In vitro efficacy of beta-lactam/beta-lactamase inhibitor combinations against bacteria involved in mixed infections

Genomic Determinants of Pathogenicity and Antimicrobial Resistance of Nosocomial Acinetobacter baumannii Clinical Isolates of Hospitalized Patients (2019-2021) from a Sentinel Hospital in Hangzhou, China

Purpose

Acinetobacter baumannii (A. baumannii or AB) is one of the most opportunistic, nosocomial pathogens threatening public healthcare across countries. A. baumannii has become a primary growing concern due to its exceptional ability to acquire antimicrobial resistance (AMR) to multiple antimicrobial agents which is increasingly reported and more prevalent every year. Therefore, there is an urgent need to evaluate the AMR knowledge of A. baumannii for effective clinical treatment of nosocomial infections. This study aimed to investigate the clinical distribution AMR phenotypes and genotypes, and genomic characteristics of A. baumannii isolates recovered from hospitalized patients of different clinical departments of a sentinel hospital to improve clinical practices.

Methods

A total of 123 clinical isolates were recovered from hospitalized patients of different clinical departments during 2019-2021 to analyze AMR patterns, and further subjected to whole-genome sequencing (WGS) investigations. Multi-locus sequence typing (MLST), as well as the presence of antimicrobial-resistant genes (ARGs), virulence factor genes (VFGs) and insertion sequences (ISs) were also investigated from WGS data.

Results

The results highlighted that A. baumannii clinical isolates had shown a high AMR rate, particularly from the intensive care unit (ICU), towards routinely used antimicrobials, ie, β-lactams and fluoroquinolones. ST2 was the most prevalent ST in the clinical isolates, it was strongly associated to the resistance of cephalosporins and carbapenems, with bla_OXA-23 and bla_OXA-66 being the most frequent determinants; moreover, high carrier rate of VFGs was also observed such as all strains containing the ompA, adeF, pgaC, lpsB, and bfmR genes.

Conclusion

Acinetobacter baumannii clinical isolates are mostly ST2 with high rates of drug resistance and carrier of virulence factors. Therefore, it requires measurements to control its transmission and infection.

Microbiology of Meropenem-Vaborbactam: A Novel Carbapenem Beta-Lactamase Inhibitor Combination for Carbapenem-Resistant Enterobacterales Infections

Vaborbactam is a novel boron-based beta-lactamase inhibitor developed to be effective against Klebsiella pneumoniae carbapenemase (KPC)-producing bacteria. This enzyme is a key driver in the global spread of β-lactam resistance among carbapenem-resistant Enterobacterales. Alone, vaborbactam has no antibacterial activity; however, the combination of meropenem-vaborbactam has enhanced activity against gram-negative organisms, particularly Enterobacterales with class A and C carbapenemases. Multiple in vitro studies evaluating isolates from various geographic regions, and over different time periods, have demonstrated the high potency of meropenem-vaborbactam against organisms containing KPC2 and KPC3. However, meropenem-vaborbactam does not have activity against OXA-48 or metallo-beta lactamases. This review covers the in vitro studies of meropenem-vaborbactam performed to date, which evaluated both large cohorts of clinical isolates and engineered isolates, to determine efficacy in various settings, including the presence of porin mutations and efflux pump upregulation.

Meropenem-vaborbactam is a new combination antibiotic that was designed specifically for efficacy against bacteria that produce the Klebsiella pneumoniae carbapenemase (KPC) enzyme, which enables resistance to beta-lactam antibiotics. The global spread and increase of difficult-to-treat infections caused by carbapenem-resistant Enterobacterales (CRE) is in part because they produce KPC enzymes. The authors review the in vitro studies of meropenem-vaborbactam activity, which have included isolates from different geographic regions, time periods, and settings, showing that it has high potency against organisms containing KPC enzymes-KPC2 and KPC3. Meropenem-vaborbactam was tested against globally sourced isolates that carried different resistance mechanisms, including carbapenem resistance, multidrug resistant (MDR), and resistance to colistin and/or tigecycline; it inhibited activity of 99.1% Enterobacterales isolates tested at ≤ 1 µg/ml, and at ≤ 8 µg/ml it inhibited 96.5% of MDR isolates and 82% of XDR isolates. Against OXA-48 or metallo-beta lactamase enzymes, meropenem-vaborbactam has limited or no activity, so in the Asia-Pacific region where MLBs are prevalent it was least effective, but and was most effective against US strains where KPC is prevalent. In multiple studies, meropenem-vaborbactam showed strong in vitro activity against E. coli, Enterobacter spp., and K. pneumoniae. Compared to available antibiotics, against both clinical and engineered isolates, as well as engineered E. coli strains with KPC, SHV, and TEM enzymes, meropenem-vaborbactam demonstrated lower MIC values. Overall, in vitro studies of meropenem-vaborbactam have shown enhanced activity against CRE and KPC producers compared to other antibiotics, which is needed in the current CRE environment where KPC is dominant.

