Characterization of integrons and antimicrobial resistance genes in clinical isolates of Gram-negative bacteria from Palestinian hospitals

Sixty Gram-negative bacterial isolates were collected from Palestinian hospitals in 2006. Thirty-two (53.3%) isolates showed multidrug resistance phenotypes. PCR and DNA sequencing were used to characterize integrons and antimicrobial resistance genes. PCR screening showed that 19 (31.7%) and five (8.3%) isolates were positive for class 1 and class 2 integrons, respectively. DNA-sequencing results for the captured antimicrobial resistance gene cassettes within class 1 integrons identified the following genes: dihydrofolate reductases, dfrA1 , dfrA5 , dfrA7 , dfrA12, dfrA17 and dfrA25 ; aminoglycoside adenyltransferases, aadA1, aadA2 , aadA5, aadA12 and aadB ; aminoglycoside acetyltransferase, aac(6')-Ib ; and chloramphenicol resistance gene, cmlA1 . ESBL were identified in 25 (41.7%) isolates. The identified ESBL were bla _CTX-M-15, bla _CTX-M-56, bla _OXA-1, bla _SHV-1, bla _SHV-12, bla _SHV-32 and bla _TEM-1 genes. Moreover, we characterized the plasmid-mediated quinolone resistance genes, aac(6')-Ib-cr and qnrB2 , which were detected in seven (11.7%) and two (3.3%) isolates, respectively. In this study various types of antibiotic resistance genes have been identified in Gram-negative bacteria from Palestinian hospitals, many of which are reported in the Middle East area for the first time.     

Genetic determinants of antibacterial resistance among nosocomial Escherichia coli, Klebsiella spp., and Enterobacter spp. isolates collected in Russia within 2003-2007

Nosocomial bacterial isolates collected within 2003-2004 (n=411) and 2005-2007 (n=422) were highly resistant to cephalosporins III-IV and antibacterials of other groups (aminoglycosides, fluoroquinolons, chloramphenicol, and co-trimoxazole). Genes encoding TEM, SHV, CTX-M, OXA-2, and AmpC types of beta-lactamases (BLs) in the E. coli, Klebsiella spp., and Enterobacter spp. isolates were detected using polymerase chain reaction (PCR). Prevalent CTX-M-type BLs were detected in 85% of the E. coli, 87% of the Klebsiella spp., and 38% of the Enterobacter spp. isolates of the first strain collection and in 94% of the E. coli, 91% of the Klebsiella spp., and 38% of the Enterobacter spp. isolates of the second one. Genes belonging to three subtypes of blacTx-M genes were identified: bla(CTX-M-1) (228 bla(CTX-M-15) and six bla(CTX-M-3) of the first strain collection; 275 bla(CTX-M-15), three bla(CTX-M-3), and one bla(CTX-M-22) of the second one), bla(CTX-M-2) (one bla(CTX-M-5) of the first strain collection and one bla(CTX-M-2) of the second one), bla(CTX-M-9) (17 bla(CTX-M-14) and one bla(CTX-M-9) of the first strain collection; seven bla(CTX-M-14) and one bla(CTX-M-9) of the second one). Three isolates of the first strain collection and one isolate of the second one carried two genes belonging to two different subtypes, i.e., bla(CTX-M-15) and bla(CTX-M-14) simultaneously. The bacterial isolates had high levels of associative resistance to ciprofloxacin, co-trimoxazole, gentamicin, amikacin, and chloramphenicol associated with the resistance gene cassettes aadA1, aadA2, aadA5, aadB, aacA4, aac(6')Ib; dfrA1, dfrA5, dfrA12, dfrA17, cmlA1, ereA2, and catB8 in the class 1 integrons and the resistance gene cassettes dfrA1, sat1, and aadA1 in the class 2 integrons.     

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.     

