Acinetobacter spp. as nosocomial pathogens: microbiological, clinical, and epidemiological features

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

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

Exceptional desiccation tolerance of Acinetobacter radioresistens

The taxonomy of the genus Acinetobacter, which includes several important nosocomial pathogens, has been confused due to a lack of discriminatory phenotypic characteristics for identification. Molecular methods such as amplified ribosomal DNA restriction analysis (ARDRA) now enable the accurate identification of species. Ten clinical isolates of Acinetobacter radioresistens had genospecies confirmed by ARDRA but the APJ 20NE system, commonly used in clinical microbiology laboratories, mis-identified them as Acinetobacter lwoffii. Desiccation resistance of Acinetobacter spp. is an important attribute for their survival in the clinical environment. We investigated the ability of A. radioresistens to survive desiccation using an established glass surface model and compared the results to A. lwoffii and Acinetobacter baumannii. The 10 strains of A. radioresistens were extremely resistant to desiccation and survived for an average of 157 days at 31% relative humidity (RH). In contrast, two strains of A. lwoffii and three strains of A. baumannii survived for an average of three and 20 days respectively, at 31% RH, which was used as an approximation to climatic conditions in UK hospitals. A. radioresistens is thus well adapted for survival in the hospital environment and carriage on human skin and yet it is reported less frequently than A. lwoffii amongst clinical isolates. Cases of A. radioresistens infection may be under-reported due to mis-identification as A. lwoffii and further studies that use molecular identification methods are required to elucidate the role of A. radioresistens in human disease.

Survival of Acinetobacter baumannii on dry surfaces: comparison of outbreak and sporadic isolates

Acinetobacter spp. are important nosocomial pathogens reported with increasing frequency in outbreaks of cross-infection during the past 2 decades. The majority of such outbreaks are caused by Acinetobacter baumannii. To investigate whether desiccation tolerance may be involved in the ability of certain strains of A. baumannii to cause hospital outbreaks, a blind study was carried out with 39 epidemiologically well-characterized clinical isolates of A. baumannii for which survival times were determined under simulated hospital conditions. The survival times on glass coverslips of 22 strains isolated from eight well-defined hospital outbreaks in a German metropolitan area were compared with the survival times of 17 sporadic strains not involved in outbreaks but rather isolated from inpatients in the same geographic area. All sporadic isolates have been shown by pulsed-field gel electrophoresis to represent different strain types. There was no statistically significant difference between the survival times of sporadic strains of A. baumannii and outbreak strains (27.2 versus 26.5 days, respectively; P < or = 0.44) by the Wilcoxon-Mann-Whitney test. All investigated A. baumannii strains, irrespective of their areas of endemicity or epidemic occurrence, have the ability to survive for a long time on dry surfaces. Antimicrobial susceptibility testing showed that A. baumannii outbreak strains were significantly more resistant to various broad-spectrum antimicrobial agents than sporadic strains. Both desiccation tolerance and multidrug resistance may contribute to their maintenance in the hospital setting and may explain in part their propensity to cause prolonged outbreaks of nosocomial infection.

Distribution of mevalonate and glyceraldehyde 3-phosphate/pyruvate routes for isoprenoid biosynthesis in some gram-negative bacteria and mycobacteria

Labeling experiments using [1-13C]acetate or [1-13C]glucose were performed with opportunistic pathogenic bacteria, with innocuous bacteria related to pathogenic species or with phytopathogenic species. The labeling pattern was determined in the isoprenic moiety of ubiquinone or menaquinone derivatives. These experiments showed that Acinetobacter, Citrobacter, Erwinia, Pseudomonas, Burkholderia, Ralstonia and Mycobacterium synthesize their isoprenoids via the mevalonate-independent glyceraldehyde 3-phosphate/pyruvate route. Enzymes of this novel bacterial metabolic route, which is apparently absent in vertebrates and man, therefore represent potential targets for a novel type of antibacterial drugs.

