Minimum Inhibitory Concentration Of Gentamicin Research Articles

Temperate phage-antibiotic synergy across antibiotic classes reveals new mechanism for preventing lysogeny.

A recent demonstration of synergy between a temperate phage and the antibiotic ciprofloxacin suggested a scalable approach to exploiting temperate phages in therapy, termed temperate phage-antibiotic synergy, which specifically interacted with the lysis-lysogeny decision. To determine whether this would hold true across antibiotics, we challenged Escherichia coli with the phage HK97 and a set of 13 antibiotics spanning seven classes. As expected, given the conserved induction pathway, we observed synergy with classes of drugs known to induce an SOS response: a sulfa drug, other quinolones, and mitomycin C. While some β-lactams exhibited synergy, this appeared to be traditional phage-antibiotic synergy, with no effect on the lysis-lysogeny decision. Curiously, we observed a potent synergy with antibiotics not known to induce the SOS response: protein synthesis inhibitors gentamicin, kanamycin, tetracycline, and azithromycin. The synergy results in an eightfold reduction in the effective minimum inhibitory concentration of gentamicin, complete eradication of the bacteria, and, when administered at sub-optimal doses, drastically decreases the frequency of lysogens emerging from the combined challenge. However, lysogens exhibit no increased sensitivity to the antibiotic; synergy was maintained in the absence of RecA; and the antibiotic reduced the initial frequency of lysogeny rather than selecting against formed lysogens. Our results confirm that SOS-inducing antibiotics broadly result in temperate-phage-specific synergy, but that other antibiotics can interact with temperate phages specifically and result in synergy. This is the first report of a means of chemically blocking entry into lysogeny, providing a new means for manipulating the key lysis-lysogeny decision.IMPORTANCEThe lysis-lysogeny decision is made by most bacterial viruses (bacteriophages, phages), determining whether to kill their host or go dormant within it. With over half of the bacteria containing phages waiting to wake, this is one of the most important behaviors in all of biology. These phages are also considered unusable for therapy because of this behavior. In this paper, we show that many antibiotics bias this behavior to "wake" the dormant phages, forcing them to kill their host, but some also prevent dormancy in the first place. These will be important tools to study this critical decision point and may enable the therapeutic use of these phages.

Effects of feeding pasteurized waste milk or saleable milk to calves on weight, health and fecal Escherichia coli antimicrobial resistance.

The aim of this study was to compare the effects of feeding pasteurized waste milk or saleable milk to calves on weight, health and emergence of antimicrobial resistance in Escherichia coli strains isolated from those calves. An experimental study under field conditions on a commercial pasture-based Argentinian dairy farm was carried out. Forty Holstein calves were assigned randomly to either pasteurized waste milk (PWM) or non-pasteurized saleable milk (SM). The antimicrobial agents (AM) used on the farm, both to treat or prevent diseases, were recorded. The passive immunity level, calf live weight, AM presence in milk, clinical examination of calves, and E. coli isolation and identification, were performed. A total of 258 E. coli strains were isolated from fecal samples (132 isolates from SM calves and 126 from PWM calves at six sampling times). All E. coli isolated were used to perform AM susceptibility tests (disc diffusion and agar dilution). No differences were observed between groups in health parameters, average daily gain or prevalence of resistant E. coli strains to any AM evaluated throughout the study. Peaks of trimethoprim, sulfamethoxazole and enrofloxacin minimum inhibitory concentration (MIC) were observed at 30 d in E. coli from both groups of calves, whilst additional peaks to tetracyclin and ampicillin were observed only in SM calves. All MIC apart from gentamicin decreased at 75 and 90 d of age (during the weaning period). Gentamicin MIC behaved differently, having no peaks and increasing at 90 d only in PWM group. In conclusion, we found no evidence that emergence of antibiotic resistance is related to the consumption of pasteurized waste milk.

Gentamicin Susceptibility and Comparison of Adhesion and Invasion of Caco-2 and HD11 Cell Lines by Salmonella enterica Serotypes

Foodborne Salmonella serovars are important facultative intracellular pathogens that cause gastroenteritis in humans. Four strains from three of the more predominant Salmonella serovars in poultry were studied: Typhimurium, Enteritidis, and Heidelberg. Gentamicin susceptibility was determined using an agar disc diffusion test and minimum inhibitory concentration (MIC) assays for S. Typhimurium ATCC 14028 and S. Heidelberg ARI-14. Both strains were susceptible to gentamicin in disc diffusion. The MIC of gentamicin was approximately 125 mg/ml for all strains tested. These strains’ adhesion and invasion abilities were determined with two different cell lines, a human intestinal epithelial cell line (Caco-2) as well as a chicken macrophage cell line (HD11). Attachment percentages for each Salmonella strain were greater than the strain’s ability to invade cells. Similar attachment percentages to Caco-2 cells were observed for S. Typhimurium and S. Heidelberg. Attachment percentages were lower in HD11 cells than in Caco-2 cells, although Salmonella exhibited higher apparent HD11 invasion, likely from HD11 phagocytosis. Salmonella Enteritidis showed lower rates of adhesion and invasion in HD11 cells compared to Salmonella Typhimurium. Developing a better understanding of Salmonella virulence mechanisms is critical to reducing Salmonella infections.

