In vitro activities of beta-lactam antibiotics alone and in combination with sulbactam against Gram-negative bacteria

Multicenter study on clinical outcomes and poor prognostic factors in patients with Klebsiella pneumoniae bacteremia receiving cefoperazone/sulbactam treatment

BACKGROUND

Infections caused by Klebsiella pneumoniae are common and result in high mortality rates. In vitro studies demonstrated the potency of cefoperazone/sulbactam (CPZ/SUL) against Klebsiella pneumoniae. However, the clinical efficacy of CPZ/SUL for the treatment of K. pneumoniae bacteremia has not been studied.

OBJECTIVES

This study aimed to associate the clinical outcomes of patients with bacteremia with the minimal inhibitory concentrations (MICs) of CPZ/SUL against the causative K. pneumoniae isolates.

METHODS

This multicenter, retrospective study was conducted in Taiwan between July 2017 and April 2021. Patients with K. pneumoniae bacteremia treated with CPZ/SUL were enrolled in this study. CPZ/SUL MICs were determined using the agar dilution method. Data on the patients' clinical outcomes and characteristics were collected and analyzed.

RESULTS

In total, 201 patients were enrolled. Among the causative K. pneumoniae isolates, 180 (89.5%) were susceptible to CPZ/SUL. Most patients (n = 156, 77.6%) had favorable outcomes. The 30-day mortality rate was 11.9% (n = 24). Multivariate risk analyses showed that higher APACHE II score (Odds Ratio [OR], 1.14; Confidence Interval [CI], 1.07-1.21; p < 0.001), metastatic tumors (OR, 5.76; CI, 2.31-14.40; p < 0.001), and causative K. pneumoniae CPZ/SUL MICs > 16 µg/ml (OR, 4.30; CI, 1.50-12.27; p = 0.006) were independently associated with unfavorable outcomes.

CONCLUSION

Patients with K. pneumoniae bacteremia treated with CPZ/SUL at a ratio 1:1 had favorable outcomes when the CPZ/SUL MICs were ≤ 16 µg/ml. Patients with higher APACHE II scores and metastatic tumors had unfavorable outcomes.

Antibiofilm Activity of β-Lactam/β-Lactamase Inhibitor Combination against Multidrug-Resistant Salmonella Typhimurium

This study was designed to assess the effect of β-lactam/β-lactamase inhibitor combinations on the inhibition of biofilm formation of Salmonella Typhimurium. The anti-planktonic and anti-biofilm activities of ampicillin (AMP), ceftriaxone (CEF), and combination treatments of antibiotics and sulbactam (AMP + SUL and CEF + SUL) were evaluated against antibiotic-sensitive S. Typhimurium ATCC 19585 (ST^AS) and clinically isolated multidrug-resistant (MDR) S. Typhimurium CCARM 8009 (ST^MDR). Compared to the control, the minimum inhibitory concentrations (MICs) of AMP against ST^AS and CEF against ST^MDR were decreased from 32 to 16 μg/mL and 0.25 to 0.125 μg/mL, respectively, in the presence of SUL. The numbers of ST^MDR treated with AMP + SUL and CEF + SUL were effectively reduced by more than 2 logs after 4 h of incubation at 37 °C. The β-lactamase activities of ST^AS and ST^MDR treated with AMP and CEF were reduced from 3.3 to 2.6 μmol/min/mL and from 8.3 to 3.4 μmol/min/mL, respectively, in the presence of SUL. The biofilm cell numbers of ST^AS and ST^MDR were reduced at all treatments after 24 h of incubation at 37 °C. The biofilm cell numbers of ST^AS and ST^MDR were reduced by more than 2 logs in the presence of SUL compared to the AMP and CEF alone. The lowest relative fitness level was 0.6 in ST^AS treated with AMP + SUL, while no significant differences in the relative fitness were observed in ST^MDR. This study suggests that β-lactamase inhibitors (BLIs) could be used for controlling biofilm formation of β-lactamase-producing multidrug-resistant S. Typhimurium.

Sulbactam Enhances in vitro Activity of β-Lactam Antibiotics Against Acinetobacter baumannii

Purpose

To evaluate in vitro activities of β-lactam antibiotics alone and in combination with sulbactam at different ratios against Acinetobacter baumannii clinical strains from China.

