Mycobacterial bacteraemia in patients infected and not infected with human immunodeficiency virus, Taiwan

Mycobacterium tuberculosis bacteremia in a human immunodeficiency virus-negative patient with liver cirrhosis: A case report

BACKGROUND

With the increasing prevalence of human immunodeficiency virus (HIV), the incidence of Mycobacterium tuberculosis (M. tuberculosis) bacteremia has also increased. As a common affliction of acquired immunodeficiency syndrome patients, M. tuberculosis infection is associated in these patients with severe sepsis and high mortality. In contrast, M. tuberculosis bacteremia is rarely seen in HIV-negative patients, and M. tuberculosis has never been reported from the blood of patients with liver cirrhosis.

CASE SUMMARY

We evaluated a 55-year-old Chinese male patient who had been admitted to the hospital with abdominal distension of unknown cause of one-week duration, accompanied by diarrhea, shortness of breath, and occasional fever. Based on these indicators of abnormal inflammation and fever, we suspected the presence of an infection. Although evidence of microbial infection was not found in routine clinical tests and the patient did not show typical clinical symptoms of infection with M. tuberculosis, next-generation sequencing of blood samples nevertheless demonstrated the presence of M. tuberculosis, which was subsequently isolated from blood samples grown in conventional BacT/ALERT FA blood culture bottles.

CONCLUSION

Our findings demonstrate that HIV-negative liver cirrhosis patients can also be infected with M. tuberculosis.

Mycobacterium abscessus: Shapeshifter of the Mycobacterial World

In this review we will focus on unique aspects of Mycobacterium abscessus (MABS) which we feel earn it the designation of "shapeshifter of the mycobacterial world." We will review its emergence as a distinct species, the recognition and description of MABS subspecies which are only now being clearly defined in terms of pathogenicity, its ability to exist in different forms favoring a saprophytic lifestyle or one more suitable to invasion of mammalian hosts, as well as current challenges in terms of antimicrobial therapy and future directions for research. One can see in the various phases of MABS, a species transitioning from a free living saprophyte to a host-adapted pathogen.

Discovery of benzothiazole amides as potent antimycobacterial agents

From a high throughput screening of commercially available libraries against nontuberculous mycobacteria and Mycobacterium tuberculosis, numerous hits were identified with moderate activity. Extensive medicinal chemistry optimization has led to a series of potent benzothiazole amide antimycobacterial agents. Replacement of the adamantyl group with cyclohexyl derivatives and further development of this series resulted in an advanced lead compound, CRS400393, which demonstrated excellent potency and a mycobacteria-specific spectrum of activity. MIC values ranged from 0.03 to 0.12 μg/mL against Mycobacterium abscessus and other rapid-grower NTM, and 1-2 μg/mL against Mycobacterium avium complex. The preliminary mechanism of action studies suggested these agents may target MmpL3, a mycobacterial mycolic acid transporter. The series has demonstrated in vivo efficacy in a proof of concept mouse model of M. abscessus infection.

Non-tuberculous mycobacterial infections at San Francisco General Hospital

BACKGROUND AND AIMS

The epidemiology of non-tuberculous mycobacteria (NTM) infection is not well defined. We evaluated the trends in incidence of NTM infections at San Francisco General Hospital (SFGH), a large metropolitan county hospital.

METHODS

We performed a retrospective review of microbiologic and clinical records of all patients with a positive NTM culture reported from 1993 to 2001. NTM infection was defined by the isolation of >1 NTM from any clinical specimen. Patients were stratified by human immunodeficiency virus (HIV) status. Univariate and multivariate logistic regression were used to identify factors that were independently associated with NTM infection. Trends over time were assessed using Poisson test for trend.

RESULTS

During the study period, 25 736 samples from 7395 patients were cultured for mycobacteria. Of these samples, 2853 (11.1%) from 1345 patients (18.2%) were culture positive for NTM. Patient characteristics associated with infection included younger age (P < 0.001), male gender (P < 0.001), White ethnicity compared with Asian and Hispanic (P < 0.001 and P = 0.01, respectively), and HIV positivity (P < 0.001). Overall, NTM infection at SFGH decreased significantly from 319 cases in 1993 to 59 in 2001 (P < 0.001). Mycobacterium avium was predominant in both HIV-positive and HIV-negative populations (74.5% and 44.6% of isolates, respectively), and Mycobacterium kansasii was the second most common NTM species isolated. The proportion of other NTM species isolated in these groups differed.

CONCLUSION

In contrast to other published studies, time-series analyses show that NTM isolation rates decreased during the study period at SFGH, where NTM was most strongly associated with HIV infection.

Transcriptional profiling of Mycobacterium tuberculosis replicating ex vivo in blood from HIV- and HIV+ subjects

Hematogenous dissemination of Mycobacterium tuberculosis (M. tb) occurs during both primary and reactivated tuberculosis (TB). Although hematogenous dissemination occurs in non-HIV TB patients, in ∼80% of these patients, TB manifests exclusively as pulmonary disease. In contrast, extrapulmonary, disseminated, and/or miliary TB is seen in 60–70% of HIV-infected TB patients, suggesting that hematogenous dissemination is likely more common in HIV+ patients. To understand M. tb adaptation to the blood environment during bacteremia, we have studied the transcriptome of M. tb replicating in human whole blood. To investigate if M. tb discriminates between the hematogenous environments of immunocompetent and immunodeficient individuals, we compared the M. tb transcriptional profiles during replication in blood from HIV- and HIV+ donors. Our results demonstrate that M. tb survives and replicates in blood from both HIV- and HIV+ donors and enhances its virulence/pathogenic potential in the hematogenous environment. The M. tb blood-specific transcriptome reflects suppression of dormancy, induction of cell-wall remodeling, alteration in mode of iron acquisition, potential evasion of immune surveillance, and enhanced expression of important virulence factors that drive active M. tb infection and dissemination. These changes are accentuated during bacterial replication in blood from HIV+ patients. Furthermore, the expression of ESAT-6, which participates in dissemination of M. tb from the lungs, is upregulated in M. tb growing in blood, especially during growth in blood from HIV+ patients. Preliminary experiments also demonstrate that ESAT-6 promotes HIV replication in U1 cells. These studies provide evidence, for the first time, that during bacteremia, M. tb can adapt to the blood environment by modifying its transcriptome in a manner indicative of an enhanced-virulence phenotype that favors active infection. Additionally, transcriptional modifications in HIV+ blood may further accentuate M. tb virulence and drive both M. tb and HIV infection.