Anti-fungal efficacy of combination of amphotericin B with colistin and gentamicin in McCarey-Kaufman corneal preservation medium.

To curtail the potential of donor corneal tissue disseminating fungi to the recipient's eye, we evaluated the addition of amphotericin B to McCarey-Kaufman (M-K)-corneal storage medium supplemented with colistin. Amphotericin B was examined for its ability to inhibit the growth of Candida albicans and Aspergillus flavus using a microbroth dilution test and checkerboard assay in combination with only gentamicin and a combination of colistin, gentamicin, and amphotericin B. The safety on epithelium and endothelium was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The minimal inhibitory concentration of gentamicin was found to be >256 μg/ml against both C. albicans and A. flavus, whereas that of amphotericin B was found to be in a range of 0.25-0.5 and 1-2 μg/ml for C. albicans and A. flavus, respectively. According to the checkerboard assay, 80% (4/5) of C. albicans isolates and 100% (5/5) of A. flavus isolates responded synergistically to the combination of amphotericin B and gentamicin, but only 20% (1/5) of C. albicans isolates showed an additive effect. None of the tested isolates displayed antagonism. The combined effect of the three drugs also did not display any antagonistic effect. Additionally, the MTT assay reveals no toxic effect of the antimicrobials used on corneal epithelial and endothelial cells. In vitro experiments demonstrate that amphotericin B is not toxic to either epithelium or endothelium and is a promising additive to the M-K medium supplemented with colistin.

Ascorbate and Antibiotics, at Concentrations Attainable in Urine, Can Inhibit the Growth of Resistant Strains of Escherichia coli Cultured in Synthetic Human Urine.

There are conflicting reports on the antibacterial activity of ascorbate; all at concentrations much higher than the typical in human plasma, but that can be reached in urine. The effect of 10 mM ascorbate (in itself not inhibitory) along with antibiotics, was tested both in Mueller-Hinton broth (MHb) and in synthetic human urine (SHU), against resistant isolates of Escherichia coli from lower urinary infections. The activity of nitrofurantoin and sulfamethoxazole was higher in SHU than in MHb; minimal inhibitory concentrations (MICs) in SHU with ascorbate were below typical urinary concentrations. For other antibiotics, MICs were the same in MHb vs. SHU, with no effect of ascorbate in MHb; but in SHU with ascorbate, MICs of ciprofloxacin and gentamicin also went below reported urinary concentrations, with a lesser effect with norfloxacin and trimethoprim, and none with ampicillin. The effect of ascorbate was independent of oxygen and not related to the susceptibility of each strain to oxidative stress. Ascorbate oxidizes during incubation in SHU, and bacterial growth partially prevented oxidation. These results suggest that 10 mM ascorbate can enhance the inhibitory activity of antibiotics upon resistant strains in urine. Clinical experimentation with ascorbate-antibiotic combinations against urinary infections caused by resistant bacteria is warranted.

Drug repurposing in the context of common bacterial pathogens

The clinical problem of multidrug resistance (MDR) in bacteria is due to the lack of novel antibiotics in development and the dwindling pipeline of drugs receiving market authorization. Repurposing of non-antibiotic pharmacological agents may be an attractive pathway to provide new antimicrobial drugs. The aim of the present study was to ascertain the antibacterial and adjuvant properties of a wide range of pharmaceuticals against antibiotic-susceptible and drug-resistant bacteria. Sixty-five (n = 65) pharmacological agents were included in our experiments. For Gram-positive bacteria, Staphylococcus aureus ATCC 43300 (methicillin-resistant), S. epidermidis ATCC 12228, Streptococcus pyogenes ATCC 12384 and Enterococcus faecalis ATCC 29212 were used, while for Gram-negative bacteria, Enterobacter cloacae ATCC 13047 (extended-spectrum β-lactamase-positive), Klebsiella pneumoniae ATCC 49619, Serratia marcescens ATCC 29632 and Pseudomonas aeruginosa ATCC 27853 were included as representative strains. The minimum inhibitory concentrations (MICs) of the tested compounds were determined using the standard broth microdilution method, while a MIC reduction assay was included to ascertain the effect of the tested compounds on the MICs of standard antibiotics (ceftriaxone, ciprofloxacin and gentamicin). Seventeen and twelve drug molecules tested showed measurable antibacterial activities (MIC: 32-512 µg/mL) against Gram-positive and Gram-negative bacteria, respectively. Several compounds decreased the MICs of ciprofloxacin and gentamicin. Although there are increasing number of studies in this field, there are still significant gaps in the evidence to the potential use of non-antibiotic drugs in antimicrobial drug repurposing.

