Experimental Chemotherapy Chemotherapy 2013;59:325–329 DOI: 10.1159/000356755
Received: July 18, 2013 Accepted after revision: October 22, 2013 Published online: February 13, 2014
Efficacy of Sulbactam and Its Combination with Imipenem, Colistin and Tigecycline in an Experimental Model of Carbapenem-Resistant Acinetobacter baumannii Sepsis Gokcen Dinc a Hayati Demiraslan b Ferhan Elmali c Salman Shaheer Ahmed b Gokhan Metan b Emine Alp b Mehmet Doganay b
c
Department of Microbiology and Clinical Microbiology, b Infectious Disease and Clinical Microbiology, and Biostatistics and Medical Informatics, Faculty of Medicine, Erciyes University, Kayseri, Turkey
Key Words Acinetobacter baumannii · Carbapenem resistance · Experimental sepsis · Sulbactam · Tigecycline · Colistin · Imipenem
Abstract Background: In recent years, multidrug-resistant Acinetobacter baumannii has been reported as an important nosocomial pathogen, and treatment options are limited. The aim of this study was to investigate the additional effect of sulbactam on monotherapy with colistin, tigecycline and imipenem in experimental sepsis with carbapenem-resistant A. baumannii in mice. Methods: Sepsis was developed in 8- to 10-week-old BALB/c mice by an intraperitoneal injection of A. baumannii. Antibiotic was given intraperitoneally 2 h after bacterial inoculation. Each experimental group had 15 mice and was divided into 3 subgroups. Mice were sacrificed at 24, 48 or 72 h. Lung, liver, heart and spleen samples were cultured, and homogenates of lung and liver were used to detect the number of colony-forming units per gram. Bacterial clearance was compared in lung and liver at different time points. Results: Imipenem did not decrease the bacterial load, but the other antibiotics showed significant bactericidal activity compared with the control group, and the combi-
© 2014 S. Karger AG, Basel 0009–3157/14/0595–0325$39.50/0 E-Mail [email protected] www.karger.com/che
nation of imipenem with sulbactam decreased the bacterial load in lung and liver. However, the addition of sulbactam to colistin and tigecycline had no significant effect on bacterial counts. Only the addition of sulbactam to imipenem showed better bactericidal activity compared to imipenem alone. Conclusions: These results suggested that combining sulbactam with tigeycline or colistin does not increase the efficiency of these antibiotics. © 2014 S. Karger AG, Basel
Introduction
Acinetobacter baumannii is an important cause of nosocomial infections. It can lead to serious infections in many organs and systems; sepsis is one of the most serious infections caused by this organism [1–3]. Increasing levels of drug resistance in A. baumannii have caused a serious therapeutic challenge. Although carbapenems were once considered the major treatment option, nowadays there has been a worldwide increase in infections
This study was presented as an oral presentation at the EKMUD 2013 Scientific Platform: Infections From Laboratory to Clinic, 20–24 March 2013, Antalya, Turkey.
Gokcen Dinc Department of Microbiology and Clinical Microbiology Faculty of Medicine, Erciyes University TR–38039 Kayseri (Turkey) E-Mail gokcendinc @ erciyes.edu.tr
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a
Materials and Methods This study was carried out at the Hakan Cetinsaya Experimental and Clinical Research Center of Erciyes University. It was approved by the Local Ethical Committee for Animal Studies of Erciyes University (No. 11/64). Laboratory Animals BALB/c mice, aged 8–10 weeks and weighing between 20 and 25 g, were used in this study. Mice were obtained from the Hakan Cetinsaya Experimental and Clinical Research Center, Erciyes University, Kayseri, Turkey. The mice were housed in separate cages and given ad libitum access to food and water. Animals were acclimatized in a 12-hour light/dark cycle. Bacterial Isolate A carbapenem-resistant (OXA-51-, OXA-58- and PER-1-positive) A. baumannii strain that was isolated from a patient with nosocomial sepsis was used. This strain was supplied by the Department of Microbiology, Faculty of Medicine, Istanbul University. This isolate was stored at –80 ° C, and fresh subcultures were prepared prior to use.