Bacteraemia in the adult intensive care unit of a teaching hospital in Nottingham, UK, 1985-1996

Bacteraemia is an important cause of morbidity and mortality in the intensive care unit. In this study the distribution of organisms causing bacteraemic episodes in patients in the adult intensive care unit of a large teaching hospital was determined. Particular emphasis was placed on the type of organisms isolated from community- and hospital-acquired bacteraemia, the suspected source of infection, the possible risk factors associated with bacteraemia, and outcome. The incidence of bacteraemia and fungaemia increased from 17.7 per 1000 admissions in 1985 to 80.3 in 1996. A total of 315 episodes of bacteraemia and fungaemia were documented over a 12-year period, of which 18% were considered community-acquired and 82% hospital-acquired. Gram-positive and gram-negative bacteria accounted for 46.9% and 31.5% of the episodes, respectively. Polymicrobial infection accounted for 17.8% and fungi for 3.8% of the episodes. Staphylococcus aureus (22.5%), Staphylococcus epidermidis (7.6%), and Streptococcus pneumoniae (7.9%) were the predominant gram-positive bacteria implicated, whereas Escherichia coli (6%), Enterobacter cloacae (7%), Klebsiella aerogenes (3.8%), Pseudomonas aeruginosa (5.1%), and Acinetobacter spp. (3.8%) were the predominant gram-negative bacteria isolated. The two most common sources of infection were the respiratory tract (39.7%) and an intravascular line (24.5%), but in 8.9% of episodes the focus of infection remained unknown. Bacteraemic patients stayed in the unit for a longer period (12 days) than did non-bacteraemic patients (3 days). The overall mortality related to bacteraemia and candidaemia was 44.4%. Surveillance of bacteraemia in the intensive care unit is important in detecting major changes in aetiology, e.g., the increasing incidence of gram-positive bacteraemia, the emergence of methicillin-resistant Staphylococcus aureus in 1995, and the emergence of Enterobacter cloacae. It is of value in determining empirical antimicrobial therapy to treat presumed infection pending a microbiological diagnosis and in directing the development of guidelines for infection prevention, e.g., guidelines for central venous catheter care.

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.

Molecular epidemiology of quinolone resistance in Acinetobacter spp

OBJECTIVE: To determine whether similar mutations to quinolone resistance in the gyrA subunit of DNA gyrase and the parC subunit of topoisomerase IV are occurring independently in genotypically unrelated clinical isolates of Acinetobacter spp., or whether worldwide clonal spread of particular resistant strains is occurring. METHODS: The genotypic relationships of 25 nosocomial isolates of Acinetobacter spp. from 15 locations in 11 different countries worldwide were examined by randomly amplified polymorphic DNA analysis. Quinolone resistance-determining regions of gyrA and parC were amplified by PCR and mutations were analyzed by restriction digestion with Hinfl and DNA sequencing. RESULTS: Twenty-four of the 25 Acinetobacter isolates were genotypically heterogeneous and 12 were resistant to both nalidixic acid and ciprofloxacin. Analysis of conserved gyrA and parC regions showed that all isolates with a ciprofloxacin MIC of 4 mg/L had a substitution of Ser83 with either Leu or Phe in the GyrA protein. Five of six isolates with ciprofloxacin MICs of 64 mg/L had additional substitutions of Ser80 with Leu in the ParC protein. CONCLUSIONS: Similar mutations to quinolone resistance, predominantly at codons 82--83 of gyrA, are occurring independently in genotypically distinct isolates of Acinetobacter spp. from different worldwide locations. Most isolates with high ciprofloxacin MICs also exhibited secondary mutations in parC at codons 79--80.

Carbapenem resistance mediated by beta-lactamases in clinical isolates of Acinetobacter baumannii in Spain

Four patients colonized/infected with carbapenem-resistant strains of Acinetobacter baumannii are described. The first patient had a decubitus ulcer infection and had been on intravenous imipenem for 50 days. Two other patients, from whom Acinetobacter baumannii was isolated from urine, were hospitalized in the same ward as the first patient. The fourth patient had been mechanically ventilated in the intensive care unit for 4 month and had nosocomial pneumonia. He had been on intravenous meropenem for 1 month. Minimum inhibitory concentrations (MICs) of imipenem (128 mg/l) and meropenem (> 128 mg/l) were the same for the isolates from the first three patients, and all of these isolates had the same repetitive extragenic palindromic polymerase chain reaction (rep-PCR) pattern. The MICs of carbapenems were lower for patient 4's isolate, which also had a different rep-PCR pattern. Beta-lactamases that hydrolyzed imipenem were detected in all four isolates; isoelectric points were 8.6-7.7 in the first three isolates and 6.8-7 in the fourth isolate.