Change in antimicrobial susceptibility of Listeria spp. in response to stress conditions

Listeria species are exposed to various stressors throughout the food chain, which are crucial for microbe mitigation strategy in the food industry. However, the survival capabilities and development of antimicrobial resistance by Listeria spp. under different food processing environments (FPEs) stressors are not yet well understood. Hence, this study aims to determine the difference in survivability and antimicrobial susceptibility of L. monocytogenes (Lm) and other Listeria species (non-Lm) strains exposed to different FPEs stressors, including heat, acidic and alkaline pH, UV irradiation, and osmotic stress. For this, a collection of 11 Lm and 10 non-Lm strains were used to conduct experiments. This study showed that Lm strains were relatively more tolerant to environmental stresses than non-Lm strains (p > 0.05). Additionally, the evaluation of stress-induced resistance toward antimicrobials showed that anaerobic incubation, after exposition to environmental stresses, rendered Lm and non-Lm more resistant to antimicrobial agents than aerobic incubation. Furthermore, the study observed that different stressors induced an increase in minimum inhibitory concentrations (MICs) of certain antimicrobials. Specifically, heat stress persuaded an increase in MICs of tetracycline under aerobic incubation, and gentamicin and ciprofloxacin under anaerobic incubation. Acidic/alkaline pH induced an increase in MICs of gentamicin, ciprofloxacin, and trimethoprim-sulfamethoxazole, especially under anaerobic incubation. However, UV stress induced increase in MICs of tetracycline and trimethoprim-sulfamethoxazole under aerobic incubation and gentamicin, ciprofloxacin, and trimethoprim-sulfamethoxazole under anaerobic incubation. Additionally, osmotic stress induced an increase in MICs of tetracycline and ampicillin under aerobic incubation and gentamicin, tetracycline, and trimethoprim-sulfamethoxazole under anaerobic incubation. Collectively, this study highlights that stress tolerance may contribute to the predominance of Listeria species among FPEs and induce the development of antimicrobial resistance even without antibiotic selection pressure. The findings of this study may guide updated strategies to mitigate Listeria species in the food industry.

Plant Secondary Metabolites on Efflux-Mediated Antibiotic Resistant Stenotrophomonas Maltophilia: Potential of Herbal-Derived Efflux Pump Inhibitors.

During the process of adapting to metal contamination, plants produce secondary metabolites that have the potential to modulate multidrug-resistant (MDR) phenotypes; this is achieved by inhibiting the activity of efflux pumps to reduce the minimum inhibitory concentrations (MICs) of antimicrobial substrates. Our study evaluated the effect of secondary metabolites of belowground parts of Pteris vittata L. and Fallopia japonica, two metal-tolerant plants from northern Vietnam, on six antibiotic-resistant Stenotrophomonas maltophilia strains possessing efflux pump resistance mechanisms that were isolated from soil and clinical samples. The chemical composition of aqueous and dichloromethane (DCM) fractions extracted from P. vittata and F. japonica was determined using UHPLC-DAD-ESI/QTOF analysis. The antibacterial and efflux pump inhibitory activities of the four fractions were evaluated for the six strains (K279a, 0366, BurA1, BurE1, PierC1, and 502) using a microdilution assay at fraction concentrations of 62.5, 125, and 250 μg/mL. The DCM fraction of F. japonica exhibited remarkable antibacterial activity against strain 0366, with a MIC of 31.25 μg/mL. Furthermore, this fraction also significantly decreased gentamicin MIC: four-fold and eight-fold reductions for BurA1 and BurE1 strains, respectively (when tested at 250 μg/mL), and two-fold and eight-fold reductions for K279a and BurE1 strains, respectively (when tested at 125 μg/mL). Pure emodin, the main component identified in the DCM fraction of F. japonica, and sennidine A&B only reduced by half the MIC of gentamicin (when tested at 30 μg/mL). Our results suggest that the DCM fraction components of F. japonica underground parts may be potential candidates for new bacterial efflux pump inhibitors (EPIs).

