Correlation of typing methods for Acinetobacter isolates from hospital outbreaks

A chronic murine model of pulmonary Acinetobacter baumannii infection enabling the investigation of late virulence factors, long-term antibiotic treatments, and polymicrobial infections

Acinetobacter baumannii can cause prolonged infections that disproportionately affect immunocompromised populations. Our understanding of A. baumannii respiratory pathogenesis relies on an acute murine infection model with limited clinical relevance that employs an unnaturally high number of bacteria and requires the assessment of bacterial load at 24-36 hours post-infection. Here, we demonstrate that low intranasal inoculums in immunocompromised mice with a tlr4 mutation leads to reduced inflammation, allowing for persistent infections lasting at least 3 weeks. Using this "chronic infection model," we determined the adhesin InvL is an imperative virulence factor required during later stages of infection, despite being dispensable in the early phase. We also demonstrate that the chronic model enables the distinction between antibiotics that, although initially reduce bacterial burden, either lead to complete clearance or result in the formation of bacterial persisters. To illustrate how our model can be applied to study polymicrobial infections, we inoculated mice with an active A. baumannii infection with Staphylococcus aureus or Klebsiella pneumoniae. We found that S. aureus exacerbates the infection, while K. pneumoniae enhances A. baumannii clearance. In all, the chronic model overcomes some limitations of the acute pulmonary model, expanding our capabilities to study of A. baumannii pathogenesis and lays the groundwork for the development of similar models for other important opportunistic pathogens.

Bacterial Whole Cell Protein Profiling: Methodology, Applications and Constraints

Background:

In the era of modern microbiology, several methods are available for identification and typing of bacteria, including whole genome sequencing. However, in microbiological laboratories or hospitals where genomic based molecular typing methods and/or trained manpower are unavailable, whole cell protein profiling using sodium dodecyl sulfate polyacrylamide gel electrophoresis might be a useful alternative/supplementary method for bacterial identification, strain typing and epidemiology. Whole cell protein profiling by SDS-PAGE is based on the principle that under standard growth conditions, a bacterial strain expresses the same set of proteins, the pattern of which can be used for bacterial identification.

Objective:

The objective of this review is to assess the current status of whole cell protein profiling by SDS-PAGE and its advantages and constraints for bacterial identification and typing.

Results and Conclusions:

Several earlier and recent studies prove the potential and utility of this technique as an adjunct or supplementary method for bacterial identification, strain typing and epidemiology. There is no denying the fact that utility of this technique as an adjunct or supplementary method for bacterial identification and typing has already been demonstrated and its practical applications need to be evaluated further.

ERIC-PCR Genotyping of Acinetobacter baumannii Isolated from Different Clinical Specimens

Background:

Acinetobacter baumannii is a major cause of hospital care-acquired infections, and this bacterium poses a significant challenge to health care worldwide. At King Fahd Hospital of the University (KFHU), Al Khobar, Saudi Arabia, there had been a significant increase in the number of cases of A. baumannii infections.

Objective:

The objective of this study was to determine the clonal relationship between A. baumannii collected from different specimens of patients admitted to KFHU using the enterobacterial repetitive intergenic consensus–polymerase chain reaction (ERIC-PCR) fingerprinting method.

Materials and Methods:

A. baumannii strains were isolated from a total of 59 specimens from inpatients admitted to KFHU between January and September 2014. These specimens were mainly collected from wound, rectal and throat swabs and transtracheal aspiration. ERIC-PCR fingerprinting was used to determine the clonal relationship between the different isolated strains.

Results:

Using ERIC-PCR fingerprinting genotype analysis, 51 strains of A. baumannii were clustered into seven groups, while the remaining 8 were single strains. The genetic relatedness of A. baumannii isolated from admitted patients was high, indicating cross-transmission within the hospitalized patients.

Conclusion:

This study found that the increase in the incidence of A. baumannii in patients at KFHU was likely due to the spread of seven epidemic clones, thereby highlighting the need for intensifying the infection control measures to prevent nosocomial transmission of A. baumannii. These results also demonstrate that ERIC-PCR is a reliable and rapid method for studying the clonal similarity between A. baumannii isolated from different clinical specimens.

Outbreak of Infection WithAcinetobacterStrain RUH 1139 in an Intensive Care Unit

Objective.

To investigate a nosocomial outbreak of infection withAcinetobacterstrain RUH 1139, in the unit of high neonatal risk at University Hospital of The Andes (Mérida, Venezuela).

Methods.

Twenty-eightAcinetobacterstrains were detected by biochemical testing and further identified to the species level by examination of the gene encoding 16S ribosomal DNA, using restriction analysis and gene sequencing. The epidemiological relationship between the strains was established by means of repetitive extragenic palindromic polymerase chain reaction (REP-PCR) and pulsed-field gel electrophoresis (PFGE), and antimicrobial susceptibilities were determined by disk diffusion.

Results.

