Antimicrobial Activity Of Antibiotics Research Articles

Protein Binding in Translational Antimicrobial Development-Focus on Interspecies Differences.

Background/Introduction: Plasma protein binding (PPB) continues to be a key aspect of antibiotic development and clinical use. PPB is essential to understand several properties of drug candidates, including antimicrobial activity, drug-drug interaction, drug clearance, volume of distribution, and therapeutic index. Focus areas of the review: In this review, we discuss the basics of PPB, including the main drug binding proteins i.e., Albumin and α-1-acid glycoprotein (AAG). Furthermore, we present the effects of PPB on the antimicrobial activity of antibiotics and the current role of PPB in in vitro pharmacodynamic (PD) models of antibiotics. Moreover, the effect of PPB on the PK/PD of antibiotics has been discussed in this review. A key aspect of this paper is a concise evaluation of PPB between animal species (dog, rat, mouse, rabbit and monkey) and humans. Our statistical analysis of the data available in the literature suggests a significant difference between antibiotic binding in humans and that of dogs or mice, with the majority of measurements from the pre-clinical species falling within five-fold of the human plasma value. Conversely, no significant difference in binding was found between humans and rats, rabbits, or monkeys. This information may be helpful for drug researchers to select the most relevant animal species in which the metabolism of a compound can be studied for extrapolating the results to humans. Furthermore, state-of-the-art methods for determining PPB such as equilibrium dialysis, ultracentrifugation, microdialysis, gel filtration, chromatographic methods and fluorescence spectroscopy are highlighted with their advantages and disadvantages.

Antimicrobial Activity of Antibiotics, Oregano and Thyme Essential Oils against Extended Spectrum Beta Lactamase Producing Klebsiella pneumoniae Clinical Isolates

Aims: The aims of this study was to investigate the susceptibility of extended-spectrum beta-lactamase (ESBL) producing Klebsiella pneumoniae clinical isolates to antibiotics and essential oils - Origanum compactum, Origanum majorana and Thymus serpyllum. 
 Study Design: Study included 30 isolates of Klebsiella pneumoniae obtained from clinical material provided from the University Clinical Center Tuzla.
 Place and Duration of Study: Department of Biology, Faculty of Science, University of Tuzla, BiH, between September 2019 to September 2020.
 Methodology: Antibiotic susceptibility testing was performed by the Kirby-Bauer disk diffusion method. The following commercially available antibiotic discs were used: amoxicillin (30µg), cefalexin (30 µg), gentamicin (10 µg), amikacin (30 µg), imipenem (10 µg), piperacillin (75µg), ampicilin (10 µg), meropenem (10 µg), ciprofloksacin (10 µg), ceftazidim (30 µg), cefotaksim (30 µg), ceftriaxone (30 µg), cefepime (30 µg) and aztreonam (30 µg). The antibacterial effect of the essential oils was tested for ESBL K. pneumoniae isolates using the diffusion method according to Clinical laboratory standards institute (CLSI) guidelines.
 Results: O. compactum and O. majorana essential oils showed the same antimicrobial activity with 80.0% effect on ESBL K. pneumoniae isolates, Thymus serpyllum EO showed antimicrobial activity of 60.0%. The lowest MIC value had the O. compactum essential oil (MIC 6 mg/ml-10.5 mg/ml), followed by the T. serpyllum (MIC 17.2 mg/ml-43 mg/ml), while the O. majorana essential oil showed MIC values in range from 11 mg/ml to 39 mg/ml.
 Conclusion: The results of the study showed the exceptional sensitivity of ESBL K. pneumoniae clinical isolates to the essential oils from Origanum and Thymus genera, which highly suggests their potential application in the struggle against these pathogens in the future.