Genetic analysis of multiple antimicrobial resistance in Salmonella isolated from diseased broilers in Egypt

To date, no information has been available on the molecular bases of antimicrobial resistance in Salmonella spp. from poultry in Egypt or even in Africa. Therefore, the objective of this study was to analyze, at the molecular level, the mechanisms of multidrug-resistance in isolates of Salmonella recovered from diseased broilers in Egypt. Twenty-one Salmonella isolates were identified; 13 of these isolates were Salmonella enterica serovar Enteritidis and eight Salmonella enterica serovar Typhimurium. 17 (81%). Salmonella isolates displayed multidrug resistance phenotypes, particularly against ampicillin, streptomycin, spectinomycin, kanamycin, tetracycline, chloramphenicol, and trimethoprim/sulfamethoxazole. PCR and DNA sequencing identified class 1 integrons in nine (42.9%) isolates and class 2 integrons in three (14.3%) isolates. The identified resistance genes within class 1 integrons were aminoglycoside adenyltransferase type A, aadA1, aadA2 and aadA5 and dihydrofolate reductase type A, dfrA1, dfrA5, dfrA12, dfrA15 and dfrA17. The β-lactamase encoding genes bla(TEM-1) and bla(CMY-2) and florfenicol resistance gene floR were also identified. Furthermore, the tetracycline resistance gene tet(A) was identified in 14 (66.7%) Salmonella isolates. To the best of our knowledge, this is the first report of the molecular basis of antimicrobial resistance in Salmonella spp. isolated from poultry in Africa.     

Molecular characterization of antimicrobial resistance in Salmonella isolated from animals in Japan

Aims:  To investigate the prevalence of integrons and antimicrobial resistance genes in Salmonella recovered from animals in Japan.
Methods and Results:  Forty-eight out of ninety-four (51·1%) Salmonella isolates showed multidrug resistance phenotypes and harboured at least one antimicrobial resistance gene. Twenty-two out of forty-seven (46·8%) Salmonella enterica serovar Typhimurium that were multidrug-resistant were of definitive phage type DT104. Class 1 integrons were identified in 34/94 isolates (36·2%): 21 isolates containing two gene cassettes, aadA2 and bla _PSE–1, and 13 containing one gene cassette, aadA1 , aadA2 or bla _PSE–1. Class 2 integrons containing estX - sat2 - aadA1 gene cassettes were only identified in Salmonella Enteritidis. The β-lactamase-encoding gene, bla _TEM, was only detected in S. Typhimurium. The plasmid-mediated quinolone resistance gene, qnrS1 , was identified in S. Typhimurium and Salmonella Thompson.
Conclusions:  Our results characterized integrons and antimicrobial resistance genes in Salmonella of animal origin. To the best of our knowledge, this is the first report of qnrS in Salmonella from Japan and also the first report of qnrS in S . Thompson.
Significance and Impact of the Study:  Little is known about the molecular basis of antimicrobial resistance in Salmonella isolated from animals. This study provides useful data on the incidence of integrons and resistance genes in Salmonella of animal origin.     

Zoo animals as reservoirs of gram-negative bacteria harboring integrons and antimicrobial resistance genes

A total of 232 isolates of gram-negative bacteria were recovered from mammals, reptiles, and birds housed at Asa Zoological Park, Hiroshima prefecture, Japan. Forty-nine isolates (21.1%) showed multidrug resistance phenotypes and harbored at least one antimicrobial resistance gene. PCR and DNA sequencing identified class 1 and class 2 integrons and many beta-lactamase-encoding genes, in addition to a novel AmpC beta-lactamase gene, bla(CMY-26). Furthermore, the plasmid-mediated quinolone resistance genes qnr and aac(6')-Ib-cr were also identified.     

Molecular characterization of multidrug-resistant Escherichia coli isolates from Irish cattle farms

This study describes the genotypic characteristics of a collection of 100 multidrug-resistant (MDR) Escherichia coli strains recovered from cattle and the farm environment in Ireland in 2007. The most prevalent antimicrobial resistance identified was to streptomycin (100%), followed by tetracycline (99%), sulfonamides (98%), ampicillin (82%), and neomycin (62%). Resistance was mediated predominantly by strA-strB (92%), tetA (67%), sul2 (90%), bla(TEM) (79%), and aphA1 (63%) gene markers, respectively. Twenty-seven isolates harbored a class 1 integrase (intI1), while qacEΔ1 and sul1 markers were identified in 25 and 26 isolates, respectively. The variable regions of these integrons contained aminoglycoside, trimethoprim, and β-lactam resistance determinants (aadA12, aadB-aadA1, bla(OXA-30)-aadA1, dfrA1-aadA1, dfrA7). Class 2 integrons were identified less frequently (4%) and contained the gene cassette array dfrA1-sat1-aadA1. Resistance to ampicillin, neomycin, streptomycin, sulfonamide, and tetracycline was associated with transferable high-molecular-weight plasmids, as demonstrated by conjugation assays. A panel of virulence markers was screened for by PCR, and genes identified included vt1, K5 in 2 isolates, papC in 10 isolates, and PAI IV(536) in 37 isolates. MDR commensal E. coli isolates from Irish cattle displayed considerable diversity with respect to the genes identified. Our findings highlight the importance of the commensal microflora of food-producing animals as a reservoir of transferable MDR.     

