The pathophysiology of disseminated Mycobacterium avium complex disease in AIDS

Disseminated Nontuberculous Mycobacterium Infection During Treatment of Multiple Myeloma: A Case Report and Review of the Literature

Multiple myeloma (MM) is a plasma B-cell malignancy characterized by immune dysfunction, with infection representing a major complication. Bacteria, including Streptococcus pneumoniae, are common pathogens in patients with MM, but reports on infections with nontuberculous mycobacteria (NTM) have been limited. We herein report a case of disseminated NTM infection in a patient with MM undergoing treatment with immunomodulatory drugs. At the diagnosis, the patient showed lymphocytopenia and was treated with clarithromycin, rifampicin, and ethambutol; however, culture positivity persisted, and the patient died. The possibility of NTM infection should be considered in cases of unexplained deterioration of the MM patient's general condition.

Mycobacterium avium complex (MAC) infection in severely immunocompromised people living with HIV: Findings from a five-year cohort

BACKGROUND

We sought to clarify the current incidence, risk factors and symptoms of disseminated Mycobacterium avium complex (dMAC) infection in admitted people living with HIV in a hospital in the Southeast of Spain.

METHODS

5-years observational, retrospective and single-centre study. Demographic, clinical and analytical variables, along with microbiological, treatment and follow-up were collected.

RESULTS

Five cases of dMAC infection in severely immunocompromised people living with HIV people living were found. dMAC was diagnosed in 22.7% of patients under 100 CD4. All patients presented with fever and clinical manifestations of pneumonia, lymphadenopathy, or gastrointestinal symptoms. Despite low CD4 levels and high viral loads in some cases, primary prophylaxis had not been previously administered.

CONCLUSIONS

Until 2018, U.S. American guidelines recommended antimycobacterial prophylaxis for patients with low CD4 cell counts, a practice not adopted in Europe. Untreated dMAC infection is associated with high morbidity and mortality rates. dMAC infection represents a prevalent disease in severely immunosuppressed people living with HIV. dMAC requires a high index of suspicion in this population, in order to perform mycobacterial cultures from different samples.

Mycobacterium marinum Infection Leading to HIV Diagnosis: A Case Report

Non-tuberculous mycobacteriosis (NTM) is a rare infection that can manifest as pulmonary, disseminated, or cutaneous disease. Cutaneous NTM infections are often associated with immunosuppressive conditions, such as HIV infection or exposure to contaminated water, but they can also occur in healthy individuals, complicating the diagnosis. We report the case of a 54-year-old male with a gradually enlarging skin ulcer on his left upper limb. Initial treatment for sporotrichosis failed, and further testing confirmed Mycobacterium marinum infection. The patient had no prior medical history, but due to the persistent nature of the symptoms, HIV testing was performed, revealing advanced HIV infection with a CD4 count of 34 cells/µl. Following appropriate antimicrobial treatment, the ulcer healed, and antiretroviral therapy (ART) was initiated, resulting in a significant improvement in immune function. This case highlights the importance of considering underlying immunosuppressive conditions, such as HIV, when diagnosing persistent cutaneous NTM infections. Early detection and prompt treatment of both M. marinum and HIV were critical in preventing the progression to disseminated disease, which is often fatal in immunocompromised patients.

Opportunistic Infections and Malignancies in a Patient With HIV/AIDS and a Critically Low CD4 Count of 1 Cell/μL

We present a 45-year-old African American male with a medical history of advanced-stage HIV/AIDS (CD4 count: 1 cell/μL) and poor adherence to highly active antiretroviral therapy (HAART), who presented with symptoms of diarrhea, weakness, and respiratory distress. Upon admission, duodenal and colonic biopsies revealed a diffuse histiocytic infiltrate consistent with Mycobacterium avium complex (MAC), and a cecal biopsy was positive for Kaposi sarcoma (KS). Further workup showed consolidation and a right pleural effusion on chest X-ray, suggesting a pneumonia infection. The patient's hypoglycemic state and lung consolidation raised concerns for sepsis, despite negative blood cultures for the first 24 hours. The patient was initiated on HAART and treated with azithromycin, rifabutin, and ethambutol for disseminated MAC. Despite the aggressive immunotherapy, the patient's condition did not improve, and he eventually expired. This case uniquely highlights the wide range of opportunistic infections and malignancies that can present in individuals with advanced-stage HIV/AIDS, underscoring the importance of early recognition and treatment. This susceptible demographic warrants further research due to the non-solidified prognosis of individuals with severe immunodeficiency.

Disseminated Mycobacterium avium Complex Infection in a Patient Treated With Immunosuppressants

Mycobacterium avium complex (MAC) is an important cause of opportunistic infections in immunosuppressed hosts, such as patients with HIV infection and solid organ transplant recipients. MAC disease usually presents in 4 distinct clinical categories: chronic pulmonary disease, disseminated disease, skin/soft-tissue infection, and superficial lymphadenitis. However, clinical reports on gastrointestinal (GI) MAC disease are rare, especially in patients without HIV infection or a history of organ transplantation. We describe a case of non-HIV-associated GI MAC disease in a patient with long-term mycophenolate mofetil use. In this case, MAC organisms in the GI tract and ascites were observed. Endoscopy revealed a unique colonic image with large, deep epithelial denudations. This suggests that apart from patients with HIV infection or transplant recipients, those treated with immunosuppressants can have disseminated MAC. Therefore, internal physicians need to monitor patients undergoing mycophenolate mofetil immunosuppressant therapy.