Antibiotics in the soil and their effect on the soil microbiot

Antibiotics have been crucial in the fight against infectious diseases for the past 50 years. In agriculture they are widely used in the treatment of animals, birds and aquaculture, to prevent spoilage of feed, as stimulators of growth and productivity of livestock, in the production of essential amino acids as impurities in feed, and so on. At present, the use of antibiotics in animal husbandry has become excessive due to the prevention of global epidemics. In turn, the ingress of antibiotics into water and soil, in particular through organic fertilizers, poses a potential threat to these environments. Thus, a variety of antibiotic resistance genes (GRAs) are spreading in soil microorganisms, which is currently a global health problem. It is believed that the stability of antibiotics after entering the soil is mainly due to their rate of decomposition and sorption to the organic soil matrix. A wide range of values of the half-life (DT50) of these compounds in soils indicates that their stability depends on a number of factors: soil properties, climatic conditions (temperature, precipitation, and humidity), physicochemical characteristics of antibiotics. High antimicrobial activity of antibiotics in the soil differentially inhibits the development of soil microorganisms, affects their species composition, which can cause changes in the ecological functionality of the soil. Thus, even low concentrations of antibiotics significantly reduce soil respiration. This phenomenon is especially noticeable in the presence of sulfamethoxazole, sulfamethazine, sulfadiazine and trimethoprim in the soil. The presence of antibiotics in the soil affects the processes of nitrification and / or denitrification, and the inhibition of these processes depends on the duration of exposure and the type of compound. Monensin and chlortetracycline at concentrations of 0.01–0.1 and 0.0003–0.3 mg/kg of soil do not affect nitrification at all. Antibiotics also affect the rate of iron transformation in the soil. Thus, sulfadiazine and monensin block the reduction of iron (Fe (III)) in the soil from a few days to 50 days. It should be noted that the lack of standardized tests hinders research that would lead to generalized conclusions about the effects of antibiotics on biogeochemical cycles, in particular on iron circulation. An important indicator of the response to antibiotics in the soil is considered to be the change in the enzymatic activity of dehydrogenase, phosphatase and urease of soil microorganisms, which may be associated with growth inhibition or death of sensitive microorganisms. In addition, the presence of some antibiotics in the soil can cause over-population of fungal populations, which are generally less sensitive to antibiotics than bacteria. There is evidence that antibiotics alter the enzymatic activity of soil microorganisms, especially they affect the ability to metabolize carbon of various origins. In addition, antibiotics not only affect the total number of microbiota, but also the relative content of different groups (gram-negative and gram-positive bacteria, fungi) in microbial populations. The importance of GRA studies of soil microorganisms is that they have led to the discovery of new genes responsible for bacterial resistance to antibiotics.

An invitro study of synergetic effect of Vitamin C on antimicrobial activity of antibiotics against isolated from respiratory samples

Vitamins are essential for various biological responses such as immune function and gene expression in humans. The infections of respiratory tract with is quite common throughout the world. Vitamin C supplements reduces the duration and symptoms of the respiratory infections shown by few therapeutic trials. This study was undertaken to find out whether Vitamin C has got any effect upon the sensitivity pattern of antibacterial prescribed for isolated from respiratory samples using disc diffusion method in vitro. In our study, by using student T test analysis, Vitamin C significantly decreased the inhibition zone of antibiotics Ciprofloxacin (40%), Imipenem (72%) indicating a decrease in their antibacterial effect invitro. Also, Vitamin C enhanced the antibacterial effect of Doxycycline (64%) and Ceftazidime-Clavulanic acid (36%) significantly. Significant decrease in zone diameter was observed on addition of Vitamin C to antibiotics, Imipenem (56%), Ciprofloxacin (40%). It is to be noted that effect of Vitamin C on Ceftazidime-Clavulanic acid is both increase and decrease in zone diameter which were also statistically significant. This might be due to small sample size of isolates (Number – 50) undertaken in the study. The observations noted in this study need further development in terms of increased number of isolates and proper standardization of Vitamin concentrations, with respect to each antibiotic. Being an invitro study, it does not establish any chemical interactions between Vitamins and antibiotics and needs further research by clinical methods. : The interaction of Vitamin C on antibacterial against common respiratory pathogens needs further exploration in the area of research as they show interesting results when studied invitro under a small sample size.