The spread of an epidemic strain ofAcinetobacterRUH 1139 among 16 patients over a period of 3 months was demonstrated using antimicrobial susceptibility testing, PFGE, and REP-PCR. The epidemic strain was also isolated in 2 of the sampled parenteral nutrition solutions. All the patients involved in the infection outbreak had received parenteral solution. Moreover, strains ofAcinetobacterRUH 1139 with another PFGE pattern and ofA. baumanniiwere sporadically isolated before and during the outbreak.

Conclusion.

This is the first description of an outbreak of infection with this genospecies ofAcinetobacterin which parenteral nutrition solution was potentially the infection source.

Antibiotic-Resistant Acinetobacter baumannii Increasing Success Remains a Challenge as a Nosocomial Pathogen

Antibiotic-resistant infectious bacteria currently imply a high risk and therefore constitute a strong challenge when treating patients in hospital settings. Characterization of these species and of particular strains is a priority for the establishment of diagnostic tests and preventive procedures. The relevance of Acinetobacter baumannii as a problematic microorganism in inpatient facilities, particularly intensive care units, has increased over time. This review aims to draw attention to (i) the historical emergence of carbapenem-resistant Acinetobacter baumannii, (ii) the current status of surveillance needs in Latin America, and (iii) recent data suggesting that A. baumannii continues to spread and evolve in hospital settings. First, we present synopsis of the series of events leading to the discovery and precise identification of this microorganism in hospital settings. Then key events in the acquisition of antibiotic-resistant genes by this microorganism are summarized, highlighting the race between new antibiotic generation and emergence of A. baumannii resistant strains. Here we review the historical development of this species as an infectious threat, the current state of its distribution, and antibiotic resistance characteristics, and we discuss future prospects for its control.

Complete genome sequence of hypervirulent and outbreak-associated Acinetobacter baumannii strain LAC-4: epidemiology, resistance genetic determinants and potential virulence factors

Acinetobacter baumannii is an important human pathogen due to its multi-drug resistance. In this study, the genome of an ST10 outbreak A. baumannii isolate LAC-4 was completely sequenced to better understand its epidemiology, antibiotic resistance genetic determinants and potential virulence factors. Compared with 20 other complete genomes of A. baumannii, LAC-4 genome harbors at least 12 copies of five distinct insertion sequences. It contains 12 and 14 copies of two novel IS elements, ISAba25 and ISAba26, respectively. Additionally, three novel composite transposons were identified: Tn6250, Tn6251 and Tn6252, two of which contain resistance genes. The antibiotic resistance genetic determinants on the LAC-4 genome correlate well with observed antimicrobial susceptibility patterns. Moreover, twelve genomic islands (GI) were identified in LAC-4 genome. Among them, the 33.4-kb GI12 contains a large number of genes which constitute the K (capsule) locus. LAC-4 harbors several unique putative virulence factor loci. Furthermore, LAC-4 and all 19 other outbreak isolates were found to harbor a heme oxygenase gene (hemO)-containing gene cluster. The sequencing of the first complete genome of an ST10 A. baumannii clinical strain should accelerate our understanding of the epidemiology, mechanisms of resistance and virulence of A. baumannii.

Dissemination of Acinetobacter nosocomialis clone among critically ill patients and the environment

We examined the environmental dissemination of Acinetobacter nosocomialis multilocus sequence typing clonal complex 260/71 in Rio de Janeiro, Brazil, including water from a dam and food samples. The increasing use of sequence based methods has demonstrated a large, previously unpredicted, dissemination of bacteria that may serve as opportunistic pathogens.

Comparison of genospecies and antimicrobial resistance profiles of isolates in the Acinetobacter calcoaceticus-Acinetobacter baumannii complex from various clinical specimens

This study was conducted to compare the prevalences of antimicrobial resistance profiles of clinical isolates in the Acinetobacter calcoaceticus-Acinetobacter baumannii complex from sterile and nonsterile sites and to further study the relationship of antimicrobial resistance profiles and genospecies by amplified rRNA gene restriction analysis (ARDRA). A total of 1,381 isolates were tested with 12 different antibiotics to show their antimicrobial susceptibility profiles. A total of 205 clinical isolates were further analyzed by ARDRA of the intergenic spacer (ITS) region of the 16S-23S rRNA gene. It was found that the overall percentage of isolates from nonsterile sites (urine, sputum, pus, or catheter tip) that were resistant to the 12 antibiotics tested was significantly higher than that of isolates from sterile sites (cerebrospinal fluid [CSF], ascites fluid, and bloodstream) (46% versus 22%; P < 0.05). After ARDRA, it was found that 97% of the 62 isolates resistant to all antibiotics tested were the A. baumannii genospecies, which was identified in only 31% of the isolates susceptible to all antibiotics tested. More genospecies diversity was identified in the isolates susceptible to all antibiotics tested, including genospecies of 13TU (34%), genotype 3 (29%), and A. calcoaceticus (5%). Furthermore, as 91% (10/11) of the isolates from CSF were susceptible to all antibiotics tested, the A. calcoaceticus-A. baumannii complex isolates with multidrug resistance could be less invasive than the more susceptible isolates. This study also indicated current emergence of carbapenem-, fluoroquinolone-, aminoglycoside-, and cephalosporin-resistant A. calcoaceticus-A. baumannii complex isolates in Taiwan.

