Multidrug resistant Acinetobacter baumannii: a descriptive study in a city hospital

Antimicrobial susceptibility of Acinetobacter clinical isolates and emerging antibiogram trends for nosocomial infection management

INTRODUCTION

The drug resistant Acinetobacter strains are important causes of nosocomial infections that are difficult to control and treat. This study aimed to determine the antimicrobial susceptibility patterns of Acinetobacter strains isolated from different clinical specimens obtained from patients belonging to different age groups.

METHODS

In total, 716 non-duplicate Acinetobacter isolates were collected from the infected patients admitted to tertiary-care hospitals at Lahore, Pakistan, over a period of 28 months. The Acinetobacter isolates were identified using API 20E, and antimicrobial susceptibility testing was performed and interpreted according to Clinical and Laboratory Standards Institute (CLSI) guidelines.

RESULTS

The isolation rate of Acinetobacter was high from the respiratory specimens, followed by wound samples. Antibiotic susceptibility analyses of the isolates revealed that the resistance to cefotaxime and ceftazidime was the most common, in 710 (99.2%) specimens each, followed by the resistance to gentamicin in 670 (93.6%) isolates, and to imipenem in 651 (90.9%) isolates. However, almost all isolates were susceptible to tigecycline, colistin, and polymyxin B.

CONCLUSIONS

The present study showed the alarming trends of resistance of Acinetobacter strains isolated from clinical specimens to the various classes of antimicrobials. The improvement of microbiological techniques for earlier and more accurate identification of bacteria is necessary for the selection of appropriate treatments.

Microbiological sentinel events at a neurological hospital: a retrospective cohort study

The purpose of this study is to describe the epidemiological surveillance of microbiological sentinel events (SEs) carried out between 2012 and 2014 at the Neurological Hospital Carlo Besta, Milano, Italy. The setting is inpatient care with multidrug-resistant infections. The aim of the procedure is to formalize the management mode, reporting and transmission of SEs. Categorical variables were described by counts and percentages, as mean and sd or median and interquartile range. The incidence rates of SE were calculated per 1000 patient-days and for 100 admissions using Poisson distribution. The incidence rate of isolation for 1000 patient-days varies from a minimum of 0.52 (95 % confidence interval, 0.23-1.15) for the second quarter of 2014 to a maximum value of 4.16 (95 % confidence interval, 3.20-5.40) for the first quarter of 2013. A decrease followed from the third quarter of 2013 that remained constant in 2014, reaching values similar to those of 2012. Preventive actions and their effectiveness on Acinetobacterbaumannii, the primary cause in our division of multidrug-resistant infections in 2012, have ensured a reduction of the incidence of the same; preventive actions and their effectiveness allowed us to intercept microbiological SE and trigger appropriate precautionary behaviour and isolation. Surveillance of healthcare-associated infections is fundamental in understanding the sources that are contributing to the growing reservoir within hospital communities.

Multidrug Resistance of Acinetobacter Baumannii in Ladoke Akintola University Teaching Hospital, Osogbo, Nigeria

Acinetobacter baumannii is a ubiquitous pathogen that has emerged as a major cause of healthcare-associated infections at Ladoke Akintola University Teaching Hospital. Isolates were assayed according to standard protocol. The isolates were subjected to molecular techniques to detect blaOXA, blaTEM, blaCTX-M, and blaSHV genes in strains of the A. baumannii isolates.

The prevalence of A. baumannii was 8.5% and was most prevalent among patients in the age group 51–60 (36%); the male patients (63.6%) were more infected than their female counterparts. Patients (72.7%) in the intensive care unit (ICU) were most infected with this organism. The isolates showed 100% resistance to both amikacin and ciprofloxacin and 90.9% to both ceftriaxone and ceftazidime, while resistance to the other antibiotics used in this study were: piperacillin (81.8%), imipenem (72.7%), gentamycin (72.2%), and meropenem (63.6%). None of the isolates was, however, resistant to colistin. PCR results showed that blaOXA, blaTEM, and blaCTX-M genes were positive in some isolates, while blaSHV was not detected in any of the isolates.

This study has revealed that the strains of A. baumannii isolated are multiple drug resistant. Regular monitoring, judicious prescription, and early detection of resistance to these antibiotics are, therefore, necessary to check further dissemination of the organism.

Antimicrobial effects of Ferula gummosa Boiss gum against extended-spectrum β-lactamase producing Acinetobacter clinical isolates

BACKGROUND AND OBJECTIVES

Acinetobacter spp. are important causes of nosocomial infections. They possess various antibiotic resistance mechanisms including extended spectrum beta lactamases (ESBLs). The aim of this study was to determine antibiotic resistance profile of Acinetobacter clinical isolates especially among ESBL-producing strains and to investigate the antimicrobial effects of oleo-gum-resin extract and essential oil of Ferula gummosa Boiss.

MATERIALS AND METHODS

120 Acinetobacter strains were isolated from various clinical samples of hospitalized patients in Baqiyatallah hospital, Tehran during 2011-2012. Antibiotic susceptibility test was performed on the isolates using disk diffusion method. To detect and confirm the ESBL-positive isolates, phenotypic and genotypic tests were performed. Three types of F. gummosa oleo-gum-resin extracts and essential oils were prepared and the bioactive components of F. gummosa Boiss extracts were determined by GC-Mass chromatography. F. gummosa antimicrobial activity was evaluated against standard strain of Acinetobacter baumannii (ATCC19606) as well as Acinetobacter clinical isolates using well and disk diffusion methods. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined by broth microdilution method.

RESULTS

46 isolates were resistant to all tested antibiotics. All clinical isolates were resistant to cefotaxime. 12.94% of the isolates were phenotypically ESBL-producing among which 94.2% carried ESBL genes ( bla_PER-1 , bla_OXA-4 and bla_CTX-M ) detected by PCR. Oleo-gum-resin of F. gummosa had significant antibacterial activity and alcoholic essential oil had higher inhibitory effect on Acinetobacter strains (MIC of 18.75 mg/ml).

CONCLUSION

Ferula gummosa extract contained components with well-known antimicrobial effects.

First Description of Two Sequence Type 2 Acinetobacter baumannii Isolates Carrying OXA-23 Carbapenemase in Pagellus acarne Fished from the Mediterranean Sea near Bejaia, Algeria

To determine the occurrence of carbapenem-resistantAcinetobacter baumanniiin fish fished from the Mediterranean Sea near the Bejaia coast (Algeria), we studied 300 gills and gut samples that had been randomly and prospectively collected during 1 year. After screening on selective agar media, using PCR arrays and whole-genome sequencing, we identified for the first time two OXA-23-producingA. baumanniistrains belonging to the widespread sequence type 2 (ST2)/international clone II and harboring aminoglycoside-modifying enzymes [aac(6')-Ib andaac(3')-I genes].

Attenuation of quorum sensing-mediated virulence of Acinetobacter baumannii by Glycyrrhiza glabra flavonoids

AIM

To develop an alternative quorum quenching therapy against multidrug-resistant Acinetobacter baumannii.

METHODS & RESULTS

Activity-guided partially purified fraction (F1) from Glycyrrhiza glabra significantly (p < 0.05) reduced quorum sensing regulated virulence factors of A. baumannii viz. motility, biofilm formation and production of antioxidant enzymes. Mechanistically, F1 downregulated the expression of autoinducer synthase gene, abaI, and consequently reduced (92%) the production of 3-OH-C12-HSL as determined by ESI-MS. Q-TOF and Q-TRAP analyses suggested the presence of flavonoids viz. licoricone, glycyrin and glyzarin as the active ingredients.

CONCLUSION

This is the first report on quorum quenching activity of G. glabra linked to its flavonoids that downregulated the expression of abaI and attenuated quorum sensing regulated virulence of A. baumannii.

