Molecular characterisation of multidrug-resistant Salmonella enterica serotype Infantis from humans, animals and the environment in Italy

During 2005–2006, Salmonella enterica serotype Infantis strains isolated from human and non-human sources and resistant to ampicillin (A), chloramphenicol (C), streptomycin (S), sulphonamide (Su), tetracycline (T), kanamycin (K) and trimethoprim/sulfamethoxazole (Sxt) emerged in Italy. The aim of this study was to analyse the molecular basis of antibiotic resistance and to evaluate the clonal origin of multiresistant S. Infantis strains isolated from different sources. Seventy S. Infantis strains, susceptible or resistant to antimicrobial drugs, were chosen for this study. Polymerase chain reaction (PCR) and conjugation experiments were performed to identify and localise the resistance genes in multidrug-resistant strains. PCR-based replicon typing was carried out for characterisation of conjugative plasmids. All strains were tested by pulsed-field gel electrophoresis (PFGE) according to the PulseNet protocol, and cluster analysis was performed using BioNumerics software. Strains with resistance (R)-type ACSSuTKSxt harboured bla_TEM-1, strA-B, sul2, tet(B), catA1 and aphA-1 resistance genes as well as a 2.2-kb class 1 integron containing folA, catB3, aadA4 and sul1 gene cassettes. A unique plasmid, belonging to the HI1 incompatibility group, harboured all the resistance genes. Cluster analysis showed that all ACSSuTKSxt-resistant strains belonged to a large cluster (A) with >90% genetic similarity. The presence of a plasmid harbouring all the resistance gene cassettes as well as molecular typing by PFGE demonstrated the circulation of a cluster of S. Infantis R-type ACSSuTKSxt during 2005–2006 in Italy. The presence of a plasmid conferring multidrug resistance could have facilitated the spread of a group of similar isolates through a variety of sources.     

Spread of multidrug-resistant IncHI1 plasmids carrying ESBL gene blaCTX-M-1 and metabolism operon of prebiotic oligosaccharides in commensal Escherichia coli from healthy horses,France

The objective of the study was to identify the genetic determinants and characteristics of expanded-spectrum cephalosporin (ESC) resistance in commensal Escherichia coli from healthy horses in France in 2015. Faecal samples from 744 adult horses were screened for ESC-resistant E. coli isolates. The extended-spectrum beta-lactamase (ESBL)/AmpC resistance genes were identified using polymerase chain reaction (PCR) and sequencing. ESC phenotypes were horizontally transferred by conjugation or transformation. Plasmids carrying ESBL/AmpC genes were typed by PCR-based replicon typing, restriction fragment length polymorphism (RFLP), and plasmid multilocus sequence typing (pMLST). The ESC-resistant E. coli isolates were typed by XbaI macrorestriction analysis. Sixteen of 41 stables harboured at least one horse carrying ESC-resistant E. coli. The proportion of individually tested horses carrying ESC-resistant E. coli was 8.5% (28/328). Fifty non-redundant ESC-resistant E. coli isolates showing a great diversity of XbaI macrorestriction profiles belonged mainly to phylogroup B1, and were negative for major E. coli virulence genes, indicating they are commensal isolates. ESBL bla_CTX-M genes were dominant (bla_CTX-M-1, n=34; bla_CTX-M-2, n=8; bla_CTX-M-14, n=2) and located on conjugative plasmids belonging to various incompatibility groups (IncHI1, IncI1, IncN, IncY, or non-typeable). Among these, the multidrug-resistant IncHI1-pST9 plasmids were dominant and simultaneously harboured the bla_CTX-M-1/2 genes and an operon enabling the metabolism of short-chain fructo-oligosaccharides (scFOS). In conclusion, commensal E. coli of French horses displayed a significant distribution of IncHI1-pST9 plasmids carrying both the bla_CTX-M-1/2 gene and the fos metabolism operon. This finding highlights the risk of co-selection of multidrug-resistant IncHI1 plasmids carrying ESBL genes possibly mediated by the use of scFOS as prebiotic in horses.     