Antibacterial activity of Lithraea molleoides Hook et Arn. and Poiretia latifolia Vogel essential oils combined with gentamicin on foodborne disease-causing bacteria

The synergy between antimicrobial substances present in plant essential oils, with the goal of decreasing the required dosage of synthetic antibiotics is a viable strategy in the control of resistant pathogens. The present work aimed to characterize the chemical composition of EOs from Lithraea molleoides Hook et Arn. and Poiretia latifolia Vogel, as well as to evaluate their antimicrobial activities against some foodborne disease causing bacteria by determining minimum inhibitory concentration (MIC) in microplates, and their synergistic effects with a synthetic antibiotic by a checkerboard assay. The main compounds found in each EO were (E)-nerolidol (19.23%), (E)-caryophyllene (12.17%) and myrcene (11.52%) for L. molleoides, and carvone (61.81%), limonene (31.33%) and β-pinene (2.28%) for P. latifolia. Both EOs inhibited the tested microorganisms in one of the concentrations evaluated. Escherichia coli, Salmonella enteritidis, Staphylococcus aureus, and Bacillus cereus were inhibited with 20 mg mL−1 of L. molleoides EO. EO of P. latifolia inhibited B. cereus and E. coli growth at lower concentrations (10 mg mL−1 and 2.5 mg mL−1, respectively) and showed higher activity against E. coli, a Gram-negative bacteria. The highest synergistic interaction (IFIC <0.5) with the tested antibiotic was observed in P. latifolia EO, which reduced the MIC of gentamicin up to three times against all microorganisms except for E. coli (FICI = 3) which indicated indifference in their interaction. The combination of the antibiotic and L. molleoides EO showed synergism against B. cereus (IFIC = 0.4 and 0.5) but was indifferent to the remaining microorganisms (IFIC = 2.5, 1 and 1.5). These findings demonstrate the potential of these EOs as natural antibacterial agents that can contribute to reducing the adverse effects attributed to gentamicin.

Effects of Sub-Minimum Inhibitory Concentrations of Gentamicin on Alginate Produced by Clinical Isolates of Pseudomonas aeruginosa.

Bacterial virulence factors may be influenced by sub-minimum inhibitory concentrations (sub-MICs) of antibiotics. The main purpose of this study was to investigate the effects of gentamicin at sub-MICs (0.5 MIC and 0.25 MIC) on alginate production of clinical isolates of Pseudomonas aeruginosa. The minimum inhibitory concentrations of gentamicin against 88 clinical isolates of P. aeruginosa were determined using the broth microdilution method. Alginate production of the isolates in the absence and presence of gentamicin at sub-MICs was assessed by the carbazole method. The presence of alginate in clinical isolates was confirmed by the detection of alginate genes (algD and algU) using the PCR method. All the isolates had the ability of alginate production and were positive for algD and algU genes. sub-MICs of gentamicin significantly increased alginate production of 34 isolates (38.6%). On the other hand, in 49 isolates (55.7%), alginate production was significantly increased after treatment with sub-MICs of gentamicin. In five isolates (5.7%), the alginate production was reduced in exposure to 0.5 MIC of gentamicin while it was increased by gentamicin at 0.25 MIC. This study showed different effects of gentamicin at sub-MICs on the alginate production of clinical isolates of P. aeruginosa. Further research is highly recommended to understand the mechanism of different responses of P. aeruginosa isolates to the exposure of sub-MICs of gentamicin.

Distribution of MIC values of antibacterial drugs for Flavobacteriales isolated from respiratory samples in Russian patients with cystic fibrosis

