Acinetobacterin Denmark: II. Molecular studies of theAcinetobacter calcoaceticus-Acinetobacter baumanniicomplex

Impaired host response and the presence of Acinetobacter baumannii in the serum microbiome of type-II diabetic patients

Type II diabetes (T2D) affects over 10% of the US population and is a growing disease worldwide that manifests with numerous comorbidities and defects in inflammation. This dysbiotic host response allows for infection of the host by numerous microorganisms. In the course of T2D disease, individuals can develop chronic infections including foot ulcers and periodontitis, which lead to further complications and opportunistic infections in multiple body sites. In this study, we investigated the serum of healthy subjects and patients with T2D with (T2DP) or without periodontitis for both microbiome signatures in addition to cytokine profiles. Surprisingly, we detected the presence of Acinetobacter baumanii in the serum of 23% individuals with T2D/T2DP tested. In T2DP, IL-1β, TNF-α, MCP-1, IL-6, IL-8, and IFN-γ were significantly elevated in ABC-positive subjects. As an emerging pathogen, A. baumanii infection represents a risk for impaired inflammation and the development of comorbidities in subjects with T2D.

Chromosome Architecture and Gene Content of the Emergent Pathogen Acinetobacter haemolyticus

Acinetobacter haemolyticus is a Gammaproteobacterium that has been involved in serious diseases frequently linked to the nosocomial environment. Most of the strains causing such infections are sensitive to a wide variety of antibiotics, but recent reports indicate that this pathogen is acquiring very efficiently carbapenem-resistance determinants like the blaNDM-1 gene, all over the world. With this work we contribute with a collection set of 31 newly sequenced nosocomial A. haemolyticus isolates. Genome analysis of these sequences and others collected from RefSeq indicates that their chromosomes are organized in 12 syntenic blocks that contain most of the core genome genes. These blocks are separated by hypervariable regions that are rich in unique gene families, but also have signals of horizontal gene transfer. Genes involved in virulence or encoding different secretion systems are located inside syntenic regions and have recombination signals. The relative order of the synthetic blocks along the A. haemolyticus chromosome can change, indicating that they have been subject to several kinds of inversions. Genomes of this microorganism show large differences in gene content even if they are in the same clade. Here we also show that A. haemolyticus has an open pan-genome.

Antibiotic Resistance Profiles, Molecular Mechanisms and Innovative Treatment Strategies of Acinetobacter baumannii

Antibiotic resistance is one of the biggest challenges for the clinical sector and industry, environment and societal development. One of the most important pathogens responsible for severe nosocomial infections is Acinetobacter baumannii, a Gram-negative bacterium from the Moraxellaceae family, due to its various resistance mechanisms, such as the β-lactamases production, efflux pumps, decreased membrane permeability and altered target site of the antibiotic. The enormous adaptive capacity of A. baumannii and the acquisition and transfer of antibiotic resistance determinants contribute to the ineffectiveness of most current therapeutic strategies, including last-line or combined antibiotic therapy. In this review, we will present an update of the antibiotic resistance profiles and underlying mechanisms in A. baumannii and the current progress in developing innovative strategies for combating multidrug-resistant A. baumannii (MDRAB) infections.

Dynamics of a Sporadic Nosocomial Acinetobacter calcoaceticus - Acinetobacter baumannii Complex Population

Our objective was to improve current knowledge of sporadic (Spo) nosocomial Acinetobactercalcoaceticus-Acinetobacter baumannii (Acb) complex populations, and thus better understand the epidemiology of Spo and endemoepidemic (EE) strains. Between 1999 and 2010, 133 isolates of Spo Acb complex were obtained from a single hospital. Species were identified by gyrB-PCR, and via gyrB- and rpoB-sequencing. Clonal analysis was undertaken using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing. Susceptibility to antimicrobial agents was determined by microdilution and E-tests. Carbapenemase genes were detected by PCR. One hundred and one PFGE types were detected. A. baumannii was the most common (67/101 PFGE types), followed by Acinetobacter pittii (22/101), Acinetobacter lactucae (6/101), and Acinetobacter calcoaceticus (2/101). gyrB, rpoB1, and rpoB2 sequencing returned 49, 13, and 16 novel sequences, respectively. Sixty-three sequence types (STs) (38 new STs and 66 new alleles) were detected; the most common were ST2 (29/133 isolates) and ST132 (14/133). Twenty-six OXA-51 allelic variants were detected, nine of which were novel. The PFGE types were generally susceptible (88/101) to all the tested antimicrobials; 3/101 were carbapenem-resistant due to the presence of the genetic structure ISAba2-bla_OXA-58-like-ISAba3, and 2/101 were multidrug-resistant. It can be concluded that the examined Spo Acb complex population was mainly composed of A. baumannii. Many different clones were detected (with ST2 clearly dominant), all largely susceptible to antimicrobials; multidrug resistance was rare. In contrast, a previously examined EE Acb population was composed of just four expanding, multidrug-resistant A. baumannii clones -ST2, ST3, ST15, and ST80-.

Molecular Epidemiology and Clinical Impact of Acinetobacter calcoaceticus-baumannii Complex in a Belgian Burn Wound Center

Multidrug resistant Acinetobacter baumannii and its closely related species A. pittii and A. nosocomialis, all members of the Acinetobacter calcoaceticus-baumannii (Acb) complex, are a major cause of hospital acquired infection. In the burn wound center of the Queen Astrid military hospital in Brussels, 48 patients were colonized or infected with Acb complex over a 52-month period. We report the molecular epidemiology of these organisms, their clinical impact and infection control measures taken. A representative set of 157 Acb complex isolates was analyzed using repetitive sequence-based PCR (rep-PCR) (DiversiLab) and a multiplex PCR targeting OXA-51-like and OXA-23-like genes. We identified 31 rep-PCR genotypes (strains). Representatives of each rep-type were identified to species by rpoB sequence analysis: 13 types to A. baumannii, 10 to A. pittii, and 3 to A. nosocomialis. It was assumed that isolates that belonged to the same rep-type also belonged to the same species. Thus, 83.4% of all isolates were identified to A. baumannii, 9.6% to A. pittii and 4.5% to A. nosocomialis. We observed 12 extensively drug resistant Acb strains (10 A. baumannii and 2 A. nosocomialis), all carbapenem-non-susceptible/colistin-susceptible and imported into the burn wound center through patients injured in North Africa. The two most prevalent rep-types 12 and 13 harbored an OXA-23-like gene. Multilocus sequence typing allocated them to clonal complex 1 corresponding to EU (international) clone I. Both strains caused consecutive outbreaks, interspersed with periods of apparent eradication. Patients infected with carbapenem resistant A. baumannii were successfully treated with colistin/rifampicin. Extensive infection control measures were required to eradicate the organisms. Acinetobacter infection and colonization was not associated with increased attributable mortality.

