Mycobacterium haemophilum: an emerging pathogen

Disseminated non-tuberculous mycobacterial infection caused by Mycobacterium obuense in an immunocompromised patient: a case report

BACKGROUND

Mycobacterium obuense (M. obuense) is a rapidly growing mycobacterium (RGM) which has been considered nonpathogenic. Here, we report a case of disseminated non-tuberculous mycobacterial (NTM) infection caused by M. obuense in an immunocompromised patient.

CASE PRESENTATION

A 16-year-old boy was referred to our hospital due to acute myeloid leukemia. During the treatment of leukemia, the patient exhibited continuous fever, and diffuse miliary nodules with random distribution were found on chest computed tomography. Repeated examinations of bacterial culture tests revealed sputum and urine samples to be smear-positive for acid-fast bacillus, and blood culture from a peripherally inserted central catheter line showed the growth of NTM. The NTM species was identified as M. obuense by mass spectrometry and confirmed by genome sequencing. Combination therapy with amikacin, rifampicin, azithromycin, and moxifloxacin significantly improved the patient's symptoms and radiological findings.

CONCLUSION

We report a case of disseminated NTM infection caused by M. obuense for which combination anti-microbial therapy was effective. An immunocompromised host indwelling catheter is at risk of RGM bloodstream infections. Although relatively rare, M. obuense may be considered as a potential pathogen causing infectious diseases, especially in high-risk patients.

The Complete Genome Sequence of the Emerging Pathogen Mycobacterium haemophilum Explains Its Unique Culture Requirements

Mycobacterium haemophilum is an emerging pathogen associated with a variety of clinical syndromes, most commonly skin infections in immunocompromised individuals. M. haemophilum exhibits a unique requirement for iron supplementation to support its growth in culture, but the basis for this property and how it may shape pathogenesis is unclear. Using a combination of Illumina, PacBio, and Sanger sequencing, the complete genome sequence of M. haemophilum was determined. Guided by this sequence, experiments were performed to define the basis for the unique growth requirements of M. haemophilum. We found that M. haemophilum, unlike many other mycobacteria, is unable to synthesize iron-binding siderophores known as mycobactins or to utilize ferri-mycobactins to support growth. These differences correlate with the absence of genes associated with mycobactin synthesis, secretion, and uptake. In agreement with the ability of heme to promote growth, we identified genes encoding heme uptake machinery. Consistent with its propensity to infect the skin, we show at the whole-genome level the genetic closeness of M. haemophilum with Mycobacterium leprae, an organism which cannot be cultivated in vitro, and we identify genes uniquely shared by these organisms. Finally, we identify means to express foreign genes in M. haemophilum. These data explain the unique culture requirements for this important pathogen, provide a foundation upon which the genome sequence can be exploited to improve diagnostics and therapeutics, and suggest use of M. haemophilum as a tool to elucidate functions of genes shared with M. leprae.

IMPORTANCE

Mycobacterium haemophilum is an emerging pathogen with an unknown natural reservoir that exhibits unique requirements for iron supplementation to grow in vitro. Understanding the basis for this iron requirement is important because it is fundamental to isolation of the organism from clinical samples and environmental sources. Defining the molecular basis for M. haemophilium's growth requirements will also shed new light on mycobacterial strategies to acquire iron and can be exploited to define how differences in such strategies influence pathogenesis. Here, through a combination of sequencing and experimental approaches, we explain the basis for the iron requirement. We further demonstrate the genetic closeness of M. haemophilum and Mycobacterium leprae, the causative agent of leprosy which cannot be cultured in vitro, and we demonstrate methods to genetically manipulate M. haemophilum. These findings pave the way for the use of M. haemophilum as a model to elucidate functions of genes shared with M. leprae.

General Overview on Nontuberculous Mycobacteria, Biofilms, and Human Infection

Nontuberculous mycobacteria (NTM) are emergent pathogens whose importance in human health has been growing. After being regarded mainly as etiological agents of opportunist infections in HIV patients, they have also been recognized as etiological agents of several infections on immune-competent individuals and healthcare-associated infections. The environmental nature of NTM and their ability to assemble biofilms on different surfaces play a key role in their pathogenesis. Here, we review the clinical manifestations attributed to NTM giving particular importance to the role played by biofilm assembly.

