Outer-membrane proteins pattern and detection of beta-lactamases in clinical isolates of imipenem-resistant Acinetobacter baumannii from Brazil

Revealing the single-channel characteristics of OprD (OccAB1) porins from hospital strains of Acinetobacter baumannii

Nowadays, reports of antimicrobial resistance (AMR) against many antibiotics are increasing because of their misapplication. With this rise, there is a serious decrease in the discovery and development of new types of antibiotics amid an increase in multi-drug resistance. Unfermented Acinetobacter baumannii from gram-negative bacteria, which is one of the main causes of nosocomial infections and multi-drug resistance, has 4 main kinds of antibiotic resistance mechanism: inactivating antibiotics by enzymes, reduced numbers of porins and changing of their target or cellular functions due to mutations, and efflux pumps. In this study, characterization of the possible mutations in OprD (OccAB1) porins from hospital strains of A. baumannii were investigated using single channel electrophysiology and compared with the standard OprD isolated from wild type ATCC 19,606. For this aim, 5 A. baumannii bacteria samples were obtained from patients infected with A. baumannii, after which OprD porins were isolated from these A. baumannii strains. OprD porins were then inserted in an artificial lipid bilayer and the current-voltage curves were obtained using electrical recordings through a pair of Ag/AgCl electrodes. We observed that each porin has a characteristic conductance and single channel recording, which then leads to differences in channel diameter. Finally, the single channel data have been compared with the gene sequences of each porin. It was interesting to find out that each porin isolated has a unique porin diameter and decreased anion selectivity compared to the wild type.

Decreased carO gene expression and OXA-type carbapenemases among extensively drug-resistant Acinetobacter baumannii strains isolated from burn patients in Tehran, Iran

A major challenge in the treatment of infections has been the rise of extensively drug resistance (XDR) and multidrug resistance (MDR) in Acinetobacter baumannii. The goals of this study were to determine the pattern of antimicrobial susceptibility, blaOXA and carO genes among burn-isolated A. baumannii strains. In this study, 100 A. baumannii strains were isolated from burn patients and their susceptibilities to different antibiotics were determined using disc diffusion testing and broth microdilution. Presence of carO gene and OXA-type carbapenemase genes was tested by PCR and sequencing. SDS-PAGE was done to survey CarO porin and the expression level of carO gene was evaluated by Real-Time PCR. A high rate of resistance to meropenem (98%), imipenem (98%) and doripenem (98%) was detected. All tested A. baumannii strains were susceptible to colistin. The results indicated that 84.9% were XDR and 97.9% of strains were MDR. In addition, all strains bore blaOXA-51 like and blaOXA-23 like and carO genes. Nonetheless, blaOXA-58 like and blaOXA-24 like genes were harbored by 0 percent and 76 percent of strains, respectively. The relative expression levels of the carO gene ranged from 0.06 to 35.01 fold lower than that of carbapenem-susceptible A. baumannii ATCC19606 and SDS - PAGE analysis of the outer membrane protein showed that all 100 isolates produced CarO. The results of current study revealed prevalence of blaOXA genes and changes in carO gene expression in carbapenem resistant A.baumannii.

Distribution of virulence-associated genes and antimicrobial susceptibility in clinical Acinetobacter baumannii isolates

