Development of a firefly luciferase-based assay for determining antimicrobial susceptibility of Mycobacterium avium subsp. paratuberculosis

ALSUntangled #66: antimycobacterial antibiotics

Several infections have been associated with motor neuron diseases resembling ALS, including species of viruses, bacteria, and parasites. Mycobacterium avium subspecies paratuberculosis (MAP), most known for its probable etiologic association with Crohn's disease, has been suggested as another possible infectious cause of motor neuron disease. Two published case reports describe the successful treatment of ALS-like symptoms with antimycobacterial antibiotics. Both cases had atypical features. Based on these, we believe it would be reasonable to begin performing chest imaging in PALS who have features of their history or exam that are atypical for ALS such as pain, fevers, or eye movement abnormalities. If the chest imaging is abnormal, more specific testing for mycobacteria may be indicated. Until there is more clear evidence of an association between mycobacteria and ALS, we cannot endorse the widespread use of potentially toxic antimycobacterial antibiotics for PALS.

Novel Amphiphilic Cyclobutene and Cyclobutane cis-C18 Fatty Acid Derivatives Inhibit Mycobacterium avium subsp. paratuberculosis Growth

Mycobacterium avium subspecies paratuberculosis (Map) is the etiologic agent of Johne’s disease in ruminants and has been associated with Crohn’s disease in humans. An effective control of Map by either vaccines or chemoprophylaxis is a paramount need for veterinary and possibly human medicine. Given the importance of fatty acids in the biosynthesis of mycolic acids and the mycobacterial cell wall, we tested novel amphiphilic C₁₀ and C₁₈ cyclobutene and cyclobutane fatty acid derivatives for Map inhibition. Microdilution minimal inhibitory concentrations (MIC) with 5 or 7 week endpoints were measured in Middlebrook 7H9 base broth media. We compared the Map MIC results with those obtained previously with Mycobacterium tuberculosis and Mycobacterium smegmatis. Several of the C₁₈ compounds showed moderate efficacy (MICs 392 to 824 µM) against Map, while a higher level of inhibition (MICs 6 to 82 µM) was observed for M. tuberculosis for select analogs from both the C₁₀ and C₁₈ groups. For most of these analogs tested in M. smegmatis, their efficacy decreased in the presence of bovine or human serum albumin. Compound 5 (OA-CB, 1-(octanoic acid-8-yl)-2-octylcyclobutene) was identified as the best chemical lead against Map, which suggests derivatives with better pharmacodynamics may be of interest for evaluation in animal models.

Development of Quantitative Real-Time PCR Assays for Postmortem Detection of Mycobacterium spp. Common in Zebrafish (Danio rerio) Research Colonies

Mycobacterium spp. infections are common in zebrafish kept in research facilities. These comorbidities can substantially modulate the responses of these fish to external and internal stimuli. Therefore, diagnostic tests to detect Mycobacterium spp. infections in zebrafish colonies prove essential. Here, we outline the development of quantitative simplex real-time PCR assays to detect the 3 Mycobacterium species most commonly identified in laboratory zebrafish. The assays targeted the heatshock protein 65 gene of M. marinum, M. chelonae, and M. haemophilum. The assays are both highly specific and sensitive for fresh-frozen samples and highly specific and moderately sensitive for formalin-fixed paraffin-embedded (FFPE) samples. Two sampling techniques for FFPE samples of sagittally sectioned zebrafish were evaluated. Both paraffin cores targeting granulomas containing bacteria and scrolls from the entire fish yielded DNA of equivalent quantity and purity. The diagnostic sensitivity of cores was superior to that of scrolls for M. chelonae and M. haemophilum but not M. marinum. The assays are cost-effective and ideally suited to diagnosing common Mycobacterium spp. infections in zebrafish.

