Investigation into antibacterial and wound healing properties of platelets lysate against Acinetobacter baumannii and Klebsiella pneumoniae burn wound infections.

BACKGROUND AND AIM: Treatment of burn wound infections has become a global challenge due to the spread of multidrug-resistant bacteria; therefore, the development of new treatment options for the mentioned infections is essential. Platelets have drawn much attention for this purpose because they are a safe and cost-effective source of different antimicrobial peptides and growth factors. The present study evaluated antibacterial effects and wound healing properties of Platelet-derived Biomaterial (PdB) against Acinetobacter baumannii and Klebsiella pneumoniae burn wound infections. METHODS: PdB was prepared through the freezing and thawing process and then, in vitro antibacterial effect was determined by disk diffusion and broth microdilution methods. Afterward, burn wound was inflicted on 56 rats, infected with both bacteria, and topical administration was performed to evaluate antibacterial effects and wound healing properties of PdB. RESULTS: In vitro results showed that PdB inhibited the growth of A. baumannii in the highest dose (0.5), while we did not detect any inhibitory effects against K. pneumoniae. By contrast, PdB significantly inhibited the growth of bacteria in treated animal wounds compared to the control groups (P value < 0.05). Macroscopic assessments pointed to the significant enhancement of wound closure in the treated animals. In addition, histopathological examination demonstrated that treatment of rats with PdB led to a considerable increase in re-epithelialization and attenuated the formation of granulation tissue (P value < 0.05). CONCLUSION: The use of topical PdB is an attractive strategy for treating A. baumannii and K. pneumoniae burn wound infections because it inhibits bacterial growth and promotes wound healing properties.

Adherence ability and serum resistance of different hospital clusters of Acinetobacter baumannii.

The role of mechanical ventilation and catheters in favouring Acinetobacter baumannii infections needs to be better understood. This study evaluated the adherence of 19 isolates of different hospital clusters of A. baumannii to abiotic surfaces and epithelial cells (HEp-2). Of the hydrophobic isolates, 80% adhered to polystyrene, indicating a close relationship between hydrophobicity and adherence. All isolates adhered to epithelial cells to different degrees, and 73·7% showed an aggregated pattern. Analysis of the serum resistance of catheter-tip isolates showed that all were resistant. These worrisome results showed that the high capacity of A. baumannii to adhere to surfaces and survive in human serum could hinder treatment and control of this pathogen.

Polyvinyl alcohol nanofiber formulation of the designer antimicrobial peptide APO sterilizes Acinetobacter baumannii-infected skin wounds in mice.

Native and designer cationic antimicrobial peptides are increasingly acknowledged as host defense molecules rather than true antimicrobials. Due to their ability to activate the innate immune system, these structures are used to treat uninfected and bacterially-infected wounds, including those harboring Acinetobacter baumannii. Previously we documented that when administered intramuscularly or topically in liquid formulations, the proline-rich host defense peptide dimer A3-APO accelerates uninfected wound re-epithelization and eliminates systemic and local A. baumannii, methicillin-resistant Staphylococcus aureus and other pathogen load from infected lesions better than conventional antibiotics. In the current study we sought to produce and characterize a novel delivery system, suitable for immediate and convenient application in non-hospital environments. The APO monomer was incorporated into polyvinyl alcohol nanofibers and the complex was polymerized into a solid patch dressing. Mice were subjected to skin abrasion where the wounds were either left uninfected or were inoculated with a near lethal dose of multidrug resistant A. baumannii strain. Analyzed after 3 days, APO monomer-containing patches improved wound appearance significantly better than polymer patches without antibiotics. When compared to colistin, the APO patches accelerated wound healing, and statistically significantly reduced wound size and wound bacterial load. The in vivo antimicrobial effect was more extensive than after intramuscular administration of the peptide drug, by using only one tenth of the active pharmaceutical ingredient. These data suggest that the APO monomer-impregnated nanofiber dressing can be developed as an economical first-line treatment option to skin injuries in general and battlefield burn and blast injuries in particular.