Characterization of class 1 integrons-mediated antibiotic resistance among calf pathogenic Escherichia coli

Escherichia coli isolates from calf diarrhea cases (n=22) in the Beijing surrounding region in China were characterized for disease serotype, virulence factors, antimicrobial susceptibility pattern and class 1 integrons. 59% (n=13) of the isolates were positive for the int I1 gene. The presence and genetic content of class 1 integrons in 13 E. coli isolates were examined by PCR and sequencing. Sequencing analysis revealed six gene cassettes, which encoded resistance to trimethoprim (dfrA1, dfrA17), aminoglycosides (aadB, aadA1 and aadA5) and chloramphenicol (cmlA). The gene cassette arrays dfrA1-orf (45%) and aadB-orf-cmlA (32%) were most prevalent among these isolates. These data revealed the high prevalence of class 1 integrons among calf pathogenic E. coli isolates in the Beijing surrounding region in China, which may provide important and useful surveillance information reflecting specific antibiotic selective pressure.     

整合子与多重耐药大肠埃希菌相关性研究

目的探讨整合子在多重耐药大肠埃希菌耐药性中的作用。方法对临床分离的93株多重耐药大肠埃希菌的I、Ⅱ型整合酶基因进行检测,并分析药敏结果。结果多重耐药临床分离株中Ⅰ型整合子阳性率为60.2%。所检出整合子共有3种长度即1000、1600和2000 bp;主要携带aadA和dfrA类基因盒;未检出Ⅱ型整合子。结论整合子形成是细菌产生多重耐药的重要原因。     

Occurrence and molecular characteristics of antimicrobial resistance of Escherichia coli from broilers,pigs and meat products in Thailand and Cambodia provinces

Nine hundred and forty‐one samples were collected in Sa Keao, Thailand (n = 554) and Banteay Meanchey, Cambodia (n = 387) from July 2014 to January 2015. A total of 667 Escherichia coli isolates (381 isolates from Sa Keao and 286 isolates from Banteay Meanchey) were obtained and examined for antimicrobial susceptibility, class 1 integrons, ESBL genes and horizontal transfer of resistance determinants. Prevalence of E. coli in pig and broiler carcass samples from slaughterhouses and fresh markets was 36–85% in Sa Keao and 11–69% in Banteay Meanchey. The majority of these isolates were multidrug resistant (75.3%). Class 1 integrons were common in both Thai (47%) and Cambodian (62%) isolates, of which four resistance gene cassette arrays including aadA1, dfrA1‐aadA1, dfrA12‐aadA2 and aadA2‐linF were identified. Class 1 integrons in two broiler isolates from Sa Keao (dfrA12‐aadA2) and one broiler isolate from Banteay Meanchey (dfrA1‐aadA1) were horizontally transferable. Sixteen isolates were confirmed to be ESBL‐producing strains with ESBL gene bla_CTX‐M‐15, broad spectrum β‐lactamase gene bla_TEM‐1 and the AmpC gene bla_CMY‐2 being detected. The bla_TEM‐1 gene was most prevalent and located on a conjugative plasmid.     

Characterization of class I integrons among Salmonella enterica serovar Enteritidis isolated from humans and poultry

