Evaluation of the ability of a commercial system to identify Acinetobacter genomic species

Evaluation of Vitek-MS™ and Microflex LT™ commercial systems for identification of Acinetobacter calcoaceticus-baumannii complex

INTRODUCTION

Acinetobacter is a genus that comprises a group of opportunistic pathogens responsible for a variety of nosocomial infections. The Acinetobacter calcoaceticus-Acinetobacter baumannii (Acb) complex includes some species of clinical importance, mainly A. baumannii, A. pittii and A. nosocomialis, which share phenotypic similarities that make it very difficult to distinguish between them using a phenotypic approach. The aim of this study was to evaluate two commercial matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) systems for the identification of different Acinetobacter species, with a special focus among those belonging to the Acb complex.

METHODS

One hundred and fifty-six Acinetobacter spp. clinical strains, identified by amplified ribosomal DNA restriction analysis (ARDRA) and rpoB gene sequencing, were analysed by two different MALDI-TOF systems.

RESULTS

Considering only the 144 strains of the Acb complex evaluated in this study, the Vitek-MS™ and Microflex LT™ systems correctly identified 129 (89.6%) and 143 (99.3%) strains, respectively.

CONCLUSION

After analysing 156 strains belonging to Acinetobacter spp., both Vitek-MS™ and Microflex LT™ proved to be rapid and accurate systems for the identification of Acb complex species showing a good correlation. However, both manufacturers should improve their databases to include new species in them.

Accurate identification of clinically important Acinetobacter spp.: an update

Acinetobacter species have emerged as one of the most clinically important pathogens. The phenotypic techniques which are currently available are insufficient in accurately identifying and differentiating the closely related and clinically important Acinetobacter species. Here, we discuss the advantages and limitations of the conventional phenotypic methods, automated identification systems, molecular methods and MALDI-TOF in the precise identification and differentiation of Acinetobacter species. More specifically, several species of this genus are increasingly reported to be of high clinical importance. Molecular characterization such as of bla_OXA-51-like PCR together with rpoB sequencing has high discriminatory power over the conventional methods for Acinetobacter species identification, especially within the Acinetobacter calcoaceticus–Acinetobacter baumannii complex.

Acinetobacter species are considered to be one of the most important pathogens and associated with increased mortality. The species within the Acinetobacter calcoaceticus–Acinetobacter baumannii complex have emerged as high priority pathogens, especially in intensive care units, thereby posing a challenge to infection management practices. However, identification of Acinetobacter to the species level is difficult. Clear differentiation among various Acinetobacter species with available standard biochemical methods and automated systems is challenging. Although various molecular methods are available, they are not regularly used in diagnostic laboratories. The advantages and disadvantages of different methods useful in the accurate identification of Acinetobacter species are discussed in this review.

Reporting identification of Acinetobacter spp genomic species: A nationwide proficiency study in Spain

Acinetobacter baumannii is the most important genomic species of Acinetobacter from a clinical and epidemiological point of view. Nevertheless, genomic species other than A. baumannii are increasingly recognized as nosocomial pathogens. Molecular methods of identification (genotypic and proteomic assays) are more accurate and reliable and have greater discriminatory power than phenotypic methods. Eleven genomic species of Acinetobacter spp. (8 A. baumannii, 1 A. pittii, 1 A. nosocomialis and 1 A. lwoffii) with different antimicrobial resistance phenotypes and mechanisms of resistance to antimicrobial agents were sent to 48 participating Spanish centers to evaluate their ability for correct identification at the genomic species level. Identification of the genomic species was performed at the two Clinical Microbiology reference laboratories (Hospital Universitario Virgen Macarena, Seville, Spain; and Complejo Hospitalario Universitario de A Coruña, A Coruña, Spain) by partial DNA sequencing of the rpoB gene and MALDI-TOF. The mean percentage of agreement was 76.1%. Fifty percent of CC-01 (A. pittii) and 50% of CC-02 (A. nosocomialis) identification results were reported as A. baumannii. Discrepancies by type of systems used for identification were: MicroScan WA (51.1%), Vitek 2 (19.5%), MALDI-TOF (18.0%), Phoenix (4.5%), Wider (3.8%) and API 20 NE (3.0%). In conclusion, clinical microbiology laboratories must improve their ability to correctly identify the most prevalent non A. baumannii genomic species.

World-wide variation in incidence of Acinetobacter associated ventilator associated pneumonia: a meta-regression

Background

Acinetobacter species such as Acinetobacter baumanii are of increasing concern in association with ventilator associated pneumonia (VAP). In the ICU, Acinetobacter infections are known to be subject to seasonal variation but the extent of geographic variation is unclear. The objective here is to define the extent and possible reasons for geographic variation for Acinetobacter associated VAP whether or not these isolates are reported as Acinetobacter baumanii.

Methods

A meta-regression model of VAP associated Acinetobacter incidence within the published literature was undertaken using random effects methods. This model incorporated group level factors such as proportion of trauma admissions, year of publication and reporting practices for Acinetobacter infection.

