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

Managing Antimicrobial Resistance in the Emergency Department

(Basic awareness and understanding of antimicrobial resistance and prevailing mechanisms can aid emergency physicians in providing appropriate care to patients with infections due to a multidrug-resistant organism (MDRO). Empiric treatment of MDRO infections should be approached with caution and guided by the most likely pathogens based on differential diagnosis, severity of the illness, suspected source of infection, patient-specific factors, and local antibiotic susceptibility patterns. Newer broad-spectrum antibiotics should be reserved for critically ill patients where there is a high likelihood of infection with an MDRO.).

Healthcare-Associated Bloodstream Infections Due to Multidrug-Resistant Acinetobacter baumannii in COVID-19 Intensive Care Unit: A Single-Center Retrospective Study

Healthcare-associated infections are an emerging cause of morbidity and mortality in COVID-19 intensive care units (ICUs) worldwide, especially those caused by multidrug-resistant (MDR) pathogens. The objectives of this study were to assess the incidence of bloodstream infections (BSIs) among critically ill COVID-19 patients and to analyze the characteristics of healthcare-associated BSIs due to MDR Acinetobacter baumannii in an COVID-19 ICU. A single-center retrospective study was conducted at a tertiary hospital during a 5-month period. The detection of carbapenemase genes was performed by PCR and genetic relatedness by pulsed-field gel electrophoresis (PFGE) and multilocus-sequence typing. A total of 193 episodes were registered in 176 COVID-19 ICU patients, with an incidence of 25/1000 patient-days at risk. A. baumannii was the most common etiological agent (40.3%), with a resistance to carbapenems of 100%. The blaOXA-23 gene was detected in ST2 isolates while the blaOXA-24 was ST636-specific. PFGE revealed a homogeneous genetic background of the isolates. The clonal spread of OXA-23-positive A. baumannii is responsible for the high prevalence of MDR A. baumannii BSIs in our COVID-19 ICU. Further surveillance of resistance trends and mechanisms is needed along with changes in behavior to improve the implementation of infection control and the rational use of antibiotics.

Correlation Between Cefoperazone/Sulbactam MIC Values and Clinical Outcomes of Escherichia coli Bacteremia

INTRODUCTION

The clinical efficiency of cefoperazone/sulbactam (CPZ/SUL) against Escherichia coli bacteremia was unknown. This study aimed to explore the relationship between CPZ/SUL MIC values and clinical outcomes in Escherichia coli bacteremia.

METHODS

A multicenter, retrospective, observational cohort study was conducted in Taiwan between January 2015 and December 2020. Patients treated with CPZ/SUL for E. coli bacteremia were enrolled in the analysis. The CPZ/SUL MICs were determined by using the agar dilution method. The primary outcome was 30-day mortality.

RESULTS

Among 247 isolates, 160 (64.8%) isolates were susceptible, 8 (3.2%) were intermediate, and 79 (32.0%) were resistant to cefoperazone. The activity of cefoperazone against cefoperazone-non-susceptible E. coli (n = 87) was restored upon combination with sulbactam, with susceptibility ranging from 0% to 97.7%. The 30-day mortality was 4.5% (11/247) and overall clinical success rate was 91.9% (227/247). Multivariate Cox proportional-hazards model revealed that heart failure [adjusted relative risk (ARR), 5.49; 95% confidence interval (CI) 1.31-23.02; p = 0.020], malignancy (ARR 7.50; 95% CI 2.02-27.80; p = 0.003), SOFA score (ARR 1.29; 95% CI 1.09-1.52; p = 0.003), and CPZ/SUL MIC ≥ 64 mg/L (ARR 11.31; 95% CI 1.34-95.52; p = 0.026) were independently associated with 30-day mortality. No statistically significant differences in 30-day mortality were found between groups with or without cefoperazone susceptibility (3.4% vs. 5.0%, p = 0.751, respectively).

CONCLUSIONS

Patients with E. coli bacteremia who were treated with CPZ/SUL had a favorable outcome when the MICs of the isolates were ≤ 16 mg/L and a high risk of mortality with MICs ≥ 64 mg/L.

Growth kinetics of multiple Acinetobacter baumannii resistotype after meropenem-based antibiotic combination exposure

Background: Carbapenems are the treatment of choice for multidrug-resistant (MDR) and extensively drug-resistant (XDR)  Acinetobacter baumannii infections, but the emergence of carbapenem-resistant  A. baumannii (CRAB) has rendered it ineffective in the vast majority of cases. Combination therapy has grown in popularity over the last decade; this study aims to analyze  A.baumannii growth kinetics after exposure to meropenem and ampicillin-sulbactam compared with meropenem and amikacin antibiotic combinations in clinically relevant concentrations.  Methods: This experimental laboratory study was conducted on the  A.baumannii ATCC 19606 isolate and three clinical isolates that were intermediate or resistant to tested antibiotics. Meropenem and ampicillin-sulbactam, as well as meropenem and amikacin, were tested at four different concentrations against isolates. Turbidity measurements were taken at predetermined time points of 0, 1, 2, 4, 6, 8, and 24 hours following exposure; bacterial concentration was enumerated using the agar plate method, with the results plotted in a time-kill curve.   Results: A bactericidal effect was achieved in isolates that were intermediate to ampicillin sulbactam and resistant to meropenem after the administration of meropenem and ampicillin-sulbactam combination with a concentration of 4 µg/ml and 16/8 µg/ml, respectively. The combination of meropenem and ampicillin-sulbactam demonstrated bacteriostatic activity against isolates that were resistant to both antibiotics. Isolates treated with resistant antibiotics showed an increased growth rate compared to the growth control.  Conclusion: The combination of meropenem and ampicillin-sulbactam could be a promising combination therapy in treating CRAB infections. The mechanism and degree of antibiotic resistance in the isolates affect the efficacy of antibiotic combinations; further research is needed to corroborate the findings of this study.

Growth kinetics of multiple Acinetobacter baumannii resistotype after meropenem-based antibiotic combination exposure

Background: Carbapenems are the treatment of choice for multidrug-resistant (MDR) and extensively drug-resistant (XDR)  Acinetobacter baumannii infections, but the emergence of carbapenem-resistant  A. baumannii (CRAB) has rendered it ineffective in the vast majority of cases. Combination therapy has grown in popularity over the last decade; this study aims to analyze  A.baumannii growth kinetics after exposure to meropenem and ampicillin-sulbactam compared with meropenem and amikacin antibiotic combinations in clinically relevant concentrations.  Methods: This experimental laboratory study was conducted on the  A. baumannii ATCC 19606 isolate and three clinical isolates that were intermediate or resistant to tested antibiotics. Meropenem and ampicillin-sulbactam, as well as meropenem and amikacin, were tested at four different concentrations against isolates. Turbidity measurements were taken at predetermined time points of 0, 1, 2, 4, 6, 8, and 24 hours following exposure; bacterial concentration was enumerated using the agar plate method, with the results plotted in a time-kill curve.   Results: A bactericidal effect was achieved in isolates that were intermediate to ampicillin-sulbactam and resistant to meropenem after the administration of meropenem and ampicillin-sulbactam combination with a concentration of 4 µg/ml and 16/8 µg/ml, respectively. The combination of meropenem and ampicillin-sulbactam demonstrated bacteriostatic activity against isolates that were resistant to both antibiotics. Isolates treated with resistant antibiotics showed an increased growth rate compared to the growth control.  Conclusion: The combination of meropenem and ampicillin-sulbactam could be a promising combination therapy in treating CRAB infections. The mechanism and degree of antibiotic resistance in the isolates affect the efficacy of antibiotic combinations; further research is needed to corroborate the findings of this study.