The synergetic effect of sitafloxacin-arbekacin combination in the Mycobacterium abscessus species

Mycobacterium abscessus species (MABS) is the most commonly isolated rapidly growing mycobacteria (RGM) and is one of the most antibiotic-resistant RGM with rapid progression, therefore, treatment of MABS is still challenging. We here presented a new combination treatment with sitafloxacin that targeted rough morphotypes of MABS, causing aggressive infections. Thirty-four clinical strains of MABS were isolated from various clinical samples at the Juntendo university hospital from 2011 to 2020. The susceptibility to a combination of sitafloxacin and antimicrobial agents was compared to that of the antimicrobial agents alone. Out of 34 MABS, 8 strains treated with sitafloxacin-amikacin combination, 9 of sitafloxacin-imipenem combination, 19 of sitafloxacin-arbekacin combination, and 9 of sitafloxacin-clarithromycin combination showed synergistic effects, respectively. Sitafloxacin-arbekacin combination also exhibited the synergistic effects against 10 of 22 Mycobacterium abscessus subspecies massiliense (Mma) strains and 8 of 11 Mycobacterium abscessus subspecies abscessus (Mab) strains, a highly resistant subspecies of MABS. The sitafloxacin-arbekacin combination revealed more synergistic effects in rough morphotypes of MABS (p = 0.008). We demonstrated the synergistic effect of the sitafloxacin-arbekacin combination against MABS. Further, this combination regimen might be more effective against Mab or rough morphotypes of MABS.

Induction of killing of Mycobacterium avium subsp. hominissuis in macrophages by cytokine stimulated innate-like lymphoid cells is negatively affected by the pathogen

Mycobacterium avium subsp. hominissuis (MAH) is a common environmental bacterium that causes infection in immunocompromised patients such as those with HIV/AIDS, or patients with chronic lung disease such as cystic fibrosis. There are many strains of MAH with varying levels of virulence. Infection with MAH strains 100 and 104 has been associated with different immune responses in mice and outcome of the disease. While MAH 100 infection tends to be cleared from mice, MAH 104 is virulent and grows in host tissue. What is currently unknown are the mechanisms related to this difference in host defense and virulence. Our hypothesis is that differences in circulating innate lymphocytes response are associated with increased protection from infection. Innate lymphoid cells (ILC) are lymphoid cells with an important role in regulation of innate immune systems. ILCs can be categorized into three subpopulations ILC1, ILC2, and ILC3 based on their cytokine production and regulatory transcription factors. Investigation was carried out on how macrophage anti-MAH response change depending on activation by primary mouse lymphocytes activated with IL-12, IL-33, and IL-23, triggering differentiation into ILC-like subpopulations. Our results do not affirm the role of any one ILC subpopulation in macrophage anti-M. avium ability. Our findings instead support the conclusion that MAH infection of macrophages suppresses the stimulatory function of ILCs.

Disseminated MAI in an HIV Patient-An Unusual Presentation

Patients with Human Immunodeficiency Virus (HIV), and especially Acquired Immunodeficiency Syndrome (AIDS), can present in a multitude of ways with a variety of possible pathologies. This can prove to be a challenge to a clinician. The patient, in this case, was found to have disseminated Mycobacterium-avium-intracellulare (MAI), despite compliance with antiretroviral therapy (ART), who presented with right upper quadrant pain, isolated elevated alkaline phosphatase, and sepsis. Imaging revealed multiple splenic lesions, bilateral psoas abscesses, abdominal lymphadenopathy, and a large right pleural effusion with a mediastinal shift to the left. Psoas abscesses were drained and the cultures grew acid-fast bacilli. The patient was treated with azithromycin, ethambutol and rifabutin. Classically, MAI infections of patients compliant with ART therapy present with localized disease. This case offers a different presentation of MAI despite compliance with ART therapy.

Intestinal Mycobacterium avium Complex Infection in a Kidney Transplant Patient

Opportunistic infections are the result of infection by bacteria, viral, and fungal sources potentially leading to severe disease and death. These infections are a cause of significant morbidity and mortality among individuals with profound immunosuppression, namely human immunodeficiency virus (HIV), and organ transplant recipients on medications used to prevent organ rejection. Mycobacterium avium complex (MAC) is one of the most prevalent pathogens worldwide as it is found ubiquitously in water, food, and soil and is commonly a source of disseminated disease among the immunocompromised. However, cases of kidney transplantation remain exceedingly rare with an estimated incidence of 0.16% and 0.55%. We present the case of a 68-year-old female with a history of a kidney transplant, currently on immunosuppressant therapy, who was found to have localized MAC infection after undergoing endoscopic evaluation for symptoms of generalized weakness and unintentional weight loss secondary to anemia.

