In vitro activity of new fluoroquinolones and linezolid against non-tuberculous mycobacteria

Prevalence of Mycobacterium kansasii in clinical and environmental isolates, a systematic review and meta-analysis

Background

Mycobacterium kansasii infection is one of the most common causes of non-tuberculosis mycobacterial (NTM) disease worldwide. However, accurate information on the global prevalence of this bacterium is lacking. Therefore, this study was conducted to investigate the prevalence of M. kansasii in clinical and environmental isolates.

Methods

Databases, including PubMed, Scopus, and the Web of Science, were utilized to gather articles on the prevalence of M. kansasii in clinical and environmental isolates. The collected data were analyzed using Comprehensive Meta-Analysis software.

Results

A total of 118 and 16 studies met the inclusion criteria and were used to analyze the prevalence of M. kansasii in clinical and environmental isolates, respectively. The prevalence of M. kansasii in NTM and environmental isolates were 9.4 and 5.8%, respectively. Subsequent analysis showed an increasing prevalence of M. kansasii over the years. Additionally, the results indicated a significant difference in the prevalence of this bacteria among different regions.

Conclusion

The relatively high prevalence of M. kansasii among NTM isolates suggests the need for further implementation of infection control strategies. It is also important to establish appropriate diagnostic criteria and management guidelines for screening this microorganism in environmental samples in order to prevent its spread, given its high prevalence in environmental isolates.

Treatment strategies with alternative treatment options for patients with Mycobacterium avium complex pulmonary disease

Diseases caused by Mycobacterium avium complex (MAC) infection in the lungs are increasing worldwide. The recurrence rate of MAC-pulmonary disease (PD) has been reported to be as high as 25-45%. A significant percentage of recurrences occurs because of reinfection with a new genotype from the environment. A focus on reducing exposure to MAC organisms from the environment is therefore an essential component of the management of this disease as well as standard MAC-PD treatment. A macrolide-containing three-drug regimen is recommended over a two-drug regimen as a standard treatment, and azithromycin is recommended rather than clarithromycin. Both the 2007 and 2020 guidelines recommend a treatment duration of MAC-PD of at least one year after the culture conversion. Previous clinical studies have reported that ethambutol could prevent macrolide resistance. Furthermore, the concomitant use of aminoglycoside, amikacin liposomal inhalation, clofazimine, linezolid, bedaquiline, and fluoroquinolone with modification of guideline-based therapy has been studied. Long-term management of MAC-PD remains challenging because of the discontinuation of multi-drug regimens and the acquisition of macrolide resistance. Moreover, the poor compliance of guideline-based therapy for MAC-PD treatment worldwide is concerning since it causes macrolide resistance. Therefore, in this review, we focus on MAC-PD treatment and summarize various treatment options when standard treatment cannot be maintained, with reference to the latest ATS/ERS/ESCMID/IDSA clinical practice guidelines revised in 2020.

Moxifloxacin resistance and genotyping of Mycobacterium avium and Mycobacterium intracellulare isolates in Japan

BACKGROUND

Although fluoroquinolones are considered as alternative therapies of pulmonary Mycobacterium avium complex (MAC) disease, the association between fluoroquinolone resistance and MAC genotypes in clinical isolates from individuals not previously treated for MAC infection is not fully clear.

METHODS

Totals of 154 M. avium isolates and 35 Mycobacterium intracellulare isolates were obtained from treatment-naïve patients with pulmonary MAC disease at the diagnosis of MAC infection at 8 hospitals in Japan. Their susceptibilities of moxifloxacin were determined by broth microdilution methods. Moxifloxacin-resistant isolates were examined for mutations of gyrA and gyrB. Variable numbers of tandem repeats (VNTR) assay was performed using 15 M. avium VNTR loci and 16 M. intracellulare VNTR loci.

RESULTS

Moxifloxacin susceptibility was categorized as resistant and intermediate for 6.5% and 16.9%, respectively, of M. avium isolates and 8.6% and 17.1% of M. intracellulare isolates. Although the isolates of both species had amino acid substitutions of Thr 96 and Thr 522 at the sites corresponding to Ser 95 in the M. tuberculosis GyrA and Gly 520 in the M. tuberculosis GyrB, respectively, these substitutions were observed irrespective of susceptibility and did not confer resistance. The VNTR assays showed revealed three clusters among M. avium isolates and two clusters among M. intracellulare isolates. No significant differences in moxifloxacin resistance were observed among these clusters.