Disseminated Mycobacterium haemophilum infection in an ASSAM trinket snake (Elaphe frenata)

A sub-adult male Assam trinket snake (Elaphe frenata) that was confiscated from an exotic animal dealer was found dead in its enclosure after a 17-mo quarantine. The snake had grown well during that period and had no physical examination or bloodwork abnormalities during the quarantine. On gross necropsy, masses were found in the epaxial musculature and stomach, the lung was diffusely thickened, the ventricular wall was mottled, and there was intracoelomic and pericardial effusion. Histopathology revealed diffusely disseminated granulomatous infiltrates throughout the lung interstitium and multifocal granulomatous infiltrates in the transmural gastric mass, within the myocardium and pericardial adipose tissue, in the liver and kidney parenchyma, in the cervical region surrounding the trachea and thyroid, and replacing the myofibers of the craniolateral epaxial muscles. Fite-Farracho acid-fast staining revealed numerous intracytoplasmic acid-fast bacilli within macrophages, and polymerase chain reaction testing on frozen tissues followed by nucleic acid sequencing of polymerase chain reaction amplicons identified Mycobacterium haemophilum.

Clinical manifestations, diagnosis, and treatment of Mycobacterium haemophilum infections

Mycobacterium haemophilum is a slowly growing acid-fast bacillus (AFB) belonging to the group of nontuberculous mycobacteria (NTM) frequently found in environmental habitats, which can colonize and occasionally infect humans and animals. Several findings suggest that water reservoirs are a likely source of M. haemophilum infections. M. haemophilum causes mainly ulcerating skin infections and arthritis in persons who are severely immunocompromised. Disseminated and pulmonary infections occasionally occur. The second at-risk group is otherwise healthy children, who typically develop cervical and perihilar lymphadenitis. A full diagnostic regimen for the optimal detection of M. haemophilum includes acid-fast staining, culturing at two temperatures with iron-supplemented media, and molecular detection. The most preferable molecular assay is a real-time PCR targeting an M. haemophilum-specific internal transcribed spacer (ITS), but another approach is the application of a generic PCR for a mycobacterium-specific fragment with subsequent sequencing to identify M. haemophilum. No standard treatment guidelines are available, but published literature agrees that immunocompromised patients should be treated with multiple antibiotics, tailored to the disease presentation and underlying degree of immune suppression. The outcome of M. haemophilum cervicofacial lymphadenitis in immunocompetent patients favors surgical intervention rather than antibiotic treatment.

Atypical focal osteomyelitis as initial manifestation of AIDS

Persistent pain development after a skeletal contusion rarely poses the diagnosis of osteomyelitis. We report the case of a fibular head contusion as an initial manifestation of a focal abscess development in a healthy young patient. The traditional treatment of surgical drainage revealed the presence of an atypical Mycobacterium haemophilum isolates in the abscess. This lead to further investigations that concluded and established the diagnosis of AIDS. Conclusion. Isolation of an atypical Mycobacterium haemophilum in any abscess should lead the physician to accomplish further investigations and look for AIDS even in young healthy subjects.

The diagnosis of two cases of cutaneous ulcer caused by infection with Mycobacterium haemophilum: direct identification in a clinical sample by polymerase chain reaction-restriction endonuclease analysis

BACKGROUND

Mycobacterium haemophilum was first recovered from subcutaneous lesions of a patient with Hodgkin's disease. Because of its special growth requirements (it grows at 30-32 degrees C and requires iron-supplemented medium), the organism cannot be isolated using routine culture techniques for other mycobacteria. Only a few developed countries have reported infection with this mycobacterium. We report the first two cases diagnosed in Venezuela.

METHODS

The diagnosis of the first case was established using polymerase chain reaction (PCR)-restriction endonuclease analysis of the gene encoding the 65-kDa heat shock protein (hsp65) for the direct identification of M. haemophilum in a clinical specimen in which bacilli were observed on acid-fast smear, but growth was not detected by standard culture procedures.

RESULTS

After recognizing this bacterium as a possible cause of infection in our setting, clinical samples of cutaneous lesions were routinely cultured on blood agar at 30 degrees C for at least 6 weeks, which resulted in the diagnosis of the second case.

CONCLUSIONS

Dermatologists should consider this bacterium in immunocompromised patients with cutaneous ulcerating lesions. Material from the lesions can be screened for mycobacteria using an acid-fast stain and, if acid-fast bacilli are seen, PCR analysis of mycobacterial hsp65 can be an effective tool for early diagnosis. Appropriate culture methods are required for bacteriologic confirmation of infection with M. haemophilum.

