Spread of amikacin resistance in Acinetobacter baumannii strains isolated in Spain due to an epidemic strain

Genomic epidemiology of carbapenemase-producing Gram-negative bacteria at the human-animal-environment interface in Djibouti city, Djibouti

The emergence of carbapenem resistance is a major public health threat in sub-Saharan Africa but remains poorly understood, particularly at the human-animal-environment interface. This study provides the first One Health-based study on the epidemiology of Carbapenemase-Producing Gram-Negative Bacteria (CP-GNB) in Djibouti City, Djibouti, East Africa. In total, 800 community urine samples and 500 hospital specimens from humans, 270 livestock fecal samples, 60 fish samples, and 20 water samples were collected and tested for carbapenem resistance. The overall estimated CP-GNB prevalence was 1.9 % (32/1650 samples) and specifically concerned 0.3 % of community urine samples, 2.8 % of clinical specimens, 2.6 % of livestock fecal samples, 11.7 % of fish samples, and 10 % of water samples. The 32 CP-GNB included 19 Escherichia coli, seven Acinetobacter baumannii, five Klebsiella pneumoniae, and one Proteus mirabilis isolate. Short-read (Illumina) and long-read (Nanopore) genome sequencing revealed that carbapenem resistance was mainly associated with chromosomal carriage of blaNDM-1, blaOXA-23, blaOXA-48, blaOXA-66, and blaOXA-69 in A. baumannii, and with plasmid carriage in Enterobacterales (blaNDM-1 and blaOXA-181 in E. coli, blaNDM-1, blaNDM-5 and blaOXA-48 in K. pneumoniae, and blaNDM-1 in P. mirabilis). Moreover, 17/32 CP-GNB isolates belonged to three epidemic clones: (1) A. baumannii sequence type (ST) 1697,2535 that showed a distribution pattern consistent with intra- and inter-hospital dissemination; (2) E. coli ST10 that circulated at the human-animal-environment interface; and (3) K. pneumoniae ST147 that circulated at the human-environment interface. Horizontal exchanges probably contributed to carbapenem resistance dissemination in the city, especially the blaOXA-181-carrying ColKP3-IncX3 hybrid plasmid that was found in E. coli isolates belonging to different STs. Our study highlights that despite a relatively low CP-GNB prevalence in Djibouti City, plasmids harboring carbapenem resistance circulate in humans, animals and environment. Our findings stress the need to implement preventive and control measures for reducing the circulation of this potentially emerging public health threat.

The Role of Uniform Meropenem Usage in Acinetobacter baumannii Clone Replacement

The dominant carbapenem resistant Acinetobacter baumannii harboring bla_OXA-23-like carbapenemase was replaced by bla_OXA-40-like carriers in a Hungarian tertiary-care center with high meropenem but relatively low imipenem use. We hypothesized that alterations in antibiotic consumption may have contributed to this switch. Our workgroup previous study examined the relation between resistance spiral and the antibiotic consumption, and the results suggest that the antibiotic usage provoked the increasing resistance in case of A. baumannii. We aimed at measuring the activity of imipenem and meropenem to compare the selection pressure exerted by the different carbapenems in time-kill assays. Strain replacement was confirmed by whole genome sequencing, core-genome multilocus sequence typing (cgMLST), and resistome analysis. Based on results of the time-kill assays, we found a significant difference between two different sequence-types (STs) in case of meropenem, but not in case of imipenem susceptibility. The newly emerged ST636 and ST492 had increased resistance level against meropenem compared to the previously dominant ST2 and ST49. On the other hand, the imipenem and colistin resistance profiles were similar. These results suggest, that the uniform meropenem usage may have contributed to A. baumannii strain replacement in our setting.

Amikacin resistance due to the aphA6 gene in multi-antibiotic resistant Acinetobacter baumannii isolates belonging to global clone 1 from Iran

Background

TnaphA6-carrying repAci6 plasmids have been detected in Acinetobacter baumannii isolates belonging to global clones, GC1 and GC2, worldwide. Here, we examined whether RepAci6 plasmids family play a role in the dissemination of the aphA6 in GC1 A. baumannii isolates from Iran.

Results

We found that 22 isolates carried the repAci6 gene, suggesting that they contain a RepAci6 plasmid family. Using the primers linking the aphA6 gene to the backbone of repAci6 plasmid, it was revealed that 16 isolates from different hospitals harbored TnaphA6 on a repAci6 plasmid.

Conclusions

This study provides evidence for the dissemination of TnaphA6 on the plasmids encoding RepAci6 in Iranian A. baumannii isolates. Furthermore, it seems that TnaphA6 might be acquired by distinct plasmids separately as it was found to be located on the variants of repAci6 plasmids.

Genetic Mechanisms of Antimicrobial Resistance of Acinetobacter baumannii

OBJECTIVE

To summarize published data identifying known genetic mechanisms of antibiotic resistance in Acinetobacter baumannii and the correlating phenotypic expression of antibiotic resistance.

DATA SOURCES

MEDLINE databases (1966-July 15, 2010) were searched to identify original reports of genetic mechanisms of antibiotic resistance in A. baumannii.

DATA SYNTHESIS

Numerous genetic mechanisms of resistance to multiple classes of antibiotics are known to exist in A. baumannii, a gram-negative bacterium increasingly implicated in nosocomial infections. Mechanisms may be constitutive or acquired via plasmids, integrons, and transposons. Methods of resistance include enzymatic modification of antibiotic molecules, modification of antibiotic target sites, expression of efflux pumps, and downregulation of cell membrane porin channel expression. Resistance to β-lactams appears to be primarily caused by β-lactamase production, including extended spectrum β-lactamases (b/aTEM, blaSHV, b/aTX-M,b/aKPC), metallo-β-lactamases (blaMP, blaVIM, bla, SIM), and most commonly, oxacillinases (blaOXA). Antibiotic target site alterations confer resistance to fluoroquinolones (gyrA, parC) and aminoglycosides (arm, rmt), and to a much lesser extent, β-lactams. Efflux pumps (tet, ade, abe) contribute to resistance against β-lactams, tetracyclines, fluoroquinolones, and aminoglycosides. Finally, porin channel deletion (carO, oprD) appears to contribute to β-lactam resistance and may contribute to rarely seen polymyxin resistance. Of note, efflux pumps and porin deletions as solitary mechanisms may not render clinical resistance to A. baumannii.

CONCLUSIONS

A. baumannii possesses copious genetic resistance mechanisms. Knowledge of local genotypes and expressed phenotypes for A. baumannii may aid clinicians more than phenotypic susceptibilities reported in large epidemiologic studies.