Class 1 integrons and virulence genes in Salmonella enterica isolates from pork and humans

In this study, 183 Salmonella enterica isolates were characterised for integrons and virulence genes. Among the isolates, 46% were positive for intI1, but no isolates carried intI2 or intI3. Eighteen class 1 integrons (21%) contained resistance gene cassettes (i.e. dfrA1-orfC, dfrA12-aadA2, bla(PSE-1) and aadA2) and five class 1 integrons with the dfrA12-aadA2 array were conjugally transferable. Two Salmonella pork isolates of serotypes Albany and Kedougou possessed Salmonella genomic island 1 variants SGI1-G and SGI1-F, respectively. Four class 1 integrons contained an atypical 3'-CS linked to the qacH-sul3 domain, and three were not a sul type. Two novel GyrA mutations (Pro-45→Ser and Met-48→Ile) and three novel ParC mutations (Ser-5→Arg, Thr-31→Met and Leu-77→Arg) were identified in ciprofloxacin-resistant isolates. At least 90% of the Salmonella isolates contained pagC, prgH, sitC, sipB or spaN, whereas all isolates harboured invA, msgA, spiA and tolC.     

Molecular characterisation of multiple drug-resistant Acinetobacter baumannii isolates in southern Taiwan

The purpose of this study was to develop a multiplex polymerase chain reaction (mt-PCR) assay for synchronous detection of carbapenem resistance genes and/or pandrug resistance genes in clinical isolates of multidrug-resistant Acinetobacter baumannii (MDR-AB) and to investigate the association between the genetic make-up and a drug-resistant pattern. In total, 213 MDR-AB isolates were collected. All clinical isolates underwent antimicrobial susceptibility testing and were analysed for the presence of oxacillinase genes (bla_OXA-23, bla_OXA-24, bla_OXA-51-like and bla_OXA-58), class A and C β-lactamase genes (bla_TEM-1 and bla_AmpC, respectively), and an integron-associated antibiotic resistance gene (int1) by an in-house-designed mt-PCR assay. Of the 213 isolates, 73.87% harboured both bla_TEM-1 and bla_AmpC and 83.92% carried at least three oxacillinase genes. Moreover, 64.82% of the isolates were significant in that they had two β-lactamase genes and three oxacillinase genes (P < 0.001), indicating the complexity of the genetic make-up of carbapenem-resistant A. baumannii. The bla_OXA-51-like allele was detected in the majority of these A. baumannii isolates (97.49%), whereas bla_OXA-23 was rarely prevalent in these isolates. In multivariate logistic regression, the presence of bla_OXA-23 and bla_TEM-1 had a statistically significant association with imipenem resistance [bla_OXA-23, P = 0.004, odds ratio (OR) = 10.52, 95% confidence interval (CI) 2.12–52.17; bla_TEM-1, P = 0.005, OR = 6.14, 95% CI 1.74–21.62]. These results suggest that detecting bla_OXA-23 and bla_TEM-1 genes could be used to predict imipenem resistance in MDR-AB isolates. A mt-PCR for detecting carbapenem resistance genes and pandrug resistance genes of A. baumannii isolates was developed to provide an assay to quickly screen for potential imipenem-resistant A. baumannii in the clinic.     

Comparative genomics of rmtB-carrying IncI1 ST136 plasmids in avian escherichia coli isolates from chickens in China

Eight rmtB-carrying avian Escherichia coli strains from a farm in China were characterised in our previous study, but little is known about the backbones and entire multiresistance regions (MRRs) of these plasmids. Here, three rmtB-carrying IncI1 ST136 plasmids were analysed by whole-plasmid sequencing and were compared. These plasmids were composed of an 83 470-bp IncI1 backbone carrying genes responsible for plasmid replication, transfer, maintenance and stability functions, as well as a 17 330-bp MRR for pEC006 and pEC007, and a 34 626-bp MRR for pEC008. Plasmid pEC006 was not transferable, thus truncation of the traI gene may explain the inability to conjugate. pEC008 harboured the bla_TEM-1, rmtB, aacC2, tetA, floR and strAB genes as well as a class 1 integron cassette array (|dfrA12|orfF|aadA2|), which were interspersed with different mobile elements, including Tn2, Tn1721, Tn1722, Tn5393, ISCfr1, IS5057, ISCR1 and ISCR2, and three copies of IS26. The MRR of pEC008 may have resulted from transposition of Tn1722 into the plasmid backbone. Acquisition and rearrangement of MRRs demonstrated the accumulation of different resistance determinants.     

