In vitro activities of ampicillin-sulbactam and amoxicillin-clavulanic acid against Acinetobacter baumannii

How to treat severe Acinetobacter baumannii infections

PURPOSE OF REVIEW

To update the management of severe Acinetobacter baumannii infections (ABI), particularly those caused by multi-resistant isolates.

RECENT FINDINGS

The in vitro activity of the various antimicrobial agents potentially helpful in treating ABI is highly variable and has progressively decreased for many of them, limiting current therapeutic options. The combination of more than one drug is still advisable in most circumstances. Ideally, two active first-line drugs should be used. Alternatively, a first-line and a second-line drug and, if this is not possible, two or more second-line drugs in combination. The emergence of new agents such as Cefiderocol, the combination of Sulbactam and Durlobactam, and the new Tetracyclines offer therapeutic options that need to be supported by clinical evidence.

SUMMARY

The apparent limitations in treating infections caused by this bacterium, the rapid development of resistance, and the serious underlying situation in most cases invite the search for alternatives to antibiotic treatment, the most promising of which seems to be bacteriophage therapy.

Outbreak of Infection WithAcinetobacterStrain RUH 1139 in an Intensive Care Unit

Objective.

To investigate a nosocomial outbreak of infection withAcinetobacterstrain RUH 1139, in the unit of high neonatal risk at University Hospital of The Andes (Mérida, Venezuela).

Methods.

Twenty-eightAcinetobacterstrains were detected by biochemical testing and further identified to the species level by examination of the gene encoding 16S ribosomal DNA, using restriction analysis and gene sequencing. The epidemiological relationship between the strains was established by means of repetitive extragenic palindromic polymerase chain reaction (REP-PCR) and pulsed-field gel electrophoresis (PFGE), and antimicrobial susceptibilities were determined by disk diffusion.

Results.

The spread of an epidemic strain ofAcinetobacterRUH 1139 among 16 patients over a period of 3 months was demonstrated using antimicrobial susceptibility testing, PFGE, and REP-PCR. The epidemic strain was also isolated in 2 of the sampled parenteral nutrition solutions. All the patients involved in the infection outbreak had received parenteral solution. Moreover, strains ofAcinetobacterRUH 1139 with another PFGE pattern and ofA. baumanniiwere sporadically isolated before and during the outbreak.

Conclusion.

This is the first description of an outbreak of infection with this genospecies ofAcinetobacterin which parenteral nutrition solution was potentially the infection source.

Analysis of penicillin-binding proteins (PBPs) in carbapenem resistant Acinetobacter baumannii

BACKGROUND & OBJECTIVES

Acinetobacter baumannii is a Gram-negative, cocco-bacillus aerobic pathogen responsible for nosocomial infections in hospitals. In the recent past A. baumannii had developed resistance against β-lactams, even against carbapenems. Penicillin-binding proteins (PBPs) are crucial for the cell wall biosynthesis during cell proliferation and these are the target for β-lactams. Therefore, the present study was carried out to identify the PBPs in three (low, intermediate and high MICs) groups of carbapenem resistant isolates strains of A. baumannii.

METHODS

ATCC 19606 and 20 β-lactam resistant isolates of A. baumannii were obtained. Selective identification of the PBPs was done using Bocillin FL, a non-radioactive fluorescent derivative of penicillin.

RESULTS

The fluorescence emission from Bocillin-tag in SDS-PAGE gel of native strain identified eight PBPs, with apparent molecular weight of 94, 65, 49, 40, 30, 24, 22 and 17 kDa, however, these PBPs revealed alteration in carbapenem-resistant isolates.

INTERPRETATION & CONCLUSIONS

A comparative analysis of PBPs in the resistant isolates with those of ATCC revealed a decreased expression of all PBPs except that of 65 and 17 kDa PBPs which were marginally downregulated, and simultaneous appearance of new 28 kDa PBP (in low and intermediate resistant isolates) and 36 kDa in high meropenem resistant group of A. baumannii. The present study indicated an association between alteration in PBPs and β-lactam resistance in A. 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.