Effect of carbapenem consumption patterns on the molecular epidemiology and carbapenem resistance of Acinetobacter baumannii

This study investigated the molecular epidemiology of Acinetobacter baumannii in the University of Debrecen in relation to antibiotic consumption. Overall and ward-specific antibiotic consumption was measured by the number of defined daily doses (DDD) per 100 bed-days between 2002 and 2012. Consumption was analysed against the number of A. baumannii positive patients per 100 bed-days, number of isolates per positive sample, and proportion of carbapenem resistant A. baumannii, using time-series analysis. Altogether 160 A. baumannii isolates from different wards were collected and analysed. Carbapenemase genes blaOXA-23-like , blaOXA-24-like , blaOXA-48-like , blaOXA-51-like , blaOXA-58-like and integrons were sought by PCR. Relatedness of isolates was assessed by PFGE. Prevalence and carbapenem resistance of A. baumannii were statistically associated with carbapenem consumption. Prevalence data followed carbapenem usage with three quarterly lags (r = 0.51–0.53, P<0.001), and meropenem and ertapenem, but not imipenem usage, affected prevalence. Colistin usage, in turn, lagged behind prevalence with one lag (r = 0.68–0.70, P<0.001). Six clusters were identified; the neurology ward with the lowest carbapenem consumption was associated with the carbapenem-susceptible cluster, as well as with the carbapenem-susceptible isolates in the cluster with variable susceptibility. Wards with high carbapenem usage almost exclusively harboured isolates from carbapenem-resistant clusters. All clusters were dominated by isolates of one or two wards, but most wards were represented in multiple clusters. Increases in prevalence and carbapenem resistance of A. baumannii were associated with usage of meropenem and ertapenem but not of imipenem, which led to the spread of multiple clones in the University.

Origin in Acinetobacter guillouiae and dissemination of the aminoglycoside-modifying enzyme Aph(3')-VI

The amikacin resistance gene aphA6 was first detected in the nosocomial pathogen Acinetobacter baumannii and subsequently in other genera. Analysis of 133 whole-genome sequences covering the taxonomic diversity of Acinetobacter spp. detected aphA6 in the chromosome of 2 isolates of A. guillouiae, which is an environmental species, 1 of 8 A. parvus isolates, and 5 of 34 A. baumannii isolates. The gene was also present in 29 out of 36 A. guillouiae isolates screened by PCR, indicating that it is ancestral to this species. The P_native promoter for aphA6 in A. guillouiae and A. parvus was replaced in A. baumannii by P_aphA6, which was generated by use of the insertion sequence ISAba125, which brought a −35 sequence. Study of promoter strength in Escherichia coli and A. baumannii indicated that P_aphA6 was four times more potent than P_native. There was a good correlation between aminoglycoside MICs and aphA6 transcription in A. guillouiae isolates that remained susceptible to amikacin. The marked topology differences of the phylogenetic trees of aphA6 and of the hosts strongly support its recent direct transfer within Acinetobacter spp. and also to evolutionarily remote bacterial genera. Concomitant expression of aphA6 must have occurred because, contrary to the donors, it can confer resistance to the new hosts. Mobilization and expression of aphA6 via composite transposons and the upstream IS-generating hybrid P_aphA6, followed by conjugation, seems the most plausible mechanism. This is in agreement with the observation that, in the recipients, aphA6 is carried by conjugative plasmids and flanked by IS that are common in Acinetobacter spp. Our data indicate that resistance genes can also be found in susceptible environmental bacteria.

 

We speculated that the aphA6 gene for an enzyme that confers resistance to amikacin, the most active aminoglycoside for the treatment of nosocomial infections due to Acinetobacter spp., originated in this genus before disseminating to phylogenetically distant genera pathogenic for humans. Using a combination of whole-genome sequencing of a collection of Acinetobacter spp. covering the breadth of the known taxonomic diversity of the genus, gene cloning, detailed promoter analysis, study of heterologous gene expression, and comparative analysis of the phylogenetic trees of aphA6 and of the bacterial hosts, we found that aphA6 originated in Acinetobacter guillouiae, an amikacin-susceptible environmental species. The gene conferred, upon mobilization, high-level resistance to the new hosts. This work stresses that nonpathogenic bacteria can act as reservoirs of resistance determinants, and it provides an example of the use of a genomic library to study the origin and dissemination of an antibiotic resistance gene to human pathogens.

Directed evolution of aminoglycoside phosphotransferase (3') type IIIa variants that inactivate amikacin but impose significant fitness costs

The rules that govern adaptive protein evolution remain incompletely understood. Aminoglycoside aminotransferase (3′) type IIIa (hereafter abbreviated APH(3′)-IIIa) is a good model enzyme because it inactivates kanamycin efficiently; it recognizes other aminoglycoside antibiotics, including amikacin, but not nearly as well. Here we direct the evolution of APH(3′)-IIIa variants with increased activity against amikacin. After four rounds of random mutation and selection in Escherichia coli, the minimum inhibitory concentration of amikacin rose from 18 micrograms/mL (wild-type enzyme) to over 1200 micrograms/mL (clone 4.1). The artificially evolved 4.1 APH(3′)-IIIa variant exhibited 19-fold greater catalytic efficiency (k_cat/K_M) than did the wild-type enzyme in reactions with amikacin. E. coli expressing the evolved 4.1 APH(3′)-IIIa also exhibited a four-fold decrease in fitness (as measured by counting colony forming units in liquid cultures with the same optical density) compared with isogenic cells expressing the wild-type protein under non-selective conditions. We speculate that these fitness costs, in combination with the prevalence of other amikacin-modifying enzymes, hinder the evolution of APH(3′)-IIIa in clinical settings.

DNA microarray for genotyping antibiotic resistance determinants in Acinetobacter baumannii clinical isolates

In recent decades, Acinetobacter baumannii has emerged as an organism of great concern due to its ability to accumulate antibiotic resistance. In order to improve the diagnosis of resistance determinants in A. baumannii in terms of lead time and accuracy, we developed a microarray that can be used to detect 91 target sequences associated with antibiotic resistance within 4 h from bacterial culture to result. The array was validated with 60 multidrug-resistant strains of A. baumannii in a blinded, prospective study. The results were compared to phenotype results determined by the automated susceptibility testing system VITEK2. Antibiotics considered were piperacillin-tazobactam, ceftazidime, imipenem, meropenem, trimethoprim-sulfamethoxazole, amikacin, gentamicin, tobramycin, ciprofloxacin, and tigecycline. The average positive predictive value, negative predictive value, sensitivity, and specificity were 98, 98, 99, and 94%, respectively. For carbapenemase genes, the array results were compared to singleplex PCR results provided by the German National Reference Center for Gram-Negative Pathogens, and results were in complete concordance. The presented array is able to detect all relevant resistance determinants of A. baumannii in parallel. The short handling time of 4 h from culture to result helps to provide fast results in order to initiate adequate anti-infective therapy for critically ill patients. Another application would be data acquisition for epidemiologic surveillance.

Diversity of aminoglycoside modifying enzyme genes among multidrug resistant Acinetobacter baumannii genotypes isolated from nosocomial infections in Tehran hospitals and their association with class 1 integrons

The aim of the present study was to investigate, for the first time, the diversity of the genes encoding aminoglycoside-modifying enzymes (AME) and their association with class 1 integrons in Iranian Acinetobacter baumannii strains. A total of 100 multidrug resistant A. baumannii, isolated from eight distinct hospitals in Tehran, were enrolled in this study. Susceptibility of these isolates to antimicrobial agents including gentamicin and amikacin was determined by E-test. Aminoglycoside resistant isolates were then tested by PCR for AME genes, including aphA6, aacC1, aacC2, aacA4, aadB, aadA1, classes 1 integron, 5'-CS-3' and typed by RAPD PCR. The rate of resistance to imipenem, meropenem, gentamicin and amikacin were 39%, 39%, 38% and 32%, respectively. Intermediate resistance phenotype to gentamicin and amikacin was observed in 2% and 5% of all the isolates, respectively. After aph6 with 90% (n = 36/40), aadA1, aacC1 and aadB with 82.5% (n = 33/40), 65% (n = 26/40) and 20% (n = 8/40) were the most prevalent AME genes among aminoglycosides resistant A. baumannii isolates. A combination of two to four different resistance genes was observed in 39 of 40 strains (97.5%), with a total of 7 different combinations. PCR of integrase genes revealed that AME gene was associated with 67% of class 1 integrons. RAPD analysis showed three predominant genotypes A (n = 20), B (n = 10) and 10 unrelated genotypes. The occurrence of identical resistance genes, gene combinations and class 1 integrons associated with these genes in clonally distinct strains indicates that horizontal gene transfer plays a major role in the dissemination of aminoglycoside resistance in A. baumannii.