Iron-withdrawing anti-infectives for new host-directed therapies based on iron dependence, the Achilles' heel of antibiotic-resistant microbes.

The iron dependence of antibiotic-resistant microbes represents an Achilles’ heel that can be exploited broadly. The growing global problem of antibiotic resistance of microbial pathogens wherein microbes become resistant to the very antibiotics used against them during infection is linked not only to our health uses but also to agribusiness practices and the changing environment. Here we review mechanisms of microbial iron acquisition and host iron withdrawal defense, and the influence of iron withdrawal on the antimicrobial activity of antibiotics. Antibiotic-resistant microbes are unaltered in their iron requirements, but iron withdrawal from microbes enhances the activities of various antibiotics and importantly suppresses outgrowth of antibiotic-exposed resistant microbial survivors. Of the three therapeutic approaches available to exploit microbial iron susceptibility, including (1) use of gallium as a non-functional iron analogue, (2) Trojan horse conjugates of microbial siderophores carrying antibiotics, and (3) new generation iron chelators, purposely designed as anti-microbials, the latter offers various advantages. For instance, these novel anti-microbial chelators overcome the limitations of conventional clinically-used hematological chelators which display host toxicity and are not useful antimicrobials. 3-Hydroxypyridin-4-one-containing polymeric chelators appear to have the highest potential. DIBI (developmental code name) is a well-developed lead candidate, being a low molecular weight, water-soluble copolymer with enhanced iron binding characteristics, strong anti-microbial and anti-inflammatory activities, low toxicity for animals and demonstrated freedom from microbial resistance development. DIBI has been shown to enhance antibiotic efficacy for antibiotic-resistant microbes during infection, and it also prevents recovery growth and resistance development during microbe exposure to various antibiotics. Because DIBI bolsters innate iron withdrawal defenses of the infected host, it has potential to provide a host-directed anti-infective therapy.

Changes in antimicrobial activity and resistance of antibiotics in meat patties during in vitro human digestion

We aimed to determine changes in the antimicrobial activity of penicillin, cephalosporin, tetracycline, and ofloxacin present in patties cooked at 150, 200, or 250 °C, at different stages of in vitro human digestion, over Staphylococcus aureus (S. aureus) and Methicillin-resistant Staphylococcus aureus (MRSA). Results revealed that the antimicrobial activity of antibiotics were the same regardless of meat types and cooking temperatures. However, after small intestine digestion, some differences were observed, especially in tetracycline and ofloxacin activities. The antimicrobial activity of tetracycline was slightly higher over S. aureus than over MRSA. Besides, the activity of ofloxacin was relatively maintained, compared to the rest of the antibiotics, showing antimicrobial activity against S. aureus regardless of in vitro digestion. These results may provide an insight on antimicrobial activity changes of antibiotics under various condition. Notably, they suggest that ofloxacin residues in meat may have a higher activity than other antibiotics.

Antibiotic resistance in Acinetobacter baumannii as agent of surgery infection and approaches to its overcoming by means of deca-methoxinum antiseptic

