Differences In Minimum Inhibitory Concentrations Research Articles

Differences in Minimum Inhibitory Concentrations of Probiotics and Prebiotics on Staphylococcus aureus

Currently, the use of antibiotics has increased sharply and use in the long term will have a bad impact on health. So the emergence of efforts in the form of making natural antibiotics by utilizing materials that are easily available in the environment. One of them is milk, where milk is a food product produced by farm animals, for example cows. This milk can be used as a probiotic. This probiotic is made by adding a bacterium and the bacterium that is often used is Lactobacillus casei. In addition to milk, the material that can be used is telang flower, which is one of the typical plants of Ternate, Maluku with purple, white, pink, and blue petals. Telang flower is often used as a traditional medicine because it has many benefits and content in it. Therefore, in this study Telang flower was used as a prebiotic tested on Staphylococcus aureus bacteria. The study was carried out in vitro by the method of laboratory experiments. The design used is Post Test control group only. The test is repeated at each concentration 3 times to obtain accurate results. The inhibition zone is measured using a caliper. The result of the inhibition zone formed from 3 repetitions is taken as the average value. The test results of the minimum inhibitory concentration of probiotics against Staphylococcus aureus bacteria showed results if at a concentration of 1.25% can form an inhibitory zone of 9.47 mm. While the minimum inhibitory concentration test on prebiotics against Staphylococcus aureus bacteria showed results at a concentration of 2.5% can form an inhibitory zone of 9.02 mm. This suggests that probitiks and prebiotics can be used as antibacterials, since at the lowest concentrations used they can form an inhibitory zone. So the higher the concentration of probiotics and prebiotics used, the inhibition zone formed will be greater.

Effect of Group Housing of Preweaned Dairy Calves: Health and Fecal Commensal Antimicrobial Resistance Outcomes.

The objectives of this study were to investigate the effects of group housing (three calves per group) on bovine respiratory disease (BRD), diarrhea and antimicrobial resistance (AMR) to fecal commensal Escherichia coli (EC) and enterococci/streptococci (ES). Our study comprised two arms, one experimental and one observational. In the experimental arm, preweaned calves on a California dairy were randomized to either individual (IND; n = 21) or group (GRP; n = 21) housing, using a modified California-style wooden hutch. The study period lasted from birth to 56 days of age, during which calves were health scored daily. Cumulative incidence and hazard ratios were estimated for disease. Antimicrobial resistance outcomes were assessed using a prospective cohort design; feces were collected from each calf three times per week and EC and ES were evaluated for AMR using the broth microdilution method against a panel of 19 antimicrobial drugs (AMD). Analysis of treatment records was used to select calves that had been exposed (EXP) to an AMD-treated calf. In GRP, exposure occurred when a calf was a hutchmate with an AMD-treated calf. In IND, exposure occurred when a calf was a neighbor with an AMD-treated calf (TRT). Age-matched unexposed calves (UNEXP) were then selected for comparison. Proportions of AMR in fecal commensals among EXP, UNEXP, and TRT calves were compared between GRP and IND. Accelerated failure time survival regression models were specified to compare differences in minimum inhibitory concentration (MIC) of fecal commensals between EXP and UNEXP calves within each of GRP and IND calves separately. Group calves had a BRD hazard 1.94 times greater that of IND calves (p = 0.03), using BRD treatment records as the outcome. For AMR in EC isolates, higher resistance to enrofloxacin was detected in enrofloxacin-EXP GRP isolates compared with enrofloxacin-EXP IND isolates, and UNEXP GRP calves had lower resistance to ceftiofur compared with enrofloxacin-EXP and enrofloxacin-TRT calves. A significant housing-by-time interaction was detected for EC ceftiofur MIC in EXP GRP calves at 4-14 days post exposure to enrofloxacin (MIC EXP-UNEXP: µg/mL (95% CI): 10.62 (1.17, 20.07)), compared with UNEXP calves. The findings of this study show an increase in BRD hazard for group-housed calves and an increase in ceftiofur resistance in group-housed calves exposed to an enrofloxacin-treated calf.

In Vitro Antifungal Activity of Green Synthesized Silver Nanoparticles in Comparison to Conventional Antifungal Drugs Against Trichophyton Interdigitale, Trichophyton Rubrum and Epidermophyton Floccosum.