Results

The search identified 117 studies from seven worldwide regions over 29 years. There is significant variation in Acinetobacter species associated VAP incidence among seven world-wide regions. The highest incidence is amongst reports from the Middle East (mean; 95 % confidence interval; 8.8; 6 · 2–12 · 7 per 1000 mechanical ventilation days) versus that from North American ICU’s (1 · 2; 0 · 8–2 · 1). There is a similar geographic related disparity in incidence among studies reporting specifically as Acinetobacter baumanii. The incidence in ICU’s with a majority of admission being for trauma is >2.5 times that of other ICU’s.

Conclusion

There is greater than fivefold variation in Acinetobacter associated VAP among reports from various geographic regions worldwide. This variation is not explainable by variations in rates of VAP overall, admissions for trauma, publication year or Acinetobacter reporting practices as group level variables.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-016-1921-4) contains supplementary material, which is available to authorized users.

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.

A retrospective study of the incidence, clinical characteristics, identification, and antimicrobial susceptibility of bacteremic isolates of Acinetobacter ursingii

BACKGROUND

Acinetobacter ursingii bacteremia is rarely reported. We investigated the incidence and clinical features of A. ursingii bacteremia, performance of the identification system, and antimicrobial susceptibility of the isolates. Acinetobacter ursingii bacteremia patients were compared with A. baumannii bacteremia patients.

METHODS

In this 9-year retrospective study, A. ursingii was identified using 16S rRNA and 16S-23S rRNA internal transcribed spacer sequence analysis. The performances of the Vitek 2, Phoenix, and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometer systems for identifying isolates were tested. Pulsed-field gel electrophoresis (PFGE) was used to determine the clonality of the isolates. The minimal inhibitory concentrations of the antimicrobials were determined using the Vitek 2 system.

RESULTS

Nineteen patients were identified. Acinetobacter ursingii was noted in 1.5-5.2 % of all Acinetobacter bacteremia cases. For the PFGE analysis, two isolates had smeared DNA, two had 93 % similarity, and 15 had similarity <80 %. Among 16 patients with complete medical records, 10 (62.5 %) had no identifiable source of A. ursingii bacteremia. Most patients (n = 12) had underlying malignant disease. Patients with A. ursingii bacteremia had lower Acute Physiology and Chronic Health Evaluation II scores than those with A. baumannii bacteremia (median [interquartile range], 17.1 [10.0-24.7] vs. 24.9 [14.6-35.1]). Patients with A. ursingii bacteremia were also less likely admitted to the intensive care unit than patients with A. baumannii bacteremia (18.8 % vs 63.5 %, p value < 0.01). About half of the patients with A. ursingii (50.8 %) and A. baumannii bacteremia (62.5 %) had received inappropriate antimicrobial therapy within 48 h after bacteremia onset. However, patients with A. ursingii bacteremia had significantly lower 14-day (6.25 % vs 29.8 %, p value = 0.04) and 28-day mortality rates (6.25 % vs 37.3 %, p value = 0.02) than patients with A. baumannii bacteremia. Nine isolates (47.4 %) were correctly identified as A. ursingii and the other 10 isolates (52.6 %) were incorrectly identified as A. lwoffii by the Vitek 2 system. The Phoenix system incorrectly identified all 19 isolates. The MALDI-TOF mass spectrometer system correctly identified all 19 isolates. All the A. ursingii isolates were resistant or showed intermediate susceptibility to ceftriaxone and ceftazidime, but were susceptible to levofloxacin and imipenem.

CONCLUSIONS

Acinetobacter ursingii is a rare pathogen that mostly caused primary bacteremia in patients with malignancies. Patients with A. ursingii bacteremia had significantly lower disease severity and mortality rates than patients with A. baumannii bacteremia.

Use of 16S rRNA gene for identification of a broad range of clinically relevant bacterial pathogens

According to World Health Organization statistics of 2011, infectious diseases remain in the top five causes of mortality worldwide. However, despite sophisticated research tools for microbial detection, rapid and accurate molecular diagnostics for identification of infection in humans have not been extensively adopted. Time-consuming culture-based methods remain to the forefront of clinical microbial detection. The 16S rRNA gene, a molecular marker for identification of bacterial species, is ubiquitous to members of this domain and, thanks to ever-expanding databases of sequence information, a useful tool for bacterial identification. In this study, we assembled an extensive repository of clinical isolates (n = 617), representing 30 medically important pathogenic species and originally identified using traditional culture-based or non-16S molecular methods. This strain repository was used to systematically evaluate the ability of 16S rRNA for species level identification. To enable the most accurate species level classification based on the paucity of sequence data accumulated in public databases, we built a Naïve Bayes classifier representing a diverse set of high-quality sequences from medically important bacterial organisms. We show that for species identification, a model-based approach is superior to an alignment based method. Overall, between 16S gene based and clinical identities, our study shows a genus-level concordance rate of 96% and a species-level concordance rate of 87.5%. We point to multiple cases of probable clinical misidentification with traditional culture based identification across a wide range of gram-negative rods and gram-positive cocci as well as common gram-negative cocci.