Analysis of plasmid-mediated multidrug resistance in Escherichia coli and Klebsiella oxytoca isolates from clinical specimens in Japan

This study investigated the relationship of plasmid-mediated quinolone resistance (PMQR) and aminoglycoside resistance among oxyimino-cephalosporin-resistant Escherichia coli (n = 46) and Klebsiella oxytoca (n = 28) clinical isolates in Japan. Seventy-three isolates appeared to produce an extended-spectrum β-lactamase (ESBL) and one K. oxytoca isolate produced IMP-1 metallo-β-lactamase (MBL). Polymerase chain reaction (PCR) and sequencing confirmed that eight CTX-M-9/SHV-12-producing isolates, one IMP-1-producing K. oxytoca isolate, and six ESBL-positive E. coli isolates respectively possessed PMQR genes qnrA1, qnrB6, and aac(6′)-Ib-cr. All qnr-positive isolates also carried either aac(6′)-Ib or aac(6′)-IIc aminoglycoside acetyltransferase genes. Resistance determinants to β-lactams, quinolones and aminoglycosides were co-transferred with a plasmid of ca. 140 kb. The qnrA1 gene was located downstream of insertion sequence ISCR1 in complex class 1 integrons. A novel qnrA1-carrying class 1 integron with the cassette arrangement aac(6′)-IIc–aadA2 as well as a unique class 1 integron with bla_IMP-1–aac(6′)-IIc cassettes on the plasmid carrying qnrB6 were found in K. oxytoca isolates. We describe the identification of qnrB6 and aac(6′)-Ib-cr and the close association of qnr with aac(6′)-Ib and aac(6′)-IIc for the first time in clinical isolates producing ESBL or MBL in Japan.     

Stenotrophomonas maltophilia resistance to trimethoprim/sulfamethoxazole mediated by acquisition of sul and dfrA genes in a plasmid-mediated class 1 integron

Stenotrophomonas maltophilia is becoming a more and more common cause of infections. In this study, the minimal inhibitory concentrations of trimethoprim/sulfamethoxazole (SXT), ceftazidime, minocycline, levofloxacin, chloramphenicol and ticarcillin/clavulanic acid were determined and the distribution of integrons and sul1, sul2 and dfrA genes was investigated in 102 S. maltophilia isolates collected from patients treated in 31 hospitals in Anhui, China, in the month of September in 2006-2008. The rate of resistance to SXT was up to 30.4%, and 64.7% of isolates were class 1 integron-positive. Sequencing data revealed the following novel gene cassettes embedded in class 1 integrons: dfrA17-aadA5; dfrA12-aadA2; aacA4-catB8-aadA1; aadB-aac(6')-II-bla(CARB-8); and arr-3-aacA4. This is the first report of the gene cassettes dfrA17-aadA5 and dfrA12-aadA2 and of sul2 genes in SXT-resistant S. maltophilia isolates in China. None of the SXT-susceptible S. maltophilia isolates were positive for sul2 or dfrA gene products by polymerase chain reaction (PCR), but PCR products for sul1 were detected in 27 SXT-susceptible and 25 SXT-resistant isolates. The findings from this study indicate that the sul1 gene, in combination with dfrA17 and dfrA12 gene cassettes and sul2 genes located within a 7.3kb plasmid, lead to a high rate of SXT resistance and also confirm the need for ongoing resistance surveillance.     

Molecular diversity of class 2 integrons in antibiotic-resistant gram-negative bacteria found in wastewater environments in China