CONCLUSIONS

Although resistance or intermediate resistance to moxifloxacin was observed in approximately one-fourth of M. avium and M. intracellulare isolates, this resistance was not associated with mutations in gyrA and gyrB or with VNTR genotypes.

New Insights in to the Intrinsic and Acquired Drug Resistance Mechanisms in Mycobacteria

Infectious diseases caused by clinically important Mycobacteria continue to be an important public health problem worldwide primarily due to emergence of drug resistance crisis. In recent years, the control of tuberculosis (TB), the disease caused by Mycobacterium tuberculosis (MTB), is hampered by the emergence of multidrug resistance (MDR), defined as resistance to at least isoniazid (INH) and rifampicin (RIF), two key drugs in the treatment of the disease. Despite the availability of curative anti-TB therapy, inappropriate and inadequate treatment has allowed MTB to acquire resistance to the most important anti-TB drugs. Likewise, for most mycobacteria other than MTB, the outcome of drug treatment is poor and is likely related to the high levels of antibiotic resistance. Thus, a better knowledge of the underlying mechanisms of drug resistance in mycobacteria could aid not only to select the best therapeutic options but also to develop novel drugs that can overwhelm the existing resistance mechanisms. In this article, we review the distinctive mechanisms of antibiotic resistance in mycobacteria.

Mycobacterium avium Complex Disease

Despite the ubiqitous nature of Mycobacterium avium complex (MAC) organisms in the environment, relatively few of those who are infected develop disease. Thus, some degree of susceptibility due to either underlying lung disease or immunosuppression is required. The frequency of pulmonary MAC disease is increasing in many areas, and the exact reasons are unknown. Isolation of MAC from a respiratory specimen does not necessarily mean that treatment is required, as the decision to treatment requires the synthesis of clinical, radiographic, and microbiologic information as well as a weighing of the risks and benefits for the individual patient. Successful treatment requires a multipronged approach that includes antibiotics, aggressive pulmonary hygiene, and sometimes resection of the diseased lung. A combination of azithromycin, rifampin, and ethambutol administered three times weekly is recommend for nodular bronchiectatic disease, whereas the same regimen may be used for cavitary disease but administered daily and often with inclusion of a parenteral aminoglycoside. Disseminated MAC (DMAC) is almost exclusively seen in patients with late-stage AIDS and can be treated with a macrolide in combination with ethambutol, with or without rifabutin: the most important intervention in this setting is to gain HIV control with the use of potent antiretroviral therapy. Treatment outcomes for many patients with MAC disease remain suboptimal, so new drugs and treatment regimens are greatly needed. Given the high rate of reinfection after cure, one of the greatest needs is a better understanding of where infection occurs and how this can be prevented.

Specific gyrA gene mutations predict poor treatment outcome in MDR-TB

OBJECTIVES

Mutations in the gyrase genes cause fluoroquinolone resistance in Mycobacterium tuberculosis. However, the predictive value of these markers for clinical outcomes in patients with MDR-TB is unknown to date. The objective of this study was to determine molecular markers and breakpoints predicting second-line treatment outcomes in M. tuberculosis patients treated with fourth-generation fluoroquinolones.

METHODS

We analysed treatment outcome data in relation to the gyrA and gyrB sequences and MICs of ofloxacin, gatifloxacin and moxifloxacin for pretreatment M. tuberculosis isolates from 181 MDR-TB patients in Bangladesh whose isolates were susceptible to injectable drugs.

RESULTS

The gyrA 90Val, 94Gly and 94Ala mutations were most frequent, with the highest resistance levels for 94Gly mutants. Increased pretreatment resistance levels (>2 mg/L), related to specific mutations, were associated with lower cure percentages, with no cure in patients whose isolates were resistant to gatifloxacin at 4 mg/L. Any gyrA 94 mutation, except 94Ala, predicted a significantly lower proportion of cure compared with all other gyrA mutations taken together (all non-94 mutants + 94Ala) [OR = 4.3 (95% CI 1.4-13.0)]. The difference in treatment outcome was not explained by resistance to the other drugs.

CONCLUSIONS

Our study suggests that gyrA mutations at position 94, other than Ala, predict high-level resistance to gatifloxacin and moxifloxacin, as well as poor treatment outcome, in MDR-TB patients in whom an injectable agent is still effective.