Evaluation of matrix-assisted laser desorption ionization-time of flight mass spectrometry-based VITEK MS system for the identification of Acinetobacter species from blood cultures: comparison with VITEK 2 and MicroScan systems

Background

Acinetobacter species are the leading cause of bloodstream infection (BSI), but their correct identification is challenging. We evaluated the matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS)-based VITEK MS (bioMérieux, France), and two automated systems, VITEK 2 (bioMérieux) and MicroScan (Siemens, USA) for identification of Acinetobacter BSI isolates.

Methods

A total of 187 BSI isolates recovered at a university hospital in Korea between 2010 and 2012 were analyzed. The identification results obtained using VITEK MS and two automated systems were compared with those of rpoB sequencing.

Results

Of 187 isolates analyzed, 176 were identified to the species level by rpoB sequencing: the Acinetobacter baumannii group (ABG; 101 A. baumannii, 43 A. nosocomialis, 10 A. pittii isolates) was most commonly identified (82.4%), followed by Acinetobacter genomic species 13BJ/14TU (5.3%), A. ursingii (2.1%), A. soli (2.1%), A. bereziniae (1.1%), and A. junii (1.1%). Correct identification rates to the species group (ABG) level or the species level was comparable among the three systems (VITEK MS, 90.3%; VITEK 2, 89.2%; MicroScan, 86.9%). However, VITEK MS generated fewer misidentifications (0.6%) than VITEK 2 (10.8%) and MicroScan (13.1%) (P<0.001). In addition, VITEK MS demonstrated higher specificity (100%) for discrimination between ABG and non-ABG isolates than the other systems (both, 31.8%) (P<0.001).

Conclusions

The VITEK MS system is superior to the VITEK 2 and MicroScan systems for identification of Acinetobacter BSI isolates, with fewer misidentifications and better discrimination between the ABG and non-ABG isolates.

Identification, genotypic relation, and clinical features of colistin-resistant isolates of Acinetobacter genomic species 13BJ/14TU from bloodstreams of patients in a university hospital

Colistin resistance remains rare among clinical isolates of Acinetobacter species. We noted the emergence of colistin-resistant bloodstream isolates of the Acinetobacter genomic species (GS) 13BJ/14TU from patients at a university hospital between 2003 and 2011. We report here, for the first time, the microbiological and molecular characteristics of these isolates, with clinical features of Acinetobacter GS 13BJ/14TU bacteremia. All 11 available patient isolates were correctly identified as Acinetobacter GS 13BJ/14TU using partial rpoB gene sequencing but were misidentified using the phenotypic methods Vitek 2 (mostly as Acinetobacter baumannii), MicroScan (mostly as A. baumannii/Acinetobacter haemolyticus), and the API 20 NE system (all as A. haemolyticus). Most isolates were susceptible to commonly used antibiotics, including carbapenems, but all were resistant to colistin, for which it is unknown whether the resistance is acquired or intrinsic. However, the fact that none of the patients had a history of colistin therapy strongly suggests that Acinetobacter GS 13BJ/14TU is innately resistant to colistin. The phylogenetic tree of multilocus sequence typing (MLST) showed that all 11 isolates formed a separate cluster from other Acinetobacter species and yielded five sequence types. However, pulsed-field gel electrophoresis (PFGE) revealed 11 distinct patterns, suggesting that the bacteremia had occurred sporadically. Four patients showed persistent bacteremia (6 to 17 days), and all 11 patients had excellent outcomes with cleared bacteremia, suggesting that patients with Acinetobacter GS 13BJ/14TU-associated bacteremia show a favorable outcome. These results emphasize the importance of precise species identification, especially regarding colistin resistance in Acinetobacter species. In addition, MLST offers another approach to the identification of Acinetobacter GS 13BJ/14TU, whereas PFGE is useful for genotyping for this species.

Multiplex PCR to detect the genes encoding naturally occurring oxacillinases in Acinetobacter spp

OBJECTIVES

Bacteria of the genus Acinetobacter are increasingly being isolated in hospitals and are recognized as emerging nosocomial pathogens. Species identification is difficult and there is a need for simple molecular methods to differentiate between the species. Naturally occurring oxacillinase genes (blaOXA) have been identified in several Acinetobacter species and their detection by PCR can aid in species identification. The aim of this study was to develop a multiplex PCR to identify intrinsic blaOXA genes (i.e. bla(OXA-134-like), bla(OXA-211-like), bla(OXA-213-like), bla(OXA-214-like) and bla(OXA-228-like)) from Acinetobacter spp. for use as a tool for rapid species identification.

METHODS

Primers were designed to selectively amplify internal fragments of intrinsic blaOXA from Acinetobacter lwoffii/Acinetobacter schindleri (bla(OXA-134-like)), Acinetobacter johnsonii (bla(OXA-211-like)), Acinetobacter calcoaceticus (bla(OXA-213-like)), Acinetobacter haemolyticus (bla(OXA-214-like)) and Acinetobacter bereziniae (bla(OXA-228-like)). Multiplex PCR was performed in a total of 100 Acinetobacter isolates. Flanking primers were designed for each blaOXA subgroup and products were sequenced.