The molecular architecture of class 2 integrons among gram-negative bacteria from wastewater environments was investigated in Jinan, China. Out of the 391 antibiotic-resistant bacteria found, 38 isolates harboring class 2 integrons encoding potentially transferrable genes that could confer antibiotic resistance were found. These isolates were classified into 19 REP-PCR types. These strains were identified using 16S rRNA gene sequencing and found to be as follows: Proteus mirabilis (16), Escherichia coli (7), Providencia spp. (7), Proteus spp. (2), P. vulgaris (3), Shigella sp. (1), Citrobacter freundii (1), and Acinetobacter sp. (1). Their class 2 integron cassette arrays were amplified and then either analyzed using PCR–RFLP or sequenced. The typical array dfrA1-sat2-aadA1 was detected in 27 isolates. Six atypical arrays were observed, including three kinds of novel arrangements (linF2(?attC1)-dfrA1(?attC2)-aadA1-orf441 or linF2(?attC1)-dfrA1(?attC2)-aadA1, dfrA1-catB2-sat2-aadA1, and estX _Vr -sat2-aadA1) and a hybrid with the 3′CS of class 1 integrons (dfrA1-sat2-aadA1-qacH), and dfrA1-sat1. Twenty-four isolates were also found to carry class 1 integrons with 10 types of gene cassette arrays. Several non-integron-associated antibiotic resistance genes were found, and their transferability was investigated. Results showed that water sources in the Jinan region harbored a diverse community of both typical and atypical class 2 integrons, raising concerns about the overuse of antibiotics and their careless disposal into the environment.     

临床分离志贺菌耐药性分析及1类整合子的检测

目的了解2007年至2010年安徽省临床分离志贺菌耐药性和1类整合酶基因(intⅠ1)、qacE△1-sul1基因及整合子携带的耐药基因盒的分布。方法琼脂稀释法检测21种抗菌药物对志贺菌的最低抑菌浓度。PCR扩增intⅠ1和qacE△1-sul1基因,对阳性菌株可变区基因盒序列进行分析。结果 137株志贺菌对萘啶酸、氨苄西林、磺胺甲噁唑/甲氧苄啶的耐药率均80.0%以上,且多重耐药率达94.2%,但对三代头孢菌素和氟喹诺酮类耐药率在33.0%以下。intⅠ1的检出率为89.1%(122/137),检出dfrA17-aadA5和aar-3-aacA4两种基因盒,首次在志贺菌中检测到aar-3-aacA4基因,GenBank登录号JF271916。结论安徽省临床分离志贺菌多重耐药现象严重。临床仍可选用氟喹诺酮类和三代头孢菌素作为本地区细菌性痢疾的经验性治疗。1类整合子与志贺菌的耐药具有一定的相关性。     

Multiclonal spread of VIM-1-producing Enterobacter cloacae isolates associated with In624 and In488 integrons located in an IncHI2 plasmid

Over a 6-year period (2007–2012), the emergence of Enterobacter cloacae isolates resistant to β-lactams and with reduced susceptibility to carbapenems was observed in Hospital Universitario 12 de Octubre (Madrid, Spain). To determine the possible role of metallo-β-lactamases (MBLs) in the resistance profile of these isolates, a molecular and clinical epidemiological study was performed, including determination of patients’ clinical characteristics, genetic diversity of strains, resistance mechanisms to carbapenems, and the genetic environment of VIM-1. A total of 73 E. cloacae isolates showed resistance to extended-spectrum cephalosporins and reduced susceptibility to at least one carbapenem during 2007–2012. PCR amplification revealed the presence of bla_VIM-1 gene in 37 isolates, bla_VIM-2 in 1 isolate and bla_KPC in 5 isolates. Molecular typing showed high clonal diversity of E. cloacae isolates carrying bla_VIM-1. The genetic environment of bla_VIM-1 was investigated and two integron structures were found: intI–bla_VIM-1–aacA4–dfrB1–aadA1–catB2–qacEΔ1/sul1 (In624); and intI–bla_VIM-1–aacA4–aadA1–qacEΔ1/sul1 (In488). Isolates belonging to three clones (A, F and G) harboured different types of integron (In624 or In488) despite belonging to the same clone. Conjugal experiments showed an association with a conjugative plasmid of ca. 300 kb belonging to IncHI2 group, which is common in Spanish hospitals, suggesting that the widespread dissemination of bla_VIM-1 may be due to horizontal transfer of mobile genetic determinants rather than the result of spreading of a few clones. These results have implications for infection control programmes in the hospital.     

