Prevalence and characterization of class 1 integrons in Escherichia coli of poultry and human origin

Detecting Class 1 Integrons and Their Variable Regions in Escherichia coli Whole-Genome Sequences Reported from Andean Community Countries

Various genetic elements, including integrons, are known to contribute to the development of antimicrobial resistance. Class 1 integrons have been identified in E. coli isolates and are associated with multidrug resistance in countries of the Andean Community. However, detailed information on the gene cassettes located on the variable regions of integrons is lacking. Here, we investigated the presence and diversity of class 1 integrons, using an in silico approach, in 2533 whole-genome sequences obtained from EnteroBase. IntFinder v1.0 revealed that almost one-third of isolates contained these platforms. Integron-bearing isolates were associated with environmental, food, human, and animal origins reported from all countries under scrutiny. Moreover, they were identified in clones known for their pathogenicity or multidrug resistance. Integrons carried cassettes associated with aminoglycoside (aadA), trimethoprim (dfrA), cephalosporin (blaOXA; blaDHA), and fluoroquinolone (aac(6')-Ib-cr; qnrB) resistance. These platforms showed higher diversity and larger numbers than previously reported. Moreover, integrons carrying more than three cassettes in their variable regions were determined. Monitoring the prevalence and diversity of genetic elements is necessary for recognizing emergent patterns of resistance in pathogenic bacteria, especially in countries where various factors are recognized to favor the selection of resistant microorganisms.

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 of integrons in multidrug-resistant Escherichia coli isolates from waters and vegetables in Nsukka and Enugu, Southeast Nigeria

Irrigation of fresh produce with poorly treated wastewater or contaminated freshwater sources can lead to produce contamination and foodborne illnesses, as well as the dissemination of antimicrobial resistance determinants. In this study, we assessed the presence of integrons in multidrug-resistant Escherichia coli isolated from the University of Nigeria, Nsukka Wastewater Treatment Plant effluent, tap water, vegetables from irrigated gardens and vegetables sold in selected markets from Nsukka and Enugu cities. E. coli was isolated following standard laboratory procedure and confirmed through beta-glucuronidase (uidA)-targeted polymerase chain reaction (PCR). The antibiotic resistance of the isolates was determined using Bauer-Kirby disk diffusion assay, and multiplex PCR was used to determine the presence of class 1 and 2 integrons. Our result revealed a total of 188 E. coli isolates from WWTP effluent (n = 41), tap water (n = 10) and vegetables from greenhouse (n = 46), farms (n = 55) and market (n = 36). Multidrug resistance was detected in all the isolates, ranging from three-drug resistance in a single isolate to 7-drug resistance patterns in two different isolates. Of the total isolates, class 1 integrons were abundantly detected in 175 (93.1%) and class 2 in 5 (2.7%). All the class 2 integrons were found in isolates that were positive for class 1. The abundance of multidrug-resistant E. coli harbouring class 1 integrons in the effluent and vegetable samples is a potential public health risk. Therefore, the appropriate measures for the safe use of poorly treated wastewater for vegetable farm irrigation are required to be put in place to reduce the microbial load of the discharged effluent. Also, education of farmers and the community on the dangers of wastewater effluent-grown plants and proper methods for cleaning harvested vegetable is recommended.

High incidence of multidrug resistance and class 1 and 2 integrons in Escherichia coli isolated from broiler chickens in South of Iran

The objective was to investigate the multidrug resistance and presence of class 1 and 2 integrons in 300 Escherichia coli isolates obtained from 20 broiler farms during three rearing periods (one-day-old chicks, thirty-day-old chickens, and one day before slaughter) in Fars, South Iran. Results showed that 81.00%, 82.00%, and 85.00% of isolates were multidrug-resistant on the first day, thirty-day-old chickens, and one day before slaughter, respectively. Multidrug-resistant E. coli isolates were further examined for the presence of class 1 and 2 integrons using PCR assay. The existence of class 1 integron-integrase gene (intI1) was confirmed in 68.40%, 72.70%, and 60.90% of multidrug-resistant isolates from stage 1, stage 2, and stage 3 of the rearing period, respectively. The frequency of class 2 integron-integrase gene (intI2) during the first to the third stage of sampling was 2.60%, 25.50%, and 30.40%. Also, sequence analysis of the cassette arrays within class 1 integron revealed the presence of the genes associated with resistance for trimethoprim (dfrA), streptomycin (aadA), erythromycin (ereA), and orfF genes. The results revealed that percentages of antimicrobial resistance in E. coli isolates were significantly higher in the middle and end stages of the rearing period. In conclusion, widespread dissemination of class 1 integrons in all three stages and rising trends of class 2 integrons existence in E. coli isolates during the rearing period of broiler chickens could exacerbate the spread of resistance factors among bacteria in the poultry industry. Future research is needed to clarify its implication for human health.