Genetic basis of resistance to aminoglycosides in Acinetobacter spp. and spread of armA in Acinetobacter baumannii sequence group 1 in Korean hospitals

A total of 75 Acinetobacter isolates resistant to all available aminoglycosides obtained from 2 Korean hospitals were studied for the genetic basis of resistance to aminoglycosides. The MIC(50) and MIC(90) of Acinetobacter baumannii isolates (n = 61) to amikacin, gentamicin, isepamycin spectinomycin, streptomycin, and tobramycin were higher than those of Acinetobacter genomic species 13TU isolates (n = 14). Genes encoding aminoglycoside-modifying enzymes, ant(3")-Ia, aac(6')-Ib, aph(3')-1a, aac(3)-Ia, and aph(3')-VI, and 16S ribosomal RNA (rRNA) methylase armA were detected. ant(3")-Ia and aac(6')-Ib were commonly detected in both Acinetobacter spp., but armA and aph(3")-Ia were only detected in A. baumannii. armA was located on the plasmids. A. baumannii isolates carrying armA were classified into 7 pulsotypes but belonged to sequence group 1. The combination of aminoglycoside-modifying enzymes is responsible for the moderate-level resistance to aminoglycosides in Acinetobacter genomic species 13TU, whereas armA is responsible for the high-level resistance to aminoglycosides in A. baumannii sequence group 1.

Molecular characterization of carbapenem-resistant Acinetobacter species in an Irish university hospital: predominance of Acinetobacter genomic species 3

A 30 month prospective study of Acinetobacter species encountered in the Central Pathology Laboratory of St James's Hospital, Dublin, Ireland, was conducted to investigate the prevalence and molecular epidemiology of carbapenem resistance in such isolates. Acinetobacter genomic species 3 (AG3) was found to be the predominant Acinetobacter species (45/114, 39 %) in our institution. A total of 11 % of all Acinetobacter species (12/114) and 22 % of AG3 isolates (10/45) were carbapenem resistant. Carbapenem resistance was mediated by Ambler class D beta-lactamase OXA-23 in all 12 isolates, with insertion sequence ISAba1 found upstream of bla(OXA-23). ISAba1 was also found upstream of bla(ADC-25), which encodes the enzyme AmpC, in an Acinetobacter baumannii isolate, and upstream of the aminoglycoside-acetyltransferase-encoding gene aacC2 in three AG3 isolates. Inter-species plasmidic transfer was most likely involved in the emergence and spread of bla(OXA-23) among the Acinetobacter isolates within our institution. The emergence of carbapenem resistance was associated not only with prior carbapenem use but also with the use of other antimicrobial agents, most notably beta-lactam/beta-lactamase-inhibitor combinations. The study demonstrated the emerging trend of carbapenem resistance in the wider context of the Acinetobacter genus, and reiterated the paramount importance of the prudent use of antimicrobial agents, stringent infection control measures and resistance surveillance of pathogens.

Epidemiologic characterization of nosocomial Acinetobacter baumannii infections in a Turkish university hospital by pulsed-field gel electrophoresis

BACKGROUND

Although members of the Acinetobacter genus are not commonly part of the human flora, their relatively high prevalence in hospital environment frequently results in colonization of the skin and respiratory tract.

OBJECTIVES

The present investigation was carried out to elucidate epidemiologic characteristics of nosocomial Acinetobacter baumannii infections in a teaching hospital.

METHODS

Epidemiologic, clinical, and demographic features of the 66 patients with A baumannii infection during a 14-month period were recorded. Antibiotic susceptibilities of the isolates were determined by the standardized disk-diffusion method, and the clonal relationship of the isolates was analyzed by pulsed-field gel electrophoresis (PFGE).

RESULTS

The incidence of A baumannii infection was especially high in January, April, May, and June 2006. The isolates were most frequently obtained from blood and tracheal aspirates sent from the intensive care unit and neurosurgery ward. Although the most frequently identified predisposing factors were cerebrovascular disease and surgical operation, the main risk factors identified in these patients were catheterization and mechanical ventilation. Genotype analysis of the 66 A baumannii strains by PFGE revealed the circulation of 36 different PFGE types, of which type A (12) and K (17) accounted for 44% of the isolates. We found high clonal relationship (80.3%) among the typed strains. Thirteen antibiotypes were observed. Most of the isolates were multidrug resistant. Resistance to imipenem, meropenem, gentamicin, amikacin, tobramycin, netilmicin, ampicillin-sulbactam, trimethoprim-sulfamethoxazole, piperacillin-tazobactam, cefoperazone-sulbactam, ciprofloxacin, and levofloxacin were found in 44%, 47%, 47%, 84.8%, 21.2%, 3%, 62.1%, 57.6%, 94%, 62.1%, 95.5%, and 95.5% of the isolates, respectively.

CONCLUSION

The epidemiologic data obtained suggested that the increase in the number of A baumannii infections in our hospital was caused by the interhospital spread of especially 2 epidemic clones. We determined that clonally related strains can survive for a long time in our hospital and cause nosocomial infections in the predisposed patients.

Genetic basis of multidrug resistance in Acinetobacter baumannii clinical isolates at a tertiary medical center in Pennsylvania

A total of 49 unique clinical isolates of multidrug-resistant (MDR) Acinetobacter baumannii identified at a tertiary medical center in Pittsburgh, Pennsylvania, between August 2006 and September 2007 were studied for the genetic basis of their MDR phenotype. Approximately half of all A. baumannii clinical isolates identified during this period qualified as MDR, defined by nonsusceptibility to three or more of the antimicrobials routinely tested in the clinical microbiology laboratory. Among the MDR isolates, 18.4% were resistant to imipenem. The frequencies of resistance to amikacin and ciprofloxacin were high at 36.7% and 95.9%, respectively. None of the isolates was resistant to colistin or tigecycline. The presence of the carbapenemase gene bla(OXA-23) and the 16S rRNA methylase gene armA predicted high-level resistance to imipenem and amikacin, respectively. bla(OXA-23) was preceded by insertion sequence ISAba1, which likely provided a potent promoter activity for the expression of the carbapenemase gene. The structure of the transposon defined by ISAba1 differed from those reported in Europe, suggesting that ISAba1-mediated acquisition of bla(OXA-23) may occur as an independent event. Typical substitutions in the quinolone resistance-determining regions of the gyrA and parC genes were observed in the ciprofloxacin-resistant isolates. Plasmid-mediated quinolone resistance genes, including the qnr genes, were not identified. Fifty-nine percent of the MDR isolates belonged to a single clonal group over the course of the study period, as demonstrated by pulsed-field gel electrophoresis.

