Type 1 integrons in epidemiologically unrelated Acinetobacter baumannii isolates collected at Spanish hospitals

Prevalence of Integrons and Antibiotic Resistance Pattern in Acinetobacter baumannii Isolated from Clinical Samples of Iranian Patients: A Systematic Review and Meta-analysis

BACKGROUND

Acinetobacter baumannii is an important opportunistic nosocomial pathogen. Class 1 integrons in A. baumannii plays a significant role in antibiotic resistance. Therefore, this study aimed to investigate the prevalence of integrons and antibiotic resistance pattern in A. baumannii isolated from clinical samples of Iranian patients.

METHODS

The Medical Subject Headings (MeSH) and the keywords with the help of Boolean operators ("AND" or "OR") were used alone or in combination to conduct the search. The searching process was conducted in the Web of Science, PubMed, Cochrane Library, Scopus, and Google Scholar databases and, also Iranian databases. The search was restricted to relevant English and Persian cross-sectional publications reporting the prevalence of Int1 in A. baumannii isolated from clinical samples from 1 January 2000 to 31 December 2018. The data were analyzed using Comprehensive Meta-Analysis software. Regarding the heterogeneity of studies, the random effects model was used. Cochrane Q and I2 tests was used to evaluate statistical heterogeneity between the studies.

RESULTS

Fifteen studies were included in the analysis. The combined prevalence of class 1 integrons in A. baumannii was 55.2% (95% CI: 44.8-65.1). The pooled prevalence of MDR A. baumannii isolates was 68.1%. The highest resistance belonged to Aztreonam, followed by Ciprofloxacin, and Ceftazidime with a resistance rate of 97.6%, 92.8%, and 91.6%, respectively. Tobramycin was reported as an effective antibiotic.

CONCLUSIONS

The present study reported an alarmingly high prevalence of class 1 Integrons, and MDR isolates of A. baumannii recovered from clinical samples that should be considered.

The Frequency of Antibiotic Resistance and ESBLs Among Clinically Acinetobacter baumannii Strains Isolated from Patients in a Major Hospital in Tehran, Iran

Background:

Bacterial resistance to antibiotics limits treatment options, increases morbidity and mortality, and raises the risk of antibiotic-associated adverse events. Antibacterial resistance emerges rapidly following an increase in the consumption of antibiotics against infectious diseases. The spread of ESBL producing strains has a limiting factor based on antibiotic function for the treatment of infections particularly caused by Acinetobacter baumannii (A. baumannii).

Objective:

This study was conducted to evaluate the prevalence of antimicrobial resistance and distribution of bla_TEM, bla_CTX, and bla_SHV genes among A. baumannii strains isolated from clinical samples at a major hospital in Teheran, Iran.

Methods:

A. baumannii strains were isolated and identified using standard microbiological methods. The disc diffusion and combined discs methods were used for testing antimicrobial susceptibility and to identify the strains producing Extended-Spectrum Beta-Lactamases (ESBL), respectively. DNA extraction was done by boiling method. Finally, the frequency of resistant genes including bla_TEM, bla_CTX, and bla_SHV in ESBL producing isolates was studied by PCR.

Results:

Gender distribution in this study was 53 (53%) samples for men and 47 (47%) for women. Totally, one hundred A. baumannii strains were isolated. More than 93% of the isolates were multi drug resistant. The highest to lowest antibiotic resistance was observed against amoxicillin/clavulanic acid (98%), ceftriaxone (96%), cefotaxime (94%), and ceftazidime (93%), respectively. The frequency of positive phenotypic test of ESBL was 19% and 16% for CAZ-C and CTX-C, respectively. The frequency of bla_TEM, bla_CTX, and bla_SHV genes was 52.1, 43.4, and 21.7, respectively.