Induction therapy with linezolid/clarithromycin combination for Mycobacterium chelonae skin infections in immunocompromised hosts

BACKGROUND

The optimal management of Mycobacterium chelonae disease in immunocompromised patients remains unclear. A combination of antimicrobial agents is recommended as monotherapy with clarithromycin has been associated with clinical failures due to acquired resistance.

OBJECTIVES

We aim to report the efficacy and tolerability of linezolid in association with clarithromycin for the treatment of M. chelonae infections in immunocompromised patients.

METHODS

We describe four immunocompromised patients treated by linezolid and clarithromycin for cutaneous M. chelonae disease.

RESULTS

This combination was associated with rapid clinical efficacy in all patients with no relapse observed after a median follow-up of 2.25 years (1.4 years). However, this treatment was responsible for frequent adverse events including thrombocytopaenia, myalgia and mitochondrial toxicity. All adverse effects were reversible after linezolid discontinuation.

CONCLUSIONS

We therefore suggest linezolid/clarithromycin combination as the initial therapeutic strategy for M. chelonae skin infections in immunocompromised patients.

Pulmonary disease caused by nontuberculous mycobacteria

The propensity of various nontuberculous mycobacteria to cause lung disease varies widely and is conditioned by host factors; infection is believed to occur from environmental sources. Nontuberculous mycobacteria pulmonary disease (PNTM) is increasing worldwide and Mycobacterium avium complex is the most common cause. PNTM usually occurs in one of three prototypical forms: hypersensitivity pneumonitis, cavitary tuberculosis-like disease or nodular bronchiectasis. PNTM has been linked in some patients to genetic variants of the cystic fibrosis transmembrane conductance regulator gene and a distinct patient phenotype. Interactions between PNTM and other comorbidities are also increasingly appreciated. Guidelines for diagnosis, emphasizing chest imaging and microbiology, have been published; speciation using molecular techniques is critical for accuracy and for treatment decisions. Clinical trials are lacking to inform treatment for many species and experience with M. avium complex and several others species serves as a guide instead. Use of multiple drugs for a period of at least 12 months following sputum conversion is the norm for most species. In vitro drug susceptibility results for many drugs may not correlate with clinical outcomes and such testing should be done on a selective basis.

[Infections due to rapidly growing mycobacteria]

Rapidly growing mycobacteria (RGM) are ubiquitous in nature and widely distributed in water, soil and animals. During the past three decades we have observed a notable increment of infections caused by RGM, both localized and disseminated, as well as nosocomial outbreaks of contaminated medical equipment. The microbiological diagnosis of RGM infections includes direct microscopic observation and culture. The taxonomic identification is performed by phenotypic, biochemical, chromatographic and molecular biology techniques. The treatment differs from that of other mycobacteriosis like tuberculosis, owing to the variable in vitro susceptibility of the species of this group. The RGM are resistant to conventional antituberculous drugs, but can be susceptible to broad spectrum antimicrobial agents. In this study we comment on the significant aspects of human infections by RGM, including their biology, epidemiology, pathology, microbiological diagnosis, taxonomic identification, antimicrobial susceptibility and treatment.

[Diagnosis and treatment of atypical mycobacterial infections of the respiratory tract]

INTRODUCTION

Non tuberculous mycobacteria (NTM), unlike tuberculous mycobacteria, are not strictly human pathogens. The diagnosis of infection and the choice of treatment remain difficult.

BACKGROUND

Evidence of a NTM in a pulmonary sample is not synonymous with infection. The diagnosis depends on the association of clinical, radiological and microbiological factors. If a NTM is isolated from a respiratory sample, the probability of infection depends on the species. The main NTMs responsible for pulmonary infection in France are Mycobacterium avium intracellulare, Mycobacterium xenopi, Mycobacterium kansasi and Mycobacterium abscessus. Their management is difficult and poorly understood. Treatment is well established for M. avium intracellulare and M. kansasii, with combinations of clarithromycin-rifampicin-ethambutol and isoniazid-rifampicin-ethambutol respectively. For M. xenopi, the optimal treatment is not known and a combination of clarithromycin-rifampicin-ethambutol, with moxifloxacin as an alternative, is currently recommended. In general, treatment is prolonged and often associated with problems of tolerance.

VIEWPOINT AND CONCLUSION

The management of NTM infection, taking into account of the increase in patients "at risk", is an important issue. Further studies are needed to improve the criteria for infection and to find the optimal therapeutic combinations.