Dermatophytosis is a globally distributed fungal infection. Treatment failure and relapse is common in this disease. Silver nanoparticles are known for their promising antimicrobial activity. The aim of this study was to determine the antifungal activity of these nanoparticles against common dermatophyte species. A set of 30 molecularly identified dermatophytes including Trichophyton interdigitale (n=10), Trichophyton rubrum (n=10), and Epidermophyton floccosum (n=10) were used in this study. Green synthesized silver nanoparticles using chicory (Cichorium intybus) were tested for their antifungal activity in comparison to fluconazole, itraconazole and terbinafine. Interspecies differences in minimum inhibitory concentrations of antifungal drugs and silver nanoparticles were tested using Kruskal-Wallis test in SPSS software version 21. The highest minimum inhibitory concentrations (MICs) among antifungal drugs were observed for fluconazole [range: 4-64 μg/mL, geometric mean (GM) =17.959 μg/mL], followed by itraconazole (range: 0.008-0.5, GM= 0.066) and terbinafine (range: 0.004-0.25 μg/mL, GM=0.027 μg/mL). Silver nanoparticles showed potent antifungal activity against all dermatophyte isolates with MICs (range: 0.25-32 μg/mL, GM=4.812 μg/mL) higher than those of itraconazole and terbinafine, but lower than fluconazole. MIC values of silver nanoparticles demonstrated significant differences between species (P=0.044), with E. floccosum having the highest MICs (GM=9.849 μg/mL) compared to T. interdigitale (GM=3.732 μg/mL) and T. rubrum (GM=3.031 μg/mL). Silver nanoparticles demonstrated promising anti-dermatophyte activity against the studied dermatophytes. Due to their wide-spectrum activity against other fungal and bacterial pathogens, they could be a potential choice, at least in the case of cutaneous and superficial infections.

The molecular basis of antibiotic treatment failure in chronic urinary tract infections

Urinary tract infections (UTIs) are amongst the most common infections worldwide, and are becoming increasingly difficult to treat. In addition to the acceleration of classic antimicrobial resistance, recurrence after initial resolution is common. Our clinical experience is that chronically infected patients sometimes fail to respond to antibiotics predicted to be effective from culture-based sensitivity testing, while antibiotics predicted to be unsuitable can succeed. We hypothesized that the bladder environment could lead to differential bacterial gene expression, resulting in differences in minimum inhibitory concentration (MICs) compared with standard culture. Here, using strains of Escherichia coli evolved in the lab to be resistant to amoxicillin–clavulanic acid, we present data that MICs differ depending on which media the assay is performed in (M9, ISO, LB, human urine), as well as in urine-containing supernatant enriched from urothelial organoids. Next, we examined the behaviour of patient-derived Enterococcus faecalis, one of the main causative agents of chronic UTIs in the elderly. We are in the process of evaluating the MIC of first-line UTI antibiotics using growth media supplemented with urine, to more closely mimic the native uropathogen environment. Moreover, we are characterising the resistance genes expressed in those differing environments using next generation sequencing technology and comparing the results with those obtained from bacteria grown on standard diagnostic media. Our work demonstrates the danger of extrapolating biological behaviour from artificial culture substrates and may lead to better diagnostic tests and treatments for chronic UTI.

Outcomes of Extended Infusion Cefepime in Pediatric Patients

Background Extended infusions of cefepime optimize pharmacokinetic and pharmacodynamic parameters and improve clinical outcomes in adults with gram-negative infections, but there are no similar studies in children. The objective of this study was to compare clinical outcomes in children receiving extended and traditional infusion cefepime. Methods This was a retrospective cohort study of patients aged 31 days to 17 years receiving extended or traditional infusion cefepime for at least 48 hours for a susceptible gram-negative bacteremia at a tertiary care children's hospital. The primary outcome was a composite clinical outcome comprised of infection-related mortality within 14 days of antibiotic initiation, bacteremic relapse within 30 days of culture clearance, and treatment failure. Results Sixty-seven patients were included; 21 (31.3%) received extended infusion, and 46 (68.7%) received traditional infusion. Extended infusion patients were older and larger than traditional infusion patients with a median (interquartile range) age of 7 (0.8–11.5) years versus 0.5 (0.2–2) years (P = 0.05) and weight of 23.7 (8.2–44.2) kg versus 6.2 (2.4–13.1) kg (P < 0.05). The most common pathogens within the extended infusion group were Enterobacter cloacae (23.8%) and Klebsiella oxytoca (23.8%), whereas Escherichia coli was the most common within the traditional infusion group (28.2%). There was no difference in minimum inhibitory concentrations, as the most common minimum inhibitory concentrations were less than or equal to 1 μg/mL in both extended (95.2%) and traditional infusion (87.0%) (P = nonsignificant). The primary outcome occurred in 2 extended (9.5%) and 3 traditional infusion patients (6.5%) (P = nonsignificant). Conclusions Clinical outcomes were similar with extended and traditional infusion cefepime in this cohort of children with susceptible gram-negative bacteremia.