Spinal intradural Mycobacterium haemophilum granuloma in an American Bison (Bison bison)

Mycobacterium haemophilum, a nontuberculous mycobacterium, is a pathogen in immunocompromised human patients. We report a case of M haemophilum-induced granuloma in the spinal cord of an American Bison (Bison bison). M haemophilum infection was diagnosed by sequencing a portion of the 16 S ribosomal DNA and comparing the amplicon sequence with sequences in GenBank.

Mycobacterium haemophilum osteomyelitis: case report and review of the literature

Background

Mycobacterium haemophilum is a slow-growing, fastidious, iron-requiring microorganism that, relative to other non-tuberculous mycobacterial species, has rarely been documented as a cause of human infection. This microorganism appears to be acquired via environmental exposure although its natural habitat and mode of acquisition are unknown. It has primarily been implicated as a cause of ulcerating cutaneous or subcutaneous nodular skin lesions, particularly in immunocompromised patients, although infections at extracutaneous sites have also been described. Osteomyelitis, while rarely documented, appears to be an important complication of infection with M. haemophilum in these patients.

Case presentation

We describe a unique case of culture-confirmed M. haemophilum osteomyelitis in an adult woman with polycythemia vera and review the world literature on bone infections due to this organism.

Conclusion

Mycobacterium haemophilum is an important but infrequently encountered cause of osteomyelitis in immunocompromised patients, often requiring months to years of medical therapy, with or without surgery, to effect a clinical cure.

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.

Cervicofacial Lymphadenitis in Children Caused by Mycobacterium haemophilum

BACKGROUND

Nontuberculous mycobacterial (NTM) lymphadenitis in children is most often caused by Mycobacterium avium. In a prospective, multicenter trial of the optimal treatment, 23.7% of the NTM cervicofacial lymphadenitis cases in children were caused by Mycobacterium haemophilum. In this article, we describe the epidemiological and clinical features of M. haemophilum cervicofacial lymphadenitis.

METHODS

The diagnosis of Mycobacterium avium or M. haemophilum infection was established by culture or polymerase chain reaction. Demographic characteristics and data regarding clinical presentation and possible environmental exposure were compared for patients infected with M. avium and those infected with M. haemophilum.

RESULTS

Ninety-four (69.9%) of 135 infections were caused by M. avium, 32 (23.7%) by M. haemophilum, and 9 (6.4%) by other NTM species. The median age of the M. haemophilum-infected children was 72 months, compared with 41 months for the M. avium-infected children (P < .001), with an equal distribution for both sexes. Involvement of multiple lymph nodes was frequently observed among the M. haemophilum-infected patients (56% of patients). Extranodal localizations were only observed in M. haemophilum-infected patients. Children with M. haemophilum infection were more likely to have a non-Dutch background (P = .001), and in most cases, they had a history of contact with swimming water (P = .03), whereas M. avium-infected patients were more likely to have a history of playing in sandpits (P = .01). In a multivariate analysis, only older age and a non-Dutch background were predisposing risk factors for M. haemophilum infection, compared with M. avium infection.

CONCLUSION

Higher age, non-Dutch background, and involvement of multiple cervicofacial lymph nodes with extranodal localizations distinguished M. haemophilum infection from M. avium infection.

Disseminated Mycobacterium haemophilum infection as initial manifestation of AIDS

Mycobacterium haemophilum has rarely been implicated in human disease. The organisms have been isolated mainly in patients with human immunodeficiency virus (HIV) disease or transplant recipients. We describe the first case of a disseminated M. haemophilum infection as initial manifestation of AIDS in Europe.

Direct identification of Mycobacterium haemophilum in skin lesions of immunocompromised patients by PCR-restriction endonuclease analysis

PCR-restriction endonuclease analysis (PRA) was used for direct identification of Mycobacterium haemophilum in clinical specimens from immunocompromised patients. PRA correctly identified M. haemophilum in four smear-positive specimens. Direct identification by PRA takes 2 to 3 working days compared to the 3 to 5 weeks required for culture isolation and identification by conventional methods.