DNA capturing machinery through spore-displayed proteins

AIMS

The purpose of this study was to develop a general method for the facile development of a new DNA biosensor which utilizes streptavidin-displayed spores as a molecular machinery.

METHODS AND RESULTS

Fluorescence spectroscopy was used as a monitoring tool for the streptavidin displayed on the surface of Bacillus thuringiensis spores and as a diagnosis method for DNA detection. As a proof-of-concept, four pathogenic bacteria including Pseudomonas aeruginosa, Acinetobacter baumannii, Escherichia coli and Klebsiella pneumonia were used for the detection of pathogenic species. In addition, a set of mutant variants of Wilson's disease were also used for the detection of single nucleotide polymorphism (SNP) in this system.

CONCLUSIONS

This strategy, utilizing streptavidin-displayed spores, is capable of capturing DNA targets for the detection of pathogenic bacteria and for mutation analysis in Wilson's disease.

SIGNIFICANCE AND IMPACT OF THE STUDY

This approach could be useful as a simple platform for developing sensitive spore-based biosensors for any desired DNA targets in diagnostic applications.

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)).

The population structure of Acinetobacter baumannii: expanding multiresistant clones from an ancestral susceptible genetic pool

Outbreaks of hospital infections caused by multidrug resistant Acinetobacter baumannii strains are of increasing concern worldwide. Although it has been reported that particular outbreak strains are geographically widespread, little is known about the diversity and phylogenetic relatedness of A. baumannii clonal groups. Sequencing of internal portions of seven housekeeping genes (total 2,976 nt) was performed in 154 A. baumannii strains covering the breadth of known diversity and including representatives of previously recognized international clones, and in 19 representatives of other Acinetobacter species. Restricted amounts of diversity and a star-like phylogeny reveal that A. baumannii is a genetically compact species that suffered a severe bottleneck in the recent past, possibly linked to a restricted ecological niche. A. baumannii is neatly demarcated from its closest relative (genomic species 13TU) and other Acinetobacter species. Multilocus sequence typing analysis demonstrated that the previously recognized international clones I to III correspond to three clonal complexes, each made of a central, predominant genotype and few single locus variants, a hallmark of recent clonal expansion. Whereas antimicrobial resistance was almost universal among isolates of these and a novel international clone (ST15), isolates of the other genotypes were mostly susceptible. This dichotomy indicates that antimicrobial resistance is a major selective advantage that drives the ongoing rapid clonal expansion of these highly problematic agents of nosocomial infections.

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.

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.

Use of sequence-based typing and multiplex PCR to identify clonal lineages of outbreak strains of Acinetobacter baumannii

Representatives (n = 31) of outbreak strains of Acinetobacter baumannii from five countries fell into three clear groups, designated Groups 1-3, based on their ompA (outer-membrane protein A), csuE (part of a pilus assembly system required for biofilm formation) and bla(OXA-51-like) (the intrinsic carbapenemase gene in A. baumannii) gene sequences. With the exception of the closely related alleles within the Group 1 clonal complex, alleles at each locus were highly distinct from each other, with a minimum of 14 nucleotide differences between any two alleles. Isolates within a group shared the same combination of alleles at the three loci, providing compelling evidence that the outbreak strains investigated belonged to three clonal lineages. These corresponded to the previously identified European clones I-III. Sequence differences among the alleles were used to design multiplex PCRs to rapidly assign isolates belonging to particular genotypes to sequence groups. In the UK, genotypes belonging to the Group 1 clonal complex have been particularly successful, accounting for the vast majority of isolates referred from hospitals experiencing problems with Acinetobacter.

Guidelines for the validation and application of typing methods for use in bacterial epidemiology

For bacterial typing to be useful, the development, validation and appropriate application of typing methods must follow unified criteria. Over a decade ago, ESGEM, the ESCMID (Europen Society for Clinical Microbiology and Infectious Diseases) Study Group on Epidemiological Markers, produced guidelines for optimal use and quality assessment of the then most frequently used typing procedures. We present here an update of these guidelines, taking into account the spectacular increase in the number and quality of typing methods made available over the past decade. Newer and older, phenotypic and genotypic methods for typing of all clinically relevant bacterial species are described according to their principles, advantages and disadvantages. Criteria for their evaluation and application and the interpretation of their results are proposed. Finally, the issues of reporting, standardisation, quality assessment and international networks are discussed. It must be emphasised that typing results can never stand alone and need to be interpreted in the context of all available epidemiological, clinical and demographical data relating to the infectious disease under investigation. A strategic effort on the part of all workers in the field is thus mandatory to combat emerging infectious diseases, as is financial support from national and international granting bodies and health authorities.