Acinetobacter seifertii Isolated from China: Genomic Sequence and Molecular Epidemiology Analyses

Clinical infections caused by Acinetobacter spp. have increasing public health concerns because of their global occurrence and ability to acquire multidrug resistance. Acinetobacter calcoaceticus-Acinetobacter baumannii (ACB) complex encompasses A. calcoaceticus, A. baumannii, A. pittii (formerly genomic species 3), and A nosocomial (formerly genomic species 13TU), which are predominantly responsible for clinical pathogenesis in the Acinetobacter genus. In our previous study, a putative novel species isolated from 385 non-A. baumannii spp. strains based on the rpoB gene phylogenetic tree was reported. Here, the putative novel species was identified as A. seifertii based on the whole-genome phylogenetic tree. A. seifertii was recognized as a novel member of the ACB complex and close to A. baumannii and A. nosocomials. Furthermore, we studied the characteristics of 10 A. seifertii isolates, which were distributed widely in 6 provinces in China and mainly caused infections in the elderly or children. To define the taxonomic status and characteristics, the biochemical reactions, antimicrobial susceptibility testing, pulsed field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and whole-genome sequence analysis were performed. The phenotypic characteristics failed to distinguish A. serfertii from other species in the ACB complex. Most of the A. seifertii isolates were susceptible to antibiotics commonly used for nosocomial Acinetobacter spp. infections, but one isolate (strain A362) was resistant to ampicillin/sulbactam, ceftazidime and amikacin. The different patterns of MLST and PFGE suggested that the 10 isolates were not identical and lacked clonal relatedness. Our study reported for the first time the molecular epidemiological and genomic features of widely disseminated A. seifertii in China. These observations could enrich the knowledge of infections caused by non-A. baumannii and may provide a scientific basis for future clinical treatment.

Acinetobacter seifertii sp. nov., a member of the Acinetobacter calcoaceticus-Acinetobacter baumannii complex isolated from human clinical specimens

This study aimed to define the taxonomic status of a phenetically distinct group of 16 strains that corresponds to Acinetobacter genomic species 'close to 13TU', a provisional genomic species of the Acinetobacter calcoaceticus-Acinetobacter baumannii (ACB) complex recognized by Gerner-Smidt and Tjernberg in 1993. These strains have been isolated in different countries since the early 1990s and were mostly recovered from human clinical specimens. They were compared with 45 reference strains representing the known taxa of the ACB complex using taxonomic methods relevant to the genus Acinetobacter. Based on sequence analysis of the concatenated partial sequences (2976 bp) of seven housekeeping genes, the 16 strains formed a tight and well-supported cluster (intracluster sequence identity of ≥98.4 %) that was clearly separated from the other members of the ACB complex (≤94.7 %). The species status of the group was supported by average nucleotide identity values of ≤91.7 % between the whole genome sequence of representative strain NIPH 973(T) (NCBI accession no. APOO00000000) and those of the other species. In addition, whole-cell matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) MS analyses indicated the distinctness of the group at the protein level. Metabolic and physiological tests revealed several typical features of the group, although they did not allow its reliable differentiation from the other members of the ACB complex. We conclude that the 16 strains represent a distinct novel species, for which we propose the name Acinetobacter seifertii sp. nov. The type strain is NIPH 973(T) ( = CIP 110471(T) = CCUG 34785(T) = CCM 8535(T)).

Isolation and characterization of two plasmids in a clinical Acinetobacter nosocomialis strain

Background

Acinetobacter species are recognised as important nosocomial pathogens that have become a major cause of invasive opportunistic infections in hospitalised patients. Their clinical significance is largely due to the rapid development of antimicrobial resistance among strains. The development of antibiotic resistance among bacterial strains occurs frequently by the acquisition of resistance genes by gene transfer systems such as bacterial plasmids.

Method

Multi-antibiotic resistant Acinetobacter nosocomialis strain 178 was isolated from a hospital in Melbourne, Australia. This strain was screened for the presence of plasmids. The two plasmids isolated were sequenced and annotated.

Results

Two plasmids isolated from a single clinical Acinetobacter nosocomialis strain were sequenced. One plasmid, designated pRAY*-v3, appears to have evolved via the same lineage as the pRAY plasmid isolated from an Acinetobacter baumannii in South Africa. The other plasmid, designated pAB49-v1, appears to be an evolutionary descendent from a cryptic plasmid isolated from an A. baumannii almost 20 years ago. Both of the plasmid sequences here share a high level of sequence similarity with their ancestors, however differences are noted.

Conclusion

The isolation of these plasmid-lineages across different decades and continents suggests their global dissemination.

Insertions or deletions (Indels) in the rrn 16S-23S rRNA gene internal transcribed spacer region (ITS) compromise the typing and identification of strains within the Acinetobacter calcoaceticus-baumannii (Acb) complex and closely related members

To determine whether ITS sequences in the rrn operon are suitable for identifying individual Acinetobacter Acb complex members, we analysed length and sequence differences between multiple ITS copies within the genomes of individual strains. Length differences in ITS reported previously between A. nosocomialis BCRC15417^T (615 bp) and other strains (607 bp) can be explained by presence of an insertion (indel 13i/1) in the longer ITS variant. The same Indel 13i/1 was also found in ITS sequences of ten strains of A. calcoaceticus, all 639 bp long, and the 628 bp ITS of Acinetobacter strain BENAB127. Four additional indels (13i/2–13i/5) were detected in Acinetobacter strain c/t13TU 10090 ITS length variants (608, 609, 620, 621 and 630 bp). These ITS variants appear to have resulted from horizontal gene transfer involving other Acinetobacter species or in some cases unrelated bacteria. Although some ITS copies in strain c/t13TU 10090 are of the same length (620 bp) as those in Acinetobacter strains b/n1&3, A. pittii (10 strains), A. calcoaceticus and A. oleivorans (not currently acknowledged as an Acb member), their individual ITS sequences differ. Thus ITS length by itself can not by itself be used to identify Acb complex strains. A shared indel in ITS copies in two separate Acinetobacter species compromises the specificity of ITS targeted probes, as shown with the Aun-3 probe designed to target the ITS in A. pitti. The presence of indel 13i/5 in the ITS of Acinetobacter strain c/t13TU means it too responded positively to this probe. Thus, neither ITS sequencing nor the currently available ITS targeted probes can distinguish reliably between Acb member species.