Characterising the Transmission Dynamics of Acinetobacter baumannii in Intensive Care Units Using Hidden Markov Models

Little is known about the transmission dynamics of Acinetobacter baumannii in hospitals, despite such information being critical for designing effective infection control measures. In the absence of comprehensive epidemiological data, mathematical modelling is an attractive approach to understanding transmission process. The statistical challenge in estimating transmission parameters from infection data arises from the fact that most patients are colonised asymptomatically and therefore the transmission process is not fully observed. Hidden Markov models (HMMs) can overcome this problem. We developed a continuous-time structured HMM to characterise the transmission dynamics, and to quantify the relative importance of different acquisition sources of A. baumannii in intensive care units (ICUs) in three hospitals in Melbourne, Australia. The hidden states were the total number of patients colonised with A. baumannii (both detected and undetected). The model input was monthly incidence data of the number of detected colonised patients (observations). A Bayesian framework with Markov chain Monte Carlo algorithm was used for parameter estimations. We estimated that 96-98% of acquisition in Hospital 1 and 3 was due to cross-transmission between patients; whereas most colonisation in Hospital 2 was due to other sources (sporadic acquisition). On average, it takes 20 and 31 days for each susceptible individual in Hospital 1 and Hospital 3 to become colonised as a result of cross-transmission, respectively; whereas it takes 17 days to observe one new colonisation from sporadic acquisition in Hospital 2. The basic reproduction ratio (R0) for Hospital 1, 2 and 3 was 1.5, 0.02 and 1.6, respectively. Our study is the first to characterise the transmission dynamics of A. baumannii using mathematical modelling. We showed that HMMs can be applied to sparse hospital infection data to estimate transmission parameters despite unobserved events and imperfect detection of the organism. Our results highlight the need to optimise infection control in ICUs.

Clinical importance and cost of bacteremia caused by nosocomial multi drug resistant acinetobacter baumannii

BACKGROUND

A. baumannii is an important nosocomial pathogen associated with high mortality, morbidity and medical cost.

AIM

The aim of this study was to investigate risk factors for MDR A. baumannii bacteremia and also evaluate cost of hospitalization of these patients.

METHODS

Study was conducted in Ankara Atatürk Training and Research Hospital. Patients who were hospitalized in ICU and diagnosed for nosocomial blood stream infection (BSI) between January 2007 and December 2010 were checked retrospectively. Patients with nosocomial BSI caused by multidrug resistant A. baumannii were compared with the patients who had BSI caused by other Gram-negative microorganisms in terms of risk factors, mortality and medical costs.

FINDINGS

In multivariate analysis previous use of carbapenem, quinolone and metronidazole, and SAPS II score were found as independent risk factors. In case group; immunosupression, SAPS II score, and hospital stay until infection were independently associated with mortality in multivariate analysis.

CONCLUSION

Our results suggest that the occurrence of MDR A.baumannii bacteremia was related with the usage of the wide spectrum antibiotics, and mortality rates were increased in patients that high SAPS II scores, long term hospitalization. Infection control procedures and limited antibiotic usage are very important for prevent nosocomial infections.

Phenotypic and Molecular Epidemiology of Acinetobacter calcoaceticus baumannii Complex Strains Spread at Nemazee Hospital of Shiraz, Iran

Background

Acinetobacter calcoaceticus baumannii (ACB) complex are Gram-negative opportunistic bacteria with low virulence properties. Their resistance to antibiotics has become a matter of concern in hospital infections.

Objectives

The present study aimed to determine the prevalence and antimicrobial susceptibility of ACB isolates collected from the Nemazee hospital of Shiraz. In addition, Pulsed Field Gel Electrophoresis (PFGE) was used to determine the genetic patterns of these strains.

Patients and Methods

In this cross-sectional study, 93 strains of ACB complex were isolated from patients of Nemazee hospital, Shiraz, Iran. The antibiotic susceptibility patterns of the isolates to the following 15 antibiotics were determined: gentamicin, ticarcillin, ceftazidime, co-trimoxazole, imipenem, piperacillin tazobactam, amikacin, aztreonam, sulbactam, meropenem, tobramycin, cefotaxime, ceftriaxone, colistin, polymyxin B. Pulsed Field Gel Electrophoresis was used to determine the clonal relationship of these strains.

Results

Most of the isolates were found to be resistant to cefotaxime, co-trimoxazole, ceftriaxone, aztreonam, ceftazidime and ticarcillin (90%), and the least resistance was observed to colistin and polymyxin B. Among the 93 tested samples, 35 antimicrobial susceptibility patterns and 47 PFGE patterns were obtained.

Conclusions

High resistance to antibiotics was observed among the strains of ACB complex and the least resistance was towards colistin and polymyxin B, indicating that these antibiotics could be effective for treatment, in case there is no other choice. Using PFGE, the similarity between some strains of Acinetobacter was determined, which indicated epidemics in different parts of the hospital; such epidemics can in turn lead to increased incidence of Acinetobacter infections.

A Epidemiological Investigation of a Nosocomial Outbreak of Multidrug-Resistant Acinetobacter baumannii in a Critical Care Center in Japan, 2011-2012

In 2011, a multidrug-resistant Acinetobacter baumannii (MDRAB) outbreak occurred at a Japanese critical care center (CCC) in a tertiary care hospital. Multidrug-resistance in Japan is defined as resistance to the antimicrobials amikacin, carbapenem, and fluoroquinolone. We conducted a retrospective epidemiological investigation of this outbreak to identify the risk factors for MDRAB respiratory tract acquisition in this hospital. Cases were defined as hospitalized patients with MDRAB-positive cultures at least 3 days post admission to the CCC between June 1, 2011 and April 20, 2012. Fifteen MDRAB cases were identified, including 3 with infection and 12 with colonization. This case-control study demonstrated that hypoalbuminemia along with carbapenem administration were associated with MDRAB respiratory tract acquisition. Pulsed-field gel electrophoresis analysis and multilocus sequence typing using MDRAB isolates suggested a clonal dissemination of MDRAB strains with sequence type 74 occurred primarily among patients admitted to the CCC. From April 16, 2012, a decreased isolation rate of MDRAB in the hospital occurred after the implementation of the following infection control measures: closing the emergency room, discontinuing admission to the CCC, isolating patients with MDRAB colonization or infection to single room status, and conducting environmental cleaning. No MDRAB cases were detected between March 23 and April 20, 2012.

A data-driven mathematical model of multi-drug resistant Acinetobacter baumannii transmission in an intensive care unit

Major challenges remain when attempting to quantify and evaluate the impacts of contaminated environments and heterogeneity in the cohorting of health care workers (HCWs) on hospital infections. Data on the detection rate of multidrug-resistant Acinetobacter baumannii (MRAB) in a Chinese intensive care unit (ICU) were obtained to accurately evaluate the level of environmental contamination and also to simplify existing models. Data-driven mathematical models, including mean-field and pair approximation models, were proposed to examine the comprehensive effect of integrated measures including cohorting, increasing nurse-patient ratios and improvement of environmental sanitation on MRAB infection. Our results indicate that for clean environments and with strict cohorting, increasing the nurse-patient ratio results in an initial increase and then a decline in MRAB colonization. In contrast, in contaminated environments, increasing the nurse-patient ratio may lead to either a consistent increase or an initial increase followed by a decline of MRAB colonization, depending on the level of environmental contamination and the cohorting rate. For developing more effective control strategies, the findings suggest that increasing the cohorting rate and nurse-patient ratio are effective interventions for relatively clean environments, while cleaning the environment more frequently and increasing hand washing rate are suitable measures in contaminated environments.

Prognostic factors associated with mortality of drug-resistant Acinetobacter baumannii ventilator-associated pneumonia

Background

Ventilator-associated pneumonia (VAP) caused by drug-resistant Acinetobacter baumannii is associated with high mortality in critically ill patients. We identified the prognostic factors of 30-day mortality in patients with VAP caused by drug-resistant A. baumannii and compared survival outcomes among multidrug-resistant (MDR), extensively drug-resistant (XDR) and pandrug-resistant (PDR) A. baumannii VAP.