Acinetobacter baumannii: emergence of a successful pathogen

Acinetobacter baumannii has emerged as a highly troublesome pathogen for many institutions globally. As a consequence of its immense ability to acquire or upregulate antibiotic drug resistance determinants, it has justifiably been propelled to the forefront of scientific attention. Apart from its predilection for the seriously ill within intensive care units, A. baumannii has more recently caused a range of infectious syndromes in military personnel injured in the Iraq and Afghanistan conflicts. This review details the significant advances that have been made in our understanding of this remarkable organism over the last 10 years, including current taxonomy and species identification, issues with susceptibility testing, mechanisms of antibiotic resistance, global epidemiology, clinical impact of infection, host-pathogen interactions, and infection control and therapeutic considerations.

Molecular epidemiology of clinical Acinetobacter baumannii and Acinetobacter genomic species 13TU isolates using a multilocus sequencing typing scheme

To further expand the limited multilocus sequence typing (MLST) database for Acinetobacter baumannii, 53 clinical isolates from various outbreaks in Europe and the USA, collected between 1991 and 2004, plus the A. baumannii reference strain ATCC 19606(T) and 20 clinical Acinetobacter genomic species 13TU isolates from the same period, were analyzed using a new MLST scheme based on fragments of the gltA, gyrB, gdhB, recA, cpn60, gpi and rpoD genes. Data were compared with typing results generated using pulsed-field gel electrophoresis (PFGE) and randomly amplified polymorphic DNA (RAPD)-PCR. In total, 50 sequence types (STs) were distinguished among the A. baumannii isolates investigated, and the MLST data were in high concordance with the PFGE and RAPD-PCR results. Only five clonal complexes were identified by eBURST analysis, including the 21 STs listed in a previous study, suggesting high diversity among the A. baumannii isolates. With one exception, there was no relatedness among isolates from outbreaks in different countries (Europe) or regions (USA). No intercontinental spread was revealed. Acinetobacter genomic species 13TU isolates could also be analyzed using the A. baumannii MLST scheme (18 different STs) and could be distinguished from A. baumannii isolates according to characteristic sequences. It was concluded that the MLST scheme provides a high level of resolution and is a promising tool for studying the epidemiology of A. baumannii and Acinetobacter genomic species 13TU.

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.

Genotypic diversity of imipenem resistant isolates of Acinetobacter baumannii in Spain

OBJECTIVES

To investigate relevant clinical and microbiological features of Acinetobacter baumannii in Spanish hospitals and to establish the genotypic diversity of imipenem resistant isolates.

MATERIAL AND METHODS

Seven Spanish hospitals collected 354 consecutive isolates that were subjected to antimicrobial susceptibility testing by standard methods. Further genetic analysis was determined by PFGE in a subset of 135 isolates from three hospitals selected because each of them presented high-, medium-, and low imipenem resistance rates.

RESULTS

Most isolates were from males (61.9%), age >65 years (52.3%), admitted to ICU (35.6%), and isolated from the respiratory tract (31.1%). Rates of carbapenem- and sulbactam resistance were 44.9% and 39.9%, respectively. Colistin was active against multiresistant isolates. Rates of imipenem resistance varied according to individual hospital (average: 43.8%; range: 13.5%-85.0%), medical department (more prevalent in ICU), and clinical sample (higher in isolates from the respiratory tract). Of the 135 isolates studied by PFGE (64 of them imipenem-resistant), 115 (85.1%) were distributed among 14 clusters and 20 were unrelated. Of the imipenem-resistant isolates, 45 (70.3%) belonged to six clusters that also had imipenem- susceptible isolates; 14 constituted four exclusive clusters, and five were unrelated.

CONCLUSIONS

Acquisition of imipenem resistance in A. baumannii is likely due to both clonal and non-clonal dissemination; resistance rates strongly vary between different hospitals and even between different hospital departments.

In vitro activities of various antimicrobials alone and in combination with tigecycline against carbapenem-intermediate or -resistant Acinetobacter baumannii

The activities of tigecycline alone and in combination with other antimicrobials are not well defined for carbapenem-intermediate or -resistant Acinetobacter baumannii (CIRA). Pharmacodynamic activity is even less well defined when clinically achievable serum concentrations are considered. Antimicrobial susceptibility testing of clinical CIRA isolates from 2001 to 2005 was performed by broth or agar dilution, as appropriate. Tigecycline concentrations were serially increased in time-kill studies with a representative of the most prevalent carbapenem-resistant clone (strain AA557; imipenem MIC, 64 mg/liter). The in vitro susceptibility of the strain was tested by time-kill studies in duplicate against the average free serum steady-state concentrations of tigecycline alone and in combination with various antimicrobials. Ninety-three CIRA isolates were tested and were found to have the following antimicrobial susceptibility profiles: tigecycline, MIC(50) of 1 mg/liter and MIC(90) of 2 mg/liter; minocycline, MIC(50) of 0.5 mg/liter and MIC(90) of 8 mg/liter; doxycycline, MIC(50) of 2 mg/liter and MIC(90) of > or =32 mg/liter; ampicillin-sulbactam, MIC(50) of 48 mg/liter and MIC(90) of 96 mg/liter; ciprofloxacin, MIC(50) of > or =16 mg/liter and MIC(90) of > or =16 mg/liter; rifampin, MIC(50) of 4 mg/liter and MIC(90) of 8 mg/liter; polymyxin B, MIC(50) of 1 mg/liter and MIC(90) of 1 mg/liter; amikacin, MIC(50) of 32 mg/liter and MIC(90) of > or =32 mg/liter; meropenem, MIC(50) of 16 mg/liter and MIC(90) of > or =128 mg/liter; and imipenem, MIC(50) of 4 mg/liter and MIC(90) of 64 mg/liter. Among the tetracyclines, the isolates were more susceptible to tigecycline than minocycline and doxycycline, according to FDA breakpoints (95%, 88%, and 71% of the isolates were susceptible to tigecycline, minocycline, and doxycycline, respectively). Concentration escalation studies with tigecycline revealed a maximal killing effect near the MIC, with no additional extent or rate of killing at concentrations 2x to 4x the MIC for tigecycline. Time-kill studies demonstrated indifference for tigecycline in combination with the antimicrobials tested. Polymyxin B, minocycline, and tigecycline are the most active antimicrobials in vitro against CIRA. Concentration escalation studies demonstrate that tigecycline may need to approach concentrations higher than those currently achieved in the bloodstream to adequately treat CIRA bloodstream infections. Future studies should evaluate these findings in vivo.