A total of 84 Salmonella enterica serovar Enteritidis (S. Enteritidis) isolates, 42 of human and 42 of poultry origin, were characterized for antimicrobial resistance patterns and class I integrons. Among them, 58 (69%) S. Enteritidis were multidrug-resistant (MDR) and showed resistance to two or more antibiotic classes. By PCR assays and DNA sequencing, 50 (59.5%) S. Enteritidis isolates were found to carry class I integrons. Amplification of internal variable regions of class I integrons revealed five different arrays (0.75 kb only, 1 kb only, 1.3 kb only, both 1 and 1.2 kb, and both 1 and 1.3 kb). The integrons were further sequenced and the dfrA25 (0.75 kb), aadA1 (1 kb), aadA2 (1 kb), bla(PSE1) (1.2 kb) aadA6-orfD (1.3 kb) gene cassette arrays were identified. Ciprofloxacin minimum inhibitory concentration (MIC) values for the three isolates that showed resistance or reduced susceptibility via the disc diffusion method were 0.5-4 μg mL(-1), although only three isolates exhibited resistance to cefteriaxone (MIC: 128-256 μg mL(-1)) and four isolates were resistant to florfenicol (MIC: 32-128 μg mL(-1)). In conclusion, the high rates of multidrug-resistance and class I integrons found among S. Enteritidis isolates in humans and poultry in Tehran suggest that efforts are needed to confine the prevalence of MDR Salmonella isolates.     

Class 1 and class 2 integrons in multidrug-resistant gram-negative bacteria isolated from the Salmon River, British Columbia

Using an enrichment protocol, we isolated 16 gram-negative, multidrug-resistant strains of known or opportunistic bacterial pathogens from the Salmon River in south-central British Columbia from 2005 to 2009, and investigated the genetic basis of their resistance to a variety of antibiotics. Of the 16 strains, 13 carried class 1 integrons and three carried class 2 integrons. Genes found in cassettes associated with the integrons included those for dihydrofolate reductases (dfrA1, dfrA12, dfrA17, and dfrB7), aminoglycoside adenyltransferases (aadA1, aadA2, aadA5, and aadB), streptothricin acetyltransferase (sat), and hypothetical proteins (orfF and orfC). A new gene cassette of unknown function, orf1, was discovered between dfrA1 and aadA5 in Escherichia sp. Other genes for resistance to tetracycline, chloramphenicol, streptomycin, and kanamycin (tetA, tetB, tetD; catA; strA-strB; and aphA1-Iab, respectively) were outside the integrons. Several of these resistance determinants were transferable by conjugation. The detection of organisms and resistance determinants normally associated with clinical settings attest to their widespread dispersal and suggest that regular monitoring of their presence in aquatic habitats should become a part of the overall effort to understand the epidemiology of antibiotic resistance genes in bacteria.     

A multiresistant clone of Shiga toxin-producing Escherichia coli O118:[H16] is spread in cattle and humans over different European countries

Multiresistant Shiga toxin-producing Escherichia coli (STEC) O118:H16 and O118 nonmotile strains (designated O118:[H16]) were detected by examination of 171 STEC isolates for their antimicrobial sensitivity. Of 48 STEC O118:[H16] strains, 98% were resistant to sulfonamide, 96% were resistant to streptomycin, 79% were resistant to kanamycin, 75% were resistant to tetracycline, 67% were resistant to ampicillin, 60% were resistant to chloramphenicol, 48% were resistant to trimethoprim, and 10% each were resistant to gentamicin and nalidixic acid. Nalidixic acid resistance and reduced susceptibility to ciprofloxacin were associated with the mutation gyrA(LEU-83). The STEC O118:[H16] strains were found to belong to a single genetic clone as investigated by multilocus enzyme electrophoresis and by multilocus sequence analysis of E. coli housekeeping genes. The STEC O118:[H16] strains originated from humans and cattle and were isolated in seven different countries of Europe between 1986 and 1999. Strains showing multiresistance to up to eight different antimicrobials predominated among the more recent STEC O118:[H16] strains. The genes in parentheses were associated with resistance to kanamycin (aphA1-Ia), chloramphenicol (catA1), tetracycline [tet(A)], and ampicillin (bla(TEM-1)). Class 1 integrons containing sulI (sulfonamide resistance), aadA1a (streptomycin resistance), or dfrA1 (trimethoprim resistance)-aadA1a gene cassettes were detected in 28 strains. The bla(TEM-1b) gene was present in 18 of 21 strains that were examined by nucleotide sequencing. Class 1 integrons and bla(TEM) genes were localized on plasmids and/or on the chromosome in different STEC O118:[H16] strains. Hybridization of XbaI-digested chromosomal DNA separated by pulsed-field gel electrophoresis revealed that bla(TEM) genes were integrated at different positions in the chromosome of STEC O118:[H16] strains that could have occurred by Tn2 insertion. Our data suggest that strains belonging to the STEC O118:[H16] clonal group have a characteristic propensity for acquisition and maintenance of resistance determinants, thus contrasting to STEC belonging to other serotypes.     

