In vitro activities of tigecycline, ertapenem, isepamicin, and other antimicrobial agents against clinically isolated organisms in Taiwan

In-vitro Activity of Isepamicin against Gram-negative Bacteria in Comparison to Other Aminoglycosides Routinely used at a Teaching Hospital in Northern India

Background  Isepamicin is a 1-N-S-a-hydroxy-b-aminopropionyl derivative of gentamicin B and the spectrum of pathogenic microorganisms covered by it and its effectiveness is similar to that of amikacin except the action of aminoglycoside inhibitor enzymes is ineffectual on it. Material and Methods  We performed a prospective study in the Bacteriology section of the Department of Microbiology at a 1,600-bedded hospital in Northern India from Jan 2022 to March 2022. Isepamicin was tested for susceptibility against gram-negative bacteria, identified by routine biochemicals and matrix-assisted-desorption/ionization -time of flight-mass spectrometry (MALDI-TOF-MS) assay. The antibiotic susceptibility testing for each of the isolates was performed by Kirby Bauer's disc diffusion method, according to the CLSI 2019 guidelines. Results  The majority of isolates were obtained from blood samples (50, 39.1%). Among the non-inducible Enterobacteriaceae , Escherichia coli was least susceptible to amikacin (8/27, 29.63%) and most susceptible to isepamicin (18/27, 66.67%). Klebsiella pneumoniae followed the same pattern of susceptibility as E. coli and was least susceptible to Amikacin (20/46, 43.48%) and most susceptible to isepamicin (24/46, 52.17%). Enterobacter cloacae (6/7, 85.71%) was most susceptible to both amikacin and isepamicin, followed by 71.43% (5/7, 71.43%) susceptibility to gentamicin and tobramycin each. Enterobacter aerogenes was equally 53.33% (8/15) susceptible to all antibiotics. Pseudomonas aeruginosa was the most susceptible isolate to all antibiotics (18/21, 85.71%). Conclusion  Isepamicin is a potential antimicrobial agent for treating an array of gram-negative bacteria-associated infections and shows better in vitro activity than older aminoglycoside agents.

Investigation of isepamicin in vitro efficiency in Gram negative bacteria efficacy of isepamicin

CONTEXT

Isepamicin is a new semisynthetic aminoglycoside derived from gentamicin B and it is effective against Gram negative bacteria. Antibiotic resistance is an emerging problem and new options need for the treatment of infections caused by Gram negative bacteria.

AIMS

In this study we aimed to investigate the in vitro efficiency in carbapenem susceptible and nonsusceptible Enterobacterales and Pseudomonas aeruginosa.

METHODS AND MATERIAL

A total of 214 isolates of Gram-negative bacteria (Enterobacterales n = 129 and P. aeruginosa n = 85). Identification of the bacteria was tested in Vitek MS (Biomeriux, France). Susceptibility of isepamicin, amikacin, gentamicin, tobramycin and netilmicin was determined by Kirby Bauer disc diffusion method. The breakpoints for susceptibility to isepamicin, amikacin, gentamicin, streptomycin, tobramycin and netilmicin were evaluated according to the Comité de l'Antibiogramme dela Société Française de Microbiologie (CA-SFM) and EUCAST, respectively. Aminoglycoside modifying enzyme (AME) genes were investigated by multiplex PCR method.

RESULTS

Isepamicin susceptibility was determined as 92.3% for Enterobacterales and 67% for P. aeruginosa and 94.4% for carbapenem resistant Enterobacterales. The most common AME gene was aac (6')-Ib in both Enterobacterales (76%) and P. aeruginosa (14.1%). Seven of the isepamicin intermediate or resistant isolates were positive aac (6')-Ib in Enterobacterales and P. aeruginosa.

CONCLUSIONS

In this study, isepamicin showed good efficiency against both susceptible and carbapenem nonsusceptible Enterobacterales. But amikacin was prior to isepamicin P. aeruginosa isolates. Isepamicin could be a therapeutic option for the infections caused by Enterobacterales.