Conclusion:

A. baumannii isolates exhibited an extremely worrying level of antibiotic resistance, and a high percentage of the isolates showed MDR in this study. This is a serious warning because ESBLs are a major threat to the effectiveness of antibiotics that are currently available for medical uses. The frequency of genes encoded ESBL isolates of A. baumannii may be due to overuse and misuse of antibiotics.

Antibiotic resistance and carriage class 1 and 2 integrons in clinical isolates of Acinetobacter baumannii from Tehran, Iran

OBJECTIVE

To investigate antibiotic resistance and carriage class 1 and 2 integrons in clinical isolates of Acinetobacter baumannii (A. baumannii) from Tehran, Iran.

METHODS

Antimicrobial susceptibility testing was performed according to the Clinical and Laboratory Standards Institute. The presence of integrons was investigated by PCR using specific primers.

RESULTS

Among isolated A. baumannii strains, 82% were multidrug resistant, 27 samples (54%) were resistant to three or more than three antibiotics and 16 samples (32%) showed resistance to two antibiotics. Integrons were detected from 44 of 50 isolates (88%), with classes 1 and 2 being observed in 42% (21/50) and 82% (41/50) of isolates, respectively. Integron-positive A. baumannii isolates showed higher antibiotic resistance than integron-negative isolates and all showed a multidrug-resistant phenotype.

CONCLUSIONS

Our findings show that classes 1 and 2 integrons, and especially classes 2 integrons are widely disseminated among A. baumannii strains isolated from Tehran and these structures are playing a major role in the acquisition of multidrug resistance in these strains. So monitoring of drug resistance with investigating carriage class 1 and 2 integrons is very important to plan specific infection control measures due to multidrug resistance A. baumannii in Iran hospitals.

Various pathways leading to the acquisition of antibiotic resistance by natural transformation

Natural transformation can lead to exchange of DNA between taxonomically diverse bacteria. In the case of chromosomal DNA, homology-based recombination with the recipient genome is usually necessary for heritable stability. In our recent study, we have shown that natural transformation can promote the transfer of transposons, IS elements, and integrons and gene cassettes, largely independent of the genetic relationship between the donor and recipient bacteria. Additional results from our study suggest that natural transformation with species-foreign DNA might result in the uptake of a wide range of DNA fragments; leading to changes in the antimicrobial susceptibility profile and contributing to the generation of antimicrobial resistance in bacteria.

Integrons: Vehicles and pathways for horizontal dissemination in bacteria

Integrons are genetic elements first described at the end of the 1980s. Although most integrons were initially described in human clinical isolates, they have now been identified in many non-clinical environments, such as water and soil. Integrons are present in ≈10% of the sequenced bacterial genomes and are frequently linked to mobile genetic elements (MGEs); particularly the class 1 integrons. Genetic linkage to a diverse set of MGEs facilitates horizontal transfer of class 1 integrons within and between bacterial populations and species. The mechanistic aspects limiting transfer of MGEs will therefore limit the transfer of class 1 integrons. However, horizontal movement due to genes provided in trans and homologous recombination can result in class 1 integron dynamics independent of MGEs. A key determinant for continued dissemination of class 1 integrons is the probability that transferred MGEs will be vertically inherited in the recipient bacterial population. Heritability depends both on genetic stability as well as the fitness costs conferred to the host. Here we review the factors known to govern the dissemination of class 1 integrons in bacteria.

Prevalence of PER and VEB Type Extended Spectrum Betalactamases among Multidrug Resistant Acinetobacter baumannii Isolates in North-West of Iran

OBJECTIVE(S)

Drug resistant Acinetobacter baumannii have emerged as a major problem in many hospitals and intensive care units. Various types of extended spectrum beta-lactamases (ESBLs) are responsible for resistance to beta-lactam antibiotics in different parts of the world. The objective of this study was to determine the prevalence of integron class1 (INT 1) and ESBL types PER-1, PER-2 and VEB-1 among A. baumannii strains isolated from Tabriz, North-West of Iran.

