Susceptibility Of Mycobacterium Avium Complex Research Articles

The use of dual β-lactams to restore susceptibility of Mycobacterium avium complex.

The Mycobacterium avium complex (MAC) are non-tuberculous mycobacteria responsible for chronic and debilitating conditions. Guideline-recommended therapy for MAC is a combination of clarithromycin/azithromycin, ethambutol and a rifamycin. However, culture conversion rates with this regimen are 67%. Alternative treatment options are needed. Recent findings of β-lactam combinations in the treatment of other mycobacterial diseases have been promising. The proposed mechanism is an additive inhibition of multiple enzymes in the peptidoglycan synthesis pathway by the β-lactam combinations. Given the similarity in cell wall structures of MAC and M. abscessus, we hypothesize that using dual β-lactams will result in interruption of peptidoglycan synthesis in MAC and reduction of MIC. In this study, we sought to determine the MIC of meropenem in combination with ceftaroline, cefdinir and cefuroxime in MAC. A total of 31 clinical MAC isolates were used for susceptibility testing using broth microdilution method. MICs were tested for meropenem, ceftaroline, cefdinir and cefuroxime, alone, as well as combinations of meropenem plus ceftaroline, cefdinir, or cefuroxime. In vitro MAC susceptibility to meropenem was significantly enhanced with the addition of ceftaroline, cefdinir, and cefuroxime. This effect was most significant with addition of ceftaroline and cefdinir, with a change of meropenem MIC50/MIC90 from 16/32 to 0.125/0.5 and 0.125/4 mg/L, respectively (P value ≤0.0001, Wilcoxon signed-rank test). This study demonstrates that the susceptibility of MAC to meropenem is restored with the addition of ceftaroline and cefdinir. These findings underscore the potential effectiveness of combining β-lactams as an alternative therapeutic strategy for MAC infections.

Effect of efflux pump inhibitors on the susceptibility of Mycobacterium avium complex to clarithromycin.

In this study we aimed to evaluate the effect of the combination of clarithromycin and four inhibitors of efflux pumps (EPIs), including berberine (BER), carbonyl cyanide m-chlorophenylhydrazone (CCCP), piperine (PIP) and tetrandrine (TET), against 12 Mycobacterium avium complex clinical isolates. The minimum inhibitory concentration (MIC) of clarithromycin showed at least a fourfold reduction in presence of BER (83% of total isolates), CCCP (67%), PIP (25%) and TET (75%). Our results showed that the EPIs tested are active against both clarithromycin susceptible and resistant isolates. In particular, among the six resistant isolates, TET reversed the resistance phenotype of three strains, BER of two strains, and CCCP and PIP of one strain. Overall, our findings show the importance of these compounds in increasing the efficacy of clarithromycin in MAC clinical isolates.

Persimmon-derived tannin has bacteriostatic and anti-inflammatory activity in a murine model of Mycobacterium avium complex (MAC) disease.

Nontuberculous mycobacteria (NTM), including Mycobacterium avium complex (MAC), cause opportunistic chronic pulmonary infections. Notably, MAC susceptibility is regulated by various factors, including the host immune system. Persimmon (Ebenaceae Diospyros kaki Thunb.) tannin is a condensed tannin composed of a polymer of catechin groups. It is well known that condensed tannins have high antioxidant activity and bacteriostatic properties. However, it is hypothesized that condensed tannins might need to be digested and/or fermented into smaller molecules in vivo prior to being absorbed into the body to perform beneficial functions. In this study, we evaluated the effects of soluble persimmon-derived tannins on opportunistic MAC disease. Soluble tannins were hydrolyzed and evaluated by the oxygen radical absorbance capacity (ORAC) method. The ORAC value of soluble tannin hydrolysate was approximately five times greater than that of soluble tannin powder. In addition, soluble tannin hydrolysate exhibited high bacteriostatic activity against MAC in vitro. Furthermore, in an in vivo study, MAC infected mice fed a soluble tannin-containing diet showed significantly higher anti-bacterial activity against MAC and less pulmonary granuloma formation compared with those fed a control diet. Tumor necrosis factor α and inducible nitric oxide synthase levels were significantly lower in lungs of the soluble tannin diet group compared with the control diet group. Moreover, proinflammatory cytokines induced by MAC stimulation of bone marrow-derived macrophages were significantly decreased by addition of soluble tannin hydrolysate. These data suggest that soluble tannin from persimmons might attenuate the pathogenesis of pulmonary NTM infection.