Introduction. Non-fermenting Gram-negative bacilli are known as one of the most frequent causative agents of hospital-acquired infections. Acinetobacter baumannii, as causative agent of infection complications of different localization, has obtained recently high resistance to anti-biotics and has belonged to ESKAPE group of pathogens. Antimicrobials, recommended for the prophylaxis and therapy of hospital-acquired infections, have been failing in their effectiveness and lead to selection of antibiotic resistant strains of A. baumannii.
 The aim of this research was to substantiate the way of overcoming of resistance in clinical strains of A. baumannii, by means of synergic antimicrobial activity of antibiotics and antiseptic decamethoxinum®.
 Material and methods. The research was carried out on 190 clinical strains of A. baumannii, isolated from patients with burn disease during the period 2011–2015. The sensitivity of clinical strains of A. baumannii was determined to such antibiotics as ampicillin/sulbactam, cefoperazone, cefoperazone/sulbactam, meropenem, imipenem, amikacin, ciprofloxacin, gatifloxacin and antiseptic decamethoxinum® (DCM; Registration certificate No UA/14444/01/01 since 24.06.2015. Order of the Ministry of Health of Ukraine No 373). The sensitivity of A. baumannii to antibiotics and DCM was determined by means of disk diffusion test and serial dilution (Order of the Ministry of Health of Ukraine No167 since 05.04.2007; EUCAST expert rules).The study of the influence of antiseptic DCM on the sensitivity of acinetobacteria to antibiotics was studied on 35 clinical strains of A. baumannii, drafted from the general number of isolates enrolled in the research. For this, the sensitivity of A. baumannii to antibiotics in the presence of sub-minimal inhibitory concentrations (subMIC) of DCM was identified. The received experimental data were analyzed by “Statistica 6.0”.
 Results and discussion. The changes of antibiotic sensitivity profile of A. baumannii for five years were shown. It was found that the sensitivity of A. baumannii to majority of antibiotics, selected for study, decreased significantly. But the only ampicillin/sulbactam was found to have vice versa tendency. We found the rising quantity of antibiotic resistant strains of A. baumannii. At the same time, high resistance of acinetobacteria to fluoroquinolones (ciprofloxacin– 96,1%; gatifloxacin– 95,8%) was found in 2015.
 The in vitro research of combined activity of DCM antiseptic remedy and early mentioned antibiotics against clinical strains of A. baumannii demonstrated the reveal antibiotic effectiveness. As follows, minimal inhibitory concentrations of antibiotics decreased in 1.5–4 times in the mediums which contained subMIC of DCM. Especially this tendency was found in resistant clinical strains.
 Conclusion. Under selective influence of antibiotics protected by β-lactamase inhibitors, carbapenems, fluoroquinolones aminoglycosides increase the antibiotic resistance in A. baumannii, causative agents of infectious complications in patients with burn disease. The antiseptic remedy decamethoxinum® helps to improve antibiotic sensitivity in resistant A. baumannii.

Antimicrobial Susceptibility Testing Methods for Acinetobacter spp.

Serial twofold dilution methods are most commonly used to identify the antimicrobial activities of antibiotics. This can be achieved by different methods like broth dilution or agar dilution. Though these methods are simple, they can be influenced by various experimental factors and result in discrepancy. The following protocol has been validated for Acinetobacter species, including A. baumannii. It is important to include appropriate control strains to determine the minimum inhibitory concentration values and to compare the experiment results.

Changes in resistance to and antimicrobial activity of antibiotics during in vitro human digestion.

This study was performed to determine changes in (i) the antimicrobial activity of antibiotics (tetracycline, ofloxacin and penicillin) and (ii) the resistance of Staphylococcus aureus RN4220 (SA RN4220) and methicillin-resistant S. aureus (MRSA) to these antibiotics during in vitro human digestion. A human gastrointestinal digestion model simulating the conditions of the mouth, stomach, small intestine and large intestine (with intestinal microbial application) was used in this study. Antimicrobial susceptibility testing was performed by the disk diffusion method according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Concentrations of the three antibiotics decreased during digestion. In particular, the three antibiotics were unstable under conditions of stomach to large intestine digestion, and thus a decrease in antibiotic concentration could cause a reduction in antimicrobial activity during in vitro human digestion. The resistance of SA RN4220 and MRSA to the three antibiotics increased after in vitro human digestion. SA RN4220 and MRSA showed less resistance to ofloxacin compared with tetracycline and penicillin during in vitro human digestion. These results may help to explain the factors affecting antimicrobial activity and resistance to antibiotics during digestion in the human alimentary canal.