Mycobacteriosis in zebrafish (Danio rerio) research facilities

The Zebrafish International Resource Center was established to support the zebrafish research community, and includes a diagnostic service. One of the most common diseases that we have diagnosed is mycobacteriosis, which represented 18% of the diagnostic cases submitted from November 1999 to June 2003. We describe here the severity of the disease and associated pathological changes of 24 diagnostic cases from 14 laboratories. Identifications of the bacteria are provided for seven of these cases. For two cases in which culture of the organism was not successful, these identifications were based on ribosomal DNA (rDNA) sequence analysis obtained directly from infected tissues. Biochemical characteristics and rDNA sequence analysis from cultures are reported for the other isolates. Two severe outbreaks from different facilities on different continents were associated with an organism identified as Mycobacterium haemophilum based on rDNA sequence from tissues. Another severe outbreak was associated with an organism most closely related to Mycobacterium peregrinum. These species are recognized pathogens of humans, but this is the first report of them from fish. Bacteria identified as Mycobacterium chelonae or M. abscessus were recovered from fish in cases categorized as moderate disease or as an incidental finding. These findings indicate that species of Mycobacterium previously undescribed from fish (i.e., M. haemophilum and M. peregrinum) may pose significant health problems in zebrafish research facilities, whereas species and strains that are already recognized as common in fish usually cause limited disease on a population basis in zebrafish.

Mycobacterium haemophilum infection in an SLE patient on mycophenolate mofetil

We describe a case of Mycobacterium haemophilum in an immunocompromised patient with systemic lupus erythematosus (SLE). Mycobacterium haemophilum is a recently described pathogen which has not been previously described either in SLE patients or patients on Mycophenolate Mofetil. Mycobacterium haemophilum can be difficult to diagnose, as it may not have the granulomas characteristic of atypical mycobacterial infections. Combination therapy with at least two drugs for several months is required and the outcome depends on the patient's underlying immunocompromised state. Our report highlights the need for early diagnosis and treatment of Mycobacterium haemophilum in immunocompromised patients with SLE.

Mycobacterium haemophilum infections in heart transplant recipients: case report and review of the literature

Non-tuberculous mycobacteria are becoming increasingly important pathogens among transplant recipients. We report a case of disseminated Mycobacterium haemophilum infection in a heart transplant recipient, manifesting as cellulitis, subcutaneous nodules, septic arthritis, and pneumonitis. Our case illustrates diverse challenges in the identification and treatment of this pathogen, such as its unique culture requirements and variable antimicrobial susceptibilities. Heightened clinical suspicion is necessary to establish a timely diagnosis so that optimal treatment can be administered.

The cutaneous manifestations of HIV infection

Dermatologic disease is extremely common and varied in HIV-infected patients. While some cutaneous findings are nearly exclusive to HIV-seropositive individuals, many are found in the general population. However, HIV-infected individuals often have an increased prevalence or severity, atypical presentations, or difficulty with treatment of the disease. Immune reconstitution with HAART significantly reduces the prevalence of many dermatologic diseases, but also has associated cutaneous side effects. Correct and early diagnosis of skin disease in HIV-infected individuals allows for early management and improved quality of life. Because dermatologic manifestations may be the first clue of HIV infection, offering HIV testing to affected individuals can lead to early diagnosis and treatment of HIV infection and, ideally, a decrease in disease progression and transmission.

Newly described or emerging human species of nontuberculous mycobacteria

The advent of molecular testing in the laboratory has brought about the recognition of multiple newly characterized mycobacterial species not previously recognizable with most standard techniques. Some of the species are nonpathogenic, but the majority may cause clinical disease. Each is likely to have its own biology, drug susceptibility pattern, and response to drug/surgical therapy. Thus, it is important to try to recognize these new species in the laboratory. A study of the phenotypic and genotypic characteristics of these new species also may help to elucidate the epidemiology and pathogenesis of these organisms. In addition, there are multiple emerging species of nontuberculous mycobacteria including M. ulcerans, M. haemophilum, M. xenopi, and M. malmoense. [table: see text] These species are being recognized increasingly as a cause of human disease and recovered within the laboratory. The clinician must learn about these new pathogens to recognize them clinically and assist the laboratory in their recovery.