Moxifloxacin in the treatment of skin and skin structure infections

Moxifloxacin is a recent addition to the fluoroquinolone class, differing from ciprofloxacin and other older agents in having much better in vitro activity against Gram-positive aerobes while retaining potent activity against Gram-negative aerobes. It is also active against the pathogens of human and animal bite wounds and those species of atypical mycobacteria associated with dermatologic infections. Its activity against anaerobes is quite variable. Moxifloxacin penetrates well into inflammatory blister fluid and muscle and subcutaneous adipose tissues. Moxifloxacin should thus be a reasonable option for the treatment of skin and skin structure infections (SSSIs). In 3 randomized controlled trials (RCTs), oral moxifloxacin was as effective as cephalexin in the treatment of uncomplicated SSSIs in adults while in 2 RCTs, intravenous/oral moxifloxacin was as effective as intravenous/oral β-lactam/β-lactamase inhibitor therapy in the treatment of complicated SSSIs in adults. Moxifloxacin does not inhibit cytochrome P450 enzymes and thus interact with warfarin or methylxanthines. However, multivalent cations can reduce its oral bioavailability substantially. Dosage adjustment is not required in the presence of renal or hepatic impairment. The clinical relevance of its electrophysiologic effects (QT_c prolongation) remains unresolved.

Blurring the lines in interferon {gamma} receptor deficiency: an infant with near-fatal airway disease

Deficiencies of the interferon γ (IFN-γ) pathway have become a well-recognized cause of nontuberculous mycobacterial infection. We report here a case of autosomal dominant IFN-γ receptor 1 (IFN-γ-R1) deficiency presenting at the unusually young age of 16 months with a severe clinical course. Mycobacterium avium complex was cultured from bronchial washings of a child who presented with primary endobronchial disease after a 4-month history of rhinorrhea, wheeze, and acute lobar consolidation. A maternal history of multifocal Mycobacterium kansasii osteomyelitis and cutaneous M avium complex led to genetic confirmation of IFN-γ-R1 818del4 deletion (a 4 base pair deletion at nucleotide position 818) in both family members. This case demonstrates the link between mycobacterial disease and IFN-γ pathway deficiency, the diagnosis of which facilitates more accurate therapy and genetic counseling. The case also raises questions about the reported distinct presentation, treatment, and prognosis of autosomal dominant and recessive IFN-γ-R1 phenotypes.

Clarithromycin and amikacin vs. clarithromycin and moxifloxacin for the treatment of post-acupuncture cutaneous infections due to Mycobacterium abscessus: a prospective observational study

An outbreak of post-acupuncture cutaneous infections due to Mycobacterium abscessus occurred in Ansan, Korea, from November 2007 through to May 2008. During this time a prospective, observational, non-randomized study was conducted involving 52 patients that were diagnosed with cutaneous M. abscessus infection. We compared the clinical response between patients treated with clarithromycin plus amikacin regimen and those treated with clarithromycin plus moxifloxacin regimens with regard to time to resolution of the cutaneous lesions. Among the 52 study patients, 33 were treated with clarithromycin plus amikacin, and 19 were treated with clarithromycin plus moxifloxacin. The baseline characteristics for the treatment groups were not significantly different, except for initial surgical excision (n = 27 vs. 6, respectively, p = 0.001). The median time (weeks) to resolution of the lesions in the clarithromycin plus moxifloxacin-treated subjects was significantly shorter than that in the clarithromycin plus amikacin-treated subjects (17 ± 1.1 vs. 20 ± 0.9, respectively, p = 0.017). With adjustments for age, location of lesions, prior incision and drainage, and excision during medical therapy, clarithromycin plus moxifloxacin-treated subjects were more likely to have resolved lesions (hazard ratio, 0.387; 95% confidence interval, 0.165-0.907; p = 0.029). The frequency of drug-related adverse events in the two treatment groups was not significantly different (n = 18 vs. 14, respectively; p = 0.240). The most common adverse event was gastrointestinal discomfort. The results of our study showed that the combination regimen of clarithromycin and moxifloxacin resulted in a better clinical response than a regimen of clarithromycin plus amikacin when used for treatment of cutaneous M. abscessus infection.

Nontuberculous mycobacterial lung diseases

Nontuberculous mycobacteria (NTM) are generally hardy, ubiquitous environmental bacteria that vary in geographic distribution and pulmonary pathogenicity. Relatively few of the more than 115 species of NTM have been associated with lung disease. Diagnosis of disease due to NTM relies on a combination of clinical, imaging, and microbiologic data. Because NTM may present as acid-fast bacilli in respiratory secretions of patients with clinical and radiologic features that mimic tuberculosis, laboratory discrimination of NTM from Mycobacterium tuberculosis is a priority. This discrimination is now often rapidly achievable using molecular techniques, although some tests have limited sensitivity. NTM species have different antibiotic response patterns, and success with medical treatment alone varies. Macrolides are an essential component of therapy for many species but must be combined with other drugs.