Bacteraemia caused by Mycobacterium abscessus subsp. abscessus and M. abscessus subsp. bolletii: clinical features and susceptibilities of the isolates

Mycobacterium abscessus complex (M. abscessus subsp. abscessus and M. abscessus subsp. bolletii) is an emerging pathogen causing various human infections. However, few studies have focused on M. abscessus complex bacteraemia with detailed species differentiation. The clinical characteristics of patients with bacteraemia due to M. abscessus complex treated at National Taiwan University Hospital from 2005-2012 were evaluated. Species identification was performed by molecular methods, and minimum inhibitory concentrations (MICs) were determined using a Sensititre RAPMYCO Panel Test for preserved M. abscessus complex isolates. During the study period, 15 patients with M. abscessus complex bacteraemia were found but only 14 isolates from 13 patients were preserved for analysis. One patient had two episodes of bacteraemia (one caused by M. abscessus subsp. bolletii and one by M .abscessus subsp. abscessus with a 9-month interval). Of the remaining 12 patients, 9 patients had M. abscessus subsp. bolletii bacteraemia and 3 had M .abscessus subsp. abscessus bacteraemia. Patients were mainly middle-aged adults with various co-morbidities. Steroid usage and malignancy (5/15) were the most common immunocompromised statuses, followed by diabetes mellitus (4/15). Surgical wound infection was the most common infection foci in all patients (5/15), particularly in M. abscessus subsp. bolletii bacteraemia patients. Clarithromycin and tigecycline exhibited good in vitro activities. Overall, the 14-day mortality was 20% (3/15). M. abscessus complex bacteraemia should be considered an emerging opportunistic infection in immunocompromised hosts. Clarithromycin and tigecycline have potent in vitro activities and are promising agents for treating infections due to M. abscessus complex.

Mycobacterium tuberculosis bacteraemia: experience from a non-endemic urban centre

The isolation of Mycobacterium tuberculosis from blood culture specimens has been associated with human immunodeficiency virus (HIV) co-infection with variable impact on tuberculosis (TB) mortality reported. The overwhelming majority of M. tuberculosis bacteraemia cases were described in developing countries. We present a nested case-control analysis of clinical, sociodemographic and behavioural risk factors in patients with positive M. tuberculosis blood cultures compared with patients with negative blood cultures from a 9-year population-based active TB surveillance study conducted in Houston, Texas. There were 42 patients with M. tuberculosis bacteraemia, 47 blood culture negative patients and 3573 patients for whom no mycobacterial blood culture was requested. HIV infection was more common in patients for whom a mycobacterial blood culture was requested (79.8% versus 15.1% p <0.001). Of the patients with M. tuberculosis bacteraemia, six were HIV negative or had no documentation of HIV status, including five with immunosuppressive conditions other than HIV. Patients with M. tuberculosis bacteraemia were more likely than patients with negative blood cultures to be deceased at diagnosis or to die while on TB therapy (50.0% versus 17.0%, p <0.01), to report men-who-have-sex-with-men behaviour (31.7% versus 13.0%, p 0.03), to have renal failure (28.6% versus 6.4%, p 0.01), and to have HIV RNA levels higher than 500 000 copies/mL (61.9% versus 17.2%, p ≤0.01). Requests for mycobacterial culture of blood specimens were more common in HIV-infected individuals, and the presence of M. tuberculosis bacteraemia was associated with a significant increase in mortality.

Mycobacterial bone marrow infections at a medical centre in Taiwan, 2001-2009

Mycobacterial bone marrow (BM) infection is the most common diagnosis established by BM examinations for fever of unknown origin. In this study, clinical features and outcomes of patients who fulfilled the criteria for BM infection due to Mycobacterium tuberculosis (MTB) and non-tuberculous mycobacteria (NTM) at a medical centre in Taiwan from 2001 to 2009 were investigated. The BM histopathological findings were also analysed. A total of 24 patients (16 men, eight women) with mycobacterial BM infections were found. Of these, nine (38%) were positive for human immunodeficiency virus (HIV) and six (25%) had no pre-existing immunocompromised conditions. MTB isolates were obtained from 11 (46%) patients and NTM species were isolated from 10 (42%) patients, including M. avium complex (MAC, n = 7) and M. kansasii (n = 3). Patients with MTB infections were significantly older than those with NTM infections (60·5 vs. 47·7 years, P = 0·043) and were less likely to have a positive BM culture (45% vs. 100%, P = 0·012). The 90-day survival rates for MTB and NTM BM infections were 68% and 60%, respectively (P = 0·61). In addition, the presence of BM granulomas was significantly more common in patients with MTB BM infections than in those with NTM infections (82% vs. 30%, P = 0·030). In Taiwan, the importance of NTM was not inferior to MTB and besides MAC, M. kansasii might be an important pathogen in non-HIV-infected patients. The presence of BM granulomas and caseation provides valuable information regarding early treatment pending culture results.