In vitro activity of antibiotics potentially effective against difficult-to-treat strains of Gram-negative rods: retrospective study

Bacterial resistance surveillance is one of the main outputs of microbiological laboratories and its results are important part of antimicrobial stewardship (AMS). In this study, the susceptibility of specific bacteria to selected antimicrobial agents was tested. The susceptibility of 90 unique isolates of pathogens of critical priority obtained from clinically valid samples of ICU patients in 2017-2021 was tested. 50% of these fulfilled difficult-to-treat resistance (DTR) criteria and 50% were susceptible to all antibiotics included in the definition. 10 Enterobacterales strains met DTR criteria, and 2 (20%) were resistant to colistin (COL), 2 (20%) to cefiderocol (FCR), 7 (70%) to imipenem/cilastatin/relebactam (I/R), 3 (30%) to ceftazidime/avibactam (CAT) and 5 (50%) to fosfomycin (FOS). For Enterobacterales we also tested aztreonam/avibactam (AZA) for which there are no breakpoints yet. The highest MIC of AZA observed was 1 mg/l, MIC range in the susceptible cohort was 0.032-0.064 mg/l and in the DTR cohort (incl. class B beta-lactamase producers) it was 0.064-1 mg/l. Two (13.3%) isolates of Pseudomonas aeruginosa (15 DTR strains) were resistant to COL, 1 (6.7%) to FCR, 13 (86.7%) to I/R, 5 (33.3%) to CAT, and 5 (33.3%) to ceftolozane/tazobactam. All isolates of Acinetobacter baumannii with DTR were susceptible to COL and FCR, and at the same time resistant to I/R and ampicillin/sulbactam. New antimicrobial agents are not 100% effective against DTR. Therefore, it is necessary to perform susceptibility testing of these antibiotics, use the data for surveillance (including local surveillance) and conform to AMS standards.

Metallo-beta-lactamases: mechanisms, treatment challenges, and future prospects

INTRODUCTION

Metallo-beta-lactamases (MBLs) are responsible for resistance to almost all beta-lactam antibiotics. Found predominantly in Gram-negative bacteria, they severely limit treatment options. Understanding the epidemiology, risk factors, treatment, and prevention of infections caused by MBL-producing organisms is essential to reduce their burden.

AREAS COVERED

The origins and structure of MBLs are discussed. We describe the mechanisms of action that differentiate MBLs from other beta-lactamases. We discuss the global epidemiology of MBL-producing organisms and their impact on patients' outcomes. By exposing the mechanisms of transmission of MBLs among bacterial populations, we emphasize the importance of infection prevention and control.

EXPERT OPINION

MBLs are spreading globally and challenging the majority of available antibacterial agents. Genotypic tests play an important role in the identification of MBL production. Phenotypic tests are less specific but may be used in low-resource settings, where MBLs are more predominant. Infection prevention and control are critical to reduce the spread of organisms producing MBL in healthcare systems. New combinations such as avibactam-aztreonam and new agents such as cefiderocol have shown promising results for the treatment of infections caused by MBL-producing organisms. New antibiotic and non-antibiotic agents are being developed and may improve the management of infections caused by MBL-producing organisms.

Activity of imipenem/relebactam and comparators against KPC-producing Klebsiella pneumoniae and imipenem-resistant Pseudomonas aeruginosa

PURPOSE

Relebactam is a novel β-lactamase inhibitor, which, when combined with imipenem/cilastatin, is active against both class A and class C β-lactamases. To evaluate in vitro antimicrobial activity of imipenem/relebactam against a collection of recent clinical isolates of carbapenem-non-susceptible P. aeruginosa and K. pneumoniae ST258 and ST512 KPC producers belonging to different lineages from hospitals in Southern Spain.

METHODS

Six hundred and seventy-eight isolates were tested: 265 K. pneumoniae (230 ST512/KPC-3 and 35 ST258/KPC-3) and 413 carbapenem-non-susceptible P. aeruginosa. Imipenem, piperacillin/tazobactam, ceftazidime, cefepime, aztreonam, ceftolozane/tazobactam, meropenem, amikacin, ciprofloxacin, colistin, and ceftazidime/avibactam were used as comparators against P. aeruginosa. Against K. pneumoniae ceftazidime, cefepime, aztreonam, and ceftolozane/tazobactam were not tested, and tigecycline was studied instead. MICs were determined in duplicate by broth microdilution according to EUCAST guidelines.

RESULTS

Imipenem/relebactam displayed potent in vitro activity against both sequence types of KPC-3-producing K. pneumoniae. MIC50 and MIC90 values were 0.25 mg/L and 1 mg/L, respectively, with percent of susceptible isolates >97%. Only three K. pneumoniae ST512/KPC-3 isolates and one ST258/KPC-3 were resistant to imipenem/relebactam. Relebactam sensitized 98.5% of K. pneumoniae isolates resistant to imipenem. The activity of imipenem/relebactam against P. aeruginosa was moderate (susceptibility rate: 62.7%). Analysis of the acquired and mutational resistome of isolates with high levels of resistance to imipenem/relebactam has not shown a clear association between them.

CONCLUSION

Imipenem/relebactam showed excellent activity against K. pneumoniae KPC-3. The activity of imipenem/relebactam against imipenem-resistant P. aeruginosa was moderate.

Co-transfer of IncFII/IncFIB and IncFII plasmids mediated by IS26 facilitates the transmission of mcr-8.1 and tmexCD1-toprJ1

PURPOSE

This study aimed to characterise the whole-genome structure of two clinical Klebsiella pneumoniae strains co-harbouring mcr-8.1 and tmexCD1-toprJ1, both resistant to colistin and tigecycline.

METHODS

K. pneumoniae strains TGC-02 (ST656) and TGC-05 (ST273) were isolated from urine samples of different patients hospitalised at separate times in 2021. Characterisation involved antimicrobial susceptibility testing (AST), conjugation assays, whole-genome sequencing (WGS), and bioinformatics analysis. Comparative genomic analysis was conducted on mcr-8.1-carrying and tmexCD1-toprJ1-carrying plasmids.

RESULTS

Both K. pneumoniae isolates displayed a multidrug-resistant phenotype, exhibiting resistance or reduced susceptibility to ampicillin, ampicillin/sulbactam, cefazolin, aztreonam, amikacin, gentamicin, tobramycin, ciprofloxacin, levofloxacin, nitrofurantoin, trimethoprim/sulfamethoxazole, apramycin, tigecycline and colistin. WGS analysis revealed that clinical strain TGC-02 carried the TmexCD1-toprJ1 gene on a 200-Kb IncFII/IncFIB-type plasmid, while mcr-8 was situated on a 146-Kb IncFII-type plasmid. In clinical strain TGC-05, TmexCD1-toprJ1 was found on a 300-Kb IncFIB/IncHI1B/IncR-type plasmid, and mcr-8 was identified on a 137-Kb IncFII/IncFIA-type plasmid. Conjugation experiments assessed the transferability of these plasmids. While transconjugants were not obtained for TGC-05 despite multiple screening with tigecycline or colistin, pTGC-02-tmex and pTGC-02-mcr8 from clinical K. pneumoniae TGC-02 demonstrated self-transferability through conjugation. Notably, the rearrangement of pTGC-02-tmex and pTGC-02-mcr8 via IS26-based homologous recombination was observed. Moreover, the conjugative and fusion plasmids of the transconjugant co-harboured the tmexCD1-toprJ1 gene cluster and mcr-8.1, potentially resulting from IS26-based homologous recombination.

CONCLUSION

The emergence of colistin- and tigecycline-resistant K. pneumoniae strains is concerning, and effective surveillance measures should be implemented to prevent further dissemination.

