found in 54 isolates. One isolate of Pseudomonas putida carried qnrB, and sequence analysis of the PCR product revealed 96% identity to qnrB2. The qnr genes were found coresiding and were cotransferred with bla genes in two isolates. Twelve isolates were positive for the class 1 integrase gene, and four isolates carried the class 2 integrase gene. However, no class 3 integrase gene was detected. One isolate of Proteus mirabilis carried dfrA32-ereA-aadA2, and this unusual array could be transferred to Escherichia coli. Nonclassic class 1 integrons lacking qacEΔ1 and sul1 genes were found in 2 of the 12 intI1-positive isolates. Our results revealed the presence of multidrug-resistant bacteria in cooked meats and the presence and transferability of resistance genes in some isolates, suggesting that cooked meat products may act as reservoirs of drug-resistant bacteria and may facilitate the spread of resistance genes.

Prevalence of plasmid-mediated quinolone resistance in Escherichia coli isolated from diseased animals in Taiwan

Escherichia coli (E. coli) is a zoonotic pathogen that often causes diarrhea, respiratory diseases or septicemia in animals. Fluoroquinolones are antimicrobial agents used to treat pathogenic E. coli infections. In this study, 1,221 E. coli strains were isolated between March, 2011 and February, 2014. The results of the antimicrobial susceptibility testing showed a high prevalence of quinolone resistance. The antimicrobial resistance rates of these E. coli isolates to nalidixic acid (NAL) were 72.0% in swine, 81.9% in chickens, 81.0% in turkeys, 64.0% in ducks and 73.2% in geese. Among these isolates, the positive rate for the plasmid-mediated quinolone resistance (PMQR) determinant was 14.8% (181/1,221); the detection rate for qnrS1 was the highest (10.2%), followed by aac(6')-Ib-cr (4.5%) and qnrB2 (0.3%). The quinolone-resistance determining regions (QRDRs) analysis for the PMQR-positive isolates showed that the strains with mutations at codon 83 or 87 in GyrA were resistant to NAL. To the best of our knowledge, this is the first report of occurrence of qnrB2, qnrS1 and aac(6')-Ib-cr genes and high frequency (56.4%; 102/181) of mutation in gyrA or parC among PMQR-positive E. coli strains derived from diseased animals in Taiwan.

Modelling of tetracycline resistance gene transfer by commensal Escherichia coli food isolates that survived in gastric fluid conditions

Antimicrobial resistance (AR) is a major public health concern and a food safety issue worldwide. Escherichia coli strains, indicators of antibiotic resistance, are a source of horizontal gene transfer to other bacteria in the human intestinal system. A probabilistic exposure model was used to estimate the transfer of the AR gene tet(A). The acid resistance and kinetic behaviour of E. coli was analysed as a function of pH to describe the inactivation of E. coli in simulated gastric fluid (SGF), the major host barrier against exogenous micro-organisms. The kinetic parameters of microbial inactivation in SGF were estimated using GInaFiT, and log-linear + tail and Weibull models were found to be suitable for commensal and enterohaemorrhagic E. coli (EHEC), respectively. A probabilistic exposure model was developed to estimate E. coli survival in gastric pH conditions as well as gene transfer from resistant to susceptible cells in humans. E. coli-contaminated retail foods for consumption without further cooking and gastric pH data in South Korea were considered as an example. The model predicts that 22-33% of commensal E. coli can survive under gastric pH conditions of Koreans. The estimated total mean tet(A) transfer level by commensal E. coli was 1.68 × 10^-4-8.15 × 10^-4 log CFU/mL/h. The inactivation kinetic parameters of E. coli in SGF and the quantitative exposure model can provide useful information regarding risk management options to control the spread of AR.

Antimicrobial Resistance, Extended-Spectrum β-Lactamase Productivity, and Class 1 Integrons in Escherichia coli from Healthy Swine

Administration of antimicrobials to food-producing animals increases the risk of higher antimicrobial resistance in the normal intestinal flora of these animals. The present cross-sectional study was conducted to investigate antimicrobial susceptibility and extended-spectrum β-lactamase (ESBL)-producing strains and to characterize class 1 integrons in Escherichia coli in healthy swine in Thailand. All 122 of the tested isolates had drug-resistant phenotypes. High resistance was found to ampicillin (98.4% of isolates), chloramphenicol (95.9%), gentamicin (78.7%), streptomycin (77.9%), tetracycline (74.6%), and cefotaxime (72.1%). Fifty-four (44.3%) of the E. coli isolates were confirmed as ESBL-producing strains. Among them, blaCTX-M (45 isolates) and blaTEM (41 isolates) were detected. Of the blaCTX-M-positive E. coli isolates, 37 carried the blaCTX-M-1 cluster, 12 carried the blaCTX-M-9 cluster, and 5 carried both clusters. Sequence analysis revealed blaTEM-1, blaTEM-135, and blaTEM-175 in 38, 2, and 1 isolate, respectively. Eighty-seven (71%) of the 122isolates carried class 1 integrons, and eight distinct drug-resistance gene cassettes with seven different integron profiles were identified in 43 of these isolates. Gene cassettes were associated with resistance to aminoglycosides (aadA1, aadA2, aadA22, or aadA23), trimethoprim (dfrA5, dfrA12, or dfrA17), and lincosamide (linF). Genes encoding β-lactamases were not found in class 1 integrons. This study is the first to report ESBL-producing E. coli with a class 1 integron carrying the linF gene cassette in swine in Thailand. Our findings confirm that swine can be a reservoir of ESBL-producing E. coli harboring class 1 integrons, which may become a potential health risk if these integrons are transmitted to humans. Intensive analyses of animal, human, and environmental isolates are needed to control the spread of ESBL-producing E. coli strains.