In vitro activity of a new isothiazoloquinolone, ACH-702, against Mycobacterium tuberculosis and other mycobacteria

In this work, we describe the activity of ACH-702 against clinical isolates of Mycobacterium tuberculosis and six different nontuberculous mycobacteria. The MIC(50) and MIC(90) of both susceptible and drug-resistant M. tuberculosis strains tested were 0.0625 and 0.125 microg/ml, respectively. The MIC(50) and MIC(90) values for Mycobacterium fortuitum isolates were 0.0625 microg/ml in both cases; Mycobacterium avium complex isolates showed MIC(50) and MIC(90) values of 0.25 and 4 microg/ml, respectively.

Current treatment of atypical mycobacteriosis

BACKGROUND

Atypical mycobacteria are a heterogeneous group of organisms that are of increasing importance because of the growing number of infections they cause. This rising rate of infection is due mainly to the increase in the number of susceptible (and especially immunosuppressed) patients.

OBJECTIVE

To revise the currently used treatment schemes of the most commonly isolated atypical mycobacteria.

METHODS

Literature review using reference books and PubMed with specific keywords for each mycobacteria.

RESULTS/CONCLUSION

The first important step in the management of atypical mycobacteria is to recognize the true infections caused by these organisms. The treatment required varies according to species. Well-characterized combinations exist for most common isolates, with the use of first-line antituberculous drugs (isoniazid, rifampin, ethambutol), clarithromycin, aminoglycosides and/or quinolones for slowly growing species (Mycobacterium avium complex, Mycobacterium kansasii, Mycobacterium xenopi, Mycobacterium ulcerans, Mycobacterium marinum, Mycobacterium lentiflavum, Mycobacterium malmoense) and macrolides, quinolones, amikacin and other antibiotics for rapidly growing mycobacteria (Mycobacterium abscessus, Mycobacterium chelonae, Mycobacterium fortuitum). Surgical therapy is also important for some species (Mycobacterium ulcerans, Mycobacterium scrofulaceum) and for localized infections. The treatment of uncommon species is not well defined and is determined by the results of in vitro tests of individual strains. Because of the increasing number of resistant strains, new antibiotics need to be used for the treatment of these strains.

Unusual infection in the foot of a barefoot gardener

We report a case of an unusual and unsuspected chronic infection creating a soft-tissue mass in the foot of a 35-year-old woman. The causative agent, Mycobacterium gordonae, is usually encountered as a laboratory contaminant. Only rarely does it manifest as a clinical infection. The patient's presumed predisposing risk factor was a history of barefoot gardening. An iatrogenic source, corticosteroid injections, was also considered.

In vitro and in vivo activities of novel fluoroquinolones alone and in combination with clarithromycin against clinically isolated Mycobacterium avium complex strains in Japan

The recommended treatments for Mycobacterium avium complex (MAC) infectious disease are combination regimens of clarithromycin (CLR) or azithromycin with ethambutol and rifamycin. However, these chemotherapy regimens are sometimes unsuccessful. Recently developed antimicrobial agents, such as newer fluoroquinolones (FQs) containing C-8 methoxy quinolone (moxifloxacin [MXF] and gatifloxacin [GAT]), are expected to be novel antimycobacterial agents. Here, we evaluated the in vitro and in vivo antimycobacterial activities of three FQs (MXF, GAT, and levofloxacin) and CLR against clinically isolated MAC strains. Subsequently, the in vitro and in vivo synergic activities of FQ-CLR combinations against MAC strains were investigated. CLR and the individual FQs alone showed promising activity against MAC strains in vitro, and the bacterial counts in organs (lungs, liver, and spleen) of MAC-infected mice treated with single agents were significantly reduced compared to control mice. CLR showed the best anti-MAC effect in vivo. When the three FQs were individually combined with CLR in vitro, mild antagonism was observed for 53 to 57% of the tested isolates. Moreover, mice were infected with MAC strains showing mild antagonism for FQ-CLR combinations in vitro, and the anti-MAC effects of the FQ-CLR combinations were evaluated by counting the viable bacteria in their organs and by histopathological examination after 28 days of treatment. Several FQ-CLR combinations exhibited bacterial counts in organs significantly higher than those in mice treated with CLR alone. Our results indicate that the activity of CLR is occasionally attenuated by combination with an FQ both in vitro and in vivo and that this effect seems to be MAC strain dependent. Careful combination chemotherapy using these agents against MAC infectious disease may be required.