Successful Treatment of Postneurosurgical Ventriculitis Caused by Extensively Drug-resistant Acinetobacter baumannii in a Child: Case Report

Introduction: The incidence of postneurosurgical Acinetobacter baumannii ventriculitis/meningitis, primarily due to drug-resistant strains, has increased considerably in recent years. However, limited therapeutic options are available because most antibiotics poorly penetrate the blood-brain barrier, especially in pediatric patients. Case Presentation: A five-year-old boy developed ventriculitis due to extensively drug-resistant A. baumannii (XDRAB) after bilateral frontal external ventricular drainage for spontaneous intraventricular hemorrhage. The boy was safely and successfully treated with intraventricular (IVT)/intrathecal (ITH) polymyxin B together with intravenous tigecycline plus cefoperazone/sulbactam. Conclusions: In the present case, postneurosurgical XDRAB ventriculitis was closely associated with intraventricular hemorrhage and the placement of external ventricular drainage. IVT/ITH polymyxin B combined with intravenous tigecycline and cefoperazone sulbactam could be a therapeutic option against XDRAB ventriculitis in children.

Effects of dosing frequency on the clinical efficacy of ampicillin/sulbactam in Japanese elderly patients with pneumonia: A single-center retrospective observational study

This study sought to investigate whether dosing frequency (the number of doses per day) affects the antimicrobial efficacy and safety of ampicillin/sulbactam (ABPC/SBT) in Japanese elderly pneumonia patients treated with ABPC/SBT at 6 g/day. This was a retrospective observational study that included hospitalized elderly patients (aged ≥75 years, 10 ml/min ≤CLcr <50 ml/min) who received 3 g every 12 h (BID; n = 61) or 1.5 g every 6 h (QID; n = 45) for the treatment of pneumonia. The primary endpoint was clinical response, assessed by measuring body temperature, white blood cell count, and C-reactive protein levels. Pharmacokinetic and pharmacodynamic simulations were conducted in silico to rationalize the clinical findings. The clinical response rates (extremely effective and effective) in the BID and QID groups were 36.1% and 55.6%, respectively (p = .0459). QID tended to be more effective in patients with gram-negative rods detected (p = .0563). According to the simulated minimum plasma ABPC concentrations at steady state for BID and QID were 2.5 and 7.3 μg/ml, respectively (p < .0001). Based on the simulated time above minimum inhibitory concentration (MIC), pharmacological (not clinical) efficacy was predicted to be higher with QID. Both groups had similar safety profiles. The main adverse event in both groups was liver damage. The present retrospective survey demonstrated that ABPC/SBT treatment for elderly patients with pneumonia and renal dysfunction was more effective with QID than with BID. Therefore, the QID regimen is worthy of consideration to improve the clinical outcomes of ABPC/SBT therapy in the present patient population.

Intraventricular administration of antibiotics by ommaya reservoir for patients with multidrug-resistant Acinetobacter baumannii central nervous system infection

AIM

To investigate whether the Ommaya reservoir can be used to treat multiple drug-resistant Acinetobacter baumannii (MDR-AB) infections in the central nervous system (CNS).

METHODS

Retrospectively analyzed the clinical records and data of 15 MDR-AB CNS infection patients who were treated in our neuro-ICU. Four patients with MDR-AB CNS infection were involved in this study.

RESULTS

We report the successful treatment of MDR-AB CNS infection by Ommaya reservoirs and intraventricular antibiotic (IVA) administration. Ommaya reservoirs allow serial CSF sampling and IVA injection. Furthermore, debridement can be performed during the operation to insert the Ommaya.

CONCLUSION

Ommaya reservoirs can be used as an effective treatment approach of MDR-AB or other multidrug-resistant Gram-negative bacteria CNS infections.

Avibactam Sensitizes Carbapenem-Resistant NDM-1-Producing Klebsiella pneumoniae to Innate Immune Clearance

Infections caused by New Delhi metallo-β-lactamase (NDM)–producing strains of multidrug-resistant Klebsiella pneumoniae are a global public health threat lacking reliable therapies. NDM is impervious to all existing β-lactamase inhibitor (BLI) drugs, including the non–β-lactam BLI avibactam (AVI). Though lacking direct activity against NDMs, AVI can interact with penicillin-binding protein 2 in a manner that may influence cell wall dynamics. We found that exposure of NDM-1–producing K. pneumoniae to AVI led to striking bactericidal interactions with human cathelicidin antimicrobial peptide LL-37, a frontline component of host innate immunity. Moreover, AVI markedly sensitized NDM-1–producing K. pneumoniae to killing by freshly isolated human neutrophils, platelets, and serum when complement was active. Finally, AVI monotherapy reduced lung counts of NDM-1–producing K. pneumoniae in a murine pulmonary challenge model. AVI sensitizes NDM-1–producing K. pneumoniae to innate immune clearance in ways that are not appreciated by standard antibiotic testing and that merit further study.

Multidrug-resistant Acinetobacter baumannii strains with NDM-1: Molecular characterization and in vitro efficacy of meropenem-based combinations

Acinetobacter baumannii is an important cause of hospital-acquired, multidrug-resistant (MDR) infections occurring worldwide. Anti-microbial combination regimens may be the only feasible treatment option for affected patients. In the present study, the efficacy of the combined therapy of meropenem with colistin, ampicillin-sulbactam, tazobactam and vancomycin against clinical strains of MDR A. baumannii was determined. Anti-microbial susceptibility testing was performed and resistance genes were characterized by a multiplex polymerase chain reaction (PCR)-reverse line blot assay. The genetic background of New Delhi metallo-β-lactamase 1 (NDM-1) was analysed by primer walking. The presence of NDM-1 was detected using the modified Hodge test and the EDTA-combined disk test. To screen for synergistic drug effects, the fractional inhibitory concentration index was calculated using a checkerboard assay. The results of the PCR as well as the sequence analyses suggested that NDM-1 was located downstream of the ISAba125 element. In addition, a synergistic effect was determined for meropenem + vancomycin, meropenem + tazobactam and meropenem + ampicillin + sulbactam in two strains each, and in four strains for meropenem + colistin. A total of five A. baumannii strains with resistance to numerous antibiotics and carrying numerous resistance genes were identified. In the strains of A. baumannii, the NDM-1 gene was integrated in a transposon structure with a copy of the ISAba125 insertion sequence. However, the genetic background was not identical among the different species and strains. The genetic variability of NDM-1 may facilitate the rapid dissemination of this gene. In conclusion, meropenem may enhance the efficacy of antibiotics in A. baumannii strains with NDM-1-associated MDR.