Antimicrobials Sulbactam (Mustafa Nevzat Pharmaceutical, Turkey), colistimethate sodium (Koçak Farma, Turkey), tigecycline (Wyeth, UK) and imipenem-cilastatin (MSD, Turkey) were used in the study. Determination of Minimum Inhibitory Concentration Values Minimum inhibitory concentration (MIC) values of sulbactam, colistin, imipenem-cilastatin and tigecycline were determined by Etest (Diagnostic Liofilchem, Italy) according to the manufacturer’s guidelines and by the standard microdilution method [10]. For Etests, A. baumannii suspension prepared to 0.5 McFarland standard was cultured in Mueller-Hinton agar (Lab M Ltd., UK), and Etest strips were placed in the agar. After 24 h of incubation, the MIC values were determined. In a broth microdilution test, the concentrations of all antibiotics used in this study were between 0.125 and 256 μg/ml. Escherichia coli ATCC 25922 was used as a control. This test was performed according to the Clinical and Laboratory Standards Institute M07-A9 guidelines [10]. MIC breakpoints for A. baumannii against tigecycline, colistin, sulbactam and imipenem-cilastatin were from the Clinical and Laboratory Standards Institute M07-A9 guidelines [10] and European Committee on Antimicrobial Susceptibility Testing breakpoint tables, version 3.1 [11].
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Chemotherapy 2013;59:325–329 DOI: 10.1159/000356755
Study Design and Experimentation The mice were weighed and divided into 2 main groups, namely controls (positive, negative) and the study group. A total of 135 mice were used in this experiment. All experimental groups consisted of 15 mice, and each group was divided into 3 subgroups of 5 mice each. The study subgroups received the following treatments: imipenem, colistin, tigecycline, sulbactam, imipenem + sulbactam, colistin + sulbactam or tigecycline + sulbactam. Sepsis was developed by the intraperitoneal injection of 108 colony-forming units (CFU)/ml A. baumannii suspension (determined in a preliminary study). All groups except the negative control group were injected with 0.5 ml of 108 CFU/ml A. baumannii suspension. Two hours after intraperitoneal injection of the bacterial suspension, antibiotic treatments were initiated. Sulbactam (240 mg/kg), colistimethate sodium (5 mg/kg) and tigecycline (20 mg/kg) were given in 2 divided doses, and imipenem-cilastatin (200 mg/kg) was administered in 3 divided doses, all intraperitoneally. Drug dosages were administered according to previous experimental studies [2, 3]. All mice in the subgroups were sacrificed at 24, 48 or 72 h with an overdose of anesthetic (150 mg/kg ketamine hydrochloride, Pfizer, Turkey). Samples were taken from the lung, liver, spleen and heart and cultured on trypticase soy agar (Merck, Germany) to check both for the growth of bacteria and development of sepsis. A quantitative culture on trypticase soy agar was made from 10-fold dilutions of lung and liver homogenates. The bacterial load was detected as CFU per gram at 24, 48 and 72 h. Statistical Analysis Results were analyzed using SPSS 15.0 (SPSS Inc., Chicago, Ill., USA). Data were presented as the mean ± standard error of the mean. Logarithmic transformations were used when constructing statistical models to describe the relationship between two measurements. One-way analysis of variance was used for data with a normal distribution pattern. All pairwise multiple comparison procedures were performed by the Student-Newman-Keuls method. A p value of 256 μg/ml for imipenem-cilastatin. OXA-51, OXA-58 and PER-1 were positive in A. baumannii. Therapeutic Efficacy of Antibiotics Lung and liver bacterial counts for treated and control animals are shown in table 1. The bacterial counts of lung and liver were not statistically significant between the control and imipenem group (p > 0.05). However, the other antibiotics showed significant bactericidal activity in reducing lung and liver bacterial counts compared with the control group (p < 0.05). On the other hand, the addition of sulbactam to colistin and tigecycline had no significant effect on bacterial counts in lung and liver. Only Dinc/Demiraslan/Elmali/Ahmed/Metan/ Alp/Doganay
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caused by carbapenem-resistant Acinetobacter. This poses a serious challenge in the therapy alternatives for these cases [4–6]. Colistin, tigecycline and sulbactam are commonly used antibiotics for the treatment of serious infections. However, the optimal therapeutic regimen is uncertain and needs to be clarified [7–9]. The aim of this study was to assess the efficacy of sulbactam alone and in combination with imipenem, colistin and tigecycline against carbapenem-resistant A. baumannii in experimental sepsis.