Acinetobacter baumannii is undoubtedly one of the most clinically significant pathogens. The multidrug resistance and virulence potential of A. baumannii are responsible for hospital-acquired nosocomial infections. Unlike numerous investigations on the drug-resistant epidemiology of A. baumanni, virulence molecular epidemiology is less studied. Here, we collected 88 A. baumannii clinical isolates, tested their antimicrobial susceptibility to 10 commonly used antibiotics and analyzed the distribution of 9 selected virulence-associated genes, aims to investigate the primary characteristics of the virulence-associated genes that exist in clinically multidrug resistant (MDR) and non-MDR isolates of A. baumannii. The MIC results showed the resistance rates of ciprofloxacin (68.2%, 60/88), gentamicin (67.0%, 59/88), amikacin (58.0%, 51/88), tobramycin (58.0%, 51/88), doxycycline (67.0%, 59/88), meropenem (54.5%, 48/88) and imipenem (65.9%, 58/88) were all above 50%, except for levofloxacin (34.1%, 30/88), minocycline (1.1%, 1/88) and polymyxin B (0%, 0/88). The Pulsed field gel electrophoresis (PFGE) analysis revealed that the resistance rate of MDR A. baumannii isolates in the Epidemic group was predominant (79.5%, 44/58), but in the Sporadic group was only 6.7% (2/30). Further investigation on the distribution of virulence genes showed the virulence genes bap (95.5%), surA1 (92.0%), BasD (92.0%), paaE (88.6%), pld (87.5%), BauA (62.5%), omp33-36 (59.1%) and pglC (53.4%) were accounted for high proportion, except for traT (0%). Overall, our results revealed that MDR isolates predominated in the Epidemic A. baumannii isolates, and contained a very high proportion of virulence genes, which may lead to high risk, high pathogenicity and high treatment challenge.

Genetic Mechanisms of Antimicrobial Resistance of Acinetobacter baumannii

OBJECTIVE

To summarize published data identifying known genetic mechanisms of antibiotic resistance in Acinetobacter baumannii and the correlating phenotypic expression of antibiotic resistance.

DATA SOURCES

MEDLINE databases (1966-July 15, 2010) were searched to identify original reports of genetic mechanisms of antibiotic resistance in A. baumannii.

DATA SYNTHESIS

Numerous genetic mechanisms of resistance to multiple classes of antibiotics are known to exist in A. baumannii, a gram-negative bacterium increasingly implicated in nosocomial infections. Mechanisms may be constitutive or acquired via plasmids, integrons, and transposons. Methods of resistance include enzymatic modification of antibiotic molecules, modification of antibiotic target sites, expression of efflux pumps, and downregulation of cell membrane porin channel expression. Resistance to β-lactams appears to be primarily caused by β-lactamase production, including extended spectrum β-lactamases (b/aTEM, blaSHV, b/aTX-M,b/aKPC), metallo-β-lactamases (blaMP, blaVIM, bla, SIM), and most commonly, oxacillinases (blaOXA). Antibiotic target site alterations confer resistance to fluoroquinolones (gyrA, parC) and aminoglycosides (arm, rmt), and to a much lesser extent, β-lactams. Efflux pumps (tet, ade, abe) contribute to resistance against β-lactams, tetracyclines, fluoroquinolones, and aminoglycosides. Finally, porin channel deletion (carO, oprD) appears to contribute to β-lactam resistance and may contribute to rarely seen polymyxin resistance. Of note, efflux pumps and porin deletions as solitary mechanisms may not render clinical resistance to A. baumannii.

CONCLUSIONS

A. baumannii possesses copious genetic resistance mechanisms. Knowledge of local genotypes and expressed phenotypes for A. baumannii may aid clinicians more than phenotypic susceptibilities reported in large epidemiologic studies.

A conserved region from biofilm associated protein as a biomarker for detection of Acinetobacter baumannii

Acinetobacter baumannii is the leading cause of nosocominal infection within the family Moraxellaceae. Due to multiple antibiotic resistances of the bacteria, the treatment is very difficult, hence specific and economical test for early diagnosis of infection is needed. Development of such a test requires targeting specific cell surface antigens. Bacterial ability of biofilm formation grants major contribution in antimicrobial resistance and other environmental stresses such as nutrient limitation and dehydration. Biofilm associated protein (Bap), a specific cell surface protein, is directly involved in A. baumannii biofilm formation. The goal of this study is diagnosis of A. baumannii infection exploiting specific target from Bap. A selected subunit of Bap was cloned, expressed and purified. Mice were divided into three groups. Group one was immunized with recombinant Bap subunit, mice in group two were infected with A. baumannii (positive control) and mice in groups three served as negative control. Immunization with Bap subunit resulted in high antibody titers. Animals in control group that received same amount of adjuvant and PBS showed no Bap-specific antibodies. Sensitivity and specificity of the antibodies raised were determined by ELISA and Western blotting. Recombinant Bap subunit was tested by ELISA using sera obtained from A. baumannii infected patients and healthy individuals. This conserved and immunodominant region of Bap could serve as an appropriate target for diagnosis A. baumannii infection.