Co-existence of blaOXA-23 and armA in multidrug-resistant Acinetobacter baumannii isolated from a hospital in South Korea

The co-existence of carbapenemase, 16S rRNA methylase and mutated quinolone resistance-determining regions (QRDRs) can cause serious difficulty in treating infections with multidrug-resistant Acinetobacter baumannii. In this study, we aimed to determine the mechanisms of imipenem, amikacin and ciprofloxacin resistance in A. baumannii isolates with resistance to these antibiotics. A total of 31 non-duplicate isolates of amikacin- and ciprofloxacin-resistant Acinetobacter isolates were identified from April to August 2010 from a single hospital in South Korea. To assess the clonal relatedness of the 31 Acinetobacter isolates, multilocus sequence typing, network phylogenetic analysis and enterobacterial repetitive intergenic consensus-PCR were utilized. Detection of OXA-type carbapenemase and 16S rRNA methylase was conducted using a multiplex PCR assay. The QRDRs of the gyrA and parC genes were amplified and sequenced. The result showed that 30/31 isolates harboured the blaOXA-23-like carbapenemase, which made them resistant to imipenem (MICs ≥16 µg ml(-1)). Twenty-eight of the 31 isolates were found to possess armA, a 16S rRNA methylase gene, and showed resistance to amikacin, arbekacin, gentamicin and tobramycin (MICs >256 µg ml(-1)). All of the isolates were determined to carry QRDR mutations in both gyrA and parC: a Ser83Leu substitution in gyrA and a Ser80Leu substitution in parC, causing a ciprofloxacin MIC ≥64 µg ml(-1). In conclusion, A. baumannii with co-existence of carbapenemase, 16S rRNA methylase and mutated QRDRs are extremely prevalent in South Korea, which may cause serious problems in the treatment of A. baumannii infections using carbapenem, amikacin and ciprofloxacin.

Acinetobacter indicus sp. nov., isolated from a hexachlorocyclohexane dump site

The taxonomic position of a Gram-negative, non-motile, oxidase negative and catalase positive strain, A648(T), isolated from a hexachlorocyclohexane (HCH) dump site located in Lucknow, India, was ascertained by using a polyphasic approach. A comparative analysis of a partial sequence of the rpoB gene and the 16S rRNA gene sequence revealed that strain A648(T) belonged to the genus Acinetobacter. DNA-DNA relatedness values between strain A648(T) and other closely related members (16S rRNA gene sequence similarity greater than 97%), namely Acinetobacter radioresistens DSM 6976(T), A. venetianus ATCC 31012(T), A. baumannii LMG 1041(T), A. parvus LMG 21765(T) A. junii LMG 998(T) and A. soli JCM 15062(T), were found to be less than 8%. The major cellular fatty acids of strain A648(T) were 18:1ω9c (19.6%), summed feature 3 (15.9%), 16:0 (10.6%) and 12:0 (6.4%). The DNA G+C content was 40.4 mol%. The polar lipid profile of strain A648(T) indicated the presence of diphosphatidylglycerol, phosphatidylethanolamine, followed by phosphatidylglycerol and phosphatidylcholine. The predominant polyamine of strain A648(T) was 1,3-diaminopropane and moderate amounts of putrescine, spermidine and spermine were also detected. The respiratory quinone consisted of ubiquinone with nine isoprene units (Q-9). On the basis of DNA-DNA hybridization, phenotypic characteristics and chemotaxonomic and phylogenetic comparisons with other members of the genus Acinetobacter, strain A648(T) is found to be a novel species of the genus Acinetobacter, for which the name Acinetobacter indicus sp. nov. is proposed. The type strain is A648(T) ( = DSM 25388(T) = CCM 7832(T)).

Acinetobacter: a potential reservoir and dispenser for β-lactamases

Innate resistance and remarkable ability to acquire additional resistance determinants underline the clinical importance of Acinetobacter. Over 210 β-lactamases belonging to 16 families have been identified in the genus, mostly in clinical isolates of A. baumannii. In this review, we update the current taxonomy of the genus Acinetobacter and summarize the β-lactamases detected in Acinetobacter spp. with an emphasis on Acinetobacter-derived cephalosporinases (ADCs) and carbapenem-hydrolysing class D β-lactamases (CHDLs). We also discuss the roles of integrons and insertion sequence (IS) elements in the expression and dissemination of such resistance determinants.

Antimicrobial resistance determinants in imipenem-nonsusceptible Acinetobacter calcoaceticus-baumannii complex isolated in Daejeon, Korea

Background

Members of the Acinetobacter calcoaceticus-baumannii (Acb) complex are important opportunistic bacterial pathogens and present significant therapeutic challenges in the treatment of nosocomial infections. In the present study, we investigated the integrons and various genes involved in resistance to carbapenems, aminoglycosides, and fluoroquinolones in 56 imipenem-nonsusceptible Acb complex isolates.

Methods

This study included 44 imipenem-nonsusceptible A. baumannii, 10 Acinetobacter genomic species 3, and 2 Acinetobacter genomic species 13TU strains isolated in Daejeon, Korea. The minimum inhibitory concentrations (MICs) were determined by Etest. PCR and DNA sequencing were used to identify the genes that potentially contribute to each resistance phenotype.

Results

All A. baumannii isolates harbored the bla_OXA-51-like gene, and 21 isolates (47.7%) co-produced OXA-23. However, isolates of Acinetobacter genomic species 3 and 13TU only contained bla_IMP-1 or bla_VIM-2. Most Acb complex isolates (94.6%) harbored class 1 integrons, armA, and/or aminoglycoside-modifying enzymes (AMEs). Of particular note was the fact that armA and aph(3')-Ia were only detected in A. baumannii isolates, which were highly resistant to amikacin (MIC₅₀≥256) and gentamicin (MIC₅₀≥1,024). In all 44 A. baumannii isolates, resistance to fluoroquinolones was conferred by sense mutations in the gyrA and parC. However, sense mutations in parC were not found in Acinetobacter genomic species 3 or 13TU isolates.

Conclusions

Several differences in carbapenem, aminoglycoside, and fluoroquinolone resistance gene content were detected among Acb complex isolates. However, most Acb complex isolates (87.5%) possessed integrons, carbapenemases, AMEs, and mutations in gyrA. The co-occurrence of several resistance determinants may present a significant threat.

Clinical impact and molecular basis of antimicrobial resistance in non-baumannii Acinetobacter

Species of Acinetobacter other than Acinetobacter baumannii are involved in nosocomial infections. Acinetobacter lwoffii, Acinetobacter genomospecies 3 and Acinetobacter genomospecies 13TU are found in community- and nosocomial-acquired infections as well as in neonatal intensive care units. The non-baumannii Acinetobacter are normally highly susceptible to ciprofloxacin, ampicillin/sulbactam, gentamicin and tigecycline. Carbepenems show good activity although resistant isolates have been reported. Resistance to β-lactams other than carbapenems is associated with overexpression of chromosomal cephalosporinases and extended-spectrum β-lactamase acquisition, whereas resistance to carbapenems involves acquisition of carbapenemases. Quinolone resistance is related to gyrA and/or parC mutations but overexpresion of efflux proteins also plays an important role. With the development of novel and more accurate typing methodologies, an increase in infections caused by non-baumannii Acinetobacter might be observed in the future.