Skin and joint infection by Mycobacterium chelonae: Rescue treatment with interferon gamma

INTRODUCTION

Atypical mycobacteria are environmental organisms that cause opportunistic infections in humans.

CASE REPORT

A 50-year-old electronics engineer sought advice about starting TNFalpha antagonist therapy for ankylosing spondylitis. Disease duration was 23 years and current treatment was methylprednisolone 4 mg/d. Atypical skin lesions and knee arthritis were noted. Fluid aspirated from the knee showed inflammatory properties and a few acid-fast bacteria, which a line probe assay identified as Mycobacterium chelonae. The same organism was found in a skin biopsy from a thigh lesion. Antimicrobial treatment was started immediately. Inadequate results 6 months later prompted synovectomy of the knee followed by interferon gamma, 50 microg/m(2) body surface area subcutaneously 3 times a week. After 16 months, there were no new skin or joint lesions, and the antimicrobials and interferon gamma were therefore discontinued.

CONCLUSION

This highly unusual case suggests that interferon gamma may be effective in patients with M. chelonae infection that fails to respond adequately to antimicrobials.

Infections Due to Rapidly Growing Mycobacteria

Rapidly growing mycobacteria, generally of low virulence, are capable of causing a wide spectrum of infections. Increasing reports in the literature, referral center experiences, and data from the Infectious Disease Society of America Emerging Infectious Disease Network suggest that greater numbers of infections are occurring. Epidemiological study is imperative in understanding the true incidence of these infections and preventing disease in vulnerable hosts. Especially problematic is pulmonary infection due to Mycobacterium abscessus, which is difficult to cure. New agents with enhanced activity against this group and other nontuberculous mycobacteria are needed. Here, we focus on the members of the rapidly growing mycobacteria because of their emerging importance in both sporadic infections and outbreak settings.

Recalcitrant Post-LASIK Mycobacterium chelonae Keratitis Eradicated after the Use of Fourth-Generation Fluoroquinolone

OBJECTIVE

To report a patient with Mycobacterium chelonae keratitis after LASIK and discuss therapeutic measures.

DESIGN

Interventional case report and literature review.

INTERVENTION

A healthy, 25-year-old man presented 6 weeks after LASIK with infectious keratitis in the left eye. Scrapings were obtained from the central stromal bed after lifting the flap and inoculated on culture media.

MAIN OUTCOME MEASURES

Response to medical treatment.

RESULTS

Mycobacterium chelonae was identified from stromal bed scrapings. The protracted course of the infection necessitated surgical debridement and flap amputation with slow and suboptimal response to prolonged (14 weeks) treatment with topical amikacin 3.3%, clarithromycin 1%, and levofloxacin 0.5%. The substitution of levofloxacin 0.5% with gatifloxacin 0.3% resulted in closure of the epithelial defect within 1 week and resolution of the infiltrates in 3 weeks. The combined regimen of gatifloxacin 0.3%, amikacin 3.3%, and clarithromycin 1% was continued for a total of 4 months. The patient remains infection free 1 year after stopping all antibiotics.

CONCLUSION

Treatment of post-LASIK nontuberculous mycobacteria remains a challenge. Institution of combination therapy including fortified amikacin, clarithromycin 1%, and a fourth-generation fluoroquinolone appeared to be beneficial in this patient.

Lung Disease Due to the More Common Nontuberculous Mycobacteria

As the prevalence of tuberculosis (TB) declines in the developed world, the proportion of mycobacterial lung disease due to nontuberculous mycobacteria (NTM) is increasing. It is not clear whether there is a real increase in prevalence or whether NTM disease is being recognized more often because of the introduction of more sensitive laboratory techniques, and that more specimens are being submitted for mycobacterial staining and culture as the result of a greater understanding of the role of NTM in conditions such as cystic fibrosis, posttransplantation and other forms of iatrogenic immunosuppression, immune reconstitution inflammatory syndrome, fibronodular bronchiectasis, and hypersensitivity pneumonitis. The introduction of BACTEC liquid culture systems (BD; Franklin Lakes, NJ) and the development of nucleic acid amplification and DNA probes allow more rapid diagnosis of mycobacterial disease and the quicker differentiation of NTM from TB isolates. High-performance liquid chromatography, polymerase chain reaction, and restriction fragment length polymorphism analysis have helped to identify new NTM species. Although treatment regimens that include the newer macrolides are more effective than the earlier regimens, failure rates are still too high and relapse may occur after apparently successful therapy. Moreover, treatment regimens are difficult to adhere to because of their long duration, adverse effects, and interactions with the other medications that these patients require. The purpose of this article is to review the common presentations of NTM lung disease, the conditions associated with NTM lung disease, and the clinical features and treatment of the NTM that most commonly cause lung disease.