Salmonella enterica isolated from infections in Australian livestock remain susceptible to critical antimicrobials

Salmonella enterica is a zoonotic pathogen causing a variety of diseases in humans and animals. Many countries are reporting an increase in the prevalence of multidrug-resistant (MDR) S. enterica in food animals. The aim of this study was to determine whether S. enterica isolated from livestock in New South Wales, Australia, have similar resistance traits to those reported internationally. Salmonella enterica (n = 165) from clinical infections in food animals between 2007 and 2011 were serotyped and tested for susceptibility to 18 antimicrobials. Also, 22 antimicrobial resistance genes (ARGs), 3 integrons and 18 plasmid replicon types were screened for using PCR. Most isolates (66.1%) remained susceptible to all antimicrobials; 8.5% of the isolates were resistant to four or more antimicrobials. Antimicrobials with the highest prevalence of resistance were sulfafurazole (28.5%), ampicillin (17.0%), tetracycline (15.8%) and trimethoprim (8.5%). There was no resistance to fluoroquinolones or third-generation cephalosporins. The most common ARGs were bla_TEM (15.2%), sul2 (10.3%), tetB (9.1%), tetA (5.5%), aphA1 (4.8%) and dhfrV (4.8%). Class 1 integrons (7.9%) and IncFIIA (69.7%) were the most commonly detected integron and plasmid replicon types, respectively. Class 1 integrons were positively associated with MDR phenotypes and ARG carriage (P ≤ 0.001). Internationally prominent MDR serovars associated with severe disease in humans (e.g. AmpC-positive Salmonella Newport) were not detected. Overall, the comparatively favourable resistance status of S. enterica in Australian livestock represents minimal public health risk associated with MDR strains and supports a conservative approach to the registration of antimicrobial drug classes in food-producing animals.     

Antibiotic resistance genes in phage particles isolated from human faeces and induced from clinical bacterial isolates

Phage particles have emerged as elements with the potential to mobilise antibiotic resistance genes (ARGs) in different environments, including the intestinal habitat. This study aimed to determine the occurrence of ARGs in phage particles present in faecal matter and induced from strains isolated from faeces. Nine ARGs (bla_TEM, bla_{CTX-M-1 group}, bla_{CTX-M-9 group}, bla_OXA-48, qnrA, qnrS, mecA, sul1 and armA) were quantified by qPCR in the phage DNA fractions of 150 faecal samples obtained from healthy individuals who had not received antibiotic treatment or travelled abroad in the 3 months prior to sample collection. On the suspicion that the detected particles originated from bacterial flora, 82 Escherichia coli and Klebsiella pneumoniae isolates possessing at least one identified ARG (bla_TEM, bla_{CTX-M-1 group}, bla_{CTX-M-9 group}, armA, qnrA, qnrS and sul1) were isolated and their capacity to produce phage particles carrying these ARGs following induction was evaluated. Of 150 samples, 72.7% were positive for at least one ARG, with bla_TEM and bla_{CTX-M-9 group} being the most prevalent and abundant. Of the 82 isolates, 51 (62%) showed an increase in the number of copies of the respective ARG in the phage fraction following induction, with bla_TEM, bla_{CTX-M-1 group}, bla_{CTX-M-9 group} and sul1 being the most abundant. Phages induced from the isolates were further purified and visualised using microscopy and their DNA showed ARG levels of up to 10¹⁰ gene copies/mL. This study highlights the abundance of phage particles harbouring ARGs and indicates that bacterial strains in the intestinal habitat could be source of these particles.     

Role of rifampicin in limiting Escherichia coli O157:H7 Shiga-like toxin expression and enhancement of survival of infected BALB/c mice

Plasmid-mediated 16S rRNA methylases such as ArmA, which confer high levels of resistance to aminoglycosides, are increasingly reported in Enterobacteriaceae. This study investigated the molecular mechanism of β-lactam and aminoglycoside resistance in extended-spectrum β-lactamase (ESBL)-producing Salmonella enterica serotype Infantis isolated at the 53-bed neonatology ward of University Hospital Benabib in Constantine, Algeria. From September 2008 to January 2009, 200 S. enterica isolates were obtained from 138 patients (age range 8-80 months) hospitalised in the neonatology ward. Most isolates were from stool cultures, but also from two blood cultures and one gastric fluid. The isolates were multidrug-resistant and produced TEM-1 and CTX-M-15 enzymes as well as the 16S RNA methylase ArmA. The armA, bla_CTX-M-15 and bla_TEM-1 genes were located on the same 140-kb self-transferable plasmid belonging to the IncL/M incompatibility group. All of the S. Infantis isolates belonged to a single clone. Increased infection control measures and thorough biodecontamination of the rooms led to control of the outbreak but did not eradicate the epidemic strain. This study further illustrates the global emergence of ArmA methylase and its frequent association with bla_CTX-M genes. Spread of 16S RNA methylase determinants at the same level as bla_CTX-M genes in Enterobacteriaceae may seriously compromise the efficacy of aminoglycosides for treating Gram-negative infections.     