Methods

A retrospective cohort study was conducted in the Medical Intensive Care Unit at Chiang Mai University Hospital, Thailand. All adult patients diagnosed with A. baumannii VAP between 2005 and 2011 were eligible. Univariable and multivariable Cox’s proportional hazards regression were performed to identify the prognostic factors of 30-day mortality.

Results

A total of 337 patients with microbiologically confirmed A. baumannii VAP were included. The proportion of drug-sensitive (DS), MDR, XDR, and PDR A. baumannii were 9.8%, 21.4%, 65.3%, and 3.6%, respectively. The 30-day mortality rates were 21.2%, 31.9%, 56.8%, and 66.7%, respectively. The independent prognostic factors were SOFA score >5 (hazard ratio (HR) = 3.33, 95% confidence interval (CI) 1.94–5.72, P < 0.001), presence of septic shock (HR = 2.66, 95% CI 1.71–4.12, P < 0.001), Simplified Acute Physiology Score (SAPS) II >45 (HR = 1.58, 95% CI 1.01–2.46, P = 0.045), and inappropriate initial antibiotic treatment (HR = 1.53, 95% CI 1.08–2.20, P = 0.016).

Conclusions

Drug-resistant A. baumannii, particularly XDR and PDR, was associated with a high mortality rate. Septic shock, high SAPS II, high SOFA score, and inappropriate initial antibiotic treatment were independent prognostic factors for 30-day mortality.

Assessing the Burden of Acinetobacter baumannii in Maryland: A Statewide Cross-Sectional Period Prevalence Survey

Objective.

To determine the prevalence ofAcinetobacter baumannii, an important healthcare-associated pathogen, among mechanically ventilated patients in Maryland.

Design.

The Maryland MDRO Prevention Collaborative performed a statewide cross-sectional active surveillance survey of mechanically ventilated patients residing in acute care and long-term care (LTC) facilities. Surveillance cultures (sputum and perianal) were obtained from all mechanically ventilated inpatients at participating facilities during a 2-week period.

Setting.

All healthcare facilities in Maryland that provide care for mechanically ventilated patients were invited to participate.

Patients.

Mechanically ventilated patients, known to be at high risk for colonization and infection withA. baumannii, were included.

Results.

Seventy percent (40/57) of all eligible healthcare facilities participated in the survey, representing both acute care (n= 30) and LTC (n= 10) facilities in all geographic regions of Maryland. Surveillance cultures were obtained from 92% (358/390) of eligible Patients.A. baumanniiwas identified in 34% of all mechanically ventilated patients in Maryland; multidrug-resistantA. baumanniiwas found in 27% of all Patients.A. baumanniiwas detected in at least 1 patient in 49% of participating facilities; 100% of LTC facilities had at least 1 patient with A.baumannii, compared with 31% of acute care facilities.A. baumanniiwas identified from all facilities in which 10 or more patients were sampled.

Conclusions.

A.baumanniiis common among mechanically ventilated patients in both acute care and LTC facilities throughout Maryland, with a high proportion of isolates demonstrating multidrug resistance.

The impact of inadequate terminal disinfection on an outbreak of imipenem-resistant Acinetobacter baumannii in an intensive care unit

Background

This study was conducted to investigate an outbreak caused by imipenem-resistant Acinetobacter baumannii (IRAB) in a medical intensive care unit (ICU) in a regional hospital.

Methods

In response to an IRAB outbreak from October 2012 to February 2013, we developed several infection control measures, including an extensive review process of environmental cleaning and disinfection, and used molecular methods to identify each clinical and environmental IRAB isolate.

Results

During this five-month period, 22 patients were colonized with IRAB and 18 patients had IRAB infections. The in-hospital mortality rate was significantly higher among patients with infections rather than colonizations (44.4% vs 9.1%, p = 0.028). Additionally, nine environmental specimens, including five specimens collected after terminal disinfection, were positive for IRAB. 12 environmental isolates and 28 of 36 available clinical isolates belonged to one unique pulsotype A, which was confirmed by molecular methods. We found the concentration of disinfectant, 0.08% sodium hypochlorite, was inadequate. After correcting the environmental cleansing methods, the surveillance study showed no further IRAB isolates on the control panel surfaces of the medical equipment or in patients in the ICU. Additionally, an invitro study of IRAB immersed in different concentrations of sodium hypochlorite showed that 0.5% sodium hypochlorite eradicates IRAB after 30 seconds of inoculation, but 0.08% sodium hypochlorite only reduces the bacterial load.

Conclusions

This study highlights the importance of the preparation of disinfectants to adequately achieve environmental disinfection in the control of IRAB outbreaks in the ICU.

In vitro activity of WQ-3810, a novel fluoroquinolone, against multidrug-resistant and fluoroquinolone-resistant pathogens

The aim of this study was to examine the in vitro antibacterial activity of WQ-3810, a new fluoroquinolone, against clinically relevant pathogens such as Acinetobacter baumannii, Escherichia coli and Streptococcus pneumoniae, including multidrug-resistant (MDR) and fluoroquinolone-resistant (FQR) isolates, compared with those of ciprofloxacin, levofloxacin, moxifloxacin and gemifloxacin. WQ-3810 demonstrated the most potent activity against the antimicrobial-resistant pathogens tested. Against A. baumannii, including MDR isolates, the potency of WQ-3810 [minimum inhibitory concentration for 90% of the organisms (MIC(90))=1 mg/L] was more than eight-fold higher than that of ciprofloxacin (64 mg/L) and levofloxacin (8 mg/L). Against E. coli and S. pneumoniae, including FQR isolates, WQ-3810 (MIC(90)=4 mg/L and 0.06 mg/L, respectively) was also more active than ciprofloxacin (64 mg/L and 2 mg/L) and levofloxacin (32 mg/L and 2 mg/L). Furthermore, WQ-3810 was the most potent among the fluoroquinolones tested against meticillin-resistant Staphylococcus aureus (MRSA) and Neisseria gonorrhoeae, including FQR isolates. In particular, WQ-3810 demonstrated highly potent activity against FQR isolates of A. baumannii, E. coli and S. pneumoniae with amino acid mutation(s) in the quinolone resistance-determining region of DNA gyrase and/or topoisomerase IV, which are the target enzymes of fluoroquinolones. An enzyme inhibition study performed using FQR E. coli DNA gyrase suggested that the potent antibacterial activity of WQ-3810 against drug-resistant isolates partly results from the strong inhibition of the target enzymes. In conclusion, this study demonstrated that WQ-3810 exhibits extremely potent antibacterial activity over the existing fluoroquinolones, particularly against MDR and FQR pathogens.

Infections Caused by Acinetobacter baumannii in Recipients of Hematopoietic Stem Cell Transplantation

Acinetobacter baumannii (A. baumannii) is a Gram-negative, strictly aerobic, non-fermentative coccobacillus, which is widely distributed in nature. Recently, it has emerged as a major cause of health care-associated infections (HCAIs) in addition to its capacity to cause community-acquired infections. Risk factors for A. baumannii infections and bacteremia in recipients of hematopoietic stem cell transplantation include: severe underlying illness such as hematological malignancy, prolonged use of broad-spectrum antibiotics, invasive instrumentation such as central venous catheters or endotracheal intubation, colonization of respiratory, gastrointestinal, or urinary tracts in addition to severe immunosuppression caused by using corticosteroids for treating graft versus host disease. The organism causes a wide spectrum of clinical manifestations, but serious complications such as bacteremia, septic shock, ventilator-associated pneumonia, extensive soft tissue necrosis, and rapidly progressive systemic infections that ultimately lead to multi-organ failure and death are prone to occur in severely immunocompromised hosts. The organism is usually resistant to many antimicrobials including penicillins, cephalosporins, trimethoprim-sulfamethoxazole, almost all fluoroquinolones, and most of the aminoglycosides. The recently increasing resistance to carbapenems, colistin, and polymyxins is alarming. Additionally, there are geographic variations in the resistance patterns and several globally and regionally resistant strains have already been described. Successful management of A. baumannii infections depends upon appropriate utilization of antibiotics and strict application of preventive and infection control measures. In uncomplicated infections, the use of a single active beta-lactam may be justified, while definitive treatment of complicated infections in critically ill individuals may require drug combinations such as colistin and rifampicin or colistin and carbapenem. Mortality rates in patients having bacteremia or septic shock may reach 70%. Good prognosis is associated with presence of local infection, absence of multidrug resistant strain, and presence of uncomplicated infection while poor outcome is associated with severe underlying medical illness, bacteremia, septic shock, multi-organ failure, HCAIs, admission to intensive care facilities for higher levels of care, and culture of certain aggressive genotypes of A. baumannii.