Table 1. Effects of antibiotic therapies on bacterial counts in lung and liver tissues
Group
Bacterial count, log10 CFU/g lung
Control (n = 15) Sulbactam (n = 15) Colistin (n = 15) Imipenem (n = 15) Tigecycline (n = 15) Imipenem + sulbactam (n = 15) Colistin + sulbactam (n = 15) Tigecycline + sulbactam (n = 15)
liver
24 h
48 h
72 h
24 h
48 h
72 h
7.14±0.29a 5.23±0.69a, b 2.86±1.21b 7.24±0.19a 1.91±1.21b 5.05±1.29a, b 3.31±1.09b 2.95±1.25b
6.63±0.17a 1.74±1.08b 1.62±1.00b 5.83±0.68a 1.43±0.91b 2.80±1.15b 1.56±0.96b 1.01±0.64b
4.90±0.31a 0±0b 0±0b 3.56±0.98a 1.24±0.76b 1.31±0.80b 1.16±0.71b 0.54±0.54b
7.11±0.23a 5.25±1.05a, b 1.86±0.79c 6.93±0.24a 1.36±0.84c 2.68±1.10b, c 2.65±1.05b, c 2.43±1.15b, c
6.16±0.89a 1.33±0.82b 1.08±0.69b 5.70±0.66a 0.96±0.60b 1.80±1.10b 1.18±0.76b 0.98±0.60b
4.88±0.31a 0.0±0.0c 0.0±0.0c 2.32±0.71b 0.89±0.55c 1.26±0.77b, c 0.0±0.0c 0.44±0.44c
the addition of sulbactam to imipenem showed better bactericidal activity compared with imipenem alone. When sulbactam was added to colistin, the bacterial load of lung was significantly higher at 72 h compared to colistin or sulbactam alone (p < 0.05). Colistin and tigecycline monotherapy had earlier bactericidal activity compared to sulbactam; however, at 72 h colistin and sulbactam were the most active agents. Overall, the most effective therapy among all the groups was colistin.