Epidemiology of carbapenem resistant Enterobacteriaceae (CRE) during 2000-2012 in Asia

BACKGROUND

Over the past decade, the worldwide emergence of carbapenem resistance in Enterobacteriaceae has become a severe public health issue. This meta-analysis aims to describe the epidemiology of carbapenem resistant Enterobacteriaceae (CRE) during the years of 2000-2012 in Asian area.

METHODS

PubMed and Embase databases were searched to identify the qualified papers. Random or fixed-effect model was used to deal with the data.

RESULTS

Over all the 49 Asian countries (or regions), only 37.5% [19] of them contributed epidemiology data of CRE, and the rest ones provided either only case reports or no information at all. In Asia, the prevalence of CRE was still low during the study period with average resistance rates of 0.6% (95% CI, 0.6-0.8%, imipenem) and 0.9% (95% CI, 0.7-1.2%, meropenem). Resistance rates to imipenem and meropenem in Enterobacteriaceae exhibited stably escalating trend. Similar trend can also be observed among each Enterobacteriaceae genus, such as E. coli, Klebsiella spp. and Enterobacer spp. Klebsiella spp. accounted for the largest proportion among the isolates resistant to imipenem, and then followed by E. coli and Serratia. The rank order of resistance rates to imipenem among Enterobacteriaceae genus during the period of 2000-2012 was as follows: Serratia spp. (1.8%) > Proteus spp. (1.6%) > Klebsiella spp. (0.8%) = Citrobacter spp. (0.8%) > Enterobacer spp. (0.7%) > E. coli (0.2%).

CONCLUSIONS

Given the fact that the prevalence of CRE was increasing during the past decade, it is urgent for us to establish regional surveillance worldwide, carry out more effective antibiotic stewardship and infection control measures to prevent further spread of carbapenem resistance in Enterobacteriaceae.

In vitro antimicrobial activity of "last-resort" antibiotics against unusual nonfermenting Gram-negative bacilli clinical isolates

In this prospective multicentric study, we assessed the in vitro antimicrobial activity of carbapenems (imipenem, meropenem, and doripenem), tigecycline, and colistin against 166 unusual nonfermenting Gram-negative bacilli (NF-GNB) clinical isolates collected from nine French hospitals during a 6-month period (from December 1, 2008, to May 31, 2009). All NF-GNB isolates were included, except those phenotypically identified as Pseudomonas aeruginosa or Acinetobacter baumannii. Minimal inhibitory concentrations (MICs) of antimicrobial agents were determined by using the E-test technique. The following microorganisms were identified: Stenotrophomonas maltophilia (n=72), Pseudomonas spp. (n=30), Achromobacter xylosoxidans (n=25), Acinetobacter spp. (n=18), Burkholderia cepacia complex (n=9), Alcaligenes faecalis (n=7), and Delftia spp. (n=5). All isolates of Acinetobacter spp., A. faecalis, and Delftia spp. were susceptible to the three carbapenems. Imipenem exhibited the lowest MICs against Pseudomonas spp., and meropenem, as compared with imipenem and doripenem, displayed an interesting antimicrobial activity against A. xylosoxidans and B. cepacia complex isolates. Conversely, no carbapenem exhibited any activity against S. maltophilia. Except for S. maltophilia isolates, tigecycline and colistin exhibited higher MICs than carbapenems, but covered most of the microorganisms tested in this study. To our knowledge, no prior study has compared antimicrobial activity of these five antibiotics, often considered as "last-resort" treatment options for resistant Gram-negative infections, against unusual NF-GNB clinical isolates. Further studies should be carried out to assess the potential clinical use of these antibiotics for the treatment of infections due to these microorganisms.

Overexpression of the adeB gene in clinical isolates of tigecycline-nonsusceptible Acinetobacter baumannii without insertion mutations in adeRS

Thirteen clinical isolates of multidrug-resistant Acinetobacter baumannii resistant to carbapenems (MRAB-C) with tigecycline nonsusceptibility were collected from individual patients in this study. None of the 13 isolates shared the same strain characteristics in molecular typing. All of them showed increased adeB transcription, as predicted. However, none of these tigecycline-nonsusceptible MRAB-C isolates were found to possess previously known adeRS mutations. Upregulation of adeB transcription may result from cross stimulation by other mechanisms.

