Carbapenem resistance in Acinetobacter baumannii, and their importance in hospital-acquired infections: a scientific review.

Carbapenem is an important therapy for serious hospital-acquired infections and for the care of patients affected by multidrug-resistant organisms, specifically Acinetobacter baumannii; however, with the global increase of carbapenem-resistant A. baumannii, this pathogen has significantly threatened public health. Thus, there is a pressing need to better understand this pathogen in order to develop novel treatments and control strategies for dealing with A. baumannii. In this review, we discuss an overview of carbapenem, including its discovery, development, classification and biological characteristics, and its importance in hospital medicine especially in critical care units. We also describe the peculiarity of bacterial pathogen, A. baumannii, including its commonly reported virulence factors, environmental persistence and carbapenem resistance mechanisms. In closing, we discuss various control strategies for overcoming carbapenem resistance in hospitals and for limiting outbreaks. With the appearance of strains that resist carbapenem, the aim of this review is to highlight the importance of understanding this increasingly problematic healthcare-associated pathogen that creates significant concern in the field of nosocomial infections and overall public health.

Escherichia coli cellular responses to exposure to atmospheric-pressure dielectric barrier discharge plasma-treated N-acetylcysteine solution.

AIM: To understand the underlying cellular mechanisms during inactivation of Escherichia coli in response to antimicrobial solution of nonthermal plasma-activated N-acetylcysteine (NAC). METHODS AND RESULTS: The recommended techniques were used to demonstrate E. coli cellular and transcriptomic changes caused associated with peroxynitrite and compared with plasma-treated NAC solution. The findings demonstrate that E. coli cells respond to plasma-treated NAC and undergo severe oxidative and nitrosative stress, and leading to stress-induced damages to different components of bacterial cells, which includes loss of membrane potential, formation of oxidized glutathione (GSSG), formation of nitrotyrosine (a known marker of nitrosative stress), DNA damage, and generated a prominent pool of peroxynitrite. Reverse-transcriptase (RT)-polymerase chain reaction analysis of reactive nitrogen species (RNS) responsive genes indicated their differential expressions. CONCLUSION: For the first time, we report that the plasma-treated NAC solution activates predominantly nitrosative stress-responsive genes in E. coli and is responsible for cell death. SIGNIFICANCE AND IMPACT OF THE STUDY: The reactive species generated in solutions by nonthermal plasma treatment depends on the type of solution or solvent used. The plasma-treated NAC solution rapidly inactivates E. coli, mostly involving highly RNS generated in NAC solution, and has high potential as disinfectant.

Plumbagin exerts antiobesity effects through inhibition of pancreatic lipase and adipocyte differentiation.

Plumbagin is a naphthoquinone found in the roots of Plumbago zeylanica. Here, we report an investigation to evaluate its antiobesity activity. The preliminary binding affinity of plumbagin to human pancreatic lipase (PL) was determined using molecular docking simulation. The in vitro PL inhibitory potential and the kinetics of inhibition were studied to validate and confirm the results obtained from molecular docking. The IC50 for PL was found to be 82.08 ± 9.47 µM, and the kinetics of inhibition was found to be of the mixed type. Further, the in vivo evaluation revealed that rats treated with plumbagin 1 mg/kg showed significant decrease in serum triglycerides (TG) and area under the curve of serum TG when compared with vehicle-treated rats. It was also seen that plumbagin possessed significant antiadipogenic effect as demonstrated by reduced oil red O staining and decreased TG contents. Thus, we conclude that plumbagin is a promising molecule to combat obesity and further optimization of plumbagin to yield plumbagin analogues will result in its improved activity profile.

Studies on Acinetobacter baumannii involving multiple mechanisms of carbapenem resistance.