Class 1 integrons as predominant carriers in Escherichia coli isolates from waterfowls in Hainan, China

This study was conducted to determine the prevalence of integrons and associated gene cassettes in Escherichia coli (E. coli) isolates from waterfowls in Hainan, China. The antimicrobial resistance profile of the isolates was examined by using disc diffusion test. In addition, PCR, RFLP, plasmid replicon typing and DNA sequencing analyses were used for the characterization of integrase genes (class 1, 2 and 3) and associated gene cassettes. Approximatively, 90% of the isolates were positive for the integrase genes by PCR. Specifically, class 1 and class 2 integrons were found in 252 (81%) and 7 (2.3%) strains, respectively. While 21 (6.7%) isolates were positive for both class 1 and class 2 integrons. However, none of the isolate was positive for the class 3 integrons. In addition, 5 various cassette arrays, dfrA1-orfC, aadA2, aadA1, dfrA1-aadA1, and dfrA1-orfC- aadA1, were found within the variable regions (VRs) of class 1 integron isolates. While only single cassette array, dfrA1-sat2- aadA1, was identified within VRs of class 2 integron isolates. We identified incF plasmid as the most common plasmid type, which was detected in 81 of 243 VRs containing isolates. This study is the first report showing the baseline characteristics of integrons in E. coli isolates from waterfowls in Hainan, China. Our results provide evidence of the waterfowl birds as a reservoir of class 1 and class 2 integrons carrying antibiotic resistance gene cassettes. Therefore, strict preventive measures should be taken to avoid the spread of mobile genetic resistance elements in waterfowls in China.

Integron Digestive Carriage in Human and Cattle: A "One Health" Cultivation-Independent Approach

Objectives: Dissemination of antimicrobial resistance (AMR) is a global issue that requires the adoption of a "One-Health" approach promoting integration of human and animal health. Besides culture-dependent techniques frequently used for AMR surveillance, cultivation-independent methods can give additional insights into the diversity and reservoir of AMR genetic determinants. Integrons are molecular markers that can provide overall and reliable estimation of AMR dissemination. In this study, considering the "One-Health" approach, we have analyzed the integron digestive carriage from stools of humans and cattle living in a same area and exposed to different antibiotic selection pressures. Methods: Three collections of human [general population (GP) and intensive care unit patients (ICUs)] and bovine (BOV) stool samples were analyzed. The three main classes of integrons were detected using a multiplex qPCR both from total DNA extracted from stools, and from Gram-negative bacteria obtained by culture after an enrichment step. Results: With the cultivation-independent approach, integron carriage was 43.8, 52.7, and 65.6% for GP, ICU, and BOV respectively, percentages being at least twofold higher to those obtained with the cultivation-dependent approach. Class 1 integrons were the most prevalent; class 2 integrons seemed more associated to cattle than to humans; no class 3 integron was detected. The integron carriage was not significantly different between GP and ICU populations according to the antibiotic consumption, whatever the approach. Conclusion: The cultivation-independent approach constitutes a complementary exploratory method to investigate the integron digestive carriage of humans and bovines, notably within subjects under antibiotic treatment. The high frequency of carriage of integrons in the gut is of clinical significance, integrons being able to easily acquire and exchange resistant genes under antibiotic selective pressure and so leading to the dissemination of resistant bacteria.