Methods

A total of 300 clinical isolates of A. baumannii were collected from 29 hospitals across China in 2018. Susceptibility to common antibiotics was assessed, and β-lactamase genes were detected. In vitro activity of ampicillin, cefoperazone and imipenem was tested alone and in combination with sulbactam at the ratios of 2:1, 1:1, 1:1.5, 1:2, 1:2.5 and 1:3.

Results

High resistant rates for common antibiotics were observed except tigecycline and polymyxin B. Among carbapenem-resistant A. baumannii, 97.3% isolates harbored bla_OXA-23. MIC₅₀ and MIC₉₀ values for sulbactam were 32 mg/L and 64 mg/L, respectively. High resistant rates for ampicillin, cefoperazone and imipenem were observed (92.3%, 93% and 85.3%, respectively). A stepwise increase in the ratio of sulbactam to partner β-lactam antibiotics led to a stepwise decrease in the MICs and a stepwise increase in the susceptible rates. The susceptible rates for imipenem-sulbactam 1:3, ampicillin-sulbactam 1:3 and cefoperazone-sulbactam 1:3 reached 16.3%, 58.3% and 91%, respectively.

Conclusion

The increasing proportion of sulbactam could enhance antimicrobial activities of imipenem-sulbactam, ampicillin-sulbactam and cefoperazone-sulbactam combinations against A. baumannii clinical strains in China, with cefoperazone-sulbactam as the most potent compound.

In Vitro Synergistic Effect and Mutant Prevention Concentrations of Cefepime Alone or in Combination with Sulbactam Against OXA-48-positive Klebsiella pneumoniae Isolates

The aim of this study is to investigate the combination of cefepime and sulbactam. Sulbactam, when administered , will effectively inhibit all Extended-spectrum beta lactamases (ESBLs) of the microorganism, while cefepime will inhibit the growth of the resistant microorganisms since it will not be hydrolyzed by OXA-48. Forty OXA-48-producing K. pneumoniae strains were investigated for their Minimum inhibitory concentrations (MICs) for carbapenems, cefepime, and cefepime + sulbactam by broth microdilution method. Also, the mutant prevention concentration (MPC)s of cefepime alone or in combination with sulbactam was determined. Additionally, the bactericidal activities of cefepime and cefepime + sulbactam were evaluated by the time-kill curve (TKC) assay against selected strains. Also, the in vitro synergistic activity of cefepime + sulbactam combination was determined by TKC. Based on MIC results, up to 35/40 and 34/40 of the strains were resistant to carbapenems and cefepime, respectively. Cefepime + sulbactam MIC range was lower than those for cefepime alone against all the studied isolates. Moreover, cefepime + sulbactam combination presented lower MPC values than cefepime alone. The synergistic interactions of cefepime + sulbactam were also achieved against studied strains at 24 h. No antagonism was observed against studied K. pneumoniae strains. The findings of this study displayed that cefepime + sulbactam combination had synergistic or additive effect against OXA-48-producing K. pneumoniae strains. Additionally, it was first observed that this combination could display a lower MPC than cefepime alone. Further investigations may be helpful for understanding the effectiveness of cefepime + sulbactam combinations for OXA-48-positive carbapenem-resistant K. pneumoniae isolates.

Dual-channel Microchip Electrophoresis with Amperometric Detection System for Rapid Analysis of Cefoperazone and Sulbactam

A dual-channel microchip electrophoresis (ME) with in-channel amperometric detection was developed for cefoperazone and sulbactam determination simultaneously. In this study, a microelectrode detector was made of gold nanoparticles (GNPs) modified indium tin oxide (ITO)-coated poly-ethylene terephthalate (PET) film. The parameters including detection potential applied on working electrode, buffer concentration and pH value were optimized to improve the detection sensitivity and separation efficiency of cefoperazone and sulbactam. Under the optimal conditions, sensitive detection of cefoperazone and sulbactam was obtained with limits of detection (LODs) (S/N = 3) of 0.52 and 0.75 μg/mL, respectively. The plasma sample, which was from a patient with a brain injury taking Sulperazone, was successfully detected with a simple sample pretreatment process by dual-channel ME amperometric detection. This rapid and sensitive method possesses practical potential in clinical applications, and could provide a guidance for clinical rational drug use.

The impact of inoculum size on the activity of cefoperazone-sulbactam against multidrug resistant organisms

OBJECTIVES

This study aims to assess the in vitro activity of cefoperazone alone and different cefoperazone-sulbactam ratios against different inoculum sizes of multidrug resistant organisms.

