In-vitro activity of seventeen antimicrobial compounds against seven species of mycobacteria

Minocycline: old and new therapeutic uses

Since the introduction of minocycline HCl in the late 1960's, it has been used for disease states that have ranged from typical community-acquired infectious diseases to others that are non-infectious, such as resistant rheumatoid arthritis. Owing to its high penetration characteristics throughout the body, minocycline can be used in the treatment of a wide variety of extracellular and intracellular pathogens. This review examines the known and potential therapeutic uses of minocycline in a clinical setting.

New anti-tuberculosis agents amongst known drugs

Mycobacterium tuberculosis has an on-going impact on global public health and new therapeutics to treat tuberculosis are urgently required. The emergence of drug resistant tuberculosis poses a serious threat to the control of this pathogen, and the development of drugs that are active against the resistant strains is vital. A medium-throughput assay using the Alamar Blue reagent was set-up to identify novel inhibitors of M. tuberculosis from a library of known drugs, for which there has already been extensive research investigating their suitability and safety as human therapeutics. Of the 1514 compounds screened, 53 were demonstrated to possess inhibitory properties against M. tuberculosis at a concentration of 5microM or below. Of these, 17 were novel inhibitors while 36 were known tuberculosis drugs or had been previously described as possessing anti-tuberculosis activity. Five compounds were selected as those which represent the most promising starting points for new anti-tuberculosis agents. It was demonstrated that all five were active against intracellular M. tuberculosis in a macrophage model of infection. The anti-tuberculosis agents identified in this screen represent promising new scaffolds on which future drug development efforts can be focused.

PCR screening reveals unexpected antibiotic biosynthetic potential in Amycolatopsis sp. strain UM16

AIMS

To assess the antibiotic biosynthetic potential of Amycolatopsis sp. strain UM16 and eight other Amycolatopsis species.

METHODS AND RESULTS

Amycolatopsis genomic DNA was screened by PCR for the glycopeptide, Type-II (aromatic) polyketide and ansamycin biosynthetic gene clusters. Amycolatopsis sp. strain UM16, which exhibits weak antitubercular activity, was shown to have the glycopeptide oxyB gene and the Type-II (aromatic) polyketide-synthase KSalpha-KSbeta tandem gene pair, but not the AHBA synthase gene. The ristocetin (glycopeptide) producer, Amycolatopsis lurida NRRL 2430(T), was shown to have the oxyB gene and the Type-II polyketide-synthase KSalpha-KSbeta tandem gene pair. Amycolatopsis alba NRRL 18532(T) was shown to have the glycopeptide oxyB gene and the AHBA synthase gene. Phylogenetic analyses using Amycolatopsis oxyB and KSalpha-KSbeta gene sequences were conducted.

CONCLUSIONS

Amycolatopsis sp. strain UM16 appears to have the biosynthetic potential to produce glycopeptide and Type-II polyketide antibiotics, but not ansamycins. The potential to synthesize aromatic polyketides may be more widely distributed in Amycolatopsis than is currently recognized.

SIGNIFICANCE AND IMPACT OF THE STUDY

PCR screening is a very useful tool for rapidly identifying the biosynthetic potential of an antibiotic-producing actinomycete isolate. Advanced knowledge of the type of antibiotic(s) produced will allow appropriate methods to be selected for antibiotic purification.

Mycobacterium simiae: A Previously Undescribed Pathogen in Peritoneal Dialysis Peritonitis

Peritonitis is a major complication of peritoneal dialysis (PD). Coagulase-negative staphylococcus, Staphylococcus aureus , and Gram-negative bacteria cause the majority of these infections and usually are amenable to conventional antibiotic therapy, allowing continuation of PD. Mycobacterial and fungal peritonitis represent a more difficult clinical challenge. The infecting organism is often difficult to isolate and can rarely be eradicated without catheter removal. Immunocompromised patients are susceptible to opportunistic infection and, in the context of PD, may have PD peritonitis with different organisms from immunocompetent patients. Here the authors report for the first time PD peritonitis caused by Mycobacterium simiae , a nontuberculous mycobacterium, in a human immunodeficiency virus-positive patient. In addition the difficulty in diagnosing and managing nontuberculous PD peritonitis is discussed.

Concurrent infection due to Shewanella putrefaciens and Mycobacterium marinum acquired at the beach

Infection with marine bacteria is uncommon. A patient with systemic lupus erythematosus who developed concurrent infection with Shewanella putrefaciens and Mycobacterium marinum (M. marinum) is described. After bathing leg ulcers in sea water, severe cellulitis of the left leg with necrotic areas and extensive bullae developed. Infection due to S. putrefaciens was confirmed and a long course of hospitalization, oral ciprofloxacin and skin grafting was required. During hospitalization subcutaneous nodules developed on the other leg. Biopsy revealed acid-fast bacilli and culture grew M. marinum. These lesions responded to rifampicin and cotrimoxazole. Patients with leg ulcers, peripheral vascular disease, diabetes, or receiving immunosuppressive drugs may acquire unusual infections after salt water exposure.