In silico prediction and a systematic toxicology-based in vivo investigation uncovering the mechanism of aquatic toxicity caused by beta-lactam antibiotics

Recently, beta-lactam antibiotics have gained attention as significant contributors to public health and environmental issues due to their potential toxicity. Our study employed machine learning to develop a model for assessing the aquatic toxicity of beta-lactam antibiotics on zebrafish. Notably, aztreonam (AZT), a synthetic monobactam and a subclass of beta-lactam antibiotics, demonstrated developmental effects in zebrafish embryos comparable to cephalosporins, indicating a potential for toxicity. Using a systems toxicology-based approach, we identified apoptosis and metabolic disorders as the primary pathways affected by AZT and its impurity F exposure. During the administration of monobactams, we noted that ctsbb, nos2a, and dgat2, genes associated with apoptosis and the metabolic pathway, exhibited significant differential expression. Molecular docking studies were conducted to ascertain the binding affinity between monobactam compounds and their potential targets-Ctsbb, Nos2a, and Dgat2. Furthermore, our research revealed that monobactams influence pre-mRNA alternative splicing, resulting in disruptions in the expression of genes involved in hair cells, brain, spinal cord, and fin regeneration (e.g., krt4, krt5, krt17, cyt1). Notably, we observed a correlation between the levels of rpl3 and rps7 genes, both important ribosomal proteins, and the detected alternative splicing events. Overall, this study enhances our understanding of the toxicity of beta-lactam antibiotics in zebrafish by demonstrating the developmental effects of monobactams and uncovering the underlying mechanisms at the molecular level. It also identifies potential targets for further investigation into the mechanisms of toxicity and provides valuable insights for early assessment of biological toxicity associated with antibiotic pollutants.

Treatment approaches for severe Stenotrophomonas maltophilia infections

PURPOSE OF REVIEW

Stenotrophomonas maltophilia is an emerged opportunistic pathogen. Intrinsic multidrug resistance makes treating infections caused by S. maltophilia a great clinical challenge. Herein, we provide an update on the most recent literature on treatment options for severe S. maltophilia infections.

RECENT FINDINGS

Trimethoprim-sulfamethoxazole (SXT) is recognized as the first-line therapy for S. maltophilia infections. However, its clinical use is based on good in vitro activity and favorable clinical outcomes, rather than on solid minimum inhibitory concentration (MIC) correlations with pharmacokinetic/pharmacodynamics (PK/PD) and/or clinical outcomes. The same is true for other treatment options like levofloxacin (LVX) and minocycline (MIN). Recent PK/PD studies question the current clinical breakpoints for SXT, LVX, and MIN. Based on this, the latest guidance issued by the Infectious Diseases Society of America (IDSA) recommends using these agents only as part of a combination therapy. Alternatively, novel therapeutic options such as cefiderocol (FDC) and ceftazidime-avibactam plus aztreonam (CZA-ATM) are suggested, based on limited but promising clinical data.

SUMMARY

PK/PD data and controlled clinical studies are needed to optimize current treatment options. Presently, combination therapy of SXT, LVX, MIN, or FDC, or monotherapy with CZA-ATM are recommended therapeutic options for severe-to-moderate S. maltophilia infections.

Antimicrobial Prophylaxis for Percutaneous Nephrolithotomy: Contemporary Practice Patterns

Background: Updated in 2019, the American Urological Association's (AUA) Best Practice Statement on Urologic Procedures and Antimicrobial Prophylaxis outlines prophylaxis for percutaneous nephrolithotomy (PCNL). Recent studies have challenged these recommendations. We hypothesized that endourologists do not routinely follow the AUA's statement on antibiotic use during PCNL and assessed their prescribing patterns. Methods: A 24-question survey was distributed to members of the Endourological Society. The primary outcome was adherence to the AUA's recommendations. Two multiple logistic regression analyses were performed with demographics and antibiotic preference as predictors of following the AUA. Results: A total of 51.4% of endourologists follow the AUA Best Practice Statement for antimicrobial prophylaxis of uncomplicated PCNL. No demographic data were predictive of following the AUA. 90.9% and 83.6% reported they have "never" used the first-line recommendation options of metronidazole and aztreonam, respectively. Preferred antibiotics were cephalosporins (uncomplicated 60%, complicated 52.6%), fluoroquinolones (13.3%, 7.2%), aminoglycosides (12.7%, 17.8%), penicillins (7.9%, 11.2%), carbapenems (0.6%, 0.7%), trimethoprim-sulfamethoxazole (2.4%, 5.9%), fosfomycin (0.6%, 0.7%), nitrofurantoin (2.4%, 2.6%), aztreonam (0%, 0.7%), and clindamycin (0%, 0.7%). For uncomplicated PCNL, 63.1% prescribe ≤24 hours of perioperative antibiotics. For complicated PCNL, 16.2% prescribe ≤24 hours of perioperative antibiotics, while 20.4% begin antibiotics 7 or more days prior. Conclusions: Nearly half of respondents do not follow the AUA's recommendations for antibiotic choice for PCNL. Few endourologists prescribe 7 days of preoperative antibiotics for complicated PCNL despite supporting data. Metronidazole and aztreonam are rarely used as a first-line antibiotic choice for PCNL and their roles needs to be further evaluated as first-line prophylaxis recommendations. Updates on antibiotic recommendations for PCNL are needed based on current literature, antimicrobial stewardship, and contemporary practice patterns.

Defining standard and high dosages for β-lactam agents administered by intermittent, prolonged or continuous infusion: a PK/PD simulation study

BACKGROUND

The new definitions of antimicrobial susceptibility categories proposed by EUCAST in 2020 require the definition of standard and high dosages of antibiotic. For injectable β-lactams, standard and high dosages have been proposed for short-infusion regimens only.

OBJECTIVES

To evaluate dosages for β-lactams administered by prolonged infusion (PI) and continuous infusion (CI).

METHODS

Monte Carlo simulations were performed for seven injectable β-lactams: aztreonam, cefepime, cefotaxime, cefoxitin, ceftazidime, piperacillin and temocillin. Various dosage regimens based on short infusion, PI or CI were simulated in virtual patients. Pharmacokinetic (PK) profiles and PTAs were obtained based on reference population PK models, as well as PK/pharmacodynamic targets and MIC breakpoints proposed by EUCAST. Alternative dosage regimens associated with PTA values similar to those of recommended dosages up to the breakpoints were considered acceptable.

RESULTS

Adequate PTAs were confirmed for most EUCAST short-infusion dosage regimens. A total of 9 standard and 14 high dosages based on PI (3 to 4 h) or CI were identified as alternatives. For cefepime and aztreonam, only PI and CI regimens could achieve acceptable PTAs for infections caused by Pseudomonas spp.: 2 g q8h as PI of 4 h or 6 g/24 h CI for cefepime; 2 g q6h as PI of 3 h or 6 g/24 h CI for aztreonam.

CONCLUSIONS

These alternative standard and high dosage regimens are expected to provide antibiotic exposure compatible with new EUCAST definitions of susceptibility categories and associated MIC breakpoints. However, further clinical evaluation is necessary.