Randomized Noninferiority Trial of Cefoperazone-Sulbactam versus Cefepime in the Treatment of Hospital-Acquired and Healthcare-Associated Pneumonia

Cefoperazone, a third-generation cephamycin with broad-spectrum antibacterial activity and the ability to permeate bacterial cell membranes, is active against commonly encountered multidrug-resistant pathogens for hospital-acquired pneumonia (HAP) and health care-associated pneumonia (HCAP). To clarify the clinical effects of cefoperazone-sulbactam in the treatment of HAP and HCAP, we conducted an open-label, randomized, noninferiority trial that recruited patients aged ≥18 years suffering HAP/HCAP. Participants were randomly assigned to the cefoperazone-sulbactam (2 g of each per 12 h) or cefepime (2 g per 12 h) arm. Clinical and microbiological responses were evaluated at early posttherapy and test-of-cure visits. Recruited patients were allocated to subpopulations for intent-to-treat (n = 154), per-protocol (n = 147), and safety (n = 166) analyses. Intent-to-treat analysis demonstrated that (i) at the early posttherapy visit, 87.3% of patients receiving cefoperazone-sulbactam and 84.3% of patients receiving cefepime achieved clinical improvement or cure (risk difference of 3.0%; 95% confidence interval [CI], -9.0% to 15.0%), and (ii) at the test-of-cure visit, 73.1% of patients receiving cefoperazone-sulbactam and 56.8% of patients receiving cefepime were assessed as cured (risk difference of 16.3%; 95% CI, 0.0% to 33.0%). These results indicated the noninferiority of cefoperazone-sulbactam to cefepime, which was confirmed by per-protocol analysis. The chest radiographic consolidation/infiltration resolution rate, microbiological eradiation rate, and percentage of adverse events were comparable in both groups. Serious adverse events were rare, and none was judged to be related to the study drugs. Cefoperazone-sulbactam at 2 g every 12 h was noninferior to cefepime at 2 g every 2 h for patients with HCAP.

Sulbactam-enhanced cytotoxicity of doxorubicin in breast cancer cells

BACKGROUND

Multidrug resistance (MDR) is a major obstacle in breast cancer treatment. The predominant mechanism underlying MDR is an increase in the activity of adenosine triphosphate (ATP)-dependent drug efflux transporters. Sulbactam, a β-lactamase inhibitor, is generally combined with β-lactam antibiotics for treating bacterial infections. However, sulbactam alone can be used to treat Acinetobacter baumannii infections because it inhibits the expression of ATP-binding cassette (ABC) transporter proteins. This is the first study to report the effects of sulbactam on mammalian cells.

METHODS

We used the breast cancer cell lines as a model system to determine whether sulbactam affects cancer cells. The cell viabilities in the present of doxorubicin with or without sulbactam were measured by MTT assay. Protein identities and the changes in protein expression levels in the cells after sulbactam and doxorubicin treatment were determined using LC-MS/MS. Real-time reverse transcription polymerase chain reaction (real-time RT-PCR) was used to analyze the change in mRNA expression levels of ABC transporters after treatment of doxorubicin with or without sulbactam. The efflux of doxorubicin was measures by the doxorubicin efflux assay.

RESULTS

MTT assay revealed that sulbactam enhanced the cytotoxicity of doxorubicin in breast cancer cells. The results of proteomics showed that ABC transporter proteins and proteins associated with the process of transcription and initiation of translation were reduced. The mRNA expression levels of ABC transporters were also decreased when treated with doxorubicin and sulbactam. The doxorubicin efflux assay showed that sulbactam treatment inhibited doxorubicin efflux.

CONCLUSIONS

The combination of sulbactam and doxorubicin enhances the cytotoxicity of doxorubicin in the breast cancer cells by inhibiting the expression of ABC transporter proteins and proteins associated with the process of transcription and initiation of translation, and blocking the efflux of doxorubicin. Co-treatment of doxorubicin and sulbactam can be used in breast cancer treatment to decrease the prescribed dose of doxorubicin to avoid the adverse effects of doxorubicin.

Combined Rifampin and Sulbactam Therapy for Multidrug-Resistant Acinetobacter Baumannii Ventilator-Associated Pneumonia in Pediatric Patients

Background:

With essentially no drug available to control the infection caused by the extensively drug-resistant Acinetobacter baumannii (XDR-Ab) in infants and young children, this study explored the clinical outcomes of pediatric patients with drug-resistant XDR-Ab who were treated with rifampicin in combination with sulbactam sodium.

Methods:

The data for clinical outcomes, microbiological responses, and side effects were collected and evaluated for 12 critically ill infants and young children diagnosed with ventilator-associated pneumonia caused by XDR-Ab following surgical treatment for congenital heart disease in a pediatric cardiac intensive care unit. This study was approved by local institutional review board (IRB).

Results:

Two patients died from the complex underlining diseases. The other 10 patients were weaned off the mechanical ventilation successfully within 4–15 days after the start of treatment with rifampicin combined with sulbactam sodium and discharged home. Three cases experienced adverse side effects, including severe rash and elevated aminotransferase level.

Conclusion:

The combination of rifampicin and sulbactam sodium appeared to be an effective and safe therapy for severe ventilator-associated pneumonia caused by XDR-Ab in infants and young children. Side effects such as skin rashes and elevated aminotransferase levels can be reversed once rifampicin is discontinued in time. (Funded by the Department of Cardiovascular Surgery, The Second Xiangya Hospital, Central South University, Chang­sha, China; the Departments of Anesthesiology and Pain Medicine of University of California Davis Health; and the National Institutes of Health.)

Molecular Epidemiology and Mechanism of Sulbactam Resistance in Acinetobacter baumannii Isolates with Diverse Genetic Backgrounds in China

Sulbactam is a plausible option for treating Acinetobacter infections because of its intrinsic antibacterial activity against the members of the Acinetobacter genus, but the mechanisms of sulbactam resistance have not been fully studied in Acinetobacter baumannii In this study, a total of 2,197 clinical A. baumannii isolates were collected from 27 provinces in China. Eighty-eight isolates with various MICs for sulbactam were selected on the basis of their diverse clonality and underwent multilocus sequence typing (MLST), antimicrobial susceptibility testing, and resistance gene screening. The copy number and relative expression of bla_TEM-1D and ampC were measured via quantitative PCR and quantitative reverse transcription-PCR, respectively. The genetic structure of multicopy bla_TEM-1D was determined using the whole-genome sequencing technology. The cefoperazone-sulbactam resistance rate of the 2,197 isolates was 39.7%. The rate of positivity for bla_TEM-1D or ISAba1-ampC in the sulbactam-nonsusceptible group (64.91% and 78.95%, respectively) was significantly higher than that in the sulbactam-susceptible group (0% and 0%, respectively; P < 0.001). The MIC of sulbactam (P < 0.001) varied considerably between the groups expressing ampC with or without upstream ISAba1 Notably, the genetic structure of the multicopy bla_TEM-1D gene in strain ZS3 revealed that bla_TEM-1D was embedded within four tandem copies of the cassette IS26-bla_TEM-1D-Tn3-IS26 Therefore, bla_TEM-1D and ISAba1-ampC represent the prevalent mechanism underlying sulbactam resistance in clinical A. baumannii isolates in China. The structure of the four tandem copies of bla_TEM-1D first identified may increase sulbactam resistance.