Antibacterial activities of naturally occurring compounds against Mycobacterium avium subsp. paratuberculosis

The antibacterial activities of 18 naturally occurring compounds (including essential oils and some of their isolated constituents, apple and green tea polyphenols, and other plant extracts) against three strains of Mycobacterium avium subsp. paratuberculosis (a bovine isolate [NCTC 8578], a raw-milk isolate [806R], and a human isolate [ATCC 43015]) were evaluated using a macrobroth susceptibility testing method. M. avium subsp. paratuberculosis was grown in 4 ml Middlebrook 7H9 broth containing 10% oleic acid-albumin-dextrose-catalase, 0.05% Tween 80 (or 0.2% glycerol), and 2 microg/ml mycobactin J supplemented with five concentrations of each test compound. The changes in the optical densities of the cultures at 600 nm as a measure of CFU were recorded at intervals over an incubation period of 42 days at 37 degrees C. Six of the compounds were found to inhibit the growth of M. avium subsp. paratuberculosis. The most effective compound was trans-cinnamaldehyde, with a MIC of 25.9 microg/ml, followed by cinnamon oil (26.2 microg/ml), oregano oil (68.2 microg/ml), carvacrol (72.2 microg/ml), 2,5-dihydroxybenzaldehyde (74 microg/ml), and 2-hydroxy-5-methoxybenzaldehyde (90.4 microg/ml). With the exception of carvacrol, a phenolic compound, three of the four most active compounds are aldehydes, suggesting that the structure of the phenolic group or the aldehyde group may be important to the antibacterial activity. No difference in compound activity was observed between the three M. avium subsp. paratuberculosis strains studied. Possible mechanisms of the antimicrobial effects are discussed.

Correlation between rpoB gene mutation in Mycobacterium avium subspecies paratuberculosis and clinical rifabutin and rifampicin resistance for treatment of Crohn’s disease

AIM: To investigate overlapping regions of the rpoB gene previously involved with rifamycin resistance in M. tuberculosis and seek correlation between rpoB mutations in clinical MAP strains with susceptibility to RIF and RFB.

METHODS: We designed a molecular-based PCR method for the evaluation of rifabutin (RFB) and rifampicin (RIF) resistance based on probable determinant regions within the rpoB gene of MAP, including the 81 bp variable site located between nucleotides 1363 and 1443. The minimum inhibitory concentration (MIC) for RIF was also determined against 11 MAP isolates in attempt to seek correlation with rpoB sequences.

RESULTS: We determined that MAP strain 18 had an MIC of > 30 mg/L and ≤ 5 mg/L for RIF and RFB respectively, and a significant and novel rpoB mutation C1367T, compared to an MIC of ≤ 1.0 mg/L for both drugs in the wild type MAP. The 30-fold increase in the MIC was a direct result of the rpoB mutation C1367T, which caused an amino acid change Thr456 to Ile456 in the drug’s binding site. In addition, MAP strain 185 contained five silent rpoB mutations and exhibited an MIC comparable to the wild-type. Moreover, our in vitro selected mutation in MAP strain UCF5 resulted in the generation of a new resistant strain (UCF5-RIF16r) that possessed T1442C rpoB mutation and an MIC > 30 mg/L and > 10 mg/L for RIF and RFB respectively. Sequencing of the entire rpoB gene in MAP strains UCF4, 18, and UCF5-RIF16r revealed an rpoB mutation A2284C further downstream of the 81 bp variable region in UCF4, accounting for observed slight increase in MIC. In addition, no other significant mutations were found in strains 18 and UCF-RIF16r.

CONCLUSION: The data clearly illustrates that clinical and in vitro-selected MAP mutants with rpoB mutations result in resistance to RIF and RFB, and that a single amino acid change in the beta subunit may have a significant impact on RIF resistance. Unconventional drug susceptibility testing such as our molecular approach will be beneficial for evaluation of antibiotic effectiveness. This molecular approach may also serve as a model for other drugs used for treatment of MAP infections.