RESULTS

All A. lwoffii, A. schindleri, A. johnsonii, A. calcoaceticus, A. haemolyticus and A. bereziniae isolates were positive for their species-specific amplicons while other Acinetobacter species were negative. Thirty blaOXA novel variants were identified; the majority of these (21/30) were from A. calcoaceticus. ISAba11 was found upstream of bla(OXA-214) in four A. haemolyticus isolates, but was not associated with carbapenem resistance.

CONCLUSIONS

This multiplex PCR specifically detected each of the five different blaOXA subgroups. Therefore, this method has the potential to aid in the identification of these species and monitor the spread of these genes into other Acinetobacter species.

The Acinetobacter baumannii Oxymoron: Commensal Hospital Dweller Turned Pan-Drug-Resistant Menace

During the past few decades Acinetobacter baumannii has evolved from being a commensal dweller of health-care facilities to constitute one of the most annoying pathogens responsible for hospitalary outbreaks and it is currently considered one of the most important nosocomial pathogens. In a prevalence study of infections in intensive care units conducted among 75 countries of the five continents, this microorganism was found to be the fifth most common pathogen. Two main features contribute to the success of A. baumannii: (i) A. baumannii exhibits an outstanding ability to accumulate a great variety of resistance mechanisms acquired by different mechanisms, either mutations or acquisition of genetic elements such as plasmids, integrons, transposons, or resistant islands, making this microorganism multi- or pan-drug-resistant and (ii) The ability to survive in the environment during prolonged periods of time which, combined with its innate resistance to desiccation and disinfectants, makes A. baumannii almost impossible to eradicate from the clinical setting. In addition, its ability to produce biofilm greatly contributes to both persistence and resistance. In this review, the pathogenesis of the infections caused by this microorganism as well as the molecular bases of antibacterial resistance and clinical aspects such as treatment and potential future therapeutic strategies are discussed in depth.

Diverse responses to UV light exposure in Acinetobacter include the capacity for DNA damage-induced mutagenesis in the opportunistic pathogens Acinetobacter baumannii and Acinetobacter ursingii

Error-prone and error-free DNA damage repair responses that are induced in most bacteria after exposure to various chemicals, antibiotics or radiation sources were surveyed across the genus Acinetobacter. The error-prone SOS mutagenesis response occurs when DNA damage induces a cell's umuDC- or dinP-encoded error-prone polymerases. The model strain Acinetobacter baylyi ADP1 possesses an unusual, regulatory umuD allele (umuDAb) with an extended 5' region and only incomplete fragments of umuC. Diverse Acinetobacter species were investigated for the presence of umuDC and their ability to conduct UV-induced mutagenesis. Unlike ADP1, most Acinetobacter strains possessed multiple umuDC loci containing either umuDAb or a umuD allele resembling that of Escherichia coli. The nearly omnipresent umuDAb allele was the ancestral umuD in Acinetobacter, with horizontal gene transfer accounting for over half of the umuDC operons. Despite multiple umuD(Ab)C operons in many strains, only three species conducted UV-induced mutagenesis: Acinetobacter baumannii, Acinetobacter ursingii and Acinetobacter beijerinckii. The type of umuDC locus or mutagenesis phenotype a strain possessed was not correlated with its error-free response of survival after UV exposure, but similar diversity was apparent. The survival of 30 Acinetobacter strains after UV treatment ranged over five orders of magnitude, with the Acinetobacter calcoaceticus-A. baumannii (Acb) complex and haemolytic strains having lower survival than non-Acb or non-haemolytic strains. These observations demonstrate that a genus can possess a range of DNA damage response mechanisms, and suggest that DNA damage-induced mutation could be an important part of the evolution of the emerging pathogens A. baumannii and A. ursingii.

gyrB multiplex PCR to differentiate between Acinetobacter calcoaceticus and Acinetobacter genomic species 3

A previously established multiplex PCR that identifies to the species level Acinetobacter baumannii and Acinetobacter genomic species 13TU (GS13TU) was expanded to include Acinetobacter calcoaceticus and Acinetobacter genomic species 3.

Bacteremia due to Acinetobacter genomic species 10

Six patients with Acinetobacter genomic species 10 bacteremia were identified. The clinical features of the patients, phenotypic and genotypic identifications, antimicrobial susceptibilities, and genes flanking ISAba1 of the bacteria were described. The results revealed that this bacterium is a potentially lethal pathogen that can cause health care-associated infections in debilitated patients.