Management of infections caused by extended-spectrum β-lactamase-producing Enterobacteriaceae: current evidence and future prospects

INTRODUCTION

The spread of extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae has become a major public health threat worldwide. Area covered: A thorough systematic literature review describing the current evidence and future prospects of therapeutic options for infections caused by ESBL-producing Enterobacteriaceae. Expert commentary: The methods of detecting ESBLs have been evolving. The Clinical and Laboratory Standards Institute and the European Committee on Antimicrobial Susceptibility Testing lowered the MIC breakpoints of cephalosporins against ESBL-producing Enterobacteriaceae in 2010. Phenotypic testing for ESBLs is no longer recommended. Instead, the selection of appropriate antimicrobial agents largely depends on the report of minimum inhibitory concentrations (MICs). To date, therapeutic options for these multidrug-resistant organisms remain limited. The clinical efficacy of piperacillin/tazobactam and cefepime on in vitro-susceptible ESBL-producing Enterobacteriaceae remains a concern. Many studies found an in vitro-in vivo discordance based on current breakpoints. Carbapenems are the most reliable antibiotics for severe infections caused by ESBL-producing Enterobacteriaceae. However, their overuse has led to a serious problem of increasing drug resistance. Recently, ceftolozane/tazobactam and ceftazidime/avibactam have been approved for the treatment of complicated urinary tract infections and complicated intra-abdominal infections. The introduction of these new β-lactam/β-lactamase inhibitor combinations offers new carbapenem-sparing options for the treatment of ESBL infections.

Predictors of polymyxin B treatment failure in Gram-negative healthcare-associated infections among critically ill patients

BACKGROUND

With increasing prevalence and spread of multidrug resistant Gram-negative infections, parenteral polymyxins resurged in clinical practice. The primary aim of the study was to determine the predictors of treatment failure and in-hospital mortality among critically ill patients treated with polymyxin B.

METHODS

Demographic data, underlying diseases, procedures and details on polymyxin B therapy were retrospectively analyzed in a cohort of 84 patients who received intravenous polymyxin B in an intensive care unit from 2010 to 2014.

RESULTS

Polymyxin B was used to treat bacteremia (46.4% of cases) and pneumonia (53.6%). Majority of the pathogens isolated were Acinetobacter spp. (96.4%). The mortality rate was 48.8%, of which 82.9% was attributed to polymyxin B treatment failure. The independent predictors of treatment failure were low doses of polymyxin B (p = 0.002), shorter duration of therapy (p = 0.009), not combining with cefoperazone/sulbactam (p = 0.030), female gender (p = 0.004), administered for treatment of bacteremia (p = 0.023) and renal impairment (p = 0.021). Low polymyxin B doses (p = 0.007), not combining with cefoperazone/sulbactam (p = 0.024), female gender (p = 0.048) and renal impairment (p = 0.022) were also significant predictors for in-hospital mortality.

CONCLUSIONS

To the best of our knowledge, this is the first report on the association of inadequate dose of polymyxin B (<15,000 units/kg/day) with poor outcome in critically ill patients. Besides that, further clinical studies are warranted to evaluate the use of cefoperazone/sulbactam as second antibiotic in the combination therapy.

Active efflux pump adeB is involved in multidrug resistance of Acinetobacter baumannii induced by antibacterial agents

The aim of the present study was to investigate the resistance of Acinetobacter baumannii, which was induced by cefepime (FEP), cefoperazone-sulbactam (SCF), tazobactam (TZP), levofloxacin (LEV), amikacin (AK), imipenem (IPM), and ciprofloxacin (CIP), in vitro. Multi-step drug resistance selection of 16 A. baumannii strains was performed using seven antibacterial agents (FEP, TZP, CIP, AK, IPM, SCF, and LEV). The minimum inhibitory concentration (MIC) was determined using the agar dilution method. Random amplified polymorphic DNA polymerase chain reaction was performed to analyze the genotypes and the carrying rates of aac(3)-I, aac(6')-I, ant(3)-I, aph(3)-Via, OXA-23, OXA-24, AmpC, TEM-1, metallo-β-lactamase gene (IMP), armA, rmtA, rmtB, parC, gyrA and adeB. Expression of adeB was determined using semi-quantitative reverse transcription-polymerase chain reaction (Semi-qRT-PCR). Among the 16 strains, 15 strains with drug resistance (93.8%) were obtained following in vitro induction. Notable increases (8- to 128-fold) were noted in the MIC and different genotypes were showed in RAPD of the strains before and after performing the drug resistant test. PCR data revealed significant differences (P<0.05) between the carrying rates of resistant genes before and after drug induction, with the exception of rmtA, OXA-24, TEM-1, and IMP. Significant increases were demonstrated in the comparative adeB grayscale in strains that underwent drug induction when compared with the sensitive strains (55.69±43.11% vs. 10.08±26.35%; P=0.001). Findings of the present study suggest that the active efflux pump, adeB, has an important role in multidrug resistance of the A. baumannii induced by antibacterial agents in vitro.

Epidemiology and Clinical Characteristics of Acinetobacter Peritoneal Dialysis-Related Peritonitis in Hong Kong-With a Perspective on Multi-Drug and Carbapenem Resistance

♦ BACKGROUND: Acinetobacter spp. is an important cause of peritoneal dialysis (PD)-related peritonitis, but studies on Acinetobacter peritonitis have been scarce. In view of the rising concern of carbapenem-resistant Acinetobacter (CRA) and multidrug-resistant Acinetobacter (MDRA) infections, we conducted this study on the incidence of Acinetobacter peritonitis and the impact of CRA and MDRA on its outcome. ♦ METHODS: We retrospectively evaluated the clinical characteristics, prevalence, antibiotic sensitivity patterns, outcomes, and factors associated with treatment failure over the past 16 years in our patients with Acinetobacter PD-related peritonitis. ♦ RESULTS: Out of 2,389 episodes of peritonitis, there were 66 episodes (3%) of Acinetobacter peritonitis occurring in 59 patients. Twelve episodes were caused by MDRA (18%), of which 5 were CRA (8%). There was a progressive increase in the incidence of MDRA and CRA infections over the study period. Most isolates were sensitive to sulbactam combinations (ampicillin-sulbactam [95.4%] and cefoperazone-sulbactam [93.9%]), aminoglycosides (amikacin [92.4%], tobramycin [90.9%], and gentamicin [89.4%]), and carbapenems (imipenem [92.2%]). There was 1 case of relapse. Fifteen episodes resulted in catheter removal (23%), and 7 patients died (11%). Hypoalbuminemia (odds ratio [OR] = 0.85, p = 0.006) and carbapenem resistance (OR = 18.2, p = 0.049) were significantly associated with higher rates of treatment failure. ♦ CONCLUSION: Both carbapenem resistance and hypoalbuminemia were significantly associated with treatment failure. Up to 80% of peritonitis episodes by CRA resulted in catheter loss or mortality. Sulbactam combinations and/or aminoglycosides remained effective for the majority of Acinetobacter isolates. There seemed to be an increasing relative incidence of MDRA and CRA infections over the past 16 years.

Concurrent Outbreak of Multidrug-Resistant and Susceptible Subclones of Acinetobacter baumannii Affecting Different Wards of a Single Hospital

Background and Objective:

Acinetobacter baumannii has emerged as an opportunistic pathogen among acutely ill patients, especially those with thermal injury. A prospective 8-month study was conducted to describe the clinical and molecular epidemiology of multidrug-resistant A. baumannii affecting a single hospital.

Methods:

Univariate analysis comparing Smal macrorestriction patterns of A. baumannii generated by pulsed-field gel electrophoresis (PFGE) versus clinical and demographic risk factors.