Class 1 integrons are low-cost structures in Escherichia coli

Resistance integrons are bacterial genetic platforms that can capture and express antibiotic resistance genes embedded within gene cassettes. The capture and shuffling of gene cassettes are mediated by the integrase IntI, the expression of which is regulated by the SOS response in Escherichia coli. Gene cassettes are expressed from a common Pc promoter. Despite the clinical and environmental relevance of integrons, the selective forces responsible for their evolution and maintenance are poorly understood. Here, we conducted pairwise competition experiments in order to assess the fitness cost of class 1 integrons in E. coli. We found that integrons are low-cost structures and that their cost is further reduced by their tight regulation. We show that the SOS response prevents the expression of costly integrases whose cost is activity dependent. Thus, when an integron is repressed, its cost depends mostly on the expression of its gene cassettes array and increases with Pc strength and the number of cassettes in the array. Furthermore, different cassettes have different costs. Lastly, we showed that subinhibitory antibiotic concentrations promoted the selection of integron-carrying bacteria, especially those with a strong Pc promoter. These results provide new insights into the evolutionary dynamics of integron-carrying bacterial populations.

Antimicrobial resistance and integron gene cassette arrays in commensal Escherichia coli from human and animal sources in IRI

Background

The human and animal intestinal tract harbors a complex community of microbes which enables bacteria to inherit antibiotic resistance genes. The aims of this study were to investigate clonality, antimicrobial resistance, prevalence and gene cassette arrays of class I and II integrons among commensal Escherichia coli from human and animals.

Methods

A total of 200 E. coli isolates from human, chicken, cattle, and sheep were isolated followed by phenotypic antibiotic susceptibility testing and detection of class I and II integrons gene cassettes arrays. The clonal relationship of the isolates were analyzed by (GTG)₅-PCR.

Results

Of 200 isolates, 136 isolates were multi drug resistance (MDR) including 47, 40, 31 and 18 isolates from chicken, human, cattle and sheep, respectively. Class I integron was detected in 50, 38, 6 and 16 %, while class II was detected in 26, 8, 0 and 4 % of chicken, human, cattle and sheep isolates, respectively. Variable regions were amplified and sequenced. Cassette arrays in class I integrons were: dfrA1, dfrA5, dfrA7, dfrA12, aadA1, dfrA17 aadA1, aadA22, aadB–aadA2 and dfrA12–orfF–aadA2, and for class II, dfrA1-sat-aadA1, and sat-sat1-aadA1 were detected. Six class I and three class II positive strains did not produce any amplicons for variable region. Integron-positive isolates showed higher rate of resistance to streptomycin and trimethoprim–sulphamethoxazole, especially in chicken isolates which were fed antibiotics. Low similarity and great genetic diversity of class I and II integrons carrying isolates indicated no clonal relation.

Conclusions

Integrons encoding for antibiotic resistance are significantly present among non-pathogenic commensal E. coli, especially from the hosts medicated by antibiotics. Uncontrolled use of antibiotics will increase the numbers of multiple drug resistant isolates and integrons prevalence.

Microbiological Quality Assessment by PCR and Its Antibiotic Susceptibility in Mangrove Crabs (Ucides cordatus) from Guanabara Bay, Rio de Janeiro, Brazil

The bacteriological quality of crabs from three different mangroves (Itaóca, Suruí, and Piedade) from Rio de Janeiro state, Brazil, was investigated using conventional and molecular methods. The results revealed high counts for total coliforms in meat and hepatopancreas samples. PCR analyses identified 25 Escherichia coli colonies in the Itaóca, Piedade, and Suruí samples, detecting 13 enterotoxigenic colonies and 9 enteroaggregative colonies. Respectively, 12, 11, and 21 Vibrio parahaemolyticus strains were detected in the Itaóca, Piedade, and Suruí samples. Two V. cholerae strains were detected in the Piedade samples. The E. coli strains isolated in the present study showed resistance to gentamicin. E. coli strains from the Piedade samples showed 33% resistance to chloramphenicol and the strains also showed multiresistance to several antimicrobial agents with a MAR index ranging from 0.12 to 0.31. Vibrio strains from Piedade, Itaóca, and Suruí showed 86%, 78%, and 85% resistance, respectively, to ampicillin. The isolated Vibrio strains showed multiresistance to several antimicrobial agents, with a MAR index ranging from 0.12 to 0.25. The presence of these organisms in crab meat is an indication of microbial contamination, which may pose health risks to consumers when improperly cooked.