Acquisition of Tn6018-3′ CS regions increases colistin MICs against Acinetobacter baumannii isolates harboring new variants of AbaRs

Colistin is the last hope to treat extensively drug resistance (XDR) Acinetobacter baumannii (A. baumannii) infections, but resistance to colistin is currently reported in clinical centers all over the world. Here, we studied two colistin-resistant A. baumannii isolates with a difference in minimum inhibitory concentrations (MICs) that were isolated from a single burn patient during treatment in the hospitalization period. The international clonal (IC) lineage, multilocus sequence typing (MLST), and multiple loci variable number tandem repeat (VNTR) analysis (MLVA) typing were used to characterize the relatedness of A. baumannii isolates. Lipopolysaccharides (LPS) and PmrAB system analysis by PCR sequencing, polyacrylamide gel electrophoresis (PAGE), and real-time PCR were performed to determine the intactness and probable modifications of the LPS as the main resistance mechanisms to colistin. A combination of PCR, sequencing, and restriction fragment length polymorphism (RFLP) was used for A. baumannii resistance islands (AbaR) mapping as resistance-determinant reservoirs. Two isolates were identical at all MLST and VNTR marker loci that indicated the isolates were the same strain. In comparison to colistin-heteroresistant A. baumannii strain TEH267 (MIC=1.5mg/L), colistin-resistant A. baumannii strain TEH273 (MIC ≥256mg/L) acquired two genomic regions including Tn6018-topA sequence and topA sequence-3' CS in its AbaR structure containing ispA and cadA genes which, it would appear, could be associated with eightfold increase in colistin MIC. Both isolates had new variants of AbaR-like structures which could be derivatives of the typical AbaR3. According to the results of this study, AbaRs could be associated with an increase in MIC to colistin.

Sensitivity of Human Strains of Oxalobacter formigenes to Commonly Prescribed Antibiotics

To determine the sensitivity of 4 strains of Oxalobacter formigenes (Oxf) found in humans--HC1, Va3, CC13, and OxK--to varying concentrations of commonly prescribed antibiotics. Oxf gut colonization has been associated with a decreased risk of forming recurrent calcium oxalate kidney stones. For each strain and each antibiotic concentration, 100 μL of an overnight culture and 100 μL of the appropriate antibiotic were added to a 7-mL vial of oxalate culture medium containing 20 mM oxalate. On the fourth day, vials were visually examined for growth, and a calcium oxalate precipitation test was performed to determine whether Oxf grew in the presence of the antibiotic. All 4 Oxf strains were resistant to amoxicillin, amoxicillin/clavulanate, ceftriaxone, cephalexin, and vancomycin, and they were all sensitive to azithromycin, ciprofloxacin, clarithromycin, clindamycin, doxycycline, gentamicin, levofloxacin, metronidazole, and tetracycline. One strain, CC13, was resistant to nitrofurantoin, and the others were sensitive. Differences in minimum inhibitory concentration between strains were demonstrated. Four human strains of Oxf are sensitive to a number of antibiotics commonly used in clinical practice; however, minimum inhibitory concentrations differ between strains.

Changes in the antimicrobial resistance profiles of Salmonella isolated from the same Michigan dairy farms in 2000 and 2009

This study compared the antimicrobial resistance profiles of Salmonella collected from the same Michigan, USA dairy farms between the years 2000 and 2009. The specific objective was to understand the type and distribution of changes in antimicrobial resistance that occurred within farms over the past 10years. Multinomial, multilevel models were constructed to estimate the differences in minimum inhibitory concentrations (MICs) between years. The MICs of most antimicrobials were significantly lower in 2009 than in 2000, but were higher for amikacin and gentamicin. Decreases in MICs were in part due to changes in the prevalence of multidrug resistant strains, but were also distributed across the susceptible population of isolates. The type and direction of within-farm changes in MICs were similar for the majority of farms. These results suggest a decrease in antimicrobial resistance and/or a change in the population structure of Salmonella that colonize dairy farms in Michigan.

Effects of Feeding Elevated Concentrations of Copper and Zinc on the Antimicrobial Susceptibilities of Fecal Bacteria in Feedlot Cattle