Genotypic and phenotypic characterization of the Acinetobacter calcoaceticus-Acinetobacter baumannii complex with the proposal of Acinetobacter pittii sp. nov. (formerly Acinetobacter genomic species 3) and Acinetobacter nosocomialis sp. nov. (formerly Acinetobacter genomic species 13TU)

Acinetobacter genomic species (gen. sp.) 3 and gen. sp. 13TU are increasingly recognized as clinically important taxa within the Acinetobacter calcoaceticus-Acinetobacter baumannii (ACB) complex. To define the taxonomic position of these genomic species, we investigated 80 strains representing the known diversity of the ACB complex. All strains were characterized by AFLP analysis, amplified rDNA restriction analysis and nutritional or physiological testing, while selected strains were studied by 16S rRNA and rpoB gene sequence analysis, multilocus sequence analysis and whole-genome comparison. Results supported the genomic distinctness and monophyly of the individual species of the ACB complex. Despite the high phenotypic similarity among these species, some degree of differentiation between them could be made on the basis of growth at different temperatures and of assimilation of malonate, l-tartrate levulinate or citraconate. Considering the medical relevance of gen. sp. 3 and gen. sp. 13TU, we propose the formal names Acinetobacter pittii sp. nov. and Acinetobacter nosocomialis sp. nov. for these taxa, respectively. The type strain of A. pittii sp. nov. is LMG 1035(T) (=CIP 70.29(T)) and that of A. nosocomialis sp. nov. is LMG 10619(T) (=CCM 7791(T)).

In vitro activity and in vivo efficacy of clavulanic acid against Acinetobacter baumannii

Clavulanic acid (CLA) exhibits low MICs against some Acinetobacter baumannii strains. The present study evaluates the efficacy of CLA in a murine model of A. baumannii pneumonia. For this purpose, two clinical strains, Ab11 and Ab51, were used; CLA MICs for these strains were 2 and 4 mg/liter, respectively, and the imipenem (IPM) MIC was 0.5 mg/liter for both. A pneumonia model in C57BL/6 mice was used. The CLA dosage (13 mg/kg of body weight given intraperitoneally) was chosen to reach a maximum concentration of the drug in serum similar to that in humans and a time during which the serum CLA concentration remained above the MIC equivalent to 40% of the interval between doses. Six groups (n = 15) were inoculated with Ab11 or Ab51 and were allocated to IPM or CLA therapy or to the untreated control group. In time-kill experiments, CLA was bactericidal only against Ab11 whereas IPM was bactericidal against both strains. CLA and IPM both decreased bacterial concentrations in lungs, 1.78 and 2.47 log10 CFU/g (P < or = 0.001), respectively, in the experiments with Ab11 and 2.42 and 2.28 log10 CFU/g (P < or = 0.001), respectively, with Ab51. IPM significantly increased the sterility of blood cultures over that for the controls with both strains (P < or = 0.005); CLA had the same effect with Ab51 (P < 0.005) but not with Ab11 (P = 0.07). For the first time, we suggest that CLA may be used for the treatment of experimental severe A. baumannii infections.

Description of Acinetobacter venetianus ex Di Cello et al. 1997 sp. nov

The name 'Acinetobacter venetianus' has been used previously to designate three marine hydrocarbon-degrading Acinetobacter strains, of which strain RAG-1 (=ATCC 31012) has industrial applications for the production of the bioemulsifier emulsan. However, to date, the name of this taxon has not been validly published. In this study, five strains were examined to corroborate the delineation of this taxon by means of phenotypic characterization, DNA-DNA hybridization, selective restriction fragment amplification (AFLP), amplified rDNA restriction analysis (ARDRA), rpoB gene sequence analysis and tRNA intergenic spacer length polymorphism analysis (tDNA-PCR) and to emend the description of 'Acinetobacter venetianus' (ex Di Cello et al. 1997). AFLP analysis showed that the five strains formed a tight cluster at 56.8+/-5.0 % genomic relatedness that was separated from strains of other haemolytic species of the genus Acinetobacter and from the type and reference strains of other Acinetobacter species at <or=27 % relatedness, indicating the distinctiveness of the novel strains. The strains were haemolytic and able to grow on citrate (Simmons), l-histidine and malonate. The strains did not oxidize d-glucose or utilize dl-lactate or l-aspartate. The G+C contents of strains RAG-1 and of VE-C3 were 43.9 % and 43.6 mol%, respectively. The novel strains could be recognized by a characteristic ARDRA pattern (CfoI 1, AluI 3, MboI 2, RsaI 2, MspI 3). The consensus tDNA-PCR pattern for the five strains consisted of amplified fragments of 87.9, 100.2, 134.6 and 248.5 bp and was indistinguishable from that of strains of Acinetobacter genomic species 14BJ. The five strains represent a novel species for which the name Acinetobacter venetianus sp. nov. is proposed. The type strain is RAG-1(T) (=ATCC 31012(T)=CCUG 45561(T)=LMG 19082(T)=LUH 3904(T)=NIPH 1925(T)).

Validation of partial rpoB gene sequence analysis for the identification of clinically important and emerging Acinetobacter species

Bacteria belonging to the genus Acinetobacter are ubiquitous in soil and water. Only a few species, including Acinetobacter baumannii, and the unnamed Acinetobacter genomic species (gen. sp.) 3 and 13TU, which together with the soil organism Acinetobacter calcoaceticus are combined in the A. calcoaceticus–A. baumannii (Acb) complex, have been recognized as important nosocomial infectious agents. The ecology, epidemiology and pathology of most species are not yet well established. Lack of practical and accurate methods limits routine identification of clinical isolates and thus hampers precise identification of those of the Acb complex and other Acinetobacter species of possible clinical significance. We previously identified a 350 bp highly variable zone on the rpoB gene which appeared to be a promising target for rapid molecular identification. In the present study, we validated this method for accuracy on a collection of reference strains belonging to A. calcoaceticus (5 strains), Acinetobacter gen. sp. 3 (29 strains), A. gen. sp. 13TU (18 strains), A. baumannii (30 strains) and one strain each of A. radioresistens, A. gen. sp. 15TU, A. gen. sp. 10, A. gen. sp. 11, A. gen. sp. ‘between 1 and 3’ and A. gen. sp. 14TU=13BJ. This represents the largest analysis to date that compares a large number of well-identified strains of the Acb complex to assess the intra- and interspecies variation within this complex. All were correctly identified with 98.9–100 % intraspecies relatedness based on partial rpoB sequence analysis. We then applied this tool to identify 99 Acinetobacter clinical isolates from four public hospitals in Marseille, France. All isolates could easily be identified to species as they were separated into 13 species sequence types with a sequence variance of 0–2.6 % from their respective type strains. Of these 99 isolates, 10 were A. haemolyticus, 52 were A. baumannii, 27 were A. gen. sp. 3, 5 were A. schindleri, 1 was A. lwoffii, and 1 was A. gen. sp. 13TU. Three were provisionally identified as A. gen. sp. 9. This is the first work to identify all specimens of a set of clinical Acinetobacter isolates at species level using rpoB sequence analysis. Our data emphasize the recognition of A. schindleri as an emerging cause of Acinetobacter-related infection and confirm that A. gen. sp. 3 is the second most commonly isolated Acinetobacter species after A. baumannii in patients.