Integron, Plasmid and Host Strain Characteristics of Escherichia coli from Humans and Food Included in the Norwegian Antimicrobial Resistance Monitoring Programs

Antimicrobial resistant Escherichia coli (n=331) isolates from humans with bloodstream infections were investigated for the presence of class 1 and class 2 integrons. The integron cassettes arrays were characterized and the findings were compared with data from similar investigations on resistant E. coli from meat and meat products (n=241) produced during the same time period. All isolates were obtained from the Norwegian monitoring programs for antimicrobial resistance in human pathogens and in the veterinary sector. Methods used included PCR, sequencing, conjugation experiments, plasmid replicon typing and subtyping, pulsed-field-gel-electrophoresis and serotyping. Integrons of class 1 and 2 occurred significantly more frequently among human isolates; 45.4% (95% CI: 39.9-50.9) than among isolates from meat; 18% (95% CI: 13.2 -23.3), (p<0.01, Chi-square test). Identical cassette arrays including dfrA1-aadA1, aadA1, dfrA12-orfF-aadA2, oxa-30-aadA1 (class 1 integrons) and dfrA1-sat1-aadA1 (class 2 integrons) were detected from both humans and meat. However, the most prevalent cassette array in human isolates, dfrA17-aadA5, did not occur in isolates from meat, suggesting a possible linkage between this class 1 integron and a subpopulation of E. coli adapted to a human host. The drfA1-aadA1 and aadA1 class 1 integrons were found frequently in both human and meat isolates. These isolates were subjected to further studies to investigate similarities with regard to transferability, plasmid and host strain characteristics. We detected incF plasmids with pMLST profile F24:A-:B1 carrying drfA1-aadA1 integrons in isolates from pork and in a more distantly related E. coli strain from a human with septicaemia. Furthermore, we showed that most of the class 1 integrons with aadA1 were located on incF plasmids with pMLST profile F51:A-:B10 in human isolates. The plasmid was present in unrelated as well as closely related host strains, demonstrating that dissemination of this integron also could be attributed to clonal spread. In conclusion, among the systematically collected isolates from two different sources, some significant differences concerning integron prevalence and integron variants were observed. However, closely related plasmids as vehicles for specific class 1 integrons in isolates from meat and from a human with bloodstream infection were found. The occurrence of similar multi-resistance plasmids in bacteria from a food source and from a human clinical sample highlights the possible role of meat as a source of resistance elements for pathogenic bacteria.

Change of integrons over time in Escherichia coli isolates recovered from healthy pigs and chickens

The aims of this study were (a) to perform a time-related quantitative analysis of relative integron frequencies in intestinal Escherichia coli isolates from food animals (pigs and chickens) and (b) to analyse putative relationships between integrons, antimicrobial resistance and phylogenetic groups. The E. coli collection of the Spanish Veterinary Antimicrobial Resistance Surveillance Network was used to extract 393 intestinal isolates from healthy pigs and chickens belonging to the oldest (1998/99) and the latest (2006) available surveillance programs, and their quantitative antimicrobial resistance data. PCR and sequencing were used for detection and characterisation of integrons. Integron overall relative frequencies ranged between 80% and 49%, being higher in pig than in chicken E. coli isolates in both periods. Time-related analysis showed no variations when considering overall frequencies (80% versus 75% in pig E. coli isolates and 49% versus 51% in E. coli chicken isolates). Apart from the 3'-integron sul gene, six different antimicrobial-related gene cassettes (with different variants) were detected in the sequenced integron variable regions: aadA, dfrA, and sat in classes 1 and 2, and cmlA, linF and aadB only in class 1. Multiresistance profiles showed a high association between antimicrobial resistance and integron presence for those antimicrobials corresponding to the antimicrobial-related gene cassettes detected (streptomycin, trimethoprim, chloramphenicol, plus sulphonamides). However, the presence of integrons was also associated with resistance to amoxicillin and tetracycline, two antimicrobials that are widely used in animals but not linked to these genetic elements.