Prevalence and characterization of antimicrobial-resistant Escherichia coli isolated from conventional and organic vegetables

To compare the characteristics and to identify the epidemiological relationships of Escherichia coli isolated from organic and conventional vegetables, the antimicrobial resistance and genetic properties of E. coli were investigated from 2010 to 2011. E. coli was isolated from 1 of 111 (0.9%) organic vegetables and from 20 of 225 (8.9%) conventional vegetables. The majority of strains were isolated from the surrounding farming environment (n=27/150 vs. 49/97 in organic vs. conventional samples). The majority of the vegetable strains were isolated from the surrounding farming environments. E. coli isolated from organic vegetables showed very low antimicrobial resistance rates except for cephalothin, ranging from 0% to 17.9%, while the resistance rates to cephalothin (71%) were extremely high in both groups. E. coli isolates expressed various resistance genes, which most commonly included blaTEM, tet(A), strA, strB, and qnrS. However, none of the isolates harbored tet(D), tet(E), tet(K), tet(L), tet(M), or qnrA. The transferability of tet gene, tet(A), and tet(B) was identified in tetracycline-resistant E. coli, and the genetic relationship was confirmed in a few cases from different sources. With regard to the lower antimicrobial resistance found in organic produce, this production mode seems able to considerably reduce the selection of antimicrobial-resistant bacteria on vegetables.

Characterization of antibiotic resistance in Escherichia coli isolated from shrimps and their environment

Antimicrobial resistance in bacteria associated with food and water is a global concern. To survey the risk, 312 Escherichia coli isolates from shrimp farms and markets in Thailand were examined for susceptibility to 10 antimicrobials. The results showed that 17.6% of isolates (55 of 312) were resistant to at least one of the tested drugs, and high resistance rates were observed to tetracycline (14.4%; 45 of 312), ampicillin (8.0%; 25 of 312), and trimethroprim (6.7%; 21 of 312); 29.1% (16 of 55) were multidrug resistant. PCR assay of the tet (A), tet (B), tet (C), tet (D), tet (E), and tet (G) genes detected one or more of these genes in 47 of the 55 resistant isolates. Among these genes, tet (A) (69.1%; 38 of 55) was the most common followed by tet (B) (56.4%; 31 of 55) and tet (C) (3.6%; 2 of 55). The resistant isolates were further investigated for class 1 integrons. Of the 55 resistant isolates, 16 carried class 1 integrons and 7 carried gene cassettes encoding trimethoprim resistance (dfrA12 or dfrA17) and aminoglycosides resistance (aadA2 or aadA5). Two class 1 integrons, In54 (dfrA17-aadA5) and In27 (dfrA12-orfF-aadA2), were found in four and three isolates, respectively. These results indicate a risk of drug-resistant E. coli contamination in shrimp farms and selling places. The occurrence of multidrug-resistant E. coli carrying tet genes and class 1 integrons indicates an urgent need to monitor the emergence of drug-resistant E. coli to control the dissemination of drug-resistant strains and the further spread of resistance genes to other pathogenic bacteria.

Antimicrobial Susceptibility of Escherichia coli Isolated from Fresh-Marketed Nile Tilapia (Oreochromis niloticus)

The contamination of seafood by bacteria of fecal origin, especially Escherichia coli, is a widely documented sanitary problem. The objective of the present study was to isolate E. coli strains from the gills, muscle, and body surface of farmed Nile tilapias (Oreochromis niloticus) fresh-marketed in supermarkets in Fortaleza (Ceará, Brazil), to determine their susceptibility to antibiotics of different families (amikacin, gentamicin, imipenem, cephalothin, cefotaxime, ciprofloxacin, aztreonam, ampicillin, nalidixic acid, tetracycline, and sulfametoxazol-trimetoprim), and to determine the nature of resistance by plasmid curing. Forty-four strains (body surface = 25, gills = 15, muscle = 4) were isolated, all of which were susceptible to amikacin, aztreonam, cefotaxime, ciprofloxacin, gentamicin, and imipenem. Gill and body surface samples yielded 11 isolates resistant to ampicillin, tetracycline, and sulfametoxazol-trimetoprim, 4 of which of plasmidial nature. The multiple antibiotic resistance index was higher for strains isolated from body surface than from gills. The overall high antibiotic susceptibility of E. coli strains isolated from fresh-marketed tilapia was satisfactory, although the occasional finding of plasmidial resistance points to the need for close microbiological surveillance of the farming, handling, and marketing conditions of aquaculture products.

Integrons in the intestinal microbiota as reservoirs for transmission of antibiotic resistance genes

The human intestinal microbiota plays a major beneficial role in immune development and resistance to pathogens. The use of antibiotics, however, can cause the spread of antibiotic resistance genes within the resident intestinal microbiota. Important vectors for this are integrons. This review therefore focuses on the integrons in non-pathogenic bacteria as a potential source for the development and persistence of multidrug resistance. Integrons are a group of genetic elements which are assembly platforms that can capture specific gene cassettes and express them. Integrons in pathogenic bacteria have been extensively investigated, while integrons in the intestinal microbiota have not yet gained much attention. Knowledge of the integrons residing in the microbiota, however, can potentially aid in controlling the spread of antibiotic resistance genes to pathogens.