MATERIAL AND METHODS

A total of 100 A. baumannii isolates collected from different clinical samples were included in the study. Antimicrobial susceptibility profiles were determined using the Kirby Bauer disk diffusion method. Production of ESBL was investigated by testing resistance against ceftazidime, cefotaxime, ceftriaxone and verified by Double Disk Synergy Test. DNA was extracted from the isolates and the frequency of INT 1 and ESBL types PER-1, PER-2 and VEB-1 were determined by PCR using specific primers.

RESULTS

Among 100 A. baumannii isolates screened, 80 isolates were multidrug-resistant and 70 isolates were positive for ESBL production. PCR screening revealed that 74 % of the isolates contained class 1 integron, 51% were positive for PER-1 gene, 10% positive for VEB1 whereas none of the isolates were positive for PER2 type gene.

CONCLUSION

This is the first report of ESBL types VEB and PER in A. baumannii from North West of Iran. The results of this study demonstrated high prevalence of PER-1 and VEB-1 type ESBLs among A. baumannii isolates in the study region and reminded the necessity of appropriate infection control strategy to prevent further spread of infection by these organisms.

Natural transformation facilitates transfer of transposons, integrons and gene cassettes between bacterial species

We have investigated to what extent natural transformation acting on free DNA substrates can facilitate transfer of mobile elements including transposons, integrons and/or gene cassettes between bacterial species. Naturally transformable cells of Acinetobacter baylyi were exposed to DNA from integron-carrying strains of the genera Acinetobacter, Citrobacter, Enterobacter, Escherichia, Pseudomonas, and Salmonella to determine the nature and frequency of transfer. Exposure to the various DNA sources resulted in acquisition of antibiotic resistance traits as well as entire integrons and transposons, over a 24 h exposure period. DNA incorporation was not solely dependent on integrase functions or the genetic relatedness between species. DNA sequence analyses revealed that several mechanisms facilitated stable integration in the recipient genome depending on the nature of the donor DNA; homologous or heterologous recombination and various types of transposition (Tn21-like and IS26-like). Both donor strains and transformed isolates were extensively characterized by antimicrobial susceptibility testing, integron- and cassette-specific PCRs, DNA sequencing, pulsed field gel electrophoreses (PFGE), Southern blot hybridizations, and by re-transformation assays. Two transformant strains were also genome-sequenced. Our data demonstrate that natural transformation facilitates interspecies transfer of genetic elements, suggesting that the transient presence of DNA in the cytoplasm may be sufficient for genomic integration to occur. Our study provides a plausible explanation for why sequence-conserved transposons, IS elements and integrons can be found disseminated among bacterial species. Moreover, natural transformation of integron harboring populations of competent bacteria revealed that interspecies exchange of gene cassettes can be highly efficient, and independent on genetic relatedness between donor and recipient. In conclusion, natural transformation provides a much broader capacity for horizontal acquisitions of genetic elements and hence, resistance traits from divergent species than previously assumed.

Genetic elements, such as transposons and integrons, frequently carry antimicrobial resistance determinants and can be found widely disseminated among pathogenic bacteria. Their distribution pattern suggests dissemination through horizontal gene transfer. The role of natural transformation in horizontal transfer of genetic elements other than those that are self-replicative (plasmids) has remained largely unexplored. We have tested if natural transformation can facilitate transfer of transposons and class 1 integrons between bacterial species. We here provide experimental evidence showing that natural transformation can be a general mechanism for dissemination of genetic elements that by themselves do not encode interspecies transfer functions (e.g. transposons, insertion sequences). We demonstrate that antibiotic resistance determinants present in such genetic elements can spread by natural transformation between species of clinical interest. We show by quantitative data that interspecies exchange of resistance gene cassettes is highly efficient among integron-containing strains and species. Our study also provides a plausible explanation for how sequence-conserved integrons can become distributed among bacterial species.