Direct Attachment with Erythrocytes Augments Extracellular Growth of Pathogenic Mycobacteria

Pathogenic intracellular mycobacteria, such as Mycobacterium tuberculosis and Mycobacterium avium, which cause lung diseases, can grow in macrophages. Extracellular mycobacteria have been reported in the lungs, blood, and sputum of patients, indicating the involvement of these pathogens in disease progression. Erythrocytes are involved in the symptoms associated with pulmonary mycobacterial diseases, such as bloody sputum and hemoptysis; however, little attention has been paid to the role of erythrocytes in mycobacterial diseases. Herein, we found that Mycobacterium avium subsp. hominissuis (MAH) and Mycobacterium intracellulare colocalized with erythrocytes at the sites of lung infection, inside capillaries and necrotic areas of granulomas, using histopathological examinations. Electron microscopy showed that MAH adhered and entered human erythrocytes when they were cocultured in vitro. MAH adhered to erythrocytes through complement receptor 1 and cell-surface sialo-glycoproteins. Importantly, MAH grew vigorously without causing any pronounced damage to erythrocytes. This erythrocyte-mediated enhancement of MAH growth occurred extracellularly depending on its direct attachment to erythrocytes. In contrast, MAH failed to multiply inside erythrocytes. Similarly, erythrocytes augmented the growth of other pathogenic mycobacteria, such as M. intracellulare and M. tuberculosis. THP-1 cell-derived human macrophages preferentially phagocytosed erythrocytes that were attached to mycobacteria (compared to bacteria alone), suggesting that erythrocyte-attached mycobacteria are an efficient infectious source for macrophages. Our findings provide new insights into the pathogenesis of mycobacterial diseases and offer an alternative and useful strategy for treating mycobacterial disease. IMPORTANCE Pathogenic mycobacteria, such as Mycobacterium tuberculosis, Mycobacterium avium subsp. hominissuis (MAH), and Mycobacterium intracellulare, cause pulmonary infections as intracellular parasites of lung macrophages and epithelial cells. Here, using histopathological examinations we found that MAH and M. intracellulare colocalized with erythrocytes in lung infection sites. Subsequent studies demonstrated that direct interaction with erythrocytes enhances the extracellular proliferation of mycobacteria based on the following results: 1. MAH adhered and invaded human erythrocytes upon coculture in vitro; 2. MAH adhered to erythrocytes through complement receptor 1 and cell-surface sialo-glycoproteins; 3. MAH rapidly proliferated when directly attached to erythrocytes but not within them; 4. other mycobacteria, such as M. intracellulare and M. tuberculosis, also proliferated in the same way as MAH. The finding that pathogenic mycobacteria grow extracellularly in an erythrocyte-dependent manner is of considerable clinical importance for understanding disease progression and latent infection.

Varying clinical presentations of nontuberculous mycobacterial disease : Similar to but different from tuberculosis

The incidence rate of pulmonary nontuberculous mycobacterial disease (PNTMD) in Japan is the highest among major industrialized nations. Although the typical clinical course and radiological manifestations of PNTMD are different from those of pulmonary tuberculosis (TB), confusion about these mycobacterial diseases leads to a diagnostic pitfall. Diagnostic challenges include the coexistence of Mycobacterium tuberculosis (MTB) and nontuberculous mycobacteria (NTM), false positives for NTM in MTB nucleic acid amplification tests, microbial substitution, and abnormal radiological manifestations caused by NTM. Features of extrapulmonary NTM diseases, such as pleurisy, vertebral osteomyelitis, and disseminated disease, are different from the corresponding tuberculous diseases. Moreover, the immunological background of the patient (status of human immunodeficiency virus infection with or without antiviral therapy, continuation or discontinuation of immunosuppressive therapy, use of immune checkpoint inhibitor, pregnancy and delivery, etc.) influences the pathophysiology of mycobacterial diseases. This review describes the varying clinical presentations of NTM disease with emphasis on the differences from TB. J. Med. Invest. 68 : 220-227, August, 2021.

Evaluation of a new assay for nontuberculous mycobacteria species identification in diagnostic material and cultures

The purpose of the present study was to evaluate a real-time PCR system for 12 nontuberculous mycobacteria (NTM) species identification developed by Central Tuberculosis Research Institute (CTRI; Moscow, Russia) in cooperation with Syntol LLC (Moscow, Russia). NTM cultures (210 strains, 19 species), Mycobacterium tuberculosis complex (MTBC) cultures (21 strains, 2 species), non-mycobacterial microorganisms (18 strains, 13 species) were used for the first stage of the assay evaluation. Clinical samples (sputum, N = 973) positive for smear microscopy and MTBC/NTM DNA by a PCR-based screening assay collected from 819 patients were used for specificity and sensitivity evaluation. Sensitivity for determining the NTM species directly from diagnostic material was 99.71%, with the specificity of 100%. The sensitivity and specificity for NTM species identification in cultures was 99.67% and 100%, respectively. Both sensitivity and specificity for determining MTBC in cultures was 100%.

Targeting emerging Mycobacterium avium infections: perspectives into pathways and antimicrobials for future interventions

Mycobacterium avium is an emerging opportunistic pathogen, globally. Infections caused by M. avium are laborious to treat and could result in drug resistance. This review discusses the importance of many factors including the cell wall in M. avium pathogenesis, since this unique structure modulates the pathogen's ability to thrive in various hosts and environmental niches including conferring resistance to killing by antimicrobials. More research efforts in future are solicited to develop novel therapeutics targeting M. avium. The complete eradication of M. avium infection in immunocompromised individuals would need a deeper understanding of the source of infection, unique underlying mechanisms and its uncharacterized pathways. This could, perhaps in future, hold the key to target and treat M. avium more effectively.