METHODS

Minimum inhibitory concentrations (MICs) of cefoperazone, cefoperazone-sulbactam at fixed ratio of 1:1 and 2:1 against a normal inoculum size of 5 × 10⁵ CFU/ml and a high inoculum size of 5 × 10⁷ CFU/ml were measured.

RESULTS

Each 33 isolates of extended-spectrum β-lactamases (ESBL)-producing Escherichia coli, ESBL-producing Klebsiella pneumoniae, carbapenem-resistant E. coli, and carbapenem-resistant Pseudomonas aeruginosa and a total of 122 isolates of carbapenem-resistant Acinetobacter baumannii were collected. After the addition of sulbactam at a 1:1 ratio, most MIC₅₀ and MIC₉₀ values decreased. Cefoperazone-sulbactam at a 1:1 ratio had a higher susceptibility rate against ESBL-producing E. coli, carbapenem-resistant E. coli, and carbapenem-resistant A. baumannii than cefoperazone-sulbactam at a 2:1 ratio (all P < 0.05). For ESBL-producing E. coli, the susceptibility rate of cefoperazone-sulbactam at ratios of (1:1) and (2:1) decreased from 97.0 to 87.9% and 90.9 to 60.6%, for normal to high inoculum, respectively. For ESBL-producing K. pneumoniae, both susceptibility rate of cefoperazone-sulbactam at ratios of (1:1) and (2:1) decreased from 75.8%, and 63.6% at normal inoculum to 51.5% and 42.4% at high inoculum.

CONCLUSIONS

Cefoperazone-sulbactam at a 1:1 ratio has greater in vitro activity against most multidrug resistant organisms than cefoperazone-sulbactam at a 2:1 ratio. Such combinations were not influenced by the inoculum size of ESBL-producing E. coli and K. pneumoniae and could be a therapeutic option for treating severe infections.

Risk factors for bloodstream infection caused by extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae: A focus on antimicrobials including cefepime

BACKGROUND

Extended-spectrum β-lactamase (ESBL)-producing pathogens represent increasing challenges to physicians because of rising prevalence, high mortality, and challenging treatment. Identifying high risks and early appropriate therapy is critical to favorable outcomes.

METHODS

This is a 5-year retrospective case-case-control study performed at the Detroit Medical Center on adult patients with bloodstream infection (BSI) caused by ESBL-producing and non-ESBL-producing Escherichia coli or Klebsiella pneumoniae, each compared with uninfected controls. Data were collected from December 2004-August 2009. Multivariate analysis was performed using logistic regression.

RESULTS

Participants included 103 patients with BSI caused by ESBL-producing pathogens and 79 patients with BSI caused by pathogens that did not produce ESBLs. The mean age of patients in the ESBL group was 67 years; of the patients, 51% were men, 77% were black, and 38% (n = 39) died in hospital. The mean age of patients in the non-ESBL group was 58 years; of the patients, 51% were men, 92% were black, and 22% (n = 17) died in hospital. On multivariate analysis, predictors of BSI caused by ESBL-producing pathogens included central venous catheter (odds ratio [OR], 29.4; 95% confidence interval [CI], 3.0-288.3), prior β-lactam-/β-lactamase-inhibitor therapy (OR, 28.1; 95% CI, 1.99-396.5), and prior cefepime therapy (OR, 22.7; 95% CI, 2.7-192.4). The only risk factor for BSI caused by non-ESBL-producing pathogens was urinary catheter insertion (OR, 18.2; 95% CI, 3.3-100.3).

CONCLUSION

Prior antimicrobial therapy, particularly with β-lactam, was the strongest unique risk factor for BSI caused by ESBL-producing E coli or K pneumoniae.

Simultaneous spectrophotometric determination of ceftazidime and sulbactam using multivariate calibration methods

The simultaneous spectrophotometric determination of ceftazidime (CTZ) and sulbactam (SBT) in the presence of the overlapping spectra were accomplished with the partial least squares (PLS) and genetic algorithm-partial least square (GA-PLS) approaches.