Evaluation of the ability of Acinetobacter baumannii to form biofilms on six different biomedical relevant surfaces.

UNLABELLED: The human opportunistic pathogen, Acinetobacter baumannii, has the propensity to form biofilms and frequently cause medical device-related infections in hospitals. However, the physio-chemical properties of medical surfaces, in addition to bacterial surface properties, will affect colonization and biofilm development. The objective of this study was to compare the ability of A. baumannii to form biofilms on six different materials common to the hospital environment: glass, porcelain, stainless steel, rubber, polycarbonate plastic and polypropylene plastic. Biofilms were developed on material coupons in a CDC biofilm reactor. Biofilms were visualized and quantified using fluorescent staining and imaged using confocal laser scanning microscopy (CLSM) and by direct viable cell counts. Image analysis of CLSM stacks indicated that the mean biomass values for biofilms grown on glass, rubber, porcelain, polypropylene, stainless steel and polycarbonate were 0·04, 0·26, 0·62, 1·00, 2·08 and 2·70 µm(3) /µm(2) respectively. Polycarbonate developed statistically more biofilm mass than glass, rubber, porcelain and polypropylene. Viable cell counts data were in agreement with the CLSM-derived data. In conclusion, polycarbonate was the most accommodating surface for A. baumannii ATCC 17978 to form biofilms while glass was least favourable. Alternatives to polycarbonate for use in medical and dental devices may need to be considered. SIGNIFICANCE AND IMPACT OF THE STUDY: In the hospital environment, Acinetobacter baumannii is one of the most persistent and difficult to control opportunistic pathogens. The persistence of A. baumannii is due, in part, to its ability to colonize surfaces and form biofilms. This study demonstrates that A. baumannii can form biofilms on a variety of different surfaces and develops substantial biofilms on polycarbonate - a thermoplastic material that is often used in the construction of medical devices. The findings highlight the need to further study the in vitro compatibility of medical materials that could be colonized by A. baumannii and allow it to persist in hospital settings.

Synergistic anti-biofouling effect of Ag-exchanged zeolite and D-Tyrosine on PVC composite against the clinical isolate of Acinetobacter baumannii.

Due to their susceptibility to bacterial biofilm formation, commercial tubes for medical use are one of the main sources of hospital infections with Acinetobacter baumannii. The anti-biofouling activity of novel composites against the clinical isolate of the multi-drug resistant A. baumannii is reported here. The composites were prepared by addition of micronised silver-exchanged natural zeolite (Ag-NZ) into poly(vinyl chloride) (PVC), followed by coating of the composites with D-Tyrosine (D-Tyr). The Ag-NZ composites (containing 1-15 wt% of Ag-NZ) coated with D-Tyr (Ag-NZ-Tyr) showed a bactericidal effect (100% or a 6.9 log CFU reduction) towards immobilised bacterial cells. The uncoated Ag-NZ composites showed a reduction of up to 70% (4.4 log CFU) of immobilised bacteria in comparison with the original PVC. Rheological testing of the composites revealed that the addition of Ag-NZ slightly affected processability and formability of the PVC and increased the elasticity of the polymer matrix.

Acinetobacter baumannii as an oro-dental pathogen: a red alert!!

OBJECTIVES: This review highlights the existence and association of Acinetobacter baumannii with the oro-dental diseases, transforming this systemic pathogen into an oral pathogen. The review also hypothesizes possible reasons for the categorization of this pathogen as code blue due to its stealthy entry into the oral cavity. METHODOLOGY: Study data were retrieved from various search engines reporting specifically on the association of A. baumannii in dental diseases and tray set-ups. Articles were also examined regarding obtained outcomes on A. baumannii biofilm formation, iron acquisitions, magnitude of antimicrobial resistance, and its role in the oral cancers. RESULTS: A. baumannii is associated with the oro-dental diseases and various virulence factors attribute for the establishment and progression of oro-mucosal infections. Its presence in the oral cavity is frequent in oral microbiomes, conditions of impaired host immunity, age related illnesses, and hospitalized individuals. Many sources also contribute for its prevalence in the dental health care environment and the presence of drug resistant traits is also observed. Its association with oral cancers and oral squamous cell carcinoma is also evident. CONCLUSIONS: The review calls for awareness on the emergence of A. baumannii in dental clinics and for the need for educational programs to monitor and control the sudden outbreaks of such virulent and resistant traits in the dental health care settings.