A. baumannii is the most important nosocomial pathogen worldwide, often affecting intensive care unit patients. The emergence of resistance to almost all antibiotics presents a serious problem in the clinical setting. Carbapenems have been considered the most active agent against multidrug-resistant pathogens. However, carbapenem-resistant isolates have been increasing worldwide [2, 12–15]. In recent years, carbapenem resistance rates were reported to be over 50% [16–21], and in our last study it was found to be 92% in intensive care units [18]. Carbapenem-resistant A. baumannii poses a significant threat in hospitals, as therapeutic options are limited. Colistin, which was abandoned in the 1980s, was reintroduced for clinical use after the emergence of carbapenem resistance. However, the clinical effectiveness of colistin is questionable and is reported to be as low as 20% [22–24]. Resistance to colistin is the potential problem with colistin monotherapy. In recent years, many studies have investigated other antibiotics either as a monother-
apy or in combination with other antibiotics to increase the clinical success and to prevent resistance to colistin [1, 2, 19, 25–30]. Tigecycline and sulbactam have in vitro activity against carbapenem-resistant A. baumannii, and in some clinical studies the results were encouraging [8, 13, 30–32]. However, there is still debate about using these antibiotics as monotherapy or combination therapy in serious A. baumannii infections. Sulbactam is the most active β-lactamase inhibitor against A.baumannii. In recent clinical studies, especially with high-dose sulbactam, it has shown a similar effectiveness to imipenem and colistin in carbapenem-resistant A. baumannii infections. However, its single use is still controversial in life-threatening infections, and the development of resistance is a serious concern with monotherapy [1, 4, 8, 23, 27]. In vitro studies have shown synergistic activity of sulbactam when combined with colistin, tigecycline and carbapenems [1, 3, 6, 28, 31–33]. However, there still are not enough data about their in vivo efficacy, especially in serious infections. In this study, the therapeutic efficacy of sulbactam as monotherapy and in combination with colistin, tigecycline and imipenem in a sepsis model with carbapenem-resistant A. baumannii in mice was investigated. Sulbactam had no additional bactericidal effect on colistin and tigecycline monotherapy, but when it was combined with imipenem it showed better bactericidal activity compared with imipenem alone. However, imipenem + sulbactam did not have better bactericidal activity than sulbactam alone; the bactericidal effect was probably due to sulbactam. In a previous experimental study, Montero et al. [1] showed that colistin was not a good therapeutic option for treatment
Sulbactam Efficacy in Mono and Combined Therapies of A. baumannii Sepsis
Chemotherapy 2013;59:325–329 DOI: 10.1159/000356755
Discussion
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Results are shown as the mean ± standard error of the mean. Statistically significant differences between groups are indicated by different superscript letters in the same column (p < 0.05).
of patients with pneumonia due to carbapenem-resistant A. baumannii strains. Also, in another experimental study, they recommended that colistin monotherapy may not be the best option for infections caused by the highly resistant strains susceptible only to this antibiotic in vitro. A combination of rifampin-imipenem, rifampin-aminoglycoside or even rifampin-colistin may be more advisable [2]. These studies used the experimental pneumonia model where penetration of colistin and other antibiotics to the lung is inadequate. Also, in our study bacterial clearance of the liver was better than that of the lung with all antibiotics. The combination therapy did not have an additional effect on the clearance of bacteria from the lung. In our very recent clinical study, we compared the clinical and microbiological efficacy of colistin and colistin-sulbactam therapy for the treatment of multidrug-resistant A. baumannii ventilator-associated pneumonia. Although the difference was not statistically significant, the clinical cure rates and bacteriological clearance rates were more successful in the combination group [30]. In this study, colistin and tigecycline had earlier bactericidal activity than sulbactam; at 72 h, colistin and sulbactam were the most active agents. Overall, the most effective therapy in carbapenem-resistant A. baumannii sepsis was colistin.
In conclusion, the treatment of life-threatening carbapenem-resistant A. baumannii infections is a serious concern. Colistin appears to be the most effective agent against serious infections. However, toxicity, the development of resistance and the poor lung penetration of colistin lead clinicians to pursue different therapies. Sulbactam is a promising agent against carbapenem-resistant A. baumannii infections, but its single use is not advisable for serious infections as resistance may appear during treatment. Despite the results of this study, combination therapy was not superior to monotherapy. Further clinical studies are needed in order to prove if sulbactam increases the clinical effectiveness and reduces the mortality which also prevents colistin-resistant mutants. Acknowledgements The authors would like to thank Assoc. Prof. Zerrin Aktas from the Department of Microbiology, Faculty of Medicine, Istanbul University, Istanbul, Turkey, for supplying the strain of carbapenem-resistant, OXA-51-, OXA-58-, PER-1-positive A. baumannii, and Ms. Donna Sue Ozcan from the International Office of Erciyes University, Kayseri, Turkey, for suggestions regarding editing of this article in English. The Scientific Research Projects Unit of Erciyes University supported this study (Project No. TSA-11-3649).