In vitro activities of moxifloxacin and tigecycline against bacterial isolates associated with intraabdominal infections at a medical center in Taiwan, 2001-2006

A total of 569 nonduplicate isolates recovered from patients with community-onset or hospital-onset intraabdominal infections (IAIs) from 2001 to 2006 were studied. These included 28 Staphylococcus aureus and 541 Gram-negative isolates (33.6% Escherichia coli, 29.0% Klebsiella pneumoniae, 8.1% Acinetobacter baumannii, and 6.3% Pseudomonas aeruginosa). Minimum inhibitory concentrations (MICs) of the isolates to moxifloxacin, imipenem, and ciprofloxacin were determined using the agar dilution method and to tigecycline using the broth microdilution method. Extended-spectrum beta-lactamase (ESBL) producers were found in 15.5% (29 out of 182) of E. coli, 15.3% (24 out of 157) of K. pneumoniae, and 15.4% (2 out of 13) of K. oxytoca isolates. More than 85% of Enterobacteriaceae were susceptible to moxifloxacin, but this percentage was lower among E. coli (78%). The percentage of E. coli (K. pneumoniae) isolates that were not susceptible to moxifloxacin was 6% (0%) in 2001, 39% (17%) in 2003, and 21% (14%) in 2006. Tigecycline exhibited good in vitro activities against all S. aureus and >95% of all Enterobacteriaceae tested. Among the 24 isolates of ESBL-producing K. pneumoniae, 4 had tigecycline MICs > or = 2 microg/ml. Eighty percent of A. baumannii isolates exhibited tigecycline MICs of < or = 2 microg/ml. This study found that moxifloxacin and tigecycline exhibited good in vitro activity against bacterial isolates causing IAIs.

Comparative in vitro activity of tigecycline and nine other antibiotics against gram-negative bacterial isolates, including ESBL-producing strains

The enterobacteriaceae, especially Escherichia coli and Klebsiella spp., as well as Acinetobacter spp., are important agents of nosocomial infections in hospitalized patients. A total of 460 Gram-negative bacteria (GNb), were investigated for their susceptibility to tigecycline and 9 other antibiotics by the etest. ESBL production was inferred from ESBL etest phenotypes. All the GNb, including the ESBL-producers, were susceptible to tigecycline with MIC(90 )ranges of 0.25 to 2 microg/ml. Imipenem and meropenem were very active against ESBL and non-ESBL producers; mean MIC(90)s of 0.19 and 0.09 microg/ml and 0.05 microg/ml and 0.02 microg/ml, respectively. The MIC(90)s of imipenem and meropenem for the Acinetobacter spp. were 16 and >32 microg/ml, respectively with resistance rates of 64.3 and 66.1%. ESBL production was detected in 62% and 82.1% of the E. coli and K. pneumoniae isolates, respectively. Resistance to ciprofloxacin was higher among the ESBL-producing strains of E. coli and K. pneumoniae than the non-ESBL producers. Comparatively, tigecycline had excellent in vitro activities against ESBL-producing enterobacteriaceae and demonstrated superior activity against Acinetobacter spp. Increasing ESBL production and resistance to ciprofloxacin and gentamicin in enterobacteriaceae require careful selection of empirical therapy. Tigecycline holds promise as an alternative choice of therapy for infections caused by ESBL-producing isolates and multi-drug resistant Acinetobacter spp.

In-vitro activity of tigecycline against clinical isolates of Acinetobacter baumannii in Taiwan determined by the broth microdilution and disk diffusion methods