Class 1 and 2 integrons, sul resistance genes and antibiotic resistance in Escherichia coli isolated from Dongjiang River, South China

Antibiotic susceptibility, detection of sul gene types and presence of class 1, 2 and 3 integrons and gene cassettes using PCR assays were investigated in 3456 Escherichia coli isolates obtained from 38 sampling sites of the Dongjiang River catchment in the dry and wet seasons. 89.1% of the isolates were resistant and 87.5% showed resistance to at least three antibiotics. sul2 was detected most frequently in 89.2% of 1403 SXT-resistant isolates. The presence of integrons (class 1 and 2) was frequently observed (82.3%) while no class 3 integron was found. In these integrons, 21 resistance genes of 14 gene cassette arrays and 10 different families of resistance genes were identified. Three gene cassette arrays, aac(6')-Ib-cr-aar-3-dfrA27-aadA16, aacA4-catB3-dfrA1 and aadA2-lnuF, were detected for the first time in surface water. The results showed that bacterial resistance in the catchment was seriously influenced by human activities, especially discharge of wastewater.

Regional dissemination of a trimethoprim-resistance gene cassette via a successful transposable element

Background

Antimicrobial resistance is a growing international problem. We observed a 50% increase in the prevalence of trimethoprim resistance among fecal Escherichia coli from healthy Nigerian students between 1998 and 2005, a trend to increase that continued in 2009.

Methods and Findings

A PCR-based screen revealed that 131 (43.1%) of isolates obtained in Nigeria in 2005 and 2009 carried integron-borne dfrA cassettes. In the case of 67 (51.1%) of these isolates, the cassette was a class 1-integron-borne dfrA7 gene, which has been reported at high prevalence from E. coli isolates from other parts of Africa. Complete sequencing of a 27 Kb dfrA7-bearing plasmid from one isolate located the dfrA7 gene within a Tn21-type transposon. The transposon also contained an IS26-derived bla/sul/str element, encoding resistance to β-lactams, sulphonamides and streptomycin, and mercury resistance genes. Although the plasmid backbone was only found in 12 (5.8%) of trimethoprim-resistant isolates, dfrA7 and other transposon-borne genes were detected in 14 (16.3%) and 32 (26.3%) of trimethoprim resistant isolates collected in Nigeria in 2005 and 2009, respectively. Additionally, 37 (19.3%) of trimethoprim-resistant E. coli isolates collected between 2006 and 2008 from Ghana were positive for the dfrA7 and a transposon marker, but only 4 (2.1%) harbored the plasmid backbone.

Conclusions

Our data point to transposition as a principal mechanism for disseminating dfrA7 among E. coli from Nigeria and Ghana. On-going intensive use of the affordable broad-spectrum antibacterials is likely to promote selective success of a highly prevalent transposable element in West Africa.

Identification and molecular characterization of class 1 integrons in multiresistant Escherichia coli isolates from poultry litter

This study describes the prevalence of arrays of class 1 integron cassettes and Qnr determinants (A, B, and S) in 19 fluoroquinolone-resistant Escherichia coli isolates from chicken litter. qnrS and qnrA were the predominant genes in these fluoroquinolone-resistant isolates, and an uncommon array of aacA4-catB3-dfrA1 gene cassettes from a class1 integron was found. Additionally, aadA1 and dfrA1 gene cassettes, encoding resistance to streptomycin and trimethoprim, constituted the most common genes identified and was located on megaplasmids as well on the chromosome. Antibiotic resistance, pulsed-field gel electrophoresis (PFGE), and plasmid data suggest a genetically diverse origin of poultry E. coli isolates.