Results:

A total of 200 isolates from 76 patients were collected, of which 185 isolates from 76 patients were analyzed by PFGE. A total of 17 distinct PFGE clonal types were identified. One clonal type (strain A) represented 129 isolates from 49 patients. A group of related clonal types (strain A variants) were identified as 40 isolates from 20 patients. The only risk factor other than geographic location associated with the presence of strain A was prior treatment with antibiotics active against gram-negative bacteria (P = .0015). The two clonal types differed in antibiotic resistance profiles: 25% of strain A isolates, the dominant strain in the burn unit, were susceptible to at least one antibiotic tested. In contrast, approximately 80% of the other strain types were susceptible to at least one antibiotic and were cultured from patients admitted elsewhere in the hospital. No combination of antibiotics was observed to yield additive or synergistic activity.

Conclusion:

Clonally related strains of Acinetobacter that differ in susceptibility patterns may coexist within a single hospital, dependent on the selective pressure related to antibiotic exposure.

Optimizing Polymyxin Combinations Against Resistant Gram-Negative Bacteria

Polymyxin combination therapy is increasingly used clinically. However, systematic investigations of such combinations are a relatively recent phenomenon. The emerging pharmacodynamic (PD) and pharmacokinetic (PK) data on CMS/colistin and polymyxin B suggest that caution is required with monotherapy. Given this situation, polymyxin combination therapy has been suggested as a possible way to increase bacterial killing and reduce the development of resistance. Considerable in vitro data have been generated in support of this view, particularly recent studies utilizing dynamic models. However, most existing animal data are of poor quality with major shortcomings in study design, while clinical data are generally limited to retrospective analysis and small, low-power, prospective studies. This article provides an overview of clinical and preclinical investigations of CMS/colistin and polymyxin B combination therapy.

Comparison of commonly used antimicrobial susceptibility testing methods for evaluating susceptibilities of clinical isolates of Enterobacteriaceae and nonfermentative Gram-negative bacilli to cefoperazone-sulbactam

BACKGROUND/PURPOSE

The aim of this study was to investigate the cefoperazone-sulbactam (CFP-SUL) susceptibilities of important Gram-negative bacteria (GNB) by agar dilution (reference method), disk diffusion, and two automated methods.

METHODS

A total of 799 GNB isolates, including Enterobacteriaceae (n = 500) and nonfermentative GNB (NFGNB, n = 299), were recovered from various clinical specimens collected at National Taiwan University Hospital, Taipei, Taiwan from November 2013 to December 2014. The agar dilution method, disk diffusion method, and two automated susceptibility systems (Phoenix and Vitek 2) were used for testing susceptibility of the isolates to CFP-SUL. Categories of susceptibility (susceptible, intermediate, or resistant) to CFP-SUL yielded from each method were interpreted according to CFP-SUL interpretive breakpoints proposed previously. The results of categorical agreement and errors obtained between the agar dilution method and the other three methods were analyzed.

RESULTS

The Vitek 2 system had the highest error rates against Escherichia coli (n = 150) and Enterobacter cloacae (n = 77) isolates, i.e., 6.7% and 11.7% minor errors, 8.5% and 1.7% major errors, and 40% and 20% very major errors, respectively. Additionally, the Vitek 2 system was also found to have a significantly lower sensitivity (44.4%) and lower positive predictive value (18.2%) for detecting CFP-SUL nonsusceptible E. coli isolates than other methods. For carbapenem-nonsusceptible Enterobacteriaceae isolates, the Vitek 2 system failed to detect correct susceptibility to CFP-SUL. The three methods failed to correctly detect CFP-SUL susceptibility categories against all NFGNB isolates except Pseudomonas aeruginosa.

CONCLUSION

The Vitek 2 system is a suboptimal method in correctly detecting CFP-SUL susceptibility categories for E. coli, E. cloacae, and carbapenem-nonsusceptible Enterobacteriaceae isolates.

Drug concentrations in the serum and cerebrospinal fluid of patients treated with cefoperazone/sulbactam after craniotomy

BACKGROUND

To identify changes in cefoperazone/sulbactam penetration into cerebrospinal fluid (CSF) after craniotomy and to investigate preliminarily whether cefoperazone/sulbactam CSF concentration can reach therapeutic level when administered intravenously after neurosurgical operation.

METHODS

Neurosurgical patients with an indwelling ventricular drainage pipe who received prophylactic cefoperazone/sulbactam for the treatment of intracranial infection were received a cefoperazone/sulbactam 2:1, 3.0-g infusion for 3 hours every 6 hours for 24 h. Venous blood and CSF specimens were collected to determine cefoperazone/sulbactam concentrations.

RESULTS

The cefoperazone and sulbactam concentrations in serum were highest at the second hour (237.54 ± 336.72 mg/L and 66.52 ± 80.38 mg/L, respectively) and then decreased. The cefoperazone and sulbactam concentrations in CSF were highest at the 4th hour (39.22 ± 75.55 mg/L and 6.24 ± 8.35 mg/L, respectively) and then decreased. CSF penetration measured by the ratio of peak concentrations (CSF/serum) was 8.6% ± 7.2% for cefoperazone and 13.5% ± 11.9% for sulbactam, CSF penetration measured by the ratio of trough concentrations (CSF/serum) was 13.4% ± 5.3% for cefoperazone and 106.5% ± 87.5% for sulbactam. CSF penetration represented by the ratio of area under the curve (AUC) of CSF and serum was 14.5% for cefoperazone and 22.6% for sulbactam. Neurosurgical impairment of the blood-brain barrier may improve the CSF penetration of these drugs, but it is difficult to reach the MIC90 of resistant bacteria. If single intravenous administration time was extended to 3 hours, the serum concentrations of drugs were able to meet the PK/PD standard (T> MIC%> 50%) for treating common, highly resistant bacteria.

CONCLUSIONS

The CSF penetration of cefoperazone/sulbactam may be enhanced after neurosurgical impairment of the blood-brain barrier. This study is a pilot research of cefoperazone/sulbactam using in neurosurgical individuals, However, it needs to be confirmed by further large-scale studies.

Molecular mechanisms of sulbactam antibacterial activity and resistance determinants in Acinetobacter baumannii

Sulbactam is a class A β-lactamase inhibitor with intrinsic whole-cell activity against certain bacterial species, including Acinetobacter baumannii. The clinical use of sulbactam for A. baumannii infections is of interest due to increasing multidrug resistance in this pathogen. However, the molecular drivers of its antibacterial activity and resistance determinants have yet to be precisely defined. Here we show that the antibacterial activities of sulbactam vary widely across contemporary A. baumannii clinical isolates and are mediated through inhibition of the penicillin-binding proteins (PBPs) PBP1 and PBP3, with very low frequency of resistance; the rare pbp3 mutants with high levels of resistance to sulbactam are attenuated in fitness. These results support further investigation of the potential clinical utility of sulbactam.

In vitro synergistic activity of colistin with tigecycline or β-lactam antibiotic/β-lactamase inhibitor combinations against carbapenem-resistant Acinetobacter baumannii

OBJECTIVE

Nosocomial infection caused by carbapenem-resistant Acinetobacter baumannii is a worldwide problem and treatment options remain controversial. This study investigated the in vitro effect of various antibiotic combinations against carbapenem-resistant A. baumannii strains.

METHODS

Antibiotic susceptibility of A. baumannii strains was analysed. In vitro synergistic efficacy of colistin combined with tigecycline, cefoperazone/sulbactam or piperacillin/tazobactam was tested against carbapenem-resistant A. baumannii strains. Synergy studies were performed using an eplisometer test-strip method.