Activities of various β-lactams and β-lactam/β-lactamase inhibitor combinations against Acinetobacter baumannii and Acinetobacter DNA group 3 strains

Acinetobacter baumannii and Acinetobacter DNA group 3 are members of the so-called A. calcoaceticus-A. baumannii complex and are important nosocomial pathogens. Multiresistance in these organisms is increasingly frequent, and alternative treatment options are needed. The beta-lactamase inhibitors clavulanate, sulbactam and tazobactam have intrinsic activity against Acinetobacter strains. In the present study, broth microdilution was used to assess the in-vitro activities of currently available beta-lactam/beta-lactamase inhibitor combinations and sulbactam alone against 469 Acinetobacter isolates (A. baumannii, n=395; Acinetobacter DNA group 3, n=74) collected from various laboratories in Germany. Fixed concentrations and fixed ratios of beta-lactamase inhibitors were used. Sulbactam-containing combinations (susceptibility rates of 90.4-92.7% for A. baumannii and 97.3-100% for Acinetobacter DNA group 3) and sulbactam alone were superior to clavulanate- and tazobactam-containing combinations. The activity of sulbactam-containing combinations against members of the A. calcoaceticus-A. baumannii complex was conferred exclusively by the intrinsic activity of the beta-lactamase inhibitor and did not result from enhanced beta-lactam activity. Testing with the inhibitor added at a fixed ratio of inhibitor to beta-lactam appeared to give more reliable results than testing at a fixed concentration of the inhibitor. Resistance to carbapenems (0.3%) remains low in Germany.

Evaluation of the MicroScan ESBL plus confirmation panel for detection of extended-spectrum beta-lactamases in clinical isolates of oxyimino-cephalosporin-resistant Gram-negative bacteria

OBJECTIVE

We aimed to assess the performance of the MicroScan ESBL plus confirmation panel using a series of 87 oxyimino-cephalosporin-resistant Gram-negative bacilli of various species.

METHODS

Organisms tested included 57 extended-spectrum beta-lactamase (ESBL) strains comprising Enterobacter aerogenes (3), Enterobacter cloacae (10), Escherichia coli (11), Klebsiella pneumoniae (26), Klebsiella oxytoca (3) and Proteus mirabilis (4). Also included were 30 strains resistant to oxyimino cephalosporins but lacking ESBLs, which were characterized with other resistance mechanisms, such as inherent clavulanate susceptibility in Acinetobacter spp. (4), hyperproduction of AmpC enzyme in Citrobacter freundii (2), E. aerogenes (3), E. cloacae (3), E. coli (4), Hafnia alvei (1) and Morganella morganii (1), production of plasmid-mediated AmpC beta-lactamase in K. pneumoniae (3) and E. coli (3) or hyperproduction of K1 enzyme in K. oxytoca (6).

RESULTS

The MicroScan MIC-based clavulanate synergy correctly classified 50 of 57 ESBL strains as ESBL-positive and 23 of 30 non-ESBL strains as ESBL-negative (yielding a sensitivity of 88% and a specificity of 76.7%, respectively). False negatives among ESBL producers were highest with Enterobacter spp. due to masking interactions between ESBL and AmpC beta-lactamases. False-positive classifications occurred in two Acinetobacter spp., one E. coli producing plasmid-mediated AmpC beta-lactamase and two K. oxytoca hyperproducing their chromosomal K1 beta-lactamase.

CONCLUSION

The MicroScan clavulanate synergy test proved to be a valuable tool for ESBL confirmation. However, this test has limitations in detecting ESBLs in Enterobacter spp. and in discriminating ESBL-related resistance from the K1 enzyme and from inherent clavulanate susceptibility in Acinetobacter spp.

In vitro activities of the beta-lactamase inhibitors clavulanic acid, sulbactam, and tazobactam alone or in combination with beta-lactams against epidemiologically characterized multidrug-resistant Acinetobacter baumannii strains

Acinetobacter baumannii is an important nosocomial pathogen usually in the context of serious underlying disease. Multidrug resistance in these organisms is frequent. The beta-lactamase inhibitors clavulanic acid, sulbactam, and tazobactam have intrinsic activity against Acinetobacter strains. To evaluate their potential therapeutic usefulness, we determined the in vitro activity of ampicillin, sulbactam, ampicillin-sulbactam, cefoperazone, cefoperazone-sulbactam, piperacillin, piperacillin-sulbactam, tazobactam, piperacillin-tazobactam, amoxicillin, clavulanic acid, amoxicillin-clavulanic acid, ticarcillin, and ticarcillin-clavulanic acid against multidrug-resistant A. baumannii. All isolates were epidemiologically characterized by RAPD [random(ly) amplified polymorphic DNA] analysis and/or pulsed-field gel electrophoresis and represented different strain types, including sporadic strains, as well as outbreak-related strains. The MICs were determined by agar dilution on Mueller-Hinton agar (using fixed concentrations, as well as fixed ratios for beta-lactamase inhibitors) and the E-test. The majority of E-test results were within two dilutions of those recorded by agar dilution, with the exception of piperacillin-tazobactam. Sulbactam was superior to clavulanic acid and tazobactam and may represent an alternative treatment option for infections due to multiresistant A. baumannii strains. beta-Lactamase inhibitors have intrinsic activity but do not enhance activity of beta-lactams against A. baumannii. Testing with the inhibitor added at a fixed concentration as recommended for piperacillin-tazobactam and ticarcillin-clavulanic acid by the National Committee for Clinical Laboratory Standards may falsely suggest high activity or gives uninterpretable results due to trailing. If combinations are used for testing, fixed ratios may give more useful results.