Impacts of L1 Promoter Variation and L2 Clavulanate Susceptibility on Ticarcillin-Clavulanate Susceptibility of Stenotrophomonas maltophilia

Inducible expression of L1 and L2 β-lactamases is the principal mechanism responsible for β-lactam resistance in Stenotrophomonas maltophilia Ticarcillin-clavulanate (TIM) is one of the few effective β-lactams for S. maltophilia treatment. Clavulanate (CA) is a β-lactamase inhibitor that specifically targets class A, C, and D β-lactamases. In view of the presence of class B L1 β-lactamase, it is of interest to elucidate why TIM is valid for S. maltophilia treatment. The L1-L2 allelic variation and TIM susceptibilities of 22 clinical isolates were established. Based on L1 and L2 protein sequences and TIM susceptibility, three L1-based phylogenetic clusters (L1-A, L1-B, and L1-C) and three L2-based phylogenetic clusters (L2-A, L2-B1, and L2-B2) were classified. The contribution of each L1- and L2-based phylogenetic cluster to ticarcillin (TIC) and TIM susceptibility was investigated. All the L1s and L2s tested contributed to TIC resistance. The L1s tested were inert to CA; nevertheless, the sensitivities of L2s to CA were widely different. In addition, the genetic organizations upstream of the L1 gene varied greatly in these isolates. At least three different L1 promoter structures (K279a type, D457 type, and none) were found among the 22 isolates assayed. The differences in the L1 promoter structure had a great impact on TIC-induced L1 β-lactamase activities. Collectively, the L1 promoter activity in response to TIC challenge and L2 susceptibility to CA are critical factors determining TIM susceptibility in S. maltophilia.

Antianaerobic antimicrobials: spectrum and susceptibility testing

Susceptibility testing of anaerobic bacteria recovered from selected cases can influence the choice of antimicrobial therapy. The Clinical and Laboratory Standards Institute (CLSI) has standardized many laboratory procedures, including anaerobic susceptibility testing (AST), and has published documents for AST. The standardization of testing methods by the CLSI allows comparisons of resistance trends among various laboratories. Susceptibility testing should be performed on organisms recovered from sterile body sites, those that are isolated in pure culture, or those that are clinically important and have variable or unique susceptibility patterns. Organisms that should be considered for individual isolate testing include highly virulent pathogens for which susceptibility cannot be predicted, such as Bacteroides, Prevotella, Fusobacterium, and Clostridium spp.; Bilophila wadsworthia; and Sutterella wadsworthensis. This review describes the current methods for AST in research and reference laboratories. These methods include the use of agar dilution, broth microdilution, Etest, and the spiral gradient endpoint system. The antimicrobials potentially effective against anaerobic bacteria include beta-lactams, combinations of beta-lactams and beta-lactamase inhibitors, metronidazole, chloramphenicol, clindamycin, macrolides, tetracyclines, and fluoroquinolones. The spectrum of efficacy, antimicrobial resistance mechanisms, and resistance patterns against these agents are described.

Treatment of anaerobic infection

Anaerobic bacteria are the predominant flora in the normal human skin and mucous membranes and are, therefore, a common cause of endogenous infections. Since anaerobic infections are generally polymicrobial, where anaerobes are mixed with aerobic organisms, therapy should provide coverage of both types of pathogens. The isolation of anaerobes requires appropriate methods of collection, transportation and cultivation of specimens. The lack of use of any of these methods can lead to inadequate recovery of anaerobes and inappropriate therapy. Treatment of anaerobic infection is complicated by the slow growth of these organisms and the growing resistance of anaerobic bacteria to antimicrobials. The primary role of antimicrobials is to limit the local and systemic spread of infection. Surgical drainage is of primary importance. This includes debriding of necrotic tissue, draining the pus, improving circulation, alleviating obstruction and increasing tissue oxygenation. The most effective antimicrobials against anaerobic organisms are metronidazole, the carbapenems (imipenem, meropenem and ertapenem), chloramphenicol, the combinations of a penicillin and a beta-lactamase inhibitor (ampicillin or ticarcillin plus clavulanate, amoxicillin plus sulbactam, and piperacillin plus tazobactam), tigecycline and clindamycin.