Clinical experience with linezolid for the treatment of central nervous system infections

Linezolid, an oxazolidinone, exhibits bacteriostatic activity against virtually all Gram-positive bacteria and even covers atypical organisms like mycobacteria and Nocardia. However, little is known about its effectiveness for central nervous system (CNS) infections. We report on our good experience with linezolid for the treatment of CNS infections in 10 patients, amongst whom three were caused by mycobacteria. While six of our patients clinically improved during linezolid therapy even after failure of various antibiotics, it was unsuccessful in one case. Side-effects were only mild gastrointestinal problems in one patient after long term-treatment, which however led to the cessation of therapy. Linezolid appears to be a safe alternative to vancomycin for therapy-resistant CNS infections because of its good CSF penetration and few side-effects.

In Vitro Activity of Fluoroquinolones Against Mycobacterium abscessus and Mycobacterium chelonae Causing Infectious Keratitis After LASIK in Brazil

PURPOSE

To evaluate the in vitro activity of fluoroquinolones against Mycobacterium abscessus and Mycobacterium chelonae isolated from outbreaks of infectious keratitis in Brazil.

MATERIAL AND METHODS

Micobacterial isolates were recovered from infectious keratitis cases related outbreaks that occurred in Brazil after LASIK for myopia. Two outbreaks occurred in Rio de Janeiro in 1998 and 1999, and 3 in São Paulo between 2000 and 2003. All laboratorial analysis, including molecular identification and antibiotic susceptibility testing with determination of the minimum inhibitory concentration (MIC) levels for ciprofloxacin, ofloxacin, gatifloxacin, and moxifloxacin, were performed at Universidade Federal de São Paulo in Brazil.

RESULTS

Fifteen samples were identified as M. chelonae, and 3 were identified as M. abscessus. The outbreaks studied were designated SP-1 in 2000; SP-2 in 2000-2001; and SP-3 in 2003, R1 in 1988 and R2 in 1999. All but 1 of the M. chelonae were resistant to all fluoroquinolones with an MIC90 greater than 32 microg/mL. The only susceptible isolate had MIC levels for ciprofloxacin, ofloxacin, gatifloxacin, and moxifloxacin of 0.38 microg/mL, 0.032 microg/mL, 0.047 microg/mL, and 0.19 microg/mL, respectively. MIC levels for all 3 M. abscessus isolates tested were greater then 32 microg/mL for all fluoroquinolones tested.

CONCLUSIONS

Fluoroquinolone MICs for 17 M. abscessus and M. chelonae isolates recovered from infectious keratitis cases in Brazil indicate that they are not susceptible to these drugs in vitro. Further studies to investigate the in vivo effectiveness of fluoroquinolones against mycobacteria are required because in vitro tests do not support their use in the treatment of micobacterial keratitis in this particular geographic area.

In vitro activity of linezolid, clarithromycin and moxifloxacin against clinical isolates of Mycobacterium kansasii

OBJECTIVES

To compare the activity of linezolid with a range of drugs used in the treatment of Mycobacterium kansasii infections.

RESULTS

The percentages of resistant isolates against isoniazid, rifampicin and ethambutol were 2.9%, 1.9% and 2.9%, respectively. All isolates were susceptible to clarithromycin and moxifloxacin both with MIC(90) values of 0.125 mg/L. Linezolid was active against all isolates with MIC(50) and MIC(90) values of 0.5 and 1 mg/L, respectively, both below the susceptibility breakpoint established for mycobacteria.

CONCLUSION

Linezolid, clarithromycin or moxifloxacin, could be used as alternative drugs for treatment of infections due to rifampicin-resistant isolates as well as short-course or intermittent therapy of M. kansasii lung disease.