AIMS: Characterize the genetic type and resistance mechanisms of 16 carbapenem-resistant Acinetobacter baumannii (CRAB) isolates recovered between January 2010 and March 2011 from US tertiary-care hospital. METHODS AND RESULTS: A modified Hodge test demonstrated the presence of carbapenemases, but meropenem and ethylenediaminetetraacetic acid (EDTA) double-disc synergy tests and PCR for metallo-ß-lactamase (MBL) genes were negative. The genes of ampC ß-lactamase and efflux pump of adeABC and adeIJK were detected. The presence of oxacillinase (OXA)-like genes, blaOXA-51-like , blaOXA-23-like and blaOXA-40-like genes, and insertion sequence ISAba1 in promoter region of blaOXA-51-like and blaOXA-23-like genes were detected; and confirmed by RT-PCR analyses. The sequencing of blaOXA-51-like genes revealed two major alleles, blaOXA-66-like (blaOXA-82 ) and blaOXA-113 from 31·2 to 68·8% of isolates respectively. The blaOXA-23 and blaOXA-72 genes showed high expression and found co-harbouring blaOXA-51-like gene preceded by ISAba-1. All CRAB isolates revealed significant reduction in carO transcription, indicated downregulation of CarO porin system, a potentially independent mechanism of carbapenam resistance. Sequencing of carO gene from representative isolates showed no ISAba1 insertional inactivation. Pulsed-field gel electrophoresis revealed a clonal relationship. CONCLUSIONS: CRAB exhibited diversity of mechanisms of carbapenem resistance, and clonal relationship. SIGNIFICANCE AND IMPACT OF THE STUDY: Studies on distinct outbreaks of CRAB are alarming situation for clinicians.

Modulation of botulinum toxin-induced changes in neuromuscular function with antibodies directed against recombinant polypeptides or fragments.

Botulinum toxin is an agent that is typically encountered in two settings: as an agent that can cause disease (e.g. botulism), and as an agent that can be used to treat disease (i.e., a variety of neurologic disorders). In both cases it would be advantageous to develop a sound understanding of the mechanisms by which antibodies neutralize the toxin. In the present study, recombinant antigens were used to generate antibodies against the carboxyterminal half of the toxin heavy chain (HC50), the entire toxin light chain (LC), and the HA17, HA35 and HA70 components of the progenitor toxin complex. These antibodies were then evaluated for their respective abilities to alter botulinum toxin-induced changes in locomotor behavior in mice. The botulinum toxin type A complex was shown to produce dose-dependent depression of locomotor behavior within the dose range of 0.3-0.7 mouse LD50 units. At a dose of 0.5 LD50, the toxin typically reduced running behavior by 90% or more, and full recovery was not observed for approximately 4 weeks. Mice that were actively or passively vaccinated against the HC50 polypeptide were resistant to toxin action, presumably because the antibodies occluded the toxin binding domain. Interestingly, mice that were actively or passively vaccinated against LC were also resistant to toxin action. This effect may have been due to steric hindrance of the binding process. There was no scenario in which anti-HA antibodies altered the effects of toxin on locomotor behavior. This absence of effect was likely due to the fact that HAs and neurotoxin in the progenitor toxin complex spontaneously dissociate in physiologic media.

Biological responses of Bacillus stratosphericus to floating electrode-dielectric barrier discharge plasma treatment.

AIMS: Dielectric barrier discharge (DBD) plasma is used for sterilization of contaminated inanimate surfaces but seldomly optimized and depends upon the type of organisms and the plasma treatment duration, (net energy deposited) this efficacy varies. The proposed study was designed to see biological responses of one of the robust organism, Bacillus stratosphericus. METHODS AND RESULTS: DBD plasma was applied over various durations to B. stratosphericus either surface-dried or suspension in de-ionized water, and viability, culturability, and viable but nonculturability (VBNC) were assayed using standard techniques. Depending upon the exposure of B. stratosphericus to DBD plasma resulted in three viability states, viable and culturable at low plasma doses and VBNC or disintegrated bacteria at higher plasma doses. Although organism's respiration levels at relatively low levels, immediately after plasma treatment, over the course of 24-h respiratory activity was increased c. eight times (and found still nonculturable during colony assays). CONCLUSIONS: The loss of culturability is hypothesized to be induced as one of the responses to oxidative stress and it remains to be unclear if the response is temporary or indefinite. Appropriate plasma powers should be used to avoid VBNC-like status. 2,3-Bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assay is a good alternative method to detect VBNC state. SIGNIFICANCE AND IMPACT OF THE STUDY: Bacillus stratosphericus has the potential to turn into VBNC upon plasma application, and XTT assay can be an alternative method to detect VBNC state.

High frequency shear horizontal plate acoustic wave devices.