Occurrence and transmission of class 1 and 2 integrons among phenotypic highly ampicillin-resistant avian <Emphasis Type="Italic">Escherichia coli</Emphasis> isolates from Pakistan

Thirty four avian Escherichia coli isolates were collected from different cities of Punjab province, Pakistan during 2008–2009. Twenty five phenotypic highly ampicillin-resistant (MICs ≥ 256 μg/ml) avian E. coli strains were selected for the investigation of occurrence and transmission of class 1, 2 and 3 integrons and β-lactamase genes. Amoxicillin, sulfonamide, trimethoprim, enrofloxacin, pefloxacin and tetracycline were the most common phenotypic resistant among ampicillin-resistant avian E. coli strains. Integrons and β-lactamase were found 60 and 72% respectively. Class 1 and 2 integrons were found 52 and 8%, while class 3 integrons were not found in all strains. All class 1 positive strains had variable fragments associated with gene cassettes dfrA7, dfrA1-aadA1, aadA1, aadA22 and dfrA12-orfF-aadA2 respectively, which confer resistance to trimethoprim and streptomycin. Class 2-positive strains had similar gene cassettes array dfrA1-sat1-aadA1 conferring resistance to trimethoprim, streptothricin and spectinomicin/streptomycin. Integrons are frequently found in β-lactamase positive isolates and widely disseminate multidrug resistance genes but they do not play role in the spreading of β-lactamase genes. Class 1 integrons gene cassette aadA22 is reported for the first time in avian E. coli. Findings of this study may provide important and useful information reflecting specific antibiotic selective pressure in Punjab province, Pakistan.     

Identification of Antibiotic Resistance Cassettes in Class 1 Integrons in Aeromonas spp. Strains Isolated From Fresh Fish (Cyprinus carpio L.)

Forty-six Aeromonas spp. strains were isolated from fresh fish and investigated for their antimicrobial susceptibility, detection of Class 1 integrons by PCR, and arrangement of gene cassettes. Selected isolates were further characterized by enterobacterial repetitive intergenic consensus-PCR. Twenty isolates were found to carry Class 1 integrons. Amplification of the variable regions of the integrons revealed diverse bands ranging in size from 150 to 1,958 pb. Sequence analysis of the variable regions revealed the presence of several gene cassettes, such as adenylyl transferases (aadA2 and aadA5), dihydrofolate reductases (dfrA17 and dfrA1), chloramphenicol acetyl transferase (catB3), β-lactamase (oxa2), lincosamide nucleotidil transferase (linF), aminoglycoside-modifying enzyme (apha15), and oxacillinase (bla _OXA-10). Two open reading frames with an unknown function were identified as orfC and orfD. The aadA2 cassette was the most common integron found in this study. Interestingly, five integrons were detected in the plasmids that might be involved in the transfer of resistance genes to other bacteria. This is a first report of cassette encoding for lincosamides (linF) resistance in Aeromonas spp. Implications on the incidence of integrons in isolates of Aeromonas spp. from fresh fish for human consumption, and its possible consequences to human health are discussed.     

Atypical Class 1 Integron Coexists with Class 1 and Class 2 Integrons in Multi-Drug Resistant Shigella flexneri Isolates from China

The antimicrobial resistance and the character of integrons were determined in 58 Shigella flexneri strains isolated from China. All isolates were multi-drug resistant and found to carry integrons of class 1 (94.8%), class 2 (100%), or both (94.8%). No intI3 was detected. The typical class 1 integrons were found in conjugative plasmids and could be transferred to the recipient E. coli DH5α. The gene cassettes of typical class 1 integrons dfrA17-aadA5 and dfrA12-orfF-aadA2 were detected in 54 strains (93.1%) and 1 strain, respectively. Atypical class 1 integrons located on the chromosome with gene cassettes bla (oxa-30)-aadA1 were detected in 55 isolates (94.8%). All the intI2 positive isolates carried gene cassettes dfrA1-sat1-aadA1. To our knowledge, this is the first report that atypical and typical class 1 integrons coexisted with class 2 integron in multi-drug resistant S. flexneri strains.     