Parallel analysis of antimicrobial activities in microbial community by SSCP based on CE

Conventional antimicrobial activity analyses such as the broth dilution method and disk diffusion test are considerably demanding processes for new antimicrobial agent discovery and sensitive diagnosis of infectious diseases. Here, we developed a new antimicrobial activity analysis system using CE-based SSCP (CE-SSCP) combined with 16S rRNA gene-specific PCR (PCR/CE-SSCP). Using this method, the population change in the microbial community in response to specific antimicrobial agents could be quantified with a high sensitivity and accuracy from a small sample amount. Using a mixture of microorganisms comprising Escherichia coli, Corynebacterium glutamicum, Acinetobacter calcoaceticus, and Staphylococcus aureus as a model system, the linear correlation between the genomic DNA concentrations and peak areas in 16S rRNA gene-specific PCR/CE-SSCP was determined; consequently, quantification of cell concentrations could be demonstrated using this method. Compared to the minimum inhibitory concentration (MIC) values from the conventional broth dilution method, this new system provided almost the same MIC values for popular antimicrobial agents such as kanamycin, spectinomycin, and streptomycin. The results demonstrated that the newly developed method can be a substitute for the conventional antimicrobial analysis method and highlighted its high potential in the areas of new antimicrobial agent discovery and clinical diagnosis.

The application of bioluminescence assay with culturing for evaluating quantitative disinfection performance

Various methods, including bioluminescence assay, were investigated regarding their suitability for quantitatively evaluating the disinfection performance. Although bioluminescence assay itself has been widely reported as a rapid, easy and suitable method for analyzing live microorganisms, the limited sensitivity of its measurement (approximately 10(3)-10(4)cells/assay vial), which is insufficient for disinfection study, requires further study. Among three methods (amplifying by enzymatic method, membrane filtration, and amplification by culturing) examined for increasing the detection sensitivity, amplification by culturing showed the best performance as Escherichia coli was employed as an indicating microorganism. Even with a short culturing time of 4h, the detection limit of E. coli measurement was successfully improved 200-fold, and the analytical results were not dependent upon the state of E. coli growth (stationary state with E. coli stock suspension vs. growth state with E. coli). In addition, the analytical integrity of bioluminescence assay with culturing was further demonstrated in comparison with spread plate method as free chlorine and UV irradiation were employed in the disinfection study.

Low-oxygen-recovery assay for high-throughput screening of compounds against nonreplicating Mycobacterium tuberculosis

Screening for new antimicrobial agents is routinely conducted only against actively replicating bacteria. However, it is now widely accepted that a physiological state of nonreplicating persistence (NRP) is responsible for antimicrobial tolerance in many bacterial infections. In tuberculosis, the key to shortening the 6-month regimen lies in targeting this NRP subpopulation. Therefore, a high-throughput, luminescence-based low-oxygen-recovery assay (LORA) was developed to screen antimicrobial agents against NRP Mycobacterium tuberculosis. M. tuberculosis H37Rv containing a plasmid with an acetamidase promoter driving a bacterial luciferase gene was adapted to low oxygen conditions by extended culture in a fermentor with a 0.5 headspace ratio. The MICs of 31 established antimicrobial agents were determined in microplate cultures maintained under anaerobic conditions for 10 days and, for comparative purposes, under aerobic conditions for 7 days. Cultures exposed to drugs under anaerobic conditions followed by 28 h of "recovery" under ambient oxygen produced a luminescent signal that was, for most compounds, proportional to the number of CFU determined prior to the recovery phase. No agents targeting the cell wall were active against NRP M. tuberculosis, whereas drugs hitting other cellular targets had a range of activities. The calculated Z' factor was in the range of 0.58 to 0.84, indicating the suitability of the use of LORA for high-throughput assays. This LORA is sufficiently robust for use for primary high-throughput screening of compounds against NRP M. tuberculosis.

Development of luminescent Mycobacterium avium subsp. paratuberculosis for rapid screening of vaccine candidates in mice

Mycobacterium avium subsp. paratuberculosis is a slowly growing mycobacterial species, requiring 6 to 8 weeks of culture before colonies can be counted visually. Here, we describe the development of luminescent M. avium subsp. paratuberculosis expressing luxAB genes of Vibrio harveyi and its use for vaccine testing in an experimental mouse model, replacing fastidious CFU counting by rapid luminometry.