Clinical outcomes in elderly patients with infections caused by NDM-producing Klebsiella pneumoniae: results from a real-life retrospective single center study in an endemic area

Real-life outcomes data for elderly patients with infections caused by Klebsiella pneumoniae producing New Delhi metallo-beta-lactamase (NDM-Kp) are lacking. We conducted a retrospective cohort study enrolling 33 consecutive adult patients (mean age 77.4 years; 48.5% males; mean Charlson Comorbidity Index-CCI 5.9) hospitalized for NDM-Kp infections during a 24-month period in an Italian highly endemic area. 78.8% were admitted to Internal Medicine ward. 45.4% of patients had bloodstream infections (BSI), 39.4% urinary tract infections (UTI) without BSI, 9.1% respiratory tract infections and 6.1% intra-abdominal infections. 93.9% had rectal colonization.Adequate definitive antibiotic therapy (mainly represented by aztreonam plus ceftazidime/avibactam) was provided to 36.4% of cases. Mean age and CCI of patients adequately treated were significantly lower than those inadequately treated (71.2 vs 80.9 years, p = 0.041, and 4.6 vs 6.7, p = 0.040, respectively). Patients adequately treated had a mean hospitalization length significantly higher (28 vs 15 days, p = 0.016). The overall 30-day survival rate of patients adequately and inadequately treated was 83.3% and 57.1%, respectively: this difference was not statistically significant. Mean age and CCI of 22 patients who survived at 30 days were lower than those of 11 patients who died (73.7 vs 84.8 years, p = 0.003, and 5.3 vs 7.2, p = 0.049, respectively). Twelve survivors received an inadequate therapy: 8/12 had UTI. Six of nine patients inadequately treated who died within 30 days, died before microbiological diagnosis. Our study provides real-life data on outcomes of elderly and multimorbid patients hospitalized for infections caused by NDM-Kp. Further studies with larger sample size are warranted.

Direct challenges are the gold standard for most antibiotic allergy evaluations

Antibiotic allergies are frequently encountered in clinical practice, and delabeling of these allergies has individual and public health benefits. This review focuses on the evidence supporting graded challenges without preceding skin testing in adult and pediatric patients to the major groups of antibiotics including penicillins, cephalosporins, sulfamethoxazole, fluoroquinolones, tetracyclines, macrolides, metronidazole, carbapenems, and aztreonam. The cost savings, time savings, and evidence for performing graded challenges outside of an allergy/immunology office are also reviewed for graded challenges to penicillins.

Impact of an Inpatient Allergy Guideline on β-Lactam and Alternative Antibiotic Use

BACKGROUND

A guideline identifying when inpatients with penicillin or cephalosporin antibiotic allergy labels (PCAAL) can receive β-lactam antibiotics increased β-lactam receipt at a large northeastern US health care system.

OBJECTIVE

To report outcomes of implementing a similar guideline and electronic order set (OS) at an independent academic health care system.

METHODS

Penicillin/cephalosporin receipt (percentage of inpatients receiving full doses) and alternative antibiotic use (days of therapy per 1000 patient-days [DOT/1000PD]) were compared over 3 periods before (February 1, 2017, to January 31, 2018) and after guideline implementation (February 1, 2018, to January 31, 2019), and after OS implementation (February 1, 2019, to January 31, 2020) among inpatients with PCAAL admitted on medical services with access to guideline/OS and education (Medical-PCAAL, n = 8721), surgical services with access to guideline/OS without education (Surgical-PCAAL, n = 5069), and obstetrics/gynecology services without interventions (Ob/Gyn-PCAAL, n = 798) and inpatients without PCAAL admitted on the same services (Medical-No-PCAAL, n = 50,840; Surgical-No-PCAAL, n = 29,845; Ob/Gyn-No-PCAAL, n = 6109). χ2 tests were used to compare categorical variables, and analysis of variance was used to compare continuous and interrupted time series analyses (ITSA) to investigate the guideline/OS implementation effect on penicillin/cephalosporin receipt.

RESULTS

In the Medical-PCAAL group, penicillin/cephalosporin receipt increased (58%-68%, P < .001), specifically for cefazolin (8%-11%, P = .02) and third- to fifth-generation cephalosporins (43%-48%, P = .04), and aztreonam use decreased (12 DOT/1000PD, P = .03). In the Medical-No-PCAAL group, penicillin/cephalosporin receipt increased (88%-90%, P = .004), specifically for penicillin (40%-44%, P < .001), without changes in aztreonam use. Significant changes were not observed in these outcomes on surgical or obstetrics/gynecology services. Per ITSA, guideline/OS implementation was associated with increased penicillin/cephalosporin receipt in the Medical-PCAAL group only.

CONCLUSION

Guideline and OS implementation was associated with improved antibiotic stewardship on inpatient services that also received allergy education.

Multi-drug resistance pattern of bacterial isolates from urinary tract infection

In the community and among hospitalized patients, urinary tract infections (UTIs) rank as the most common bacterial infections. The researchers processed urine samples obtained from affiliated hospitals of Peshawar Medical College. The samples were examined under a microscope to assess the presence of bacteria, pus cells and red blood cells. Following this, the samples were inoculated on MacConkey and blood agar and subsequent antibiotic susceptibility testing was conducted. The findings revealed that 35.9% of hospitalized patients and 16.9% of outpatients were diagnosed with UTIs. Furthermore, 82.2% of the identified UTIs were found to be multidrug-resistant (MDR), with MDR Escherichia coli accounting for 77% of cases. Trimethoprim sulfamethazine (26.8%), penicillin (0%), cefepime (27.8%), cefotaxime (23.7%), aztreonam (2.1%), meropenem (86.6%), ciprofloxacin (51.5%), amoxicillin/clavulanic acid (37.1%), nitrofurantoin (70.1%), gentamycin (73%), ceftazidime (19.5%), levofloxacin (51.5%) and ceftriaxone (25.77%) were subjected to antibiotic susceptibility testing. It is concerning that among the 13 antibiotics examined, solely nitrofurantoin displayed oral efficacy as an effective treatment choice for UTIs.

Conjugates of monocyclic β-lactams and siderophore mimetics: a patent evaluation (WO2023023393)

INTRODUCTION

β-Lactams, which include monobactams, remain the most important class of antibiotics worldwide. Aztreonam, the only monobactam in clinical use, has remarkable activity against many Gram-negative bacteria, but limited activity against some of the most problematic multidrug-resistant (MDR) pathogens, such as MDR Pseudomonas aeruginosa and Acinetobacter baumannii co-expressing extended-spectrum- and metallo-β-lactamases, which can inactivate aztreonam by hydrolysis.

AREAS COVERED

Structurally novel siderophore-conjugated aztreonam derivatives with improved antibacterial properties against several high-priority pathogens are claimed. This invention reports that sidechain extension of aztreonam is tolerated; the coupling of its aminothiazoloxime carboxylic acid part with a siderophore mimetic significantly improved the antibacterial activity against several problematic strains, including MDR A. baumannii isolates with carbapenemase/cephalosporinase activity.

EXPERT OPINION

Finding new strategies to tackle bacterial resistance to β-lactam antibiotics is critical. Considering that β lactams are validated and safe drugs, this research may stimulate the field to develop new ideas in the arena of antimicrobial drug discovery, particularly with respect to siderophore mimetics.