Acinetobacter soli sp. nov., isolated from forest soil

A non-motile and rod shaped bacterium, designated strain B1(T), was isolated from forest soil at Mt. Baekwoon, Republic of Korea. Cells were Gram-negative, catalase-positive, and oxidase-negative. The major fatty acids were 9-octadecenoic acid (C(18:1) omega9c; 42%) and hexadecanoic acid (C(16:0); 25.9%) and summed feature 3 (comprising iso-C(15:0) 2-OH and/or C(16:1) omega7c; 10.0%). The DNA G+C content was 44.1 mol%. A phylogenetic tree based on 16S rRNA gene sequences showed that strain B1(T) formed a lineage within the genus Acinetobacter and was closely related to A. baylyi DSM 14961(T) (98.6% sequence similarity), followed by A. baumannii DSM 30007(T) (97.4%), A. calcoaceticus DSM 30006(T) (97.0%) and 3 genomic species (96.8 approximately 7.6%). Phenotypic characteristics, gyrB gene sequence analysis and DNA-DNA relatedness data distinguished strain B1(T) from type strains of A. baylyi, A. baumannii, and A. calcoaceticus. On the basis of the evidence presented in this study, strain B1(T) represents a novel species of the genus Acinetobacter, for which the name Acinetobacter soli sp. nov. is proposed. The type strain is B1(T) (= KCTC 22184(T)= JCM 15062(T)).

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.

Oligonucleotide array-based identification of species in the Acinetobacter calcoaceticus-A. baumannii complex in isolates from blood cultures and antimicrobial susceptibility testing of the isolates

Acinetobacter calcoaceticus, A. baumannii, Acinetobacter genomic species (gen. sp.) 3, and Acinetobacter gen. sp. 13TU, which are included in the A. calcoaceticus-A. baumannii complex, are difficult to distinguish by phenotypic methods. An array with six oligonucleotide probes based on the 16S-23S rRNA gene intergenic spacer (ITS) region was developed to differentiate species in the A. calcoaceticus-A. baumannii complex. Validation of the array with a reference collection of 52 strains of the A. calcoaceticus-A. baumannii complex and 137 strains of other species resulted in an identification sensitivity and specificity of 100%. By using the array, the species distribution of 291 isolates of the A. calcoaceticus-A. baumannii complex from patients with bacteremia were determined to be A. baumannii (221 strains [75.9%]), Acinetobacter gen. sp. 3 (67 strains [23.0%]), Acinetobacter gen. sp. 13TU (2 strains [0.7%]), and unidentified Acinetobacter sp. (1 strain [0.3%]). The identification accuracy of the array for 12 randomly selected isolates from patients with bacteremia was further confirmed by sequence analyses of the ITS region and the 16S rRNA gene. Antimicrobial susceptibility testing of the 291 isolates from patients with bacteremia revealed that A. baumannii strains were less susceptible to antimicrobial agents than Acinetobacter gen. sp. 3. All Acinetobacter gen. sp. 3 strains were susceptible to ampicillin-sulbactam, imipenem, and meropenem; but only 67.4%, 90%, and 86% of the A. baumannii strains were susceptible to ampicillin-sulbactam, imipenem, and meropenem, respectively. The observed significant variations in antimicrobial susceptibility among different species in the A. calcoaceticus-A. baumannii complex emphasize that the differentiation of species within the complex is relevant from a clinical-epidemiological point of view.

An increasing threat in hospitals: multidrug-resistant Acinetobacter baumannii

Since the 1970s, the spread of multidrug-resistant (MDR) Acinetobacter strains among critically ill, hospitalized patients, and subsequent epidemics, have become an increasing cause of concern. Reports of community-acquired Acinetobacter infections have also increased over the past decade. A recent manifestation of MDR Acinetobacter that has attracted public attention is its association with infections in severely injured soldiers. Here, we present an overview of the current knowledge of the genus Acinetobacter, with the emphasis on the clinically most important species, Acinetobacter baumannii.

Distinct antimicrobial resistance patterns and antimicrobial resistance-harboring genes according to genomic species of Acinetobacter isolates

Using 58 isolates of Acinetobacter species recovered from a university hospital between August 2004 and March 2005, we performed genomic identification by amplified rRNA gene restriction analysis (ARDRA) and investigated the existence of metallo-beta-lactamase (MBL) producers and extended-spectrum beta-lactamase (ESBL) producers. Genomic species identification of Acinetobacter strains using ARDRA showed that 40 strains were genomic species 2 (Acinetobacter baumannii), 9 were 13 sensu Tjernberg and Ursing (13TU), 5 were Acinetobacter phenon 6/ct 13TU, and 4 were Acinetobacter genospecies 3. Among 58 strains, 13 isolates were MBL producers carrying bla(IMP-1) or bla(VIM-2) and 13 isolates were ESBL producers carrying bla(PER-1). Notably, the MBL producers were mostly 13TU, Acinetobacter phenon 6/ct 13TU, and Acinetobacter genospecies 3, which showed susceptibility to ciprofloxacin and ampicillin-sulbactam. However, 12 of 13 strains carrying bla(PER-1) were A. baumannii, showing multidrug resistance. The data revealed that the antimicrobial resistance patterns and resistance-harboring genes of Acinetobacter species are remarkably distinct according to the genomic species of Acinetobacter isolates.

Estimation of ribosomal RNA operon (rrn) copy number in Acinetobacter isolates and potential of patterns of rrn operon-containing fragments for typing strains of members of this genus

The copy number of the rrn operon in 70 strains of Acinetobacter including the type strains of almost all the genomic species with validated names was estimated after digestion of their genomic DNA by the restriction enzymes BglII and PstI, and Southern blotting. Copy number estimates varied between and among species, with between 3 and 7 rrn operon copies detected. Copy number estimates obtained from the same strain with the two enzymes sometimes varied. BglII generated RFLP patterns of the rrn containing fragments obtained from Southern blots after agarose gel electrophoresis were examined for their value in identifying Acinetobacter isolates. This method was very reproducible with the same fragment pattern always generated from the same isolate on repeated analysis. Often multiple strains of the same genomic species gave identical or very similar patterns (e.g. Acinetobacter baylyi), clustering closest together on the dendrogram generated after numerical analysis of these patterns. However, with some, like BG5 and BG8, the patterns derived from the different strains, some of which had been placed in this genomic species from DNA:DNA hybridization data, varied considerably to each other and to the type strain. Little similarity was seen when relationships between these strains based on these patterns were compared to those using DNA:DNA hybridization data. Often these patterns could be used to question earlier identification of strains using phenotypic characters. Thus, strain AB82 thought to belong to genomic species 5 gave an identical pattern to A. bouvetii(T) (DSM 14964). In some cases this pattern analysis suggested that novel species of Acinetobacter might exist among the strains examined.