Johne's disease, inflammatory bowel disease, and Mycobacterium paratuberculosis

Johne's disease is a chronic diarrhea affecting all ruminants. Mycobacterium avium subsp. paratuberculosis (MAP), a slowly growing mycobacteria, is the etiologic agent. There is also a concern that MAP might be a causative agent of some cases of inflammatory bowel disease in humans, especially Crohn's disease. Food products including pasteurized bovine milk have been suggested as potential sources of human infection. This review addresses microbial factors that may contribute to its pathogenicity. In addition, the experimental evidence defining MAP as the cause of Johne's disease and the issues and controversies surrounding its potential pathogenic role in humans are discussed.

Quinones as antimycobacterial agents

Mycobacterium tuberculosis is a serious worldwide health threat, killing almost 3 million people per year. Other mycobacterial species, especially Mycobacterium avium, are emerging pathogens in the immunocompromised population, most notably AIDS patients. These nontuberculous mycobacteria (NTM) are ubiquitous in the environment, and naturally resistant to many disinfection procedures. Treatment options are limited, and no new antibiotics have been developed against mycobacteria since the 1970s. There is a desperate need for new biocides and antibiotics to prevent and treat mycobacterial infections. A small aromatic compound library has been screened for effectiveness in growth inhibition or killing of mycobacteria. Four species, representing the M. tuberculosis complex, the slow-growing NTM, and the rapid-growing NTM were used. Active compounds had minimal inhibitory concentrations as low as 12.5 microg/mL, with the active component being a quinone. The primarily bactericidal activity observed represents a unique mechanism of action. A fluorescent assay involving M. smegmatis expressing gfp was analyzed as a rapid assay for predicting inhibitory activity, but failed to predict activity well. Our compounds may have significant utility as soluble biocides against mycobacteria and other hardy nosocomial pathogens.

Susceptibility of Mycobacterium avium sbsp paratuberculosis to monensin sodium or tilmicosin phosphate in vitro and resulting infectivity in a murine model

This study was designed to determine the susceptibility in vitro and infectivity of 1 field isolate of Mycobacterium avium sbsp paratuberculosis after exposure to monensin sodium and tilmicosin phosphate. Minimum inhibitory concentrations (0.39 microg monensin sodium/mL; 1.60 microg tilmicosin phosphate/mL) were determined in quintuplicate. Organisms were then incubated with 3 different concentrations of each medication for 3 different lengths of time, then washed and resuspended in sterile physiologic saline and injected intraperitoneally into mice that were genetically susceptible to infection. Mice were euthanatized 50 d later and the number of hepatic granulomas was used as the indicator of infectivity. Neither time of incubation nor concentration of medication had any effect on the infectivity of the organisms. Monensin sodium significantly reduced the number of hepatic granulomas in genetically susceptible mice while tilmicosin phosphate did not. Antimycobacterial activity of monensin sodium suggests that the role of monensin in the control of bovine paratuberculosis should be evaluated further.

Growth, Congo Red agar colony morphotypes and antibiotic susceptibility testing of Mycobacterium avium subspecies paratuberculosis

OBJECTIVE

Mycobacterium avium subspecies (subsp.) paratuberculosis (MAP) is the causative agent of Johne's disease in ruminants and has been associated with Crohn's disease in humans. We sought to test growth rates and susceptibilities of various strains of MAP in two available growth media.

DESIGN

Paired comparison design.

METHODS

Using the BACTEC macrobroth radiometric growth system and Congo Red-staining agar media, we determined inherent differences in growth characteristics of three bovine and two human strains of MAP and compared susceptibility results obtained in each growth system.

