Identification of Acinetobacter species

Pseudo-outbreak of Acinetobacter Iwoffii Infection in a Tertiary Care Center in Thailand

We describe a pseudo-outbreak ofAcinetobacter Iwoffiiinfection that was recognized early. The pseudo-outbreak involved 16 patients and occurred 3.5 months after the GNS-506 Vitek automated system was introduced in the microbiology laboratory. Prompt confirmation of incomplete use of the automated system's algorithm as the point source of the misidentifiedA. Iwoffiiclinical isolates averted a full outbreak investigation and excess use of infection control resources.

Evaluation of Ciprofloxacin (gyrA, parC Genes) and Tetracycline (tetB Gene) Resistance in Nosocomial Acinetobacter baumannii Infections

Background:

Acinetobacter baumannii plays an important role in some types of nosocomial infections as an opportunist microorganism which increases levels of resistance to antibacterial drugs and disinfectants.

Objectives:

The aim of this study was to determine the resistance and sensitivity of A. baumannii to different antibiotics and evaluate the minimal inhibitory concentration (MIC) for Ciprofloxacin and Tetracycline; in addition to Surfanios, Citron and Aniosyme DD1 disinfectants, and also to detect the presence of gyrA, parC and tetB gene bands in the isolates.

Materials and Methods:

In this study, 65 A. baumannii isolates were collected from the hospitalized patients in NIOC hospital (National Iranian Oil Company hospital) of Tehran, Iran during 2010-2011. The pattern of sensitivity to antibiotics was determined using CSLI disk diffusion and MIC methods. Furthermore, resistance of isolates to the common disinfectants (Surfanios Citron and Aniosyme DD1) was determined in different hospital wards. Presence of gyrA, parC and tetB gene bands was also detected by PCR method.

Results:

Frequency of Acinetobacter resistance to Amikacin, Ciprofloxacin, co-Trimoxazole, Ceftazidime and Ceftriaxone was 100% in the isolates reviewed in this study. The frequency of resistance to Gentamicin and Tetracycline were 86.1% in the isolates. The MIC of Ciprofloxacin in all (100%) of isolates was 32-64 μg/mL which showed the resistance to Ciprofloxacin In 86.1% of cases the Gentamicin and Tetracycline MIC were ≥ 16 μg/mL and in 13.9% of isolates the Gentamicin and Tetracycline MIC were 4 μg/mL, these results showed the resistance and sensitivity to the Gentamicin and Tetracycline, respectively. Additionally, all (100%) of the A. baumannii isolates were resistant to disinfectant concentrations, which were used with the methods recommended by manufacturers (0.5%). In 100% of the isolates parC and gyrA genes bands were detected, and tetB gene was also detected in 86.1% of Tetracycline resistant isolates.

Conclusions:

Due to the high resistance of A. baumannii isolates to most antibiotics in our study and also its high resistance to the common disinfectants usually used in hospitals, it seems that more attentions should be paid for applying disinfectants. Since most of the isolates were collected from tracheal and sputum samples (46%), it seems that respiratory tract is the most t prevalent site of infection among Acinetobacter infections. Therefore, disinfecting the respiratory tract related equipment and instruments by using proper disinfectants seems to be an appropriate way to prevent these infections.

Characterization of the carbapenem-hydrolyzing oxacillinase oxa-58 in an Acinetobacter genospecies 3 clinical isolate

Based on imipenem resistance in an Acinetobacter genospecies 3 clinical isolate, we were able to identify, for the first time in this genomic species, a plasmid-encoded bla(OXA-58) gene that was 100% homologous to the same gene in Acinetobacter baumannii.

Characterization of the carbapenem-hydrolyzing oxacillinase OXA-58 in an Acinetobacter phenon 6/ct13TU clinical isolate

The bla(OXA-58) gene identified in the Acinetobacter phenon 6/ct13TU clinical isolate presented 100% homology with the same gene in Acinetobacter baumannii. Its location in a plasmid suggests that these resistance genes may be transferred from 1 species to another.

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.

[Acinetobacter baumannii bacteremia: clinical and prognostic features]

OBJECTIVE

The incidence, clinical features, and prognosis of bacteremia due to Acinetobacter baumannii were investigated.

METHODS

Prospective study of all episodes of A. baumanii bacteremia detected during the period of January 1995 to December 1998. A. baumannii was identified using recent standard methods.

RESULTS

A total of 133 episodes of bacteremia due to A. baumannii were studied, all of them nosocomial-acquired. The incidence-density diminished from 2.02 episodes per 10,000 patient-days to 0.40 episodes per 10,000 patient-days after the implementation of a control program. Most of the patients (70%) were, or had been, in the ICU when bacteremia occurred. Some 80% of patients had a chronic illness and 62% had a Hilf's severity score > 4. Among the strains identified, 74% were multidrug-resistant and 28% were imipenem-resistant. Attributable mortality was 25.6%. Multivariate analysis showed that inappropriate antibiotic treatment, septic shock, and high Hilf's severity score were associated with poorer prognosis.