Comparative in vitro potency of amoxycillin-clavulanic acid and four oral agents against recent North American clinical isolates from a global surveillance study

The in vitro activity of amoxycillin-clavulanic acid was compared with four comparator oral antimicrobial agents; ampicillin, azithromycin, cefuroxime and trimethoprim-sulphamethoxazole against 4536 recent clinical isolates covering 29 species isolated in the US and Canada between 1997 and 1999. Based upon Minimum inhibitory concentrations (MICs), amoxycillin-clavulanic acid was the most active agent against many Gram-positive species and phenotypes including methicillin susceptible Staphylococcus aureus (MSSA) Staphylococcus epidermidis, Enterococcus faecalis, Streptococcus pyogenes, Streptococcus pneumoniae including penicillin intermediate and macrolide resistant strains and was as active as ampicillin against Streptococcus agalactiae, penicillin resistant S. pneumoniae and viridans streptococci. Against Enterobacteriaceae amoxycillin-clavulanic acid in general, displayed weak activity with only Proteus mirabilis and Proteus vulgaris displaying levels of susceptibility above the 90th percentile. Amoxycillin-clavulanic acid had significant activity against many species of Gram-negative non-Enterobacteriaceae including Haemophilus influenzae, Haemophilus parainfluenzae and Moraxella catarrhalis but negligible activity against Burkholderia cepacia, Pseudomonas aeruginosa and Stenotrophomonas maltophilia. Amoxycillin-clavulanic acid continues to retain excellent activity against the majority of targeted pathogens despite 20 years of clinical use.

Pandrug-resistant Acinetobacter baumannii causing nosocomial infections in a university hospital, Taiwan

The rapid emergence (from 0% before 1998 to 6.5% in 2000) of pandrug-resistant Acinetobacter baumannii (PDRAB) was noted in a university hospital in Taiwan. To understand the epidemiology of these isolates, we studied 203 PDRAB isolates, taken from January 1999 to April 2000: 199 from 73 hospitalized patients treated at different clinical settings in the hospital and 4 from environmental sites in an intensive-care unit. Pulsed-field gel electrophoresis analysis and random amplified polymorphic DNA (RAPD) generated by arbitrarily primed polymerase chain reaction of these 203 isolates showed 10 closely related genotypes (10 clones). One (clone 5), belonging to pulsotype E and RAPD pattern 5, predominated (64 isolates, mostly from patients in intensive care). Increasing use of carbapenems and ciprofloxacin (selective pressure) as well as clonal dissemination might have contributed to the wide spread of PDRAB in this hospital.

Pandrug-resistant Acinetobacter baumannii causing nosocomial infections in a university hospital, Taiwan

The rapid emergence (from 0% before 1998 to 6.5% in 2000) of pandrug-resistant Acinetobacter baumannii (PDRAB) was noted in a university hospital in Taiwan. To understand the epidemiology of these isolates, we studied 203 PDRAB isolates, taken from January 1999 to April 2000: 199 from 73 hospitalized patients treated at different clinical settings in the hospital and 4 from environmental sites in an intensive-care unit. Pulsed-field gel electrophoresis analysis and random amplified polymorphic DNA (RAPD) generated by arbitrarily primed polymerase chain reaction of these 203 isolates showed 10 closely related genotypes (10 clones). One (clone 5), belonging to pulsotype E and RAPD pattern 5, predominated (64 isolates, mostly from patients in intensive care). Increasing use of carbapenems and ciprofloxacin (selective pressure) as well as clonal dissemination might have contributed to the wide spread of PDRAB in this hospital.