It has been shown recently that shear horizontal acoustic waves propagating in piezoelectric plates whose thickness h is much less than the acoustic wavelength lambda possess a number of attractive properties for use in sensor and signal processing applications. In order to exploit the potential benefits of these waves, however, one needs to fabricate devices on very thin plates. We have developed a suitable fabrication method which can be used to realize devices on such thin plates. In this method, the device is first fabricated on a plate of normal thickness (approximately 500 microm) and the substrate is then lapped from the back side to reduce the thickness. The technique has been utilized to realize devices on plates of thickness less than 70 microm. A shear horizontal plate acoustic wave (SH-PAW) delay line of fundamental resonant frequency greater than 25 MHz and insertion loss less than 7 dB has been realized on a 60 microm thick Y--cut, X--propagation lithium niobate substrate. The device also shows strong response near the third harmonic frequency of 75 MHz.

Characteristics of fundamental acoustic wave modes in thin piezoelectric plates.

The characteristics of the three lowest order plate waves (A(0), S(0), and SH(0)) propagating in piezoelectric plates whose thickness h is much less than the acoustic wavelength lambda are theoretically analyzed. It is found that these waves can provide much higher values of electromechanical coupling coefficient K(2) and lower values of temperature coefficient of delay (TCD) than is possible with surface acoustic waves (SAWs). For example, in 30Y-X lithium niobate, the SH(0) mode has K(2)=0.46 and TCD=55 ppm/degrees C. The corresponding values for SAW in the widely used, strong coupling material of 128Y-X lithium niobate are K(2)=0.053 and TCD=75 ppm/degrees C. Another important advantage of plate waves is that, unlike the case of SAWs, they can operate satisfactorily in contact with a liquid medium, thus making possible their use in liquid phase sensors.

Characteristics of sludge developed under different loading conditions during UASB reactor start-up and granulation.

Sludge characteristics available inside the reactor are of vital importance to maximize advantages of UASB reactor. The organic loading rate and sludge loading rate applied during start-up are among the important parameters to govern the sludge characteristics. Effects of these loading rates on the characteristics of the sludge developed are evaluated in six laboratory scale UASB reactors. The sludge characteristics considered are VSS/SS ratio of the sludge, sludge volume index, specific gravity, settling velocity and metal contents of the sludge developed under different loading rates. The experimental results indicate that, for developing good characteristics sludge, during primary start-up from flocculent inoculum sludge, organic loading rate and sludge loading rate should be in the range of 2.0-4.5 kg COD/m3 d and 0.1-0.25 kg COD/kg VSS d, respectively (chemical oxygen demand, COD). Proper sludge granulation and higher COD removal efficiency will be achieved by these loading rates.

Investigation of acoustic waves of higher order propagating in plates of lithium niobate.

This paper presents theoretical investigation of higher order acoustic plate waves propagating in single crystals of lithium niobate. The dependencies of wave velocity and electromechanical coupling coefficient of antisymmetric, symmetric, and shear horizontal modes on the parameter hf (h=plate thickness, f=operating frequency) are calculated as a function of propagation direction on X-, Y-, and Z-cut lithium niobate plates. It is found that several modes can provide values of K2 that are much greater than can be obtained with surface acoustic waves (SAWs). For example, K2 as high as 0.26 and 0.38 can be obtained from SH1 and A2 modes, respectively. This compares with a maximum value of K2=0.055 for SAWs. It is further shown that there are several crystal cut and propagation directions that can allow efficient excitation and detection of a single mode with minimal interference due to other modes.

Liquid level sensor using ultrasonic Lamb waves.

This paper describes a novel, noninvasive method for measurement of liquid level in closed metal tanks that are under high pressure. It is based on the use of ultrasonic Lamb waves propagating along the tank wall. Contact with liquid substantially changes the characteristics of these waves and this can be used as an indicator of liquid presence. Theoretical analysis shows that the symmetric and antisymmetric Lamb wave modes, both fundamental and higher order, are sensitive to presence of the liquid. The optimal wave frequency depends on the thickness of the tank wall and wall material. A prototype level sensor based on this principle has been developed. It uses two pairs of wedge transducers to generate and detect Lamb waves propagating along the circumference of the gas tank. An operating frequency of 100 kHz is found to be optimal for use with tanks having a wall thickness of 30-50 mm. Prototype sensors developed under this program have been used successfully in oil fields in the far northern region of Russia.

Improved equivalent circuits for acoustic plate wave devices.