Species-level identification of isolates of the Acinetobacter calcoaceticus-Acinetobacter baumannii complex by sequence analysis of the 16S-23S rRNA gene spacer region

The species Acinetobacter calcoaceticus, A. baumannii, genomic species 3, and genomic species 13TU included in the Acinetobacter calcoaceticus-Acinetobacter baumannii complex are genetically highly related and difficult to distinguish phenotypically. Except for A. calcoaceticus, they are all important nosocomial species. In the present study, the usefulness of the 16S-23S rRNA gene intergenic spacer (ITS) sequence for the differentiation of (genomic) species in the A. calcoaceticus-A. baumannii complex was evaluated. The ITSs of 11 reference strains of the complex and 17 strains of other (genomic) species of Acinetobacter were sequenced. The ITS lengths (607 to 638 bp) and sequences were highly conserved for strains within the A. calcoaceticus-A. baumannii complex. Intraspecies ITS sequence similarities ranged from 0.99 to 1.0, whereas interspecies similarities varied from 0.86 to 0.92. By using these criteria, 79 clinical isolates identified as A. calcoaceticus (18 isolates) or A. baumannii (61 isolates) with the API 20 NE system (bioMerieux Vitek, Marcy l'Etoile, France) were identified as A. baumannii (46 isolates), genomic species 3 (19 isolates), and genomic species 13TU (11 isolates) by ITS sequencing. An identification rate of 96.2% (76 of 79 isolates) was obtained by using ITS sequence analysis for identification of isolates in the A. calcoaceticus-A. baumannii complex, and the accuracy of the method was confirmed for a subset of strains by amplified rRNA gene restriction analysis and genomic DNA analysis by AFLP analysis by using libraries of profiles of reference strains. In conclusion, ITS sequence-based identification is reliable and provides a promising tool for elucidation of the clinical significance of the different species of the A. calcoaceticus-A. baumannii complex.

Molecular characterization of the gene encoding a new AmpC beta-lactamase in a clinical strain of acinetobacter genomic species 3

A presumptive chromosomal cephalosporinase (pI, 9.0) from a clinical strain of Acinetobacter genomic species 3 (AG3) is reported. The nucleotide sequence of this beta-lactamase shows for the first time the gene encoding an AmpC enzyme in AG3. In addition, the biochemical properties of the novel AG3 AmpC beta-lactamase are reported

Antimicrobial susceptibility and mechanisms of resistance to quinolones and beta-lactams in Acinetobacter genospecies 3

Antimicrobial susceptibility was determined in 15 epidemiologically unrelated clinical isolates of Acinetobacter genospecies 3. Moreover, the mechanisms of resistance to some beta-lactam antibiotics may be associated with the presence of a chromosomal cephalosporinase, AmpC, and the resistance to quinolones related to mutations in the gyrA and parC genes.

Susceptibility of the Acinetobacter calcoaceticus–A. baumannii complex to imipenem, meropenem, sulbactam and colistin

The Acinetobacter calcoaceticus-Acinetobacter baumannii complex includes some of the most clinically relevant species of the genus Acinetobacter due to their capacity to cause epidemic nosocomial outbreaks as well as their increasing resistance to antibiotics. Susceptibility of Acinetobacter strains varies greatly depending on origin, thus highlighting the importance of local analyses of susceptibility profiles. Two hundred twenty-one strains of the A. calcoaceticus-A. baumannii complex were identified using biochemical tests and were biotyped. Strain susceptibility to imipenem, meropenem, colistin and sulbactam was studied using agar dilution. Eight different biotypes were found, type 1 accounting for 69.2% of the strains. MIC(50) and MIC(90) to imipenem, meropenem, colistin and sulbactam were 4 and 8 mg/l, 16 and 32 mg/l, 0.5 and 1mg/l, and 8 and 16 mg/l, with susceptibility rates of 64.3, 22.6, 98.2 and 73.8%, respectively. Biotype 1 was the most resistant. A statistically significant difference was observed for the mean MIC of the four predominant biotypes to imipenem, meropenem and sulbactam but not to colistin.

Acinetobacter parvus sp. nov., a small-colony-forming species isolated from human clinical specimens

The taxonomic status of seven glucose-non-acidifying, non-proteolytic Acinetobacter strains characterized by forming small colonies on agar media was studied. With one exception, all strains were from human specimens. They could be distinguished from all described Acinetobacter (genomic) species by their ability to grow on ethanol and acetate as sole sources of carbon but not on 22 other substrates tested including DL-lactate or DL-4-aminobutyrate. DNA-DNA hybridization studies, 16S rRNA gene sequence analysis, amplified rDNA restriction analysis and DNA polymorphism analysis by AFLP showed that these strains represent a hitherto unknown species of the genus Acinetobacter, for which the name Acinetobacter parvus (type strain LMG 21765(T)=LUH 4616(T)=NIPH 384(T)=CCM 7030(T)) is proposed.

Seven novel species of Acinetobacter isolated from activated sludge

Thirteen isolates of Acinetobacter were obtained from activated sludge plants in Victoria, Australia. Earlier 16S-23S rDNA genomic fingerprinting and partial 16S rDNA sequence data had suggested that these isolates might contain previously undescribed species. This view was confirmed here. A polyphasic taxonomic approach involving phenotypic characterization, near-complete 16S rDNA sequence data and DNA-DNA hybridization analyses support the view that seven novel genomic species can be differentiated in this group of isolates. However, when fluorescence in situ hybridization (FISH) studies were performed with a 16S-rRNA-targeted probe specific for the genus Acinetobacter, used to identify Acinetobacter in activated sludge plants, all these strains responded positively. This suggests that these isolates would not have been missed in earlier FISH studies where their role as polyphosphate-accumulating bacteria has been questioned. This report describes these isolates and proposes that they be named Acinetobacter baylyi (type strain B2T = DSM 14961T = CIP 107474T), Acinetobacter bouvetii (type strain 4B02T = DSM 14964T = CIP 107468T), Acinetobacter grimontii (type strain 17A04T = DSM 14968T = CIP 107470T), Acinetobacter tjernbergiae (type strain 7N16T = DSM 14971T = CIP 107465T), Acinetobacter towneri (type strain AB1110T = DSM 14962T = CIP 107472T), Acinetobacter tandoii (type strain 4N13T = DSM 14670T = CIP 107469T) and Acinetobacter gerneri (type strain 9A01T = DSM 14967T = CIP 107464T).

Comparison of a repetitive extragenic palindromic sequence-based PCR method and clinical and microbiological methods for determining strain sources in cases of nosocomial Acinetobacter baumannii bacteremia

Using a repetitive extragenic palindromic PCR (REP-PCR), we genotypically characterized strains causing nosocomial Acinetobacter baumannii infections and analyzed the source of bacteremia in 67 patients from an institution in which infections by this bacterium were endemic. Six different genotypes were found, including 21, 27, 3, 9, 3, and 4 strains. The probable source of bacteremia, according to clinical and/or microbiological criteria, was known in 42 patients (63%): respiratory tract (n = 19), surgical sites (n = 12), intravascular catheters (n = 5), burns (n = 3), and urinary tract (n = 3). The definite source of bacteremia, according to REP-PCR, could be established in 30 (71%) out of the 42 patients with strains from blood and other sites; in these cases clinical and microbiological criteria for the source of bacteremia were thus confirmed. In the remaining 12 patients (29%) the probable source was refuted by the REP-PCR method. The definite sources of bacteremia according to genotype were as follows: respiratory tract in 13 patients (31%), surgical sites in 8 (19%), intravascular catheters in 4 (9%), burns in 3 (7%), and urinary tract in 2 (5%). A comparison of strains from blood cultures and other sites with regard to their REP-PCR and antimicrobial resistance profiles was also made. Taking the REP-PCR as the "gold standard," the positive predictive value of antibiotype was 77% and the negative predictive value was 42%. In summary, the utility of the diagnosis of the source of nosocomial A. baumannii bacteremia using clinical and/or microbiological criteria, including antibiotyping, is limited, as demonstrated by REP-PCR.