Pyocyanin stimulates quorum sensing-mediated tolerance to oxidative stress and increases persister cell populations in Acinetobacter baumannii

Acinetobacter baumannii and Pseudomonas aeruginosa are nosocomial pathogens with overlapping sites of infection. This work reports that the two can coexist stably in mixed-culture biofilms. In a study intended to improve our understanding of the mechanism of their coexistence, it was found that pyocyanin, produced by P. aeruginosa that generally eliminates competition from other pathogens, led to the generation of reactive oxygen species (ROS) in A. baumannii cells, which in response showed a significant (P ≤ 0.05) increase in production of enzymes, specifically, catalase and superoxide dismutase (SOD). This work shows for the first time that the expression of catalase and SOD is under the control of a quorum-sensing system in A. baumannii. In support of this observation, a quorum-sensing mutant of A. baumannii (abaI::Km) was found to be sensitive to pyocyanin compared to its wild type and showed significantly (P ≤ 0.001) lower levels of the antioxidant enzymes, which increased on addition of 5 μM N-(3-hydroxydodecanoyl)-l-homoserine lactone. Likewise, in wild-type A. baumannii, there was a significant (P < 0.01) decrease in the level of anti-oxidant enzymes in the presence of salicylic acid, a known quencher of quorum sensing. In the presence of amikacin and carbenicillin, A. baumannii formed 0.07 and 0.02% persister cells, which increased 4- and 3-fold, respectively, in the presence of pyocyanin. These findings show that pyocyanin induces a protective mechanism in A. baumannii against oxidative stress and also increases its persistence against antibiotics which could be of clinical significance in the case of coinfections with A. baumannii and P. aeruginosa.

Rapid efficient synthesis and characterization of silver, gold, and bimetallic nanoparticles from the medicinal plant Plumbago zeylanica and their application in biofilm control

BACKGROUND

Nanoparticles (NPs) have gained significance in medical fields due to their high surface-area-to-volume ratio. In this study, we synthesized NPs from a medicinally important plant - Plumbago zeylanica.

MATERIALS AND METHODS

Aqueous root extract of P. zeylanica (PZRE) was analyzed for the presence of flavonoids, sugars, and organic acids using high-performance thin-layer chromatography (HPTLC), gas chromatography-time of flight-mass spectrometry (GC-TOF-MS), and biochemical methods. The silver NPs (AgNPs), gold NPs (AuNPs), and bimetallic NPs (AgAuNPs) were synthesized from root extract and characterized using ultraviolet-visible spectra, X-ray diffraction (XRD), energy-dispersive spectrometry (EDS), transmission electron microscopy (TEM), and dynamic light scattering (DLS). The effects of these NPs on Acinetobacter baumannii, Staphylococcus aureus, and Escherichia coli biofilms were studied using quantitative biofilm inhibition and disruption assays, as well as using fluorescence, scanning electron microscopy, and atomic force microscopy.

RESULTS

PZRE showed the presence of phenolics, such as plumbagin, and flavonoids, in addition to citric acid, sucrose, glucose, fructose, and starch, using HPTLC, GC-TOF-MS, and quantitative analysis. Bioreduction of silver nitrate (AgNO₃) and chloroauric acid (HAuCl₄) were confirmed at absorbances of 440 nm (AgNPs), 570 nm (AuNPs), and 540 nm (AgAuNPs), respectively. The maximum rate of synthesis at 50°C was achieved with 5 mM AgNO₃ within 4.5 hours for AgNPs; and with 0.7 mM HAuCl4 within 5 hours for AuNPs. The synthesis of AgAuNPs, which completed within 90 minutes with 0.7 mM AgNO₃ and HAuCl₄, was found to be the fastest. Fourier-transform infrared spectroscopy confirmed bioreduction, while EDS and XRD patterns confirmed purity and the crystalline nature of the NPs, respectively. TEM micrographs and DLS showed about 60 nm monodispersed Ag nanospheres, 20-30 nm Au nanospheres adhering to form Au nanotriangles, and about 90 nm hexagonal blunt-ended AgAuNPs. These NPs also showed antimicrobial and antibiofilm activity against E. coli, A. baumannii, S. aureus, and a mixed culture of A. baumannii and S. aureus. AgNPs inhibited biofilm in the range of 96%-99% and AgAuNPs from 93% to 98% in single-culture biofilms. AuNPs also showed biofilm inhibition, with the highest of 98% in S. aureus. AgNPs also showed good biofilm disruption, with the highest of 88% in A. baumannii.

CONCLUSION

This is the first report on rapid and efficient synthesis of AgNPs, AuNPs and AgAuNPs from P. zeylanica and their effect on quantitative inhibition and disruption of bacterial biofilms.

Detection of colistin sensitivity in clinical isolates of Acinetobacter baumannii in Iran

BACKGROUND

Nosocomial infection caused by Acinetobacter baumannii has emerged as a serious problem world-wide. Finding the suitable drug is an important priority. The aim of this study was to determine colistin (polymyxin E) resistance in clinical isolates of A. baumannii from intensive care units (ICUs) of Al Zahra Hospital.

MATERIALS AND METHODS

Sixty isolates of A. baumannii from patients hospitalized in ICU (Al Zahra Hospital, Isfahan University of Medical Sciences [IUMS]) were studied. All isolates of A. baumannii were tested for colistin susceptibility by Eopsilometer test (E-test).

RESULTS

Of the 60 isolates 57, (95%) were multidrug resistant (MDR) and 76.6% (46/60) were highly resistant. The rate of colistin resistant with the E-test method was 11.6% (7/60).

CONCLUSION

As the frequency of resistance to colistin is low, it can be used as an easily available drug for treatment of MDR A. baumannii strains, which are susceptible to colistin.

Draft Genome Sequence of Multidrug-Resistant Acinetobacter baumannii Strain MMC4, Isolated from a Patient in Tennessee

Acinetobacter baumannii multidrug-resistant strain MMC4 was isolated from a bronchoalveolar lavage fluid sample from a patient in Nashville, TN, USA. Here, we report a draft genome sequence with a size of 3,985,367 bp, an average G+C content of 39.8%, and 3,863 predicted protein-coding sequences.

Nosocomial urinary tract infections caused by Pseudomonas aeruginosa and Acinetobacter species: sensitivity to antibiotics and risk factors

BACKGROUND

Pseudomonas aeruginosa and Acinetobacter species frequently cause intrahospital urinary tract infections (IUTI), contributing to increased hospital morbidity and mortality. Our objective was further exploration of possible risk factors for development of IUTI caused by P aeruginosa and Acinetobacter spp, including their resistance to various antibiotics.

METHODS

The prospective case control study was conducted in Clinical Center Kragujevac, Serbia, during the period January 2009 to December 2011 and covered all patients with IUTI according to the Centers for Disease Control and Prevention criteria. The patients classified as "cases" had an IUTI caused by P aeruginosa or Acinetobacter spp. The control patients were matched to the cases and selected randomly from the remaining patients.

RESULTS

There were 79 cases (11.9%) and 586 (88.1%) controls in the study. According to the multivariate binary logistic regression, there were 3 significant predictors of P aeruginosa and Acinetobacter spp IUTI: male sex (odds ratio [OR], 0.423; 95% confidence interval [CI]: 0.251-0.711; P = .001), stay in another hospital ward before emergence of IUTI (OR, 1.704; 95% CI: 1.013-2.864; P = .044), and previous use of penicillins and their combinations with inhibitors of β-lactamases (OR, 2.643; 95% CI: 1.044-6.692; P = .040).