Ciprofloxacin once daily versus twice daily for the treatment of pulmonary tuberculosis

Ciprofloxacin was used as an antituberculous drug in adult patients who could not tolerate standard regimens or had to be treated with alternative combinations for resistance problems. During October 1986 to December 1991, 241 patients received ciprofloxacin in two daily 500 mg doses administered under supervision at 8.30 a.m. and 5 p.m., respectively. This group of patients was submitted to retrospective analysis for tolerability and clinical as well as microbiological efficacy. In January 1992, a once daily regimen with 1,000 mg of ciprofloxacin was introduced in order to simplify drug administration together with the other combination partners and to take advantage of higher drug levels at the site of infection. These patients were followed prospectively for safety and efficacy. Until July 1993, 227 patients with smear-positive pulmonary tuberculosis were included in this open study. Comparative analysis was carried out for a selected group of patients who had remained smear and culture positive for more than 27 days after start of treatment. Fifty-four patients who had received ciprofloxacin twice daily and 35 patients on the once daily regimen were evaluable. Both regimens were equally well tolerated. The once daily regimen was associated with a trend towards earlier conversion to smear negativity and a significantly shorter time to culture negativity. Smears became negative on average within 84 days with the once daily and in 94 days with the twice daily schedule (p = 0.19). Culture negativity occurred at 60 and 76 days in the respective groups (p = 0.0013; log Rank test). Of the patients who received ciprofloxacin twice daily, 33% were still smear and culture positive 90 days after start of treatment compared to only 15% of the patients treated with the once daily schedule. We conclude that ciprofloxacin, given as a single daily dose of 1,000 mg is as safe as two 500 mg doses, more convenient to apply and probably more efficacious.

Intracellular accumulation of norfloxacin in Mycobacterium smegmatis

To evaluate the intracellular accumulation of norfloxacin in mycobacteria, two methods were used with Mycobacterium smegmatis. A radiometric method (K. V. Cundy, C. E. Fasching, K. E. Willard, and L. R. Peterson, J. Antimicrob. Chemother. 28:491-497, 1991) was used without great modification, but the fluorometric method (P. G. S. Mortimer and L. J. V. Piddock, J. Antimicrob. Chemother. 28:639-653, 1991) was changed considerably. Indeed, adsorption of the quinolone to the bacterial surface was characterized by measuring the level of accumulation of 0 degree C. Taking into account the adsorption, the pH of the washing buffer was increased from 7.0 to 9.0 to improve the desorption of norfloxacin from the cell surface. Both the fluorometric method, with the technical improvement, and the radiometric method could be used to estimate the intracellular accumulation of norfloxacin, which resulted from the difference between the whole uptake measured at 37 degrees C and the adsorption measured at 0 degrees C. A total of 35 ng of norfloxacin per mg of cells (dry weight) penetrated into the M. smegmatis cell, and the steady state was achieved in 5 min. Use of inhibitors of the proton motive force revealed that transport of norfloxacin was energy independent. Thus, the same mechanisms of quinolone accumulation that occur in eubacteria seem to occur in mycobacteria, at least in M. smegmatis.

Mycobacterium marinum arthritis

Mycobacterium marinum is an atypical acid-fast organism that is rarely associated with septic arthritis. Most often this is seen in patients with monarticular synovitis of the hands or wrists, especially in association with a history of periarticular trauma or exposure to marine environments. From tissue obtained by aspiration or synovectomy, Mycobacterium marinum can be identified by Ziehl-Nielson stain and has optimal growth in Lowenstein-Jenson medium. Therapy should consist of at least two antimycobacterial agents for a minimum 6 months. Surgical debridement also may be beneficial. The clinician must have a high index of suspicion that exposure to Mycobacterium marinum has occurred so appropriate stains and cultures can be obtained and antimycobacterial therapy initiated.

Cutaneous nodules of Mycobacterium chelonae in an immunosuppressed patient with preexisting pulmonary colonization

A 30-year-old immunocompromised man with known pulmonary Mycobacterium chelonae colonization developed a systemic infection with cutaneous manifestations. The eruption consisted of multiple, nontender, subcutaneous nodules on the extremities. A diagnosis of disseminated M. chelonae was made on the basis of recovery of M. chelonae subspecies abscessus from blood and bronchoalveolar lavage fluid and histologic evidence of acid-fast bacilli in a skin biopsy specimen. We believe this is the first reported case of disseminated M. chelonae infection in an immunocompromised host in whom a primary source of the infection was identified.

Osteomyelitis and synovitis produced by Mycobacterium marinum in a fisherman

We report a case of osteomyelitis and synovitis produced by Mycobacterium marinum in the left index finger of a fisherman. A combination of surgical intervention and antimicrobial therapy with minocycline, rifampin, and ethambutol was efficacious.