Antimicrobial treatment of anaerobic infections

The nitric oxide paradox: antimicrobial and inhibitor of antibiotic efficacy

It is well-known that antibiotics target energy-consuming processes and a significant body of research now supports the conclusion that the metabolic state of bacteria can have a profound impact upon the efficacy of antibiotics. Several articles implicate bacterial energetics and the respiratory inhibitor nitric oxide (NO) in this process, although pinpointing the precise mechanism for how NO can diminish the potency of a range of antibiotics through modulating bacterial energy metabolism has proved challenging. Herein, we introduce the role of NO during infection, consider known links between NO and antibiotic efficacy, and discuss potential mechanisms via which NO present at the site of infection could mediate these effects through controlling bacterial energetics. This perspective article highlights an important relationship between NO and antibiotic action that has largely been overlooked and outlines future considerations for the development of new drugs and therapies that target bacterial energy metabolism.

Significance of pleural effusion detected by metagenomic next-generation sequencing in the diagnosis of aspiration pneumonia

Objective

Using metagenomic next-generation sequencing (mNGS) to profile the bacterial pathogen of pleural infection in aspiration pneumonia for therapeutic decision-making.

Methods

Collection and analysis of the clinical and laboratory data of aspiration pneumonia patients who underwent mNGS detection of pleural effusion at the Second Hospital of Jilin University from November 2020 and March 2022.

Results

Nine males and one female were included, aged 33 to 69 years. All patients had chest pain, fever, cough, and hypoxemia symptoms; 90% had expectoration. The laboratory tests revealed that all patients had elevated white blood cell, neutrophil, and C-reactive protein (CRP) levels. Furthermore, erythrocyte sedimentation rate (ESR) increased in 8 patients, and procalcitonin increased in only one patient. Chest CT indicated different degrees of lobar pneumonia and pleural effusion in all patients, and biochemical results implied exudative effusion according to Light criteria. Most routine culture results were negative. Among bacteria identified by mNGS, Fusobacterium nucleatum (n=9) was the most common, followed by Parvimonas micra (n=7) and Filifactor alocis (n=6). Three patients underwent surgical treatment after applying targeted antibiotics, thoracic puncture and drainage, and fibrinolytic septum treatment. After the adjusted treatment, the number of white blood cells, neutrophils, and lymphocytes decreased significantly, indicating the eradication of the infection.

Conclusions

Improving the vigilance of atypical people suffering from aspiration pneumonia is essential. The mNGS detection of pleural effusion clarified the microbial spectrum of aspiration pneumonia, allowing targeted antibiotic administration.

Increasing Fusobacterium infections with Fusobacterium varium, an emerging pathogen

Infections caused by Fusobacterium species are rare; however serious infections with complications or mortality may occur occasionally. We conducted a retrospective study to investigate the clinical features of patients with Fusobacterium infections and the differences between infections caused by the species F. necrophorum, F. nucleatum, and F. varium. Additionally, we attempted to identify risk factors for Fusobacterium-associated mortality. This study included all patients at a large tertiary care teaching hospital in South Korea with Fusobacterium infections from January 2006 to April 2021. Demographic, clinical, laboratory, and outcome data were analyzed. Multiple logistic regression analysis was performed to assess the risk factors for in-hospital mortality associated with F. nucleatum and F. varium infections. We identified 272 patients with Fusobacterium infections during the study period. The number of Fusobacterium cases has increased recently, with F. varium infections markedly increasing since 2016 and causing a significant proportion of infections. Patients with F. varium infections were older and had a higher proportion of nosocomial infections than the other groups. The F. nucleatum and F. varium groups showed higher in-hospital mortality than the F. necrophorum group. Through logistic regression analysis, APACHE II score and serum albumin level were considered risk factors for in-hospital mortality. APACHE II score was positively correlated with age, red cell distribution width, and serum blood urea nitrogen, and negatively correlated with serum albumin level. Infections caused by Fusobacterium species are increasing. F. varium causes a significant proportion of severe infections.