Comparative studies of the Acinetobacter genus and the species identification method based on the recA sequences

The recA gene is indispensable for a maintaining and diversification of the bacterial genetic material. Given its important role in ensuring cell viability, it is not surprising that the RecA protein is both ubiquitous and well conserved among a range of prokaryotes. Previously, we reported Acinetobacter genomic species identification method based on PCR amplification of an internal fragment of the recA gene with subsequent restriction analysis (RFLP) with HinfI and MboI enzymes. In present study, the PCR products containing the internal fragment of the recA gene, for 25 Acinetobacter strains belonging to all genomic species, were sequenced. Based on the nucleotide sequences the restriction maps and phylogenetic tree were prepared. The restriction maps revealed that Tsp509I restriction enzyme is the most discriminating for RFLP. To verify the computer analysis, the amplified DNAs from all reference genomic species available (43 strains) and 34 clinical strains were digested with each of the three restriction endonucleases mentioned. The results of digestion confirmed the computer analysis. The reconstructed phylogenetic tree showed linkages between genomic species 1 (Acinetobacter calcoaceticus), 2 (Acinetobacter baumannii), 3, 'between 1 and 3', TU13 and 'close to TU13'; genomic species 4, 6, BJ13, BJ14, BJ15, BJ16 and BJ17; genomic species 7 (Acinetobacter johnsonii) and TU14; genomic species 10 and 11; genomic species 8 (Acinetobacter Iwoffii), 9, 12 (Acinetobacter radioresistens) and TU15; and genomic species 5 (Acinetobacter junii). It is interesting that one branch in the phylogenetic tree contains haemolytic species-genomic species 4 (A. haemolyticus), BJ13, BJ14, BJ15, BJ16 and BJ17. The proposed genotypic method clearly revealed that the RFLP profiles obtained with Tsp509I enzyme might be useful for species identification of Acinetobacter strains. In this context, recA/RFLP genotypic method should be seen as an ideal preliminary screening method for large numbers of isolates, with the ultimate confirmatory role reserved for DNA hybridization analysis.

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.

Pyrolysis mass spectrometry (PyMS) and 16S-23S rDNA spacer region fingerprinting suggests the presence of novel acinetobacters in activated sludge

Screening of large numbers of Acinetobacter spp. from activated sludge systems with Pyrolysis Mass Spectrometry (PyMS) showed that many did not cluster tightly with the currently described genomic species which have been obtained mainly from clinical sources. Selected isolates were then genotypically fingerprinted using their 16S-23S rDNA spacer region, and again the data revealed considerable differences in the genomic fingerprints of many of these activated sludge isolates to the predominantly clinical genomic species. In fact, few could be identified from them. The possibility that the current speciation within this genus is not adequate to encompass all these environmental isolates is addressed in relation to the methods used to study the population dynamics of Acinetobacter in activated sludge.

RAPD-PCR typing of Acinetobacter isolates from activated sludge systems designed to remove phosphorus microbiologically

AIMS

This study investigated whether there were differences in RAPD fingerprints between already described genomic species of Acinetobacter and those from activated sludge systems. Whether plant-specific populations of acinetobacters exist was also examined.

METHODS AND RESULTS

Fifty-two isolates of Acinetobacter from four biological phosphorus removal (EBPR) systems of different configurations, and the known genomic species, were characterized using RAPD-PCR, and fragments separated on agarose gels. Patterns were analysed using Gel Pro software and data analysed numerically. RAPD-PCR produced patterns suggesting that many environmental isolates differ from known genomic species. In two cases, strains from individual plants clustered closely enough together to imply that there may be plant-specific populations of acinetobacters.

CONCLUSION

The data suggest that current understanding of the taxonomic status of Acinetobacter may need modifying to accommodate non-clinical isolates, as many of the clusters emerging after numerical analysis of RAPD-PCR fragments from activated sludge isolates were quite separate from the clusters containing the already described genomic species. Some evidence was also obtained from the clusters generated to support a view that particular populations of Acinetobacter may occur in individual activated sludge plants.

SIGNIFICANCE AND IMPACT OF THE STUDY

These data suggest that the current understanding of the systematics of Acinetobacter, based as it is almost exclusively on clinical isolates, may need drastic revision to accommodate environmental strains. They also suggest that a re-examination of the importance and role of Acinetobacter in the activated sludge process may be appropriate.

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.

Examination of polyclonal rabbit immune sera against serovars of Acinetobacter baumannii and genospecies 3 for cross-reactions with reference strains of other named/unnamed genospecies of Acinetobacter

Polyclonal rabbit immune sera against 38 serovars of Acinetobacter baumannii and genospecies 13 capable of growth at 44 degrees C and against 26 serovars of genospecies 3 and genospecies 13 incapable of growth at 44 degrees C were examined for serological cross-reactivity with reference strains comprising 17 genospecies (among them 6 named species) of Acinetobacter. Checkerboard agglutination tests yielded very few cross-reactions. Specifically, genospecies 17 cross-reacted weakly with A. baumannii serovar 27; strains genospecies 13 (Bouvet), TU 14, and 'close to TU 13' were strongly agglutinated by antiserum against A. baumannii serovar 18. Genospecies 14 (Bouvet) yielded a very weak cross-reaction with genospecies 3 serovar 20, and genospecies TU 13 reacted weakly with anti-genospecies 3 serovar 15 serum. The 'between genospecies 1 and 3' reference strain proved to be A. baumannii serovar 5 as determined with absorption tests.

Outer-membrane proteins pattern and detection of beta-lactamases in clinical isolates of imipenem-resistant Acinetobacter baumannii from Brazil

In order to compare imipenem-sensitive and -resistant Acinetobacter baumannii strains isolated from three patients, ribotyping, plasmid, beta-lactamase detection and outer-membrane analysis were performed. Ribotyping and the use of a beta-lactam during the period when the strains were isolated suggested that they had a common origin and that resistance occurred in vivo. Outer membrane analysis showed no difference between susceptible and resistant strains with the exception of an A2 imipenem-resistant strain that lost a protein band of 31-36 kDa. Beta-lactamases were detected using isoelectric focusing in all strains (pI of 7.4). In addition, two beta-lactamases (pI of 5.9 and 6.7) were found in imipenem-resistant isolates. The double-disc technique demonstrated the presence of a beta-lactamase capable of imipenem inactivation in resistant strains. Plasmid analysis showed that all susceptible strains had the same pattern, one resistant strain did not have any plasmid, one had the same plasmid pattern of its susceptible pair and only one had a different pattern when compared with its susceptible pair.