CONCLUSION

A. baumannii bacteremia mainly affects severely ill patients who have undergone several invasive procedures, and who may have relevant associated morbidity and mortality. Among other variables, inappropriate antibiotic treatment was a risk factor for increased mortalilty.

Epidemiology and infection control implications of Acinetobacter spp. in Hong Kong

In a previous study, we showed that Acinetobacter genomic DNA group 3 was the most common species among blood culture isolates and was commonly found on superficial carriage sites of the healthy and the sick, which are different findings from those reported in Europe and North America. We used amplified ribosomal DNA restriction analysis and pulsed-field gel electrophoresis to study further the molecular epidemiology of acinetobacters in our region. Over a study period of 6 weeks with 136 consecutive routine clinical isolates (1.33% of all specimens), genomic DNA groups 2 (Acinetobacter baumannii), 3, and 13TU were obtained from 59 of 69 positive patients. There is a significant difference in the specimen sources of the three genomic DNA groups, with group 13TU being significantly associated with the respiratory tract (chi-square exact test, P = 0.0064). Settle plates showed a significantly heavier environmental load from the intensive care unit (ICU) than from the four surgical wards examined (22 of 70 versus 76 of 120 plates with <5 colonies; chi-square test, P < 0. 0001). Genomic group 3 accounted for 6 of 12 clusters of possibly related strains among patients, between patients and the ICU environment, and in the ICU environment. Genomic groups 2 and 3 accounted for 21% of the 132 genomically identified isolates recovered from 21 of 41 local vegetables, 53 of 74 fish and meat samples, and 22 of 60 soil samples. Group 13TU was present only in patients' immediate surroundings. The role played by the environment and by human carriage should be evaluated in order to devise a cost-effective infection control program pertinent to our situation of acinetobacter endemicity.

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.

Specificity of rabbit antisera against lipopolysaccharide of Acinetobacter

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

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

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

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.

Use of interrepeat PCR fingerprinting to investigate an Acinetobacter baumannii outbreak in an intensive care unit

An epidemiological investigation of an outbreak of Acinetobacter baumannii among patients on 2 closely related intensive care units (ICU) was performed by molecular typing with interrepeat polymerase chain reaction (interrepeat PCR). 31 A. baumannii isolates obtained from 15 ICU patients were characterized. All patients were infected or colonized with A. baumannii. After identification of the outbreak, 6 environmental isolates were collected from tap-water, sinks and cleaning detergents. PCR fingerprinting identified 3 genotypes among the outbreak-related strains. One predominant genotype was demonstrated in 14/15 patients and this genotype was also found among all environmental isolates. The cluster of A. baumannii represented an outbreak of 1 genotype, suggesting cross-contamination. The finding of the identical genotype among all environmental strains indicated a common environmental source causing the outbreak. The outbreak was controlled after reimplementation of an effective disinfection of workplace surfaces. This survey proved interrepeat PCR to be a rapid and reliable method to differentiate A. baumannii strains, thereby allowing epidemiological surveillance of large amounts of strains and early interventions to control outbreaks.

Nosocomial bacteremia due to Acinetobacter baumannii. Clinical features, epidemiology, and predictors of mortality

To study the possible predisposing factors, clinical features, molecular epidemiology, and factors affecting mortality associated with bacteremia due to Acinetobacter baumannii, we reviewed 87 episodes of A. baumannii bacteremia occurring in 79 patients hospitalized at 2 university tertiary care centers and 4 community-based hospitals during a recent 18-month period. Plasmid DNA analysis and analysis of genomic DNA with pulsed-field gel electrophoresis was performed to investigate possible epidemiologic relationship. All patients acquired their infections in the hospital, and no seasonal variation was observed. Among patients with A. baumannii bacteremia, 91% were hospitalized in an intensive care unit, 99% had indwelling vascular catheters, 81% received prior broad spectrum antimicrobial therapy, 70% were mechanically ventilated, and 47% had major surgical procedures. In 39 cases (45%) the infection was related to indwelling vascular access devices. Other infections included pneumonia (9%), tracheobronchitis (22%), meningitis (2%), and burn wound infections (4%). Septic shock occurred in 30% of patients. All isolates were multidrug resistant. Polymicrobial bacteremia was observed in 35% of cases. The crude mortality rate was 44%. Death was considered attributable to A. baumannii bacteremia in 15 (19%) patients. All patients with pneumonia as the primary site of infection died. Using multivariate analysis, we identified 3 independent predictors of mortality: the presence of a rapidly or ultimately fatal underlying disease (p = 0.0009), septic shock at the onset of bacteremia (p = 0.0013), and mechanical ventilation (p = 0.016). Epidemiologic typing revealed that 82 episodes were associated with different hospital outbreaks of infection, and only 7 episodes were due to epidemiologically unrelated strains.

