Atypical mycobacteria: an important differential for the general physician

Atypical mycobacterium infection following anterior cruciate ligament reconstruction

A man in his 20s presented with instability of the right knee following an incident of fall from a height. He was clinicoradiologically diagnosed to have an anterior cruciate ligament (ACL) tear for which he underwent ACL reconstruction. Postoperatively, he was started on an accelerated ACL rehabilitation protocol. Six weeks postoperatively, he developed features of subclinical septic arthritis for which he underwent arthroscopic debridement. Intraoperative samples cultured Mycobacterium abscessus complex on MGIT 960 system. The patient subsequently had to undergo another debridement after 1 month as there were clinical signs of persisting infection. The graft was intact even on the second debridement and after removing the implants. This case reports a rare complication of ACL reconstruction with infection by atypical mycobacterium and the clinical outcome. It also emphasises that prompt surgical intervention can save the graft.

Novel pyrimidine-1,3,4-oxadiazole hybrids and their precursors as potential antimycobacterial agents

Background: Molecular hybridization and isostery are proven approaches in medicinal chemistry, and as such we used them to design novel compounds that we investigated as potential antimycobacterials to combat drug-resistant strains. Methods & results: Prepared N-alkyl-2-(pyrimidine-5-carbonyl)hydrazine-1-carboxamides were cyclized to N-alkyl-5-(pyrimidin-5-yl)-1,3,4-oxadiazol-2-amines along with their analogues. A total of 48 compounds were tested against Mycobacterium tuberculosis H37Rv, Mycobacterium avium and Mycobacterium kansasii, with oxadiazoles and C8-C12 alkyls being the most effective from a concentration of 2 μM. Multidrug-resistant strains were inhibited at same concentrations as the susceptible strain. For the most potent N-dodecyl-5-(pyrimidin-5-yl)-1,3,4-oxadiazol-2-amine, the mechanism of action related to cell wall biosynthesis was investigated. Conclusion: Pyrimidine-1,3,4-oxadiazole hybrids are unique antimycobacterial agents inhibiting mainly M. tuberculosis strains without cross-resistance to current drugs and are thus promising drug candidates.

Blood antimicrobial activity varies against different Mycobacterium spp

In vitro analysis of mycobacterial pathogenicity or host susceptibility has traditionally relied on the infection of macrophages, the target cell of mycobacteria, despite difficulties reproducing their antimycobacterial activity. We have employed alternative models, namely whole blood and leukocytes in plasma, from QuantiFERON negative individuals, and performed infections with the pathogenic M. tuberculosis, the less pathogenic M. avium, M. kansasii and M. chelonae and the occasionally pathogenic M. gordonae and M. bovis. The anticoagulant used in blood extraction, heparin or EDTA, had a major influence in the outcome of the infection. Thus, while in the heparinized models a similar number of bacteria were enumerated in the inoculum and after seven days, in the presence of EDTA a killing effect was observed, despite the inhibitory effect of EDTA on cellular functions like the production of cytokines or reactive oxygen species (ROS). A special case was the rapidly growing mycobacteria M. chelonae, that multiplied in heparinized models but was eliminated in models with EDTA. We verified that EDTA is not responsible for the bactericidal effect, but acts as a bacteriostatic agent. Further work will determine whether blood derived models are a better alternative to the classical macrophage.

Disseminated Mycobacterium avium Complex With Cutaneous Lesions

BACKGROUND

Although most commonly encountered in patients with human immunodeficiency virus infection, disseminated Mycobacterium avium complex (MAC) is becoming more common in patients receiving immunosuppressive medications. Disseminated MAC with skin lesions may occur, and several presentations have been reported, including panniculitis, cutaneous granulomas, pustules, ulcerations, and erythematous skin lesions.

OBJECTIVES

The objective of this report is to describe an unusual presentation of MAC that is unlikely to be encountered frequently in the outpatient dermatology setting, especially in a patient without human immunodeficiency virus infection.

METHODS

The authors present a case of disseminated MAC infection with cutaneous manifestations in an iatrogenically immunocompromised patient.

CONCLUSIONS

Diagnosis of MAC infection is challenging given the varied clinical presentations and the difficulty in culturing MAC. In addition, the acid-fast stain is nonspecific. Clinicians should remember to consider MAC infection in patients with acid-fast-positive skin lesions, as the selection of appropriate antibiotic therapy is species specific.