Role of fibronectin in the adhesion of Acinetobacter baumannii to host cells

Adhesion to host cells is an initial and important step in Acinetobacter baumannii pathogenesis. However, there is relatively little information on the mechanisms by which A. baumannii binds to and interacts with host cells. Adherence to extracellular matrix proteins, such as fibronectin, affords pathogens with a mechanism to invade epithelial cells. Here, we found that A. baumannii adheres more avidly to immobilized fibronectin than to control protein. Free fibronectin used as a competitor resulted in dose-dependent decreased binding of A. baumannii to fibronectin. Three outer membrane preparations (OMPs) were identified as fibronectin binding proteins (FBPs): OMPA, TonB-dependent copper receptor, and 34 kDa OMP. Moreover, we demonstrated that fibronectin inhibition and neutralization by specific antibody prevented significantly the adhesion of A. baumannii to human lung epithelial cells (A549 cells). Similarly, A. baumannii OMPA neutralization by specific antibody decreased significantly the adhesion of A. baumannii to A549 cells. These data indicate that FBPs are key adhesins that mediate binding of A. baumannii to human lung epithelial cells through interaction with fibronectin on the surface of these host cells.

Loss of the 29-kilodalton outer membrane protein in the presence of OXA-51-like enzymes in Acinetobacter baumannii is associated with decreased imipenem susceptibility

Carbapenem resistance in Acinetobacter baumannii is increasing these days. We investigated the roles of outer membrane proteins and efflux pumps in carbapenem resistance of A. baumannii which showed no carbapenemase activity in modified Hodge test. Among 58 carbapenem-resistant isolates collected from the Korea University Medical Center between January 2002 and March 2006, 17 isolates showed negative results in modified Hodge test. In outer membrane protein analysis, loss of the 29-kDa protein band was related with higher imipenem minimum inhibitory concentrations especially in the presence of OXA-51-like enzymes. Efflux pump-mediated carbapenem resistance was found in one out of the 17 isolates (5.9%). All of the 58 carbapenem-resistant strains and 5 of the 10 carbapenem-susceptible strains had OXA-51-like carbapenemase genes, suggesting that OXA-51-like enzymes may be naturally existing in A. baumannii and have very weak carbapenem hydrolyzing activity.

Role of tigecycline in the control of a carbapenem-resistant Acinetobacter baumannii outbreak in an intensive care unit

The incidence of Acinetobacter baumannii infection has greatly increased over recent decades with infections occurring more in critically ill hospitalised patients. Hospital outbreaks of multiple antibiotic-resistant strains are posing an increasing threat to public health. Three different outbreaks of multidrug-resistant A. baumannii (MRAB) infections involving 24 patients, aged 16-75 years occurred in the intensive care unit in the course of one year. The isolates were cultured from clinical samples and identified using automated Vitek II ID system and the API 20NE system. Susceptibility testing was done by the E-test method. Molecular typing of the isolates was determined by pulsed-field electrophoresis. Screening of both patients and the environment was carried out. The acquisition time, i.e. the time of admission to time of acquiring infection, ranged from 3 to 31 days. All isolates were multiply resistant (MRAB), including resistance to carbapenems (MRAB-C) in the majority of cases but susceptible to tigecycline, with a minimum inhibitory concentration (MIC(90)) of 2 microg/mL. The overall mortality rate was 16.7%. Time-to-clearance of the MRAB-C was 8.3 days in the first outbreak, when tigecycline was not used, and 2.8 and 3.1 days during the second and third outbreaks, respectively, when tigecycline was used, and all but one patient survived. Environmental screening revealed gross contamination of many surfaces and equipment within the unit. The outbreak strains belonged to two distinct clones (D and E) whereas the 14 environmental strains belonged to three distinct groups (A-C). The outbreak of infections treated with tigecycline was successfully eliminated in conjunction with an aggressive infection control strategy.