Presence of integrons in isolates of different biotypes of Acinetobacter baumannii from Chilean hospitals

Class 1 and class 2 integrons were investigated by hybridisation in 100 isolates of multiresistant biotypes of Acinetobacter baumannii from Chilean hospitals. Most isolates of A. baumannii biotype 9, the prevalent biotype, harboured integrons of class 2 (Tn7-like) whereas no integrons were detected in infrequent biotypes. Integron-carrying isolates exhibited broader antibiotic resistance patterns as well as higher resistance levels to various antimicrobials.

Surveillance of an adult intensive care unit for long-term persistence of a multi-resistant strain of Acinetobacter baumannii

Sporadic infections with Acinetobacter spp., punctuated with prolonged outbreaks of infection involving larger numbers of patients and a particular epidemic strain of Acinetobacter baumannii, have occurred in the adult intensive care unit (ICU) of Nottingham University Hospital since 1985. The aim of this study was to screen patients admitted to the ICU for three or more days during a non-outbreak period in 1994-1995 and to use DNA fingerprinting techniques to compare any isolates of Acinetobacter spp. with isolates obtained from the same ICU during the previous ten years. In the present study, almost 20% of the ICU patients screened during 1994-1995 became colonized with Acinetobacter spp. The commonest species isolated from patients was Acinetobacter baumannii; five different strains were identified by random amplified polymorphic DNA fingerprinting, including the epidemic strain responsible for outbreaks of infection in 1985-1986 and 1992-1993. Environmental sampling yielded Acinetobacter spp. from one or more samples on four occasions; Acinetobacter radioresistens was the commonest species isolated, and Acinetobacter baumannii (not the epidemic strain) was isolated on only one occasion from the environment. The long-term persistence of a potentially epidemic strain in the ICU, even during a non-outbreak period, indicates a need for continued vigilance. Consequently, periodic patient and environmental surveillance, combined with typing of isolates, is recommended for ICUs where significant outbreaks of Acinetobacter infection have occurred in the past.

Eradication of Acinetobacter baumannii by photosensitized agents in vitro

The photodynamic effects of photosensitizers on Acinetobacter baumannii were studied. These Gram negative bacteria have recently been implicated in various infections, mainly acquired in hospitals. They have outstanding characteristics of multidrug high resistance to antimicrobial agents. The best photodynamic effect was obtained when A. baumannii cultures were treated with light activated deuteroporphyrin (Dp) at a concentration of 34 mumoles l-off and polymyxin nonapeptide (PMNP) at a concentration of 200 mumoles l-1. At these concentrations the culture in brain heart infusion (BHI) broth was found to be sterile after l h of treatment. Some inhibition was also obtained under the same conditions with Cd-texaphyrin (Cd-Tx) in the presence of PMNP. Treatment with various other photosensitizers in the presence of PMNP exhibited only marginal antibacterial activity. The cationic photosensitizer tetra-methylpyridyl porphine (TMPyP) did not exhibit any photodynamic effect on A. baumannii when illuminated during its growth in BHI broth. Bacteria grown in nutrient broth or suspended in saline and treated by TMPyP resulted in a significant photoinactivation by the sensitizer alone even in the absence of PMNP. It was found that a high concentration of the proteins present in BHI or in serum prevent TMPyP from acting as a photosensitizer against A. baumannii. Bovine serum albumin at the same high protein concentration prevents Dp (in the presence of PMNP) to act as a photosensitizer. The anionic photosensitizer tetra-sulfonatophenyl porphine (TPPS4) did not show any photodynamic effect in high or low protein media. In this study it was found that despite the high resistance of the Acinetobacter baumannii to antibiotics, these bacteria can be significantly photoinactivated by treatment with either Dp + PMNP or TMPyP in low protein content environments. When the protein concentration is high photoinactivation efficiency depends on the type of protein present in the medium.

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.

Multicenter study using standardized protocols and reagents for evaluation of reproducibility of PCR-based fingerprinting of Acinetobacter spp