Antibacterial evaluation of a collection of norfloxacin and ciprofloxacin derivatives against multiresistant bacteria

The objective of this study was to analyse an array of ciprofloxacin and norfloxacin derivatives in order to determine those with good activity against bacteria that already present fluoroquinolone resistance associated with mutations in the gyrA and/or parC genes. Four norfloxacin and 20 ciprofloxacin derivatives were synthesised and tested against quinolone-susceptible and -resistant Escherichia coli, Acinetobacter baumannii, Stenotrophomonas maltophilia and Staphylococcus aureus strains using a microdilution test. Among the derivatives, the 4-methyl-7-piperazine ciprofloxacin derivative showed a minimum inhibitory concentration for 50% of the organisms that was 16- and 8-fold lower than ciprofloxacin for A. baumannii and S. maltophilia, respectively. When the methyl group at position 4 in the piperazine ring was substituted by ethyl, butyl or heptyl groups, activity against A. baumannii steadily decreased. The 7-(4-methyl)-piperazine ciprofloxacin derivative (UB-8902) showed very good activity against these multiresistant microorganisms including A. baumannii and S. maltophilia.

Distribution of tetracycline resistance genes in genotypically related and unrelated multiresistant Acinetobacter baumannii strains from different European hospitals

The presence of tetracycline (TET) resistance genes was investigated in 49 genotypically related and unrelated multidrug-resistant Acinetobacter baumannii (MDRAB) strains from European hospitals including representatives of pan-European clones I and II. Except for one strain, all MDRAB strains displayed resistance to tetracycline (MIC range of 16 to > 512 microg/ml) but were susceptible (MIC < 4 microg/ml) or exhibited intermediate resistance (MIC of 4-8 microg/ml) to minocycline (MIN). In 37 strains, either tet(A) or tet(B) was detected and one of these strains possessed both tet(A) and tet(M). In addition, all MDRAB strains contained the aspecific efflux gene adeB irrespectively of whether they harbored tet genes or not. Repetitive DNA element (rep)-PCR fingerprinting using the (GTG)5 primer [(GTG)5-PCR] revealed that strains previously assigned to pan-European clones I and II were grouped into two separate clusters. In addition, these clusters also contained strains that had not been typed previously, indicating that (GTG)5-PCR is a valuable method for recognizing putative new members of MDRAB clones. Most, but not all, members of clones I and II were linked to the presence of either tet(A) or tet(B) and displayed different levels of TET resistance with MIC values of 32 to > 512 microg/ml and > 512 microg/ml, respectively. Of these two genes only tet(B) encodes an efflux of both TET and MIN, which was reflected by the relatively high MIC values for MIN (4 microg/ml) shown by the majority of the tet(B)-carrying clone II strains as opposed to the low MIC values for MIN (< 1 microg/ml) displayed by most tet(A)-containing clone I strains. Collectively, our phenotypic and genotypic resistance data support the therapeutic evaluation of second-generation tetracyclines like MIN as promising agents for treating MDRAB infections.

Prevalence of Acinetobacter baumannii and other Acinetobacter spp. in faecal samples from non-hospitalised individuals

In total, 226 individuals from the community were investigated for faecal carriage of Acinetobacter spp. by broth enrichment culture, followed by growth on blood agar and/or Leeds Acinetobacter Medium (LAM). Acinetobacter baumannii was isolated on both LAM and blood agar from one of 100 specimens in the UK and one of 126 specimens in The Netherlands. The predominant species were Acinetobactor johnsonii and genomic sp. 11, which were cultured from 22 and five specimens, respectively. A. baumannii did not seem to be widespread in the faecal flora of individuals in the community.

Antimicrobial susceptibility testing of Acinetobacter spp. by NCCLS broth microdilution and disk diffusion methods

Although both broth microdilution (BMD) and disk diffusion (DD) are listed by NCCLS as acceptable methods for testing Acinetobacter spp. for antimicrobial susceptibility, few studies have compared the results generated by the two methods. We tested 196 isolates of Acinetobacter spp. from nine U.S. hospitals and from the Centers for Disease Control culture collection by using BMD and DD and clinically appropriate antimicrobial agents. Categorical results for amikacin, ciprofloxacin, gatifloxacin, gentamicin, imipenem, levofloxacin, meropenem, tobramycin, and trimethoprim-sulfamethoxazole were comparable for the two methods: there was only one very major (VM) error, with tobramycin, and only one major (M) error, with meropenem, when DD results were compared with BMD results. However, VM errors were frequent with the beta-lactams and beta-lactam-beta-lactam inhibitor combinations, while M errors were often observed with tetracyclines. For BMD, tests frequently exhibited subtle growth patterns that were difficult to interpret, especially for beta-lactams. If subtle growth (i.e., granular, small button, or "starry" growth) was considered positive, error rates between BMD and DD were unacceptably high for ampicillin-sulbactam (VM error, 9.8%; minor [m] error, 16.1%), piperacillin (VM error, 5.7%; m error, 13.5%), piperacillin-tazobactam (VM error, 9.3%; m error, 12.9%), ceftazidime (VM error, 6.2%; m error, 11.4%), cefepime (VM error, 6.2%; m error, 13.0%), cefotaxime (m error, 21.2%), ceftriaxone (m error, 23.3%), tetracycline (M error, 11.4%; m error, 32.1%), and doxycycline (M error, 2.6%). When subtle growth patterns were ignored, the agreement still did not achieve acceptable levels. To determine if the problems with BMD testing occurred in other laboratories, we sent frozen BMD panels containing beta-lactam drugs and nine isolates to six labs with experience in performing BMD and DD. Among these laboratories, cefepime MICs ranged from < or =8 to > or =32 microg/ml for four of the nine strains, confirming the problem in interpreting BMD results. Discrepancies between the categorical interpretations of BMD and DD tests were noted primarily with cefepime and piperacillin, for which the BMD results were typically more resistant. Clinical laboratories should be aware of these discrepancies. At present, there are no data to indicate which method provides more clinically relevant information.

Genotypic Characterization of Carbapenem-NonsusceptibleAcinetobacterspp. Isolated in Latin America

The principal aim of this study was to evaluate the genomic diversity among the imipenem-nonsusceptible Acinetobacter spp. (INSA) collected from the Latin American medical centers within the SENTRY Antimicrobial Surveillance Program. The INSA isolates were collected from patients with bloodstream infections, who were hospitalized in seven Latin American countries between 1997 and 1999. For epidemiologic comparison, 20 carbapenem-susceptible Acinetobacter spp. (CSA) isolates were collected in the same period of time from the respective medical centers. A total of 23 Acinetobacter spp. isolates exhibiting imipenem MIC values of >/=8 microg/ml were typed by ribotyping, an automated molecular method. The isolates showing an identical ribogroup were also typed by pulsed-field gel electrophoresis (PFGE). The antimicrobial susceptibility to various antimicrobial agents was evaluated using a reference broth microdilution technique. Among the INSA isolates, 13 distinct ribogroups were observed, whereas 16 ribogroups were detected among the CSA. Nearly 57% of the INSA belonged to only four ribogroups. Identical ribogroups and PFGE patterns were observed among INSA and CSA isolates collected from medical centers located in different countries (Brazil and Argentina). Our results showed: (1) a higher genomic variability among the CSA; (2) presence of epidemic clones among INSA isolates encountered in Latin American medical centers; and (3) spread of INSA and CSA epidemic clones between Latin American countries.

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.