Role of fluorescence in situ hybridization in detecting mycobacterium avium complex presenting as fever in treatment failure HIV

A 49-year-old male HIV positive patient on treatment failure presented with complaints of fever and dysphagia of three weeks duration and later on developed cervical lymphadenopathy along with severe vomiting and abdominal pain. Liver function tests were found to be worsening with severe drop in CD4 counts. An extensive workup for pyrexia was done. FNAC and biopsy of lymph node showed features suggestive of granulomatous lymphadenitis. CBNAAT of the lymph node aspirate was negative for MTB. Blood culture and lymph node cultures were negative for Mycobacterium Avium Complex (MAC). MAC was however, finally detected and reported positive on Fluorescence in Situ Hybridization (FISH) of the cervical lymph node aspirate. Prompt treatment for MAC was initiated with Ethambutol 800 mg OD and Azithromycin 500 mg OD following which fever spikes subsided and lymph node resolved. The Patient's condition gradually improved and was discharged shortly with a good recovery on subsequent follow ups. Fever is one of the common symptoms in patients with MAC infection. Some other clinical manifestations include weight loss, hepatosplenomegaly and intra-abdominal lymphadenopathy. Diagnostic evaluation should be aggressive. As there is a high risk for MAC infection in advanced HIV cases with poor HAART compliance, FISH can be a valuable and effective diagnostic tool in early detection and treatment of MAC.

General Overview of Nontuberculous Mycobacteria Opportunistic Pathogens: Mycobacterium avium and Mycobacterium abscessus

Nontuberculous mycobacteria (NTM) are emerging human pathogens, causing a wide range of clinical diseases affecting individuals who are immunocompromised and who have underlying health conditions. NTM are ubiquitous in the environment, with certain species causing opportunistic infection in humans, including Mycobacterium avium and Mycobacterium abscessus. The incidence and prevalence of NTM infections are rising globally, especially in developed countries with declining incidence rates of M. tuberculosis infection. Mycobacterium avium, a slow-growing mycobacterium, is associated with Mycobacterium avium complex (MAC) infections that can cause chronic pulmonary disease, disseminated disease, as well as lymphadenitis. M. abscessus infections are considered one of the most antibiotic-resistant mycobacteria and are associated with pulmonary disease, especially cystic fibrosis, as well as contaminated traumatic skin wounds, postsurgical soft tissue infections, and healthcare-associated infections (HAI). Clinical manifestations of diseases depend on the interaction of the host's immune response and the specific mycobacterial species. This review will give a general overview of the general characteristics, vulnerable populations most at risk, pathogenesis, treatment, and prevention for infections caused by Mycobacterium avium, in the context of MAC, and M. abscessus.

Therapeutic implications of nano-encapsulated rifabutin, azithromycin & ethambutol against experimental Mycobacterium avium infection in mice

Background & objectives

Mycobacterium avium causes atypical infection in both immunocompetent and immunocompromised individuals. Conventional chemotherapy for M. avium infection is not efficient due to lengthy course of treatment and drug-associated toxic side effects. The present study was aimed at reducing dosing frequency of antimicrobial regimen consisting of azithromycin (AZM), rifabutin (RBT) and ethambutol (EMB) by encapsulation of drugs in nanoparticles (NPs) in experimental M. avium infection in mice.

Methods

Poly (DL-lactide-co-glycolide) NPs containing anti-M. avium drugs were prepared, characterized and studied for their pharmacokinetics and pharmacodynamics parameters. Drug-loaded NPs were further analyzed for their therapeutic efficacy against experimental M. avium infection in mice.

Results

Drug-loaded NPs were of size 227.3±16.4 for RBT, 334.35±11.7 for AZM and 509.85±20.5 for EMB with smooth surface morphology and negative zeta potential. AZM, EMB and RBT from NPs were detectable for 6, 4 and 5 days, respectively, in the mice plasma, whereas free drugs were cleared from mice circulation within 24 h. Chemotherapeutic effects of weekly administered drug-loaded NPs were equivalent to daily administered free drugs.

Interpretation & conclusions

Our findings showed that NPs gave sustained release of drugs inside plasma and organs, thus decreasing dosage frequency, and their weekly dosage had therapeutic efficacy equivalent to daily dosage of free drugs.

A rare case of disseminated Mycobacterium avium complex with colitis in a renal transplant recipient

Mycobacterium avium complex (MAC) colitis is a rare complication of immunosuppression in solid organ transplant (SOT) recipients. Here, we describe a case of disseminated MAC infection with colitis following renal transplantation. Despite common pathways of immunosuppression, SOT recipients and human immunodeficiency virus (HIV)-infected patients differ in their typical presentations of MAC infection. Intestinal infections have been more commonly reported in HIV-infected patients than in SOT recipients. The explanation for this difference may be related to HIV's targeted effects on the CD4⁺ T-cell reservoir in gut-associated lymphoid tissue.

High mortality in peritonitis due to Mycobacterium avium complex: retrospective study and systematic literature review

BACKGROUND

Mycobacterium avium complex (MAC) infection is often disseminated and mainly involves lymph nodes, spleen, liver or bone marrow. Peritonitis due to MAC infection (PMAC) is a very uncommon manifestation.

METHODS

In this report, after describing the case of the only PMAC infection in our 10-year retrospective study, which occurred in an AIDS patient who was non-adherent to highly active antiretroviral therapy (HAART), we performed a systematic literature review of documented bacteriological PMAC.