A diversity of OXA-carbapenemases and class 1 integrons among carbapenem-resistant Acinetobacter baumannii clinical isolates from Sweden belonging to different international clonal lineages

This study was aimed to investigate the molecular epidemiology, mechanism of carbapenem resistance, and occurrence of class 1 integrons among 13 carbapenem-resistant clinical isolates of Acinetobacter baumannii obtained between 2004 and 2007 from Sweden. Nine isolates were linked with hospitalization abroad. Molecular epidemiology was investigated by multilocus sequence typing, multiplex PCRs for major international clones/sequence groups (SGs), and pulsed-field gel electrophoresis. OXA-carbapenemase genes/genetic surroundings and class 1 integrons were examined by PCRs and sequencing. The isolates belonged to sequence type (ST) 2/international clone II (n=6), ST23/SG5 (n=2), ST25 (n=2), ST5/SG7 (n=1), and ST109 (n=2). OXA-58, OXA-23, and OXA-24 were detected in seven, five, and one isolate, respectively. Different genetic structures surrounded the bla(OXA-58-like) and bla(OXA-23-like) genes. Interestingly, ISAba825 was detected upstream bla(OXA-58-like) in two isolates. Class 1 integrons with three different variable regions (VR) were detected. VR1 (aacA4-orfO-bla(OXA-20)) was found in four isolates from ST2/international clone II, with three of them imported from Greece. VR2 (aadB-aadA1-IS) was detected in one ST5 isolate imported from Poland, and VR3 (bla(GES-11)-aacA4-dfrA7) was present in a nonimport ST25 isolate. In conclusion, a variety of clonal lineages, OXA-carbapenemases genes and genetic structures, and class 1 integrons were detected among carbapenem-resistant A. baumannii from Sweden.

Clinical features of infections and colonization by Acinetobacter genospecies 3

Two hundred twenty-one isolates of Acinetobacter baumannii and 15 of Acinetobacter genospecies 3 (AG3) were consecutively collected in a 30-day period during the nationwide project GEIH-Ab2000. Nosocomial acquisition (P=0.01), intensive care unit admission (P=0.02), and antibiotic pressure (P = 0.03) were observed to be lower in the AG3 group. AG3 isolates were more frequently implied in wound infections (P=0.05), while A. baumannii tended to be recovered from respiratory samples (P=0.08). To our knowledge, this is the first report analyzing the clinical differences among Acinetobacter genospecies, with our findings suggesting that clinical features of AG3 may not be equivalent to those traditionally described for A. baumannii.

Molecular epidemiology of aminoglycosides resistance in acinetobacter spp. With emergence of multidrug-resistant strains

BACKGROUND

Acinetobacter spp. is characterized as an important nosocomial pathogen and increasing antimicrobial resistance. Our aim was to evaluate antimicrobial susceptibility and aminoglycosides resistance genes of Acinetobacter spp. isolated from hospitalized patients.

METHODS

Sixty isolates were identified as Acinetobacter species. The isolates were tested for antibiotic resistance by disc diffusion method for 12 antimicrobials. The presence of aphA6, aacC1 aadA1, and aadB genes were detected using PCR.

RESULTS

From the isolated Acinetobacter spp. the highest resistance rate showed against amikacin, tobramycin, and ceftazidim, respectively; while isolated bacteria were more sensitive to ampicillic/subactam. More than 66% of the isolates were resistant to at least three classes of antibiotics, and 27.5% of MDR strains were resistant to all seven tested classes of antimicrobials. The higher MDR rate presented in bacteria isolated from the ICU and blood samples. More than 60% of the MDR bacteria were resistance to amikacin, ceftazidim, ciprofloxacin, piperacillin/tazobactam, doxycycline, tobramycin and levofloxacin. Also, more than 60% of the isolates contained phosphotransferase aphA6, and acetyltransferase genes aacC1, but adenylyltransferase genes aadA1 (41.7%), and aadB (3.3%) were less prominent. 21.7% of the strains contain three aminoglycoside resistance genes (aphA6, aacC1 and aadA1).