Molecular epidemiology of sequential outbreaks of Acinetobacter baumannii in an intensive care unit shows the emergence of carbapenem resistance

The molecular epidemiology of multidrug-resistant Acinetobacter baumannii was investigated in the medical-surgical intensive care unit (ICU) of a university hospital in Italy during two window periods in which two sequential A. baumannii epidemics occurred. Genotype analysis by pulsed-field gel electrophoresis (PFGE) of A. baumannii isolates from 131 patients identified nine distinct PFGE patterns. Of these, PFGE clones B and I predominated and occurred sequentially during the two epidemics. A. baumannii epidemic clones showed a multidrug-resistant antibiotype, being clone B resistant to all antimicrobials tested except the carbapenems and clone I resistant to all antimicrobials except ampicillin-sulbactam and gentamicin. Type 1 integrons of 2.5 and 2.2 kb were amplified from the chromosomal DNA of epidemic PFGE clones B and I, respectively, but not from the chromosomal DNA of the nonepidemic clones. Nucleotide analysis of clone B integron identified four gene cassettes: aacC1, which confers resistance to gentamicin; two open reading frames (ORFs) coding for unknown products; and aadA1a, which confers resistance to spectinomycin and streptomycin. The integron of clone I contained three gene cassettes: aacA4, which confers resistance to amikacin, netilmicin, and tobramycin; an unknown ORF; and bla(OXA-20), which codes for a class D beta-lactamase that confers resistance to amoxicillin, ticarcillin, oxacillin, and cloxacillin. Also, the bla(IMP) allele was amplified from chromosomal DNA of A. baumannii strains of PFGE type I. Class 1 integrons carrying antimicrobial resistance genes and bla(IMP) allele in A. baumannii epidemic strains correlated with the high use rates of broad-spectrum cephalosporins, carbapenems, and aminoglycosides in the ICU during the study period.

Identification of a new geographically widespread multiresistant Acinetobacter baumannii clone from European hospitals

The aim of the study was to investigate the genetic diversity of Acinetobacter baumannii clinical strains that had previously been allocated to three major groups based on automated ribotyping. Forty-seven isolates from European hospitals and one isolate from a South African hospital, geographically representative of the three ribogroups (ribogroups 1, 2 and 3 with 10, 23 and 15 isolates, respectively), were analysed using the highly discriminatory fingerprinting methods AFLP and pulsed-field gel electrophoresis (PFGE). Based on AFLP data, the isolates clustered into three main groups, each corresponding to one ribogroup. Inclusion of reference strains of the previously described clones I and II, responsible for outbreaks in northwestern European hospitals, showed that ribogroups 1 and 2 correspond to clones I and II, respectively, whereas ribogroup 3 apparently represents a new clone. This clone III was found in France, The Netherlands, Italy and Spain. Clones I and II were not limited to northwestern European countries, as they were also recovered from Spain, South Africa, Poland and Italy (clone I) and from Spain, Portugal, South Africa, France, Greece and Turkey (clone II). Combined AFLP and PFGE data showed intraclonal diversity and led to the distinction of 23 different genotypes. Three genotypes, two of them belonging to clone II and one to clone III, were found in different hospitals and may correspond to subsets of isolates with a more recent clonal relationship, which emphasizes the epidemic potential of these organisms.

Diversidad clonal y sensibilidad a los antimicrobianos de Acinetobacter baumannii aislados en hospitales españoles. Estudio multicéntrico nacional: proyecto GEIH-Ab 2000

INTRODUCTION

A nationwide multicenter study was performed in Spain to evaluate the clonal diversity and antimicrobial susceptibility of Acinetobacter baumannii clinical isolates.

METHODS

A total of 221 consecutive A. baumannii isolates recovered from clinical samples from 25 Spanish hospitals during November 2000 were studied. Isolate identification was performed by phenotyping methods and by amplified rDNA restriction analysis. Clonal relationships among A. baumannii isolates were determined by pulsed field gel electrophoresis. MICs of amikacin (AK), ampicillin (AP), cephalothin (CF), cefoxitin (FX), ceftazidime (CZ), ciprofloxacin (CP), cotrimoxazole (T/S), doxycycline (DX), gemifloxacin (GX), gentamicin (GN), imipenem (IP), meropenem (MP), minocycline (MI), piperacillin (PP), polymyxin B (PB), rifampicin (RI), tetracycline (TT), sulbactam (SB) and tobramycin (TO) were determined by microdilution (NCCLS guidelines).

RESULTS

Seventy-nine A. baumannii clones were differentiated. MIC50/MIC90 (mg/L) values for the 221 A. baumannii isolates were PP: > 512/> 512; AP, CF, FX: > 256/> 256; TT, GN: > 128/> 128; CZ: 128/> 256; CP: > 64/> 64; FP: 64/256; AK: 32/256; DX: 32/64; GX: > 16/> 16; TO: 16/128; SB, T/S: 16/64; MP: 8/> 128; IP: 4/128; RF: 4/8; MI: 2/16 and PB: 1/2. Percentages of susceptible isolates were PB: 100%; MI: 65.8%; IP: 52.5%, RF: 49.3%; SB: 46.7%; MP: 43.1%; AK: 34.7%; DX: 32.0%; TO: 21.3% and CZ, FP, GN, T/S, TT, GX, CP, AP, PP, CF and FX: < 20%.

CONCLUSIONS

A. baumannii isolates show high clonal variability in Spain. The most active antimicrobial agents against this organism were polymyxin B, minocycline, rifampicin, imipenem, sulbactam, meropenem, amikacin and doxycycline.

Multiresistant Acinetobacter baumannii isolates in intensive care units in Greece

One hundred and twenty-one clinical isolates of Acinetobacter baumannii recovered from the intensive care units (ICUs) of nine tertiary-care hospitals in Athens, Greece were studied in order to determine whether the increasing appearance of resistant acinetobacters is due to the spread of epidemic strains. The majority of the isolates exhibited resistance to ampicillin-sulbactam, and the most common antibiotic resistance profiles comprised resistance to nine and eight of the 11 potentially active antibiotics tested, respectively. Pulsed-field gel electrophoresis showed that 68% of the isolates, recovered from all ICUs, belonged to two clonal groups, indicating inter-hospital dissemination of multiresistant A. baumannii in our region.

Epidemiology of rifampin ADP-ribosyltransferase (arr-2) and metallo-beta-lactamase (blaIMP-4) gene cassettes in class 1 integrons in Acinetobacter strains isolated from blood cultures in 1997 to 2000

We characterized two new gene cassettes in an Acinetobacter isolate: one harbored the metallo-beta-lactamase (IMP-4) gene bla(IMP-4), the other harbored the rifampin ADP-ribosyltransferase (ARR-2) gene arr-2, and both arrayed with the aminoglycoside acetyltransferase [AAC(6')-Ib(7)] gene cassette aacA4 in two separate class 1 integrons. The epidemiology of these gene cassettes in isolates from blood cultures obtained from 1997 to 2000 was studied. Isolates bearing either the bla(IMP-4) or the arr-2 gene cassette or both represented 17.5% (10 of 57) of isolates in 1997, 16.1% (10 of 62) in 1998, 2.5% (1 of 40) in 1999, and 0% (0 of 58) in 2000. These two gene cassettes, probably borne on two separate integrons, were found in at least three genomic DNA groups, with evidence of clonal dissemination in the intensive care unit during 1997 to 1998. Seventeen of the 52 Acinetobacter baumannii (genomic DNA group 2) isolates from 1997 to 2000 harbored intI1, but only one was positive for these gene cassettes, whereas 20 of the 21 intI1-positive isolates of all other genomic DNA groups were positive for either or both of them. Reduced susceptibility to imipenem and rifampin was seen only in isolates harboring the bla(IMP-4) and arr-2 cassettes, respectively. The aminoglycoside phosphotransferase [APH(3')-VIa] gene aph(3')-VIa was detected in all 21 isolates for which the MIC of amikacin was >/=8 micro g/ml, with or without aacA4, whereas aacA4 alone was found in isolates for which the MIC of amikacin was 0.5 to 2 micro g/ml. Significant differences between the 17 intI1-positive and 47 intI1-negative isolates belonging to genomic DNA group 3 from 1997 to 1998 in the MICs of amikacin, gentamicin, imipenem, sulfamethoxazole, and ceftazidime were observed (Mann-Whitney test, P < 0.001 to 0.01).