CONCLUSION

Knowing that IUTI caused by above-mentioned bacteria are especially frequent among male patients, after previous use of penicillins, and in patients who spent some time previously at other wards, sound strategies for prevention of such infections in clinical practice should be developed.

Effects of a combination of amlodipine and imipenem on 42 clinical isolates of Acinetobacter baumannii obtained from a teaching hospital in Guangzhou, China

Background

The clonal spread of Acinetobacter baumannii is a global problem, and carbapenems, such as imipenem, remain the first-choice agent against A. baumannii. Using synergy to enhance the antibiotic activity of carbapenems could be useful. Here, amlodipine (AML) was tested alone and with imipenem against A. baumannii isolates.

Methods

Forty-two isolates of A. baumannii were collected. Multilocus sequence typing (MLST) assessed the genetic relationship of the isolates. The resistance phenotypes were determined using disc diffusion. The minimum inhibitory concentrations (MICs) of the drugs were determined by broth microdilution. The combined effects of the drugs were determined by a checkerboard procedure. Metallo-β-lactamase (MBL) was determined using the MBL Etest.

Results

Forty-two A. baumannii isolates were collected from 42 patients who were mostly older than 65 years and had long inpatient stays (≥7 days). A. baumannii was mostly recovered from the respiratory system (N = 35, 83.3%). Most patients (N = 27, 64.3%) received care in intensive care units (ICUs). Disc diffusion testing demonstrated that A. baumannii susceptibility to polymyxin B was 100%, while susceptibility to other antimicrobial agents was less than 30%, classifying the isolates into 10 MDR and 32 XDR strains. MLST grouped the A. baumannii isolates into 4 existing STs and 6 new STs. STn4 carried allele G1, with a T → C mutation at nt3 on the gpi111 locus. STn5 carried allele A1, possessing A → C mutations at nt156 and nt159 on the gltA1 locus. ST195 and ST208 accounted for 68.05% (29/42) of the isolates. Clonal relation analysis showed that ST195 and ST208 belonged to clonal complex (CC) 92. The inhibitory concentration of imipenem ranged from 0.5 to 32 μg/ml, and that of AML ranged from 40 to 320 μg/ml. In combination, the susceptibility rate of A. baumannii isolates increased from 16.7% to 54.8% (P = 0.001). In the checkerboard procedure, half of the isolates (N = 21, 50.0%) demonstrated synergy or partial synergy with the drug combination. The MBL Etest revealed that 1 A. baumannii strain (N = 1, 2.4%) produced MBL.

Conclusions

CC92 was the major clone spreading in our hospital. AML improved the activity of imipenem against A. baumannii isolates in vitro but did not inhibit MBL.

Early detection of nosocomial outbreaks caused by rare pathogens: a case study employing score prediction interval

Objectives

Nosocomial outbreaks involve only a small number of cases and limited baseline data. The present study proposes a method to detect the nosocomial outbreaks caused by rare pathogens, exploiting score prediction interval of a Poisson distribution.

Methods

The proposed method was applied to three empirical datasets of nosocomial outbreaks in Japan: outbreaks of (1) multidrug-resistant Acinetobacter baumannii (n = 46) from 2009 to 2010, (2) multidrug-resistant Pseudomonas aerginosa (n = 18) from 2009 to 2010, and (3) Serratia marcescens (n = 226) from 1999 to 2000.

Results

The proposed method successfully detected all three outbreaks during the first 2 months. Both the model-based and empirically derived threshold values indicated that the nosocomial outbreak of rare infectious disease may be declared upon diagnosis of index case(s), although the sensitivity and specificity were highly variable.

Conclusion

The findings support the practical notion that, upon diagnosis of index patient(s), one should immediately start the outbreak investigation of nosocomial outbreak caused by a rare pathogen. The proposed score prediction interval can permit easy computation of outbreak threshold in hospital settings among healthcare experts.

Frequency, risk factors, and antibiogram of Acinetobacter species isolated from various clinical samples in a tertiary care hospital in Odisha, India

BACKGROUND

For the past two decades, Acinetobacter spp. have emerged as an important pathogen globally in various infections.

OBJECTIVES

This study was conducted to determine the frequency, risk factors, and antibiotic resistance pattern of Acinetobacter spp. from various clinical samples.

MATERIALS AND METHODS

This retrospective, hospital record-based, cross-sectional study included a total of 8749 clinical samples collected from patients at a tertiary care hospital in Odisha, India from July 2010 to December 2012. The samples were processed and identified by standard protocol. The Acinetobacter isolates were tested for antibiotic resistance by Kirby-Bauer disk diffusion method [according to the Clinical and Laboratory Standards Institute (CLSI) guidelines].

RESULTS

From 8749 clinical samples, 4589 (52.5%) yielded significant growth and only 137 (3%, 137/4589) Acinetobacter spp. were isolated. Maximum (56.9%) isolates were obtained from pus/swab, followed by blood (13.1%) and urine (12.4%). Elderly age, being inpatients, longer duration of stay in the hospital, associated co-morbidity, and invasive procedure were found to be significant risk factors in the setup investigated (P is less than 0.05). Out of 137 isolates, 75 (54.7%) were resistant to more than three classes of antibiotics (multidrug resistant) and 8 (5.8%) were resistant to all commonly used antibiotics (pan-drug resistant). Majority of the isolates were sensitive to imipenem, meropenem, and piperacillin/tazobactam, and showed resistance rates of 19%, 22%, and 23%, respectively. All eight pan-drug resistant isolates were 100% sensitive to colistin.

CONCLUSION

This hospital-based epidemiological data will help to implement better infection control strategies and improve the knowledge of antibiotic resistance patterns in our region.

Risk factors and mortality of patients with nosocomial carbapenem-resistant Acinetobacter baumannii pneumonia

BACKGROUND

Acinetobacter baumannii is characterized by strictly aerobic, gram-negative, nonmotile, nonlactose-fermenting, oxidase-negative, catalase-positive coccobacilli, and the combination of its environmental resilience and its rapid development of resistance to multiple classes of antimicrobials renders it a successful nosocomial pathogen.

OBJECTIVES

The aim of this study was to identify specific risk factors and outcome of nosocomial pneumonia because of carbapenem-resistant Acinetobacter baumannii (CRAB).

METHODS

The retrospective study, set in a 1,500-bed referral and tertiary care hospital, was conducted to analyze the clinical and microbiologic data of patients with nosocomial pneumonia because of Acinetobacter baumannii (A baumannii) from January 2006 to December 2011. Comparisons were made between patients with CRAB pneumonia and patients with carbapenem-susceptible A baumannii (CSAB) pneumonia. Only the first isolation of A baumannii was considered.

RESULTS

A total of 145 patients with CSAB pneumonia and 97 patients with CRAB pneumonia was included. Among these patients, the independent risk factors for acquiring CRAB pneumonia were Acute Physiology and Chronic Health Evaluation II (APACHE II) score (>20) at admission, systemic illnesses (chronic respiratory disease and cerebrovascular accident), presence of excess noninvasive or invasive devices (mechanical ventilation), and ever used antibiotics within 28 days (carbapenem and cefepime). The patients with CRAB pneumonia had higher mortality rate than CSAB pneumonia. Multivariate analysis showed that, among patients with A baumannii pneumonia, APACHE II score (>20) at pneumonia onset, infections with other microorganisms, and inappropriate therapy were independently associated with 28-day mortality.

CONCLUSION

Patients with CRAB pneumonia have a higher mortality rate than those with CSAB pneumonia. The nosocomial occurrence of CRAB pneumonia is strongly related to systemic illnesses, APACHE II score, mechanical ventilation, and ever used antibiotics within 28 days.