Objective. Analysis of the distribution of the values of the minimum inhibitory concentrations (MIC) of a number of antibacterial drugs in relation to representatives of the order Flavobacteriales isolated from respiratory samples from patients with cystic fibrosis of the Russian Federation by the method of double serial dilutions. Materials and Methods. The distribution of the values of MIC of a number of antibacterial drugs was evaluated in relation to 100 strains of bacteria, representatives of the order Flavobacteriales, isolated from respiratory samples from patients with cystic fibrosis from 60 regions of the Russian Federation as part of a routine microbiological examination. Of these, 75 representatives of Chryseobacterium spp., among which C. arthrospherae – 28, C. formosense – 1, C. gambrini – 3, C. gleum – 10, C. indologenes – 20, C. joostei – 1, C. oraniemense – 10, C. shandongense – 2 strains, 4 strains of Elizabethkingia spp., among which 2 – E. miricola, and one strain of E. meningoseptica and E. anopheles, respectively, as well as 21 strains of E. falsenii. Identification of all isolated cultures was carried out using MALDI-ToF mass spectrometry (Bruker, Germany). The MIC values were determined for 17 antimicrobial drugs: amikacin, amoxicillin/clavulanate, aztreonam, cefotaxime, ceftazidime, ceftazidime/avibactam, ceftolozane/ tazobactam, ciprofloxacin, colistin, ertapenem, gentamicin, imipenem, meropenem, piperacillin/ tazobactam, tigecycline, tobramycin and trimethoprim/sulfamethoxazole using Sensititre kits DKMGN. Results. The MIC values of colistin, cefotaxime and tobramycin more than 8 µg/ml, as well as more than 2 µg/ml with respect to ertapenem was demonstrated for 100% of isolates. For most strains, the MIC values of imipenem and meropenem were more than 4 µg/ml. MIC of ceftazidime against 20% of Chryseobacterium spp. strains was up to 2 µg/ml. Indicators of MIC of amikacin in relation to Elizabethkingia spp. strains were 32 µg/ml or more. For 38% of the strains of Chryseobacterium spp. and E.falsenii, this value did not exceed 8 µg/ml. As in the case of amikacin, all Elizabethkingia spp. strains demonstrated high levels of gentamicin MIC – 8 µg/ml (25% of strains) and more (75% of strains). For 20% of all tested strains, the MIC value was in the range of ≤ 2 µg/ml. In relation to half of the tested isolates, the MIC values for ceftazidime/avibactam, as well as ceftolozane/tazobactam were at the level of up to 2⁄4 µg/ml inclusive. More than a third of the strains had a level of MIC ciprofloxacin up to 0.25 µg/ml inclusive. For 25% of strains, the level of MIC of tigecycline was up to 0.5 µg/ml, inclusive, the lowest MIC indicators for the tested group of strains were demonstrated for trimethoprim/sulfamethoxazole: for 88% of strains, the MIC value was ≤ 1⁄19 µg/ml, for another 9% of strains, this indicator was 2⁄38 µg/ml. Conclusions. Representatives of the order Flavobacteriales are a group of microorganisms characterized by multiple antibiotic resistance. Most strains isolated from patients with cystic fibrosis in the Russian Federation retain low MIC values for trimethoprim/sulfamethoxazole.

Variability in Adaptive Resistance of Salmonella Typhimurium to Sublethal Levels of Antibiotics.

This study was designed to evaluate the adaptive resistance of Salmonella Typhimurium under continuous sublethal selective pressure. Salmonella Typhimurium ATCC 19585 (STATCC) and S. Typhimurium CCARM 8009 (STCCARM) were sequentially cultured for 3 days at 37 °C in trypticase soy broth containing 1/2 × MICs of cefotaxime (CEF1/2), chloramphenicol (CHL1/2), gentamicin (GEN1/2), and polymyxin B (POL1/2). The STATCC and STCCARM exposed to CEF1/2, CHL1/2, GEN1/2, and POL1/2 were evaluated using antibiotic susceptibility, cross-resistance, and relative fitness. The susceptibilities of STATCC exposed to GEN1/2 and POL1/2 were increased by a 2-fold (gentamicin) and 8-fold (polymyxin B) increase in minimum inhibitory concentration (MIC) values, respectively. The MIC values of STCCARM exposed to CEF1/2, CHL1/2, GEN1/2, and POL1/2 were increased by 4-fold (cefotaxime), 2-fold (chloramphenicol), 2-fold (gentamicin), and 8-fold (polymyxin B). The highest heterogeneous fractions were observed for the STATCC exposed to CEF1/2 (38%) and POL1/2 (82%). The STCCARM exposed to GEN1/2 was cross-resistant to cefotaxime (p &lt; 0.05), chloramphenicol (p &lt; 0.01), and polymyxin B (p &lt; 0.05). The highest relative fitness levels were 0.92 and 0.96, respectively, in STATCC exposed to CEF1/2 and STCCARM exposed to POL1/2. This study provides new insight into the fate of persistent cells and also guidance for antibiotic use.

Identification, characterization and antibiotic susceptibility testing for Bacillus species.

With the increase in immunosuppressed patients and antimicrobial misuse, Bacillus species have risen as opportunistic pathogens in hospitalized patients. The present study aimed at comparing chromogenic media, automated identification cards versus MALDI-TOF as the gold standard method for identification of different Bacillus species and determining minimal inhibitory concentration (MIC) of different antibiotics by broth microdilution method (BMD) to suggest recommendations for Bacillus treatment. The study included 30 Bacillus species isolates recovered from normally sterile sites of the human body and were subjected to identification by MALDI-TOF, Vitek-2c, and HiCrome Bacillus Agar. BMD test was performed to determine the MIC of vancomycin, gentamicin, and ciprofloxacin. Our study showed B. cereus was the most commonly isolated species (76.66%) followed by B. subtilis (23.33%). Regarding the different methods of identification, the highest agreement with MALDI-TOF was exhibited by HiCrome agar without polymyxin B (93.3%) followed by Vitek-2C and HiCrome agar with polymyxin with an agreement of 83.3%. Concerning the antibiogram, the tested isolates showed a susceptibility of 93.3%, 86.6%, and 83.3% towards vancomycin, gentamicin, and ciprofloxacin respectively. In conclusion, we spotlight that Bacillus species should no longer be considered contaminant bacteria in cultures, particularly in immunosuppressed patients. HiCrome Bacillus Agar without polymyxin B displayed the highest agreement with MALDI-TOF. Hence, it represents a good option for identification for routine laboratories where expensive instruments are unavailable. The high susceptibility towards the tested antibiotics can suggest the possibility of empirical use of vancomycin, gentamicin, and ciprofloxacin.