Identification of Acinetobacter species and genotyping of Acinetobacter baumannii by multilocus PCR and mass spectrometry

Members of the genus Acinetobacter are ubiquitous in soil and water and are an important cause of nosocomial infections. A rapid method is needed to genotype Acinetobacter isolates to determine epidemiology and clonality during infectious outbreaks. Multilocus PCR followed by electrospray ionization mass spectrometry (PCR/ESI-MS) is a method that uses the amplicon base compositions to genotype bacterial species. In order to identify regions of the Acinetobacter genome useful for this method, we sequenced regions of six housekeeping genes (trpE, adk, efp, mutY, fumC, and ppa) from 267 isolates of Acinetobacter. Isolates were collected from infected and colonized soldiers and civilians involved in an outbreak in the military health care system associated with the conflict in Iraq, from previously characterized outbreaks in European hospitals, and from culture collections. Most of the isolates from the Iraqi conflict were Acinetobacter baumannii (189 of 216 isolates). Among these, 111 isolates had genotypes identical or very similar to those associated with well-characterized A. baumannii isolates from European hospitals. Twenty-seven isolates from the conflict were found to have genotypes representing different Acinetobacter species, including 8 representatives of Acinetobacter genomospecies 13TU and 13 representatives of Acinetobacter genomospecies 3. Analysis by the PCR/ESI-MS method using nine primer pairs targeting the most information-rich regions of the trpE, adk, mutY, fumC, and ppa genes distinguished 47 of the 48 A. baumannii genotypes identified by sequencing and identified at the species level at least 18 Acinetobacter species. Results obtained with our genotyping method were essentially in agreement with those obtained by pulse-field gel electrophoresis analysis. The PCR/ESI-MS genotyping method required 4 h of analysis time to first answer with additional samples subsequently analyzed every 10 min. This rapid analysis allows tracking of transmission for the implementation of appropriate infection control measures on a time scale previously not achievable.

Differential Roles of CD14 and Toll-like Receptors 4and 2 in MurineAcinetobacterPneumonia

RATIONALE

Acinetobacter baumannii is an opportunistic bacterial pathogen that is increasingly associated with gram-negative nosocomial pneumonia, but the molecular mechanisms that play a role in innate defenses during A. baumannii infection have not been elucidated.

OBJECTIVE

To gain first insight into the role of CD14 and Toll-like receptors 4 and 2 in host response to A. baumannii pneumonia.

METHODS

Respective gene-deficient mice were intranasally infected with A. baumannii, and bacterial outgrowth, lung inflammation, and pulmonary cytokine/chemokine responses were determined. To study the importance of LPS in the inflammatory response, mice were also challenged with A. baumannii LPS.

MEASUREMENTS AND MAIN RESULTS

Bacterial counts were increased in CD14 and Toll-like receptor 4 gene-deficient mice, and only these animals developed bacteremia. The pulmonary cytokine/chemokine response was impaired in Toll-like receptor 4 knockout mice and the onset of lung inflammation was delayed. In contrast, Toll-like receptor 2-deficient animals displayed an earlier cell influx into lungs combined with increased macrophage inflammatory protein-2 and monocyte chemoattractant protein-1 concentrations, which was associated with accelerated elimination of bacteria from the pulmonary compartment. Neither CD14 nor Toll-like receptor 4 gene-deficient mice responded to intranasal administration of LPS, whereas Toll-like receptor 2 knockout mice were indistinguishable from wild-type animals.

CONCLUSIONS

Our results suggest that CD14 and Toll-like receptor 4 play a key role in innate sensing of A. baumannii via the LPS moiety, resulting in effective elimination of the bacteria from the lung, whereas Toll-like receptor 2 signaling seems to counteract the robustness of innate responses during acute A. baumannii pneumonia.

Rapid epidemiological analysis of Acinetobacter strains by Raman spectroscopy

From earlier publications, we noticed that Raman spectra could potentially be used for subspecies identification of microorganisms. Here we evaluated the technique for its use as a typing tool of Acinetobacter species, using a collection of well-characterised strains from five hospital outbreaks. The strains were previously analysed using molecular techniques as cell envelope protein profiling and ribotyping. In this study, we have typed the strains by AFLP analysis and Raman spectroscopy. We compared the results using hierarchical cluster analysis, which showed highly similar groupings by both techniques. There seemed to be some misclassification between two sets of outbreak strains in the Raman analysis. We ascribe this to the clonal relationship between the strains of both outbreaks, described earlier. This results from a highly similar biochemical composition of the strains involved, and hence a highly similar Raman spectrum. We conclude that Raman spectroscopy could be an easy-to-use alternative in epidemiological studies of Acinetobacter strains and a promising starting point for the development of epidemiological studies in general.