Antibiotic resistance patterns and sequencing of class I integron from uropathogenic Escherichia coli in Lebanon

Aim: To study the prevalence and molecular basis of antimicrobial resistance in UPEC. Methods and Results: PCR was used to detect the presence of the Class I integron variable region (VR). The VR amplicons were then characterized by partial sequencing and restriction digestion with AluI. VR negative isolates showed more antibiotic susceptibility than VR positive isolates. 30% of the isolates were positive for the VR and carried the genes dfrA7, dfrA17‐aadA5, dfrA1‐aadA1, dfrA12‐orf5‐aadA2 and bla_OXA‐30‐aadA1. Five restriction patterns were detected and isolates with the same VR amplicon size had the same restriction pattern. Conclusions: Our data demonstrated that Class I integrons are widely disseminated in Lebanon and showed their importance for the occurrence and transmission of multidrug resistance. Significance and Impact of the Study: These findings will facilitate greater understanding of the factors that contribute to the presence and transfer of integron‐associated antibiotic resistance genes in UPEC.     

Distribution of class 1 integrons among enteropathogenic Escherichia coli

The aim of this study was to investigate the incidence of and resistance gene content of class 1 integrons among enteropathogenic Escherichia coli (EPEC) and non-EPEC and to investigate intraspecies genetic diversity of EPEC strains isolated from children with diarrhea in Iran. Twenty-eight EPEC and 16 non-EPEC strains isolated from children with diarrhea were tested for the presence of a class 1 integron associated integrase gene (int1). Sequence analysis was performed to identify the resistance gene content of integrons. Genetic diversity and cluster analysis of EPEC isolates were also investigated using enterobacterial repetitive intergenic concensus-polymerase chain reaction (ERIC-PCR) fingerprinting. Twenty-three (82%) EPEC isolates and 11 (68.7%) non-EPEC isolates harbored the int1 gene specific to the conserved integrase region of class 1 integrons. Sequence analysis revealed the dominance of dfrA and aadA gene cassettes among the isolates of both groups. ERIC-PCR fingerprinting of EPEC isolates revealed a high diversity among these isolates. The widespread distribution of 2 resistance gene families (dfrA and aadA) among both groups of EPEC and non-EPEC isolates indicates the significance of integrons in antibiotic resistance transfer among these bacteria. Furthermore, clonal diversity of EPEC isolates harbouring a class 1 integron also suggests the circulation of these mobile elements among a diverse population of EPEC in this country.     

Class 1 and class 2 integrons and plasmid-mediated antibiotic resistance in coliforms isolated from ten rivers in northern Turkey

We aimed to determine the molecular mechanisms of antibiotic resistance in coliforms isolated from ten rivers in northern region of Turkey. A total of 183 isolates were tested for antimicrobial susceptibility by disk diffusion and agar dilution methods. Resistance to ampicillin, streptomycin, trimethoprim, tetracycline, and chloramphenicol was detected in 58%, 51.9%, 24%, 28.4%, and 12.5%, respectively. Twelve (6.5%) phylogenetically distant organisms were detected to harbor self-transmissible plasmids ranging 52 to >147 kb in sizes. Resistances to ampicillin, tetracycline, trimethoprim, streptomycin, and nalidixic acid were commonly transferable traits. Transferable nalidixic acid-resistant strains harbored qnrS gene, which was the first report of plasmid-mediated quinolone resistance in bacteria of environmental origin in Turkey. Fourteen and five coliforms harbored class 1 and class 2 integrons, respectively, and some of them were located on transferable plasmids. Sequence analyses of variable regions of the class 1 and 2 integrons harbored various gene cassettes, dfrA1, dfr2d, dfrA7, dfrA16, dfrA17, aadA1, aadA5, bla _oxA-30, and sat1. A gene cassette array, dfrA16 has been demonstrated for the first time in a Citrobacter koseri isolate. Class 1 and class 2-bearing strains were clustered in different groups by BOX-PCR fingerprinting. Rivers in the northern Turkey may act as receptacle for the multi-drug resistant enterobacteria and can serve as reservoirs of the antimicrobial resistance determinants in the environment. The actual risk to public health is the transfer of resistance genes from the environmental bacteria to human pathogens. This study was presented in part at the 2^nd World Conference on Magic Bullets, held October 3–5, 2008 in Nurnberg, Germany.