Carbapenem-resistant Acinetobacter baumannii outbreak at university hospital

Nineteen clonally related imipenem-resistant Acinetobacter baumannii isolates were recovered from eight intensive care unit patients. All isolates harboured bla_OXA-51-like β-lactamase genes and showed the absence of 22 kDa fraction in outer membrane porin profile analysis. It suggests a combination of two mechanisms as responsible for carbapenem–resistant phenotypes.

Diversity of carbapenem resistance mechanisms in Acinetobacter baumannii from a Taiwan hospital: spread of plasmid-borne OXA-72 carbapenemase

OBJECTIVES

We investigated the molecular epidemiology of carbapenem-resistant Acinetobacter baumannii from a Taiwanese hospital and determined the mechanisms responsible for resistance.

METHODS

Ninety-two consecutive meropenem-resistant A. baumannii isolates collected between January 2005 and June 2007 were screened for genes encoding OXA carbapenemases, metallo-beta-lactamases and for the carO gene encoding an outer membrane protein. PFGE was used to define clonal relatedness. PCR mapping was used to examine the linkage of insertion sequences and bla(OXA) genes. Southern hybridization of plasmid extracts and I-CeuI-restricted chromosomal DNA was used to locate bla(OXA-24-like) genes. Sequences of selected bla(OXA-24-like) and carO genes were determined and loss of CarO expression was confirmed by SDS-PAGE.

RESULTS

Most (70/92, 76%) isolates belonged to one of three PFGE pulsotypes, indicating clonal spread. Fifty-nine isolates, including the majority of those of pulsotypes I and III, produced OXA-72 carbapenemase. The bla(OXA-72) gene was located on a 54 kb plasmid in selected isolates. Thirty-three (36%) isolates, including all 16 of pulsotype II, had ISAba1 preceding the bla(OXA-51-like) gene, promoting its expression. In addition to OXA-72 carbapenemase, two pulsotype I and three pulsotype III isolates did not produce CarO protein as the carO gene was disrupted by insertion of an ISAba1 element. Two isolates of a minor pulsotype had a bla(OXA-58-like) gene and a single PFGE-unique isolate had a bla(OXA-23-like) gene.

CONCLUSIONS

Although diverse mechanisms were identified, production of OXA-72 carbapenemase was the most common mechanism of carbapenem resistance in A. baumannii from this Taiwanese hospital. The plasmidic location of the gene had facilitated its spread to multiple strains.

Acinetobacter baumannii: emergence of a successful pathogen

Acinetobacter baumannii has emerged as a highly troublesome pathogen for many institutions globally. As a consequence of its immense ability to acquire or upregulate antibiotic drug resistance determinants, it has justifiably been propelled to the forefront of scientific attention. Apart from its predilection for the seriously ill within intensive care units, A. baumannii has more recently caused a range of infectious syndromes in military personnel injured in the Iraq and Afghanistan conflicts. This review details the significant advances that have been made in our understanding of this remarkable organism over the last 10 years, including current taxonomy and species identification, issues with susceptibility testing, mechanisms of antibiotic resistance, global epidemiology, clinical impact of infection, host-pathogen interactions, and infection control and therapeutic considerations.