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 strains IH9 and OCI1, two rhizospheric phosphate solubilizing isolates able to promote plant growth, constitute a new genomovar of Acinetobacter calcoaceticus

During a screening of phosphate solubilizing bacteria (PSB) in agricultural soils, two strains, IH9 and OCI1, were isolated from the rhizosphere of grasses in Spain, and they showed a high ability to solubilize phosphate in vitro. Inoculation experiments in chickpea and barley were conducted with both strains and the results demonstrated their ability to promote plant growth. The 16S rRNA gene sequences of these strains were nearly identical to each other and to those of Acinetobacter calcoaceticus DSM 30006(T), as well as the strain CIP 70.29 representing genomospecies 3. Their phenotypic characteristics also coincided with those of strains forming the A. calcoaceticus-baumannii complex. They differed from A. calcoaceticus in the utilization of l-tartrate as a carbon source and from genomospecies 3 in the use of d-asparagine as a carbon source. The 16S-23S intergenic spacer (ITS) sequences of the two isolates showed nearly 98% identities to those of A. calcoaceticus, confirming that they belong to this phylogenetic group. However, the isolates appeared as a separate branch from the A. calcoaceticus sequences, indicating their molecular separation from other A. calcoaceticus strains. The analysis of three housekeeping genes, recA, rpoD and gyrB, confirmed that IH9 and OCI1 form a distinct lineage within A. calcoaceticus. These results were congruent with those from DNA-DNA hybridization, indicating that strains IH9 and OCI1 constitute a new genomovar for which we propose the name A. calcoaceticus genomovar rhizosphaerae.

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.

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.

Comparison of one-tube multiplex PCR, automated ribotyping and intergenic spacer (ITS) sequencing for rapid identification of Acinetobacter baumannii

Acinetobacter baumannii has emerged as a serious cause of nosocomial infections. Rapid identification of this pathogen is required so that appropriate therapy can be given and outbreaks controlled. This study evaluated a multiplex PCR and an automated ribotyping system for the rapid identification of Acinetobacter baumannii. In total, 22 different reference strains and 138 clinical isolates of Acinetobacter spp., identified by 16S-23S rRNA intergenic spacer (ITS) sequence analysis, were evaluated. All A. baumannii isolates (82 clinical isolates and one reference strain) were identified by the multiplex PCR method (specificity 100%). The sensitivity and specificity of the ribotyping system for identification of A. baumannii were 85.5% (71/83) and 93.5% (72/77), respectively. An additional 100 clinical isolates belonging to the Acinetobacter calcoaceticus-A. baumannii complex were used to compare these two methods for identification of A. baumannii, and this comparison revealed a level of disagreement of 14% (14 isolates). The accuracy of the multiplex PCR was 100%, which was confirmed by sequence analysis of the ITS and recA gene of these isolates. Thus, the multiplex PCR method dramatically increased the efficiency and speed of A. baumannii identification.

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.

Nosocomial bacteremia due to an as yet unclassified acinetobacter genomic species 17-like strain

We describe a case of bacteremia due to an as yet unclassified Acinetobacter genomic species 17-like strain. The recognition of this microorganism as non-Acinetobacter baumannii may have important epidemiological implications, as it relieves the hospital of the implementation of barrier precautions for patients infected or colonized as may be necessary with a multiresistant A. baumannii epidemic.

Bacterial identification, clinical significance, and antimicrobial susceptibilities of Acinetobacter ursingii and Acinetobacter schindleri, two frequently misidentified opportunistic pathogens

The species belonging to the Acinetobacter genus are currently reported as opportunistic pathogens in hospitalized patients with underlying predispositions. However, except for the Acinetobacter calcoaceticus-Acinetobacter baumannii complex, the identification of other species is frequently unreliable, especially for Acinetobacter ursingii and Acinetobacter schindleri, newly described in 2001. Thus, the clinical significance, phenotypic features, and antimicrobial susceptibilities of these two misidentified species remain unclear. Of 456 Acinetobacter sp. clinical strains isolated from 2002 to 2005 in Henri Mondor Hospital, 15 isolates (10 A. ursingii and 5 A. schindleri isolates) were studied. They were characterized using a phenotypic approach (API 20 NE and VITEK 2 systems), 16S rRNA gene sequencing, and susceptibility to antimicrobial agents with evaluation of impact in clinical relevance. The two corresponding type strains were also included for comparison. All isolates were identified to the species level using molecular tools, whereas the phenotypic methods remained unreliable due to the absence of these two species in the manufacturers' databases. However, the API 20 NE system appeared to be a reasonably reliable phenotypic alternative for the identification of A. ursingii when the numerical code 0000071 was found. Conversely, no discriminative phenotypic alternative existed for A. schindleri isolates. Concerning antimicrobial susceptibility, A. ursingii strains appeared to be more resistant to antibiotics than A. schindleri strains, which could imply therapeutic consequences. Finally, the prevalence of infections caused by A. ursingii and A. schindleri (representing 9.7% and 4.8% of non-A. calcoaceticus-A. baumannii complex strains, respectively) seems to be underestimated.

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

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

OPPORTUNITIES FOR GENETIC INVESTIGATION AFFORDED BYACINETOBACTER BAYLYI, A NUTRITIONALLY VERSATILE BACTERIAL SPECIES THAT IS HIGHLY COMPETENT FOR NATURAL TRANSFORMATION

The genetic and physiological properties of Acinetobacter baylyi strain ADP1 make it an inviting subject for investigation of the properties underlying its nutritional versatility. The organism possesses a relatively small genome in which genes for most catabolic functions are clustered in several genetic islands that, unlike pathogenicity islands, give little evidence of horizontal transfer. Coupling mutagenic polymerase chain reaction to natural transformation provides insight into how structure influences function in transporters, transcriptional regulators, and enzymes. With appropriate selection, mutants in which such molecules have acquired novel function may be obtained. The extraordinary competence of A. baylyi for natural transformation and the ease with which it expresses heterologous genes make it a promising platform for construction of novel metabolic systems. Steps toward this goal should take into account the complexity of existing pathways in which transmembrane trafficking plays a significant role.