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Received: July 18, 2013 Accepted after revision: October 22, 2013 Published online: February 13, 2014
Efficacy of Sulbactam and Its Combination with Imipenem, Colistin and Tigecycline in an Experimental Model of Carbapenem-Resistant Acinetobacter baumannii Sepsis Gokcen Dinc a Hayati Demiraslan b Ferhan Elmali c Salman Shaheer Ahmed b Gokhan Metan b Emine Alp b Mehmet Doganay b
c
Department of Microbiology and Clinical Microbiology, b Infectious Disease and Clinical Microbiology, and Biostatistics and Medical Informatics, Faculty of Medicine, Erciyes University, Kayseri, Turkey
Key Words Acinetobacter baumannii · Carbapenem resistance · Experimental sepsis · Sulbactam · Tigecycline · Colistin · Imipenem
Abstract Background: In recent years, multidrug-resistant Acinetobacter baumannii has been reported as an important nosocomial pathogen, and treatment options are limited. The aim of this study was to investigate the additional effect of sulbactam on monotherapy with colistin, tigecycline and imipenem in experimental sepsis with carbapenem-resistant A. baumannii in mice. Methods: Sepsis was developed in 8- to 10-week-old BALB/c mice by an intraperitoneal injection of A. baumannii. Antibiotic was given intraperitoneally 2 h after bacterial inoculation. Each experimental group had 15 mice and was divided into 3 subgroups. Mice were sacrificed at 24, 48 or 72 h. Lung, liver, heart and spleen samples were cultured, and homogenates of lung and liver were used to detect the number of colony-forming units per gram. Bacterial clearance was compared in lung and liver at different time points. Results: Imipenem did not decrease the bacterial load, but the other antibiotics showed significant bactericidal activity compared with the control group, and the combi-
© 2014 S. Karger AG, Basel 0009–3157/14/0595–0325$39.50/0 E-Mail [email protected] www.karger.com/che
nation of imipenem with sulbactam decreased the bacterial load in lung and liver. However, the addition of sulbactam to colistin and tigecycline had no significant effect on bacterial counts. Only the addition of sulbactam to imipenem showed better bactericidal activity compared to imipenem alone. Conclusions: These results suggested that combining sulbactam with tigeycline or colistin does not increase the efficiency of these antibiotics. © 2014 S. Karger AG, Basel
Introduction
Acinetobacter baumannii is an important cause of nosocomial infections. It can lead to serious infections in many organs and systems; sepsis is one of the most serious infections caused by this organism [1–3]. Increasing levels of drug resistance in A. baumannii have caused a serious therapeutic challenge. Although carbapenems were once considered the major treatment option, nowadays there has been a worldwide increase in infections
This study was presented as an oral presentation at the EKMUD 2013 Scientific Platform: Infections From Laboratory to Clinic, 20–24 March 2013, Antalya, Turkey.
Gokcen Dinc Department of Microbiology and Clinical Microbiology Faculty of Medicine, Erciyes University TR–38039 Kayseri (Turkey) E-Mail gokcendinc @ erciyes.edu.tr
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a
Materials and Methods This study was carried out at the Hakan Cetinsaya Experimental and Clinical Research Center of Erciyes University. It was approved by the Local Ethical Committee for Animal Studies of Erciyes University (No. 11/64). Laboratory Animals BALB/c mice, aged 8–10 weeks and weighing between 20 and 25 g, were used in this study. Mice were obtained from the Hakan Cetinsaya Experimental and Clinical Research Center, Erciyes University, Kayseri, Turkey. The mice were housed in separate cages and given ad libitum access to food and water. Animals were acclimatized in a 12-hour light/dark cycle. Bacterial Isolate A carbapenem-resistant (OXA-51-, OXA-58- and PER-1-positive) A. baumannii strain that was isolated from a patient with nosocomial sepsis was used. This strain was supplied by the Department of Microbiology, Faculty of Medicine, Istanbul University. This isolate was stored at –80 ° C, and fresh subcultures were prepared prior to use.