Seven laboratories in six European countries examined 40 isolates belonging to the Acinetobacter calcoaceticus-Acinetobacter baumannii complex to investigate whether standardized protocols and quality-controlled reagents could produce reliable, discriminatory, and reproducible PCR-based fingerprinting results. Four PCR protocols with different primers (primers DAF4, ERIC-2, M13, and REP1 + REP2) were used. The epidemiological conclusions reached by the participating laboratories were substantially correct, with 96.4% of the total isolate grouping allocations agreeing with the consensus view. All laboratories identified the main epidemiological clusters, and each laboratory also identified two non-outbreak-related isolates. There were no significant differences between the isolate grouping results obtained by the different protocols and with the different primers. Visual comparison indicated that the standardized protocols and reagents yielded reproducible fingerprint patterns, but with some variations in particular band intensities. Minor variations in fingerprint profiles were detected, but computer-assisted analysis of PCR fingerprints obtained on agarose gels demonstrated that 88.3 to 91.6% (depending on the source of DNA) of the patterns clustered correctly, while 96.4 to 98.9% of the patterns clustered correctly following automated high-resolution laser fluorescence analysis. Correlation of the patterns for isogenic isolates ranged from 83.3 to 86.6% but was slightly better (mean correlation, 87.1%) for centrally prepared DNA extracts than for DNA extracts prepared by individual laboratories (mean correlation, 84.7%). It was concluded that independently produced PCR fingerprint patterns can be obtained reproducibly for Acinetobacter spp. at the practical level if (i) quality-controlled reagents, (ii) standardized extraction of DNA, and (iii) standardized amplification conditions are used.

Cloning and nucleotide sequence analysis of a gene encoding an OXA-derived beta-lactamase in Acinetobacter baumannii

A clinical strain of Acinetobacter baumannii (strain Ab41) that was resistant to all beta-lactam antibiotics tested except ceftazidime, ceftriaxone, ceftizoxime, and imipenem produced three beta-lactamases: a presumptive chromosomal cephalosporinase, a TEM-1-like beta-lactamase (pI 5.4), and a novel OXA-derived beta-lactamase named OXA-21 (pI 7.0). The gene encoding OXA-21 was located in an integron. The nucleotide sequence showed three mutations compared with the sequence of OXA-3, with two being silent; the nonsilent mutation generated a substitution of Ile-217 to Met.

Epidemiological significance of cutaneous, pharyngeal, and digestive tract colonization by multiresistant Acinetobacter baumannii in ICU patients

The aim of this prospective study was to assess the relative epidemiological role of digestive tract colonization by Acinetobacter baumannii, in comparison with other body site colonizations, in patients admitted to intensive care units (ICUs). From January to May 1995, axillary, pharyngeal and rectal swabs were taken together within the first 48 h of admission, and then weekly during ICU stay. Seventy-three patients were included, 48 of them (66%) had axillary, pharyngeal, or rectal colonization with A. baumannii, nine (19%) of these 48 during the first 48 h and the remaining 28 (77%) during the first week. Twenty-one (29%) had clinical samples positive for A. baumannii and axillary, pharyngeal, or rectal colonization. In 15 of these 21 (71%), colonization on body sites occurred prior to isolation from clinical samples (mean seven days, range 1-20). Throughout admission, rates of detection of A. baumannii were 75% (36/48) for axillary or pharyngeal swabs and 77% (37/48) for rectal swabs. Combination of two body site swabs yielded culture positive rates of 90% (43/48) for axillary-pharyngeal or axillary-rectal sites, and 96% (46/48) for pharyngeal-rectal. Two epidemic clones were defined by antibiotype and pulsed-field gel electrophoresis (PFGE) of SmaI DNA digests in 48 isolates from 11 patients. We conclude that body sites of patients were a major reservoir for A. baumannii infections in the outbreak. This finding cases doubt on the value of selective decontamination of the digestive tract as an additional infection control measure in this kind of outbreak. The weekly performance of pharyngeal and rectal swabs appears to detect A. baumannii colonization early among ICU patients and enables barrier methods to be applied rapidly.

Distribution of Acinetobacter species on human skin: comparison of phenotypic and genotypic identification methods

At least 19 genomic species are recognized as constituting the genus Acinetobacter. However, little is known about the natural reservoirs of the various members of the genus. An epidemiological study was therefore performed to investigate the colonization with Acinetobacter spp. of the skin and mucous membranes of 40 patients hospitalized in a cardiology ward and 40 healthy controls. Single samples were obtained once from each of nine different body sites, i.e., forehead, ear, nose, throat, axilla, hand, groin, perineum, and toe web. Identification of Acinetobacter isolates was achieved by using phenotypic properties and was compared to identification by amplified ribosomal DNA restriction analysis. Selected isolates were further investigated with sodium dodecyl sulfate-polyacrylamide gel electrophoresis, ribotyping, and DNA-DNA hybridization. Plasmid profile analysis was used for epidemiological typing. Thirty patients (75%) and 17 controls (42.5%) were found to be colonized with Acinetobacter spp., and the colonization rates of patients increased during their hospital stay. The most frequently isolated species were Acinetobacter lwoffii (47%), A. johnsonii (21%), A. radioresistens (12%), and DNA group 3 (11%). In contrast, A. baumannii and DNA group 13TU, the most important nosocomial Acinetobacter spp., were found only rarely on human skin (0.5 and 1%, respectively) and their natural habitat remains to be defined. A good correlation between phenotypic and genotypic methods for identification of Acinetobacter spp. was observed, and only two isolates could not be assigned to any of the known DNA groups.