Protective effect of procysteine on Acinetobacter pneumonia in hyperoxic conditions

OBJECTIVES

Ventilator-associated pneumonia (VAP) is an important cause of morbidity and mortality in critical care settings. Acinetobacter has become a leading cause of VAP. In particular, the appearance and spread of multidrug-resistant Acinetobacter is of great concern. In this study, we examined the effect of the antioxidant procysteine on Acinetobacter murine pneumonia in hyperoxic conditions in order to simulate VAP.

METHODS

Acinetobacter was administered intranasally to BALB/c mice kept in hyperoxic conditions. At designated timepoints, bacterial number, cytokine production and histopathological findings in the lungs were examined. The effects of procysteine on survival rates, lung bacterial burdens and the phagocytic activities of alveolar macrophages were evaluated.

RESULTS

Drastic decreases in survival were observed when the infected mice were kept in hyperoxic conditions (P < 0.001). Significant differences in pulmonary bacterial number and neutrophil accumulation were observed between mice kept in hyperoxic or normoxic conditions on day 3. Although all mice infected with Acinetobacter spp. and kept in hyperoxic conditions died by day 3, procysteine treatment significantly improved survival (60% survival on day 7, P < 0.01). Procysteine treatment decreased the lung bacterial burden on days 2 and 3. Finally, improved uptake of FITC-labelled beads by alveolar macrophages from mice treated with procysteine and kept in hyperoxic conditions was noted.

CONCLUSIONS

These results suggest that hyperoxia increases mortality in mice with Acinetobacter pneumonia and that procysteine improves survival by increasing the phagocytic activity of alveolar macrophages in mice kept in hyperoxic conditions.

A systematic quantitative proteomic examination of multidrug resistance in Acinetobacter baumannii

Multidrug-resistant Acinetobacter baumannii strains have been examined at the DNA sequence level, but seldom using large-scale quantitative proteomics. We have compared the proteome of the multidrug resistant strain BAA-1605, with the proteome of the drug-sensitive strain ATCC 17978, using iTRAQ labeling and online 2D LC/MS/MS for peptide/protein identification. Of 1484 proteins present in at least 2 of 4 independent experiments, 114 are 2-fold to 66-fold more abundant in BAA-1605, and 99 are 2-fold to 50-fold less abundant. Proteins with 2-fold or greater abundance in the multidrug resistant strain include drug-, antibiotic-, and heavy metal-resistance proteins, stress-related proteins, porins, membrane transporters, proteins important for acquisition of foreign DNA, biofilm-related proteins, cell-wall and exopolysaccharide-related proteins, lipoproteins, metabolic proteins, and many with no annotated function. The porin CarO, inactivated in carbapenem-resistant strains, is 2.3-fold more abundant in BAA-1605. Likewise, the porin OmpW, less abundant in carbapenem- and colistin-resistant A. baumannii strains, is 3-fold more abundant in BAA-1605. Nine proteins, all present in the drug-sensitive strain but from 2.2-fold to 16-fold more abundant in the MDR strain, can potentially account for the observed resistance of BAA-1605 to 18 antibiotics.

BIOLOGICAL SIGNIFICANCE

Multidrug resistant (MDR) strains of the pathogen Acinetobacter baumannii are a significant cause of hospital-acquired infections, are associated with increased mortality and length of stay, and may be a major factor underlying the spread of this pathogen, which is difficult to eradicate from clinical settings. To obtain a better understanding of antimicrobial resistance mechanisms in MDR A. baumannii, we report the first large scale 2D LC/MS/MS-based quantitative proteomics comparison of a drug-sensitive strain and an MDR strain of this pathogen. Ca. 20% of the expressed proteome changes 2-fold or more between the compared strains, including 42 proteins with literature or informatics annotations related to resistance mechanisms, modification of xenobiotics, or drug transport. Other categories of proteins differing 2-fold or more between strains include stress-response related proteins, porins, OMPs, transporters and secretion-related proteins, cell wall- and expolysaccharide-related proteins, lipoproteins, and DNA- and plasmid-related proteins. While the compared strains also differ in other aspects than multi-drug resistance, the observed differences, combined with protein functional annotation, suggest that complex protein expression changes may accompany the MDR phenotype. Expression changes of nine proteins in the MDR strain can potentially account for the observed resistance to 18 antibiotics.

Structure determination of LpxD from the lipopolysaccharide-synthesis pathway of Acinetobacter baumannii

Acinetobacter baumannii is a Gram-negative bacterium that is resistant to many currently available antibiotics. The protein LpxD is a component of the biosynthetic pathway for lipopolysaccharides in the outer membrane of this bacterium and is a potential target for new antibacterial agents. This paper describes the structure determination of apo forms of LpxD in space groups P2(1) and P4(3)22. These crystals contained six and three copies of the protein molecule in the asymmetric unit and diffracted to 2.8 and 2.7 Å resolution, respectively. A comparison of the multiple protein copies in the asymmetric units of these crystals reveals a common protein conformation and a conformation in which the relative orientation between the two major domains in the protein is altered.

Structure determination of LpxA from the lipopolysaccharide-synthesis pathway of Acinetobacter baumannii

Acinetobacter baumannii is a Gram-negative pathogenic bacterium which is resistant to most currently available antibiotics and that poses a significant health threat to hospital patients. LpxA is a key enzyme in the biosynthetic pathway of the lipopolysaccharides that are components of the bacterial outer membrane. It is a potential target for antibacterial agents that might be used to fight A. baumannii infections. This paper describes the structure determination of the apo form of LpxA in space groups P2(1)2(1)2(1) and P6(3). These crystal forms contained three and one protein molecules in the asymmetric unit and diffracted to 1.8 and 1.4 Å resolution, respectively. A comparison of the conformations of the independent protein monomers within and between the two crystal asymmetric units revealed very little structural variation across this set of structures. In the P6(3) crystal form the enzymatic site is exposed and is available for the introduction of small molecules of the type used in fragment-based drug discovery and structure-based lead optimization.

Risk factors and outcomes in patients with carbapenem-resistant Acinetobacter infection

INTRODUCTION

Acinetobacter spp. are important pathogens increasingly reported as the cause of outbreaks of nosocomial infections. The aim of our study was to identify the risk factors and assess their influence on outcomes in patients with infections caused by carbapenem-resistant Acinetobacter spp.

METHODS

A retrospective data analysis was performed to evaluate risk factors and mortality in patients with Acinetobacter spp. infections. Methods used for the statistical analysis were the Student's t-test, Chi-square test, and multivariate analysis; p < 0.05 was considered statistically significant.

RESULTS

A total of 99 patients with an Acinetobacter spp. infection were identified. Comparing patients with carbapenem-sensitive and carbapenem-resistant Acinetobacter spp. infection, significant differences were found in the mean length of intensive care unit stay (4.17 ± 3.61 vs 7.92 ± 6.74 days, p = 0.038) and mechanical ventilation (3.25 ± 2.61 and 7.07 ± 5.79 days, p = 0.009). The previous use of carbapenems (odds ratio (OR) 10.1, 95% confidence interval (CI) 1.16-87.20) and fluoroquinolones (OR 3.6, 95% CI 1.13-11.51) was independently associated with resistance to carbapenems. Of the Acinetobacter spp. strains, 94.9% (n = 94) were resistant to piperacillin-tazobactam, 88.9% (n = 88) to ceftazidime, 85.9% (n = 85) to ciprofloxacin, 83.8% (n = 83) to gentamicin, 79.8 (n = 79) to amikacin, and 48.5% (n = 48) to cefepime.

CONCLUSIONS

Intensive care unit stay before infection and source of infection in the respiratory tract were independently associated with patient mortality. Resistance to carbapenems had no impact on mortality rates. Carbapenem-resistant Acinetobacter spp. isolates had high resistance rates to other antimicrobial drugs.