RESULTS

Of the 50 carbapenem-resistant A. baumannii strains tested, 96% were susceptible to colistin and 64% were susceptible to tigecycline. Colistin-tigecycline, colistin-cefoperazone/sulbactam and colistin-piperacillin/tazobactam combinations were found to have synergistic effects against six (12%), two (4%), and one (2%), respectively, of the strains tested.

CONCLUSIONS

Colistin combined with tigecycline, cefoperazone/sulbactam or piperacillin/tazobactam revealed synergistic effects in some carbapenem-resistant A. baumannii strains. These results, together with the shortage of treatment options and the risk of developing resistance to colistin, suggest that clinicians should use colistin combined with other antibiotics or β-lactamase inhibitors when treating carbapenem-resistant A. baumannii infection.

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.

Population pharmacokinetics of ampicillin and sulbactam in patients with community-acquired pneumonia: evaluation of the impact of renal impairment

AIMS

The aims of this study were to develop a population pharmacokinetic (PK) model of ampicillin and sulbactam, to identify patient characteristics influencing the PK, and to explore the relationship between dose regimen and degree of renal impairment with exposure and time above minimum inhibitory concentration (MIC).

METHODS

This analysis was performed on PK data for ampicillin and sulbactam and MIC data from a clinical trial in Japanese patients with community acquired pneumonia. Simulations were performed to investigate the effects of different dosing intervals on exposure and time above MIC in various degrees of renal impairment.

RESULTS

The plasma concentrations from 47 patients were adequately described by a two compartment model with simultaneous fit of ampicillin and sulbactam PK data, where creatinine clearance on clearance and body weight on volume in the peripheral compartment were identified as covariates for both drugs. Creatinine clearance contributed to reducing inter-individual variability of clearance by 16%. Mean clearance (inter-individual variability) for ampicillin and sulbactam was estimated to be 10.7 l h(-1) (14.8%) and 10.4 l h(-1) (15.2%), respectively. The time above MIC for each pathogen was generally > 50% of the treatment period. Simulations for exposure and time above MIC supported currently recommended dose adjustments.

CONCLUSIONS

This study provided a PK model for ampicillin and sulbactam, the time above MICs for identified pathogens and associated simulation results. These findings provide useful information and augment evidence for the established dosage regimens in patients with various degrees of renal impairment.

Treatment options for multidrug-resistant bacteria

As a consequence of antibiotic overuse and misuse, nosocomial infections caused by multidrug-resistant bacteria represent a physician's nightmare throughout the world. No newer antimicrobials active against Pseudomonas aeruginosa, the main multidrug-resistant nosocomial pathogen, are available or under investigation. The only exceptions are linezolid, some newer glycopeptides (dalbavancin, oritavancin and telavancin) and daptomycin (a lipopeptide), which are active against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) strains, as well as tigecycline, a potent in vitro glycylcycline against MRSA, VRE, Acinetobacter baumannii and entended-spectrum beta-lactamase (ESBL)+ Enterobacteriaceae. Colistin, an antibiotic of the 1950s has been rediscovered by intensive care unit physicians for use against ESBL+ Enterobacteriaceae, as well as against multidrug-resistant P. aeruginosa and A. baumannii isolates. Although success rates with colistin range between 50 and 73%, almost all studies are retrospective. Immunostimulation efforts against S. aureus are still under development. As antibiotic research and development stagnate, rational policies for prescribing existing antibiotics plus strict infection control are the current mainstay efforts for preventing and combating multidrug-resistant bacterial infections.

Combination therapy for carbapenem-resistant Gram-negative bacteria

The emergence of resistant to carbapenems Gram-negative bacteria (CR GNB) has severely challenged antimicrobial therapy. Many CR GNB isolates are only susceptible to polymyxins; however, therapy with polymyxins and other potentially active antibiotics presents some drawbacks, which have discouraged their use in monotherapy. In this context, along with strong pre-clinical evidence of benefit in combining antimicrobials against CR GNB, the clinical use of combination therapy has been raised as an interesting strategy to overcome these potential limitations of a single agent. Polymyxins, tigecycline and even carbapenems are usually the cornerstone agents in combination schemes. Optimization of the probability to attain the pharmacokinetic/pharmacodynamic targets by both cornerstone drug and adjuvant drug is of paramount importance to achieve better clinical and microbiological outcomes. Clinical evidence of the major drugs utilized in combination schemes and how they should be prescribed considering pharmacokinetic/pharmacodynamic characteristics against CR GNB will be reviewed in this article.

Antibacterial susceptibility patterns and cross-resistance of acinetobacter, isolated from hospitalized patients, southern iran

BACKGROUND

Acinetobacter is a multi-drug resistant and nosocomial pathogen. The aim of this study was to determine antibacterial susceptibility patterns and cross-resistance of Acinetobacter species.

METHODS

This study was conducted in Nemazee Hospital, Shiraz, Iran from October 2007 to September 2008. Species identification was carried out by API E20. Minimum inhibitory concentration and cross-resistance of the isolated strains to 12 antibiotics were determined by E-test method.

RESULTS

Eighty eight isolates of Acinetobacter were collected from patients' samples. Acinetobacter baumannii was isolated most frequently (79; 89.8%). Colistin, imipenem and meropenem were found to be the three most effective antibiotics with 97.7%, 77.3% and 72.7% activity against the isolates, respectively. Multi-drug resistance was revealed among 2 to 11 antibiotics and high cross-resistance was also noticed.

CONCLUSION

To alleviate the situation, strict control measures and appropriate effective antibiotic therapy should be adopted to reduce hospital costs and related mortality.

Pharmacokinetic study of sulbactomax

We have evaluated pharmacokinetics of a fixed dose combination (FDC) of ceftriaxone and sulbactam (2:1) or sulbactomax in eight healthy volunteers. A 1.5 g dose of sulbactomax, 1 g dose of ceftriaxone and 0.5 g sulbactam were given intravenously in a balanced two-ways cross-over study. Serially collected plasma sample was analyzed for ceftriaxone and sulbactam by high performance liquid chromatography (HPLC). The mean peaks of ceftriaxone and sulbactam concentrations in plasma were 152.06+/-6.65 microg/ml and 21.32+/-1.80 microg/ml, respectively and plasma half-lives for ceftriaxone and sulbactam were 5.2+/-0.35 hr and 0.94+/-0.038 hr, respectively. The AUC0-24 for ceftriaxone and sulbactam was 760.16+/-27.68 microg.hr/ml and 20.74+/-2.34 microg.hr/ml, respectively, with elimination rate constant of 0.133+/-0.009 hr(-1) and 0.732+/-0.029 hr(-1), respectively. The kinetics of ceftriaxone and sulbactum did not change in combination as compared to the alone treatment. Also, concentration of the ceftriaxone after 24 hr is higher than the minimum inhibitory concentration (MIC) of the most of the gram positive and gram negative bacteria indicating that one dose in a day is sufficient to treat the disease caused by these organisms.