Biochemical and structural characterization of Haemophilus influenzae nitroreductase in metabolizing nitroimidazoles

Nitroheterocycle antibiotics, particularly 5-nitroimidazoles, are frequently used for treating anaerobic infections. The antimicrobial activities of these drugs heavily rely on the in vivo bioactivation, mainly mediated by widely distributed bacterial nitroreductases (NTRs). However, the bioactivation can also lead to severe toxicities and drug resistance. Mechanistic understanding of NTR-mediated 5-nitroimidazole metabolism can potentially aid addressing these issues. Here, we report the metabolism of structurally diverse nitroimidazole drug molecules by a NTR from a human pathogen Haemophilus influenzae (HiNfsB). Our detailed bioinformatic analysis uncovered that HiNfsB represents a group of unexplored oxygen-insensitive NTRs. Biochemical characterization of the recombinant enzyme revealed that HiNfsB effectively metabolizes ten clinically used nitroimidazoles. Furthermore, HiNfsB generated not only canonical nitroreduction metabolites but also stable, novel dimeric products from three nitroimidazoles, whose structures were proposed based on the results of high resolution MS and tandem MS analysis. X-ray structural analysis of the enzyme coupled with site-directed mutagenesis identified four active site residues important to its catalysis and broad substrate scope. Finally, transient expression of HiNfsB sensitized an E. coli mutant strain to 5-nitroimidazoles under anaerobic conditions. Together, these results advance our understanding of the metabolism of nitroimidazole antibiotics mediated by a new NTR group and reinforce the research on the natural antibiotic resistome for addressing the antibiotic resistance crisis.

The nitroreductase of Haemophilus influenzae metabolizes clinically used nitroimidazoles, generates dimeric metabolites and anaerobically sensitizes an E. coli mutant to antibiotics. We further uncover its biochemical and structural details.

An Updated Review on the Synthesis and Antibacterial Activity of Molecular Hybrids and Conjugates Bearing Imidazole Moiety

The rapid growth of serious infections caused by antibiotic resistant bacteria, especially the nosocomial ESKAPE pathogens, has been acknowledged by Governments and scientists and is one of the world's major health problems. Various strategies have been and are currently investigated and developed to reduce and/or delay the bacterial resistance. One of these strategies regards the design and development of antimicrobial hybrids and conjugates. This unprecedented critical review, in which our continuing interest in the synthesis and evaluation of the bioactivity of imidazole derivatives is testified, aims to summarise and comment on the results obtained from the end of the 1900s until February 2020 in studies conducted by numerous international research groups on the synthesis and evaluation of the antibacterial properties of imidazole-based molecular hybrids and conjugates in which the pharmacophoric constituents of these compounds are directly covalently linked or connected through a linker or spacer. In this review, significant attention was paid to summarise the strategies used to overcome the antibiotic resistance of pathogens whose infections are difficult to treat with conventional antibiotics. However, it does not include literature data on the synthesis and evaluation of the bioactivity of hybrids and conjugates in which an imidazole moiety is fused with a carbo- or heterocyclic subunit.

Microbiology and antibiotic therapy of subperiosteal orbital abscess in children with acute ethmoiditis

OBJECTIVE

The objective of this study was to investigate the microbiological cultures and the management of acute ethmoiditis complicated by subperiosteal orbital abscess (SPOA) in a pediatric population.

METHODS

The medical records of children under 18 years old was performed in a tertiary referral pediatric center from January 2009 to April 2017. Clinical examination, computed tomography scans, medical and surgical treatments were reviewed and compared to other studies in literature.

RESULTS

One hundred and twenty-nine children were hospitalized for acute ethmoiditis. Among them, forty eight were complicated by SPOA. The mean age of these children were 7 years (range 10 months-16 years). Thirtyfour underwent surgical drainage; for the others the medical treatment was sufficient. Microbiological samples were obtained during the surgical intervention and were contributive in 91% of cases. Streptococcus spp was the most frequently encountered bacteria (60% of cases). We also found anaerobic bacteria (12%), and Staphylococcus aureus (12%). 94% of children received two intravenous antibiotics (a third-generation cephalosporin and metronidazole) for a mean duration of four days. Then the oral treatment was based on amoxicillin-clavulanate during about 8.5 days. All children were cured without sequelae.

CONCLUSIONS

For five years Streptococcus milleri, Staphylococcus spp and anaerobic bacteria are on the rise in acute ethmoiditis complicated by SPOA. That is why antibiotics must be adapted to these bacteria even in children under ten years old.

Identification and Antimicrobial Susceptibility Testing of Anaerobic Bacteria: Rubik's Cube of Clinical Microbiology?