RESULTS

Including our patient, 51 cases of PMAC have been reported. Patients were most often male (sex ratio 2.14), with a median age of 41 years (2.8-72) and an immunodeficiency in all cases, most often AIDS (57%), cirrhosis (20%) and continuous ambulatory peritoneal dialysis (CAPD) (18%). Ascites was more often chylous (54%) than exudative (46%) and, in this case, lymphocytic (60%), with an inconstantly positive acid-fast bacilli smear (54%). Non-disseminated PMAC patients were more likely to have peritoneal dialysis (39% versus 6.5%, p < .01) or cancer with immunosuppressive therapy (39% versus 0%, p < .0001), while AIDS was the leading underlying disease in disseminated-PMAC patients (83% versus 11%, p < .001). Mortality was high (50%), with no difference between disseminated and non-disseminated PMAC.

CONCLUSIONS

This report highlights the need to be aware of an atypical presentation of PMAC infection, which is associated with a high rate of mortality even for non-disseminated infection.

Incidence of disseminated Mycobacterium avium-complex infection in HIV patients receiving antiretroviral therapy with use of Mycobacterium avium-complex prophylaxis

The incidence of disseminated Mycobacterium avium complex (MAC) infection in HIV patients has fallen markedly since the introduction of effective antiretroviral therapy (ART). However, current guidelines still recommend primary prophylaxis. We conducted a retrospective cohort study in a university-affiliated hospital from January 1998 to January 2014. During that period, HIV patients who had at least one CD4 cell count below 50 cells/mm³ and had been treated with ART were enrolled. We compared incidence of disseminated MAC infection in the 12 months after the first CD4 cell count below 50 cells/mm³ between prophylaxis and nonprophylaxis groups. A total of 157 patients were enrolled and the total observation period was 144 patient-years (PY). Thirty-three patients (21%) received primary MAC prophylaxis. The initial CD4 cell count of the prophylaxis group was lower than that of the nonprophylaxis group ( P = 0.024), but the proportion of patients who reached a CD4 cell count >100 cells/mm³ ( P = 0.234) and were virologically suppressed ( P = 0.513) 12 months after ART commencement was not different in the prophylaxis and nonprophylaxis groups. The incidence of MAC did not differ significantly between the groups (3.4/100 PY versus 0.8/100 PY, P = 0.368). Routine MAC prophylaxis may be not required in the era of effective ART.

Mycobacterium avium complex-associated cholecystitis in AIDS patient: a case description and review of literature

AIDS-related cholangiopathy was common in patients with AIDS prior to the advent of highly active antiretroviral therapy. Mycobacterium avium complex (MAC) is the most common opportunistic bacterial infection seen in AIDS patients and one of many opportunistic pathogens implicated in AIDS cholangiopathy. We describe a case of acute cholecystitis secondary to MAC in a patient with likely AIDS cholangiopathy. The patient, a 37-year-old Hispanic woman with CD4⁺ cell count of 10 cells/mm³ who was previously diagnosed with disseminated MAC, presented with a eight days of diffuse abdominal pain and anorexia. Radiologic imaging suggested acute cholecystitis, so the patient underwent open cholecystectomy. Pathology staining of the gall bladder wall revealed acid-fast bacilli consistent with MAC. The patient had been receiving appropriate therapy as an outpatient for MAC with presumed reliable adherence, but we suggest her burden of disease was high due to her severe immunosuppressive state. A thorough review of the literature showed that there are many infectious and non-infectious aetiologies for AIDS-associated cholangiopathy. Acute cholecystitis can develop in the setting of AIDS cholangiopathy, potentially secondary to the opportunistic infection that initially caused the cholangiopathy. MAC-related gallbladder disease needs to be considered in patients with advanced AIDS who present with evidence of acute cholecystitis.

Mycobacterium avium Complex Infection in a Patient with Sickle Cell Disease and Severe Iron Overload

A 34-year-old female with sickle cell anemia (hemoglobin SS disease) and severe iron overload presented to our institution with the subacute presentation of recurrent pain crisis, fever of unknown origin, pancytopenia, and weight loss. A CT scan demonstrated both lung and liver nodules concerning for granulomatous disease. Subsequent biopsies of the liver and bone marrow confirmed the presence of noncaseating granulomas and blood cultures isolated Mycobacterium avium complex MAC. Disseminated MAC is considered an opportunistic infection typically diagnosed in the immunocompromised and rarely in immunocompetent patients. An appreciable number of mycobacterial infection cases have been reported in sickle cell disease patients without immune dysfunction. It has been reported that iron overload is known to increase the risk for mycobacterial infection in vitro and in vivo studies. While iron overload is primarily known to cause end organ dysfunction, the clinical relationship with sickle cell disease and disseminated MAC infection has not been reported. Clinical iron overload is a common condition diagnosed in the sub-Saharan African population. High dietary iron, genetic defects in iron trafficking, as well as hemoglobinopathy are believed to be the etiologies for iron overload in this region. Patients with iron overload in this region were 17-fold more likely to die from Mycobacterium tuberculosis. Both experimental and clinical evidence suggest a possible link to iron overload and mycobacterial infections; however larger observational studies are necessary to determine true causality.

Nontuberculous mycobacteria immune reconstitution syndrome

The prevalence of nontuberculous mycobacteria infection (NTM) in Sub-Saharan Africa is estimated to be less than 1%. NTM is often underdiagnosed or misdiagnosed as tuberculosis in patients who present with immune reconstitution syndrome (IRS) following initiation of antiretroviral treatment (ART). Immune reconstitution syndrome is common in patients who start ART with low CD4 counts and high HIV viral load. Furthermore, Mycobacterium avium complex (MAC) commonly infects those with CD4 counts less than 50 cells/mm³. Three patients, with low baseline CD4 counts, presenting with NTM following the initiation of antiretroviral treatment are described in this case series. The first patient presented with disseminated NTM two weeks after commencing antiretroviral treatment. Acid fast bacilli were found in the liver, duodenum, and bone marrow and were suggestive of MAC microscopically. The second developed cervical lymphadenitis following the initiation of ART. Lymph node aspirate culture grew NTM. The last patient developed pancytopenia after 3 months of ART. AFB was seen on bone marrow biopsy. Culture of the bone marrow aspirate was suggestive of NTM. All three patients improved on ethambutol, clarithromycin, and rifampicin. NTM may be underdiagnosed in areas with a high TB prevalence and should be actively excluded by culture.