Mycobacterium haemophilum infection in a Japanese patient with AIDS

Mycobacterium haemophilum has been described as a pathogen that causes cutaneous lesions in immunocompromised patients. A specimen from a skin ulcer on the leg of a Japanese patient with acquired immunodeficiency syndrome yielded acid-fast bacilli on blood agar plates after 4 weeks of incubation at 30 degrees C, but the organism was not found on Ogawa egg slants. The organism was identified as M. haemophilum, on the basis of 16S rRNA gene sequence analysis. Prolonged culture in an optimal environment that includes an iron supplement, and growth temperatures at 28 degrees to 33 degrees C are necessary to grow M. haemophilum. Genotypic characterization of 16S rRNA is useful for a rapid diagnosis of this slowly growing mycobacterium.

Mycobacterium haemophilum in immunocompromised patients

Mycobacterium haemophilum, a recently described pathogen, can cause an array of symptoms in immunocompromised patients. To date, 90 patients with this infection have been described worldwide. We report our institution's experience with 23 patients who were treated from 1990 through 2000. Fourteen patients had undergone bone marrow transplantation, 5 were infected with human immunodeficiency virus, 3 had hematologic malignancies, and 1 had no known underlying immunosuppression. Clinical syndromes on presentation included skin lesions alone in 13 patients, arthritis or osteomyelitis in 4 patients, and lung disease in 6 patients. Although patients with skin or joint involvement had favorable outcomes, 5 of 7 patients with lung infection died. Prolonged courses of multidrug therapy are required for treatment. A diagnosis of M. haemophilum infection must be considered for any immunocompromised patient for whom acid-fast bacilli are identified in a cutaneous, synovial fluid or respiratory sample or for whom granulomas are identified in any pathological specimen.

Dermatologic infections in the immunocompromised (non-HIV) host

The immunocompromised host's susceptibility to infections often present a difficult diagnostic challenge to the physician. A working knowledge of the host immune defenses and microbiologic complications that can occur when these functions are compromised provides a more focused framework for further evaluation and management. Infections in these patients are often morbid and life-threatening, creating an urgent need for prompt diagnosis. The skin may manifest the first clue(s) of a serious underlying infection. Appropriate workup and diagnosis of cutaneous lesions provide an expeditious, noninvasive, and potentially life-saving approach to the immunocompromised host with a dermatologic infection.

An annular plaque due to Mycobacterium haemophilum infection in a patient with AIDS

Infections with mycobacteria are of importance in the differential diagnosis of skin lesions in immunocompromised patients. We report the case of a human immunodeficency virus (HIV)-infected patient who presented with an annular plaque as cutaneous manifestation of Mycobacterium haemophilum. Improvement of the immunologic status is important for successful treatment. Complete resolution was only observed when the antimycobacterial therapy was combined with antiretroviral therapy.

Nontuberculous mycobacterial infections of the skin

Nontuberculous mycobacteria are playing an increasingly important role in human disease owing to higher prevalence of antibiotic resistance and immunodeficiency. These organisms cause a variety of cutaneous findings which are often misdiagnosed by the clinician. Compounding this problem is the fact that most mycobacteria require special culture conditions, which if not specifically requested, are frequently not used. Recognition of susceptible patients is imperative and is not limited to the immunocompromised. Successful treatment of mycobacterial infections requires knowledge of currently available and recommended antibiotics followed by tailoring of the antimicrobial regimen after sensitivity testing is performed.

Optimal detection and identification of Mycobacterium haemophilum in specimens from pediatric patients with cervical lymphadenopathy

Acid-fast bacilli from pediatric patients with lymphadenopathy were detected in the BACTEC radiometric system and in MB Redox broth, but not on Löwenstein Jensen medium. PCR amplification identified the isolates as Mycobacterium haemophilum, which has special nutrition requirements (iron supplements) for growth. Suitable culture medium ensures optimal recovery of this microorganism, avoiding underdiagnosis.

Emergence of a unique group of necrotizing mycobacterial diseases

Although most diseases due to pathogenic mycobacteria are caused by Mycobacterium tuberculosis, several other mycobacterial diseases-caused by M. ulcerans (Buruli ulcer), M. marinum, and M. haemophilum-have begun to emerge. We review the emergence of diseases caused by these three pathogens in the United States and around the world in the last decade. We examine the pathophysiologic similarities of the diseases (all three cause necrotizing skin lesions) and common reservoirs of infection (stagnant or slow-flowing water). Examination of the histologic and pathogenic characteristics of these mycobacteria suggests differences in the modes of transmission and pathogenesis, though no singular mechanism for either characteristic has been definitively described for any of these mycobacteria.