Contemporary Evaluation of Tebipenem In Vitro Activity against Enterobacterales Clinical Isolates Causing Urinary Tract Infections in US Medical Centers (2019-2020)

Tebipenem pivoxil is an oral broad-spectrum carbapenem. This study evaluated the activity of tebipenem and comparators against UTI Enterobacterales from US hospitals (2019-2020). 3,576 Enterobacterales causing UTI in 52 centers in 9 US Census Divisions were included. Susceptibility testing followed the CLSI broth microdilution method. Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis with an MIC of ≥2 μg/mL for ceftazidime, ceftriaxone, and/or aztreonam were designated ESBL. Isolates were also grouped based on MDR phenotype. Tebipenem, meropenem, and ertapenem had MIC₉₀ against Enterobacterales of 0.06 μg/mL, 0.06 μg/mL and 0.03 μg/mL, respectively. Low susceptibility results for aztreonam (87.1% susceptible), cefazidime (88.1%), ceftriaxone (84.8%), and other agents were observed. Tebipenem and ertapenem were equally potent (MIC₉₀, 0.015 to 0.03 μg/mL) against E. coli and K. pneumoniae, whereas ertapenem showed an MIC 8-fold lower than tebipenem against P. mirabilis. Oral agents, such as amoxicillin-clavulanate, levofloxacin, and trimethoprim-sulfamethoxazole, showed elevated nonsusceptibility rates in the Middle Atlantic region (26, 45, 47, and 41%, respectively). ESBL prevalence varied from 7% to 16%, except in the Middle Atlantic region (42%). The carbapenems were active against ESBL and MDR isolates (93.7 to 96.8% susceptible). Elevated rates of ESBL in UTI pathogens in US hospitals were noted as well as a uniform in vitro potency (MIC₉₀) of tebipenem and the intravenous carbapenems, regardless of phenotype. IMPORTANCE The occurrence of urinary-tract Enterobacterales pathogens producing ESBL enzymes in community and nosocomial settings continues to increase, as does the coresistance to fluoroquinolones, trimethoprim-sulfamethoxazole and nitrofurantoin often exhibited by these pathogens. This scenario complicates the clinical empirical and guided management of UTI by precluding the use of oral and many intravenous options. Oral options appear compromised even among some ESBL-negative isolates, against which the use of parenteral agents may be required. In addition, the interregional variability of susceptibility results of US UTI pathogens provides a less predictable susceptibility pattern to inform empirical treatment decisions. This study evaluated the in vitro activity of tebipenem against contemporary uropathogens, including those resistant to currently available oral options.

Pathogenicity and transcriptome analysis of a strain of Vibrio owensii in Fenneropenaeus merguiensis

Vibrio is an important conditional pathogen in shrimp aquaculture. This research reported a dominant bacteria strain E1 isolated from a shrimp tank with the method of biofloc culture, which was further identified as Vibrio owensii. To understand the interaction between V. owensii and the host shrimp, we studied the pathogenicity of the V. owensii and the molecular mechanisms of the Fenneropenaeus merguiensis immunity during the Vibrio invasion. Drug susceptibility tests showed that V. owensii was resistant to antibiotics streptomycin oxacillin, tetracycline, minocycline, and aztreonam, but highly sensitive to cefazolin, cefotaxime, and ciprofloxacin, and moderately sensitive to cefotaxime, ampicillin, and piperacillin. Lethal concentration 50 (LC₅₀) test was performed to evaluate the toxicity of V. owensii to F. merguiensis. The LC₅₀ of V. owensii infected F. merguiensis after 24, 48, 72, 96, 120, 144 and 168 h were 1.21 × 10⁷, 1.68 × 10⁶, 6.36 × 10⁵, 2.15 × 10⁵, 7.58 × 10⁴, 5.55 × 10⁴ and 4.33 × 10⁴ CFU/mL. In order to explore the molecular response mechanism of F. merguiensis infected with V. owensii, the hepatopancreas of F. merguiensis were sequenced at 24 hpi and 48 hpi, and a total 40,181 of unigenes were obtained. Through comparative transcriptomic analysis, 86 differentially expressed genes (DEGs) (including 38 up-regulated DEGs, and 48 down-regulated DEGs) and 305 DEGs (including 150 up-regulated DEGs, and 155 down-regulated DEGs) were identified at 24 hpi and 48 hpi, respectively. Annotation and classification analysis of these 391 DEGs showed that most of the DEGs were annotated to metableolic and immune pathways, which indicated that F. merguiensis responded to the invasion through the regulation of material metableolism and immune system genes during V. owensii infection. In the KEGG enrichment analysis, some pathways related to immune response were significantly influenced by V. owensii infection, including phagosome, MAPK signalling pathway and PI3K-Akt signalling pathway. In addition, some pathways related to the warburg effect were also significantly enriched after V. owensii infection, including pyruvate metableolism, glycolysis/gluconeogenesis, and citrate cycle (TAC cycle). Further analysis showed that C-type lectins and ficolin were also play important roles in the immune response of F. merguiensis against V. owensii infection. The current research preliminarily revealed the immune response of F. merguiensis to V. owensii infection at the molecular level, which provided valuable information to further understand the disease control and the interaction between shrimp and Vibrio.

Antibiotic-Resistant Bacteria in Drinking Water from the Greater Accra Region, Ghana: A Cross-Sectional Study, December 2021-March 2022

With safely managed water accessible to only 19% of the population in Ghana, the majority of its residents are at risk of drinking contaminated water. Furthermore, this water could be a potential vehicle for the transmission of antimicrobial-resistant bacteria. This study assessed the presence of bacteria and the antibiotic resistance profile of Escherichia coli and Pseudomonas aeruginosa in drinking-water sources using membrane filtration and Kirby-Bauer disc diffusion methods. A total of 524 water samples were analyzed for total coliforms, total heterotrophic bacteria, E. coli and P. aeruginosa. Samples included sachets, bottled water, tap water, borehole and well water. Most of the sachet and bottled water samples were within the limits of Ghana's standards for safe drinking water for the parameters tested. Over 50% of tap and borehole water was also free of E. coli and P. aeruginosa. Overall, of 115 E. coli isolates from tap and ground water samples, most were resistant to cefuroxime (88.7%), trimethoprim-sulfamethoxazole (62.6%) and amoxicillin-clavulanate (52.2%). P. aeruginosa isolates were most resistant to aztreonam (48%). Multidrug resistance was predominantly seen among E. coli isolates (58%). Evidence from this study calls for routine antimicrobial resistance surveillance in drinking water across the country and additional treatment of water sources at household levels.

Factors associated with recruitment success in the phase 2a study of aztreonam-avibactam development programme: a descriptive qualitative analysis among sites in Spain

OBJECTIVE

Successful clinical trials are subject to recruitment. Recently, the REJUVENATE trial, a prospective phase 2a open-label, single-arm interventional clinical trial conducted within the Innovative Medicines Initiative-supported Combatting Bacterial Resistance in Europe-Carbapenem Resistance project, was published, with 85% of the recruitment performed in Spain. We analysed the recruitment success in this trial by establishing a model of recruitment practice.

METHODS

A descriptive qualitative study was performed from May 2016 to October 2017 at 10 participating Spanish centres. Data were extracted from: (1) feasibility questionnaires to assess the centre's potential for patient enrolment; (2) delegation of responsibility records; (3) pre-screening records including an anonymised list of potentially eligible and (4) screening and enrolment records. A descriptive analysis of the features was performed by the participating centre. Pearson's and Spearman's correlation coefficients were calculated to determine factors of recruitment success.

RESULTS

The highest recruitment rate was observed in Hospitals 3 and 6 (58.8 and 47.0 patients per month, respectively). All the study teams were multidisciplinary with a median of 15 members (range: 7-22). Only Hospitals 3, 5 and 6 had dedicated nursing staff appointed exclusively to this study. Moreover, in those three hospitals and in Hospital 9, the study coordinator performed exclusive functions as a research planner, and did not assume these functions for the other hospitals. The univariate analysis showed a significant association between recruitment success and months of recruitment (p=0.024), number of staff (p<0.001), higher number of pharmacists (p=0.005), infectious disease specialists (p<0.001), the presence of microbiologist in the research team (p=0.018) and specifically dedicated nursing staff (p=0.036).

CONCLUSIONS

The existence of broad multidisciplinary teams with staff dedicated exclusively to the study as well as the implementation of a well-designed local patient assessment strategy were the essential optimisation factors for recruitment success in Spain.