Ampicillin/sulbactam: its potential use in treating infections in critically ill patients

The purpose of this paper was to review the potential utility of ampicillin/sulbactam (SAM) as a therapy for serious infections in critically ill patients. Data for this review were identified by searches of PubMed and of the reference lists of the included articles. We found that SAM appears to have a number of characteristics that support its use in the treatment of serious infections in critically ill patients. SAM demonstrates extensive penetration into many infection sites, supporting its use in a wide range of infection types. Microbiologically, sulbactam has strong intrinsic antibiotic activity against multidrug-resistant (MDR) bacteria, including Acinetobacter baumannii, which supports its use for the treatment of infections mediated by this pathogen. Of some concern, there have been reports showing a decline in susceptibility of some bacteria to SAM. As such, use of lower doses (4/2g/day), particularly for MDR A. baumannii, has been linked with a 30% reduced success rate in critically ill patients. The therapeutic challenges for ensuring achievement of optimal dosing of SAM result partly from bacterial susceptibility but also from the pharmacokinetic (PK) alterations common to β-lactam agents in critical illness. These PK changes are likely to reduce the ability of standard dosing to achieve the concentrations observed in non-critically ill patients. Optimisation of therapy may be more likely with the use of higher doses, administration by 4h infusion or by combination therapy, particularly for the treatment of infections caused by MDR pathogens.

In vitro effects of sulbactam combinations with different antibiotic groups against clinical Acinetobacter baumannii isolates

Treatment of multidrug resistant (MDR) Acinetobacter baumannii infections causes some problems as a result of possessing various antibacterial resistance mechanisms against available antibiotics. Combination of antibiotics, acting by different mechanisms, is used for the treatment of MDR bacterial infections. It is an important factor to determine synergy or antagonism between agents in the combination for the constitution of effective therapy. The study aimed to determine In vitro interactions interpreted according to calculated fractional inhibitory concentration (FIC) index between sulbactam and ceftazidime, ceftriaxone, cefepime, ciprofloxacin, gentamicin, meropenem, tigecycline, and colistin. Ten clinical isolates of A. baumannii were tested for determination of synergistic effects of sulbactam with different antimicrobial combinations. Minimal inhibitory concentration (MIC) values of both sulbactam and combined antibiotics decreased 2- to 128-fold. Synergy and partial synergy were determined in combination of sulbactam with ceftazidime and gentamicin (FIC index: ≤ 0.5 or >0.5 to <1) and MIC values of both ceftazidime and gentamicin for five isolates fell down below the susceptibility break point. Similarly, MIC value of ciprofloxacin for six ciprofloxacin resistant isolates was determined as below the susceptibility break point in combination. However, all isolates were susceptible to colistin and tigecycline, MIC values of both were decreased in combination with sulbactam. Although synergistic and partial synergistic effects were observed in the combination of sulbactam and ceftriaxone, all isolates remained resistant to ceftriaxone. The effect of cefepime-sulbactam combination was synergy in five, partial synergy in one and indifferent in four isolates. Meropenem and sulbactam showed a partial synergistic effect (FIC index: >0.5 to <1) in three, an additive effect (FIC index: 1) in one and an indifferent effect (FIC index: >1-2) in six isolates. Antagonism was not determined in any combination for clinical A. baumannii isolates in the study. In conclusion, sulbactam is a good candidate for combination treatment regimes for MDR A. baumannii infections.

Investigating the impact of the definition of previous antibiotic exposure related to isolation of extended spectrum β-lactamase-producing Klebsiella pneumoniae

BACKGROUND

Previous antibiotic exposure is a risk factor for extended spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae isolation, but the optimal definition of previous antibiotic exposure remains unclear.

METHODS

This was a retrospective, case-control study comparing 88 patients with ESBL-producing K pneumoniae (cases) and 88 patients with non-ESBL-producing K pneumoniae (controls). Three previous antibiotic exposure definitions were analyzed, including durations of 30, 60, and 90 days prior to organism isolation.

RESULTS

The mean cohort age was 63.6 ± 16.9 years, 43% were male, and 86% were black. In bivariate analysis, third-generation cephalosporins and cefepime were associated with ESBL-producing K pneumoniae isolation, and the odds ratios (OR) were significant regardless of previous antibiotic exposure definition. However, for fluoroquinolones and ampicillin/sulbactam, the ORs varied as a function of previous antibiotic exposure definition. In multivariate analysis, third-generation cephalosporin usage was a risk factor for ESBL-producing K pneumoniae isolation, whereas ampicillin/sulbactam usage was protective against these organisms, regardless of the time frame analyzed. Other independent predictors of ESBL-producing K pneumoniae included nursing home residence (OR, 9.30 [95% confidence interval: 3.69-23.43]) and hemodialysis (OR, 13.60 [95% confidence interval: 4.29-43.17]).