In vitro susceptibility of Mycobacterium ulcerans to clarithromycin

Buruli ulcer (BU), caused by Mycobacterium ulcerans, was recently recognized by the World Health Organization as an important emerging disease. While antimycobacterial therapy is often effective for the earliest nodular or ulcerative lesions, medical management of BU lesions in patients presenting for treatment is usually disappointing, leaving wide surgical excision the only alternative. Advanced ulcerated lesions of BU rarely respond to antimycobacterial agents; however, perioperative administration of such drugs may prevent relapses or disseminated infections. Clarithromycin possesses strong activity in vitro and in vivo against most nontuberculous mycobacteria. In this study we determined the antimycobacterial activity of this drug in vitro against 46 strains of M. ulcerans isolated from 11 countries. The MIC of clarithromycin was determined at pH 6.6 (on 7H11 agar) and at pH 7.4 (on Mueller-Hinton agar). The MICs ranged from 0.125 to 2 microg/ml at pH 6.6 and from <0.125 to 0.5 microg/ml at pH 7.4. For the majority of the strains, geographic origin did not play a significant role. Thirty-eight strains (83%) were inhibited by 0.5 microg/ml at pH 7.4. These MICs are below peak therapeutic concentrations of clarithromycin obtainable in blood. These results suggest that clarithromycin is a promising drug both for the treatment of early lesions of M. ulcerans and for the prevention of hematogenous dissemination of the etiologic agent during and after surgery. Studies should be initiated to evaluate the effects of clarithromycin in combination with ethambutol and rifampin on M. ulcerans both in vitro and in experimentally infected mice. Multidrug regimens containing clarithromycin may also help control the secondary bacterial infections sometimes seen in BU patients, most importantly osteomyelitis.

Diagnosis and treatment of disease caused by nontuberculous mycobacteria. This official statement of the American Thoracic Society was approved by the Board of Directors, March 1997. Medical Section of the American Lung Association

Diagnostic criteria of nontuberculous mycobacterial lung disease in HIV-seropositive and -seronegative hosts. The following criteria apply to symptomatic patients with infiltrate, nodular or cavitary disease, or a high resolution computed tomography scan that shows multifocal bronchiectasis and/or multiple small nodules. A. If three sputum/bronchial wash results are available from the previous 12 mo: 1. three positive cultures with negative AFB smear results or 2. two positive cultures and one positive AFB smear B. If only one bronchial wash is available: 1. positive culture with a 2+, 3+, or 4+ AFB smear or 2+, 3+, or 4+ growth on solid media C. If sputum/bronchial wash evaluations are nondiagnostic or another disease cannot be excluded: 1. transbronchial or lung biopsy yielding a NTM or 2. biopsy showing mycobacterial histopathologic features (granulomatous inflammation and/or AFB) and one or more sputums or bronchial washings are positive for an NTM even in low numbers.

COMMENTS

these criteria fit best with M. avium complex, M. abscessus, and M. kansasii. Too little is known of other NTM to be certain how applicable these criteria will be. At least three respiratory samples should be evaluated from each patient. Other reasonable causes for the disease should be excluded. Expert consultation should be sought when diagnostic difficulties are encountered.

Mycobacterial complications of HIV infection

Tuberculosis is the most common opportunistic infection worldwide and is caused by the only readily transmissible pathogen among persons with HIV infection. If treatment is initiated promptly and is supervised appropriately, cure, fortunately, is highly likely. Isoniazid preventive therapy substantially reduces the risk of tuberculosis in persons with HIV infection. Of the nontuberculous mycobacteria, Mycobacterium avium complex (MAC) is the most frequent cause of disease; however, disseminated MAC disease usually is not seen until the CD4+ cell count is less than 50 cells/L. Newer agents, such as the macrolides and rifabutin, form the nucleus of treatment regimens and also are effective in preventing the disease.