TRIAL REGISTRATION NUMBER

NCT02655419; EudraCT 2015-002726-39; analysis of pre-screened patients.

Panton-Valentine leukocidin is not the primary determinant of outcome for Staphylococcus aureus skin infections: evaluation from the CANVAS studies

The impact of Panton-Valentine leukocidin (PVL) on the severity of complicated skin and skin structure infections (cSSSI) caused by Staphylococcus aureus is controversial. We evaluated potential associations between clinical outcome and PVL presence in both methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) isolates from patients enrolled in two large, multinational phase three clinical trials assessing ceftaroline fosamil for the treatment of cSSSI (the CANVAS 1 and 2 programs). Isolates from all microbiologically evaluable patients with monomicrobial MRSA or MSSA infections (n = 473) were genotyped by PCR for pvl and underwent pulsed-field gel electrophoresis (PFGE). Genes encoding pvl were present in 266/473 (56.2%) isolates. Infections caused by pvl-positive S. aureus were associated with younger patient age, North American acquisition, and presence of major abscesses (P<0.001 for each). Cure rates of patients infected with pvl-positive and pvl-negative S. aureus were similar overall (93.6% versus 92.8%; P = 0.72), and within MRSA-infected (94.5% vs. 93.1%; P = 0.67) and MSSA-infected patients (92.2% vs. 92.7%; P = 1.00). This finding persisted after adjustment for multiple patient characteristics. Outcomes were also similar when USA300 PVL+ and non-USA300 PVL+ infections were compared. The results of this contemporary, international study suggest that pvl presence was not the primary determinant of outcome in patients with cSSSI due to either MRSA or MSSA.

Use of cephalexin-aztreonam-arabinose agar for selective isolation of Enterococcus faecium

Cephalexin-aztreonam-arabinose agar (CAA), a new selective agar, was examined in comparison with nalidixic acid-colistin agar for the differentiation of Enterococcus faecium from other enterococci and the ability to isolate the organism from feces. Two hundred sixteen enterococcus isolates and a variety of gram-positive and gram-negative control strains were inoculated onto both media. All control strains of E. faecium were easily differentiated from Enterococcus faecalis and Enterococcus durans on the basis of arabinose fermentation on CAA. Differentiation of E. faecium from other enterococci or Streptococcus bovis was not possible on nalidixic acid-colistin agar. Increased isolation of E. faecium was demonstrated on CAA when both media were compared for the isolation of the organism from feces. CAA has been shown to possess excellent differential and selective features allowing the simple and effective isolation of E. faecium from heavily contaminated sites.

Aztreonam selective agar for gram positive bacteria

Aztreonam blood agar, a new selective medium for Gram positive aerobic bacteria, was evaluated in comparison with conventional media for skin swabs. Aztreonam agar increased the number of isolates of Staphylococcus aureus by 17%. By producing purer growths on primary isolation, it significantly speeded up the identification and sensitivity testing of staphylococci and streptococci. All major Gram positive aerobic pathogens grow on this medium. Aztreonam agar is now an established addition to our culture media. It is used for swabs which are likely to have a mixed Gram positive and Gram negative flora, such as ears, burns, ulcers, and for the sputa of patients with cystic fibrosis.

Compatibility of clindamycin phosphate with aztreonam in polypropylene syringes and with cefoperazone sodium, cefonicid sodium, and cefuroxime sodium in partial-fill glass bottles

The stability and compatibility of clindamycin phosphate admixed with four beta-lactams, an experimental monobactam (aztreonam), and three cephalosporins (cefoperazone sodium, cefonicid sodium, and cefuroxime sodium), were studied. Aztreonam alone and the combination of clindamycin phosphate-aztreonam were prepared in duplicate polypropylene syringes. Each cephalosporin antibiotic as well as the three clindamycin phosphate-cephalosporin combinations were admixed in duplicate 100 ml partial-fill glass bottles containing either dextrose 5% in water or NaCl 0.9%. All solutions were examined, antibiotic concentrations were determined, and pH was measured at the time of admixture and 1, 4, 8, 12, 24, and 48 hours later. The solutions were maintained at room temperature under fluorescent lighting for the length of the study. Antibiotic concentrations were determined by drug-specific high performance liquid chromatographic assays. Significant instability or incompatibility was defined as a decrease in concentration of greater than ten percent relative to the initial concentration measured at the time of admixture. All antibiotics were stable for 48 hours. In the combination studies, clindamycin was stable for 48 hours, both in partial-fill glass bottles and syringes. Aztreonam, cefoperazone, cefonicid, and cefuroxime were also stable for 48 hours.

Comparative activity of the penem antibiotic Sch 34343 against gram-negative and gram-positive bacteria with special reference to multiresistant strains

A new penem antibiotic, Sch 34343, was shown to be active against a large number of Gram-positive bacteria. The drug inhibited penicillinase-positive and -negative staphylococci equally well, being five times more active than cefamandole and ten times more active than methicillin. Most methicillin-resistant staphylococci were inhibited by concentrations between 0.25 and 4 mg/l, but a small group of highly resistant strains were observed. Sch 34343 was eight times less active than ampicillin and penicillin G, but as active as piperacillin against enterococci. The drug showed excellent activity against various streptococci. Sch 34343 was as bactericidal as flucloxacillin, ampicillin and penicillin G against staphylococci, enterococci and streptococci, respectively, in killing kinetic tests. Enterobacteriaceae susceptible to third-generation cephalosporins were approximately five times less susceptible to Sch 34343, but MICs were far below the susceptibility breakpoint. Sch 34343 was equally active against Citrobacter and Enterobacter strains that were highly resistant to third-generation cephalosporins and to aztreonam. Together with thienamycin, this drug seems to be a good alternative for the treatment of infections caused by bacteria resistant to third-generation cephalosporins and to aztreonam.

Aztreonam versus gentamicin, each with clindamycin, in the treatment of endometritis

A randomized comparison of aztreonam (2 g intravenously every eight hours) versus gentamicin (1.5 mg/kg intravenously every eight hours), each with clindamycin (600 mg intravenously every six hours), was performed in 119 patients with endometritis after cesarean section. Patients in both groups had similar risk factors. Genital cultures revealed an average of 3.0 isolates per specimen. Eighty-five aerobic gram-negative rods were isolated from 57 (48%) patients. All were susceptible to both aztreonam and gentamicin. Of 133 anaerobic isolates, 131 (98%) were susceptible to clindamycin. The failures in the aztreonam group were associated with a wound abscess and with an enterococcal bacteremia. Of the six failures in the gentamicin group, two were associated with persistent isolation of enteric bacilli. In the other four failures, no explanation was evident. Side effects occurred in four patients, (three diarrhea, one allergic reaction). All were self-limited and appeared to be due to clindamycin. No patient showed nephrotoxicity. When used in combination with clindamycin, aztreonam gave clinical results similar to gentamicin.

Antimicrobial therapy of bacterial sepsis in the newborn infant

Septicemia continues to be an important cause of neonatal morbidity and mortality. The bacteria most commonly responsible are group B beta-hemolytic streptococci and Escherichia coli, but regional differences exist. Recently sepsis caused by Staphylococcus epidermidis has occurred with increasing frequency in several neonatal intensive care units. Other organisms are less commonly responsible. The choice of antibiotics for suspected sepsis is based on the possible organisms involved and their antibiotic susceptibility patterns, which vary from hospital to hospital and at different times in the same hospital. Currently recommended initial therapy consists of a penicillin and an aminoglycoside, usually ampicillin and gentamicin. The addition of vancomycin is indicated when staphylococcal septicemia is suspected. During outbreaks of neonatal sepsis caused by aminoglycoside-resistant gram-negative bacteria, the use of third-generation cephalosporins or acylaminopenicillins may be appropriate, depending on the results of susceptibility tests. Continuing efforts to develop antibiotics for the treatment of neonatal sepsis are warranted.