Microbiology of acute exacerbation of chronic sinusitis

OBJECTIVES

We undertook to evaluate the microbiology of acute exacerbation of chronic sinusitis (AECS).

METHODS

Repeated aspirations of maxillary sinus secretions by endoscopy were performed in 7 patients over a period of 125 to 242 days.

RESULTS

Bacteria were recovered for all 22 aspirates, and the number of isolates was between 2 and 4. A total of 54 isolates were isolated: 16 aerobic and facultative bacteria and 38 anaerobic bacteria. The aerobic bacteria were Haemophilus influenzae (7 isolates), Streptococcus pneumoniae (3), Moraxella catarrhalis (3), Staphylococcus aureus (2), and Klebsiella pneumoniae (1). The anaerobic bacteria included pigmented Prevotella and Porphyromonas spp (19), Peptostreptococcus spp (9), Fusobacterium spp (8), and Propionibacterium acnes (2). A change in the types of isolates was noted in all consecutive cultures obtained from the same patients as different organisms emerged and previously isolated bacteria were no longer recovered. An increase in antimicrobial resistance was noted in 6 instances.

CONCLUSIONS

This study illustrates the microbial dynamics of AECS in which anaerobic and aerobic bacteria prevail, and highlights the importance of obtaining cultures from patients with AECS for guidance in selection of proper antimicrobial therapy.

Piperacillin–sulbactam versus piperacillin–tazobactam: a multicentre, randomised, single-blind, controlled clinical trial

The objective of this study was to compare the efficacy and safety of piperacillin-sulbactam (PIP-SBT) and piperacillin-tazobactam (PIP-TAZ) in the treatment of bacterial respiratory and urinary tract infections. A randomised, single-blind, controlled clinical trial was performed. Differences in clinical efficacy, bacteriology and safety between the two groups were subjected to statistical analysis, including intent-to-treat (ITT) analysis. A total of 215 cases were enrolled, with 203 complete cases (99 PIP-SBT, 104 PIP-TAZ). A total of 209 cases (103 PIP-SBT, 106 PIP-TAZ) were included in the ITT analysis and a total of 212 cases (104 PIP-SBT, 108 PIP-TAZ) were included in the safety analysis. Overall efficacy rates of PIP-SBT and PIP-TAZ were 93.2% and 93.4%, respectively. Overall bacterial eradication rates of the two groups were 95% and 97.59%, respectively. Among the PIP-SBT group, eight patients (7.69%) had adverse events, including four probable drug-related events. Among the PIP-TAZ group, nine patients (8.33%) had adverse events, including one definitely drug-related and four probable drug-related events. All differences between the two groups were insignificant. PIP-SBT could be a suitable replacement for PIP-TAZ in the therapy of community-acquired respiratory and urinary tract infections caused by beta-lactamase-producing bacterial isolates.

Pharmacokinetics of a combination preparation of ampicillin and sulbactam in turkeys

OBJECTIVE

To investigate the disposition kinetics of ampicillin and sulbactam after IV and IM administration of an ampicillin-sulbactam (2:1) preparation and determine the bioavailability of the combined preparation after IM administration in turkeys.

ANIMALS

10 healthy large white turkeys.

PROCEDURE

In a crossover study, turkeys were administered the combined preparation IV (20 mg/kg) and IM (30 mg/kg). Blood samples were collected before and at intervals after drug administrations. Plasma ampicillin and sulbactam concentrations were measured by use of high-performance liquid chromatography; plasma concentration-time curves were analyzed via compartmental pharmacokinetics and noncompartmental methods.

RESULTS

The drugs were distributed according to an open 2-compartment model after IV administration and a 1-compartment model (first-order absorption) after IM administration. For ampicillin and sulbactam, the apparent volumes of distribution were 0.75+/-0.11 L/kg and 0.74+/-0.10 L/kg, respectively, and the total body clearances were 0.67+/-0.07 L x kg(-1) x h(-1) and 0.56+/-0.06 L x kg(-1) x h(-), respectively. The elimination half-lives of ampicillin after IV and IM administration were 0.78+/-0.12 hours and 0.89+/-0.17 hours, respectively, whereas the corresponding half-lives of sulbactam were 0.91+/-0.12 hours and 0.99+/-0.16 hours, respectively. Bioavailability after IM injection was 58.87+/-765% for ampicillin and 53.75+/-5.35% for sulbactam.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that a regimen of loading and maintenance doses of 300 mg of the ampicillin-sulbactam (2:1) combination/kg every 8 hours could be clinically useful in turkeys. This dosage regimen maintained plasma concentrations of ampicillin > 0.45 microg/mL in turkeys.