Dermatologic complications of HIV infection

Cutaneous disorders occur with great frequency in patients with HIV infection and increase in number and severity as the disease progresses and immune function declines. In addition, the first findings related to HIV infection are often on the skin. Cutaneous infections with herpesviruses may be severe and atypical in their presentations; papillomaviruses and MC are common as well. Bacterial infections may be primary or secondary to other skin diseases; superficial and deep fungal infections are also prevalent. Papulosquamous disorders, including seborrheic dermatitis, psoriasis, and eczema, may be disfiguring and result in secondary complications. Neoplastic disorders, especially Kaposi's sarcoma, demand early diagnosis, to afford the patient maximal treatment options. All physicians must be aware of these cutaneous manifestations to decrease morbidity and improve quality of life in the HIV-infected individual.

Evaluation of an extended blood culture protocol to isolate fastidious organisms from patients with AIDS

Recent reports of fastidious pathogens suggest the need for special blood cultures for immunocompromised patients. Blood cultures from 45 human immunodeficiency virus (HIV)-infected patients with unexplained fever (> or = 38.0 degrees C) and CD4 counts of < 125 cells per mm3 were collected into a vacuum tube with sodium polyanetholsulfonate, an Isolator tube, and BACTEC aerobic and anaerobic bottles. Blood from the sodium polyanethosulfonate tube was inoculated into BACTEC 13A bottles, which were read weekly for 16 weeks. Isolator sediment was divided among eight agar media, including four sheep blood agar media: chocolate agar, brain heart infusion blood agar, heart infusion blood agar, and brucella blood agar. Other agar plates included Sabouraud's, buffered charcoal-yeast extract, Middlebrook 7H11 (M7H11) with hemoglobin, and M7H11 with mycobactin J. Incubation conditions included air and CO2-enriched aerobic, microaerophilic, and anaerobic atmospheres. Aerobic BACTEC broths received an acridine orange stain on day 8 and were subcultured at 2, 4, and 8 weeks. Anaerobic BACTEC bottles were subcultured at 4 weeks. All solid media, including subcultures, were incubated for 8 weeks, providing a total of 16 weeks of incubation for each specimen. Clinically significant isolates included eight Mycobacterium avium complex isolates and one each of Bartonella henselae, Bartonella quintana, Shigella flexneri, Klebsiella oxytoca, and Cryptococcus neoformans. All isolates were detected with commercially available media and, with the exception of Bartonella spp., were recovered within incubation times routinely used in most clinical laboratories.

Mycobacterium haemophilum: microbiology and expanding clinical and geographic spectra of disease in humans

Reports of the association of Mycobacterium haemophilum with disease in humans have greatly increased. At least 64 cases have now been reported, with symptoms ranging from focal lesions to widespread, systemic disease. The organism is now known to cause primarily cutaneous and subcutaneous infection, septic arthritis, osteomyelitis, and pneumonitis in patients who are immunologically compromised and lymphadenitis in apparently immunocompetent children. Underlying conditions in the compromised patients have included AIDS; renal, bone marrow, and cardiac transplantation; lymphoma; rheumatoid arthritis; marrow hypoplasia; and Crohn's disease. Reports have originated from diverse geographic areas worldwide. The epidemiology of M. haemophilum remains poorly defined; there appears to be a genetic diversity between strains isolated from different regions. The organism is probably present in the environment, but recovery by sampling has not been successful. M. haemophilum has several unique traits, including predilection for lower temperatures (30 to 32 degrees C) and requirement for iron supplementation (ferric ammonium citrate or hemin). These may in the past have compromised recovery in the laboratory. Therapy has not been well elucidated, and the outcome appears to be influenced by the patient's underlying immunosuppression. The organisms are most susceptible to ciprofloxacin, clarithromycin, rifabutin, and rifampin. Timely diagnosis and therapy require communication between clinician and the laboratory.

Genetic basis for clarithromycin resistance among isolates of Mycobacterium chelonae and Mycobacterium abscessus

Resistance to clarithromycin among isolates of Mycobacterium chelonae and M. abscessus was observed in 18 of 800 (2.3%) patients tested between 1990 and 1995. Patients whose isolates were resistant had either disseminated disease or chronic lung disease, and the resistant isolates were recovered after clarithromycin monotherapy. Sequencing of the gene coding for the 23S rRNA peptidyltransferase region revealed a point mutation involving adenine at position 2058 (38%) or adenine at position 2059 (62%) in 20 of 20 relapse isolates from the first 13 patients identified. By pulsed-field gel electrophoresis or random amplified polymorphic DNA PCR, initial and relapse isolates were shown to have identical DNA patterns. M. chelonae and M. abscessus isolates were found to have only a single chromosomal copy of the rRNA operon, thus making them susceptible to single-step mutations. Thus, clarithromycin resistance in these species of rapidly growing mycobacteria relates to a point mutation in the gene coding for 23S rRNA and occurs in limited clinical situations, but was identified in almost 5% of isolates tested in 1995.