CONCLUSION

Prior use of third-generation cephalosporins, nursing home residence, and hemodialysis were independent risk factors for isolation of an ESBL-producing K pneumoniae regardless of the time frame analyzed.

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.

Simultaneous determination of ampicillin, cefoperazone, and sulbactam in pharmaceutical formulations by HPLC with β-cyclodextrin stationary phase

An accurate and reproducible method for the simultaneous determination of ampicillin (AMP), sulbactam (SUL), and cefoperazone (CFP) in pharmaceutical formulations by using HPLC with beta-CD stationary phase was developed. It involved the use of the added tetraethylammonium acetate (TEAA) reagent, pH, and methanol as the significant parameters to find the optimum separation condition. A high resolution and selectivity of analytes was obtained by running the mobile phase in methanol-5 mM TEAA buffer = 35:65 (v/v, pH 4.5) at 280 nm. The mean recoveries ranged from 96.6 to 103.3% for AMP in the synthetic mixture, 97.6 to 103.0% for SUL, and 97.0 to 104.0% for CFP. The low LOD (<1.8 microg/mL) and low CV (<0.9%) assured that this method was sensitive and reproducible. The assay of analytes in commercial products exhibited that it was convenient and reproducible for routine analyses of these components in sterilized H(2)O, saline, or 5% dextrose injection solutions.

Prognosis of adult patients with bacteremia caused by extensively resistant Acinetobacter baumannii

Nosocomial bacteremia caused by extensively resistant Acinetobacter baumannii (ERAB) is an emerging problem in Taiwanese hospitals. Accordingly, we retrospectively investigated the epidemiology and outcomes of adult patients with ERAB bacteremia (ERABB) after different treatments from January 2001 to September 2004 at the National Taiwan University Hospital, Taipei, Taiwan. A total of 56 adult patients with ERABB and without other simultaneous infections were enrolled. Demographic, clinical, and laboratory data were obtained from medical records. Clinical data included underlying diseases and conditions with onset within 7 days after ERABB, severity of ERABB, antibiotic regimens for ERABB, and clinical outcomes. Laboratory data included hemograms, liver function tests, renal function tests, and albumin levels. Coagulation profiles were obtained at ERABB onset and 7 days before and after onset. All 56 episodes of ERABB were hospital-acquired. Most patients had Acute Physiology Scores and Chronic Health Evaluation II scores >/=17 (66.1%) and Pitt bacteremia score >/=4 (66.1%). Many had comorbid diseases at ERABB onset. Crude mortality rates on days 2, 7, 15, 30, and at discharge were 23.2%, 30.4%, 37.5%, 48.2%, and 60.7%, respectively. High severity of ERABB (Pitt bacteremia score >/=4) and presence of immunosuppression were the only 2 predictors for day 30 mortality (odds ratios of 18.53 and 8.06, respectively). Antibiotic regimens for ERABB did not have a significant influence on ERABB outcomes.

Predictive value of the serum bactericidal test for mortality in patients infected with multidrug-resistant Acinetobacter baumannii

OBJECTIVE

Strains of Acinetobacter baumannii resistant to all available antibiotics except polymyxin B have circulated in Taiwan since 1998 and have caused a variety of nosocomial infections. There are no standard tests to measure outcome in patients infected with these strains. Our aim was to determine whether a serum bactericidal test (SBT) could be used for this purpose.

METHODS

This SBT was performed in 57 infected patients.

RESULTS

Among the 35 patients who survived and 22 patients who died, peak SBT titer negatively correlated with mortality rate (correlation coefficient -0.43). The survival rate in patients with a peak SBT titer > or = 1:16, > or = 1:8, and < or = 1:4 was 100%, 87.5%, and 42.4%, respectively (p=0.001). Mortality was found to be closely related to illness severity and the presence of multiple organ failure. In subgroup analysis, the power of SBT to predict mortality was significant for patients without multiple organ failure (p=0.004), and also patients without disease defined as rapidly fatal by McCabe classification (p=0.044).

CONCLUSION

In a region with few therapeutic options for multi-drug resistant Acinetobacter baumannii (MDRAB), such as in Taiwan, SBT could be used as a prognosis indicator and indicator of the need to modify treatment in patients infected with MDRAB.