Standardization and interlaboratory reproducibility assessment of pulsed-field gel electrophoresis-generated fingerprints of Acinetobacter baumannii

A standard procedure for pulsed-field gel electrophoresis (PFGE) of macrorestriction fragments of Acinetobacter baumannii was set up and validated for its interlaboratory reproducibility and its potential for use in the construction of an Internet-based database for international monitoring of epidemic strains. The PFGE fingerprints of strains were generated at three different laboratories with ApaI as the restriction enzyme and by a rigorously standardized procedure. The results were analyzed at the respective laboratories and also centrally at a national reference institute. In the first phase of the study, 20 A. baumannii strains, including 3 isolates each from three well-characterized hospital outbreaks and 11 sporadic strains, were distributed blindly to the participating laboratories. The local groupings of the isolates in each participating laboratory were identical and allowed the identification of the epidemiologically related isolates as belonging to three clusters and identified all unrelated strains as distinct. Central pattern analysis by using the band-based Dice coefficient and the unweighted pair group method with mathematical averaging as the clustering algorithm showed 95% matching of the outbreak strains processed at each local laboratory and 87% matching of the corresponding strains if they were processed at different laboratories. In the second phase of the study, 30 A. baumannii isolates representing 10 hospital outbreaks from different parts of Europe (3 isolates per outbreak) were blindly distributed to the three laboratories, so that each laboratory investigated 10 epidemiologically independent outbreak isolates. Central computer-assisted cluster analysis correctly identified the isolates according to their corresponding outbreak at an 87% clustering threshold. In conclusion, the standard procedure enabled us to generate PFGE fingerprints of epidemiologically related A. baumannii strains at different locations with sufficient interlaboratory reproducibility to set up an electronic database to monitor the geographic spread of epidemic strains.

Detection and typing of integrons in epidemic strains of Acinetobacter baumannii found in the United Kingdom

Integrons were sought in Acinetobacter isolates from hospitals in the United Kingdom by integrase gene PCR. Isolates were compared by pulsed-field gel electrophoresis, and most belonged to a small number of outbreak strains or clones of A. baumannii, which are highly successful in the United Kingdom. Class 1 integrons were found in all of the outbreak isolates but in none of the sporadic isolates. No class 2 integrons were found. Three integrons were identified among the main outbreak strains and clones. While a particular integron was usually associated with a strain or clone, some members carried a different integron. Some integrons were associated with more than one strain. The cassette arrays of two of the integrons were very similar, both containing gene aacC1, which confers resistance to gentamicin, two open reading frames coding for unknown products (orfX, orfX'), and gene aadA1a, which confers resistance to spectinomycin and streptomycin. The larger of these integrons had two copies of the first (orfX) of the gene cassettes coding for unknown products. The third integron, with a cassette array containing gene aacA4, which codes for amikacin, netilmicin, and tobramycin resistance; a chloramphenicol acetyltransferase, catB8; and gene aadA1, conferring resistance to spectinomycin and streptomycin, was associated with an OXA-23 carbapenemase-producing clone, which has spread rapidly in hospitals in the United Kingdom during 2003 and 2004. These integron cassette arrays have been found in other outbreak strains of A. baumannii from other countries. We conclude that integrons are useful markers for epidemic strains of A. baumannii and that integron typing provides valuable information for epidemiological studies.

Activities of various β-lactams and β-lactam/β-lactamase inhibitor combinations against Acinetobacter baumannii and Acinetobacter DNA group 3 strains

Acinetobacter baumannii and Acinetobacter DNA group 3 are members of the so-called A. calcoaceticus-A. baumannii complex and are important nosocomial pathogens. Multiresistance in these organisms is increasingly frequent, and alternative treatment options are needed. The beta-lactamase inhibitors clavulanate, sulbactam and tazobactam have intrinsic activity against Acinetobacter strains. In the present study, broth microdilution was used to assess the in-vitro activities of currently available beta-lactam/beta-lactamase inhibitor combinations and sulbactam alone against 469 Acinetobacter isolates (A. baumannii, n=395; Acinetobacter DNA group 3, n=74) collected from various laboratories in Germany. Fixed concentrations and fixed ratios of beta-lactamase inhibitors were used. Sulbactam-containing combinations (susceptibility rates of 90.4-92.7% for A. baumannii and 97.3-100% for Acinetobacter DNA group 3) and sulbactam alone were superior to clavulanate- and tazobactam-containing combinations. The activity of sulbactam-containing combinations against members of the A. calcoaceticus-A. baumannii complex was conferred exclusively by the intrinsic activity of the beta-lactamase inhibitor and did not result from enhanced beta-lactam activity. Testing with the inhibitor added at a fixed ratio of inhibitor to beta-lactam appeared to give more reliable results than testing at a fixed concentration of the inhibitor. Resistance to carbapenems (0.3%) remains low in Germany.