Anaerobic bacteria have pivotal roles in the microbiota of humans and they are significant infectious agents involved in many pathological processes, both in immunocompetent and immunocompromised individuals. Their isolation, cultivation and correct identification differs significantly from the workup of aerobic species, although the use of new technologies (e.g., matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, whole genome sequencing) changed anaerobic diagnostics dramatically. In the past, antimicrobial susceptibility of these microorganisms showed predictable patterns and empirical therapy could be safely administered but recently a steady and clear increase in the resistance for several important drugs (β-lactams, clindamycin) has been observed worldwide. For this reason, antimicrobial susceptibility testing of anaerobic isolates for surveillance purposes or otherwise is of paramount importance but the availability of these testing methods is usually limited. In this present review, our aim was to give an overview of the methods currently available for the identification (using phenotypic characteristics, biochemical testing, gas-liquid chromatography, MALDI-TOF MS and WGS) and antimicrobial susceptibility testing (agar dilution, broth microdilution, disk diffusion, gradient tests, automated systems, phenotypic and molecular resistance detection techniques) of anaerobes, when should these methods be used and what are the recent developments in resistance patterns of anaerobic bacteria.

Anaerobic bacteria growth in the presence of cathelicidin LL-37 and selected ceragenins delivered as magnetic nanoparticles cargo

BACKGROUND

Cationic antibacterial peptides (CAPs) and synthetic molecules mimicking the amphiphilic structure of CAPs, such as ceragenins, are promising compounds for the development of new antimicrobials.

RESULTS

We tested the in vitro activity of ceragenins CSA-13 and CSA-131 against several anaerobic bacteria including Bacteroides spp. and Clostridium difficile. We compared results to the activity of cathelicidin LL-37, metronidazole and nanosystems developed by attachment of CSA-13 and CSA-131 to magnetic nanoparticles (MNPs). The antibacterial effect was tested using killing assay and modified CLSI broth microdilution assay. Ceragenins CSA-13 and CSA-131 displayed stronger bactericidal activity than LL-37 or metronidazole against all of the tested bacterial strains. Additionally CSA-131 revealed an enhanced ability to prevent the formation of Bacteroides fragilis and Propionibacterium acnes biofilms.

CONCLUSIONS

These data confirmed that ceragenins display antimicrobial activity against a broad range of microorganisms including anaerobic bacteria and deserve further investigations as compounds serving to develop new treatment against anaerobic and mixed infections.

Microbiology and choice of antimicrobial therapy for acute sinusitis complicated by subperiosteal abscess in children

OBJECTIVES

Review past studies of the microbiology of subperiosteal abscesses (SPOA) complicating sinusitis in children and their implications of the antimicrobials administered to treat the infection.

METHODS

Literature search was conducted of the Cochrane Library, EMBASE, TRIP, EMBASE, and MEDLINE databases from their inception.

RESULTS

The most common pathogens isolated from studies of SPOA complicating sinusitis are aerobic (Streptococcus pneumoniae, Streptococcus spp., Haemophilus spp., Eikenella corrodens), anaerobic (Peptostreptococcus, Fusobacterium, Prevotella, Porphyromonas, Bacteroides, and Veillonella spp.), and micoaerophilic streptococci (Streptococcus anginosus/Streptococcus milleri group), all members of the oropharyngeal flora. S. pneumoniae and S. aureus were more frequently recovered in children >7 years old, while polymicrobial aerobic-anaerobic flora were more often isolated from those >15 years. The introduction of pneumococcal vaccine reduced the rate of isolation of S. pneumoniae, and correlated with increase of recovery of S. aureus including methicillin resistant strains, as well as Streptococcus pyogenes and S. anginosus/milleri group.

CONCLUSIONS

The microbiology and consequently the treatment of respiratory infections including sinusitis and its complications has evolved over the past decades. Establishing the microbiology of SPOA by obtaining appropriate cultures for both aerobic and anaerobic bacteria are essential for proper antimicrobial selection.

Infection, antibiotic therapy and risk of colorectal cancer: a nationwide nested case-control study in patients with Type 2 diabetes mellitus