A total of 393 isolates of A. baumannii were collected from patients treated at 19 teaching hospitals in Taiwan. Minimum inhibitory concentrations (MICs) and inhibitory zone diameters for tigecycline were determined by the broth microdilution method and the disk diffusion method, respectively. The MIC results were interpreted using the US FDA tigecycline susceptibility breakpoints for Enterobacteriaceae (susceptible [S] <or=2 microg/mL; intermediate [I] 4 microg/mL; resistant [R] >or=8 microg/mL). The disk diffusion results were interpreted by criteria recommended by Jones et al. (S >or=16 mm; I 13-15 mm; R <or=12 mm) and also by those recommended by the US FDA for Enterobacteriaceae (S >or=19 mm; I 15-18 mm; R <or=14 mm). The percentages of susceptible, intermediate and resistant isolates determined by the broth microdilution method were 80.9%, 12.2%, and 6.9%, respectively. The rates of susceptible, intermediate and resistant isolates by the disk diffusion method using the criteria of Jones et al. were 88.3%, 9.9% and 1.8% and using the US FDA criteria were 44.0%, 51.7% and 4.3%. Using the criteria recommended by Jones et al., the total error rate of the disk diffusion method in comparison with the broth microdilution method was 14.2% (56/393). For routine susceptibility testing of tigecycline against A. baumannii the broth microdilution method, not the disk diffusion method, should be used due to the poor correlation of results between these two methods interpreted either by the Jones et al. or US FDA criteria.

Phenotypic and molecular characterization of Acinetobacter baumannii clinical isolates from nosocomial outbreaks in Los Angeles County, California

Multidrug-resistant Acinetobacter baumannii strains have increasingly resulted in nosocomial outbreaks worldwide, leaving limited options for treatment. To date, little has been reported on the antimicrobial susceptibilities and genomic profiles of A. baumannii strains from hospital outbreaks in the Greater Los Angeles area. In this study, we examined the susceptibilities and genetic profiles of 20 nonduplicate isolates of A. baumannii from nosocomial outbreaks in Los Angeles County (LAC) and determined their mechanisms of fluoroquinolone resistance. Antibiotic susceptibility testing indicated that the majority of these LAC isolates were not susceptible to 14 of the 17 antibiotics tested, with the exception of doxycycline, minocycline, and tigecycline. In particular, all isolates were found to be resistant to ciprofloxacin. Genomic DNA analysis revealed eight epidemiologically distinct groups among these 20 A. baumannii isolates, consistent with antibiotic susceptibility profiles. Sequencing analysis confirmed that concurrent GyrA and ParC amino acid substitutions in the "hot spots" of their respective quinolone resistance-determining regions were primarily responsible for the high-level ciprofloxacin resistance of these isolates. Antibiotic susceptibility testing using two efflux pump inhibitors suggested that the presence of efflux pumps was only a secondary contributor to ciprofloxacin resistance for some of the isolates. In summary, the present study has revealed good correlation between the antibiotic susceptibility profiles and genetic fingerprints of 20 clinical isolates from nosocomial outbreaks in Los Angeles County and has determined their mechanisms of fluoroquinolone resistance, providing an important foundation for continued surveillance and epidemiological analyses of emerging A. baumannii isolates in Los Angeles County hospitals.

Old antibiotics for infections in critically ill patients

PURPOSE OF REVIEW

The alarming epidemic of multidrug-resistant bacteria and the reluctance of the pharmaceutical industry to invest in the development of new antibiotics have forced clinicians to reintroduce forgotten antibiotics into their practice. This review highlights the effectiveness and safety of older antibiotics when used in the treatment of infections of critically ill patients.

RECENT FINDINGS

Polymyxins emerged as useful antibiotics for the treatment of infections due to multidrug-resistant Gram-negative bacteria, in particular Acinetobacter baumannii, Pseudomonas aeruginosa and Klebsiella pneumoniae. The nephrotoxicity and neurotoxicity associated with their use are less frequent and serious than previously reported. In addition, aerosolized polymyxins may be a useful weapon in the treatment of hospital-acquired pneumonia. Fosfomycin and chloramphenicol have a wide antimicrobial spectrum, are used extensively in Europe and Africa, respectively, and may have an expanded role in our antimicrobial arsenal. Fusidic acid remains active against various staphylococcal strains, while isepamicin (an aminoglycoside used in some European countries) is slightly more effective than amikacin against some Gram-negative bacteria.

SUMMARY

The declining investment of the pharmaceutical industry in the development of new antibiotics and the increasing antimicrobial resistance create a fertile ground for the study and, probably, revival of older antibiotics for use, especially in critically ill patients.