Three decades of beta-lactamase inhibitors

Since the introduction of penicillin, beta-lactam antibiotics have been the antimicrobial agents of choice. Unfortunately, the efficacy of these life-saving antibiotics is significantly threatened by bacterial beta-lactamases. beta-Lactamases are now responsible for resistance to penicillins, extended-spectrum cephalosporins, monobactams, and carbapenems. In order to overcome beta-lactamase-mediated resistance, beta-lactamase inhibitors (clavulanate, sulbactam, and tazobactam) were introduced into clinical practice. These inhibitors greatly enhance the efficacy of their partner beta-lactams (amoxicillin, ampicillin, piperacillin, and ticarcillin) in the treatment of serious Enterobacteriaceae and penicillin-resistant staphylococcal infections. However, selective pressure from excess antibiotic use accelerated the emergence of resistance to beta-lactam-beta-lactamase inhibitor combinations. Furthermore, the prevalence of clinically relevant beta-lactamases from other classes that are resistant to inhibition is rapidly increasing. There is an urgent need for effective inhibitors that can restore the activity of beta-lactams. Here, we review the catalytic mechanisms of each beta-lactamase class. We then discuss approaches for circumventing beta-lactamase-mediated resistance, including properties and characteristics of mechanism-based inactivators. We next highlight the mechanisms of action and salient clinical and microbiological features of beta-lactamase inhibitors. We also emphasize their therapeutic applications. We close by focusing on novel compounds and the chemical features of these agents that may contribute to a "second generation" of inhibitors. The goal for the next 3 decades will be to design inhibitors that will be effective for more than a single class of beta-lactamases.

Ampicillin-sulbactam: an update on the use of parenteral and oral forms in bacterial infections

Ampicillin-sulbactam has a wide range of antibacterial activity that includes Gram-positive and Gram-negative aerobic and anaerobic bacteria. However, the drug is not active against Pseudomonas aeruginosa and pathogens producing extended-spectrum beta-lactamases. The combination could be considered particularly active against Acinetobacter baumannii infections due to the intrinsic activity of sulbactam. The drug is indicated as empirical therapy for a broad range of community acquired infections supervened in adults or children and is effective in either parenteral (ampicillin-sulbactam) or oral (as a mutual prodrug sultamicillin) form. In clinical trials, sultamicillin has proved clinically and bacteriologically effective in adults and children against a variety of frequently encountered infections, including mild upper and lower respiratory tract infections, urinary tract infections, diabetic foot and skin and soft tissue infections. Furthermore, adverse effects rarely occur with the diarrhoea to represent the most commonly reported. The parenteral ampicillin-sulbactam is indicated for community infections of mild-to-moderate severity acquired infections such as intra-abdominal or gynecological. Moreover, it seems to represent the alternative of choice for the treatment of A. baumannii infections for carbapenem-resistant strains in the nosocomial setting. Thus, ampicillin-sulbactam remains a valuable agent in the physician's armamentarium in the management of adult and pediatric infections.

Acinetobacter: an old friend, but a new enemy

Acinetobacter emerged as a significant nosocomial pathogen during the late 1970s, probably as a consequence, at least in part, of increasing use of broad-spectrum antibiotics in hospitals. Most clinically significant isolates belong to the species Acinetobacter baumannii or its close relatives, with many infections concentrated in intensive care, burns or high dependency units treating severely ill or debilitated patients. Large outbreaks can occur in such units, involving the infection or colonisation of numerous patients by specific epidemic strains of A. baumannii. Recently, a particular problem has concerned cross-infection of injured military patients repatriated from combat regions of the world (e.g. Iraq and Afghanistan). Carbapenems have previously been the treatment of choice for infected patients, but increasing reports worldwide now describe A. baumannii isolates resistant to all conventional antimicrobial regimens. Data to support therapeutic use of the limited number of new antimicrobial agents (e.g. tigecycline) with in-vitro activity against these pathogens are still very limited. Detailed advice concerning prevention and control of outbreaks caused by multidrug-resistant strains of acinetobacter is available from the UK Health Protection Agency. In addition to antibiotic prescribing policies and audit, these measures focus on reinforcing standard infection control procedures and precautions, with particular attention to thorough cleaning of patient areas to take account of the long-term survival of acinetobacter after drying and inadequate disinfection. Despite these measures, the problem continues to escalate, with many hospitals worldwide now reporting outbreaks caused by multidrug-resistant strains of acinetobacter.

High-dose ampicillin-sulbactam as an alternative treatment of late-onset VAP from multidrug-resistant Acinetobacter baumannii

The increased incidence of multidrug-resistant (MDR) Acinetobacter baumannii ventilator-associated pneumonia in critically ill patients poses a severe therapeutic problem. The aim of this study was to evaluate the efficacy and safety of 2 high-dose treatment regimens of ampicillin-sulbactam (A/S) for MDR Acinetobacter baumannii VAP. We undertook a randomized, prospective trial of critically ill patents with (MDR) Acinetobacter baumannii VAP. Patients were randomly assigned to 1 of 2 treatment regimens of A/S (at a rate 2:1 every 8 h): 1) group A, 18/9 g daily dose (n = 14); and 2) group B, 24/12 g daily dose (n = 13). The duration of therapy was 8+/-2 d for both groups. A total of 27 patients were enrolled in the study. Clinical improvement was seen in 66.7% of the study population in 9/14 (64.3%) of group A patients and 9/13 (69.2%) of group B patients, respectively. Bacteriological success was achieved in 77.8% of the study population (12/14, 85.7% of group A) and in 9/13 (69.2%) of group B patients. The 14-d mortality rate was 25.9% and the all cause 30-d mortality was 48.1%. Both mortality rates did not differ significantly between the 2 groups. No major adverse reactions were recorded. We concluded that clinical and bacteriological results of the study support the use of high-dose regimen of ampicillin-sulbactam for MDR Acinetobacter baumannii VAP.

Acinetobacter baumannii: emergence of a successful pathogen

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

Multidrug-resistant Acinetobacter baumannii outbreak in an intensive care unit

Carbapenem-resistant Acinetobacter baumannii was isolated from 15 colonized or infected patients (carriers) between April and July 2004, in a teaching hospital ICU in Rome, Italy. All isolated strains were susceptible only to gentamicin, ampicillin-sulbactam and colistin and displayed the same Random Amplified Polymorphic DNA (RAPD) 1 pattern. Twelve out of 15 strains were susceptible to tigecycline, whereas the remaining three showed intermediate susceptibility. Although infection control measures were reinforced and carriers isolated in separate rooms, A. baumannii transmission continued. Therefore, finally A. baumannii carriers were moved to another available subintensive unit, which was re-equipped, and cared for by dedicated personnel, whereas only the non infected/colonized patients remained in the ICU. This study shows that during an outbreak by multiresistant A. baumannii it may be indispensable to geographically isolate not only patients but also dedicated staff.

Acinetobacter baumannii: a universal threat to public health?

Acinetobacter spp. are non-fermentative, strictly aerobic, Gram-negative microorganisms with a confusing taxonomic history. The Acinetobacter baumannii-Acinetobacter calcoaceticus complex is the species most commonly isolated from clinical specimens. It is ubiquitous in nature and has been found as part of the normal skin, throat and rectal flora as well as in food and body lice. It colonises patients in Intensive Care Units and contaminates inanimate hospital surfaces and devices as well as wounds, including war injuries. Although a frequent coloniser, Acinetobacter can be the cause of severe and sometimes lethal infections, mostly of nosocomial origin, predominantly ventilator-associated pneumonia. Bacteraemic infections are rare but may evolve to septic shock. Acinetobacter also emerges as a cause of nosocomial outbreaks and is characterised by increasing antimicrobial multiresistance. Antibiotic use, especially carbapenems and third-generation cephalosporins, is recognised as the most important risk factor for multiresistance. Described resistance mechanisms include hydrolysis by beta-lactamases, alterations in outer membrane proteins and penicillin-binding proteins, and increased activity of efflux pumps. Today, Acinetobacter resistant to carbapenems, aminoglycosides and fluoroquinolones presents a challenge to the clinician. However, sulbactam, tigecycline and colistin represent the current therapeutic approaches, which are associated with satisfactory efficacy.