The discriminatory power of ribo-PCR compared to conventional ribotyping for epidemiological purposes

Molecular typing techniques have become increasingly important for confirmation of epidemiological relationships and delimitation of nosocomial outbreaks. The discriminatory power of the two DNA-based typing methods, conventional ribotyping and ribo-PCR, was assessed to distinguish between selected strains of Acinetobacter calcoaceticus, Enterobacter cloacae, Serratia marcescens and Pseudomonas aeruginosa. Overall, conventional ribotyping was more discriminatory than ribo-PCR.

Use of a murine O-antigen-specific monoclonal antibody to identify Acinetobacter strains of unnamed genomic species 13 Sensu Tjernberg and Ursing

A monoclonal antibody against the O-antigenic polysaccharide chain of the lipopolysaccharide (LPS) of Acinetobacter strains belonging to the unnamed genomic species 13 Sensu Tjernberg and Ursing (13TU) was obtained after immunization of BALB/c mice with heat-killed bacteria and was characterized by enzyme immunoassay and Western blot analysis, by use of LPS and proteinase K-treated bacterial lysates, analyses in which the antibody was shown to be highly specific for the homologous antigen. In addition, when tested in dot and Western blots, reactivity was observed with 9 of 18 Acinetobacter strains of genomic species 13TU which had been isolated in Germany and Denmark; no reactivity was observed with strains of other genomic species, including the closely related genomic groups 1 (A. calcoaceticus), 2 (A. baumannii), and 3 (unnamed), or with other gram-negative bacteria. The antibody described here represents a convenient reagent for the simple, economical, and accurate differentiation of clinical isolates of genomic species 13TU from other Acinetobacter strains. Although the antibody does not identify all isolates of this genomic group, it is evident that it will be a useful reagent in the development of a serotyping scheme for clinical laboratories.

Identification of Acinetobacter baumannii strains with monoclonal antibodies against the O antigens of their lipopolysaccharides

Despite the emergence of Acinetobacter baumannii strains as nosocomial pathogens, simple methods for their phenotypic identification are still unavailable. Murine monoclonal antibodies specific for the O-polysaccharide moiety of the lipopolysaccharide (LPS) of two A. baumannii strains were obtained after immunization with heat-killed bacteria. The monoclonal antibodies were characterized by enzyme immunoassay and by Western and dot blot analyses and were investigated for their potential use for the identification of A. baumannii strains. The antibodies reacted with 46 of the 80 A. baumannii clinical isolates that were investigated, and reactivity was observed with 11 of 14 strains which were isolated during outbreaks in different northwestern European cities; no reactivity was observed with Acinetobacter strains of other genomic species, including the closely related genomic species 1 (Acinetobacter calcoaceticus), 3, and 13 sensu Tjernberg and Ursing, or with other gram-negative bacterial strains. The results show that O-antigen-specific monoclonal antibodies such as the ones described are convenient reagents which can be used to identify Acinetobacter strains in clinical and research laboratories.

Characterization of oligonucleotide probes for the identification of Acinetobacter spp., A. baumannii and Acinetobacter genomic species 3

The 16S-23S intergenic spacer regions of four Acinetobacter genomic species belonging to the A. calcoaceticus-A. baumannii (Acb) complex, i.e. genomic species 1 (A. calcoaceticus), genomic species 2 (A. baumannii), genomic species 3 and Tjernberg and Ursing (TU) genomic species 13, have been cloned and sequenced. Sequence analysis led to the discovery of a single copy of IIe and Ala tRNA genes within each spacer. Sequence comparison allowed the identification of a 192-base-pair long highly conserved sequence between the 3' end of the 16S rRNA and the 5' end of the tRNA(Ala) genes. Moreover, two short regions, which were specific to, respectively, genomic species 2 and 3, could be identified. Oligonucleotides corresponding to these sequences were constructed and tested for the ability to hybridize with chromosomal DNA extracted from Acinetobacter belonging to different genomic species and with chromosomal DNA of other bacterial genera. One of these oligonucleotides was demonstrated to be useful as a sensitive and specific probe for A. baumannii. A less sensitive probe for Acinetobacter genomic species 3 was also developed.

Evaluation of amplified ribosomal DNA restriction analysis for identification of Acinetobacter genomic species

Further to a previous study, the usefulness of amplified ribosomal DNA restriction analysis (ARDRA) for identification of Acinetobacter genomic species (DNA groups) was tested. A set of 202 Acinetobacter strains of 18 described genomic species and 17 unclassified strains were used. Restriction patterns obtained with a standard panel of restriction enzymes CfoI, AluI, MboI, RsaI and MspI allowed for separation of 11 DNA groups. With the additional use of restriction enzymes BfaI and BsmAI, five other (genomic) species could be differentiated, leaving only A. haemolyticus and DNA group 13BJ/14TU unseparated. With the standard panel of enzymes, ten new ARDRA profiles were noted in 14 unclassified strains. Two other unclassified strains had a profile in common with DNA group 15BJ, but were differentiated from this DNA group by restriction with bfaI. One remaining unclassified strain could not be differentiated from DNA group 17 by the standard panel of enzymes or by the enzymes BfaI and BsmAI. Results demonstrate the utility of ARDRA for identification of most genomic species of Acinetobacter. Furthermore, new ARDRA profiles that were shared by several unclassified strains may indicate so far undescribed genomic species in the genus.

PCR-amplified 16S and 23S rDNA restriction analysis for the identification of Acinetobacter strains at the DNA group level

The genus Acinetobacter is phenotypically rather homogeneous, but genotypically heterogeneous. In this study, a simple method based on restriction analysis of a PCR-amplified large fragment (4.5 kb) of most of the ribosomal operon (16S and 23S ribosomal genes and the spacer in-between) was investigated. Sixty-seven collection strains belonging to the 20 DNA groups proposed until 1993 were studied. Using the enzyme Sau3AI, 25 DNA profiles were obtained. Strains belonging to DNA groups 1, 3, 6, TU13 and TU15 showed two profiles each, and DNA groups 4, 5 and 7 showed profiles with variants showing less intensive additional bands. The remaining 12 groups showed 12 different profiles. The profiles obtained were DNA-group-specific except for one profile which was shared between the unnamed DNA group 3 and a rarely encountered genotypically related DNA group. These two DNA groups could be separated by using the enzyme Hinf1. Twenty-five additional clinical isolates previously characterized by standard DNA-DNA hybridization were selected in a double-blind fashion for identification at the DNA group level to check the reliability of the assay. All strains were correctly identified at the DNA group level. PCR-amplified 16S and 23S rDNA restriction analysis is both an accurate and rapid method for the identification of Acinetobacter at the DNA group level.