Chlorhexidine decreases the risk of ventilator-associated pneumonia in intensive care unit patients: a randomized clinical trial.

BACKGROUND AND OBJECTIVE: The aim was to evaluate whether oral swabbing with 0.2% chlorhexidine gluconate (CHX) decreases the risk of ventilator-associated pneumonia (VAP) in intensive care unit (ICU) patients. MATERIAL AND METHODS: Sixty-one dentate patients scheduled for invasive mechanical ventilation for at least 48 h were included in this randomized, double-blind, controlled study. As these patients were variably incapacitated, oral care was provided by swabbing the oral mucosa four times/d with CHX in the CHX group (29 patients) and with saline in the control group (32 patients). Clinical periodontal measurements were recorded, and lower-respiratory-tract specimens were obtained for microbiological analysis on admission and when VAP was suspected. Pathogens were identified by quantifying colonies using standard culture techniques. RESULTS: Ventilator-associated pneumonia developed in 34/61 patients (55.7%) within 6.8 d. The VAP development rate was significantly higher in the control group than in the CHX group (68.8% vs. 41.4%, respectively; p = 0.03) with an odds ratio of 3.12 (95% confidence interval = 1.09-8.91). Acinetobacter baumannii was the most common pathogen (64.7%) of all species identified. There were no significant differences between the two groups in clinical periodontal measurements, VAP development time, pathogens detected or mortality rate. CONCLUSION: The finding of the present study, that oral care with CHX swabbing reduces the risk of VAP development in mechanically ventilated patients, strongly supports its use in ICUs and indeed the importance of adequate oral hygiene in preventing medical complications.

A Multiepitope Peptide, rOmp22, Encapsulated in Chitosan-PLGA Nanoparticles as a Candidate Vaccine Against Acinetobacter baumannii Infection.

BACKGROUND: The development of vaccines is a promising and cost-effective strategy to prevent emerging multidrug-resistant (MDR) Acinetobacter baumannii (A. baumannii) infections. The purpose of this study was to prepare a multiepitope peptide nanovaccine and evaluate its immunogenicity and protective effect in BALB/c mice. METHODS: The B-cell and T-cell epitopes of Omp22 from A. baumannii were predicted using bioinformatics methods and identified by immunological experiments. The optimal epitopes were conjugated in series by 6-aminocaproic acid and chemically synthesized multiepitope polypeptide rOmp22. Then, rOmp22 was encapsulated by chitosan (CS) and poly (lactic-co-glycolic) acid (PLGA) to prepare CS-PLGA-rOmp22 nanoparticles (NPs). The immunogenicity and immunoprotective efficacy of the vaccine were evaluated in BALB/c mice. RESULTS: CS-PLGA-rOmp22 NPs were small (mean size of 272.83 nm) with apparently spherical structures, positively charged (4.39 mV) and nontoxic to A549 cells. A high encapsulation efficiency (54.94%) and a continuous slow release pattern were achieved. Compared with nonencapsulated rOmp22, CS-PLGA-rOmp22 immunized BALB/c mice induced higher levels of rOmp22-specific IgG in serum and IFN-γ in splenocyte supernatant. Additionally, lung injury and bacterial burdens in the lung and blood were suppressed, and potent protection (57.14%-83.3%) against acute lethal intratracheal A. baumannii challenge was observed in BALB/c mice vaccinated with CS-PLGA-rOmp22. CONCLUSION: CS-PLGA-rOmp22 NPs elicited specific IgG antibodies, Th1 cellular immunity and protection against acute lethal intratracheal A. baumannii challenge. Our results indicate that this nanovaccine is a desirable candidate for preventing A. baumannii infection.