Antimicrobial resistance of Acinetobacter spp. in Europe

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

Outbreak of nosocomial meningitis caused by Acinetobacter baumannii in neurosurgical patients

An outbreak of nosocomial meningitis caused by Acinetobacter baumannii, which developed postoperatively in seven neurosurgical patients is described. The clinical isolates of A. baumannii were typed by biochemical profiles and antibiogram patterns, and by random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) and amplified fragment length polymorphism (AFLP) fingerprinting. The implicated strain was multi-drug resistant, however, susceptibility to imipenem and netilmicin was detected. An extensive search for the environmental source of the epidemic strain was carried out. Two of several isolates from hospital environment, corresponded to the A. baumannii outbreak strain, one being cultured from the suctioning equipment used in the care of these patients. The introduction of multiresistant epidemic A. baumannii into a neurosurgical unit is a severe risk factor for patients undergoing neurosurgical procedures. Genotypic typing methods are important for definitive identification of these strains in patients and their environment.

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.

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.

Efficacy of two DNA fingerprinting methods for typing Acinetobacter baumannii isolates

Performance of macrorestriction and repetitive extragenic palindromic DNA sequence-based PCR (REP-PCR) to type Acinetobacter baumannii isolates was quantitatively estimated using a test population of 54 outbreak-related, 29 endemic infection-related and 17 epidemiologically-unrelated isolates. Reproducibility and stability for macrorestriction were 100%, and REP-PCR showed only slightly lower stability. Macrorestriction resolved 18 fingerprints and REP-PCR 10 DNA patterns, forming eight and seven clusters at 75% of similarity level, respectively. Intercluster band variation was > 7 bands for both methods. Although, all endemic isolates, except one, were concordantly grouped by both methods, macrorestriction distinguished a greater number of subtypes over one year study. For outbreaks, the epidemiologic concordance for both methods was 88%. The discriminatory index for macrorestriction and REP-PCR was 0.884 and 0.877, respectively. In conclusion, both methods showed similar efficacy as epidemiological markers, and by concordance, this study demonstrated that for REP-PCR typing, a > or = 7 bands difference seemed an appropriate threshold to identify unrelated strains.

PCR-based DNA fingerprinting (REP-PCR, AP-PCR) and pulsed-field gel electrophoresis characterization of a nosocomial outbreak caused by imipenem- and meropenem-resistant Acinetobacter baumannii

OBJECTIVE

To demonstrate the usefulness of REP-PCR and AP-PCR on molecular typing of A. baumannii isolates.

METHOD

From February to November 1997, 29 inpatients at Ramón y Cajal Hospital, Madrid-23 in five intensive care units (ICUs) and six at two different medical departments-were either colonized or infected with imipenem- and meropenem-resistant Acinetobacter baumannii (IMRAB) strains (MICs of 64-256 mg/L). A wide antibiotic multiresistance profile was observed with IMRAB strains, and only tobramycin, sulbactam and colistin displayed valuable activity. For typing IMRAB isolates, repetitive extragenic palindromic sequence-based polymerase chain reaction (REP-PCR) and arbitrary primer sequence-based polymerase chain reaction (AP-PCR) methods were used and compared with pulsed-field gel electrophoresis (PFGE) as reference technique. For comparative purposes, 30 imipenem- and meropenem-susceptible A. baumannii (IMSAB) strains isolated before, during and after the outbreak were included in this study.

RESULTS

The molecular typing results showed that the outbreak was caused by a single IMRAB strain (genotype 1). On the other hand, seven different genotypes were observed in the pre-, at- and post-outbreak strains tested by REP-PCR. Regarding AP-PCR, three of four at-outbreak IMSAB strains were indistinguishable from the IMRAB profile. Thus, with AP-PCR, only six genotypes were obtained, apart from the IMRAB genotype.

CONCLUSION

Under our experimental conditions, REP-PCR had a higher discriminatory power than AP-PCR, with PFGE as reference technique. The REP-PCR technique is a useful and expeditious method for the epidemiologic characterization of A. baumannii nosocomial outbreaks, the results being comparable to those obtained with the PFGE technique.

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

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

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

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

Characterization of a nosocomial outbreak caused by a multiresistant Acinetobacter baumannii strain with a carbapenem-hydrolyzing enzyme: high-level carbapenem resistance in A. baumannii is not due solely to the presence of beta-lactamases