In Vitro Study of the Interaction of Gentamicin with Ceftriaxone and Azithromycin against Neisseria gonorrhoeae Using Agar Dilution Method.

The susceptibility to gentamicin of N. gonorrhoeae isolates collected in three Chinese provinces and the correlation among the MICs of gentamicin, azithromycin, and ceftriaxone were investigated in this study. The effects of combinations from those three antibiotics were also in the scope of this study to determine the efficacy of gentamicin as a combination therapeutic drug. The agar dilution method was used to measure the minimum inhibitory concentrations (MICs) of ceftriaxone, azithromycin and gentamicin on N. gonorrhoeae isolates. The synergy between these three antimicrobials were determined using the agar dilution checkerboard method. Subgroup studies were conducted to explore differences between azithromycin- and ceftriaxone-sensitive and resistant isolates. A total of 139 (36.60%) and 233 (61.30%) isolates demonstrated full susceptibility and intermediate susceptibility to gentamicin, respectively. The correlation analysis showed that the MICs of ceftriaxone and azithromycin weakly correlated with the value of gentamicin. The overall results of the three antibiotic combinations revealed indifferent effects. Combination therapy established a significant reduction on the MIC value. Most of the N. gonorrhoeae isolates tested in this study demonstrated a certain degree of susceptibility to gentamicin. Overall, antimicrobial combinations of gentamicin with ceftriaxone or azithromycin demonstrate indifferent effects.

Tranexamic Acid in Combination With Vancomycin or Gentamicin Has a Synergistic Effect Against Staphylococci.

BackgroundTranexamic acid (TXA) is an antifibrinolytic agent applied in orthopedic surgery and has been proven to reduce post-surgery infection rates. We previously showed that TXA also had an additional direct antimicrobial effect against planktonic bacteria. Therefore, we aimed to evaluate whether it has a synergistic effect if in combination with antibiotics.Materials and MethodsThree ATCC and seven clinical strains of staphylococci were tested against serial dilutions of vancomycin and gentamicin alone and in combination with TXA at 10 and 50 mg/ml. The standardized microtiter plate method was used. Minimal inhibitory concentrations (MICs) were calculated by standard visualization of well turbidity (the lowest concentration at which complete absence of well bacterial growth was observed by the researcher) and using the automated method (the lowest concentration at which ≥80% reduction in well bacterial growth was measured using a spectrophotometer).ResultsTranexamic acid-10 mg/ml reduced the MIC of vancomycin and gentamicin with both the standard method (V: 1-fold dilution, G: 4-fold dilutions) and the automated turbidity method (vancomycin: 8-fold dilutions, gentamicin: 8-fold dilutions). TXA-50 mg/ml reduced the MIC of gentamicin with both the standard turbidity method (6-fold dilutions) and the automated turbidity method (1-fold dilutions). In contrast, for vancomycin, the MIC remained the same using the standard method, and only a 1-fold dilution was reduced using the automated method.ConclusionOurs was a proof-of-concept study in which we suggest that TXA may have a synergistic effect when combined with both vancomycin and gentamicin, especially at 10 mg/ml, which is the concentration generally used in clinical practice.

Effect of gentamicin and doxycycline on expression of relB and relE genes in Klebsiella pneumonia

The goal of study was determined that Klebsiella pneumoniae isolates possessed Toxin-Antitoxin II genes such as relE and relB, other than if there was a correlation between the expression of these two genes and antibiotics, and they may participate in increasing the resistance to antibiotics in K. pneumoniae. Fifty-seven urine samples were collected, from Baghdad s’ hospitals, diagnosed and identified by phenotype and biochemical tests, and confirmed with VITEK 2 compact system. Only fifteen isolates which were identified as K. pneumoniae. Antibiotic sensitivity was identified by using twelve antibiotics discs and K. pneumoniae were resisted in 100% to Ceftriaxone, Amoxicillin, Ticarcillin, Ticarcillin+Clavulanic acid, Ceftazidime, Tetracycline, while other antibiotics were showed less percent of resistant. Minimum inhibitory concentrations (MICs) of antibiotics detected by using macro tube dilution method to identify the antimicrobial activity for K. pneumoniae, the MIC of Gentamicin and Doxycycline antibiotics was 1024 Mg/ml, 512 Mg/ml respectively. By polymerase chain reaction detected genes of relB, relE with 115bp. and 136pb. respectively, then gene expression of relB, relE was conducted by using (RT-qPCR) technique with treated sub MIC concentration of (Gentamicin and Doxycycline) antibiotics. This study was found only ten isolates harbored the two genes as well as, value of folding was increased expression fold of relB gene, but in the same time relE gene was decreased its fold change according to control infB1 gene expression results. This means the bacterial cell tolerance antibiotics sub MIC concentrations by maintaining the number of bacteria under stress of antibiotics. Finally, these findings suggest the potential of relB to give K. pneumoniae resistant to antibiotics in their infections when it was being under stress of antibiotics by toxin-antitoxin II system to stay life.