Antimicrobials Sulbactam (Mustafa Nevzat Pharmaceutical, Turkey), colistimethate sodium (Koçak Farma, Turkey), tigecycline (Wyeth, UK) and imipenem-cilastatin (MSD, Turkey) were used in the study. Determination of Minimum Inhibitory Concentration Values Minimum inhibitory concentration (MIC) values of sulbactam, colistin, imipenem-cilastatin and tigecycline were determined by Etest (Diagnostic Liofilchem, Italy) according to the manufacturer’s guidelines and by the standard microdilution method [10]. For Etests, A. baumannii suspension prepared to 0.5 McFarland standard was cultured in Mueller-Hinton agar (Lab M Ltd., UK), and Etest strips were placed in the agar. After 24 h of incubation, the MIC values were determined. In a broth microdilution test, the concentrations of all antibiotics used in this study were between 0.125 and 256 μg/ml. Escherichia coli ATCC 25922 was used as a control. This test was performed according to the Clinical and Laboratory Standards Institute M07-A9 guidelines [10]. MIC breakpoints for A. baumannii against tigecycline, colistin, sulbactam and imipenem-cilastatin were from the Clinical and Laboratory Standards Institute M07-A9 guidelines [10] and European Committee on Antimicrobial Susceptibility Testing breakpoint tables, version 3.1 [11].
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Study Design and Experimentation The mice were weighed and divided into 2 main groups, namely controls (positive, negative) and the study group. A total of 135 mice were used in this experiment. All experimental groups consisted of 15 mice, and each group was divided into 3 subgroups of 5 mice each. The study subgroups received the following treatments: imipenem, colistin, tigecycline, sulbactam, imipenem + sulbactam, colistin + sulbactam or tigecycline + sulbactam. Sepsis was developed by the intraperitoneal injection of 108 colony-forming units (CFU)/ml A. baumannii suspension (determined in a preliminary study). All groups except the negative control group were injected with 0.5 ml of 108 CFU/ml A. baumannii suspension. Two hours after intraperitoneal injection of the bacterial suspension, antibiotic treatments were initiated. Sulbactam (240 mg/kg), colistimethate sodium (5 mg/kg) and tigecycline (20 mg/kg) were given in 2 divided doses, and imipenem-cilastatin (200 mg/kg) was administered in 3 divided doses, all intraperitoneally. Drug dosages were administered according to previous experimental studies [2, 3]. All mice in the subgroups were sacrificed at 24, 48 or 72 h with an overdose of anesthetic (150 mg/kg ketamine hydrochloride, Pfizer, Turkey). Samples were taken from the lung, liver, spleen and heart and cultured on trypticase soy agar (Merck, Germany) to check both for the growth of bacteria and development of sepsis. A quantitative culture on trypticase soy agar was made from 10-fold dilutions of lung and liver homogenates. The bacterial load was detected as CFU per gram at 24, 48 and 72 h. Statistical Analysis Results were analyzed using SPSS 15.0 (SPSS Inc., Chicago, Ill., USA). Data were presented as the mean ± standard error of the mean. Logarithmic transformations were used when constructing statistical models to describe the relationship between two measurements. One-way analysis of variance was used for data with a normal distribution pattern. All pairwise multiple comparison procedures were performed by the Student-Newman-Keuls method. A p value of 256 μg/ml for imipenem-cilastatin. OXA-51, OXA-58 and PER-1 were positive in A. baumannii. Therapeutic Efficacy of Antibiotics Lung and liver bacterial counts for treated and control animals are shown in table 1. The bacterial counts of lung and liver were not statistically significant between the control and imipenem group (p > 0.05). However, the other antibiotics showed significant bactericidal activity in reducing lung and liver bacterial counts compared with the control group (p < 0.05). On the other hand, the addition of sulbactam to colistin and tigecycline had no significant effect on bacterial counts in lung and liver. Only Dinc/Demiraslan/Elmali/Ahmed/Metan/ Alp/Doganay
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caused by carbapenem-resistant Acinetobacter. This poses a serious challenge in the therapy alternatives for these cases [4–6]. Colistin, tigecycline and sulbactam are commonly used antibiotics for the treatment of serious infections. However, the optimal therapeutic regimen is uncertain and needs to be clarified [7–9]. The aim of this study was to assess the efficacy of sulbactam alone and in combination with imipenem, colistin and tigecycline against carbapenem-resistant A. baumannii in experimental sepsis.