Mechanisms of resistance to ciprofloxacin,ampicillin/sulbactam and imipenem in Acinetobacter baumannii clinical isolates in Taiwan

Nosocomial infections caused by multidrug-resistant (MDR) Acinetobacter baumannii have been increasing in recent years, posing a threat to public health worldwide. The susceptibility to eight antimicrobial agents of 35 clinical A. baumannii isolates from Taiwan was tested. Isolates were examined by polymerase chain reaction (PCR) and sequencing for β-lactamase genes and mutations in the gyrA and parC genes. Expression of AdeB, an efflux pump protein, was evaluated by real-time quantitative PCR. The level of adeB expression correlated with resistance to ciprofloxacin and ampicillin/sulbactam in A. baumannii isolates. Almost all isolates with full resistance to ciprofloxacin had both high adeB expression and point mutations in parC and gyrA, but 4 intermediate-resistant isolates had only high adeB expression without point mutations in gyrA or parC, in contrast to 18 susceptible isolates with low adeB expression and without mutations in gyrA or parC. Sixteen isolates (45.7%) carrying a type 1 integron were MDR as well as being more resistant to imipenem, amikacin, gentamicin, ceftazidime or cefepime than those without the integron. The class 1 integron in A. baumannii carried different resistance gene cassettes, including 5′CS-bla_IMP-1–aadA4–3′CS, 5′CS–aacA4–aadA1–3′CS and 5′CS–aacC1–aadA1–3′CS. In conclusion, expression of the adeB gene was associated with resistance to ciprofloxacin and ampicillin/sulbactam in A. baumannii. Multiple mutations in gyrA and parC also played a role in ciprofloxacin resistance. The major metallo-β-lactamase contributing to imipenem resistance in A. baumannii in Taiwan was bla_IMP-1, which was carried by the class 1 integron. The class 1 integron was associated with the MDR phenotype in A. baumannii.     

Prevalence and characterization of the mechanisms of macrolide, lincosamide and streptogramin resistance in viridans group streptococci

The presence of erm genes conferring constitutive and inducible resistance, as well as that of the mefA gene conferring only constitutive resistance, was investigated using PCR in 70 erythromycin resistant (MIC≥1 mg/l) strains of viridans group streptococci (VGS) (18 Streptococcus mitis biotype 1, 16 S. mitis biotype 2, 15 S. oralis, 12 S. salivarius and nine S. sanguis) isolated from the oropharynx of healthy Greek children. All of the 56 isolates belonging to resistance phenotype M harbored the mefA gene. All of the 14 isolates constitutively resistant to macrolides and lincosamides (phenotype CR) harbored the ermB gene. Co-presence of both genes was not observed, whereas class A erm gene (previously known as ermTR) was not detected. Our results are consistent with a possible role of VGS as a reservoir of resistance genes now prevalent in pathogenic species of streptococci.     

Genetic environment of sul genes and characterisation of integrons in Escherichia coli isolates of blood origin in a Spanish hospital

The prevalence and characterisation of integrons and the genetic environment of sulphonamide resistance genes were studied in 135 Escherichia coli isolates recovered from blood cultures in a Spanish hospital during 2007. Class 1 and 2 integrons were identified in 54 isolates (intI1, 52 isolates; intI2, 1 isolate; and intI1 + intI2, 1 isolate). Of the 53 intI1-positive isolates, 36 (67.9%) contained the classic class 1 integron including the qacEΔ1–sul1 region, and 11 different gene cassette arrangements were demonstrated in 33 of these isolates. Seventeen intI1-positive isolates lacked the qacEΔ1–sul1 region, and 8 gene cassette arrangements were demonstrated in 12 of these isolates. Seventy-one isolates showed a sulphonamide-resistant phenotype, 63 of which contained sul genes. The sul1 gene was associated with intI1 in 36 of 42 sul1-positive isolates, and the sul3 gene was associated with non-classic class 1 integrons in 5 of 7 sul3-positive isolates. Finally, sul2 was found associated with strA–strB genes in 32 of 35 sul2-positive isolates, identifying 11 genetic structures, 1 of them presenting the IS150 element disrupting the strB gene; this structure was included in GenBank with accession no. FJ705354. Almost one-half of the E. coli isolates from blood cultures contained integrons and sul genes. Moreover, sul genes were detected in different structures, one of them new, and could be important determinants in antibiotic resistance dissemination.     