English

Now-a-days majority of world population rely on the plant preparations as medicines to cure diseases, as they are considered safe and as effective as allopathic preparations without any side effects. Spices are plant products having aroma, are mainly used during cooking to impart flavor and taste to the dish and also possess medicinal values. The present study was designed to evaluate the antimicrobial activity of four Indian spices: clove (Syzygium aromaticum), cinnamon (Cinnamomum verum), turmeric (Curcuma longa), and black pepper (Piper nigrum) against Gram positive and Gram negative pathogenic bacteria viz., Staphylococcus aureus (ATCC 25923), Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), and Klebsiella pneumoniae (ATCC 70063) using aqueous, 75% ethanol and 75% chloroform extracts. The antibacterial activity of spices extract and spices which are used in powder form was determined by agar well diffusion method and the antimicrobial activity of antibiotics (Clindamycin, Ciprofloxacin, Gentamycin) was measured by disc diffusion method. The clove and cinnamon extracts had exhibited maximum antibacterial property against pathogens; also, turmeric had shown less antimicrobial activity, while black pepper had exhibited moderate activity. Spices (powder) had shown highest antimicrobial activity than spice extracts. Phytochemical screening was carried out on ethanol, chloroform and distilled water extracts of spices for its chemical composition. Qualitative phytochemical analysis of these spice extracts confirm the presence of various phytochemicals like alkaloids, terpanoids, flavonoids, saponins, steroids and tannins. Key words: Antimicrobial activity, Piper nigrum, agar well diffusion method and phytochemicals.

Antimicrobial activity of Antibiotics and Antiseptics (Dettol and Betadine) against Clinical Isolates of Pseudomonas aeruginosa

Antimicrobial activity of Antibiotics and Antiseptics (Dettol and Betadine) against Clinical Isolates of Pseudomonas aeruginosa

Human Bile Reduces Antimicrobial Activity of Selected Antibiotics against Enterococcus faecalis and Escherichia coli In Vitro.

It has been known from previous studies that body fluids, such as cerebrospinal fluid, lung surfactant, and urine, have a strong impact on the bacterial killing of many anti-infective agents. However, the influence of human bile on the antimicrobial activity of antibiotics is widely unknown. Human bile was obtained and pooled from 11 patients undergoing cholecystectomy. After sterilization of the bile fluid by gamma irradiation, its effect on bacterial killing was investigated for linezolid (LZD) and tigecycline (TGC) against Enterococcus faecalis ATCC 29212. Further, ciprofloxacin (CIP), meropenem (MEM), and TGC were tested against Escherichia coli ATCC 25922. Time-kill curves were performed in pooled human bile and Mueller-Hinton broth (MHB) over 24 h. Bacterial counts (in CFU per milliliter after 24 h) of bile growth controls were approximately equal to MHB growth controls for E. coli and approximately 2-fold greater for E. faecalis, indicating a promotion of bacterial growth by bile for the latter strain. Bile reduced the antimicrobial activity of CIP, MEM, and TGC against E. coli as well as the activity of LZD and TGC against E. faecalis This effect was strongest for TGC against the two strains. Degradation of TGC in bile was identified as the most likely explanation. These findings may have important implications for the treatment of bacterial infections of the gallbladder and biliary tract and should be explored in more detail.

Synergistic Effect of Metal Nanoparticles on the Antimicrobial Activities of Antibiotics against Biorecycling Microbes

Biorecycling microbes, which have critical functionalities in natural cycles, are essential to sustain ecosystem of the earth. Any alterations in these cycles caused by the mutations of microbes could be a potential threat to life on earth. Antibiotics leached from pharmaceutical waste, animal food and agribusiness products are accumulating in the environment. Metal nanoparticles are also accumulating in environment because of their extensive use as biocidal agent in domestic products. Interaction of antibiotics and metal nanoparticles with eco-friendly microorganisms has a potential to alter the ecosystem of the earth. In this article, we have studied the antibacterial activities of silver and copper nanoparticles and their formulations with antibiotics, tetracycline, and kanamycin against biorecycling microbes, Bacillus subtilis and Pseudomonas fluorescens. Strong synergistic effect of metal nanoparticles on the antimicrobial activities of commercial antibiotics has been observed. Antimicrobial activity of tetracycline improves by 286%–346% and 0%–28% when being tested in the presence of 250 ppm of silver and copper nanoparticles, respectively. For kanamycin, the improvement is 154%–289% for silver and 3%–20% for copper nanoparticles. Irrespective of the antibiotics and tested organisms, synergy is more prominent for silver nanoparticles even at their minimum active concentration (100 ppm). This study demonstrates that the combination of metal nanoparticles with antibiotics could be more fatal to ecosystem than either the metal nanoparticles or the antibiotics alone.