CONCLUSION

The rising trend of resistance to aminoglycosides poses an alarming threat to treatment of such infections. The findings showed that clinical isolates of Acinetobacter spp. in our hospital carrying various kinds of aminoglycoside resistance genes.

Therapeutic options for Acinetobacter baumannii infections

Acinetobacter baumannii is an important cause of nosocomial infections, mainly in patients in intensive care units. This microorganism, although with slight differences depending on the country, presents resistance to multiple antimicrobial agents, occasionally including resistance to colistin: hence, it can be considered the paradigm of nosocomial multiresistant bacteria. This review analyzes the evolution of antimicrobial resistance and the molecular bases associated with the increase in antimicrobial resistance, as well as the current treatment of Acinetobacter infections. Although controversy remains, the pooled data suggest that infections by A. baumannii may be associated with considerable attributable mortality. Moreover, in cases of pneumonia and bacteraemia, inappropriate treatment is associated with, among other factors, mortality. Therefore, treatment should be carefully considered.

Molecular epidemiology of a clonal outbreak of multidrug-resistant Acinetobacter baumannii in a university hospital in Italy

This study investigated the molecular epidemiology of a clonal outbreak of multidrug-resistant Acinetobacter baumannii that occurred between June 2003 and June 2004 in a tertiary-care hospital in Naples, Italy. A. baumannii was isolated from 74 patients, of whom 38 were infected and 36 were colonised. Thirty-three patients had ventilator-associated pneumonia, three had hospital-acquired pneumonia, and two had sepsis. Genotypic analysis of 45 available A. baumannii isolates revealed two distinct pulsed-field gel electrophoresis (PFGE) patterns. Of these, PFGE pattern 1 was represented by isolates from 44 patients and was identical to that of an epidemic A. baumannii clone isolated in another hospital of Naples during 2002. All A. baumannii isolates of PFGE type 1 showed identical multiresistant antibiotypes, characterised by resistance to all antimicrobial agents tested, including carbapenems, with the exception of colistin. In these isolates, inhibition of OXA enzymes by 200 mM NaCl reduced the imipenem MIC by up to four-fold. Molecular analysis of antimicrobial resistance genes showed that all A. baumannii isolates of PFGE type 1 harboured a class 1 integron containing the aacA4, orfX and bla(OXA-20) gene cassettes, an ampC gene and a bla(OXA-51)-like allele. Moreover, a bla(OXA-58)-like gene surrounded by the regulatory elements ISAba2 and ISAba3 was identified in a 30-kb plasmid from A. baumannii isolates of PFGE type 1, but not PFGE type 2. Thus, selection of a single A. baumannii clone producing an OXA-58-type carbapenem-hydrolysing oxacillinase was responsible for the increase in the number of A. baumannii infections that occurred in this hospital.

Porins, efflux pumps and multidrug resistance in Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic pathogen, causing infections mainly in patients in intensive care units where the extensive use of antimicrobial agents can select for the emergence of multiresistant strains. In fact, since strains resistant to all antimicrobial agents have been reported, A. baumannii is considered the paradigm of multiresistant bacteria. Both acquired and intrinsic resistance can contribute to multiresistance. The ability to acquire multidrug resistance can be due to either the acquisition of genetic elements carrying multiple resistant determinants or mutations affecting the expression of porins and/or efflux pump(s), which can affect unrelated antimicrobial agents. Meanwhile, intrinsic resistance can be generated by the interplay of decreased permeability and constitutive expression of active efflux systems and it too can affect unrelated antimicrobial agents. This review is focused on the current knowledge of porins and efflux pump(s) in this microorganism.