Ampicillin/Sulbactam

Ampicillin/sulbactam is a beta-lactam/beta-lactamase inhibitor combination with a broad spectrum of antibacterial activity against Gram-positive, Gram-negative and anaerobic bacteria. Data from comparative studies justify the use of ampicillin/sulbactam in a 2 : 1 ratio in various severe bacterial infections. In comparative clinical trials, ampicillin/sulbactam has proved to be a significant drug in the therapeutic armamentarium for lower respiratory tract infections and aspiration pneumonia, gynaecological/obstetrical infections, intra-abdominal infections, paediatric infections such as acute epiglottitis and periorbital cellulitis, diabetic foot infections, and skin and soft tissue infections. Of particular interest during this era of increasing antimicrobial resistance in various settings and populations is the effectiveness of sulbactam against a considerable proportion of infections due to Acinetobacter baumannii.

In vitro activities of various piperacillin and sulbactam combinations against bacterial pathogens isolated from Intensive Care Units in Taiwan: SMART 2004 programme data

We investigated the in vitro activity of various piperacillin and sulbactam combinations against Gram-negative bacterial isolates from Intensive Care Units (ICUs) in Taiwan. Antimicrobial susceptibility testing of 1030 bacterial isolates recovered from ICUs of nine major teaching hospitals was performed using the agar dilution method. Sulbactam was added to piperacillin either at a fixed sulbactam concentration of 4 mg/L and 8 mg/L or at a piperacillin:sulbactam ratio of 2:1 and 4:1. Piperacillin/sulbactam at a ratio of 2:1 or a fixed 8 mg/L concentration of sulbactam had better activities against Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis and Serratia marcescens than other piperacillin/sulbactam formulations. For Pseudomonas aeruginosa, piperacillin/sulbactam (2:1 or 4:1 ratios) had MIC(90) values (minimum inhibitory concentration for 90% of the organisms) of 64 mg/L (>90% susceptibility) compared with 64 mg/L for cefoperazone/sulbactam (68% susceptibility) and 128 mg/L for piperacillin/tazobactam (82% susceptibility). For Acinetobacter baumannii, both piperacillin/sulbactam (either 2:1 ratio or a fixed 8 mg/L sulbactam) and cefoperazone/sulbactam were the most potent agents. Adding sulbactam to piperacillin resulted in increased susceptibility rates among piperacillin-resistant P. aeruginosa (53-57% in either 2:1 or 4:1 ratios) and A. baumannii (38-46% in either 2:1 ratio or a fixed 8 mg/L concentration of sulbactam) isolates. Results of susceptibility tests with piperacillin/sulbactam are dependent on the method used. Piperacillin/sulbactam combinations possessed better in vitro activities than piperacillin alone or piperacillin/tazobactam against P. aeruginosa and A. baumannii.

Comparison of antimicrobial resistance of Acinetobacter baumannii clinical isolates from Shanghai and Hong Kong

OBJECTIVE

To compare the antimicrobial resistance patterns of Acinetobacter baumannii isolates from Shanghai and Hong Kong.

MATERIALS AND METHODS

A total of 212 A. baumannii strains of one isolate per patient were collected from Shanghai and Hong Kong from August 2002 to August 2003 that were tested against 15 commonly used antimicrobial agents by the agar dilution method according to the NCCLS guidelines.

RESULTS

Most beta-lactams showed no significant increase in activity after adding beta-lactamase inhibitors. The resistance rates of the isolates against ticarcillin-clavulanate, piperacillin-tazobactam and ampicillin-sulbactam were for Shanghai 74.9, 70.9, 69.1% and Hong Kong 24.3, 18.9, 13.5%, respectively. Only cefoperazone-sulbactam showed a significant increase in activity against both Shanghai and Hong Kong strains, as the resistance rates dropped from 93.7 to 8.6% and 83.8 to 5.4%, respectively. The resistance rates of ceftazidime, cefepime, and gentamicin against Shanghai strains were 69.7, 72.0, 73.7% and Hong Kong strains 69.7, 29.7, 18.9%, respectively. About 65% of Shanghai strains were found to be amikacin-resistant, however, all Hong Kong strains were sensitive. Fluoroquinolones including ciprofloxacin and levofloxacin had resistance rates over 60% against Shanghai strains, but only 13.5% against Hong Kong strains. Shanghai strains had imipenem and meropenem resistance rate of 6.3%. Though 10.8% Hong Kong strains were resistant to meropenem, only 2.7% of them were resistant to imipenem.

CONCLUSION

A. baumannii isolated from Shanghai were more resistant to all drugs except meropenem than Hong Kong isolates. The results indicate a need for measures to control the abuse of antibiotic usage in order to prevent the emergence of more multidrug-resistant isolates in both cities.