Rapid development of Acinetobacter baumannii resistance to tigecycline

A 53-year-old woman experienced a multidrug-resistant (MDR) Acinetobacter baumannii urinary tract infection 5 months after undergoing kidney and liver transplantation. The tigecycline minimum inhibitory concentration (MIC) for her A. baumannii isolate was 1.5 microg/ml; the patient received 2 weeks of therapy with intravenous tigecycline as a 100-mg loading dose followed by 50 mg every 12 hours, with no lapses in treatment and with resolution of the infection. Three weeks later, MDR A. baumannii was isolated from her sputum in the setting of clinical evidence of pneumonia, and tigecycline was restarted; the tigecycline MIC for the A. baumannii isolate was 2 microg/ml. At approximately the same time, the patient was found to have a paraspinal abscess and spinal osteomyelitis. Cultures of the abscess fluid grew A. baumannii with a tigecycline MIC of 24 microg/ml. A follow-up sputum culture again yielded A. baumannii, but with a tigecycline MIC of 24 microg/ml. Urine culture at that time also grew A. baumannii with a tigecycline MIC of 24 microg/ml. Clinicians should be aware that tigecycline MICs for A. baumannii isolates may increase during therapy with tigecycline after only brief exposure to the drug. Patients receiving tigecycline for Acinetobacter should be monitored for the development of clinical resistance, and isolates should be monitored for evidence of microbiologic resistance.

Non-fermentative Gram-negative bacteria

Over the past decade, non-fermenting Gram-negative bacteria have emerged as important opportunistic pathogens in the increasing population of patients who are immunocompromised by their disease or medical treatment. These bacteria are assisted by their ubiquitous distribution in the environment and have a propensity for multiple, intrinsic or acquired drug resistance. The infections that they cause now pose significant problems in terms of treatment and infection control, whilst the commonly observed rapid emergence of bacterial resistance to new antimicrobial compounds raises concerns regarding the clinical lifespan of these agents. Studies are urgently required to assess whether combination therapy can improve the long-term utility of new drugs in the treatment of patients infected with non-fermenters.

In Vitro activities of isepamicin, other aminoglycosides, and capreomycin against clinical isolates of rapidly growing mycobacteria in Taiwan

The in vitro activities of isepamicin against 117 Mycobacteria abscessus, 48 Mycobacterium fortuitum, and 20 Mycobacterium chelonae isolates were evaluated by a microdilution test. Isepamicin MIC(90)s were < or =16 microg/ml for the three species. Isepamicin was as active as amikacin and kanamycin and more active than tobramycin, capreomycin, gentamicin, and streptomycin.

Tigecycline: a new glycylcycline antimicrobial

Tigecycline is a new glycyclcycline antimicrobial recently approved for use in the USA, Europe and elsewhere. While related to the tetracyclines, tigecycline overcomes many of the mechanisms responsible for resistance to this class. It demonstrates favourable in vitro potency against a variety of aerobic and anaerobic Gram-positive and Gram-negative pathogens, including those frequently demonstrating resistance to multiple classes of antimicrobials. This includes methicillin-resistant Staphylococcus aureus, penicillin-resistant S. pneumoniae, vancomycin-resistant enterococci, Acinetobacter baumannii, beta-lactamase producing strains of Haemophilis influenzae and Moraxella catarrhalis, and extended-spectrum beta-lactamase producing strains of Escherichia coli and Klebsiella pneumoniae. In contrast, minimum inhibitory concentrations for Pseudomonas and Proteus spp. are markedly elevated. Tigecycline is administered parenterally twice daily. Randomised, controlled trials have demonstrated that tigecycline is non-inferior to the comparators for the treatment of complicated skin and skin structure infections, as well as complicated intra-abdominal infections. The most frequent and problematic side effect associated with its administration to date has been nausea and/or vomiting.

Susceptibility of acinetobacter strains isolated from deployed U.S. military personnel

The susceptibilities of 142 Acinetobacter baumannii-calcoaceticus complex isolates (95 from wounded U.S. soldiers deployed overseas) to 13 antimicrobial agents were determined by broth microdilution. The most active antimicrobial agents (> or =95% of isolates susceptible) were colistin, polymyxin B, and minocycline.