Characterization of Antimicrobial Resistance of Escherichia coli Recovered from Foods of Animal and Fish Origin in Korea

Antimicrobial-resistant Escherichia coli is transferred from food-producing animals to humans through the food chain. We investigated the prevalence of antimicrobial resistance and resistance determinants and characterized the integrons of foodborne E. coli in Korea. In total, 162 E. coli isolates from commercial foods (raw meat, fish, and processed foods) were collected by the National Antimicrobial Resistance Management Program from 2004 to 2006. Susceptibility to 20 antibiotics was tested by disk diffusion, and resistance determinants were detected using PCR and genomic sequence analysis. The isolates were highly resistant to antibiotics commonly used in livestock farming. Resistance to tetracycline (74.7%) was the most frequently observed, followed by streptomycin (71%) and ampicillin (51.2%). Class 1 integrons were detected in 13 isolates (8%), and nine of these integrons were located on conjugative plasmids. None of the isolates produced extended-spectrum β-lactamase. One isolate (0.6%) harbored blaCMY-2, which was located on a conjugative plasmid. Although the qnr gene was not detected, aac(6′)-Ib-cr was present in two isolates (1.2%). This is the first report of aac(6′)-1b-cr in food isolates. Three or four amino acid substitutions at positions 83 and 87 in gyrA and at positions 80 and/or 84 in parC were found in six isolates, representing high resistance to ciprofloxacin (MIC ≥ 16 mg/liter). These results suggest that E. coli isolates carrying resistance genes and integrons are present in the Korean food chain.

Antimicrobial resistance and resistance genes in Escherichia coli strains isolated from commercial fish and seafood

The purpose of this study was to investigate the antimicrobial resistance and to characterize the implicated genes in Escherichia coli isolated from commercial fish and seafood. Fish and seafood samples (n=2663) were collected from wholesale and retail markets in Seoul, Korea between 2005 and 2008. A total of 179 E. coli isolates (6.7%) from those samples were tested for resistance to a range of antimicrobial agents. High rates of resistance to the following drugs were observed: tetracycline (30.7%), streptomycin (12.8%), cephalothin (11.7%), ampicillin (6.7%) and ticarcillin (6.1%). No resistances to amikacin, amoxicillin/clavulanic acid and cefoxitin were observed. Seventy out of 179 isolates which were resistant to one or more drugs were investigated by PCR for the presence of 3 classes of antimicrobial resistance genes (tetracycline, aminoglycosides and beta-lactams), class 1, 2 and 3 integrons. Gene cassettes of classes 1 and 2 integrons were further characterized by amplicon sequencing. The tetracycline resistance genes tetB and tetD were found in 29 (41.4%) isolates and 14 (20%) isolates, respectively. The beta-lactam resistance gene, bla(TEM) was found in 15 (21.4%) isolates. The aminoglycoside resistance gene, aadA was found in 18 (25.7%) isolates. Class 1 integron was detected in 41.4% (n=29) of the isolates, while only 2.9% (n=2) of the isolates were positive for the presence of class 2 integron. Two different gene cassettes arrangements were identified in class 1 integron-positive isolates: dfrA12-aadA2 (1.8 kb, five isolates) and aadB-aadA2 (1.6 kb, four isolates). One isolate containing class 2 integron presented the dfrA1-sat-aadA1 gene cassette array. These data suggest that commercial fish and seafood may act as the reservoir for multi-resistant bacteria and facilitate the dissemination of the resistance genes.

Gene flow, mobile genetic elements and the recruitment of antibiotic resistance genes into Gram-negative pathogens

Antibiotics were one of the great discoveries of the 20th century. However, resistance appeared even in the earliest years of the antibiotic era. Antibiotic resistance continues to become worse, despite the ever-increasing resources devoted to combat the problem. One of the most important factors in the development of resistance to antibiotics is the remarkable ability of bacteria to share genetic resources via Lateral Gene Transfer (LGT). LGT occurs on a global scale, such that in theory, any gene in any organism anywhere in the microbial biosphere might be mobilized and spread. With sufficiently strong selection, any gene may spread to a point where it establishes a global presence. From an antibiotic resistance perspective, this means that a resistance phenotype can appear in a diverse range of infections around the globe nearly simultaneously. We discuss the forces and agents that make this LGT possible and argue that the problem of resistance can ultimately only be managed by understanding the problem from a broad ecological and evolutionary perspective. We also argue that human activities are exacerbating the problem by increasing the tempo of LGT and bacterial evolution for many traits that are important to humans.