Acquisition of a plasmid-borne blaOXA-58 gene with an upstream IS1008 insertion conferring a high level of carbapenem resistance to Acinetobacter baumannii

The oxacillinase gene was reported to confer limited resistance to carbapenem in Acinetobacter baumannii. In this study, we have demonstrated that an A. baumannii clinical isolate harboring a plasmid, pTVICU53, has 11,037 bp encoding 13 open reading frames. A bla(OXA-58) gene with an upstream insertion of truncated ISAba3 (DeltaISAba3) and IS1008 was found in this plasmid. DeltaISAba3and IS1008 provided two independent promoters for the transcription control of the bla(OXA-58) gene. The transformation of pTVICU53 or a shuttle vector bearing IS1008-DeltaISAba3-bla(OXA-58) to different A. baumannii recipients can increase their MICs of carbapenem 64- to 256-fold. The deletion of promoters provided by IS1008 resulted in dramatic decreases in bla(OXA-58) transcription and a 32- to 64-fold reduction in the carbapenem MIC. These findings highlight that A. baumannii might develop carbapenem resistance with a single transformation step, taking up a plasmid containing a genetic construct with a potentially high level of transcription of the bla(OXA-58) gene.

Isolation and characterization of the Omp-PA porin from Porphyromonas asaccharolytica, determination of the omp-PA gene sequence and prediction of Omp-PA protein structure

A single monomeric porin, Omp-PA (37kDa), was isolated from the outer membrane of the gram-negative anaerobic rod Porphyromonas asaccharolytica. Further characterization revealed that this porin consists of two different fractions: a heat-modifiable fraction which in its denatured form migrated on SDS-PAGE as a protein with a molecular weight of 41kDa and a heat-resistant fraction which did not change its migration on SDS-PAGE after boiling. A liposome swelling assay revealed that only the heat-resistant fraction was able to transport sugars after its incorporation into the liposomes, although it did not discriminate between differently sized sugars. We hypothesize that the heat-modifiable fraction corresponds to the "closed" conformer of Omp-PA, whereas the heat-resistant fraction corresponds to the "open" conformer of the protein. Cloning of the omp-PA gene revealed an open reading frame of 1161 bases, with a predicted protein sequence of 387 amino acids. The mature protein consists of 366 amino acids with a calculated MW of 41,102Da and an estimated pI of 7.24. The C-terminal domain of Omp-PA is homologous to the characteristic OmpA signature domain (71% similarity with the OmpA consensus domain). Sequence comparison with other anaerobes from the Bacteroides family demonstrated homology across the entire ORF. Digestion of the P. asaccharolytica outer membrane analysis of trypsin-digested Omp-PA yielded two proteins migrating with apparent molecular weights of 37 and 27kDa. These data fully supported our hypothesis that the C-terminal domain of the two-domain "closed" conformer of Omp-PA was digested by trypsin, whereas the single domain beta-barrel "open" conformer was inaccessible to trypsin.

Global Comparison of the Membrane Subproteomes between a Multidrug-ResistantAcinetobacterbaumanniiStrain and a Reference Strain

Acinetobacter baumannii causes severe infections in compromised patients. We combined SDS-PAGE, two-dimensional gel electrophoresis and mass spectrometry (LC-MS/MS and MALDI-TOF) to separate and characterize the proteins of the cell envelope of this bacterium. In total, 135 proteins (inner and outer membrane proteins) were identified. In this analysis, we described the expression by this bacterium of RND-type efflux systems and some potential virulence factors. We then compared the membrane subproteome of a clinical multidrug-resistant (MDR) isolate with that of a reference strain. We found that the MDR strain expressed lower levels of the penicillin-binding-protein 1b, produced a CarO protein having different primary and quaternary structures to that of the reference strain, and expressed OmpW isoforms. We also showed that the clinical strain has a high ability to form biofilms consistent with the accumulation of some outer membrane proteins (OMPs) such as NlpE or CsuD that have already been described as involved in bacterial adhesion. These features may partly explain the MDR emergence of the clinical isolate.