Endemic carbapenem resistance associated with OXA-40 carbapenemase among Acinetobacter baumannii isolates from a hospital in northern Spain

Eighty-two carbapenem-resistant isolates of Acinetobacter baumannii from a single hospital in Bilbao were typed into two major clusters and several subclusters. Disk synergy tests and PCR indicated the production of a zinc-independent OXA-class carbapenemase. Sequencing identified this enzyme, OXA-40, as a variant of the OXA-24-OXA-25-OXA-26 cluster.

[Interpretative reading of the non-fermenting gram-negative bacilli antibiogram]

Among non-fermenting Gram-negative rods, the most clinically important species are Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia, which are frequently multiresistant. P. aeruginosa resistance to beta-lactams depends on the production of chromosomal and plasmid-mediated beta-lactamases, altered permeability (loss of OprD porin is related to carbapenem-resistance) and active efflux pumps, particularly MexAB-OprM. In aminoglycoside-resistant strains the main mechanism of resistance is the production of inactivating enzymes; the efflux pump MexXY-OprM is also involved. Quinolone-resistance in P. aeruginosa is related to changes in topoisomerases, altered permeability and efflux pumps. The mechanisms of resistance of A. baumannii have not been well characterized, which makes interpretative reading of the antibiogram in this organism difficult. Resistance to beta-lactams is associated with the production of beta-lactamases and altered penicillin-binding proteins. Resistance to aminoglycosides has been related to modifying enzymes and resistance to quinolones to altered targets. S. maltophilia is resistant to carbapenems and other beta-lactams because of the production of two beta-lactamases (L-1 and L-2). Aminoglycoside-modifying enzymes have also been described in this species. In contrast to what is observed in other organisms, S. maltophilia resistance to quinolones has been mainly related to active efflux, rather than to target alterations.

Molecular epidemiology of nosocomial infection associated with multi-resistant Acinetobacter baumannii by infrequent-restriction-site PCR

Acinetobacter baumannii was considered endemic in a university-affiliated tertiary hospital. A significant increase was noted in the proportion of nosocomial infections associated with this micro-organism from 1996 to 1999, although no apparent clusters could be found. Between July 1998 and February 2000, 58 nosocomial isolates of A. baumannii were collected and characterized by antibiotyping and a genotyping method, infrequent-restriction-site PCR (IRS-PCR). High resistance to the 14 antimicrobial agents examined was observed among the isolates. Of the 13 antibiograms detected, eight were multi-resistant to gentamicin and almost all of the traditional and extended-spectrum beta-lactams. These multi-resistant strains consisted of 41 isolates (71%), distributed amongst different wards and intensive care units (ICUs). By IRS-PCR, 23 types were obtained, with one major type found among 28 (48%) isolates. All of these 28 isolates were collected from surgical ICUs. It appears that a single strain of multi-resistant A. baumannii was responsible for the prevalence of nosocomial infection amongst surgical patients, clearly differentiating this outbreak from the previous endemic situation. An efficient molecular typing method played a vital role in making this discrimination.

Identification of Acinetobacter isolates from species belonging to the Acinetobacter calcoaceticus-Acinetobacter baumannii complex with monoclonal antibodies specific for O Antigens of their lipopolysaccharides

The unambiguous identification of Acinetobacter strains, particularly those belonging to the Acinetobacter calcoaceticus-Acinetobacter baumannii complex, is often hindered by their close geno- and phenotypic relationships. In this study, monoclonal antibodies (MAbs) against the O antigens of the lipopolysaccharides from strains belonging to the A. calcoaceticus-A. baumannii complex were generated after the immunization of mice with heat-killed bacteria and shown by enzyme immunoassays and Western blotting to be specific for their homologous antigens. Since the A. calcoaceticus-A. baumannii complex comprises the most clinically relevant species, the MAbs were subsequently tested in dot and Western blots with proteinase K-treated lysates from a large collection of Acinetobacter isolates (n = 631) to determine whether the antibodies could be used for the reliable identification of strains from this complex. Reactivity was observed with 273 of the 504 isolates (54%) from the A. calcoaceticus-A. baumannii complex which were included in this study. Isolates which reacted positively did so with only one antibody; no reactivity was observed with isolates not belonging to the A. calcoaceticus-A. baumannii complex (n = 127). To identify additional putative O serotypes, isolates from the A. calcoaceticus-A. baumannii complex which showed no MAb reactivity were subjected to a method that enables the detection of lipid A moieties in lipopolysaccharides with a specific MAb on Western blots following acidic treatment of the membrane. By this method, additional serotypes were indeed identified, thus indicating which strains to select for future immunizations. This study contributes to the completion of a serotype-based identification scheme for Acinetobacter species, in particular, those which are presently of the most clinical importance.

Characteristics of clinical Acinetobacter spp. strains

Resistance to 13 antimicrobial agents, resistance to the bactericidal activity of human serum, hydrophobic properties, lipolytic activity and production of histamine were determined in a total of 50 clinical Acinetobacter spp. strains (A. baumannii, A. lwoffii, A. calcoaceticus, A. haemolyticus). None of the tested isolates showed resistance to meropenem and none of A. lwoffii, A. calcoaceticus and A. haemolyticus strains were resistant to amikacin. Forty-six strains (92%) manifested resistance to ampicillin, 90% to cefuroxime, 68% to ciprofloxacin, 58% to piperacillin, gentamicin and cotrimaxazole, 50% to cefotaxime, 44% to amikacin, 42% to ceftazidime, 38% to piperacillin/tazobactam, 24% to netilmicin and 16% to ampicillin/sulbactam. In particular, A. baumannii and A. calcoaceticus strains showed considerable antibiotic resistance. Thirty-one isolates (62%) showed serum resistance; intermediate sensitivity was found in 19 isolates (38%). The majority of the strains (72%) demonstrated a strongly hydrophobic character; 16% of isolates exhibited moderate hydrophobic properties. All strains showed lipolytic activity; production of histamine was detected in 14 of 43 strains examined.