Basic aspects of and general problems in surgical infections

Antibiotics are important in the prophylaxis and treatment of surgical infections as well as in the management of nosocomial infections acquired postoperatively in surgical patients. Surgeons encounter a range of infectious conditions, including established single-pathogen infections of soft tissues, polymicrobial intra-abdominal infections, and resistant gram-negative nosocomial infections such as ventilator-associated and aspiration pneumonia. Preoperative antibiotic administration has been shown to reduce the risk of surgical site infections and is now an accepted part of the standard care for most surgical patients. In patients with established single-pathogen or polymicrobial infections requiring surgery, studies have shown appropriate empiric antibiotic therapy to be an important adjunct to surgical intervention and general supportive measures in improving patient outcome. Antibiotics are also essential for those who develop postoperative nosocomial infections. Empiric coverage of the most likely causative organisms, especially in synergistic polymicrobial mixed infections, is one of the keys to successful prophylaxis and treatment of surgical infections.

Comparative in vitro activity of piperacillin, piperacillin–sulbactam and piperacillin-tazobactam against nosocomial pathogens isolated from intensive care patients

We investigated the antimicrobial activity of piperacillin-tazobactam versus piperacillin-sulbactam against common nosocomial pathogens (n = 565) isolated from intensive care patients. For Gram-positive bacteria, antimicrobial susceptibilities to the two piperacillin-beta-lactamase inhibitor combinations were almost identical. For Gram-negative bacteria, piperacillin-tazobactam exhibited greater activity against Escherichia coli and Proteus vulgaris than piperacillin-sulbactam. Both combinations, however, were equally effective against the other Enterobacteriaceae and Pseudomonas aeruginosa isolates. Piperacillin-sulbactam exhibited better antimicrobial activity against Acinetobacter baumannii. Our findings might prove important for the appropriate choice of antibiotic therapy with beta-lactam-beta-lactamase inhibitor combinations.

Beta-lactam/beta-lactamase inhibitor combinations in empiric management of pediatric infections

Beta-lactam antibiotics have long played a central role in the management of pediatric infections. However, widespread beta-lactam resistance among community- and hospital-acquired pathogens, mainly due to beta-lactamase production, has reduced the usefulness of these trusted and well-tolerated agents. Many regions have reported an increase in beta-lactamase-mediated resistance to cephalosporins and carbapenems as well as penicillins among clinically important Gram-positive and Gram-negative aerobes and anaerobes. For some pathogens such as Moraxella catarrhalis, Klebsiella species and Pseudomonas aeruginosa, virtually all strains worldwide are beta-lactamase producers. The development of beta-lactamase inhibitors for co-administration with a number of established beta-lactam agents has restored their usefulness in pediatric patients. The combination of ampicillin plus sulbactam has broad anti-aerobic and anti-anaerobic activity in vitro and achieves high concentrations in many body tissues and fluids. The availability of a mutual oral prodrug, sultamicillin, has enabled the development of an oral formulation. Excellent clinical response and bacterial eradication rates with ampicillin/sulbactam and sultamicillin have been demonstrated for upper and lower respiratory tract infections, urinary tract infections, osteomyelitis, and meningitis in pediatric patients and neonates. Furthermore, many studies have demonstrated an excellent tolerability profile. Thus, ampicillin/sulbactam has an important role in the management of pediatric infections.

Anaerobic infections in the surgical patient: microbial etiology and therapy

Anaerobic infections occur in surgical patients in part because of structural or functional defects in the host that (1) cause a breech in the normal mucosal barriers, (2) create localized vascular insufficiencies, or (3) produce an obstruction. Any or all of these events may compromise the oxidation-reduction potential within the tissues, encouraging rapid anaerobic growth. Although diverse anaerobic populations are spread throughout the gastrointestinal tract, a relatively limited number of organisms are responsible for clinical infection in the surgical patient. Many of these offending organisms express overt virulence factors that enhance microbial adherence, tissue destruction, and, in the case of Bacteroides fragilis, facilitate abscess formation. The selection of an appropriate perioperative or therapeutic agent requires a fundamental knowledge of the microbial ecology of this microbial population. The failure to consider the anaerobic flora as a component in the etiology of mixed surgical infections is associated with a high rate of perioperative and therapeutic failures.