In vitro activity of aztreonam--a new monocyclic beta-lactam antibiotic

The in vitro antibacterial activity of aztreonam (SQ 26776), a new beta-lactam antibiotic, was measured by the agar dilution technique. Aztreonam is known to have a narrow spectrum with activity only against Gram negative bacteria. The strains tested were 223 clinical isolates from blood cultures obtained at Rigshospitalet, Copenhagen, Denmark. Its activity against E. coli, Klebsiella spp., Proteus spp., Enterobacter spp., Citrobacter, Salmonella typhimurium and Serratia marcescens was satisfactory with MIC values normally below 0.5 mg/l. However, six out of 135 strains of E. coli showed surprisingly high MIC values of eight and 16 mg/l. The activity against Pseudomonas spp. and Acinetobacter spp. were limited, but the majority were inhibited by concentrations of aztreonam between 2.0 and 8.0 mg/l. The MIC values for the tested anaeobic bacteria were high, ranging from 8.0 to above 512 mg/l. With its narrow spectrum of activity, aztreonam seems to be a valuable addition to the antibiotic arsenal. Clinical studies will determine its real value.

Antibiotic monitoring in body fluids

Analytical procedures recently described for the quantitative determination of antibiotics in body fluids are reviewed. High-performance liquid chromatography (HPLC) and immunoassays appear as an alternative to current microbiological assays. HPLC has been applied to most antibiotics in clinical use and a major part of the review deals with this technique. Attention is given to sample pretreatment, characteristics of chromatography and detection, and limit of sensitivity. Non-isotopic immunoassays have been essentially applied to aminoglycosides and vancomycin and are also reviewed. Advantages and drawbacks of HPLC and immunoassays are presented.

In vitro activities of Ro 17-2301 and aztreonam compared with those of other new beta-lactam antibiotics against clinical isolates of Pseudomonas aeruginosa

The in vitro activities of Ro 17-2301 and aztreonam against 191 Pseudomonas aeruginosa isolates were compared with those of five other beta-lactam antibiotics. Both compounds showed activities comparable to that of ceftazidime and were bactericidal. They were as effective against gentamicin-or carbenicillin-resistant isolates as against susceptible ones.

Stability of intravenous admixtures of aztreonam and ampicillin

The stability of aztreonam and ampicillin in intravenous admixtures containing both drugs was studied. Each of the following drugs and combinations of drugs was added to both 5% dextrose injection and 0.9% sodium chloride injection: aztreonam 10 and 20 mg/mL, ampicillin sodium 5 and 20 mg/mL, aztreonam 20 mg/mL and ampicillin sodium 20 mg/mL, aztreonam 20 mg/mL and ampicillin sodium 5 mg/mL, aztreonam 10 mg/mL and ampicillin sodium 20 mg/mL, and aztreonam 10 mg/mL and ampicillin sodium 5 mg/mL. One of each of these admixtures was stored at 25 degrees C for 48 hours and 4 degrees C for seven days. At various storage times the admixtures were inspected for visual changes and 2-mL samples were examined microscopically for crystalline and particulate matter, tested for pH, and assayed by high-performance liquid chromatography. No visual changes were observed. In the two-drug solutions, pH was influenced by concentrations of the two drugs and stability of the drugs was influenced by the solution pH. The pH of single-drug aztreonam admixtures did not change during storage, but the pH of single-drug and two-drug admixtures containing ampicillin decreased. In single-drug admixtures, aztreonam loss under both storage conditions was less than 10% but ampicillin loss was more than 10% in 0.9% sodium chloride injection and more than 50% in 5% dextrose injection. The stability of ampicillin was increased in the presence of aztreonam, and the stability of aztreonam was decreased in the presence of ampicillin.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of aztreonam on the colon microflora in patients undergoing colorectal surgery

Aztreonam was given intravenously at a dose of 1 g at induction of anaesthesia, followed by subsequent doses of 1 g at eight hour intervals during 48 hours to 20 patients undergoing colorectal surgery. A series of serum and faecal specimens were taken for analysis of aztreonam concentrations. Tissue samples from the gut wall were taken at surgery. The maximum serum concentrations (mean value 114.7 mg/l) during surgery were reached 15 minutes after aztreonam administration. The aztreonam concentration in the tissue samples varied from 4.1-28.3 mg/kg and the concentration in the faecal samples from 0.4-34.4 mg/kg. Faecal samples were also collected during the investigation period for cultivation of aerobic and anaerobic bacteria. Enterobacteria were suppressed significantly during the prophylaxis period and there was a significant increase of staphylococci in ten of the patients. Three of these patients developed postoperative wound infections with staphylococci. Among the anaerobic bacteria, only minor changes were observed during the same period. After two weeks, the microflora was normalized in all patients. Five postoperative infections including an anastomose dehiscence in one patient occurred.

[Comparative in vitro activity of 2 monobactams (RO 172301 (AMA 1080)and aztreonam), ceftazidime and cefotaxime on Gram-negative bacilli]

In vitro activities of two monobactams (RO 172301 and aztreonam), ceftazidime and cefotaxime against 739 bacterial strains belonging to different species of Gram negative aero-anaerobic bacilli were studied comparatively. Strains were studied according to their resistance phenotype to beta-lactams. Minimal inhibitory concentrations (MIC) of the four antibiotics were determined using the agar dilution method. RO 172301 and aztreonam exhibited a similar activity against P. aeruginosa with a MIC around 2 mg/l for 50% of strains and around 4 mg/l for 90% of strains. As compared to the two monobactams, ceftazidime was more active and cefotaxime less active (one halving dilution either way). Activity of antibiotics was not dependent upon the mechanism of resistance to beta-lactams, except for strains producing a constitutive cephalosporinase. Against Enterobacteriaceae, RO 172301 proved slightly more active than aztreonam and cefotaxime; ceftazidime was the least active drug. Only 12 of the 739 strains tested (1.6%) had a MIC for RO 172301 above 32 mg/l. The percentage of resistant strains was 2.4% for aztreonam and ceftazidime and 8.8% for cefotaxime.

Penetration of aztreonam into human cerebrospinal fluid in the presence of meningeal inflammation

Cerebrospinal fluid of aztreonam were measured in 11 patients with meningeal inflammation. Two to eight hours after a single 2 gm intravenous dose, CSF aztreonam levels ranged from 0.76 to 16.6 mg/l. The mean CSF concentration in four patients with viral meningitis was 1.28 mg/l, which was lower than the mean concentration of 7.2 mg/l in the five with bacterial, cryptococcal or carcinomatous meningitis. Two patients with infected subdural drains were also sampled serially and had CSF levels greater than 1 mg/l between 1 and 8 h post dose. Penetration of aztreonam into the CSF in the presence of meningeal inflammation appears adequate to warrant therapeutic trials in patients infected with susceptible organisms.

Aztreonam in human serum and breast milk

Serum and milk concentrations of aztreonam were studied in 12 lactating, healthy subjects over the 8 h period after the administration of a single intramuscular or intravenous 1 g dose. Milk concentrations of aztreonam were found to be much lower than serum concentrations at all time points after both routes of injection. Peak milk concentrations of aztreonam averaged less than 1% of peak serum concentrations. Times to peak concentrations averaged 6 and 10 times longer in milk than in serum after intramuscular and intravenous injections, respectively. The low milk levels, as well as the previously determined poor oral absorption of aztreonam, suggest a low risk of untoward effects in the nursing infant.