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.

Manual and automated instrumentation for identification of Enterobacteriaceae and other aerobic gram-negative bacilli

Identification of gram-negative bacilli, both enteric and nonenteric, by conventional methods is not realistic for clinical microbiology laboratories performing routine cultures in today's world. The use of commercial kits, either manual or automated, to identify these organisms is a common practice. The advent of rapid or "spot" testing has eliminated the need for some commonly isolated organisms to be identified with the systems approach. Commercially available systems provide more in-depth identification to the species level as well as detect new and unusual strains. The answers obtained from these systems may not always be correct and must be interpreted with caution. The patient demographics, laboratory workload and work flow, and technologist's skill levels should dictate the system of choice. Cost considerations introduce another variable into the equation affecting choice. Each system has its own strengths and weaknesses, and each laboratory must decide on the level of sophistication that fulfills its particular needs.

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.

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.

Prevalence and in-vitro antimicrobial susceptibility patterns of Acinetobacter strains isolated from patients in intensive care units

Fifty-six Acinetobacter species strains (49 Acinetobacter baumanii, 5 Acinetobacter calcoaceticus, 2 Acinetobacter iwoffii) were detected using both conventional methods and gas chromatography of bacterial fatty acids with the MIDI Sherlock Microbial Identification System. The susceptibilities of these strains to 16 antimicrobial agents were investigated by the disc-diffusion method according to the National Committee for Clinical Laboratory Standards. The production of extended-spectrum beta-lactamases (ESBLs) and inducible beta-lactamases (IBLs) by the strains were investigated by the double-disc-synergy and disc-approximation methods, respectively. Imipenem was the most effective agent for Acinetobacter baumanii strains (95.9% of strains were sensitive), while meropenem and netilmicin showed moderate activity (87.7% and 79.6% of strains, respectively, responded). Acinetobacter baumanii strains were less sensitive to cefoperazone-sulbactam (53.1%), ofloxacin (51.0%), ciprofloxacin (42.8%), and amikacin (36.7%). Acinetobacter calcoaceticus and Acinetobacter iwoffii strains were sensitive to imipenem, meropenem and netilmicin. IBLs and ESBLs were produced, respectively, by 8.9% and 7.1% of all bacterial strains. The strains isolated were sufficiently sensitive to imipenem, but not to ofloxacin or ciprofloxacin, and were very resistant to amikacin.

Bacteremia caused by Acinetobacter ursingii

Acinetobacter ursingii has not been reported in infectious processes apart from its recent description as a new species. A bacteremia caused by A. ursingii in a patient with a pulmonary adenocarcinoma confirms that this microorganism is an opportunistic human pathogen. The isolate was susceptible to imipenem, aminoglycosides, rifampin, and fluoroquinolones.

Environmental contamination during a carbapenem-resistant Acinetobacter baumannii outbreak in an intensive care unit

During a three-month period in 1999, 25 strains of carbapenem resistant Acinetobacter baumannii were isolated from 12 of 170 hospitalized intensive care unit (ICU) patients, of which 16 were considered to be clinically significant. These strains were indistinguishable by biotyping and antibiograms, but genotyping was not performed. Appropriate antibiotic treatment, isolation precautions, and infection control education of the staff failed to halt the outbreak. Environmental contamination was therefore investigated, and A. baumannii was found out in 22 (39.3%) of 56 environmental samples obtained by swabbing. Different antibiotic sensitivity patterns were obtained in the majority of these isolates, but four (7.1%) of the strains were found to have the same sensitivity pattern as the strain causing the outbreak. As a result the ICU was closed, equipment and the environment cleaned, with hypochlorite and terminal disinfection carried out. No bacteria were grown on repeat environmental cultures. Environmental contamination has an important reservoir role in outbreaks of A. baumannii in ICUs and must be eradicated in order to overcome such outbreaks.

Outbreak of a susceptible strain of Acinetobacter species 13 (sensu Tjernberg and Ursing) in an adult neurosurgical intensive care unit

Between December 1999 and June 2000, an outbreak caused by Acinetobacter emerged on the neurosurgical intensive care unit of our hospital. It was shown using automated ribotyping using Eco RI and pulsed-field gel electrophoresis that the outbreak was caused by spread of a single strain, which was identified by ribotyping and amplified ribosomal DNA restriction analysis as Acinetobacter DNA group 13TU (sensu Tjernberg and Ursing). The outbreak strain, which showed no antibiotic resistance, was identified in 23 patients, five of whom developed an infection. The organism was also isolated from various environmental sites. Cross-transmission among patients continued despite contact isolation of colonized patients and reinforcement of basic disinfection procedures. Eventually, after implementation of additional stringent measures such as cohorting of positive patients and daily disinfection of the floor, the outbreak was brought under control. This study demonstrates that apart from Acinetobacter baumanii, Acinetobacter 13TU strains, even when they are fully susceptible, may cause outbreaks that are difficult to control. Correct identification to the species level of Acinetobacter by genotypic methods is necessary to get insight in the importance of the different Acinetobacter genomic species in hospital epidemiology.