Risk factors for nosocomial colonization with multiresistant Acinetobacter baumannii

A six-month prospective survey was carried out in a university hospital to assess the incidence of Acinetobacter baumannii cross-contamination and to identify risk factors for colonization. Clinical isolates obtained during the study period were biotyped and genotyped by pulsed-field gel electrophoresis after ApaI macrorestriction of total DNA. Case-control univariate and multivariate analyses were performed to identify risk factors for Acinetobacter baumannii colonization. One hundred forty-seven patients hospitalized in 36 units were colonized or infected, of whom 52 were in three intensive care units. The urinary (29%) and bronchopulmonary tracts (26%) were the most frequently colonized sites. Nine major restriction patterns were identified: two were exhibited by epidemic multi-resistant strains of biotype 9 which were isolated from 65 patients hospitalized in ten units. Multivariate analysis showed that case-patients were (a) more likely than non-infected controls to be male, to have been previously hospitalized in another unit and to have had longer stays in the unit before colonization and hyperalimentation; and (b) more likely than controls colonized with other gram-negative bacilli to be male, to have had longer hospitalization, to have received treatment with third-generation cephalosporins and to have had a urinary catheter. The high incidence of colonization with Acinetobacter baumannii can thus be attributed to frequent cross-contamination and the use of broad-spectrum antibiotics. Colonized patients appear to be the major source of cross-contamination as epidemic strains spread throughout the hospital.

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.

Clinical and epidemiological investigations of Acinetobacter genomospecies 3 in a neonatal intensive care unit

A prospective study of Acinetobacter isolates from a neonatal intensive care unit was performed for 24 months. Fifty-six isolates were obtained from 21 patients, and another eight were obtained from environmental specimens. Infection due to Acinetobacter organisms was established for 16 patients, 6 with septicemia, 9 with pneumonia, and 1 with a wound infection. Further investigations were performed with 38 representative isolates. Twenty-nine isolates were identified as unnamed DNA-DNA hybridization group (genomospecies) 3, three were identified as genomospecies 2 (Acinetobacter baumannii), one was identified as genomospecies 5 (Acinetobacter junii), three were identified as genomospecies 14, and two were unclassified. Eight distinguishable protein profiles, coded I through VIII, were found by cell envelope protein electrophoresis. Profile V, a common profile, was observed for 17 isolates that had been recovered from 11 patients and 1 dust specimen. These isolates, all of which belonged to genomospecies 3, had similar antibiograms and biotypes. This study has revealed that genomospecies 3 can be associated with infection and be spread in hospitals.

Clinical and bacteriological features of relapsing shunt-associated meningitis due to Acinetobacter baumannii

A case is reported of a patient who developed Acinetobacter baumannii meningitis ten days after a ventriculoperitoneal shunt had been placed for control of elevated intracranial pressure. Intravenous antimicrobial therapy was instituted with imipenem and tobramycin after shunt removal and insertion of a ventriculostomy tube. Following the placement of a ventriculoatrial shunt, clinical and microbiological relapse occurred that was eventually cured after complete removal of the ventricular drainage system and a second course of systemic antibiotics. Relapse was confirmed by modern molecular typing techniques including plasmid DNA fingerprinting and analysis of total genomic DNA by pulsed-field gel electrophoresis.

Identification of Acinetobacter genomic species by amplified ribosomal DNA restriction analysis

A total of 53 field and reference strains, including the type strains of the seven named species (nomenspecies) and belonging to the 18 described genomic species (DNA groups) of the genus Acinetobacter, were studied by amplified ribosomal DNA restriction analysis (ARDRA). Restriction analysis with the enzymes AluI, CfoI, MboI, RsaI, and MspI of the enzymatically amplified 16S rRNA genes allowed us to identify all species except the genomic species 4 (Acinetobacter haemolyticus) and 7 (A. johnsonii), 5 (A. junii) and 17, and 10 and 11, which clustered pairwise in three respective groups. Further analysis with the enzyme HaeIII, HinfI, NciI, ScrFI, or TaqI did not allow us to differentiate the species within these three clusters. However, use of a few additional simple phenotypic tests (hemolysis, growth at 37 degrees C, production of acid from glucose, and gelatin hydrolysis) can be used to differentiate between the species within these clusters. ARDRA proved to be a rapid and reliable method for the identification of most of the Acinetobacter genomic species, including the closely related DNA groups 1 (A. calcoaceticus), 2 (A. baumannii), 3, and 13. The results of this study suggest that ARDRA can be used for the identification of Acinetobacter species and as such may help to elucidate the ecology and clinical significance of the different species of this genus. Since ARDRA uses universal 16S rRNA gene primers, it is expected to be applicable to the identification of most bacterial species. Furthermore, ARDRA is less prone to contamination problems than PCR for detection, since the use of cultured organisms results in a large initial quantity of target DNA.