Emergence and rapid spread of carbapenem resistance during a large and sustained hospital outbreak of multiresistant Acinetobacter baumannii

Beginning in 1992, a sustained outbreak of multiresistant Acinetobacter baumannii infections was noted in our 1,000-bed hospital in Barcelona, Spain, resulting in considerable overuse of imipenem, to which the organisms were uniformly susceptible. In January 1997, carbapenem-resistant (CR) A. baumannii strains emerged and rapidly disseminated in the intensive care units (ICUs), prompting us to conduct a prospective investigation. It was an 18-month longitudinal intervention study aimed at the identification of the clinical and microbiological epidemiology of the outbreak and its response to a multicomponent infection control strategy. From January 1997 to June 1998, clinical samples from 153 (8%) of 1,836 consecutive ICU patients were found to contain CR A. baumannii. Isolates were verified to be A. baumannii by restriction analysis of the 16S-23S ribosomal genes and the intergenic spacer region. Molecular typing by repetitive extragenic palindromic sequence-based PCR and pulsed-field gel electrophoresis showed that the emergence of carbapenem resistance was not by the selection of resistant mutants but was by the introduction of two new epidemic clones that were different from those responsible for the endemic. Multivariate regression analysis selected those patients with previous carriage of CR A. baumannii (relative risk [RR], 35.3; 95% confidence interval [CI], 7.2 to 173.1), those patients who had previously received therapy with carbapenems (RR, 4.6; 95% CI, 1.3 to 15.6), or those who were admitted into a ward with a high density of patients infected with CR A. baumannii (RR, 1.7; 95% CI, 1.2 to 2.5) to be at a significantly greater risk for the development of clinical colonization or infection with CR A. baumannii strains. In accordance, a combined infection control strategy was designed and implemented, including the sequential closure of all ICUs for decontamination, strict compliance with cross-transmission prevention protocols, and a program that restricted the use of carbapenem. Subsequently, a sharp reduction in the incidence rates of infection or colonization with A. baumannii, whether resistant or susceptible to carbapenems, was shown, although an alarming dominance of the carbapenem-resistant clones was shown at the end of the study.

Molecular surveillance of European quinolone-resistant clinical isolates of Pseudomonas aeruginosa and Acinetobacter spp. using automated ribotyping

Nosocomial isolates of Pseudomonas aeruginosa and Acinetobacter spp. exhibit high rates of resistance to antibiotics and are often multidrug resistant. In a previous study (D. Milatovic, A. Fluit, S. Brisse, J. Verhoef, and F. J. Schmitz, Antimicrob. Agents Chemother. 44:1102-1107, 2000), isolates of these species that were resistant to sitafloxacin, a new advanced-generation fluoroquinolone with a high potency and a broad spectrum of antimicrobial activity, were found in high proportion in 23 European hospitals. Here, we investigate the clonal diversity of the 155 P. aeruginosa and 145 Acinetobacter spp. sitafloxacin-resistant isolates from that study by automated ribotyping. Numerous ribogroups (sets of isolates with indistinguishable ribotypes) were found among isolates of P. aeruginosa (n = 34) and Acinetobacter spp. (n = 16), but the majority of the isolates belonged to a limited number of major ribogroups. Sitafloxacin-resistant isolates (MICs > 2 mg/liter, used as a provisional breakpoint) showed increased concomitant resistance to piperacillin, piperacillin-tazobactam, ceftriaxone, ceftazidime, amikacin, gentamicin, and imipenem. The major ribogroups were repeatedly found in isolates from several European hospitals; these isolates showed higher levels of resistance to gentamicin and imipenem, and some of them appeared to correspond to previously described multidrug-resistant international clones of P. aeruginosa (serotype O:12) and Acinetobacter baumannii (clones I and II). Automated ribotyping, when used in combination with more discriminatory typing methods, may be a convenient library typing system for monitoring future epidemiological dynamics of geographically widespread multidrug-resistant bacterial clones.

Nosocomial bloodstream infections caused by Acinetobacter species in United States hospitals: clinical features, molecular epidemiology, and antimicrobial susceptibility

We examined the clinical and epidemiological features of nosocomial bloodstream infections (BSIs) caused by Acinetobacter species and observed from 1 March 1995 through 28 February 1998 at 49 United States hospitals (SCOPE National Surveillance Program). Acinetobacter species were found in 24 hospitals (49%) and accounted for 1.5% of all nosocomial BSIs reported. One hundred twenty-nine isolates were identified either as A. baumannii (n=111) or other Acinetobacter species (n=18). Patients with A. baumannii BSI, compared with patients with nosocomial BSI caused by other gram-negative pathogens, were more frequently observed in the intensive care unit (69% vs. 47%, respectively; P<.001; odds ratio [OR] 2.4; 95% confidence interval [CI] 1.6-3.7) and were more frequently receiving mechanical ventilation (58% vs. 30%, respectively; P<.001; OR 3.2; 95% CI 2.1-4.8). Crude mortality in patients with A. baumannii BSI was 32%. Molecular relatedness of strains was studied by use of polymerase chain reaction-based fingerprinting. Clonal spread of a single strain occurred in 5 hospitals. Interhospital spread of epidemic A. baumannii strains was not observed. The most active antimicrobial agents against A. baumannii (90% minimum inhibitory concentration values) were imipenem (1 mg/L; 100% of isolates susceptible), amikacin (8 mg/L; 96%), tobramycin (4 mg/L; 92%), and doxycycline (4 mg/L; 91%). Thirty percent of isolates were resistant to > or =4 classes of antimicrobials and were considered to be multidrug resistant.

Geography is destiny: global nosocomial infection control

The global nature of the emergence and spread of multiresistant bacteria has resulted in a slow response from governmental bodies, but surveillance networks are being set up and there is evidence, cited in this review, of an element of cooperation among professional bodies. Most developed and many developing countries have recognized the need for nosocomial infection control.

Comparative activities of ciprofloxacin, clinafloxacin, gatifloxacin, gemifloxacin, levofloxacin, moxifloxacin, and trovafloxacin against epidemiologically defined Acinetobacter baumannii strains

In vitro activities of seven fluoroquinolones against 140 clinical Acinetobacter baumannii isolates representing 138 different strain types were determined. The rank order of activity was clinafloxacin > gatifloxacin > levofloxacin > trovafloxacin > gemifloxacin = moxifloxacin > ciprofloxacin. The 31 outbreak-related A. baumannii strains were significantly more resistant than were 109 sporadic strains.

Detection of carbapenemase-producing Acinetobacter baumannii in a hospital

Acinetobacter baumannii strains resistant to both imipenem (IPM) and ceftazidime (CAZ) were isolated from 1994 through 1996 at Gunma University Hospital. Nine isolates from different inpatients were examined for carbapenem-hydrolyzing activity and for the carbapemase gene bla(IMP) by the PCR method. All nine isolates were carbapenemase-producing strains that hydrolyzed IPM and that harbored bla(IMP). The bla(IMP) gene was transmissible by conjugation to an IPM-susceptible recipient strain of A. baumannii and conferred resistance to IPM, CAZ, cefotaxime (CTX), ampicillin (AMP), and piperacillin (PIP). Either intermediate or high-level resistance to amikacin (AMK) was transferred from two and five strains, respectively, concomitantly with bla(IMP), and gentamicin (GEN) resistance was also transferred in one instance of high-level AMK resistance. Comparative examination of clinical isolates for resistance patterns to nine drugs, IPM, CAZ, CTX, aztreonam, AMP, PIP, AMK, GEN, and norfloxacin, in addition to pulsed-field gel electrophoresis patterns with NotI-digested genomic DNA, confirmed nosocomial transmission of infections involving carbapenemase-producing A. baumannii strains.