Table 1. Effects of antibiotic therapies on bacterial counts in lung and liver tissues
Group
Bacterial count, log10 CFU/g lung
Control (n = 15) Sulbactam (n = 15) Colistin (n = 15) Imipenem (n = 15) Tigecycline (n = 15) Imipenem + sulbactam (n = 15) Colistin + sulbactam (n = 15) Tigecycline + sulbactam (n = 15)
liver
24 h
48 h
72 h
24 h
48 h
72 h
7.14±0.29a 5.23±0.69a, b 2.86±1.21b 7.24±0.19a 1.91±1.21b 5.05±1.29a, b 3.31±1.09b 2.95±1.25b
6.63±0.17a 1.74±1.08b 1.62±1.00b 5.83±0.68a 1.43±0.91b 2.80±1.15b 1.56±0.96b 1.01±0.64b
4.90±0.31a 0±0b 0±0b 3.56±0.98a 1.24±0.76b 1.31±0.80b 1.16±0.71b 0.54±0.54b
7.11±0.23a 5.25±1.05a, b 1.86±0.79c 6.93±0.24a 1.36±0.84c 2.68±1.10b, c 2.65±1.05b, c 2.43±1.15b, c
6.16±0.89a 1.33±0.82b 1.08±0.69b 5.70±0.66a 0.96±0.60b 1.80±1.10b 1.18±0.76b 0.98±0.60b
4.88±0.31a 0.0±0.0c 0.0±0.0c 2.32±0.71b 0.89±0.55c 1.26±0.77b, c 0.0±0.0c 0.44±0.44c
the addition of sulbactam to imipenem showed better bactericidal activity compared with imipenem alone. When sulbactam was added to colistin, the bacterial load of lung was significantly higher at 72 h compared to colistin or sulbactam alone (p < 0.05). Colistin and tigecycline monotherapy had earlier bactericidal activity compared to sulbactam; however, at 72 h colistin and sulbactam were the most active agents. Overall, the most effective therapy among all the groups was colistin.