Risk factors, clinical features and outcome of Acinetobacter bacteremia in adults

The medical records of 39 patients with Acinetobacter bacteremia identified in the period between 1985 and 1995 were reviewed. In 24 cases (62%) the bacteremia was considered to have been clinically significant. Most of the infections (79%) were nosocomial, and the majority of these were acquired in an intensive care unit. Ten (42%) patients developed septic shock complicating the bacteremia and 13 (54%) died. In most of these cases (85%), Acinetobacter bacteremia was thought to have caused or contributed to death. The following variables were associated with a greater risk of mortality: age > 65 years (OR = 16; p = 0.01); development of septic shock (OR = 22; p = 0.004); and the presence of coagulopathy (OR = 20; p = 0.03).

Molecular typing of Acinetobacter baumannii from ten different intensive care units of a university hospital

Thirty-one isolates of Acinetobacter baumannii were collected from ten intensive care units of an Austrian university hospital. All isolates were typed by enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR). Two strains colonizing 13 infants in the neonatal intensive care unit were identified by ERIC-PCR. All other Acinetobacter baumannii isolates had highly divergent ERIC-PCR patterns, despite having the same antibiogram. Thus, a hospital-wide clonal distribution, as suggested by identical antibiogram patterns, was excluded by ERIC-PCR.

Identification and characterization of an aadB gene cassette at a secondary site in a plasmid from Acinetobacter

Transformation studies showed that an aminoglycoside resistance gene, aadB, is carried on a 6.0-kb plasmid (pRAY) in a clinical isolate of Acinetobacter (strain SUN). The gene was cloned and sequenced. An analysis of the DNA sequencing data showed that although the aadB gene is part of cassette, it is not associated with an integron. Rather, the aadB cassette has recombined at a secondary site downstream of putative promoters on pRAY.

Structural studies of the O-antigenic polysaccharide of the lipopolysaccharide from Acinetobacter (DNA group 11) strain 94 containing 3-amino-3,6-dideoxy-D-galactose substituted by the previously unknown amide-linked L-2-acetoxypropionic acid or L-2-hydroxypropionic acid

A polysaccharide containing D-Gal, D-GalNAc, 3-(L-2-acetoxypropionamido)-3,6-dideoxy-D-galactose (approximately 80%) and 3-(L-2-hydroxypropionamido)-3,6-dideoxy-D-galactose (approximately 20%) was isolated by mild acid hydrolysis, followed by gel-permeation chromatography, from the phenol-soluble lipopolysaccharide (phenol/water extracted) derived from Acinetobacter strain 94. The polysaccharide, characterised by means of monosaccharide analyses, partial acid hydrolysis, and NMR studies, consisted of a branched tetrasaccharide repeating unit, as depicted below, in which Fucp3Nacyl represents 3-(L-2-hydroxypropionamido)-3,6-dideoxy-D-galactose, in which approximately 80% of the acyl residues are O-acetylated. These Fucp3N derivatives and an O-acetylated acyl group are therefore constituents of bacterial LPS, but to our knowledge are not present in any other natural carbohydrates. [sturcture: see text]

Identification and analysis of a gene encoding L-2,4-diaminobutyrate:2-ketoglutarate 4-aminotransferase involved in the 1,3-diaminopropane production pathway in Acinetobacter baumannii