Rough colony morphology of Mycobacterium massiliense Type II genotype is due to the deletion of glycopeptidolipid locus within its genome

BACKGROUND

Recently, we introduced the complete genome sequence of Mycobacterium massiliense clinical isolates, Asan 50594 belonging to Type II genotype with rough colony morphology. Here, to address the issue of whether the rough colony morphotype of M. massiliense Type II genotype is genetically determined or not, we compared polymorphisms of the glycopeptidolipid (GPL) gene locus between M. massiliense Type II Asan 50594 and other rapidly growing mycobacteria (RGM) strains via analysis of genome databases.

RESULTS

We found deletions of 10 genes (24.8 kb), in the GPL biosynthesis related gene cluster of Asan 50594 genome, but no deletions in those of other smooth RGMs. To check the presence of deletions of GPL biosynthesis related genes in Mycobacterium abscessus--complex strains, PCRs targeting 12 different GPL genes (10 genes deleted in Asan 50594 genome as well as 2 conserved genes) were applied into 76 clinical strains of the M. abscessus complex strains [54 strains (Type I: 33, and Type II: 21) of M. massiliense and 22 strains (rough morphoype: 11 and smooth morphotype: 11) of M. abscessus]. No strains of the Type II genotype produced PCR amplicons in a total of 10 deleted GPL genes, suggesting loss of GPL biosynthesis genes in the genome of M. massiliense type II genotype strains.

CONCLUSIONS

Our data suggested that the rough colony morphotype of the M. massiliense Type II genotype may be acquired via deletion events at the GPL gene locus for evolutionary adaptation between the host and pathogen.

Depression of local cell-mediated immunity and histological characteristics of disseminated AIDS-related Mycobacterium avium infection after the initiation of antiretroviral therapy

OBJECTIVE

The aim of the present study was to examine the immunohistological characteristics of disseminated Mycobacterium avium infection after the initiation of antiretroviral therapy (ART) for acquired immunodeficiency syndrome (AIDS).

METHODS

We histologically investigated five autopsied AIDS patients with systemic M. avium infection.

RESULTS

The inflammatory cell composition in the affected tissues was assessed using immunohistochemistry. The celiac lymph nodes and intestinal canal were the most commonly involved organs in the AIDS cases. The most common histological feature was unstructured aggregation of histiocytes. Immunohistochemistry revealed depression of CD4(+), CD8(+) and CD57(+) cells in the gut lamina propria and mesenteric lymph nodes.

CONCLUSION

These findings suggest that local cell-mediated immunity is depressed in affected tissues and that the primary histological feature is poor organization of granulomas in mycobacterial lesions, despite the administration of adequate ART.

Cholera- and anthrax-like toxins are among several new ADP-ribosyltransferases

Chelt, a cholera-like toxin from Vibrio cholerae, and Certhrax, an anthrax-like toxin from Bacillus cereus, are among six new bacterial protein toxins we identified and characterized using in silico and cell-based techniques. We also uncovered medically relevant toxins from Mycobacterium avium and Enterococcus faecalis. We found agriculturally relevant toxins in Photorhabdus luminescens and Vibrio splendidus. These toxins belong to the ADP-ribosyltransferase family that has conserved structure despite low sequence identity. Therefore, our search for new toxins combined fold recognition with rules for filtering sequences--including a primary sequence pattern--to reduce reliance on sequence identity and identify toxins using structure. We used computers to build models and analyzed each new toxin to understand features including: structure, secretion, cell entry, activation, NAD+ substrate binding, intracellular target binding and the reaction mechanism. We confirmed activity using a yeast growth test. In this era where an expanding protein structure library complements abundant protein sequence data--and we need high-throughput validation--our approach provides insight into the newest toxin ADP-ribosyltransferases.

Non-tuberculous mycobacteria in the sputum of HIV-infected patients: infection or colonization?

It can be difficult to establish the clinical significance of the isolation of non-tuberculous mycobacteria (NTM) from the sputum of HIV-infected patients. In this observational study, we have investigated factors associated with having NTM infection. During the period of the study, 10 patients had NTM infection and 14 had NTM colonization. Factors associated with having NTM infections were: CD4 lymphocyte count <50 cells/mL (odds ratio [OR] 10; 95% confidence interval [CI] 1.4-69.3), haemoglobin <11 g/dL (OR 7.2; 95% CI 1.08-47.9), weight loss (OR 9; 95% CI 1.3-63.9), duration of symptoms for more than a month (OR 54; 95% CI 4.2-692.5), the presence of acid fast bacilli (AFB) in sputum (OR 30.3; 95% CI 2.6-348.9) and repeated positive NTM cultures in other sputum samples (OR 4.3; 95% CI 1.6-11.7). In conclusion, we must suspect NTM infection in patients with long-standing symptoms, anaemia, low CD4 lymphocyte count, several positive sputum cultures and when AFB are seen.