An experimental study to evaluate the effect of polymixin E (Colistin) alone or in combination with gentamicin in McCarey-Kaufman corneal preservation medium on various drug resistant bacterial and fungal isolates.

To assess the efficacy of the addition of polymyxin E (colistin) in the McCarey-Kaufman (MK) corneal storage solution against multi-drug resistant strains of Enterobacteriaceae, Staphylococcus aureus, and Candida spp. A standard micro broth dilution test and a checkerboard assay were performed for five multi-drug resistant (MDR) clinical strains of P. aeruginosa and five clinical strains of methicillin-resistant S. aureus (MRSA) and C. albicans against colistin and gentamicin alone and in combination. The minimum inhibitory concentration (MIC) and the fractional inhibitory concentration index (FICI) were calculated to assess the efficacy of each combination. The MIC of colistin was in the range of 1-2 μg/mL for P. aeruginosa, whereas it was 256-1024 μg/mL against S. aureus. In comparison, the MIC of gentamicin was found to be 0.5-512 μg/mL and 0.5-8 μg/mL against P. aeruginosa and S. aureus, respectively. All five isolates of C. albicans did not exhibit any susceptibility to either colistin or gentamicin even at a concentration of ≥ 512 μg/mL each. The checkerboard assay was performed to evaluate the nature of the interaction of the combination of colistin and gentamicin. Based on the FICI, it was observed that the colistin and gentamicin combination has a maximum synergistic effect (FIC <0.5) in 80% (4/5) for S. aureus isolates, whereas the maximum additive effect (FIC >0.5-4) was 100% (5/5) for P. aeruginosa and the minimum additive effect was 20% (1/5) for S. aureus isolates. Antagonism (FIC ≥ 4) was not observed in any combination between the strains used in the study. Both colistin and gentamicin alone or in combination were, however, ineffective against Candida spp. The addition of colistin has an inhibitory effect on bacterial contamination that could be possibly caused by MDR strains and could potentially be considered as an additional additive in corneal storage media.

Gentamicin Susceptibility in Neisseria gonorrhoeae and Treatment Outcomes for Urogenital Gonorrhea After 25 Years of Sustained Gentamicin Use in Malawi.

Gentamicin has been used for the treatment of gonorrhea in Malawi since 1993. However, declining clinical cure rates have been suspected. We evaluated current Neisseria gonorrhoeae susceptibility to gentamicin in vitro and clinically. Men with acute urethritis were recruited at the Bwaila District Hospital STI Clinic in Lilongwe, Malawi, between January 2017 and August 2019. All men provided urethral swabs for etiological testing at enrollment and test of cure (TOC), 1 week later, using Gram-stained microscopy and culture. We used Etest to determine minimum inhibitory concentrations (MICs) of gentamicin, azithromycin, cefixime, ceftriaxone, ciprofloxacin, and spectinomycin; disc diffusion for tetracycline susceptibility; and whole-genome sequencing (WGS) to verify/refute treatment failure. Among 183 N. gonorrhoeae culture-positive men enrolled, 151 (82.5%) had a swab taken for TOC. Of these 151 men, 16 (10.6%) had a positive culture at TOC. One hundred forty-one baseline isolates were tested for gentamicin susceptibility using Etest: 2 (1.4%), MIC = 2 μg/mL; 111 (78.7%), MIC = 4 μg/mL; and 28 (19.9%), MIC = 8 μg/mL. All isolates were susceptible to azithromycin, cefixime, ceftriaxone, and spectinomycin, whereas 63.1% had intermediate susceptibility or resistance to ciprofloxacin. Almost all (96.1%) isolates were resistant to tetracycline. All examined isolates cultured at TOC (n = 13) had gentamicin MICs ≤8 μg/mL. Ten men had pretreatment and posttreatment isolates examined by whole-genome sequencing; 2 (20%) were verified new infections (4119 and 1272 single-nucleotide polymorphisms), whereas 8 (80%) were confirmed treatment failures (0-1 single-nucleotide polymorphism). Gentamicin MICs poorly predict gonorrhea treatment outcome with gentamicin, and treatment failures are verified with gonococcal strains with in vitro susceptibility to gentamicin. The first-line treatment of gonorrhea in Malawi should be reassessed.