Cloning, purification and preliminary X-ray crystallographic analysis of the OmpA-like domain of peptidoglycan-associated lipoprotein from Acinetobacter baumannii

Peptidoglycan-associated lipoprotein (Pal) is one component of the Tol-Pal system that is involved in maintaining the integrity and stability of the outer membrane. The C-terminal OmpA-like domain of Pal interacts noncovalently with peptidoglycan. In this study, the OmpA-like domain of Pal from Acinetobacter baumannii was overexpressed in Escherichia coli strain BL21 (DE3), purified and crystallized using the vapour-diffusion method. A native crystal diffracted to 1.4 Å resolution and belonged to space group P6(1) or P6(5), with unit-cell parameters a=b=72.58, c=44.65 Å, a calculated Matthews coefficient of 2.64 Å3 Da(-1) and one molecule per asymmetric unit.

Risk factors for carbapenem non-susceptibility and mortality in Acinetobacter baumannii bacteremia in children

OBJECTIVE

To examine the risk factors of carbapenem non-susceptibility and mortality among children with Acinetobacter baumannii bacteremia.

METHODS

A retrospective chart review was conducted of 180 cases with A. baumannii bacteremia.

RESULTS

The 30-day mortality risk of A. baumannii bacteremia was 26.1%. Carbapenem-non-susceptible A. baumannii was identified in 51.7% of cases. Logistic regression analysis indicated that prematurity, use of mechanical ventilation, and prior exposure to carbapenem antibiotics were independently associated with carbapenem-non-susceptible A. baumannii bacteremia, with adjusted odds ratios (aORs) and 95% confidence intervals (CIs) of 3.36 (1.17-9.65), 5.59 (2.24-13.97), and 2.97 (1.01-8.77), respectively. Further, carbapenem non-susceptibility, cancer-related neutropenia, organ dysfunction, admission to the intensive care unit, catheter-related bacteremia, and treatment with sulbactam-containing regimens were associated with mortality with aORs and 95% CIs of 4.76 (1.58-14.32), 4.54 (1.09-18.79), 25.95 (5.13-131.33), 3.53 (1.29-9.71), 0.25 (0.084-0.72), and 0.14 (0.046-0.45), respectively.

CONCLUSIONS

The majority of A. baumannii bacteremia was caused by carbapenem-non-susceptible strains with a high mortality rate. Carbapenem non-susceptibility, cancer-related neutropenia, the presence of organ dysfunction, and admission to an intensive care unit were associated with an increased mortality risk, whereas catheter-related bacteremia and treatment with a sulbactam-containing regimen were associated with decreased mortality among children with A. baumannii bacteremia.

Assessing the burden of Acinetobacter baumannii in Maryland: a statewide cross-sectional period prevalence survey

OBJECTIVE

To determine the prevalence of Acinetobacter baumannii, an important healthcare-associated pathogen, among mechanically ventilated patients in Maryland.

DESIGN

The Maryland MDRO Prevention Collaborative performed a statewide cross-sectional active surveillance survey of mechanically ventilated patients residing in acute care and long-term care (LTC) facilities. Surveillance cultures (sputum and perianal) were obtained from all mechanically ventilated inpatients at participating facilities during a 2-week period.

SETTING

All healthcare facilities in Maryland that provide care for mechanically ventilated patients were invited to participate.

PATIENTS

Mechanically ventilated patients, known to be at high risk for colonization and infection with A. baumannii, were included.

RESULTS

Seventy percent (40/57) of all eligible healthcare facilities participated in the survey, representing both acute care ([Formula: see text]) and LTC ([Formula: see text]) facilities in all geographic regions of Maryland. Surveillance cultures were obtained from 92% (358/390) of eligible patients. A. baumannii was identified in 34% of all mechanically ventilated patients in Maryland; multidrug-resistant A. baumannii was found in 27% of all patients. A. baumannii was detected in at least 1 patient in 49% of participating facilities; 100% of LTC facilities had at least 1 patient with A. baumannii, compared with 31% of acute care facilities. A. baumannii was identified from all facilities in which 10 or more patients were sampled.

CONCLUSIONS

A. baumannii is common among mechanically ventilated patients in both acute care and LTC facilities throughout Maryland, with a high proportion of isolates demonstrating multidrug resistance.

The importance of colonization pressure in multiresistant Acinetobacter baumannii acquisition in a Greek intensive care unit

INTRODUCTION

We investigated the role of colonization pressure on multiresistant Acinetobacter baumannii acquisition and defined patient-related predictors for carriage at admission and acquisition during hospitalization in intensive care unit (ICU) patients.

METHODS

This was a 12-month, prospective, cohort study of all patients admitted to a single ICU of a tertiary hospital. Screening samples were collected at ICU admission to identify imported carriers, and weekly during hospitalization to identify acquisition. Colonization pressure (carriers' patient-days × 100/all patients' patient-days) and the absolute number of carriers were calculated weekly, and the statistical correlation between these parameters and acquisition was explored. Multivariable analysis was performed to identify predictors for A. baumannii carriage at admission and acquisition during hospitalization. A. baumannii isolates were genotyped by repetitive-extragenic-palindromic polymerase chain reaction (PCR; rep-PCR).

RESULTS

At ICU admission, 284 patients were screened for carriage. A. baumannii was imported in 16 patients (5.6%), and acquisition occurred in 32 patients (15.7%). Acquisition was significantly correlated to weekly colonization pressure (correlation coefficient, 0.379; P = 0.004) and to the number of carriers per week (correlation coefficient, 0.499; P <0.001). More than one carrier per week significantly increased acquisition risk (two to three carriers, odds ratio (OR), 12.66; P = 0.028; more than four carriers, OR, 25.33; P = 0.004). Predictors of carriage at admission were infection at admission (OR, 11.03; confidence interval (CI), 3.56 to 34.18; P < 0.01) and hospitalization days before ICU (OR, 1.09; CI, 1.01 to 1.16; P = 0.02). Predictors of acquisition were a medical reason for ICU admission (OR, 5.11; CI, 1.31 to 19.93; P = 0.02), duration of antibiotic administration in the unit (OR, 1.24; CI, 1.12 to 1.38; P < 0.001), and duration of mechanical ventilation (OR, 1.08; CI, 1.04 to 1.13; P = 0.001). All strains were multiresistant. Rep-PCR analysis showed one dominant cluster.

CONCLUSIONS

Acquisition of multiresistant A. baumannii in ICU patients is strongly correlated to colonization pressure. High levels of colonization pressure and more than two carriers per week independently increase acquisition risk. Patient-related factors, such as infection at admission and long hospitalization before the ICU, can identify imported A. baumannii carriers. Medical patients with extended administration of antibiotics and long duration of mechanical ventilation in the ICU were the most vulnerable to acquisition.

Clinical characteristics of tertiary hospital patients from whom Acinetobacter calcoaceticus-Acinetobacter baumannii complex strains were isolated

OBJECTIVE

Acinetobacter baumannii is a worldwide nosocomial pathogen that has become increasingly common over the past few decades, and strains of multidrug-resistant A. baumannii have been increasing. The aim of this study was to assess the clinical characteristics of A. calcoaceticus-A. baumannii complex (Acb complex) strains and to determine the risk factors of this infection.

METHODS

The medical records of 121 patients at Nagasaki University Hospital from whom Acb complex had been isolated between January 2007 and December 2009 were retrospectively reviewed. Patient backgrounds, sensitivity to antibiotics, risk factors for infection, and prognosis were evaluated.

RESULTS

Lower respiratory isolates accounted for 73% (147 strains) of all 201 isolates. Most of the isolates were sensitive to carbapenems. Of the 121 patients (74 males and 47 females; mean age: 62.1 years), 48 (39.7%) had malignancy and 75 (62.0%) were treated with antibiotics prior to isolation. Thirty-seven of the patients in this study (30.6%) were infected by Acb complex and the most frequent clinical manifestation was pneumonia (18 cases; 48.6%). Approximately 60% of infected patients were treated with β-lactam agent in combination with β-lactamase inhibitors or carbapenems. The mortality rate of infected patients was significantly higher than that of colonized patients (infected: 24.3%, colonized: 6.0%, p<0.05). Risk factors for Acb complex infection include being over 60 years of age, chronic liver disease, and the use of first-generation cephalosporins prior to isolation.