Carbapenem resistance in Acinetobacter baumannii: mechanisms and epidemiology

The increasing trend of carbapenem resistance in Acinetobacter baumannii worldwide is a concern since it limits drastically the range of therapeutic alternatives. Metallo-beta-lactamases (VIM, IMP, SIM) have been reported worldwide, especially in Asia and western Europe, and confer resistance to all beta-lactams except aztreonam. The most widespread beta-lactamases with carbapenemase activity in A. baumannii are carbapenem-hydrolysing class D beta-lactamases (CHDLs) that are mostly specific for this species. These enzymes belong to three unrelated groups of clavulanic acid-resistant beta-lactamases, represented by OXA-23, OXA-24 and OXA-58, that can be either plasmid- or chromosomally-encoded. A. baumannii also possesses an intrinsic carbapenem-hydrolysing oxacillinase, the expression of which may vary, that may play a role in carbapenem resistance. In addition to beta-lactamases, carbapenem resistance in A. baumannii may also result from porin or penicillin-binding protein modifications. Several porins, including the 33-kDa CarO protein, that constitute a pore channel for influx of carbapenems, might be involved in carbapenem resistance.

Retrospective analysis of multidrug-resistant Acinetobacter baumannii strains isolated during a 4-year period in a university hospital

OBJECTIVE

To describe the epidemiology of Acinetobacter baumannii infection during 2000-2003 and to determine whether the multidrug-resistant strains were already present in our Toulouse hospital before the 2003 French national outbreak.

DESIGN

Descriptive molecular and clinical epidemiologic study of A. baumannii isolates using a combination of antibiotyping and pulsed-field gel electrophoresis (PFGE).

SETTING

A 1,000-bed university hospital in Toulouse, France.

METHODS

All clinical samples that had tested positive for A. baumannii between January 1, 2000, and December 31, 2003, were collected. Multidrug-resistant isolates of A. baumannii were then submitted to PFGE, and clinical characteristics of the source patients were noted.

RESULTS

A total of 1,277 A. baumannii samples were identified, 791 of which had not been previously identified; 148 were positive for multidrug-resistant strains. These strains were more likely to have been isolated in the intensive care unit (ICU) than were susceptible strains (P<.001; relative hazard, 3.77). The positive clinical samples were of various types (eg, nonprotected respiratory samples [43%] and blood [5%]), but no difference in type of source was seen between resistant and susceptible strains. A simultaneous analysis of pulsotypes and antibiotypes proved that the outbreak in the ICU in 2003 could be linked to an initially endemic clone that had been isolated in 2001. Furthermore, a second clone responsible for an extended-spectrum beta -lactamase phenotype was sporadically present in our institution. Although the strains isolated in the burn unit were also genetically related one to another, the specific responsible clone only appeared in 2003.

CONCLUSION

Several multidrug-resistant clones can coexist endemically for several years and can be detected during an outbreak by close survey of epidemic sources.

Cloning and functional analysis of the gene encoding the 33- to 36-kilodalton outer membrane protein associated with carbapenem resistance in Acinetobacter baumannii

We investigated a multiresistant strain of Acinetobacter baumannii isolated in our hospital. Analysis of the N-terminal peptide sequence of the outer membrane proteins (OMPs) purified from the strain allowed us to clone and sequence the nucleotides of the gene encoding the 33- to 36-kDa OMP associated with carbapenem resistance in A. baumannii.

OXA-type carbapenemases

In recent years, the number of class D beta-lactamases with carbapenem-hydrolysing properties has increased substantially. Based on amino acid sequence identities, these class D or OXA-type carbapenemases are divided into eight distantly related groups, and they are only remotely related to other class D beta-lactamases. A putative ancestor to one of the plasmid-encoded OXA-type carbapenemases has been found. OXA-type carbapenemases are not integrated into integrons as gene cassettes like many class D oxacillinases, but most of the OXA-type carbapenemases are instead encoded by chromosomal genes. Some of these OXA-type carbapenemases are widely dispersed in Pseudomonas aeruginosa and especially in Acinetobacter baumannii. Although most of the OXA-type carbapenemases show only weak carbapenemase activity, carbapenem resistance may result from a combined action an OXA-type carbapenemase and a secondary resistance mechanism such as porin deficiencies or overexpressed efflux pumps. This article reviews the phylogeny and the genetic environments of the encoding genes and kinetic properties of the OXA-type carbapenemases.