Aztreonam in the therapy of nosocomial infections in patients with impaired host defenses

A clinical trial was carried out to evaluate the effectiveness of treatment with aztreonam in hospital-acquired infections. Twenty patients (13 men and 7 women) with impaired host defenses and nosocomial infections were treated with aztreonam at a dosage ranging 4 and 6 g/day I.V. at 8 or 12-hour intervals. Average length of therapy was 10.35 +/- 4.61 days. The isolated organisms were as follows: Escherichia coli (5), Pseudomonas aeruginosa (5), Klebsiella pneumoniae (3), Enterobacter cloacae (1), Proteus mirabilis (2), Proteus vulgaris (1), Acinetobacter anitratus (1), Serratia marcescens (1), Citrobacter freundii (1), Bacteroides fragilis (3), Bacteroides melaninogenicus (1). In 5 patients (25%) a mixed infection was observed. Sixteen patients (80%) were completely cured from infection and 24 isolated organisms (88.8%) were eradicated. No adverse reactions were observed. Aztreonam has undoubtedly high clinical and bacteriological efficacy in the therapy of nosocomial infections in patients with impaired host defenses.

Aztreonam therapy in experimental meningitis due to Haemophilus influenzae type b and Escherichia coli K1

The penetration of aztreonam into cerebrospinal fluid was 7 to 15% and 9 to 25%, respectively, in experimental Haemophilus influenzae type b and Escherichia coli K1 meningitis. Aztreonam was effective in reducing the number of organisms in cerebrospinal fluid after single-dose and continuous infusion administration, and the median bactericidal titers in cerebrospinal fluid were 1:32 against both meningeal pathogens.

Effect of aztreonam on throat and stool flora of cancer patients

Eighteen patients with hematological malignancies received aztreonam in one of two dosing regimens, 1 or 2 g every 8 h for a total of 7 to 9 days. Throat and stool cultures were obtained before and during treatment with aztreonam. Aztreonam had little effect on the predominant throat flora. In contrast, facultatively anaerobic gram-negative bacilli were markedly decreased in stools during the administration of aztreonam. Strict anaerobes in the stool were variably affected by aztreonam.

Aztreonam--an overview

Aztreonam is the first synthetic monobactam to undergo clinical studies in the U.S. Aztreonam has excellent activity against P. aeruginosa and Enterobacteriaceae, but poor activity against anaerobic and gram-positive organisms. Aztreonam has poor oral bioavailability, but can be given intramuscularly or intravenously in doses of 1-2 g q6-12h. Clinical trials of aztreonam have shown it to be effective in infections of urine, lung, skin, blood, bones and joints, and abdomen with an adverse reaction profile similar to beta-lactams. Aztreonam may be an alternate to aminoglycoside therapy, with the advantage of not being nephrotoxic.

Aztreonam in patients with acute purulent exacerbations of chronic bronchitis: failure to prevent emergence of pneumococcal infections

A group of 36 patients, all requiring hospital admission because of acute purulent exacerbations of chronic bronchitis, were treated with 1 or 2 g intramuscular injections of aztreonam for ten days. Patients with Streptococcus pneumoniae infections were excluded from the study. Sputum cultures before treatment revealed the other usual respiratory pathogens but repeat cultures on days 3, 10 and 17 sometimes yielded Str. pneumoniae, occasionally combined with Haemophilus influenzae or Branhamella catarrhalis. Ten patients had to be given other antimicrobial agents for Str. pneumoniae infections which developed during the study or follow-up periods. Pseudomonas aeruginosa failed to respond well to aztreonam. All the H. influenzae strains were sensitive to aztreonam (MIC 0.25 mg/l, or less) but all strains of Str. pneumoniae were resistant (MIC greater than 32 mg/l). Ps. aeruginosa strains were moderately resistant (MIC generally 4-16 mg/l) and Bran. catarrhalis strains only moderately sensitive (MICs generally 0.5-4 mg/l). Peak serum concentrations averaging approximately 37 mg/l were observed after the 1 g injections (55 mg/l after 2 g) and the corresponding mean peak concentrations in the sputum were 1.3 mg/l and 2.5 mg/l, respectively. The penetration from blood to sputum was thus approximately 3.5% and 4.6% after the 1 g and 2 g doses. No unwanted local or general reactions were observed. The disappointing clinical results (only 23 out of 36 patients with excellent or good clinical results) one week after the end of the treatment were mainly due to the emergence of pneumococcal infections during (and immediately after) therapy. Considering that Str. pneumoniae is still one of the most important organisms associated with acute purulent exacerbations of chronic bronchitis, and that conventional sputum cultures may not always reveal its presence, there is considerable doubt if aztreonam has any place in the treatment, especially as the results in Ps. aeruginosa infections have also been much poorer than expected.

Comparative in vitro activities of aztreonam, ciprofloxacin, norfloxacin, ofloxacin, HR 810 (a new cephalosporin), RU28965 (a new macrolide), and other agents against enteropathogens

The in vitro activity of drugs currently used in the treatment of diarrhea against 595 enteropathogens from worldwide sources was compared with that of six newly developed antibiotics, ciprofloxacin; norfloxacin; ofloxacin; aztreonam; HR810, an expanded-spectrum cephalosporin; and RU28965, a new macrolide. In contrast with ampicillin and chloramphenicol, trimethoprim-sulfamethoxazole showed an excellent activity against all of the enteropathogens tested, except Campylobacter species. Ciprofloxacin had the highest activity, with an overall 90% MIC of less than or equal to 0.097 micrograms/ml, except for Campylobacter species (0.39 micrograms/ml). Unlike other cephalosporins, HR810 showed a satisfactory activity against Campylobacter species (90% MIC of 3.12 micrograms/ml). RU28965 was three times less active than erythromycin against Campylobacter species.

Effect of hemodialysis and peritoneal dialysis on aztreonam pharmacokinetics

Aztreonam, a new monobactam, will be widely used because of its broad aerobic gram-negative bacterial coverage and its apparent low risk of allergic phenomena in penicillin/cephalosporin-sensitive patients. We examined aztreonam kinetics in patients during hemodialysis and in the interdialytic period and in patients on continuous ambulatory peritoneal dialysis (CAPD), and related aztreonam to urea clearance (CL). In hemodialysis patients, aztreonam serum half-life was 7.9 hr between and 2.7 hr during dialysis sessions. CLserum, CLrenal, and CLother were 24.4, 0.5, and 23.9 ml/min, respectively, during the interdialytic period. Four hours of dialysis removed 38.2% (range, 27 to 58%) of antibiotic. CL of aztreonam by hemodialysis was 36.6 to 43.2 ml/min, 50 to 77% greater than interdialytic CL. CL of urea by hemodialysis was 112.4 to 115.6 ml/min; CLaztreonam/CLurea ratio was 0.28 to 0.33 during the hemodialysis sessions. During CAPD, aztreonam serum half-life after intravenous dosing was 7.1 hr; dialysate recovery, 9.7% of the dose; CLserum, CLrenal, CLperitoneal dialysis, and CLother were 23.8, 0.5, 2.1, and 21.3 ml/min, respectively. CLurea by CAPD was 6.5 ml/min. Thus, CLaztreonam during CAPD was 32% of CLurea. Aztreonam was detectable in dialysate at 48 hr (eight exchanges) after peritoneal administration in the first exchange. Hemodialysis and CAPD patients given aztreonam treatment should receive the standard dose of aztreonam as a loading dose, followed by one-fourth the loading dose at standard dose intervals. Hemodialysis patients should receive a supplemental dose equal to half their usual maintenance dose immediately after each dialysis session. For CAPD patients with peritonitis due to susceptible organisms, a 1-g i.v. loading dose followed by a 0.5-g i.p. dose every 6 hr is suggested. In any individual patient undergoing hemodialysis or CAPD, the relationship between CLurea and CLaztreonam should allow appropriate antibiotic dose adjustment.