Horizontal gene transfer in a polyclonal outbreak of carbapenem-resistant Acinetobacter baumannii

In the last few years, phenotypically carbapenem resistant Acinetobacter strains have been identified throughout the world, including in many of the hospitals and intensive care units (ICUs) of Australia. Genotyping of Australian ICU outbreak-associated isolates by pulsed-field gel electrophoresis of whole genomic DNA indicated that different strains were cocirculating within one hospital. The carbapenem-resistant phenotype of these and other Australian isolates was found to be due to carbapenem-hydrolyzing activity associated with the presence of the blaOXA-23 gene. In all resistant strains examined, the blaOXA-23 gene was adjacent to the insertion sequence ISAba1 in a structure that has been found in Acinetobacter baumannii strains of a similar phenotype from around the world; blaOXA-51-like genes were also found in all A. baumannii strains but were not consistently associated with ISAba1, which is believed to provide the promoter required for expression of linked antibiotic resistance genes. Most isolates were also found to contain additional antibiotic resistance genes within the cassette arrays of class 1 integrons. The same cassette arrays, in addition to the ISAba1-blaOXA-23 structure, were found within unrelated strains, but no common plasmid carrying these accessory genetic elements could be identified. It therefore appears that antibiotic resistance genes are readily exchanged between cocirculating strains in epidemics of phenotypically indistinguishable organisms. Epidemiological investigation of major outbreaks should include whole-genome typing as well as analysis of potentially transmissible resistance genes and their vehicles.

Molecular investigation of an outbreak of multidrug-resistant Acinetobacter baumannii, with characterisation of class 1 integrons

We investigated a multidrug-resistant Acinetobacter baumannii outbreak in the Intensive Care Unit (ICU) of a tertiary care hospital in Greece over a 3-month period. Molecular typing of the outbreak isolates from 31 patients revealed that two distinct genotypes were involved. Nine isolates, belonging to both genotypes, were resistant to carbapenems. Samples from the ICU environment and from the hands of personnel were collected to identify possible contamination. Class 1 integrons of 3.1, 2.5 and 2.2 kb were amplified from the clinical and environmental isolates. The 3.1 kb integron carrying five gene cassettes was found for the first time in A. baumannii. The outbreak ceased after implementation of hygienic measures in the ICU, including complete cleaning and disinfection.

Alert surveillance of intensive care unit-acquired Acinetobacter infections in a Sicilian hospital

The epidemiological impact of Acinetobacter baumannii nosocomial infections in a Sicilian intensive care unit (ICU) was investigated to determine the Acinetobacter-specific infection rates, to estimate the preventable proportion of Acinetobacter infections, i.e., those resulting from cross-transmission, and to investigate the molecular epidemiology of antimicrobial resistance in Acinetobacter. The impact of Acinetobacter nosocomial infection in the ICU was determined to be 3.0 new cases per 100 admissions. Site-specific rates confirmed that ICU-acquired pneumonia was the most important infection type. The incidence rate, adjusted by the number of patient-days, was 3.3 infections/1000 patient-days. The estimated preventable proportion of A. baumannii nosocomial infections in the ICU was 66.7%. A class 1 integron, characterised by its gene cassette content, was present in all A. baumannii isolates of four different pulsed-field gel electrophoresis types, and was associated significantly with clones implicated in cross-transmission episodes. Furthermore, the same integron was detected in two genetically distinct isolates responsible for recurrent infection in the same patient, suggesting the occurrence of horizontal gene transfer in vivo. Even in an endemic setting with low infection rates, spread of A. baumannii was caused mainly by infection control shortcomings that require appropriate surveillance and control policies.