Identification of an OprD Homologue inAcinetobacterbaumannii

With the increased number of resistant Acinetobacter baumannii strains, it is urgently required to decipher the molecular bases of outer membrane permeability. The analyses of the outer membrane from different A. baumannii strains indicated a modification in the expression of two proteins of 29 and 43 kDa, respectively. By electrophoresis and MALDI-MS analyses, the 43 kDa OMP was identified as a protein belonging to the OprD family, a basic amino acid and imipenem porin.

Emergence of an IMP-like metallo-enzyme in an Acinetobacter baumannii clinical strain from a Brazilian teaching hospital

Multidrug-resistant Acinetobacter spp. constitute a serious cause of nosocomial infection in Brazilian hospitals. This manuscript reports the first appearance of an IMP-like metallo-beta-lactamase encountered in a clinical isolate of A. baumannii from a Brazilian teaching hospital.

Severe nosocomial infections with imipenem-resistant Acinetobacter baumannii treated with ampicillin/sulbactam

Forty consecutive patients with nosomial infections caused by multidrug-resistant Acinetobacter baumannii were treated with intravenous ampicillin/sulbactam. The infections were primary bloodstream (32.5%), pneumonia (30%), urinary tract (15%), peritonitis (7.5%), surgical site (7.5%), meningitis (5%) and sinusitis (2.5%). Most were severe infections with underlying conditions (median APACHE II score: 14.5) and 72.5% occurred in the ICU. Twenty-seven (67.5%) were improved/cured, seven (17.5%) were failures and six (15%) were considered to have an indeterminate outcome because patients died within the first 48 h of treatment. Two cases of meningitis were treated and did not respond. The median daily dose of ampicillin/sulbactam was 6 g/3 g and six patients received 12 g/6 g. No adverse effects were observed. This study indicates that ampicillin/sulbactam may be a good and safe therapeutic option to treat severe nosocomial infections caused by multi-drug resistant A. baumannii.

Loss of a 29-kilodalton outer membrane protein in Acinetobacter baumannii is associated with imipenem resistance

We analyzed the possible causes of imipenem (IPM) resistance in multidrug-resistant isolates of Acinetobacter baumannii. Comparison of the outer membrane protein (OMP) profiles of two genomically related strains (Ab288 [IPM sensitive] and Ab242 [IPM resistant]) indicated the conspicuous loss of a 29-kDa polypeptide in the Ab242 strain. No carbapenemase activity was detected in any of these strains. The treatment of Ab288 with sodium salicylate resulted in IPM resistance and the loss of the 29-kDa OMP. In addition, IPM-resistant clones of Ab288 which were selected by repetitive culturing in increasing concentrations of this antibiotic also showed the absence of this 29-kDa OMP.

Multiresistant Acinetobacter infections: a role for sulbactam combinations in overcoming an emerging worldwide problem

Recent studies have highlighted the emergence of infections involving multiresistant Acinetobacter clinical isolates. Sulbactam offers direct antimicrobial activity against Acinetobacter species. Accordingly, co-administration of sulbactam with ampicillin or cefoperazone offers the potential of effective empirical therapy against Acinetobacter and other bacteria such as Enterobacteriaceae in institutions in which they are susceptible. Many in vitro studies have indicated that Acinetobacter remains fully susceptible to ampicillin-sulbactam or cefoperazone-sulbactam. Furthermore, ampicillin-sulbactam has proven clinically effective and well tolerated in the treatment of severe acinetobacter infections, including bacteremia. Therefore, ampicillin-sulbactam is a sensible option for the treatment of life-threatening acinetobacter infections.