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.

Antibiotic resistance is a major risk factor for epidemic behavior of Acinetobacter baumannii

OBJECTIVE

To study the presence of bacterial factors in clinical isolates of Acinetobacter species in order to identify markers of epidemic potential.

DESIGN

Case-control study.

METHODS

Forty-six isolates of Acinetobacter species, including 23 epidemic and 23 sporadic strains from different outbreaks in nine European countries, were compared for the presence of the following factors: hemagglutination, presence of capsules and fimbriae, binding to salivary mucins, resistance to drying, and antibiogram typing. Genotyping of all strains was performed by amplified fragment-length polymorphism (AFLP).

RESULTS

All outbreak strains except two (91%) were identified as Acinetobacter baumannii. Binding to salivary mucins and resistance to antibiotics were significantly associated with epidemic behavior. Antibiogram typing showed clustering of predominantly A baumannii strains within one group, and these strains were significantly more resistant to antibiotics than sporadic strains. AFLP genotyping revealed a great heterogeneity among the different European Acinetobacter strains. Cluster analysis of AFLP fingerprints showed several small clusters of different A baumannii outbreak strains. AFLP genotyping could not identify a common epidemic marker within the strains studied.

CONCLUSIONS

Antibiogram typing can be used in routine clinical laboratories as a screening method to recognize potentially epidemic A baumannii strains. Several other factors were found, both in different outbreaks as well as in sporadic Acinetobacter isolates. These characteristics were unable to predict epidemic behavior and therefore cannot be used as discriminative epidemic markers. AFLP genotyping demonstrated no common clonal origin of European epidemic A baumannii strains. This indicates that any clinical A baumannii isolate with resistance to multiple antibiotics can be a potential nosocomial outbreak strain.

Recognition of two novel phenons of the genus Acinetobacter among non-glucose-acidifying isolates from human specimens

Genomic species diversity among 147 Acinetobacter clinical isolates not belonging to the A. calcoaceticus- A. baumannii (ACB) complex was investigated by phenotypic and genotypic identification methods. The isolates were obtained between 1991 and 1999 from numerous diagnostic laboratories in the Czech Republic and were studied by numerical probabilistic identification using two biochemical frequency matrices and amplified rDNA restriction analysis (ARDRA). Their final identification was derived from the combined phenotypic and ARDRA results. In total, 102 isolates were unambiguously (n = 89) or presumptively (n = 13) identified as A. lwoffii (n = 63), genomic species 13BJ/14TU (n = 9), A. johnsonii (n = 7), A. haemolyticus (n = 6), A. junii (n = 5), and other genomic species (n < 5 isolates each). Forty-five isolates could not be identified as belonging to any described species. Among the unidentified isolates two large groups of non-glucose-acidifying, nonhemolytic, and non-gelatinase-producing isolates were distinguished. These groups, designated phenon 1 (n = 17) and phenon 2 (n = 15), had distinctive phenotypic features and novel ARDRA profiles, which suggests that they represent hitherto undescribed Acinetobacter species. Phenon 2 included mainly clinically insignificant isolates from outpatients, while phenon 1 comprised clinically relevant isolates mostly from the blood of hospitalized patients, and its precise taxonomic definition may therefore be of medical importance. Overall, the development of practical methods for identification required for the elucidation of the biological significance of the (genomic) species within the genus Acinetobacter remains a challenging task.

Acinetobacter baumannii-infected vascular catheters collected from horses in an equine clinic

Acinetobacter baumannii was isolated from tips clipped from seven intravenous jugular catheters collected from horses in the Ghent University equine clinic. They originated from seven different horses. Three of the seven showed evidence of local infection.

Epidemiological study of an Acinetobacter baumannii outbreak by using a combination of antibiotyping and ribotyping

From June to November 1994 (period 1) and from February to June 1995 (period 2), multiresistant Acinetobacter baumannii strains were isolated in intensive care units and surgical wards of the Amiens Teaching Hospital Center (Amiens, France). Eighteen isolates were obtained from 17 (1%) of 1,706 patients admitted during both of these periods, giving an incidence rate of nosocomial infection per 1,000 patient days of 0.6%. Of 17 infected patients, 9 had pneumonia, 3 had urinary tract infection, 2 had peritonitis, 1 had septicemia, 1 had a catheter infection, and 1 had pneumonia and urinary tract infection. According to typing results, four antibiotic resistance profiles were detected: a, b, c, and d; seven ribotypes were distinguished by both restriction enzymes EcoRI and SalI (A, B, C, D, E, F, and G). By combining antibiotyping and ribotyping, we obtained eight groups of strains (groups I to VIII). Group I contained five strains (strains 4, 5, 7, 8, and 9) which had antibiogram pattern a and ribopattern A and constituted the outbreak strains. The strains of group II (strains 3, 10, 11, 13, and 14) were closely related to outbreak strain A and appeared to be variants of ribotype A (A2 [strain 3]; A4 [strain 10]; A5 [strains 11, 13, and 14]). Groups III, IV, V, VI, VII, and VIII included strains which were epidemiologically unrelated to the strains of group I and were considered nonoutbreak strains.

