Numerical Analysis of Cell Envelope Protein Profiles of Acinetobacter Strains Classified by DNA-DNA Hybridization

3D-printed wound dressings containing a fosmidomycin-derivative prevent Acinetobacter baumannii biofilm formation

Acinetobacter baumannii causes a wide range of infections, including wound infections. Multidrug-resistant A. baumannii is a major healthcare concern and the development of novel treatments against these infections is needed. Fosmidomycin is a repurposed antimalarial drug targeting the non-mevalonate pathway, and several derivatives show activity toward A. baumannii. We evaluated the antimicrobial activity of CC366, a fosmidomycin prodrug, against a collection of A. baumannii strains, using various in vitro and in vivo models; emphasis was placed on the evaluation of its anti-biofilm activity. We also developed a 3D-printed wound dressing containing CC366, using melt electrowriting technology. Minimal inhibitory concentrations of CC366 ranged from 1 to 64 μg/mL, and CC366 showed good biofilm inhibitory and moderate biofilm eradicating activity in vitro. CC366 successfully eluted from a 3D-printed dressing, the dressings prevented the formation of A. baumannnii wound biofilms in vitro and reduced A. baumannii infection in an in vivo mouse model.

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)).

Structural and serological characterisation of the O-antigenic polysaccharide of the lipopolysaccharide from Acinetobacter baumannii strain 24

Extraction of dry bacteria of Acinetobacter baumannii strain 24 by phenol-water yielded a lipopolysaccharide (LPS) that was studied by serological methods and fatty acid analysis. After immunisation of BALB/c mice with this strain, monoclonal antibody S48-3-13 (IgG(3) isotype) was obtained, which reacted with the LPS in western blot and characterized it as S-form LPS. Degradation of the LPS in aqueous 1% acetic acid followed by GPC gave the O-antigenic polysaccharide, whose structure was determined by compositional analyses and NMR spectroscopy of the polysaccharide and O-deacylated polysaccharide as [carbohydrate structure: see text] where QuiN4N is 2,4-diamino-2,4,6-trideoxyglucose and GalNAcA 2-acetamido-2-deoxygalacturonic acid. The amino group at C-4 of the QuipN4N residues is acetylated in about 2/3 of LPS molecules and (S)-3-hydroxybutyrylated in the rest.

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.

O-antigen diversity among Acinetobacter baumannii strains from the Czech Republic and Northwestern Europe, as determined by lipopolysaccharide-specific monoclonal antibodies

O-antigen-specific monoclonal antibodies (MAbs) are currently being generated to develop an O-serotyping scheme for the genus Acinetobacter and to provide potent tools to study the diversity of O-antigens among Acinetobacter strains. In this report, Acinetobacter baumannii strains from the Czech Republic and from two clonal groups identified in Northwestern Europe (termed clones I and II) were investigated for their reactivity with a panel of O-antigen-specific MAbs generated against Acinetobacter strains from various species. The bacteria were characterized for their ribotype, biotype, and antibiotic susceptibility and the presence of the 8.7-kb plasmid pAN1. By using the combination of these typing profiles, the Czech strains could be classified into four previously defined groups (A. Nemec, L. Janda, O. Melter, and L. Dijkshoorn, J. Med. Microbiol. 48:287-296, 1999): two relatively homogeneous groups of multiresistant strains (termed groups A and B), a heterogeneous group of other multiresistant strains, and a group of susceptible strains. O-antigen reactivity was observed primarily with MAbs generated against Acinetobacter calcoaceticus and Acinetobacter baumannii strains. A comparison of reaction patterns confirmed the previously hypothesized clonal relationship between group A and clone I strains, which are also similar in other properties. The results show that there is limited O-antigen variability among strains with similar geno- and phenotypic characteristics and are suggestive of a high prevalence of certain A. baumannii serotypes in the clinical environment. It is also shown that O-antigen-specific MAbs are useful for the follow-up of strains causing outbreaks in hospitals.