A. baumannii is the most important nosocomial pathogen worldwide, often affecting intensive care unit patients. The emergence of resistance to almost all antibiotics presents a serious problem in the clinical setting. Carbapenems have been considered the most active agent against multidrug-resistant pathogens. However, carbapenem-resistant isolates have been increasing worldwide [2, 12–15]. In recent years, carbapenem resistance rates were reported to be over 50% [16–21], and in our last study it was found to be 92% in intensive care units [18]. Carbapenem-resistant A. baumannii poses a significant threat in hospitals, as therapeutic options are limited. Colistin, which was abandoned in the 1980s, was reintroduced for clinical use after the emergence of carbapenem resistance. However, the clinical effectiveness of colistin is questionable and is reported to be as low as 20% [22–24]. Resistance to colistin is the potential problem with colistin monotherapy. In recent years, many studies have investigated other antibiotics either as a monother-
apy or in combination with other antibiotics to increase the clinical success and to prevent resistance to colistin [1, 2, 19, 25–30]. Tigecycline and sulbactam have in vitro activity against carbapenem-resistant A. baumannii, and in some clinical studies the results were encouraging [8, 13, 30–32]. However, there is still debate about using these antibiotics as monotherapy or combination therapy in serious A. baumannii infections. Sulbactam is the most active β-lactamase inhibitor against A.baumannii. In recent clinical studies, especially with high-dose sulbactam, it has shown a similar effectiveness to imipenem and colistin in carbapenem-resistant A. baumannii infections. However, its single use is still controversial in life-threatening infections, and the development of resistance is a serious concern with monotherapy [1, 4, 8, 23, 27]. In vitro studies have shown synergistic activity of sulbactam when combined with colistin, tigecycline and carbapenems [1, 3, 6, 28, 31–33]. However, there still are not enough data about their in vivo efficacy, especially in serious infections. In this study, the therapeutic efficacy of sulbactam as monotherapy and in combination with colistin, tigecycline and imipenem in a sepsis model with carbapenem-resistant A. baumannii in mice was investigated. Sulbactam had no additional bactericidal effect on colistin and tigecycline monotherapy, but when it was combined with imipenem it showed better bactericidal activity compared with imipenem alone. However, imipenem + sulbactam did not have better bactericidal activity than sulbactam alone; the bactericidal effect was probably due to sulbactam. In a previous experimental study, Montero et al. [1] showed that colistin was not a good therapeutic option for treatment
Sulbactam Efficacy in Mono and Combined Therapies of A. baumannii Sepsis
Chemotherapy 2013;59:325–329 DOI: 10.1159/000356755
Discussion
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Results are shown as the mean ± standard error of the mean. Statistically significant differences between groups are indicated by different superscript letters in the same column (p < 0.05).
of patients with pneumonia due to carbapenem-resistant A. baumannii strains. Also, in another experimental study, they recommended that colistin monotherapy may not be the best option for infections caused by the highly resistant strains susceptible only to this antibiotic in vitro. A combination of rifampin-imipenem, rifampin-aminoglycoside or even rifampin-colistin may be more advisable [2]. These studies used the experimental pneumonia model where penetration of colistin and other antibiotics to the lung is inadequate. Also, in our study bacterial clearance of the liver was better than that of the lung with all antibiotics. The combination therapy did not have an additional effect on the clearance of bacteria from the lung. In our very recent clinical study, we compared the clinical and microbiological efficacy of colistin and colistin-sulbactam therapy for the treatment of multidrug-resistant A. baumannii ventilator-associated pneumonia. Although the difference was not statistically significant, the clinical cure rates and bacteriological clearance rates were more successful in the combination group [30]. In this study, colistin and tigecycline had earlier bactericidal activity than sulbactam; at 72 h, colistin and sulbactam were the most active agents. Overall, the most effective therapy in carbapenem-resistant A. baumannii sepsis was colistin.
In conclusion, the treatment of life-threatening carbapenem-resistant A. baumannii infections is a serious concern. Colistin appears to be the most effective agent against serious infections. However, toxicity, the development of resistance and the poor lung penetration of colistin lead clinicians to pursue different therapies. Sulbactam is a promising agent against carbapenem-resistant A. baumannii infections, but its single use is not advisable for serious infections as resistance may appear during treatment. Despite the results of this study, combination therapy was not superior to monotherapy. Further clinical studies are needed in order to prove if sulbactam increases the clinical effectiveness and reduces the mortality which also prevents colistin-resistant mutants. Acknowledgements The authors would like to thank Assoc. Prof. Zerrin Aktas from the Department of Microbiology, Faculty of Medicine, Istanbul University, Istanbul, Turkey, for supplying the strain of carbapenem-resistant, OXA-51-, OXA-58-, PER-1-positive A. baumannii, and Ms. Donna Sue Ozcan from the International Office of Erciyes University, Kayseri, Turkey, for suggestions regarding editing of this article in English. The Scientific Research Projects Unit of Erciyes University supported this study (Project No. TSA-11-3649).
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