The existence and expression of aminoglycoside resistance genes among multidrug-resistant Escherichia coli isolates in intensive care unit centers

BackgroundE. coli is among the substantial agents of nosocomial infections. The aim of this study was detection of the aminoglycoside resistance genes and their expression among multidrug-resistant (MDR) E. coli isolates in intensive care units (ICUs). MethodsTotally, 500 isolates of E. coli were collected from ICU centers in Baghdad, Iraq. The antibiotic susceptibility profile of them was determined using disk diffusion test in which seven antibiotics were employed. The gentamicin minimum inhibitory concentration (MIC) was determined using agar dilution method with an antibiotic dilution range of 0.5–256 μg/mL. The polymerase chain reaction (PCR) was implemented to amplify the aac(3)-IIa, ant(2″)-Ia, aac(6′)-lb, aac(3)-Ia, ant(4′)-IIb and aac(6′)-Ib-genes responsible for aminoglycosides resistance. The expression of genes was compared between MDR and non-MDR strains. ResultsThe patients' mean age included 57.33 ± 2 years (66% females vs 34% males, p = 0.0233). Four-hundred and fifty (90%) of isolates were from urinary tract infections (UTIs) and 24 from trachea (48%). Three-hundred and sixty (70%) of isolates were MDR, 260 (52%) of which being resistant to gentamicin. Prior hospitalization (p = 0.0261), prior β-lactams (p < 0.001) and aminoglycoside (p = 0.0113) consumption and diabetes (0.0117) were significant risk factors of MDR-E. coli isolation. The gentamicin MIC of MDR-E. coli included 6–256 μg/mL, 234 (46.8%) of which being in resistant range (64–256 μg/mL). The predominant gene included the aac(3)-IIa (92.6%, n = 463, MIC range: 32–256 μg/mL), followed by aac(6′)-Ib and aac(6′)-Ib-cr, aac(3)-Ia genes being in 224 (44.8%), 37 (7.4%) and 16 (2.2%) and 0% of isolates, respectively. The AMEs gene were detected among isolates with MICs>16 μg/mL and aac(3)-IIa, aac(6′)-Ib and aac(6′)-Ib-cr genes were significantly associated with MIC range of 128–256 μg/mL (p < 0.001). Most of genes expression was significantly higher in MDR than non-MDR strains. ConclusionThe majority of E. coli from ICU was MDR. Prior hospitalization, β-lactams and aminoglycoside consumption and diabetes were significant risk factors of MDR-E. coli isolation. Moreover, the aac(3)-IIa and aac(6′)-lb genes were predominant AMEs which were associated with higher MIC levels. Mechanisms affecting drug resistance genes expression in MDR strains maybe different from those in non-MDR strains.

Evaluating of the Effects of Sub-MIC Concentrations of Gentamicin on Biofilm Formation in Clinical Isolates of Pseudomonas aeruginosa

Background & Objective: The ability of Pseudomonas aeruginosa to form biofilm has an important role in establishment of chronic phase of infections. Biofilm formation can be affected by antibiotics sub-MIC concentrations. The principal aim of the present study was to evaluate the effect of gentamicin at sub-MIC concentrations on biofilm formation in 100 Pseudomonas aeruginosa clinical isolates.Methods: Determination of minimal inhibitory concentration of gentamicin for clinical isolates was done using micro broth dilution method. The amount of biofilm formation in the treated and untreated isolates with gentamicin sub-MIC (1/2&1/4MIC) concentrations was evaluated using microtitre plate assay. pelA and pslA genes were detected in clinical isolates by PCR method.Results: 99% of clinical isolates were biofilm producer. Different changes in amountof biofilm formation were observed in the treated clinical isolates with sub-MIC concentrations of gentamicin. Two dominant changes were observed in 80% of clinical isolates. These concentrations had inhibitory effect on biofilm formation in 46.4% of isolates and caused a significant decrease in its amount. While in 31.3% of the isolates, the biofilm formation was significantly increased. The frequency of pelA and pslA genes among clinical isolates was 100%. Conclusion: gentamicin sub-MIC concentrations cause different changes on biofilm formation of Pseudomonas aeruginosa clinical isolates. Therefore, further studies are needed for discovering new treatment strategies and using sub-MIC concentrations of the antibiotic in prevention and treatment of Pseudomonas aeruginosa infections.