Penetration of aztreonam into cerebrospinal fluid of patients with and without inflamed meninges

Aztreonam was administered as a single, 2-g intravenous dose to 25 patients with noninflamed meninges and to 9 patients with inflamed meninges. It was well tolerated and was detected in the cerebrospinal fluid at the initial sampling period at 1 h after the end of infusion. Aztreonam levels in the cerebrospinal fluid of patients with inflamed meninges were four times higher than those recorded for the same time period in patients with noninflamed meninges. Aztreonam concentrations in cerebrospinal fluid in the presence of normal and inflamed meninges exceeded the inhibitory and bactericidal concentrations for most gram-negative bacteria. Thus, a multiple-dose treatment regimen with 2-g intravenous doses every 6 h appears to be appropriate for clinical trials of aztreonam for the treatment of gram-negative bacillary meningitis which is caused by susceptible organisms.

Treatment of gram-negative infections with aztreonam

Twenty-one patients with serious gram-negative infections were treated with aztreonam. Twenty of these were clinical and microbiologic cures; there was one clinical improvement with microbiologic persistence. No bacteria became resistant. Cure rates were: bone and joint (11 of 11); skin and soft tissue (six of six); pneumonia (two of two); perinephric abscess (one of one); and intra-abdominal abscess (zero of one). The bacteria responsible for these infections included Pseudomonas aeruginosa (12), Serratia marcescens (two), Enterobacter gergoviae (three), Enterobacter aerogenes (two), Escherichia coli (one), Citrobacter diversus (one), and Hemophilus influenzae (one). Aztreonam was well tolerated. Significant serum glutamic-oxaloacetic transaminase/serum glutamic-pyruvic transaminase elevations developed in three patients, but none was symptomatic and all resolved after therapy was stopped. Two patients in whom a rash developed were receiving other antibiotics (vancomycin and metronidazole), making the cause of the rash unclear. Diarrhea developed in a single patient with Pseudomonas osteomyelitis, who also was receiving cefazolin for Staphylococcus aureus superinfection of his decubitus ulcer. Aztreonam was highly effective against gram-negative bacilli, including P. aeruginosa. The only clear-cut side effect was an asymptomatic rise in serum glutamic-oxaloacetic transaminase/serum glutamic-pyruvic transaminase levels in three patients.

Aztreonam: the first monobactam

A novel screening procedure led to isolation of the structurally unique, bacterially produced, monocyclic beta-lactam antibiotics early in 1979. These naturally occurring "monobactams" were not clinically useful as antibiotics because of their poor antibacterial properties. They were, however, found to interact with certain penicillin-binding proteins of bacteria and thus to interfere with the biosynthesis of bacterial cell walls. The focus of monobactam development then turned toward increasing the binding activity of the beta-lactam ring of the molecule. Aztreonam was the first compound to emerge that fulfilled the objectives of the program. It is relatively inactive against gram-positive and anaerobic bacteria but is extremely effective against aerobic gram-negative bacteria, even in low concentrations. In addition, it is highly resistant to enzymatic hydrolysis by beta-lactamases and demonstrates a high degree of stability against plasmid-mediated gram-negative lactamases. With the chromosomally mediated beta-lactamases, on the other hand, aztreonam can act either as an inhibitor or as a poor substrate. It is unique in that it does not induce production of chromosomally mediated enzymes. Interference with normal gut flora by the use of broad-spectrum antibiotics can result in decreased defense capacity and can lead to intestinal colonization by resistant pathogenic organisms. Therapy directed specifically against the invading pathogen is thus preferred. Such directed therapy is provided by aztreonam. Its narrow spectrum can, if necessary, be broadened by combining it with other antibiotics while continuing to maintain an alternative to the more generalized "shotgun" therapy with its attendant side effects such as disturbances of the natural gut flora, diarrhea, and the emergence of resistant bacteria.

Antimicrobial combinations in the therapy of infections due to gram-negative bacilli

Antimicrobial combinations are used most frequently to provide broad-spectrum coverage; however, they are also frequently employed to enhance antimicrobial activity (synergism). Although there is extensive in vitro documentation of synergism for many antibiotic combinations, a clear advantage for these combinations has been difficult to demonstrate in clinical studies. Several types of combinations have been useful in clinical medicine and frequently result in synergism. These include combinations of a cell wall-active agent with an aminoglycosidic aminocyclitol, combinations of a beta-lactamase inhibitor with a beta-lactam, and combinations of agents that inhibit sequential steps in a metabolic pathway. Given its spectrum of activity, aztreonam will often be used with clindamycin or a beta-lactam antibiotic. Combinations of beta-lactams may be synergistic via several mechanisms. However, these combinations also exhibit significant potential for antagonism when used against gram-negative bacilli and, therefore, require careful evaluation prior to clinical use.

Aztreonam: worldwide overview of the treatment of patients with gram-negative infections

Multicenter trials were conducted to determine the safety and efficacy of aztreonam in the treatment of patients with gram-negative bacterial infections. A total of 2,821 patients were treated; 2,117 received aztreonam and 704 received control antibiotics. All patients were evaluated for safety and 1,180 of those treated with aztreonam and 428 treated with the control drugs met the criteria for efficacy evaluation. The number of patients treated with aztreonam who were evaluable for efficacy and their microbiologic response rates were: urinary tract infections, 443 (82 percent); lower respiratory tract infections, 217 (79 percent); septicemia, 63 (98 percent); skin/skin structure infections, 136 (88 percent); intra-abdominal infections, 47 (85 percent); postpartum/gynecologic infections, 21 (100 percent); bone and joint infections, 12 (100 percent); acute uncomplicated gonorrhea, 209 (97 percent); and acute uncomplicated cystitis, 56 (84 percent). Adverse reactions were qualitatively similar to those reported for beta-lactam antibiotics, i.e., mild gastrointestinal upset, rash, eosinophilia, or transient increase in hepatic enzyme parameters. There was an apparent lack of adverse effects on kidney, inner ear, and blood coagulation system. The most frequent adverse effect was phlebitis at infusion site (2.4 percent of patients). Superinfections and colonization with new organisms occurred in 9.4 percent of aztreonam-treated patients and in 7.4 percent of control drug-treated patients; only 40 percent of patients in each group, approximately 4 percent of all patients receiving aztreonam and 3 percent of those receiving control antibiotics, required specific therapy for the superinfection. Overall, results indicated that aztreonam is a safe and effective antibiotic in the treatment of aerobic gram-negative infections, when used either as monotherapy or in combination with other antibiotics.

Review of the clinical pharmacology of the monobactam antibiotic aztreonam

Serum and urine levels of aztreonam after 0.5, 1, and 2 g doses are potentially therapeutic for susceptible gram-negative organisms. Aztreonam is widely distributed in body fluids and tissues, and concentrations exceeding the minimal inhibitory concentrations of important gram-negative pathogens are attained in those compartments in which infections are most common. Aztreonam is eliminated primarily in the urine in unchanged form, although it is also secreted into the bile and is metabolized to a minor extent. Renal insufficiency may significantly impair the elimination of aztreonam, thus requiring modification of the dosage regimen. The monobactam can be cleared by hemodialysis but is only minimally cleared by peritoneal dialysis. Parenterally and orally administered aztreonam can selectively reduce the population of aerobic gram-negative bacteria in the gut without notably altering the number of anaerobic organisms.