Patients with Type 2 diabetes mellitus are at a higher risk of colorectal cancer (CRC). The objective of our study was to examine the inter-relationship among infection sites, systemic antibiotic use and risk of CRC among patients with Type 2 diabetes mellitus. From a diabetic cohort from the Taiwan's National Health Insurance claims database, we identified 3,593 incident colon cancer cases, 1,979 rectal cancer cases and 22,288 controls and conducted a nested case-control study to examine the association between antibiotic use and CRC incidence. Logistic regression models were applied to estimate the odds ratio (OR) and the 95% confidence interval (95% CI) between infection sites, antibiotic use and CRC incidence. Patients with intra-abdominal infection were significantly associated with increased risk for colon cancer (OR = 2.01, 95% CI = 1.73-2.35) and rectal cancer (OR = 1.59, 95% CI = 1.26-2.00). Any antianaerobic antibiotic use was associated with a higher risk of colon cancer (OR = 2.31, 95% CI = 2.12-2.52) and rectal cancer (OR = 1.69, 95% CI = 1.50-1.90) but without an obvious dose-response relationship for cumulative use. Antianaerobic antibiotics also increased the risks for those with nonintra-abdominal infection. No association was found between antiaerobic agent use and the CRC risk. The results suggest intra-abdominal infections and antianaerobic antibiotic use may be a marker for precancerous lesions or early CRC, although the possibility of antianaerobic antibiotics playing an additional role cannot be excluded. Further research examining the relationship between intra-abdominal infection, antianaerobic antibiotics use and possible change of microbiota leading to colorectal carcinogenesis is warranted.

Synthesis and biological evaluation of novel N-substituted 1H-dibenzo[a,c]carbazole derivatives of dehydroabietic acid as potential antimicrobial agents

A series of new N-substituted 1H-dibenzo[a,c]carbazole derivatives were synthesized from dehydroabietic acid, and their structures were characterized by IR, (1)H NMR and HRMS spectral data. All compounds were evaluated for their antibacterial and antifungal activities against four bacteria (Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas fluorescens) and three fungi (Candida albicans, Candida tropicalis and Aspergillus niger) by serial dilution technique. Some of the synthesized compounds displayed pronounced antimicrobial activity against tested strains with low MIC values ranging from 0.9 to 15.6μg/ml. Among them, compounds 6j and 6r exhibited potent inhibitory activity comparable to reference drugs amikacin and ketoconazole.

Ceftaroline plus avibactam demonstrates bactericidal activity against pathogenic anaerobic bacteria in a one-compartment in vitro pharmacokinetic/pharmacodynamic model

Anaerobic pathogens are often associated with polymicrobial infections, such as diabetic foot infections. Patients with these infections are often treated with broad-spectrum, multidrug therapies targeting resistant Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus, as well as Gram-negative bacteria and anaerobes. The broad-spectrum, non-beta-lactam, beta-lactamase inhibitor avibactam has been combined with ceftaroline and may provide a single-product alternative for complicated polymicrobial infections. We compared the activity of ceftaroline-avibactam (CPA) to that of ertapenem (ERT) against common anaerobic pathogens in an in vitro pharmacokinetic/pharmacodynamic (PK/PD) model. Simulations of doses of ceftaroline-fosamil at 600 mg every 8 h (q8h) (maximum free drug concentration [fCmax], 17.04 mg/liter, and half-life [t1/2], 2.66 h) plus avibactam at 600 mg q8h (fCmax, 11.72 mg/liter, and t1/2, 1.8 h) and of ertapenem at 1 g q24h (fCmax, 13 mg/liter, and t1/2, 4 h) were evaluated against two strains of Bacteroides fragilis, one strain of Prevotella bivia, and one strain of Finegoldia magna in an anaerobic one-compartment in vitro PK/PD model over 72 h with a starting inoculum of ∼8 log10 CFU/ml. Bactericidal activity was defined as a reduction of ≥3 log10 CFU/ml from the starting inoculum. Both CPA and ERT were bactericidal against all four strains. CPA demonstrated improved activity against Bacteroides strains compared to that of ERT but had similar activity against Finegoldia magna and P. bivia, although modest regrowth was observed with CPA against P. bivia. No resistance emerged from any of the models. The pharmacokinetics achieved were 92 to 105% of the targets. CPA has potent in vitro activity against common anaerobic pathogens at clinically relevant drug exposures and may be a suitable single product for the management of complicated polymicrobial infections.

Expanded therapeutic potential in activity space of next-generation 5-nitroimidazole antimicrobials with broad structural diversity

Metronidazole and other 5-nitroimidazoles (5-NI) are among the most effective antimicrobials available against many important anaerobic pathogens, but evolving resistance is threatening their long-term clinical utility. The common 5-NIs were developed decades ago, yet little 5-NI drug development has since taken place, leaving the true potential of this important drug class unexplored. Here we report on a unique approach to the modular synthesis of diversified 5-NIs for broad exploration of their antimicrobial potential. Many of the more than 650 synthesized compounds, carrying structurally diverse functional groups, have vastly improved activity against a range of microbes, including the pathogenic protozoa Giardia lamblia and Trichomonas vaginalis, and the bacterial pathogens Helicobacter pylori, Clostridium difficile, and Bacteroides fragilis. Furthermore, they can overcome different forms of drug resistance, and are active and nontoxic in animal infection models. These findings provide impetus to the development of structurally diverse, next-generation 5-NI drugs as agents in the antimicrobial armamentarium, thus ensuring their future viability as primary therapeutic agents against many clinically important infections.