Antimicrobial chemotherapy of Mycoplasma genitalium-positive non-gonococcal urethritis

Mycoplasma genitalium is an important pathogen of acute non-gonococcal urethritis (NGU) in men and plays a significant role in persistent or recurrent NGU. In the management of patients with M. genitalium-positive NGU, eradication of the mycoplasma from the urethra is necessary to prevent persistent or recurrent NGU. Therefore, M. genitalium should be considered for antimicrobial chemotherapy of NGU. This article reviews the in vitro antimicrobial activities of antibiotics against M. genitalium and the efficacies of various antibiotic regimens against M. genitalium-positive NGU, including the doxycycline and azithromycin regimens recommended as first-line treatments for NGU in the guidelines. Selection of macrolide-resistant M. genitalium by treatment with the single-dose regimen of 1-g azithromycin and mechanisms of macrolide resistance in M. genitalium are discussed. The effectiveness of the moxifloxacin regimen against persistent or recurrent NGU, unsuccessfully treated with azithromycin and/or doxycycline regimens, is emphasized.

Antimicrobial activity of antibiotics in urine under different physiological conditions

Methods Urine obtained from healthy volunteers was pooled and sterile filtered. Microdilution tests were performed with Escherichia coli ATCC 25922 in MHB and human urine. The pH of urine was adjusted to values ranging from 5 to 8. For simulating different glucose levels in urine of diabetic patients, urine was adjusted to glucose levels of 100 and 1000 mg/dL. Bacterial growth in different media was investigated by growth curves. Results obtained from MIC testing were confirmed by use of bacterial killing curves. Klebsiella oxytoca ATCC 700324 was used to investigate transferability of finding to other strains. Each experiment was performed 5 times.

Effect of galbanic acid, a sesquiterpene coumarin from Ferula szowitsiana, as an inhibitor of efflux mechanism in resistant clinical isolates of Staphylococcus aureus

Galbanic acid, a sesquiterpene coumarin from Ferula szowitsiana roots, was investigated for its potentiating effect on the antimicrobial activity of antibiotics as well as ethidium bromide, in 6 multidrug resistance (MDR) clinical isolates of Staphylococcus aureus. Galbanic acid had inhibitory effect on none of the isolated bacteria tested (up to 800 μg /ml). The MIC range of ciprofloxacin, tetracycline and ethidium bromide, against all tested S. aureus were 10-80, 10-80 and 4-16 μg/ml, respectively. These were reduced to ≤2.5-5, 2.5-5 and 0.5-2 μg/ml in the presence of galbanic acid (300 μg /ml) or verapamil (100 μg /ml). The rate of ethidium bromide (2 μg /ml) accumulation in clinical isolates was enhanced with galbanic acid (300 μg /ml). There is also a decrease in loss of ethidium bromide from bacteria in the presence of galbanic acid. Similar results were obtained when verapamil (100 μg /ml) was used as an efflux pump inhibitor. Galbanic acid, like verapamil, a typical inhibitor of efflux pump, reduced the MIC of ethidium bromide and tested antibiotics. Since efflux is the only known reported mechanism for ethidium bromide resistance, the reduction in ethidium bromide MIC and enhanced accumulation as well as decreased efflux of ethidium bromide in the presence of galbanic acid, can be attributed to this efflux inhibitory properties.

Protein Binding of Antimicrobials: Methods for Quantification and for Investigation of its Impact on Bacterial Killing

Plasma protein binding of antimicrobial agents is considered to be a key characteristic of antibiotics as it affects both their pharmacokinetics and pharmacodynamics. However, up to the present, no standard methods for measuring protein binding or for quantification of the influence of protein binding on antimicrobial activity exist. This short-coming has previously led to conflicting results on antibacterial activity of highly protein-bound antibiotics. The present review, therefore, set out to summarize (1) methods for quantification of protein binding, (2) microbiological growth media used for determination of the impact of protein binding on antimicrobial activity of antibiotics, and (3) different pharmacodynamic in vitro studies that are used in this context. The advantages and disadvantages of a wide range of different approaches are discussed and compared. The urgent call for international standardization by microbiological societies and laboratories may be considered as a logical consequence of the presented data.