Acinetobacter baumannii can be transferred from contaminated nitrile examination gloves to polypropylene plastic surfaces.

BACKGROUND: Several observational studies suggest that gloves of health care workers are major routes of multidrug-resistant Acinetobacter baumannii transmission. However, limited experimental data are available assessing Acinetobacter transmission from gloves to environmental surfaces. This study determined whether A baumannii was easily transferred from nitrile gloves to polypropylene plastic compared with other gram-negative bacteria that cause health care-associated infections in laboratory-controlled experiments. METHODS: Gloved fingerpad-to-fomite transfer efficiency was determined for drug-resistant and -sensitive strains of A baumannii, Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, and Pseudomonas aeruginosa. RESULTS: Only A baumannii transferred from gloves to fomites 3 minutes after the bacterial transfer event. Transfer efficiency of A baumannii was 0.1%-33% at that time point. DISCUSSION: Bacterial transfer from contaminated gloves to the hospital environment may be related to the type of contaminating bacteria, inoculated bacterial level, fomites, and glove materials. Therefore, it is important to need a comprehensive assessment of the transfer efficiency. CONCLUSIONS: A baumannii can transfer easily from nitrile gloves to fomite compared with other gram-negative bacteria that cause health care-associated infections. These findings support data from previous observational studies that gloves of health care workers can be major routes of A baumannii transmission in clinical settings.

Antimicrobial effect of copper alloys on Acinetobacter species isolated from infections and hospital environment.

Background: An increased proportion of Gram-negative bacteria have recently been reported among etiologic agents of infection. In Poland, Acinetobacter baumannii is a big problem for hospitals, especially intensive care units. Touch surfaces made from materials with antimicrobial properties, especially copper alloys, are recommended as a supplementary method of increasing biological safety in the hospital environment. Aim of the study: The objective of this study is to determine the susceptibility to selected copper alloys of three clinical Acinetobacter baumannii strains, one Acinetobacter lwoffi and an A. pittii strain isolated from the hospital environment. Material and method: The modification of the Japanese Standard, which the ISO 22196:2011 norm was used for testing antimicrobial properties of CuZn37, CuSn6 and CuNi18Zn20 and Cu-ETP and stainless steel as positive and negative control, respectively. Results: The highest cidal efficiency, expressed as both time and the degree of reduction of the initial suspension density, against all of the tested Acinetobacter strains was found for ETP copper. But, the results of our study also confirmed effective activity (bacteriocidal or bacteriostatic) of copper alloys selected for the study, contrary to the stainless steel. The reduction in bacterial suspension density is significantly different depending on the strain and copper alloy composition. Conslusions: The results of our study confirmed the effective antibacterial activity of copper and its selected alloys against clinical Acinetobacter baumannii and Acinetobacter lwoffii strains, and Acinetobacter pittii strain isolated from the hospital environment.

Comparative Evaluation of Broth Microdilution with Polystyrene and Glass-Coated Plates, Agar Dilution, E-Test, Vitek, and Disk Diffusion for Susceptibility Testing of Colistin and Polymyxin B on Carbapenem-Resistant Clinical Isolates of Acinetobacter baumannii.

INTRODUCTION: With the increasing threat of multidrug-resistant organisms, such as Acinetobacter baumannii, the polymyxin class of drugs (colistin and polymyxin B) has become popular in clinical practice. A better understanding of antimicrobial susceptibility testing methods for colistin and polymyxin B is needed for optimal patient management. MATERIALS AND METHODS: Forty-two carbapenem-resistant A. baumannii isolates were subjected to susceptibility testing for colistin and polymyxin B using the following methods: broth microdilution (BMD) (glass-coated plates [BMD-Gs] and polystyrene plates [BMD-Ps]), agar dilution (AD), E-test®, Vitek®, and disk diffusion. Using BMD as the gold standard, comparative analysis between different methods was carried out. RESULTS: With BMD-Gs as reference, reliability was high for BMD-Ps and moderate for AD and Vitek for both the drugs. Similar results were obtained when the BMD-P was used as reference, but drug-polystyrene interaction was observed. CONCLUSION: Different susceptibility testing methods for polymyxins show great variation in their results and BMD using glass-coated plates can be considered the best candidate for gold standard.