Chemical and antigenic structure of the O-polysaccharide of the lipopolysaccharides from two Acinetobacter haemolyticus strains differing only in the anomeric configuration of one glycosyl residue in their O-antigens

In a previous study [Pantophlet, R., Brade, L., Dijkshoorn, L., and Brade, H. (1998) J. Clin. Microbiol. 36, 1245-1250] the O-polysaccharide of the lipopolysaccharides (LPS) from Acinetobacter haemolyticus strains 57 and 61 exhibited indistinguishable banding-patterns following Western blot and immunostaining with homologous or heterologous rabbit antiserum. In this report, the molecular basis for the observed cross-reactivity was elucidated, by determining the chemical structure of the polysaccharides by compositional analysis and NMR spectroscopy. The structures are: [sequence: see text] for strain 61 [GulpNAcA, 2-acetamido-2-deoxy-gulopyranosyluronic acid; ManpNAcA, 2-acetamido-2-deoxy-mannopyranosyluronic acid; QuipN4N, 2,4-diamino-2,4,6-trideoxy-glucopyranose; acyl (S)-3-hydroxybutyryl], thus, differing only in the anomeric configuration of the QuipN4N residue. The antigenic structures were determined by generating murine monoclonal antibodies, which were characterized by Western blot using LPS as antigen, by ELISA using LPS and de-O-acylated LPS as solid-phase antigens, and by ELISA inhibition studies using LPS, polysaccharide, and de-O-acylated LPS as inhibitors. Of the four antibodies selected, two were specific for the respective LPS moieties and two were cross-reactive. All antibodies were found to require the presence of the O-acetyl group for reactivity.

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.

Methicillin-resistant Staphylococcus aureus and Acinetobacter baumannii: an unexpected difference in epidemiologic behavior

BACKGROUND

The Dutch guideline on hospital policy for the prevention of nosocomial spread of methicillin-resistant Staphylococcus aureus (MRSA) states that patients transferred from hospitals abroad must be placed in strict isolation immediately on admission to a hospital in the Netherlands. Three patients colonized with both MRSA and a multiresistant Acinetobacter were transferred from hospitals in Mediterranean countries to 3 different hospitals in the Netherlands. Despite isolation precautions, Acinetobacter spread in 2 of the 3 hospitals, whereas nosocomial spread of MRSA did not occur.

METHODS

For outbreak analysis, the Acinetobacter isolates, identified as Acinetobacter baumannii by the use of amplified ribosomal DNA restriction analysis, were comparatively typed by 4 methods. Comparison of isolation measures in the hospitals was performed retrospectively.

RESULTS

In the 2 hospitals in which nosocomial spread of Acinetobacter occurred, most of the epidemiologically related isolates were indistinguishable from the index strains. In these 2 hospitals, isolation measures were in concordance with those recommended for the prevention of contact transmission. The precautions of the hospital in which no outbreak occurred included the prevention of airborne transmission.

CONCLUSIONS

Precautions recommended for multiresistant gram-negative organisms are insufficient for the prevention of nosocomial spread of multiresistant Acinetobacter. The airborne mode of spread of acinetobacters should be taken into account, and guidelines should be revised accordingly.

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.

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

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

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.

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]

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]

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).

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.

Structural and serological characterisation of two O-specific polysaccharides of Acinetobacter

Extraction of dry bacteria of Acinetobacter strain 34 (DNA group 2) or Acinetobacter strain 108 (DNA group 13) by phenol/water yielded a polymer that was identified by means of serological studies and fatty acid analysis as S-form lipopolysaccharide. Degradation of the lipopolysaccharides of strains 34 and 108 in 1% acetic acid and 5% acetic acid, respectively, and gel-permeation chromatography gave the respective O-antigenic polysaccharides, the structures of which were determined, by compositional analysis and NMR spectroscopy of the polysaccharide, as [Sequence: see text] for strain 108, where D-Fucp3NBuOH represents 3-[(R)-3-hydroxybutyramido] -3,6-dideoxy-D-galactose and D-GalpANAc represents 2-acetamido-2-deoxy-D-galacturonic acid. Both structures were specifically recognised in Western blots by polyclonal rabbit antisera and there was no cross-reaction between these two structures.

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.