Nationwide surveillance of antimicrobial susceptibility patterns of pathogens isolated from surgical site infections (SSI) in Japan

To investigate the trends of antimicrobial resistance in pathogens isolated from surgical site infections (SSI), a Japanese surveillance committee conducted the first nationwide survey. Seven main organisms were collected from SSI at 27 medical centers in 2010 and were shipped to a central laboratory for antimicrobial susceptibility testing. A total of 702 isolates from 586 patients with SSI were included. Staphylococcus aureus (20.4 %) and Enterococcus faecalis (19.5 %) were the most common isolates, followed by Pseudomonas aeruginosa (15.4 %) and Bacteroides fragilis group (15.4 %). Methicillin-resistant S. aureus among S. aureus was 72.0 %. Vancomycin MIC 2 μg/ml strains accounted for 9.7 %. In Escherichia coli, 11 of 95 strains produced extended-spectrum β-lactamase (Klebsiella pneumoniae, 0/53 strains). Of E. coli strains, 8.4 % were resistant to ceftazidime (CAZ) and 26.3 % to ciprofloxacin (CPFX). No P. aeruginosa strains produced metallo-β-lactamase. In P. aeruginosa, the resistance rates were 7.4 % to tazobactam/piperacillin (TAZ/PIPC), 10.2 % to imipenem (IPM), 2.8 % to meropenem, cefepime, and CPFX, and 0 % to gentamicin. In the B. fragilis group, the rates were 28.6 % to clindamycin, 5.7 % to cefmetazole, 2.9 % to TAZ/PIPC and IPM, and 0 % to metronidazole (Bacteroides thetaiotaomicron; 59.1, 36.4, 0, 0, 0 %). MIC₉₀ of P. aeruginosa isolated 15 days or later after surgery rose in TAZ/PIPC, CAZ, IPM, and CPFX. In patients with American Society of Anesthesiologists (ASA) score ≥3, the resistance rates of P. aeruginosa to TAZ/PIPC and CAZ were higher than in patients with ASA ≤2. The data obtained in this study revealed the trend of the spread of resistance among common species that cause SSI. Timing of isolation from surgery and the patient's physical status affected the selection of resistant organisms.

[Microbiologic basis of diagnosis and treatment of pelvic inflammatory disease]

Pelvic inflammatory disease (PID) is caused by a large spectrum of micro-organisms. However, the microbiological cause is unknown in approximately half of cases according to varying series. In the context of sexually transmitted disease (STD), the most frequently identified microorganisms causing PID are Neisseria gonorrhoeae, Chlamydia trachomatis and Mycoplasma genitalium. In such cases, bacterial vaginosis and Trichomonas vaginalis are frequently associated. In case of complicated PID or when PID is the consequence of delivery, abortion, intra-uterine procedure, bacteria that come from vaginal carriage may be encountered: Enterobacteriacae, Staphylococcus spp., Streptococcus spp., anaerobes. Mycopslama hominis as well as Ureaplasma urealyticum may also be found in this context. The microbiological diagnosis may be performed on samples of vaginal liquid, endocervix or, when available, surgical specimens. The microbiological diagnostic procedures that are used to identify these microrgansims are reviewed. Vaginal sampling may help to identify N. gonorrhoeae, C. trachomatis and M. genitalium using nucleic acid amplification tests (NAAT), and is also of interest because of the epidemiological association of PID to bacterial vaginosis and trichomoniasis. Samples from the endocervix, and if available, from endometrial biopsy surgical procedures, should be processed to detect N. gonorrhoeae, C. trachomatis and M. genitalium using NAAT, and to search for the presence of Neisseria gonorrhoeae (antibiogram should be performed), facultative anaerobes, anaerobes and capnophilic bacteria. The antibiotic treatment should at least cover N. gonorrhoeae, C. trachomatis and M. genitalium, and for most of the authors, anaerobes. In case, microbiological studies demonstrate the role of other bacteria (e.g., Enterobacteriacae), theses should be treated according to the results of antibiogram.