Efficacy of designer K11 antimicrobial peptide (a hybrid of melittin, cecropin A1 and magainin 2) against Acinetobacter baumannii-infected wounds.

Due to emergence of multidrug resistance in pathogens, the attention of the scientific community is now directed towards strengthening the reservoir of antimicrobial compounds. Prior to in vivo studies, the interaction and penetration of a hybrid peptide K11 in bacterial cells using confocal microscopy was assessed which was observed as early as 10 min after incubation with the peptide. Cell lysis along with leakage of cytoplasmic content was confirmed by electron microscopy. To evaluate the in vivo performance of the peptide, it was contained in carbopol hydrogel. Efficacy of the hydrogel formulation was then evaluated against Acinetobacter baumannii-infected wounds using a murine excision model. Treatment resulted in restoration of body weight, complete clearance of infection from the wound by day 7 and 99% wound enclosure by day 21, in contrast to the persistence of infection and 70% wound enclosure in the infected group. Further, this treatment resulted in a 2.6-fold decrease in the levels of malondialdehyde along with a 4.5-fold increase in the levels of catalase on day 3. Appearance of normal histo-architecture was observed in the treatment group. Based on these results, the peptide hydrogel can be exploited in future as one of the strategies for developing a topical anti-infective therapeutic agent.

A novel bacterial transport mechanism of Acinetobacter baumannii via activated human neutrophils through interleukin-8.

Hospital-acquired infections as a result of Acinetobacter baumannii have become problematic because of high rates of drug resistance. Although neutrophils play a critical role in early protection against bacterial infection, their interactions with A. baumannii remain largely unknown. To elucidate the interactions between A. baumannii and human neutrophils, we cocultured these cells and analyzed them by microscopy and flow cytometry. We found that A. baumannii adhered to neutrophils. We next examined neutrophil and A. baumannii infiltration into Matrigel basement membranes by an in vitro transmigration assay. Neutrophils were activated by A. baumannii, and invasion was enhanced. More interestingly, A. baumannii was transported together by infiltrating neutrophils. Furthermore, we observed by live cell imaging that A. baumannii and neutrophils moved together. In addition, A. baumannii-activated neutrophils showed increased IL-8 production. The transport of A. baumannii was suppressed by inhibiting neutrophil infiltration by blocking the effect of IL-8. A. baumannii appears to use neutrophils for transport by activating these cells via IL-8. In this study, we revealed a novel bacterial transport mechanism that A. baumannii exploits human neutrophils by adhering to and inducing IL-8 release for bacterial portage. This mechanism might be a new treatment target.

Fomite-fingerpad transfer efficiency (pick-up and deposit) of Acinetobacter baumannii-with and without a latex glove.