Mycobacterium avium glycopeptidolipids require specific acetylation and methylation patterns for signaling through toll-like receptor 2

Toll-like receptors (TLRs) recognize pathogen-associated molecules and play a vital role in promoting an immune response against invading microbes. TLR2, one of the key members of the TLR family, recognizes a wide variety of microbial products, including lipoproteins and lipopeptides, from a number of pathogens. Recent studies from our laboratory indicate that glycopeptidolipids (GPLs), a major surface component of Mycobacterium avium and other non-tuberculosis mycobacteria, are ligands for TLR2. However, the molecular requirements necessary for the GPL-TLR2 interaction were not defined in this report. In the present study we isolated different GPL species from M. avium, and using mass spectrometry and NMR analyses, characterized the molecular requirements of the GPL-TLR2 interaction. Interestingly, the extent of the respective acetylation and methylation of the 6-deoxytalose and rhamnose contained within the core GPL structure dictated whether the GPL signaled through TLR2. These experiments illustrate how subtle changes in a complex TLR2 ligand can alter its affinity for this important receptor, and suggest that M. avium could potentially modify its GPL structure to limit its interaction with TLR2.

The mycobacterial glycopeptidolipids: structure, function, and their role in pathogenesis

Glycopeptidolipids (GPLs) are a class of glycolipids produced by several nontuberculosis-causing members of the Mycobacterium genus including pathogenic and nonpathogenic species. GPLs are expressed in different forms with production of highly antigenic, typeable serovar-specific GPLs in members of the Mycobacterium avium complex (MAC). M. avium and M. intracellulare, which comprise this complex, are slow-growing mycobacteria noted for producing disseminated infections in AIDS patients and pulmonary infections in non-AIDS patients. Previous studies have defined the gene cluster responsible for GPL biosynthesis and more recent work has characterized the function of the individual genes. Current research has also focused on the GPL's role in colony morphology, sliding motility, biofilm formation, immune modulation and virulence. These topics, along with new information on the enzymes involved in GPL biosynthesis, are the subject of this review.

Spontaneous perforation of the terminal ileum in an AIDS patient on highly active antiretroviral therapy with disseminated non-tuberculous mycobacterial infection

BACKGROUND

Despite the impact of highly active antiretroviral therapy (HAART), mycobacterial infections in patients with AIDS remain a frequent complication. In disseminated cases, both tuberculous and non-tuberculous mycobacterial infections may involve the gastrointestinal system and cause abdominal pain and diarrhea. While there have been cases of small bowel perforation in AIDS patients with Mycobacterium tuberculosis (MTB) infection, no case of bowel perforation in non-tuberculous mycobacterial (NTM) infection has been reported to date.

CASE REPORT

We report a case of spontaneous perforation of the terminal ileum in an AIDS patient with disseminated non-tuberculous mycobacterial infection who was responding to HAART.

CONCLUSIONS

Non-tuberculous mycobacteria can lead to spontaneous bowel perforation in patients with AIDS who are responding to HAART.

Exosomes released from infected macrophages contain Mycobacterium avium glycopeptidolipids and are proinflammatory

Mycobacterium avium is a major opportunistic pathogen in HIV-positive individuals and is responsible for increased morbidity and mortality in AIDS patients. M. avium express glycopeptidolipids (GPLs) as a major cell wall constituent, and recent studies suggest that GPLs play an important role in M. avium pathogenesis. In the present study we show that M. avium-infected macrophages release GPLs, which are trafficked from the phagosome through the endocytic network to multivesicular bodies. Prior studies have shown that multivesicular bodies can fuse with the plasma membrane releasing small 50 to 100 nm vesicles known as exosomes. We found that M. avium-infected macrophages release exosomes containing GPLs leading to the transfer of GPLs from infected to uninfected macrophages. Interestingly, exosomes isolated from M. avium-infected but not from uninfected macrophages can stimulate a proinflammatory response in resting macrophages. This proinflammatory response is dependent on Toll like receptor (TLR) 2, TLR4, and MyD88 suggesting that released exosomes contain M. avium-expressed TLR ligands. Our studies are the first to demonstrate that exosomes isolated from mycobacteria-infected macrophages can induce a proinflammatory response, and we hypothesize that exosomes play an important role in immune surveillance during intracellular bacteria infections.

Palatial erosion caused by Mycobacterium Avium complex in a human immunodeficiency virus infected child

Oral manifestations of Mycobacterium Avium complex (MAC) are rare and have only been described in adults. Here we report a 10-year-old female with advanced human immunodeficiency virus infection, who presented with disseminated MAC and an erosive left palate defect.

The morphological spectrum of lymphadenopathy in HIV infected patients

AIMS

To study the histological spectrum of lymphadenopathy in human immunodeficiency virus (HIV) infected Thai patients.

METHODS

Lymph nodes from 55 HIV infected patients were accessioned over a 19 month period in two pathology laboratories in Bangkok, Thailand. These were examined with H&E, Ziehl-Neelsen, periodic acid-Schiff (PAS), PAS with diastase (PAS/D), Gram and methenamine stains.