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

A collection of 130 Acinetobacter strains identified by DNA hybridization to 18 different genomic species was used to assess the ability of the API 20NE system (bioMérieux, France) to identify Acinetobacter genomic species and to determine its accuracy. Fifty-eight (87%) of the 67 strains of genomic species defined in the database (version 5.1) were identified to the appropriate genomic species. The Acinetobacter baumannii strains and the Acinetobacter haemolyticus strains were all identified correctly. Three of five Acinetobacter junii strains, three of eight Acinetobacter johnsonii strains, and 11 of 13 Acinetobacter lwoffii strains were also identified correctly. The 58 correctly identified strains represented 45% of the total 130 strains. Thirty-six of the 72 inappropriately identified strains were designated Acinetobacter baumannii. Thirty-one of these 36 strains belonged to genomic species 1 (Acinetobacter calcoaceticus), 3, or 13TU. Analysis of the profiles showed that the API system does not discriminate between genomic species 1, 2, 3, and 13TU. Lumping of these groups into the Acinetobacter calcoaceticus-Acinetobacter baumannii complex in the API 20NE database would make the system considerably more accurate. Incorporation of these data into the database may improve identification of the remaining genomic species, including some that are not defined. However, the discriminative power of the tests in the API galleries is insufficient for correct identification of all Acinetobacter genomic species.

Differentiation of Acinetobacter calcoaceticus sensu stricto from related Acinetobacter species by electrophoretic polymorphism of malate dehydrogenase, glutamate dehydrogenase and catalase

Acinetobacter baumannii, unnamed Acinetobacter species 3 (studied by P.J.M. Bouvet and P.A.D. Grimont) and unnamed DNA group 13 (studied by I. Tjernberg and J. Ursing) are the most prevalent Acinetobacter species in hospitals. Using the identification scheme of Bouvet and Grimont, it is sometimes difficult to differentiate these species from A. calcoaceticus sensu stricto, a species of the natural environment that has seldom been found associated with human infection. Genetically identified Acinetobacter isolates belonging to A. calcoaceticus sensu stricto (n = 12), A. baumannii (n = 22), Acinetobacter species 3 (n = 15) and DNA group 13 of Tjernberg and Ursing (n = 26), Acinetobacter species 10 (n = 2), Acinetobacter species 11 (n = 2) and 3 strains ungrouped by DNA-DNA hybridization were investigated for electrophoretic separations of L-malate dehydrogenase (MDH), glutamate dehydrogenase (GDH) and catalase (CAT). All A. calcoaceticus sensu stricto isolates were easily differentiated from those of other species investigated by their high MDH values (relative mobility (Rf) = 78), their low GDH values (Rf range: 24-28) and CAT values (Rf range: 34-42). Acinetobacter species 3 was differentiated from A. baumannii and DNA group 13 of Tjernberg and Ursing by high CAT values. A. baumannii could not be differentiated from Tjernberg and Ursing DNA group 13. Acinetobacter species 10 was clearly differentiated from Acinetobacter species 11. Once an Acinetobacter is phenotypically identified with the four closely related species investigated here, electrophoretic analysis of MDH, GDH and CAT might be a useful complement to the identification scheme of Bouvet and Grimont for accurately identifying A. calcoaceticus sensu stricto.

Comparison of arbitrarily primed polymerase chain reaction and cell envelope protein electrophoresis for analysis of Acinetobacter baumannii and A. junii outbreaks

Two successive Acinetobacter outbreaks in a neonatal intensive care unit were studied with arbitrarily primed polymerase chain reaction (AP-PCR), cell envelope protein electrophoresis (protein fingerprinting) and antibiotic susceptibility testing. AP-PCR fingerprinting and protein fingerprinting yielded identical clustering of the isolates studied. Susceptibility test results were useful for rapid recognition of the outbreaks, but clustering of several isolates was different from the clustering obtained with AP-PCR fingerprinting and protein fingerprinting. Typing results indicated that the two outbreaks, which occurred at a three-month interval, were each caused by a single strain, and that both strains differed from the strains prevailing in the hospital. The strain of one outbreak was identified as A. junii, a species commonly not involved in outbreaks. A. baumannii isolates collected from different departments of this hospital during a period of four years clustered into only five different types. Moreover, strains from different departments of a second hospital belonged to the type prevailing in the first hospital, although there were no apparent connections between the two institutions. This may indicate that only a limited number of strains of the A. calcoaceticus-baumannii complex are involved in nosocomial outbreaks.