BACKGROUND: Acinetobacter baumannii is a significant health care-associated pathogen because it is easily transmitted via fomites, extremely difficult to eradicate from the environment, and highly drug resistant. Understanding the environmentally mediated transmission dynamics of A baumannii is critical for more effective infection control. However, transfer efficiency of pathogen pick-up and deposit remains poorly understood. Our study estimates the transfer efficiency of A baumannii with and without latex glove use from the fingerpad to a fomite and from a fomite to the fingerpad. METHODS: Fomite-fingerpad transfer efficiencies were determined for 6 materials (glass, stainless steel, porcelain, polypropylene, polycarbonate, and rubber). RESULTS: For A baumannii, the fomite-to-fingerpad transfer efficiency was 24.1%, and the fingerpad-to-fomite transfer efficiency was 5.6%. When latex gloves were worn, the fomite-to-fingerpad transfer efficiency was reduced by 55.9% (to 10.6%) and the fingerpad-to-fomite transfer efficiency was reduced by 47.1% (to 3.0%). The average transfer efficiency between 2 skin surfaces was 32.5%. CONCLUSIONS: The fomite-to-fingerpad transfer efficiency of A baumannii was statistically significantly higher than the fingerpad-to-fomite transfer efficiency, regardless of glove use. There was no significant difference in transfer efficiency by material type, except for rubber, which resulted in marginally higher transfer efficiencies. Our results underscore the importance of frequently changing gloves during patient care and frequent handwashing-hand hygiene during bare-handed care for the reduction of pathogen transmission.

Diversity of Acinetobacter baumannii strains isolated in humans, companion animals, and the environment in Reunion Island: an exploratory study.

OBJECTIVES: Acinetobacter baumannii can be responsible for community-acquired infections in tropical climates like that of Reunion Island. The epidemiology of these community-acquired A. baumannii infections is not well understood. The aim of this study was to characterize A. baumannii strains isolated from patients at the time of admission to the university hospital of Saint-Denis, from environmental samples, and from pets. METHODS: In this exploratory study, samples were collected by swabbing the rectum and mouth. A. baumannii isolates from positive samples were identified by VITEK 2 system, blaOXA-51-like gene PCR, and partial sequencing of the rpoB gene. Antimicrobial susceptibility testing was then performed. Strains were further analysed by multilocus sequence typing and pulsed-field gel electrophoresis. RESULTS: A high prevalence of A. baumannii carriage was found in pets (8.5%). Only one A. baumannii isolate was resistant to carbapenems (isolated from a patient). A wide variety of A. baumannii, assigned to different sequence types, were isolated from pets, humans, and the environment. CONCLUSIONS: This study shows that A. baumannii strains are present outside the hospital setting in Reunion Island and show great diversity. Further studies are needed to explore these extra-hospital reservoirs of A. baumannii in Reunion Island in greater detail and to determine their possible means of dissemination.

Code blue: Acinetobacter baumannii, a nosocomial pathogen with a role in the oral cavity.

Actinetobacter baumannii is an important nosocomial pathogen that can cause a wide range of serious conditions including pneumonia, meningitis, necrotizing fasciitis and sepsis. It is also a major cause of wound infections in military personnel injured during the conflicts in Afghanistan and Iraq, leading to its popular nickname of 'Iraqibacter'. Contributing to its success in clinical settings is resistance to environmental stresses such as desiccation and disinfectants. Moreover, in recent years there has been a dramatic increase in the number of A. baumannii strains with resistance to multiple antibiotic classes. Acinetobacter baumannii is an inhabitant of oral biofilms, which can act as a reservoir for pneumonia and chronic obstructive pulmonary disease. Subgingival colonization by A. baumannii increases the risk of refractory periodontitis. Pathogenesis of the organism involves adherence, biofilm formation and iron acquisition. In addition, A. baumannii can induce apoptotic cell death in epithelial cells and kill hyphal forms of Candida albicans. Virulence factors that have been identified include pili, the outer membrane protein OmpA, phospholipases and extracellular polysaccharide. Acinetobacter baumannii can sense blue light through a blue-light sensing using flavin (BLUF) domain protein, BlsA. The resulting conformational change in BlsA leads to changes in gene expression, including virulence genes.

Antimicrobial activity of bone cements embedded with organic nanoparticles.