Usefulness of various antibiotics against Mycobacterium avium-intracellulare, measured by their mutant prevention concentration

This study looked the selection of resistant mutants in Mycobacterium avium-intracellulare during antibiotic treatment. The mutant prevention concentration (MPC) of 20 Mycobacterium avium and 12 Mycobacterium intracellulare isolates was determined. Fifty percent of Mycobacterium avium strains had MPC (MPC50) values lower than 16, 64, 40, 55 and 60 mg/L for rifabutin, rifampicin, ciprofloxacin, levofloxacin and moxifloxacin, respectively. In the case of Mycobacterium intracellulare, 50% had MPC (MPC50) values below 60, 30, 35, 16, 2.5 and 14 mg/L for linezolid, rifabutin, levofloxacin, gatifloxacin, moxifloxacin and clarithromycin, respectively. The high capacity for selecting resistant mutants of all the antibiotics studied emphasises the need to restore the immune system if necessary and to administer combined treatments in order to cure patients.

Comparative in vitro activities of linezolid, telithromycin, clarithromycin, levofloxacin, moxifloxacin, and four conventional antimycobacterial drugs against Mycobacterium kansasii

Mycobacterium kansasii is one of the most pathogenic and frequent nontuberculous mycobacteria isolated from humans. Patients with adverse drug reactions, resistant isolates, or suboptimal response require alternative treatment regimens. One hundred forty-eight consecutive clinical isolates of M. kansasii were tested for antimicrobial susceptibilities by the BACTEC 460 system (NCCLS) with two different inoculation protocols, one conventional and one alternative. In the alternative protocol, the inoculum 12B vial was incubated until the growth index was between 250 and 500. Four conventional antimycobacterial drugs (isoniazid, rifampin, streptomycin, and ethambutol) were studied with standard critical concentrations. The in vitro activities of linezolid, telithromycin, clarithromycin, levofloxacin, and moxifloxacin were determined by measuring radiometric MICs. All isolates tested were identified as M. kansasii genotype I and were resistant to isoniazid at a concentration of 0.4 mug/ml. One hundred twenty isolates (81.1%) were inhibited by 1 microg of isoniazid per ml. A high level of resistance to isoniazid (>10 microg/ml) was observed in six isolates (4.1%). Only five strains (3.4%) were resistant to rifampin (>1 microg/ml). All isolates studied were susceptible to streptomycin and ethambutol. The MICs at which 90% of the isolates were inhibited (in micrograms per milliliter) were as follows: linezolid, 1 (range, < or =0.25 to 2); telithromycin, >16 (range, 4 to >16); clarithromycin, 0.5 (range, < or =0.03 to 1); levofloxacin, 0.12 (range, 0.12 to 0.25); and moxifloxacin, 0.06 (range, < or =0.06 to 0.12). The susceptibility testing results with both inoculation protocols showed perfect correlation. In conclusion, all M. kansasii isolates showed decreased susceptibility to isoniazid, but resistance to rifampin was infrequent. Quinolones, especially moxifloxacin, were the most active antimicrobial agents tested, followed by clarithromycin. Linezolid also showed good activity against these microorganisms, but telithromycin's in vitro activity was poor.

Mycobacterium avium complex pulmonary disease in patients without HIV infection

Mycobacterium avium complex (MAC) is ubiquitous. It is found in various freshwater and saltwater sources around the world, including hot water pipes. Although the organism was identified in the 1890s, its potential to cause human disease was only recognized 50 years later. Only a minority of people exposed to the organism will acquire MAC lung disease, usually those with underlying lung disease or immunosuppression. MAC may, however, cause progressive parenchymal lung disease and bronchiectasis in patients without underlying lung disease, particularly in middle-aged and elderly women. Preliminary data suggest that the interferon-gamma pathways may be deficient in elderly women with MAC lung disease. Other groups of patients who are more likely to harbor MAC in their lungs include patients with a cystic fibrosis or an abnormal alpha(1)-antiproteinase gene and patients with certain chest wall abnormalities. Treatment results continue to be disappointing, and the mortality of patients with MAC lung disease remains high. A PubMed search identified 38 reports of the treatment of MAC lung disease. Apart from the British Thoracic Society study, the only published controlled investigation, the studies published since 1994 have included a macrolide, either clarithromycin or azithromycin, usually in combination with ethambutol and a rifamycin. If success is defined as eradication of the organism without relapse over a period of several years after treatment has been discontinued, the reported treatment success rate with the macrolide containing regimens is approximately 55%. The prolonged treatment period, side effects, and possibly reinfection rather than relapse are responsible for the high failure rate.