Recent advances on nontuberculous mycobacteria diseases in Asia

The isolation rate of nontuberculous mycobacteria (NTM) species and the prevalence of NTM-associated diseases are on the rise worldwide; however, the species distribution of NTM isolates and the types of diseases caused by NTM species vary from region to region. Treatment of a NTM disease is complicated, and there is no comprehensive guideline regarding the in vitro susceptibility of each antimicrobial agent against NTM. Therefore, appropriate anti-NTM treatment can only be recommended based on individual NTM species and local surveillance studies of anti-NTM resistance. Previous studies on the in vitro susceptibility of Mycobacterium avium complex (MAC) to clarithromycin in some Asian countries have revealed a low rate of resistance to that antimicrobial agent. Thus, a clarithromycin-based anti-MAC regimen should be effective for MAC infections. However, clarithromycin resistance due to the mutation of the 23S rRNA gene in MAC strains has been detected in many countries. Therefore, physicians should avoid monotherapy with clarithromycin and consider the possibility of clarithromycin resistance in patients who do not respond to clarithromycin-based regimens. Rifampicin is the critical component of successful management of Mycobacterium kansasii diseases. Although most M. kansasii isolates are susceptible to rifampicin in Western countries and in Japan, this agent may not work well in Taiwan. Rapidly growing mycobacteria (RGM) is a prevalent NTM group worldwide, particularly in Asia; however, each NTM species in this group may have its own distinct antibiotic susceptibility pattern, and close monitoring of the antibiotic-resistance patterns of RGM is necessary. Most important of all, the in vitro susceptibility may not represent the in vivo activity until the confirmation of the clinical study. Therefore, further investigation of the clinical effectiveness of the anti-NTM agents is warranted.

Effects of antisense oligo DNA on the antimicrobial activity of reactive oxygen intermediates and antimycobacterial agents against Mycobacterium avium complex

There has not yet been systematic studies which attempt to elucidate detailed profiles of the interaction between antimicrobial drugs and macrophage microbicidal mechanisms. We examined the effects of antisense oligo DNAs (AsDNAs) against oxyR and ahpC on the susceptibility of Mycobacterium avium complex (MAC) to the H2O2-halogenation system and combined antimycobacterial drugs [clarithromycin (CAM) + rifampicin (RFP)], both separately and in combination. It was found that AsDNA treatment of MAC did not affect the susceptibility of the organisms to any of the antimicrobial systems tested. Since the present AsDNAs did not efficiently reduce the expression of AhpC mRNA, attempts to increase bacterial uptake of AsDNAs are necessary to achieve significant increase in the drug susceptibility of MAC organisms due to AsDNA treatment.

Evaluation of a Disk Diffusion Method for Determining Susceptibility of Mycobacterium avium Complex to Clarithromycin

We evaluated an agar disk diffusion method for determining the susceptibility of Mycobacterium avium complex to clarithromycin. Isolates were inoculated onto the surface of a Middlebrook 7H11 plate, followed by the application of a 15-μg clarithromycin disk. Zone sizes were read after 5–7 days of incubation. Zone sizes had a bimodal distribution; 40 isolates (10%) had no zone of inhibition, whereas the zone sizes for the remaining isolates ranged from 11 to 60 mm. Most isolates (37/40) having no zone of inhibition came from patients who had been treated previously with clarithromycin. Fifty-one isolates were also tested for clarithromycin susceptibility using a microdilution broth method. Defining susceptibility as a zone size of >10 mm, disk diffusion test results agreed with the results by the microdilution broth method for 50 of 51 (98%) isolates tested by both methods. Agar disk diffusion is a promising method for the determination of clarithromycin susceptibility testing for M. avium complex.