The ca. 2.2-kbp region upstream of the ddc gene encoding L-2,4-diaminobutyrate decarboxylase in Acinetobacter baumannii was sequenced and found to contain another open reading frame of 1,338 nucleotides encoding a protein with a deduced molecular mass of 47,423 Da. Analysis of the homologies observed from the deduced amino acid sequence indicated that the gene product is an enzyme belonging to subgroup II of the aminotransferases. This was first verified when examination of the crude extracts from Escherichia coli transformants led to detection of a novel aminotransferase activity catalyzing the following reversible reactions: L-2,4-diaminobutyric acid + 2-ketoglutaric acid<-->L-glutamic acid + L-aspartic beta-semialdehyde. Further confirmation was obtained when the gene was overexpressed in E. coli and the corresponding protein was purified to homogeneity. It catalyzed the same reactions and its N-terminal amino acid sequence was consistent with that deduced from the nucleotide sequence. Therefore, the gene and its product were named dat and L-2,4-diaminobutyrate:2-ketoglutarate 4-aminotransferase (DABA AT), respectively. Feeding experiments of A. baumannii with L-[U-14C]aspartic acid resulted in the incorporation of the label into 1,3-diaminopropane. Apparent homologs of dat and DABA AT were detected in other Acinetobacter species by PCR amplification and Western blotting. These results indicate that the dat gene (as well as the ddc gene) participates in the synthesis of 1,3-diaminopropane, the only diamine found in this genus. However, the biological role, if one exists, of 1,3-diaminopropane synthesis is unknown.

Activity of selected beta-lactams, ciprofloxacin, and amikacin against different Acinetobacter baumannii biotypes from Chilean hospitals

The activity of some third generation cephalosporins, aztreonam, imipenem, ciprofloxacin, and amikacin against isolates of Acinetobacter baumannii of various biotypes has been studied. The isolates, independently of the biotype, exhibited a broad multiresistance against cephalosporins. Ceftazidime was the most active and cefoperazone the least active compound. Aztreonam also showed low activity and no imipenem-resistant strains were found. Ciprofloxacin and amikacin were somewhat more active than cephalosporins, but resistant isolates were also frequent. Isolates of Biotypes 9 and 8 exhibited broader multiresistance than those of Biotype 6 and "other."

Structural investigation of the lipopolysaccharide from Acinetobacter haemolyticus strain NCTC 10305 (ATCC 17906, DNA group 4)

The structure of the lipopolysaccharide (LPS) from Acinetobacter haemolyticus strain NCTC 10305 (DNA group 4) was elucidated by means of analytical chemistry, NMR spectroscopy and fast-atom-bombardment mass spectrometry. Several oligosaccharides were obtained after deacylation or successive de-O-acylation, dephosphorylation, reduction, and de-N-acylation of LPS. In the major fraction of the LPS, the core is attached to the lipid A through D-glycero-D-talo-2-octulopyranosonic acid (Ko), whereas in a minor fraction (<20%) Ko is replaced by 3-deoxy-D-manno-octulopyranosonic acid (Kdo). The structures of the phosphorylated carbohydrate backbones of these LPS fractions are [structure: see text] with Dha = 3-deoxy-D-lyxo-2-heptulosaric acid, Sug = sugar and is Ko in a major fraction and Kdo in a minor fraction. All sugar residues have the D-configuration and are present in the pyranose form. Mass spectrometry of de-O-acylated LPS revealed the presence of an additional hexose residue in minor amounts, the position and nature of which could not be identified.

Structural and serological characterisation of the O-antigenic polysaccharide of the lipopolysaccharide from Acinetobacter strain 90 belonging to DNA group 10

Water-soluble lipopolysaccharide (phenol/water extraction) isolated from Acinetobacter strain 90, which belongs to DNA group 10, was hydrolysed with 1% acetic acid, ultracentrifuged, and water-soluble products finally eluted from a Sephadex G-50 column. The major fraction, a polysaccharide, contained D-Gal, D-GlcNAc, D-GalNAc, and 4,6-dideoxy-4-[(R)-3-hydroxybutyramido]-D-galactose (Fuc4NBuOH). The polysaccharide was characterised by means of monosaccharide analyses, Smith-degradation, N-deacetylation/deamination, and NMR studies, and was shown to have a branched pentasaccharide repeating unit. [structure in text] This structure was specifically recognised in western blots and enzyme immunoassays by polyclonal rabbit antisera.