Oil-degrading Acinetobacter strain RAG-1 and strains described as 'Acinetobacter venetianus sp. nov.' belong to the same genomic species

Acinetobacter strain RAG-1 (ATCC 31012) is an industrially important strain which has been extensively characterized with respect to its growth an hydrocarbons and its production of a high molecular mass bioemulsifier, emulsan. Although RAG-1 has been investigated in detail for specific biochemical characteristics, its taxonomic status is uncertain and it is usually referred to as A. lwoffii or A. calcoaceticus sensu lato. However, results obtained by restriction analysis of the amplified rDNA and subsequently substantiated by DNA-DNA hybridization, partial 16S rDNA nucleotide sequence comparison and biochemical characterization indicate that RAG-1 belongs to the genomic species recently described as 'A. venetianus'. Furthermore, these data confirm that 'A. venetianus' constitutes a new and distinct genomic species within the genus Acinetobacter.

Specificity of rabbit antisera against lipopolysaccharide of Acinetobacter

Acinetobacter has been reported to be involved in hospital-acquired infections with increasing frequency. However, clinical laboratories still lack simple methods that allow the accurate identification of Acinetobacter strains at the species level. For this study, proteinase K-digested whole-cell lysates from 44 clinical and environmental isolates were investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting with hyperimmune rabbit sera to examine the possibility of developing a serotyping scheme based on the O antigen of Acinetobacter lipopolysaccharide (LPS). The antisera, obtained by immunization of rabbits with 13 of the heat-killed isolates investigated, were characterized by Western blotting and enzyme immunoassay by using proteinase K-digested whole-cell lysates and phenol-water-extracted LPS as antigens. In both assays, the antisera were shown to be highly specific for the homologous antigen. In addition, assignment of Acinetobacter LPS to the smooth or the rough phenotype was shown not to be reliable when it was based only on the results obtained with silver-stained gels. O-antigen reactivity, determined by Western blot analysis, was observed with 11 of the 31 isolates, most of which belonged to the species Acinetobacter baumannii (DNA group 2) and the unnamed DNA group 3. Interestingly, some O antigens were found in a DNA group different from that of the strain used for immunization. The results indicate that O serotyping of Acinetobacter strains is feasible and thus may provide a simple method for the routine identification of these opportunistic pathogens.

Identification of acinetobacters on blood agar in presence of D-glucose by unique browning effect

A positive phenotypic characteristic of glucose-oxidizing acinetobacters was demonstrated with blood agar containing D-glucose. Glucose-oxidizing Acinetobacter baumannii, Acinetobacter genospecies 3, Acinetobacter lwoffii, and Acinetobacter genospecies 13 sensu Tjernberg and Ursing caused a unique brown discoloration of media supplemented with 5% blood (of horse, sheep, or human origin) and an aldose sugar (0.22 M D-glucose, D-galactose, D-mannose, D-xylose, or lactose). The browning effect was not observed when a ketose sugar (D-fructose or sucrose) was substituted for the aldose sugar or under high osmolarity in the presence of mannitol, glycerol, or sodium chloride. Other gram-negative nonfermenters (non-glucose-oxidizing acinetobacters, Pseudomonas aeruginosa, other Pseudomonas spp., Stenotrophomonas maltophilia, Flavobacterium spp., and Moraxella spp.) did not cause similar discoloration. This novel browning effect may serve as an alternative trait for identifying glucose-oxidizing acinetobacters.

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.

Outbreak of septicaemia in neonates caused by Acinetobacter junii investigated by amplified ribosomal DNA restriction analysis (ARDRA) and four typing methods

Septicaemia caused by Acinetobacter occurred in six infants in the neonatal unit. A total of 18 acinetobacters were isolated from blood cultures, cultures of intravascular catheters, and surveillance cultures. Twelve isolates from the six affected infants were identified as Acinetobacter junii by the use of a novel method, amplified ribosomal DNA restriction analysis (ARDRA). Typing of the organisms using the biochemical profiles of the API 20NE system, antibiogram typing, cell envelope protein electrophoresis, and PCR fingerprinting with two primer sets, ERIC1/ERIC2 and ERIC2/ 1026, showed that these 12 isolates were indistinguishable, whereas the remaining six isolates were different. The six infants recovered after therapy with ciprofloxacin alone in five cases and with a combination of ciprofloxacin and gentamicin in one case. This study showed that A. junii is capable of causing a serious, though non-fatal infection in neonates. The combined use of genotypic and phenotypic methods allowed the rapid separation of epidemic from non-epidemic isolates. It is concluded that for a better understanding of the role of the various Acinetobacter genomic species in human pathology, identification of acinetobacters according to the recent taxonomy is imperative.