Risk-factors for the acquisition of imipenem-resistant Acinetobacter baumannii in Spain: a nationwide study

Potential risk-factors for the acquisition of imipenem-resistant Acinetobacter baumannii were investigated in a cohort study in 25 Spanish hospitals. The clonal relationship among isolates was determined by pulsed-field gel electrophoresis (PFGE). In total, A. baumannii was isolated from 203 patients, with imipenem-resistant (MIC(90) 128 mg/L) isolates being obtained from 88 patients (43%), and imipenem-susceptible isolates from 115 patients (57%). A wide clonal distribution was observed among the imipenem-resistant isolates, but spread of the same clone among centres was not demonstrated. The results indicated that imipenem-resistant A. baumannii is a widely distributed nosocomial pathogen in Spain and reaches an alarming frequency in some centres. Independent risk-factors for the acquisition of imipenem-resistant A. baumannii were a hospital size of >500 beds (multivariate OR, 6.5; 95% CI, 1.8--23), previous antimicrobial treatment (multivariate OR, 4.3; 95% CI, 1.6--11), a urinary catheter (multivariate OR, 2.7; 95% CI, 1.1--6.7) and surgery (multivariate OR, 2; 95% CI, 1.07--3.8).

OXA (beta)-lactamases in Acinetobacter: the story so far

The emergence of carbapenem resistance in Acinetobacter baumannii has become a global concern since these beta-lactams are often the only effective treatment left against many multiresistant strains. A recent development has been the discovery of a novel group of narrow-spectrum OXA beta-lactamases in carbapenem-resistant strains, some of which have acquired the ability to hydrolyse the carbapenems. The first of these was found in a strain isolated in Edinburgh before imipenem was in use in the hospital. Whether these carbapenemases have been acquired or are part of the genetic make-up of this species has yet to be determined. More importantly, however, they represent an important stage in the evolution of antibiotic resistance in Acinetobacter. This paper discusses the emergence of these unusual enzymes over the past decade.

Characterization of a 2.6 kbp variable region within a class 1 integron found in an Acinetobacter baumannii strain isolated from a horse

OBJECTIVES

A complete gene cassette contained in a class 1 integron from a multidrug-resistant (MDR) isolate of Acinetobacter baumannii cultured from a horse was characterized by molecular methods.

METHODS

Template genomic DNA purified from the A. baumannii isolate was investigated by PCR. A gene cassette-associated amplicon was detected and completely characterized.

RESULTS

A 2.6 kbp DNA fragment containing four gene cassettes was amplified from the MDR A. baumannii isolate. Sequence analysis showed it was similar to sequences recently reported in Klebsiella pneumoniae, Serratia marcescens and an Escherichia coli plasmid p1658/97 which conferred aminoglycoside resistance. Aminoglycoside resistance-encoding genes aacC1 and aadA1 were located within the 2.6 kbp amplicon, separated by two open reading frames (ORFs) coding for unknown products. This cassette structure (and some variants) was identified in unrelated Acinetobacter spp. from human sources, based on sequence comparisons of the current databases.

CONCLUSIONS

Identification of a complete class 1 integron in an equine isolate of A. baumannii suggests that the screening of isolates from animals for these elements should be considered, as this information could influence the selection of chemotherapeutic agents.

Antimicrobial resistance of Acinetobacter spp. in Europe

Bacteria of the genus Acinetobacter are ubiquitous in nature. These organisms were invariably susceptible to many antibiotics in the 1970s. Since that time, acinetobacters have emerged as multiresistant opportunistic nosocomial pathogens. The taxonomy of the genus Acinetobacter underwent extensive revision in the mid-1980s, and at least 32 named and unnamed species have now been described. Of these, Acinetobacter baumannii and the closely related unnamed genomic species 3 and 13 sensu Tjernberg and Ursing (13TU) are the most relevant clinically. Multiresistant strains of these species causing bacteraemia, pneumonia, meningitis, urinary tract infections and surgical wound infections have been isolated from hospitalised patients worldwide. This review provides an overview of the antimicrobial susceptibilities of Acinetobacter spp. in Europe, as well as the main mechanisms of antimicrobial resistance, and summarises the remaining treatment options for multiresistant Acinetobacter infections.