Pillows, an unexpected source of Acinetobacter

From 1989 until 1992 an increase in the number of isolations of Acinetobacter was observed in a community hospital in The Netherlands. The organisms were spread throughout the hospital and a common source was suspected. Feather pillows were found to harbour high numbers of acinetobacters. Replacement with synthetic pillows and correction of the laundry procedure resulted in a significant reduction of Acinetobacter isolations. A number of isolates from patients and from pillows were indistinguishable using biotyping, antibiogram typing and cell envelope protein typing. By the use of DNA-DNA hybridization most isolates were identified to A. baumannii and the unnamed closely related genomic species 13. A number of isolates, mostly from pillows, were identified as A. radioresistens. The outcome of cultivation, intervention and typing suggests that the feather pillows played an important role in the outbreak.

Structure of a surface polysaccharide from Acinetobacter baumannii strain 214

A polysaccharide containing D-galactose, D-glucose, and 2-acetamido-2-deoxy-D-galactose was obtained from an aqueous phenol extract of isolated cell walls from Acinetobacter baumannii strain 214. By means of NMR studies and chemical degradations, the repeating unit of the polymer was identified as a branched trisaccharide of the structure shown. [formula: see text]

Numerical classification and identification of Acinetobacter genomic species

A total of 211 Acinetobacter strains (representing all currently recognized genomic species) were tested for 329 biochemical characters. Overall similarities of all strains were determined for 145 characters by numerical taxonomic techniques, the UPGMA algorithm and the S(SM)) and the S(J) coefficients as measures of similarity. Seven clusters (two or more strains) and three unclustered strains were recovered at a similarity level of 80.0% (S(SM). At this level a complete correspondence between phenotypic cluster and genomic species was found only for genomic species 12 (Ac. radioresistens). At higher similarity levels (84.0% to 84.6% (S(SM)), however, several subclusters were found, each representing a single genomic species. An exception were the strains belonging to the genetically closely related species of the Acinetobacter calcoaceticus-baumannii complex. These were recovered scattered in several subclusters. The degree of genomic relatedness between some DNA groups correlated with phenotypic similarities, especially for DNA group 8 (Ac. Iwoffii) and 15 of Tjernberg and Ursing, and for DNA group 4 (Ac. haemolyticus) and 6. For the majority of genomic species, two identification matrices were constructed consisting of 22 and 10 diagnostic characters, respectively. The correct identification rates for the matrices were 98.0% (22 tests) and 90.8% (10 tests) taking a Willcox probability > 0.9. For unambiguous identification of some genomic species, however, additional methods (preferably DNA-DNA hybridization or ribotyping) should be used.

Endemic acinetobacter in intensive care units: epidemiology and clinical impact

AIMS

To assess whether Acinetobacter isolates obtained over 20 months in a tertiary care hospital were epidemiologically related; to establish the clinical importance of the organisms; and to identify the isolates according to the recent taxonomy.

METHODS

Fifty eight Acinetobacter isolates from 49 patients collected during 1984 and 1985 were investigated. Most isolates were from respiratory tract specimens from intensive care patients. The organisms were typed by cell envelope protein electrophoresis and by a quantitative carbon source growth assay; patients' charts were reviewed to differentiate between colonisation and infection; representative isolates were identified to species level by DNA-DNA hybridisation.

RESULTS

Twelve protein profiles were distinguished in the isolates. Forty two isolates were of the same protein profile (profile I); other profiles were observed in a few or single isolates. Cluster analysis of carbon source growth divided profile I isolates into two groups--one of isolates from 1984 and one from 1985. They were identified as A baumannii and associated with infections in eight patients. Four other infections were caused by acinetobacters with other protein profiles (three of A baumannii; one of the unnamed DNA group 3).

CONCLUSIONS

Apart from sporadic strains, two strains of the same protein profile, but distinguishable by carbon source growth, were successively endemic. Cluster analysis was a valuable tool in the interpretation of typing and epidemiological data. The 12 (28%) infections of Acinetobacter in 43 patients in intensive care suggest that the presence of these organisms in wards of severely ill patients should be a cause of concern.

Serotyping of clinical isolates of Acinetobacter baumannii and genospecies 3: detection of additional serovars

Continued serological monitoring of clinical isolates of Acinetobacter baumannii and genospecies 3 permitted identification of 7 new serovars of A. baumannii and 8 additional serovars of genospecies 3.