100株住院儿童大肠埃希菌Ⅰ类整合子研究

目的:了解Ⅰ类整合子在住院儿童分离大肠埃希菌中分布流行情况。方法:根据NCCLS推荐的纸片扩散法进行药敏试验;PCR扩增临床大肠埃希菌Ⅰ类整合子整合酶基因和可变区基因盒。结果:患者整合酶检出率68%,Ⅰ类整合子基因盒检出率为65%。Ⅰ类整合子的大小约为772 bp～2360 bp,100株细菌各含1～2个Ⅰ类整合子,整合子中最常见的基因盒排列为dfrA17+aadA5和dfrA12+aadA2。结论:Ⅰ类整合子在多重耐药大肠埃希菌中广泛流行,是介导细菌多重耐药性的重要分子机制,应加强基因水平耐药监测。     

Emergence of multidrug-resistant Salmonella enterica serovar Typhi associated with a class 1 integron carrying the dfrA7 gene cassette in Nepal

A total of 121 Salmonella enterica serovars Typhi and Paratyphi A isolated from enteric fever patients at a university hospital in Nepal between February 2004 and January 2006 were tested for their antimicrobial susceptibility. The occurrence and cassette content of integrons as well as the molecular mechanisms of resistance among the multidrug-resistant (MDR) S. Typhi were evaluated. Thirty-nine percent of the isolates were susceptible to all the antimicrobial agents tested. Seven of the S. Typhi strains were MDR. None of the 121 S. enterica isolates were resistant to ciprofloxacin, cefazolin, rifampicin or kanamycin. All MDR S. Typhi isolates contained a class 1 integron with a single cassette, dfrA7, conferring resistance to trimethoprim. Pulsed-field gel electrophoresis (PFGE) of XbaI-generated genomic restriction fragments yielded 12 different patterns. Five of the seven MDR isolates containing class 1 integrons had an identical PFGE pattern. Resistance to sulfamethoxazole, streptomycin, ampicillin, tetracycline and chloramphenicol was mediated by sul1, strA-strB, blaTEM-like, tetB and catA genes, respectively. To the best of our knowledge, this is the first report of integron-associated multidrug resistance as well as the first molecular characterisation of the mechanism of resistance of S. Typhi isolated from Nepal. This study indicates the spread of integron-associated multidrug resistance in S. Typhi in Nepal.     

Wide dissemination of OXA-type carbapenemases in clinical Acinetobacter spp. isolates from South Korea

Carbapenem-resistant Acinetobacter spp. are being increasingly reported worldwide, including in South Korea, where we examined 144 representative isolates collected in a nationwide hospital survey in 2005. Metallo-β-lactamases were detected in only 19.4% of isolates, none of which were Acinetobacter baumannii, whereas 74.3% of isolates (mostly A. baumannii) expressed bla_OXA carbapenemase genes. Among the latter, 47 had bla_OXA-23-like genes and 56 had upregulated bla_OXA-51-like variants, including bla_OXA-66, _-83, _-109 and _-115; bla_OXA-115 was a novel variant, detected in two isolates. bla_OXA-72 (bla_OXA-40-like) was detected in only a single Acinetobacter baylyi isolate, whilst three Acinetobacter calcoaceticus isolates had both bla_VIM-2-like and bla_OXA-58 genes. Pulsed-field gel electrophoresis (PFGE) suggested the spread of A. baumannii clones with OXA carbapenemases within and between hospitals. In conclusion, the recent increase in imipenem-resistant Acinetobacter spp. from South Korea is mostly due to OXA-type carbapenemases.