Rational antibiotic therapy and the position of ampicillin/sulbactam

In the current context of increasing antimicrobial resistance, it is important to use antibiotics rationally and to re-assess regularly the clinical usefulness of commonly used agents. This review focuses on the efficacy of the beta-lactam ampicillin co-administered with the beta-lactamase inhibitor sulbactam, either parenterally (ampicillin/sulbactam) or orally (sultamicillin), for the treatment of bacterial infections. Clinical findings from the past decade confirm the results of numerous older studies and together provide good evidence to support the continued use of ampicillin/sulbactam and sultamicillin in hospital- and community-acquired infections both in adults and children. This is also recognised in recent published national and international guidelines, many of which recommend ampicillin/sulbactam as first-line therapy for various respiratory and skin infections.

Efficacy and safety of high-dose ampicillin/sulbactam vs. colistin as monotherapy for the treatment of multidrug resistant Acinetobacter baumannii ventilator-associated pneumonia

OBJECTIVE

To compare the safety and efficacy of ampicillin/sulbactam (Amp/Sulb) and colistin (COL) in the treatment of multidrug resistant Acinetobacter baumannii ventilator-associated pneumonia (VAP).

METHODS

A prospective cohort study in adult critically ill patients with VAP. Patients were randomly assigned to receive Amp/Sulb (9 g every 8h) or COL (3 MIU every 8h) intravenously. Dosage was adjusted according to creatinine clearance.

RESULTS

A total of 28 patients were enrolled (15 COL, 13 Amp/Sulb). Resolution of symptoms and signs occurred in 60% (9/15) of the COL group and 61.5% (9/13) of the Amp/Sulb group, improvement in 13.3% (2/15) vs. 15.3% (1/13) and failure in 26.6% (4/15) vs. 23% (3/13), respectively. The difference was not statistically significant. Bacteriologic success was achieved in 66.6% (10/15) vs. 61.5% (8/13) in the COL and Amp/Sulb groups, respectively (p<0.2). Mortality rates (14 days and 28 days) were 15.3% and 30% for the Amp/Sulb and 20% and 33% for the COL group, respectively. Adverse events were 39.6% (including 33% nephrotoxicity) for the COL group and 30.7% (15.3% nephrotoxicity) for the Amp/Sulb group (p=NS).

CONCLUSION

Colistin and high-dose ampicillin/sulbactam were comparably safe and effective treatments for critically ill patients with MDR A. baumannii VAP.

Sulbactam-containing beta-lactamase inhibitor combinations

Sulbactam irreversibly inhibits the hydrolytic activity of beta-lactamases. This compound is commercially available in combination with either ampicillin or cefoperazone. In each instance, the activity of the partner antibiotic against beta-lactamase-producing bacteria is restored. One of the particular advantages of using sulbactam-containing combinations is that sulbactam itself has inherent activity against some Acinetobacter baumannii. Sulbactam combinations have not demonstrated strong selective pressures for extended-spectrum beta-lactamase-producing Enterobacteriaceae and vancomycin-resistant enterococci. In contrast to clavulanate, sulbactam does not induce class I (Ampc) chromosomal beta-lactamases in Enterobacteriaceae.

Risk factors for nosocomial imipenem-resistant Acinetobacter baumannii infections

OBJECTIVES

To identify the risk factors for nosocomial imipenem-resistant Acinetobacter baumannii (IRAB) infections.

METHODS

A prospective case-control study, set in an 1100-bed referral and tertiary-care hospital, of all patients who had nosocomial A. baumannii infections between January 1 and December 31, 2004. Only the first isolation of A. baumannii was considered.

RESULTS

IRAB was isolated from 66 (53.7%) patients and imipenem-sensitive Acinetobacter baumannii (ISAB) was isolated from 57 (46.3%) patients during the study period. The mean duration of hospital stay until A. baumannii isolation was 20.8+/-13.6 days in IRAB infections, whereas it was 15.4+/-9.4 days in ISAB infections. Of the patients, 65.2% with IRAB infections and 40.4% with ISAB infections were followed at the intensive care unit (ICU). Previous carbapenem use was present in 43.9% of the patients with IRAB and 12.3% of the patients with ISAB infection. In univariate analysis female sex, longer duration of hospital stay until infection, ICU stay, emergent surgical operation, total parenteral nutrition, having a central venous catheter, endotracheal tube, urinary catheter or nasogastric tube, previous antibiotic use, and previous administration of carbapenems were significant risk factors for IRAB infections (p<0.05). In multivariate analysis, longer duration of hospital stay until A. baumannii isolation (odds ratio (OR) 1.043; 95% confidence interval (CI) 1.003-1.084; p=0.032), previous antibiotic use (OR 5.051; 95% CI 1.004-25.396; p=0.049), and ICU stay (OR 3.100; 95% CI 1.398-6.873; p=0.005) were independently associated with imipenem resistance.

CONCLUSIONS

Our results suggest that the nosocomial occurrence of IRAB is strongly related to an ICU stay and duration of hospital stay, and that IRAB occurrence may be favored by the selection pressure of previously used antibiotics.

Molecular and epidemiologic study of polyclonal outbreaks of multidrug-resistant Acinetobacter baumannii infection in an Israeli hospital

OBJECTIVES

To perform a molecular and epidemiologic investigation of multidrug-resistant (MDR) Acinetobacter baumannii in an institution were polyclonal outbreaks have been observed and determine whether these polyclonal outbreaks had an endogenous origin or were caused by in-hospital patient-to-patient transmission.

DESIGN

Retrospective analysis of prospectively collected data.

SETTING

An epidemiologic and genotypic investigation of incident cases of MDR A. baumannii infection in an Israeli university tertiary care center.

PATIENTS

Hospitalized patients with MDR A. baumannii isolated from clinical samples during a 13-week period, from April 15, 2003, through July 15, 2003.

INTERVENTION

All patients with new MDR A. baumannii infections were recruited, and isolates were typed using pulsed-field gel electrophoresis. Data on in-hospital movements and consultations were extracted from computerized databases. Quantification of transmission opportunities (TOPs), defined as encounters between an established carrier and a future carrier of MDR A. baumannii, and analysis of ward clusters were performed.

RESULTS

We studied 96 MDR A. baumannii isolates, which belonged to 18 different pulsed-field gel electrophoresis clones. In 65% of cases, TOPs involving patients with the same clone were demonstrated, which is significantly greater than the number of TOPs involving patients with different clones (P=.01).

CONCLUSION

Although outbreaks of MDR A. baumannii infection may be polyclonal, we believe that patient-to-patient transmission explains most cases of transmission. Polyclonal local outbreaks reflect several clonal outbreaks occurring simultaneously. The cause of polyclonal outbreaks of A. baumannii infections clustered by ward and time remains to be explained.