From February to November 1997, 29 inpatients at Ramón y Cajal Hospital, Madrid, Spain, were determined to be either colonized or infected with imipenem- and meropenem-resistant Acinetobacter baumannii (IMRAB) strains (MICs, 128 to 256 microg/ml). A wide antibiotic multiresistance profile was observed with IMRAB strains. For typing IMRAB isolates, pulsed-field gel electrophoresis was used. For comparative purposes, 30 imipenem- and meropenem-susceptible A. baumannii (IMSAB) strains isolated before, during, and after the outbreak were included in this study. The molecular-typing results showed that the outbreak was caused by a single IMRAB strain (genotype A). By cloning experiments we identified a class D beta-lactamase (OXA-24) encoded in the chromosomal DNA of this IMRAB strain which showed carbapenem hydrolysis. Moreover, the outer membrane profile of the IMRAB strain showed a reduction in the expression of two porins at 22 and 33 kDa when compared with genetically related IMSAB isolates. In addition no efflux mechanisms were identified in the IMRAB strains. In summary, we report here the molecular characterization of a nosocomial outbreak caused by one multiresistant A. baumannii epidemic strain that harbors a carbapenem-hydrolyzing enzyme. Although alterations in the penicillin-binding proteins cannot be ruled out, the reduction in the expression of two porins and the presence of this OXA-derived beta-lactamase are involved in the carbapenem resistance of the epidemic nosocomial IMRAB strain.

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.

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.

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.

Comparison of amplified ribosomal DNA restriction analysis, random amplified polymorphic DNA analysis, and amplified fragment length polymorphism fingerprinting for identification of Acinetobacter genomic species and typing of Acinetobacter baumannii

Thirty-one strains of Acinetobacter species, including type strains of the 18 genomic species and 13 clinical isolates, were compared by amplified ribosomal DNA restriction analysis (ARDRA), random amplified polymorphic DNA analysis (RAPD), and amplified fragment length polymorphism (AFLP) fingerprinting. ARDRA, performed with five different enzymes, showed low discriminatory power for differentiating Acinetobacter at the species and strain level. The standardized commercially available RAPD kit clearly enabled the discrimination of all Acinetobacter genomic species but showed great polymorphism between isolates of Acinetobacter baumannii. AFLP fingerprinting with radioactively as well as fluorescently labelled primers showed high discriminatory power for the identification of 18 Acinetobacter genomic species and typing of 13 clinical Acinetobacter isolates. Compared to radioactive AFLP, fluorescent AFLP was technically fast and simple to perform, and it permitted analysis with an automated DNA sequencer. Fluorescent AFLP seems particularly well suited for studying the epidemiology of nosocomial infections and outbreaks caused by Acinetobacter species.

Impact of Acinetobacter spp. in intensive care units in Great Britain and Ireland

Acinetobacter spp. are of increasing importance as hospital pathogens in intensive care units (ICUs) but it is unclear what clinical impact these bacteria have in Great Britain and Ireland. A survey was carried out by questionnaire on the impact of Acinetobacter in ICUs and the laboratory methods used to identify and type isolates. There were 70 respondents, of whom 25 reported that Acinetobacter had not been recovered from ICU patients within the previous 12 months. The remaining 45 respondents reported that the respiratory tract was the most common site from which these bacteria were isolated, but they were currently endemic in one ICU only. There were considerable differences in methods used to identify Gram-negative bacilli recovered from ICU patients, which may partly explain differences in the reported prevalence of isolates between centres, and 12 laboratories attempted to type isolates by a range of techniques. The availability and use of agreed antibiotic policies specific for ICUs may be particularly important in prevention and control where infection with Acinetobacter is prevalent.

Structures of polymeric products isolated from the lipopolysaccharides of reference strains for Acinetobacter baumannii O23 and O12

A polysaccharide containing D-galactose (Gal), 2-acetamido-2-deoxy-D-galactose (GalNAc), 2-acetamido-2-deoxy-D-glucose (GlcNAc), and 3-deoxy-3-(D-3-hydroxybutyramido)-D-quinovose (Qui3NR) was isolated from lipopolysaccharide (LPS) obtained from cells walls of the reference strain for Acinetobacter baumannii O23. By means of NMR studies, methylation analysis, and chemical degradations, the repeating unit of the polymer was identified as a branched pentasaccharide with the structure 1. The same polymer was apparently also present in LPS of the reference strain for serogroup O12, together with a second polymer based on a branched tetrasaccharide with the structure 2. This second polymer has previously been isolated as the O16 antigen of A. baumannii [Haseley, S.R., Diggle, H.J. & Wilkinson, S. G. (1996) Carbohydr. Res. 293, 259-265] and is probably present as a minor component of the LPS of A. baumannii O11 [Haseley, S.R. & Wilkinson, S.G. (1996) Eur. J. Biochem. 237, 266-271]. [Sequence: see text]

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.