Nontuberculous mycobacterial infections

OBJECTIVE

To review the epidemiology, clinical manifestations, diagnosis, and treatment of nontuberculous mycobacterial infections other than Mycobacterium avium complex (MAC).

DATA SOURCES

A MEDLINE search of English-language literature pertaining to nontuberculous mycobacteria other than MAC was performed. Additional literature was obtained from reference lists of pertinent articles identified through the search.

STUDY SELECTION AND DATA EXTRACTION

All articles were considered for possible inclusion in the review. Information judged by the author to be pertinent was selected for discussion.

DATA SYNTHESIS

Mycobacterial infections, including those caused by nontuberculous mycobacteria other than MAC, have assumed greater importance over the past decade, due in part to the changing spectrum of immunosuppression as manifested by organ transplantation and HIV infection. Many pathogenic nontuberculous mycobacteria have been identified that are associated with a wide variety of localized, organ-specific, and systemic infections. Of concern, these organisms exhibit variable, species-specific susceptibility to traditional antimycobacterial drugs and other antimicrobials. In addition, long treatment courses and adjunctive surgical therapy are often required to effect cure. Important antimicrobials for the management of these infections include cefoxitin, imipenem/cilastatin, aminoglycosides (other than streptomycin), tetracyclines, macrolides, and trimethoprim/sulfamethoxazole, as well as traditional antimycobacterials.

CONCLUSIONS

Nontuberculous mycobacteria have assumed an increasing role in disease etiology in both nonimmunocompromised and immunocompromised individuals. Advent of rapid diagnostic techniques and susceptibility testing has allowed the clinician to identify these organisms and initiate effective treatment on a more timely basis with an improved chance for cure. Few therapeutic agents are available for treatment of these infections, many of which are not considered classic antimycobacterials.

Intracellular growth and cytotoxicity of Mycobacterium haemophilum in a human epithelial cell line (Hec-1-B)

We developed an in vitro model to study the temperature-regulated cytotoxicity and intracellular growth of Mycobacterium haemophilum in cultured human epithelial and endothelial cells. M. haemophilum associated with human epithelial and endothelial cells at similar rates when incubated at 33 and 37 degrees C, but only the epithelial cell line supported the multiplication of this organism. M. haemophilum grew equally well with epithelial cells at both temperatures. The aminoglycoside antibiotic amikacin was used to study the intracellular growth of M. haemophilum in the epithelial cells at 33 and 37 degrees C. Although an approximately equal number of bacteria were found within cells after 2 days of incubation at both temperatures, intracellular replication of M. haemophilum was 1,000-fold greater at 33 than at 37 degrees C. This intracellular multiplication was associated with destruction of the monolayers at 33 but not at 37 degrees C, and only culture filtrates from infected monolayers incubated at 33 degrees C were cytotoxic to fresh epithelial cell monolayers. This strain of M. haemophilum also produced contact-dependent hemolysis of sheep erythrocytes, demonstrating the possible presence of a cytolysin. These studies suggest that M. haemophilum has a preference for growth with cultured human epithelial cells. In addition, intracellular growth is best at 33 degrees C in epithelial cells, and this correlated with cytotoxicity at this temperature. This phenotype may be caused by induction of a soluble cytotoxic component, possibly a hemolytic cytolysin.

Mycobacterial taxonomy

The minimal standards for including a species in the genus Mycobacterium are i) acid-alcohol fastness, ii) the presence of mycolic acids containing 60-90 carbon atoms which are cleaved to C22 to C26 fatty acid methyl esters by pyrolysis, and iii) a guanine + cytosine content of the DNA of 61 to 71 mol %. Currently, there are 71 recognized or proposed species of Mycobacterium which can be divided into two main groups based on growth rate. The slowly growing species require > 7 days to form visible colonies on solid media while the rapidly growing species require < 7 days. Slowly growing species are often pathogenic for humans or animals while rapidly growing species are usually considered nonpathogenic for humans, although important exceptions exist. The taxonomic and diagnostic characteristics of medically important species and of newly described species of the Mycobacterium genus are reviewed.