Infections after orthopedic surgery are a very unwelcome outcome; despite the widespread use of antibiotics, their incidence can be as high as 10%. This risk is likely to increase as antibiotics are gradually losing efficacy as a result of bacterial resistance; therefore, novel antimicrobial approaches are required. Parabens are a class of compounds whose antimicrobial activity is employed in many cosmetic and pharmaceutical products. We developed propylparaben nanoparticles that are hydrophilic, thus expanding the applicability of parabens to aqueous systems. In this paper we assess the possibility of employing paraben nanoparticles as antimicrobial compound in bone cements. The nanoparticles were embedded in various types of bone cement (poly(methyl methacrylate) [PMMA], hydroxyapatite, and brushite) and the antimicrobial activity was determined against common causes of postorthopedic surgery infections such as: Staphylococcus aureus, methicillin-resistant S. aureus, Staphylococcus epidermidis, and Acinetobacter baumannii. Nanoparticles at concentrations as low as 1% w/w in brushite bone cement were capable of preventing pathogens growth, 5% w/w was needed for hydroxyapatite bone cement, while 7% w/w was required for PMMA bone cement. No detrimental effect was determined by the addition of paraben nanoparticles on bone cement compression strength and cytocompatibility. Our results demonstrate that paraben nanoparticles can be encapsulated in bone cement, providing concentration-dependent antimicrobial activity; furthermore, lower concentrations are needed in calcium phosphate (brushite and hydroxyapatite) than in acrylic (PMMA) bone cements. These nanoparticles are effective against a wide spectrum of bacteria, including those already resistant to the antibiotics routinely employed in orthopedic applications, such as gentamicin.

High prevalence of closely-related Acinetobacter baumannii in pets according to a multicentre study in veterinary clinics, Reunion Island.

Our objective was to study the carriage of Acinetobacter baumannii (AB) in pets in Reunion Island (RI), a French territory in Indian Ocean. Overall, 138 pets were sampled (rectum, mouth, wounds if applicable) in 9 veterinary clinics (VC). The prevalence of AB carriage was 6.5% (95%CI; 2.4, 10.6) and 9 carriers were identified from 4 VC. Hospitalization in a VC and antimicrobial treatment administered within the 15 preceding days were significantly associated with AB carriage (P<0.01 and P<0.05, respectively). Despite the VC in which animals have been sampled were located all around RI, most isolates (8/9) were closely-related (>90% similarity by pulsed-field gel electrophoresis). Additional studies are needed to improve the understanding about interactions between the different reservoirs of AB in RI.

Molecular determinants of the bacterial resistance to fluoroquinolones: a computational study.

Quinolones constitute a large class of antibacterial agents whose action is mediated through the formation of a ternary complex with DNA and either, DNA Gyrase or topoisomerase IV, resulting in the inhibition of DNA replication. In order to get a deeper insight into the features of the complex formation, we carried out docking studies of fifteen diverse quinolones to the cleaved topoisomerase IV-DNA complex. Docking studies were performed using the crystal structures of the cleaved complex with levofloxacin and moxifloxacin (pdb entries 3K9F and 2XKK, respectively) using the GOLD software. Ligands dock in positions similar to those of the crystal structures. Analysis of the results reveals that bound quinolones appear intercalated between the two nucleotides that are involved in the DNA cleavage and exhibit hydrogen bonds with Arg(117) and, the latter mediated though a water molecule. Arg(117) has not been described to be involved in resistance, since it is putatively involved in the enzymatic reaction and its mutation would be lethal for the organism. Mutants of Ser(79) exhibit resistance to quinolones which can be explained by the loss of an important anchoring point. Interestingly, quinolone resistance observed in Asp(83) mutants cannot be explained directly on the basis of the loss of a direct interaction, but could be explained on the basis of its involvement at the entrance of the ligands to their binding pocket since the residue is located at the mouth of the pocket. The results of the present study suggest that the 4-keto and 3-carboxyl groups of the fluoroquinolones bind a Mg(2+) before binding to the cleaved topoisomarase IV-DNA complex and use Asp(83) for entry into the binding pocket. Accordingly, mutations that do not conserve the binding capacity for the quinolone-Mg(2+) complex will prevent the binding of this class of ligands. The results we present here are also compared with the structure of PD0305970 a 2,4-dione active against the Ser(79) and Asp(83) mutants.