Antimicrobial activity of antibiotics in combination with natural flavonoids against clinical extended‐spectrum β‐lactamase (ESBL)‐producing Klebsiella pneumoniae

Extended-spectrum beta-lactamases (ESBLs) are plasmid-mediated class A enzymes commonly found in the family Enterobacteriaceae, mainly in Klebsiella pneumoniae. Flavonoids have also been reported to possess antimicrobial activity. In this study, the in vitro activities of 18 antibiotics and 12 flavonoids against 20 ESBL-producing K. pneumoniae isolates were evaluated. All of these isolates were susceptible to imipenem and cefmetazole, but were resistant to ampicillin, ampicillin/sulbactam, aztreonam, cefazolin, cefoperazone, cefotaxime, ceftazidime, ceftriaxone, cefuroxime, piperacillin and ticarcillin. Susceptibilities to amikacin, amoxicillin/clavulanate, cefoxitin, ciprofloxacin and gentamicin were variable. Myricetin, a flavonol, inhibited ESBL-producing K. pneumoniae isolates at a high minimum inhibitory concentration (MIC) (MIC(90) value 256 mg/mL), but exhibited significant synergic activity against ESBL-producing K. pneumoniae in separate combination with amoxicillin/clavulanate, ampicillin/sulbactam and cefoxitin. Because of the low-toxic nature of flavonoids, the combination of antibiotics and flavonoids is a potential new strategy for developing therapies for infections caused by ESBL-producing bacteria in the future.

Effect of low intraphagolysosomal pH on antimicrobial activity of antibiotics against ingested staphylococci.

The ability of aminoglycoside antibiotics and rifampicin to kill Staphylococcus aureus that had been ingested by blood polymorphonuclear leukocytes (PMNs) in vitro was investigated. Gentamicin and streptomycin failed to kill intracellular staphylococci, possibly because they could not penetrate PMNs or were inactivated by the low intraphagolysosomal pH. Rifampicin accumulated within the leukocytes in a form that killed staphylococci in a cell-free medium, but the bactericidal activity of intracellular rifampicin against ingested staphylococci was much less than that in a cell-free system. Investigations with granules isolated from PMNs, at various pH-values, revealed that the impairment of rifampicin activity was a result of limitation of the staphylococcal growth rate by a low pH. These observations indicate that the inhibition of intraphagocytic bacterial growth by the low intraphagolysosomal pH and other phagolysosomal bacteristatic factors determines the antimicrobial activity of accumulated antibiotics.

Intracellular penetration and antimicrobial activity of antibiotics.

Delayed response or recurrence of clinical infections may, in part, be due to the inability of certain antibiotics to penetrate human polymorphonuclear leukocytes (PMN) and exert intracellular antibacterial activity. We determined the penetration of PMN by certain hydrophilic and certain lipophilic antibiotics, and assessed their activity against intracellular Haemophilus influenzae, type b or Staphylococcus aureus. We found that penicillin G was excluded from human PMN while chloramphenicol was concentrated within these cells; chloramphenicol killed significantly more intracellular H. influenzae than did penicillin or ampicillin. Clindamycin and trimethoprim penetrated into normal and chronic granulomatous disease (CGD) PMN equally and were at least transiently concentrated in the cells. Clindamycin and the combinations trimethoprim/sulphamethoxazole and trimethoprim/rifampicin were most effective in killing intracellular Staph. aureus in vitro; these antibiotics reduced the bacterial density in CGD PMN to values comparable to those in normal PMN. The mechanism by which clindamycin and rifampicin killed intracellular Staph. aureus appeared to be due to direct antimicrobial activity. Antibiotics that penetrate into phagocytes may be more effective in infections due to pathogens capable of intracellular survival.