Macrorestriction analysis (PFGE) of serologically cross-reactive serovars of Acinetobacter baumannii and genospecies 3

Forty-two serovar reference strains of Acinetobacter baumannii and genospecies 3, which yielded major or minor, one-way or two-way (reciprocal) serological cross-reactions, were subjected to macrorestriction (SmaI, ApaI) analysis with the aid of pulsed-field gel electrophoresis (PFGE). The PFGE patterns of serovars 3 and 21 of genospecies 3 differed by 3 (SmaI) and 2-4 (ApaI) DNA fragments and thus were closely/possibly related in their genotype. Serovars 13 and 26 of genospecies 3 differed by only 2 DNA fragments (SmaI), suggesting close genetic relatedness; however, these two particular serovars of genospecies 3 appeared to be genotypically indistinguishable following restriction with ApaI. Serovars 2, 4, and 12 of genospecies 3 appeared to be unrelated to serovar 13 of genospecies 3 (SmaI); however, restriction with ApaI indicated a possible relatedness. Genospecies 3 serovars 2 and 26 differed by 5 DNA fragments (SmaI and ApaI), implying a possible relatedness. All other cross-reactive serovars examined proved to be genotypically unrelated, i.e., differed by > or = 7 DNA fragments (SmaI restriction).

High resolution DNA fingerprinting of Acinetobacter outbreak strains

AFLP is a novel high resolution fingerprinting method that can be used to delineate intraspecific relationships among a large variety of organisms, including bacteria. In the present study, this method was tested for its usefulness in the epidemiological typing of Acinetobacter strains. A total of 25 Acinetobacter strains originating from five hospital outbreaks in three countries were used. Isolates from the same outbreak displayed identical banding patterns and each set of outbreak strains could be found in one particular AFLP cluster. These data are in good agreement with the results obtained by other typing methods previously used on the same set of strains, indicating that AFLP analysis may be a valuable alternative in epidemiological typing.

Phenotypic and genotypic characterization of clinically recovered presumptive Acinetobacter baumannii isolates which failed to grow at 44 degrees C

Eleven clinical isolates of Acinetobacter, which exhibited an identical biochemical profile compatible with genospecies 3 and failed to grow at 44 degrees C, were not agglutinated by polyclonal rabbit immune sera against 26 serovars of genospecies 3. Rather, all 11 isolates reacted strongly with antiserum against serovar 18 of A. baumannii. Macrorestriction (SmaI) analysis of genomic DNA revealed that only one isolate was genotypically different, whereas the remaining ones were either closely related or identical. However, the genomic DNA of the A. baumannii serovar 18 reference strain proved to be genotypically unrelated.

Biotypes, serovars and antimicrobial resistance patterns of Acinetobacter baumannii clinical isolates

255 Acinetobacter strains, from clinical specimens of inpatients and outpatients, were identified phenotypically according to the new taxonomy proposed by Bouvet and Grimont. A. baumannii was the most frequent species (80.8%). This species underwent biotyping and serotyping according to the scheme of Bouvet and Grimont, and that of Traub, respectively, 81.2% of samples belonged to biotypes 2, 6 and 9 with a predominance of biotype 2. 86.6% of the strains could be serotyped; 2 new serotypes were encountered. The new serotype 29, being the most frequently isolated, was related to biotype 2 (86.6%), whereas serotype 13 was related to biotype 6 (84.8%). These clones presented marked multiple resistance patterns and were widespread in different wards. No outbreak was reported during the period studied. These phenotypical methods proved to be useful in differentiating strains of A. baumannii and, if used together, they showed a high discriminatory power.

Comparison of outbreak and nonoutbreak Acinetobacter baumannii strains by genotypic and phenotypic methods

Thirty-one Acinetobacter baumannii strains, comprising 14 strains from 14 outbreaks in different northwestern European cities and 17 sporadic strains, were compared by investigating various properties of the strains including biotype, antibiogram, cell envelope protein electrophoretic profile, ribotype pattern, and the band pattern generated by a novel genomic fingerprinting method, named AFLP, which is based on the selective amplification of restriction fragments. Results showed that 12 strains from unrelated outbreaks were linked together in two clusters according to their similarities by these typing methods, whereas sporadic strains were more heterogeneous. Outbreak strains appeared to be markedly more resistant to antibiotics than nonoutbreak strains. The uniformity of typing characters in two sets of outbreak strains suggests that strains in each cluster have a common clonal origin.

Clusters of nosocomial cross-infection due to Acinetobacter baumannii and genospecies 3: comparison of serotyping with macrorestriction analysis of genomic DNA with pulsed-field gel electrophoresis

Triplets of isolates representing 20 putative clusters of nosocomial cross-infection due to Acinetobacter baumannii and genospecies 3 were examined comparatively using serotyping and analysis of restriction fragments (SmaI and ApaI) of genomic DNA with the aid of pulsed-field gel electrophoresis. Carbon source assimilation tests disclosed phenotypic variation among 6 to 20 triplets of isolates. Two misleading results of serotyping were encountered. With respect to the presumptive cluster No. 9, one of the genospecies 3 (originally serovar 4) isolates proved to be polyagglutinable upon repeat examination; this particular putative cluster was shown to be a pseudocluster by comparison of the macrorestriction profiles of the respective triple isolates. A strain of A. baumannii serovar 15 had infected 8 patients in a surgical intensive care unit, while a second, genotypically totally different strain of identical serovar had caused infection in one additional patient. With this exception, the correlation between serotyping and analysis of macrorestriction profiles was excellent.