New perspectives in antibiotic prophylaxis for intra-abdominal surgery

Effective management of intra-abdominal infections requires a combination of preoperative preparation, antibiotic prophylaxis and appropriate surgical technique. Antibacterial prophylaxis should provide coverage of all likely pathogens, including aerobic and anaerobic organisms. Whereas antibacterial combination therapy is appropriate in certain situations, single-agent prophylaxis is appropriate for the majority of patients and ampicillin/sulbactam, with its broad-spectrum anti-aerobic/anti-anaerobic activity, is an attractive prophylactic option. Surgery involving the gastrointestinal tract provides a special challenge by virtue of its high, predominantly anaerobic, bacterial load. However, the requirement for prophylaxis varies depending upon the precise site of intervention. Biliary tract surgery requires prophylaxis in high-risk patients only, whereas hepatobiliary or pancreatic surgery requires prophylaxis in all patients. Gastroduodenal operations require prophylaxis in the presence of risk factors, such as abnormal gastric acidity or bleeding. Colorectal procedures present a high risk of anaerobic infection and sepsis, and require adequate prophylaxis combined with a thorough preoperative preparation designed to reduce considerably the bacterial load of the bowel. Where peritonitis does follow intra-abdominal surgery, patients should receive antibacterial therapy commensurate with the risk of serious infection. A small proportion of patients will be at risk of severe infection and will require triple-agent therapy. However, most patients are likely to develop mild-to-moderate infections only and can be treated with a single, broad-spectrum antibiotic agent, such as ampicillin/sulbactam, a beta-lactam/beta-lactamase inhibitor.

Synthesis and conformational analysis of fusidic acid side chain derivatives in relation to antibacterial activity

Novel fusidic acid type antibiotics having flexible side chains are described. Saturation of the double bond between C-17 and C-20 of fusidic acid produces four stereoisomers differing in the configuration at C-17 and C-20. The structure-activity relationship of the stereoisomers was studied using computer-assisted analyses of low-energy conformations and crystallographic data. Only one of the four stereoisomers showed potent antibiotic activity comparable with that of fusidic acid, whereas the other three stereoisomers retained little or no activity. The orientation of the side chain is crucial, and there is only a limited space for bioactive side chain conformations. This investigation demonstrates the essential role of the side chain conformations in relation to antibacterial activity and contradicts earlier assumptions that the Delta17(20) bond is an essential feature in the molecule.

Use of ampicillin/sulbactam and sultamicillin in pediatric infections: a re-evaluation

Ampicillin/sulbactam is an effective solution to the emergence of beta-lactamase-mediated resistance among common pediatric pathogens, and is a widely recognized treatment option for a variety of pediatric infections. Recent antimicrobial surveillance data confirm the continued susceptibility of many Gram-positive and Gram-negative aerobes and anaerobes to ampicillin/sulbactam. Pharmacokinetic studies have demonstrated high drug concentrations at a variety of infection sites, including cerebrospinal fluid and bone. Furthermore, clinical studies have shown that ampicillin/sulbactam, administered intravenously, intramuscularly or orally (as the mutual prodrug sultamicillin), is clinically and bacteriologically effective against upper and lower respiratory tract infections, urinary tract infections, skin, bone and soft-tissue infections, and meningitis, and provides effective surgical prophylaxis. Sultamicillin has an excellent tolerability profile, which is associated with a low rate of treatment discontinuation. Accordingly, ampicillin/sulbactam and sultamicillin should be considered first-choice options for the management of a variety of pediatric infections.

Antibiotic prophylaxis in head and neck oncologic surgery: the role of gram-negative coverage

Many studies have elucidated the risk factors associated with peri-operative infection following head and neck cancer surgery (HNS), the implications of infection for total treatment cost, and the clinical benefits of successful antimicrobial prophylaxis. The most appropriate antibiotic use is achieved by focusing on patients with clean, contaminated wounds. Thereafter, the usefulness of an antibiotic agent depends on its antimicrobial spectrum, tolerability profile, and cost. Successful antimicrobial prophylaxis requires antimicrobial activity against gram-positive, gram-negative, and anaerobic organisms. The beta-lactam/beta-lactamase inhibitor combination, sulbactam-ampicillin, has just such an antimicrobial spectrum. A double-blind, randomized clinical trial, involving patients undergoing HNS, recorded a lower post-operative infection rate among patients receiving peri-operative sulbactam-ampicillin 0.5 g/1.0 g i.v. q6h compared with those receiving clindamycin 600 mg i.v. q6h (13.3 vs. 27.1%; P = 0.02). Culture of strains from infected individuals indicated a significantly lower proportion of gram-negative organisms for sulbactam-ampicillin than for clindamycin (32 vs. 81%; P < 0.05). There was a significant difference in the median duration of surgery between infected and non-infected individuals (8.5 vs. 5.9 h; P < 0.0001). These data support the use of sulbactam-ampicillin to reduce the incidence of post-operative infection following HNS.