CONCLUSION

Acb complex was relatively sensitive to antibiotics. The appropriate usage of antibiotics should be continued for the prevention of drug resistance in Acb complex.

N-acyl homoserine lactone mediated interspecies interactions between A. baumannii and P. aeruginosa

Acinetobacter baumannii and Pseudomonas aeruginosa are pathogens capable of colonizing the same infection sites and employing N-acyl homoserine lactone (AHL) based quorum-sensing systems to co-ordinate biofilm formation. Hence, the effect of P. aeruginosa AHLs on biofilm formation by A. baumannii and vice versa were investigated using the biofilm impaired quorum sensing mutants, A. baumannii M2 (abaI::Km) and P. aeruginosa PAO-JP2. Complementing the mutants with heterologous, extracted and pure AHLs increased biofilm mass significantly. The surface area coverage and biovolume also increased significantly as observed by confocal scanning laser microscopy which corroborated scanning electron microscope analysis. Autoinducer synthase gene promoters of A. baumannii, P( abaI)-lacZ, and P. aeruginosa, P( lasI)-lacZ, were induced (p < 0.05) by heterologous AHLs. Growth of A. baumannii was not inhibited by pyocyanin of P. aeruginosa which may allow their co-existence and interaction in the clinical setting, thereby affecting the severity of combined infections and therapeutic measures to control them.

Use of adherence monitors as part of a team approach to control clonal spread of multidrug-resistant Acinetobacter baumannii in a research hospital

BACKGROUND

Multidrug-resistant Acinetobacter baumannii (MDRAB) is difficult to treat and eradicate. Several reports describe isolation and environmental cleaning strategies that controlled hospital MDRAB outbreaks. Such interventions were insufficient to interrupt MDRAB transmission in 2 intensive care unit-based outbreaks in our hospital. We describe strategies that were associated with termination of MDRAB outbreaks at the National Institutes of Health Clinical Center.

METHODS

In response to MDRAB outbreaks in 2007 and 2009, we implemented multiple interventions, including stakeholder meetings, enhanced isolation precautions, active microbial surveillance, cohorting, and extensive environmental cleaning. We conducted a case-control study to analyze risk factors for acquiring MDRAB. In each outbreak, infection control adherence monitors were placed in MDRAB cohort areas to observe and correct staff infection control behavior.

RESULTS

Between May 2007 and December 2009, 63 patients acquired nosocomial MDRAB; 57 (90%) acquired 1 or more of 4 outbreak strains. Of 347 environmental cultures, only 2 grew outbreak strains of MDRAB from areas other than MDRAB patient rooms. Adherence monitors recorded 1,330 isolation room entries in 2007, of which 8% required interventions. In 2009, around-the-clock monitors recorded 4,892 staff observations, including 127 (2.6%) instances of nonadherence with precautions, requiring 68 interventions (1.4%). Physicians were responsible for more violations than other staff (58% of hand hygiene violations and 37% of violations relating to gown and glove use). Each outbreak terminated in temporal association with initiation of adherence monitoring.

CONCLUSIONS

Although labor intensive, adherence monitoring may be useful as part of a multifaceted strategy to limit nosocomial transmission of MDRAB.

Acinetobacter: a potential reservoir and dispenser for β-lactamases

Innate resistance and remarkable ability to acquire additional resistance determinants underline the clinical importance of Acinetobacter. Over 210 β-lactamases belonging to 16 families have been identified in the genus, mostly in clinical isolates of A. baumannii. In this review, we update the current taxonomy of the genus Acinetobacter and summarize the β-lactamases detected in Acinetobacter spp. with an emphasis on Acinetobacter-derived cephalosporinases (ADCs) and carbapenem-hydrolysing class D β-lactamases (CHDLs). We also discuss the roles of integrons and insertion sequence (IS) elements in the expression and dissemination of such resistance determinants.

In vitro antimicrobial studies of silver carbene complexes: activity of free and nanoparticle carbene formulations against clinical isolates of pathogenic bacteria

OBJECTIVES

Silver carbenes may represent novel, broad-spectrum antimicrobial agents that have low toxicity while providing varying chemistry for targeted applications. Here, the bactericidal activity of four silver carbene complexes (SCCs) with different formulations, including nanoparticles (NPs) and micelles, was tested against a panel of clinical strains of bacteria and fungi that are the causative agents of many skin and soft tissue, respiratory, wound, blood, and nosocomial infections.

METHODS

MIC, MBC and multidose experiments were conducted against a broad range of bacteria and fungi. Time-release and cytotoxicity studies of the compounds were also carried out. Free SCCs and SCC NPs were tested against a panel of medically important pathogens, including methicillin-resistant Staphylococcus aureus (MRSA), multidrug-resistant Acinetobacter baumannii (MRAB), Pseudomonas aeruginosa, Burkholderia cepacia and Klebsiella pneumoniae.

RESULTS

All four SCCs demonstrated strong efficacy in concentration ranges of 0.5-90 mg/L. Clinical bacterial isolates with high inherent resistance to purified compounds were more effectively treated either with an NP formulation of these compounds or by repeated dosing. Overall, the compounds were active against highly resistant bacterial strains, such as MRSA and MRAB, and were active against the biodefence pathogens Bacillus anthracis and Yersinia pestis. All of the medically important bacterial strains tested play a role in many different infectious diseases.

CONCLUSIONS

The four SCCs described here, including their development as NP therapies, show great promise for treating a wide variety of bacterial and fungal pathogens that are not easily killed by routine antimicrobial agents.

The activity of thyme essential oil against Acinetobacter spp

The aim of this work was to investigate the antimicrobial properties of thyme essential oil against clinical multiresistant strains of Acinetobacter spp. The antibacterial activity of oil was tested against standard and clinical bacterial strains of Acinetobacter genus. The agar diffusion method was used to check the inhibition of microbial growth at various concentrations of the oil from Thymus vulgaris. Susceptibility testing to antibiotics and chemotherapeutics was prepared using the disc-diffusion method. Identification of bacterial strains was carried out with the Vitek system and confirmed by PCR for Acinetobacter baumanii gyrB gene. The results of experiments showed that the oil from T. vulgaris exhibited an extremely strong activity against all of the clinical strains of Acinetobacter. Thyme oil demonstrated a very good efficacy against multiresistant strains of tested bacteria. Essential oils seems to be an excellent alternative for synthetic preparations and that is reason for an extensive assessment of their antimicrobial activity.

The inhibitory effect of Zingiber corallinum Hance essential oil on drug-resistant bacteria and evaluation of its acute toxicity

BACKGROUND

The excessive and irregular use of antibiotics could result in the generation and diffusion of drug-resistant bacteria. The aim of this study was to investigate the inhibitory effect of Zingiber corallinum Hance essential oil (ZCHO) on drug-resistant bacteria, especially on drug-resistant Acinetobacter baumannii.

MATERIAL/METHODS

Susceptibility testing was used to evaluate the effect of ZCHO on growth inhibition of drug-resistant bacteria by paper disk method. Mice orally administered with ZCHO were used to observe acute toxicity and to determine median lethal dose (LD₅₀) of ZCHO. Broth dilution method was used to determine minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of ZCHO on drug-resistant Acinetobacter baumannii.

RESULTS

ZCHO exhibited an obvious inhibitory effect not only on gram-negative drug-resistant bacteria including Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae and Acinetobacter baumannii, but also on gram-positive drug-resistant bacteria including Staphylococcus aureus, Staphylococcus epidermidis and Staphylococcus haemolyticus. The ZCHO containing 79% terpinen-4-ol revealed better bacteriostatic effect than ZCHO with 34% terpinen-4-ol. The LD₅₀ of ZCHO was 1790.427 mg/kg. The MIC and MBC of ZCHO on drug-resistant Acinetobacter baumannii were 1457.81 mg/L.

CONCLUSIONS

ZCHO has obvious bacteriostasis and bactericidal effects, especially against drug-resistant Acinetobacter baumannii. Therefore, ZCHO is a promising natural bioactive component with antibacterial effect and satisfactory safety due to its low toxicity.