RESULTS

Six reaction patterns were observed: (1) classic necrotising granulomas (30 cases); (2) extensive necrosis with minimal granulomatous response (5 cases); (3) sarcoid-like non-necrotising granulomas (5 cases); (4) foamy macrophage or pseudo-Gaucher cell response (5 cases); (5) inflammatory pseudotumour-like proliferation (3 cases); and (6) non-specific lymphoid hyperplasia (7 cases). Myriads of intracellular, long, slender acid-fast bacilli were found in those cases with the pseudo-Gaucher cell and inflammatory pseudotumour-like response, while variable numbers of bacilli were identified in those cases with non-necrotising sarcoid-like granulomas. Few scattered acid-fast bacilli were found in five cases with necrotising granulomas. In one case, yeast-like organisms in keeping with Cryptococcus were identified. No organisms were identified in the cases showing lymphoid hyperplasia, extensive necrosis and minimal granulomatous response, and in the remaining cases of classic necrotising granulomas.

CONCLUSIONS

The wide spectrum of histological changes in HIV-associated lymphadenomegaly requires recognition, particularly as the majority were associated with acid-fast organisms, mostly in keeping with the morphological features of Mycobacterium avium-M. intracellulare complex that was distinctively stained by Grocott methenamine-silver, Gram and PAS stains. The histological changes mimic those of infarction and other infective lymphadenitis, sarcoidosis, Whipple's disease, inflammatory pseudotumour and spindle cell neoplasms.

Elevated mitogen-activated protein kinase signalling and increased macrophage activation in cells infected with a glycopeptidolipid-deficient Mycobacterium avium

Mycobacterium avium is a significant cause of morbidity and mortality in AIDS patients. M. avium can be isolated as three major morphotypes: smooth-transparent (SmT ), smooth-opaque (SmO) and rough (Rg). Studies indicate that many Rg isolates lack or have modified glycopeptidolipids (GPLs). GPLs are major surface constituents of the M. avium cell wall and heterogeneity in their carbohydrate moieties has been used to classify M. avium into different serotypes, with serotypes 1, 4 and 8 being isolated with high frequency from AIDS patients. However, it is unclear what role GPLs play in M. avium pathogenicity. To begin to address how the absence of GPLs affects M. avium-macrophage interaction, we used the well-characterized M. avium 2151 SmT and Rg isolates which differ in GPL expression. We found macrophages infected with the Rg compared with SmT M. avium 2151 showed prolonged activation of the mitogen-activated protein kinases (MAPKs) p38 and ERK1/2. Macrophages infected with the Rg 2151 also showed increased tumour necrosis factor-alpha (TNF-alpha) production. Interestingly, TNF-alpha secretion by macrophages infected with SmO or SmT 2151 was dependent on p38, ERK1/2 and NF-kappaB while TNF-alpha secretion by Rg 2151-infected macrophages was dependent on NF-kappaB but not the MAPKs. Rg 2151-infected macrophages also produced increased levels of IL-6, IL-12, MCP-1 and RANTES relative to macrophages infected with SmT 2151. These results indicate that M. avium 2151 deficient in GPLs promote increased macrophage activation. This disparity in cellular activation stems from a quantitative and qualitative difference in the macrophage signalling response to the Rg and SmT M. avium 2151.

Nontuberculous mycobacterial infections in pediatric hematopoietic stem cell transplant recipients: case report and review of the literature

Nontuberculous mycobacterial (NTM) infections are rarely diagnosed in hematopoietic stem cell transplant (HSCT) recipients. We describe a case of disseminated Mycobacterium avium complex with gastrointestinal tract involvement in a HSCT recipient. We reviewed NTM infections among pediatric HSCT patients at our institution from 2000-2004 and identified 2 additional cases. Fourteen published case reports of NTM disease in children are reviewed.

Disseminated Mycobacterium avium infection in young cats: overrepresentation of Abyssinian cats

Disseminated Mycobacterium avium-intracellulare complex (MAC) infection was diagnosed in 10 young cats (1-5 years of age) from Australia or North America between 1995 and 2004. A further two cats with disseminated mycobacteriosis (precise agent not identified) were recognised during this period. Of the 12, 10 were Abyssinian cats, one was a Somali cat and one was a domestic shorthair cat. None of the cats tested positive for either FeLV antigen or FIV antibody. The clinical course of these infections was indolent, with cats typically presenting for weight loss, initially in the face of polyphagia, with a chronicity of up to several months. Additional clinical features included lower respiratory tract signs and peripheral lymphadenomegaly. A marked diffuse interstitial pattern was evident in thoracic radiographs, even in cats without overt respiratory involvement. Hair clipped to perform diagnostic procedures tended to regrow slowly, if at all. Diagnosis was generally made by obtaining representative tissue specimens from mesenteric lymph nodes, liver or kidney at laparotomy, or from a popliteal lymph node. The primary antecedent event was most likely colonisation of either the alimentary or respiratory tract, followed by local invasion and eventual lymphatic and haematogenous dissemination. Nine cases were treated using combination therapy with agents effective for MAC infection in human patients. Two cats are still undergoing initial therapy and have responded. Of the remaining seven, all responded during long courses (5-14 months) of clarithromycin combined with either clofazimine or rifampicin, and a fluoroquinolone or doxycycline. Of these, three cats remain well (with durations between 2 months and 2 years following therapy); two developed recurrent disease (at 3 months and 2 years, respectively, following therapy) and have restarted therapy. The remaining two cats improved 1 year and 5 months, respectively, after diagnosis but ultimately succumbed. The two cats in which therapy was restarted have improved dramatically. Certain lines of Abyssinian and Somali cats likely suffer from a familial immunodeficiency that predisposes them to infection with slow-growing mycobacteria such as MAC.