Cattle are fed elevated concentrations of copper and zinc for growth promotion. The potential mechanisms of growth promotional effects of these elements are attributed to their antimicrobial activities, similar to that of antibiotics, in that gut microbial flora are altered to reduce fermentation loss of nutrients and to suppress gut pathogens. Copper and zinc fed at elevated concentrations may select for bacteria that are resistant not only to heavy metals but also to antibiotics. Our objectives were to determine the effects of feeding elevated copper and zinc on the antimicrobial susceptibilities of fecal bacteria in feedlot cattle. Twenty heifers, fed corn-based high-grain diets, were randomly assigned to treatments in a 2 x 2 factorial arrangement with 1X or 10X National Research Council recommended copper and/or zinc. Feces, collected on days 0, 14, and 32, were cultured for commensal bacteria (Escherichia coli and Enterococcus) to determine their susceptibilities to copper, zinc, and antibiotics. Fecal DNA was extracted to detect tcrB gene and quantify erm(B) and tet(M) genes. In E. coli and Enterococcus sp., minimal differences in minimum inhibitory concentrations (MICs) of copper, zinc, and antibiotics were noticed. The mean copper MIC for E. coli increased (p < 0.05) between days 0 and 32 and days 14 and 32. The only treatment effect detected was increased zinc MIC of E. coli isolates (p < 0.01). The tcrB gene was not detected in feces or in enterococcal isolates. Proportions of erm(B) and tet(M) were unaffected by copper or zinc supplementation. However, the proportion of tet(M) increased (p < 0.05) between days 0 and 14. Feeding elevated copper and/or zinc to feedlot cattle had marginal effects on antimicrobial susceptibilities of fecal E. coli and enterococci.

Isolation, characterization, and antifungal susceptibility of melanin-deficient mutants of Scedosporium prolificans.

Scedosporium prolificans mutants lacking the ability to synthesize melanin were selected after ultraviolet light (UV) irradiation. UV exposure of S. prolificans conidia resulted in a high frequency of melanin-deficient (mel-) mutants. Stable and non-stable morphological variants were found in the population: reversion of the mutant phenotype was always to the wild-type phenotype. Based on their morphological differences, these variants were classified into five different groups that were phenotypically characterized. The mel- mutants plus the wild-type strain were examined for in vitro susceptibility to antifungal agents with different and/or the same mechanism of action. There was no apparent difference in minimum inhibitory concentrations when comparing the wild-type and the mel- mutants. Therefore, melanin does not appear to confer protection against the more important antifungal agents in S. prolificans.

Effect of temperature on aminoglycoside binding sites in Stenotrophomonas maltophilia.

In this study we used strains of Stenotrophomonas maltophilia grown at 30 degrees C and 37 degrees C to investigate the role of lipopolysaccharide (LPS) in temperature-dependent variations in sensitivity (TDVS) to gentamicin. TDVS was scored as 'good' if a four-fold or greater difference in minimum inhibitory concentration (MIC) was found between the two incubation temperatures (good TDVS strains; n = 23), and otherwise as 'poor' (poor TDVS strains; n = 15). Phosphate content of isolated LPS in the strains exhibiting good TDVS grown at 37 degrees C was significantly (P < 0.001) higher than those grown at 30 degrees C. However, the phosphate content from LPS of strains exhibiting poor TDVS did not alter significantly with growth temperature. There was no significant difference in 3-deoxy-D-manno-octulosonic acid (KDO) content between the strains grown at the different incubation temperatures. Fluorescence-activated cell sorting analysis showed significant differences in binding of fluorescein Isothiocyanate conjugated gentamicin to cells grown at 30 degrees C or 37 degrees C. We conclude that the temperature-dependent variation in the aminoglycoside susceptibility of this species was not correlated with any detectable change in KDO content, but correlated well with phosphate content of LPS and that LPS phosphate is the major site of ionic interaction for aminoglycosides in S. maltophilia.

Anaerobic susceptibility testing slight differences in inoculum size can make a difference in minimum inhibitory concentrations

In the present study, we compared the actual inoculum density from inoculated broth microdilution wells to the targeted inoculum size (10 5 CFU/well) when the inoculum was prepared using a McFarland nephelometer to achieve the standard density. Three target inoculum sizes (10 5, 5 × 10 5, and 10 6 CFU/well) were used to compare the effect of slight inoculum size increases of both ATCC and clinical strains of anaerobes on MICs of various antimicrobials. Actual colony counts of Bacteroides fragilis, Bacteroides thetaiotaomicron, Eubacterium lentum, and Veillonella parvula ranged from 0.7 × 10 5 to 1.4 × 10 5 CFU/well. As the inoculum size rose above the desired 10 5 CFU/well level, the MICs of certain antimicrobials became elevated. Ceftizoxime, cefotaxime, and ceftriaxone MICs rose 4- to 16-fold with as little as 0.5 log 10 increase in inoculum size. Other increases were also noted with E. lentum and Clostridium perfringens, but were primarily between the low and high inoculum sizes. Results with cefoxitin, cefotetan, mezlocillin, and imipenem did not show an appreciable increased inoculum effect. This study demonstrates that the variation in organism size among anaerobes (both between species and within species) does make a difference in actual inoculum size and certain anaerobes may require special adjustment to ensure proper MIC results from susceptibility testing.