Mycobacterium avium complex infection. Pharmacokinetic and pharmacodynamic considerations that may improve clinical outcomes.

Mycobacterium avium complex (MAC) is an infrequent pulmonary pathogen in immunocompetent hosts. In patients with AIDS, MAC causes disseminated infection (DMAC) in up to 50% of those with CD4+ counts less than 100 cells/mm3. A significant portion of the total body burden of MAC is found inside macrophages, and the distribution of organisms has implications for drug therapy. Clarithromycin, azithromycin, and rifabutin all appear to enter these cells well; rifampicin (rifampin), ethambutol, ciprofloxacin, and other agents also appear to enter these cells. MAC susceptibility is probably best tested using the radiometric method (BACTEC). Susceptibility break-points have been proposed for the various anti-MAC agents; however, solid clinical correlations have been achieved only for clarithromycin. Further research is required to establish break-points for the other agents. Based on current data, azithromycin and clarithromycin appear to be key drugs in the treatment of MAC, while rifabutin has been used more often than rifampicin in studies involving patients with AIDS. Among the drugs traditionally used for M. tuberculosis (TB), ethambutol, rifampicin and streptomycin are perhaps the most useful for MAC. Amikacin and clofazimine may also be useful. The limited data available on AIDS patients with MAC, plus additional data from AIDS patients with TB, suggest that malabsorption of the oral antimycobacterial drugs is common. Some drugs (rifampicin and ethambutol) appear to be particularly affected. Because most of the studies of DMAC have not evaluated the pharmacokinetics of the drugs, questions of drug efficacy cannot be separated from questions of biovailability. This significant oversight in study design should be eliminated from future investigations. Patient-specific susceptibility data combined with therapeutic drug monitoring and dosage individualisation is one way to identify problems with drug therapy and to overcome them. Because many of the drugs used in patients with AIDS affect the metabolism of concurrently used drugs, therapeutic drug monitoring is a valuable asset for untangling multiple drug interactions. Since drug therapy is the only aspect of a mycobacterial infection within our control, the better we control the drug therapy, the better our patients should do.

Rapid Drug Susceptibility of Mycobacterium avium Complex Using a Fluorescence Quenching Method

Mycobacteria Growth Indicator Tube (MGIT) is a recently introduced rapid growth detection method which uses an oxygen quenched fluorescent indicator. The present study evaluated the ability of this new method to determine the drug susceptibility of Mycobacterium avium complex (MAC). Thirty strains recovered from patients with AIDS were tested for susceptibility to clarithromycin, rifabutin, ciprofloxacin, azithromycin and amikacin using MGIT. Results were compared to susceptibilities determined by the agar dilution method. The results obtained showed a 100% correlation between MGIT and the agar dilution method for rifabutin and clarithromycin. There was a 100% correlation between the two methods for azithromycin against 27 strains. MGIT was well correlated with the agar dilution method for detecting resistance to clarithromycin, rifabutin and azithromycin in 4 days, but the correlation was poor when susceptibilities to ciprofloxacin and amikacin were determined. This rapid method is non-radiometric, noninvasive and does not require any special instruments.

Comparison of the E test and a proportion dilution method for susceptibility testing of Mycobacterium avium complex

The newly developed E test was compared with an extended 1% proportion dilution method for determining the susceptibility of Mycobacterium avium complex (MAC) strains to amikacin, streptomycin, fusidic acid, rifampicin, clarithromycin, ciprofloxacin, ofloxacin and fleroxacin. For all antibiotics tested except clarithromycin and ciprofloxacin, no more than one strain gave a different susceptibility result with the two methods. The discrepant results occurred near the chosen breakpoint concentration of clarithromycin and outside the concentration range of the E test for ciprofloxacin. For the minimum inhibitory concentration (MIC) values obtained within the range of antibiotic concentrations tested, there was good correlation between the two methods; the MICs differed by more than one two-fold dilution in no more than two strains per antibiotic. It is concluded that the E test is suitable for susceptibility testing of MAC.