This paper presents improved equivalent circuits for the analysis and design of acoustic plate wave devices. The method uses a mixed equivalent circuit for the interdigital transducer consisting of both active and passive sections placed on the surface of a piezoelectric plate. The values of the various circuit elements are obtained by carrying out a best fit between theoretical and experimental frequency dependence of the real and imaginary parts of transducer input impedance. Knowledge of the equivalent circuit parameters allows one to optimize design of the devices. The method has been successfully employed for the design of one-port shear-horizontal wave resonators on Y-X lithium niobate plates. The proposed method can also be utilized for determining acoustic wave velocity with high accuracy.

Influence of conducting layer and conducting electrode on acoustic waves propagating in potassium niobate plates.

The influence of a thin conducting layer and a conducting electrode on the characteristics of acoustic waves propagating in thin plates of potassium niobate is investigated theoretically. The variations in velocity and attenuation as high as 50% and 30 dB per wavelength, respectively, can be achieved for a change in conductance of the thin film layer from 10(-7) to 10(-5) S.

Shear-horizontal acoustic waves in piezoelectric plates bordered with conductive liquid.

The influence of a conductive liquid on the characteristics of shear-horizontal acoustic waves of zeroth order (SH0 mode) propagating in thin piezoelectric plates of lithium tantalate, lithium niobate, and potassium niobate was investigated. Experimental results obtained for SH0 mode devices fabricated on lithium niobate plates are found to be in good agreement with theory. The data presented in this paper is useful for a proper design of various acoustic wave sensors operating in contact with conductive liquids.

Investigation of acoustic waves in thin plates of lithium niobate and lithium tantalate.

The general properties of fundamental antisymmetric A0, symmetric S0, and shear horizontal SH0 acoustic waves propagating in thin piezoelectric plates have been theoretically investigated on samples of lithium niobate (LiNbO3) and lithium tantalate (LiTaO3). The results obtained will be useful for a proper development of various physical, chemical, and biological sensors and devices for signal processing based on plate acoustic waves.

Epidemiology of cholera--a five year study.

A total of 286 strains of Vibro Cholerae were isolated and tested over a period of five years. The strains were identified by standard methods and confirmed by slide agglutination tests with polyvalent, Ogawa and Inaba antisera. The non-agglutinating strains were tested with O-139 antisera. The maximum number of cases were found in the age group of 0-10 years. The number of females affected was more than the males. V. cholerae O-139 was isolated in the year 1998 and then again in 2000. V. cholerae serotype Inaba was found only in the year 1999. All of the other isolates belonged to the serotype Ogawa. The periodic shift between O1 and O-139 serogoups is reminiscent of the shifts from the Ogawa to the Inaba serotypes periodically witnessed among V. cholerae, possibly mediated by the immune pressure in the population.

Neonatal gram-negative bacteremia.

A 22 months prospective study of neonatal gram-negative bacteremia was undertaken in a 15 bed NICU to find out the incidence and antibiotic resistance patterns. Clinically suspected 1326 cases of neonatal sepsis were studied during this period. More than 25% of the cases were microbiologically positive for sepsis. Among 230 (67.2%) cases of gram-negative bacteremia, the predominant isolates were Pseudomonas aeruginosa (38.3%), Klebsiella pneumoniae (30.4%), Escherichia coli (15.6%) and Acinetobacter sp. (7.8%). Fifty-nine per cent of the neonates were born in hospital while 41% were from community and referral cases. Lower respiratory tract infection, umbilical sepsis, central intravenous line infection and infection following invasive procedures were the most commonly identified sources of septicemia. Prematurity and low birth weight were the main underlying conditions in 60% of the neonates. Total mortality was 32%. Increased mortality was mainly associated with neutropenia, nosocomial infection and inappropriate antibiotic therapy. Resistance was increasingly noted against many antibiotics. The isolates were predominantly resistant to extended spectrum cephalosporins (25%-75%), piperacillin (68%-78%), and gentamicin (23%-69%). The commonest microorganisms causing gram-negative bacteremia were Pseudomonas aeruginosa followed by Klebsiella pneumoniae. The community-acquired bacteremia was mainly due to E. coli. The proportion of preterm and low birth weight babies was significantly high, and the major contributing factor in total mortality. Sensitivity to different antibiotics conclusively proved that a combination of ampicillin + sulbactam with amikacin or ampicillin + sulbactam with ciprofloxacin is most effective.