Structural and serological characterisation of the O-antigenic polysaccharide of the lipopolysaccharide from Acinetobacter junii strain 65

A polysaccharide containing rhamnose (Rha) and Gal was isolated by acetic acid hydrolysis, followed by gel-permeation chromatography, from the water-soluble lipopolysaccharide (phenol/water extracted) from Acinetobacter junii strain 65. The polysaccharide was characterised by means of monosaccharide analyses, Smith degradation, and NMR studies, and was shown to have a linear pentasaccharide repeating unit, as depicted below. This structure was specifically recognised in western blots and enzyme immunoassays by polyclonal rabbit antisera. [structure in text]

Structural and serological characterisation of the O-antigenic polysaccharide of the lipopolysaccharide from Acinetobacter haemolyticus strain ATCC 17906

A polysaccharide containing 2-acetamido-2-deoxy-D-galacturonic acid (GalNAcA), 2.4-diacetamido-2,4,6-trideoxy-D-glucose (QuiNAc4NAc), and D-alanine (Ala) was isolated from the water-soluble lipopolysaccharide (LPS) originating from the reference strain for Acinetobacter haemolyticus (DNA group 4) strain ATCC 17906. The polysaccharide, characterised by means of monosaccharide analyses and NMR studies, was shown to be based on a linear trisaccharide repeating unit, as shown below, with the alanine group amide-bound to position 6 of one GalNAcA residue. It was specifically recognised in western blots by polyclonal rabbit antisera. [structure: see text]

The structure of the carbohydrate backbone of the lipopolysaccharide from Acinetobacter strain ATCC 17905

The structure of the carbohydrate backbone of the lipopolysaccharide from Acinetobacter strain ATCC 17905 was studied. After deacylation of the lipopolysaccharide, a mixture of two compounds (ratio approximately 2:1) was isolated by high-performance anion-exchange chromatography, the structures of which were determined by NMR spectroscopy and electrospray-mass spectrometry as [STRUCUTRE IN TEXT] [Sug, 3-deoxy-D-manno-2-octulopyranosonic acid (Kdo) in oligosaccharide 1 (major portion) and D-glycero-D-talo-2-octulopyranosonic acid (Ko) in oligosaccharide 2 (minor portion)]. All monosaccharide residues also possess the D-configuration and are present in the pyranose form.

Structural and serological characterisation of the O-specific polysaccharide from lipopolysaccharide of Acinetobacter calcoaceticus strain 7 (DNA group 1)

S-form lipopolysaccharide was isolated by phenol/water extraction from a strain of Acinetobacter calcoaceticus (DNA group 1 ). The structure of the O-antigenic polysaccharide was determined by compositional analysis and NMR spectroscopy of the de-O-acylated lipopolysaccharide. The isolated polysaccharide obtained after hydrolysis of lipopolysaccharide in 0.01 M trifluoroacetic acid has the following structure: [STRUCTURE IN TEXT] in which Pyr is pyruvate. The O-acetyl substitution of D-Gal was non-stoichiometric. The O-antigen was specifically recognised in western blots by polyclonal rabbit antisera.

Influence of relative humidity and suspending menstrua on survival of Acinetobacter spp. on dry surfaces

Acinetobacter spp. are being reported with increasing frequency as a cause of nosocomial infection and have been isolated from the skin of healthy individuals, patients, hospital staff, dry nonbiotic objects, and different pieces of medical equipment. Factors affecting the survival of Acinetobacter spp. under conditions closely similar to those found in the hospital environment were investigated in the present study to help us understand the epidemiology of nosocomial Acinetobacter infection. Bacterial cells were suspended in distilled water or bovine serum albumin and were dried onto glass coverslips and kept at different relative humidities. Cells washed from coverslips were used to determined viable counts. Freshly isolated strains of Acinetobacter spp. belonging to the clinically important Acinetobacter calcoaceticus-Acinetobacter baumannii complex were found to be more resistant to drying conditions (e.g., 30 days for A. baumannii 16/49) than American Type Culture Collection strains (e.g., 2 days for A. baumannii ATCC 9955). The majority of strains belonging to the Acb complex had survival times similar to those observed for the gram-positive organism Staphylococcus aureus tested in the experiment. Survival times were prolonged for almost all the strains tested when they were suspended in bovine serum albumin (e.g., 60 days for A. baumannii R 447) compared with those for strains suspended in distilled water (11 days for R 447). The survival times for strains at higher relative humidity (31 or 93%) were longer than those for strains of Acinetobacter kept at a relative humidity of 10% (11 days at 31% relative humidity and 4 days at 10% relative humidity for R447). These findings are consistent with the observed tendency of Acinetobacter spp. to survive on dry surfaces, and they can be transferred not only by moist vectors but also under dry conditions in a hospital environment during nosocomial infection outbreaks. The results obtained in the experiment support the previously suggested airborne spread of Acinetobacter spp. in hospital wards and repeated outbreaks after incomplete disinfection of contaminated dry surfaces.

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.