Rapid assessment of mycobacterial growth inside macrophages and mice, using the radiometric (BACTEC) method

Setting: Conventional methods of determining the growth and drug susceptibility of mycobacteria either in macrophages or in vivo are time consuming and laborious. Objective: We sought to develop a simple and rapid method for assessing growth and susceptibility of mycobacteria in macrophages and in vivo. Design: The radiometric (BACTEC) method was compared with the conventional method for rapid assessment of growth and susceptibility of Mycobacterium avium complex (MAC) to clofazimine (CFM) and its two analogues (B4100 and B4101) in macrophages and in beige mice. Results and conclusions: A linear relationship was observed between growth index (GI) readings by the BACTEC method and the colony forming unit (CFU) counts obtained by conventional plating on 7H11 agar in vitro of lysates from infected macrophages and of homogenates from the infected organs. There was also a good agreement between the two methods with respect to susceptibility of MAC to CFM and its analogues both in macrophages and in spleen. The BACTEC method, in addition to being quick and simple, was found to be more consistent. Our studies thus demonstrate that the radiometric method has potential application in rapid screening of drugs for antimycobacterial activity in macrophages and in animals besides its established value in in vitro screening.

In vitro susceptibility of Mycobacterium avium complex to the new fluoroquinolone sparfloxacin (CI-978; AT-4140) and comparison with ciprofloxacin

We tested the activity of the new fluoroquinolone sparfloxacin (CI-978; AT 4140) against 30 strains of Mycobacterium avium complex (MAC) isolated from patients with acquired immune deficiency syndrome. MICs of sparfloxacin (range, less than or equal to 0.06 to 4 micrograms/ml) were lower than MICs of ciprofloxacin for all 30 strains, and MBCs for acid-fast bacteria were lower for 28 of the 30 strains. In synergism experiments using 10 strains of MAC, fractional inhibitory concentration indices revealed that the combination of sparfloxacin plus ethambutol was synergistic against 9 strains, and the three-drug combination of sparfloxacin plus ethambutol plus rifampin was synergistic against all strains. In the absence of ethambutol, the combination of sparfloxacin plus rifampin appeared to be antagonistic against three of the MAC strains.

Susceptibility of Mycobacterium avium complex to various two-drug combinations of antituberculosis agents.

The drug susceptibility of two untypable strains of Mycobacterium avium complex were studied in 7H10 agar plates containing ethambutol (EMB), isoniazid (INH), rifampicin (RMP), ethionamide (ETH), and streptomycin (SM) alone and in two-drug combinations. The effective dose inhibiting 75% of the mycobacterial population (ED 75) was estimated by a regression analysis on the probit transformed inhibition percentages and plotted on an isobologram for each combination. No major discrepancies were found between strains. Five combinations (RMP plus INH, RMP plus EMB, EMB plus SM, INH plus EMB, and ETH plus INH) showed synergistic effect, whereas five other combinations (ETH plus EMB, ETH plus RMP, ETH plus SM, SM plus RMP, and SM plus INH) showed antagonistic effect. These in vitro results are not in combination with the known results of treatment of the M. avium diseases. We conclude that the effect of drug combinations against M. avium may be strain dependent and that it is important to determine this effect in vitro before setting up a treatment protocol.

In vitro susceptibility of Mycobacterium avium complex to antibacterial agents

In vitro agar dilution susceptibility studies were performed utilizing 20 isolates (24 against rifamycin) of Mycobacterium avium complex against several antimicrobial agents not routinely tested in the mycobacteriology laboratory. Thirteen strains were susceptible to gentamicin at 4 μg/ml, 20 to amikacin at 8 μg/ml, 18 to streptomycin at 8 μg/ml, 20 to kanamycin at 8 μg/ml, 20 to trimethoprim/sulfamethoxazole at 2 μg/ml, 12 to sulfisoxazole at 10 μg/ml, 14 to rifabutin at 1 μg/ml. No activity was found with penicillin G, cephapirin, moxalactam, vancomycin, clindamycin, erythromycin, trimethoprim, or minocycline. This data suggests a potential use of trimethoprim/sulfamethoxazole, sulfisoxazole, amikacin, gentamicin, and kanamycin in the treatment of infections caused by this group of organisms.