RESULTS

Significant differences were observed in growth rate as well as mycobactin J dependence between strains and between a laboratory-adapted isolate of the same strain in the macrobroth system. Similarly, colonial morphology and Congo Red staining on agar media were observed. Two strains, one human and one bovine, demonstrated a 100% rough transparent colony with white coloration on Congo Red agar, while one bovine isolate exclusively grew as a smooth opaque colony with red coloration on Congo Red agar. The remaining strains exhibited mixtures of these two colonial morphotypes on agar media. Comparative susceptibility results between the BACTEC radiometric macrobroth method and the agar proportionality method showed good correlation for most antibiotics/inhibitors tested. However, erratic or poor growth in the macrobroth system prevented minimal inhibitory concentration determinations for two bovine strains by this method.

CONCLUSION

This study demonstrates the variability in the colonial morphology of MAP on Congo Red agar as well as the correlation of antibiotic susceptibility results between the BACTEC macro broth method and the agar proportionality method. This study also emphasizes the need for the development of improved, standardized culture and susceptibility test methods for MAP.

B-cell epitopes in the immunodominant p34 antigen of mycobacterium avium ssp. paratuberculosis recognized by antibodies from infected cattle

Mycobacterium avium ssp. paratuberculosis (M. paratuberculosis) causes Johne's disease, a chronic and fatal enteritis in ruminants. In the last stage of the disease, antibody titres rise and levels of interferon-gamma decrease, suggesting that the host-immune response is switching from a T helper 1 (Th1) to a Th2 profile. In infected cattle, the membrane protein p34 elicits the predominant humoral response against M. paratuberculosis. To map the B-cell epitopes of this antigen, affinity-purified bovine antibodies against the carboxy-terminal region of p34 were used to screen a 12-mer phage display library. Several phage clones carrying peptides resembling fragments of p34 were affinity selected. Based on the predicted amino acid sequence, peptides were chemically synthesized, which demonstrated reactivity with serum from naturally infected and p34-vaccinated cattle. Immunization of mice with these peptides elicited an anti-p34 antibody response. Two B-cell epitopes were identified and characterized. Based on the reactivity and the type of immune response elicited, epitope A was determined to be conformational, whereas epitope B was demonstrated to be sequential. Both epitopes were shown to be present in p34 proteins from M. avium ssp. avium or M. paratuberculosis but absent from M. intracellulare, the other member of the M. avium complex. Furthermore, both epitopes were mapped to regions of p34 that display high variability when compared to homologous proteins from other mycobacterial species of public and animal health importance. We hypothesize that these variable regions of p34 may play a role in the immunobiology of M. paratuberculosis infections.

Mycobacterium avium subsp. paratuberculosis infection in a patient with HIV, Germany

Mycobacterium avium subsp. paratuberculosis (MAP), the causative agent of Johne disease in ruminants, has been incriminated as the cause of Crohn disease in humans. We report the first case of human infection with MAP in a patient with HIV; infection was confirmed by obtaining isolates from several different specimen types.

A luciferase-based method for assessing chlorine-susceptibility of Mycobacterium avium

A rapid and quantitative assay for the disinfection of the water-borne pathogen, Mycobacterium avium, was developed using firefly luciferase as a reporter gene. There was a correlation between the quantity of light produced and the number of colony-forming units. In chlorine-disinfection studies of a luciferase-carrying derivative of M. avium, there was a strong correlation (r2=0.96) between colony forming units and relative light units. It was discovered that chlorine was rapidly lost from suspensions containing 10(6) M. avium cells/ml. The luciferase-based test can be used to rapidly measure susceptibility of M. avium to different disinfectants used in water treatment.

Mycobacterium avium subsp. paratuberculosis in Veterinary Medicine

Mycobacterium avium subsp. paratuberculosis (basonym M. paratuberculosis) is the etiologic agent of a severe gastroenteritis in ruminants known as Johne's disease. Economic losses to the cattle industry in the United States are staggering, reaching $1.5 billion annually. A potential pathogenic role in humans in the etiology of Crohn's disease is under investigation. In this article, we review the epidemiology, pathogenesis, diagnostics, and disease control measures of this important veterinary pathogen. We emphasize molecular genetic aspects including the description of markers used for strain identification, diagnostics, and phylogenetic analysis. Recent important advances in the development of animal models and genetic systems to study M. paratuberculosis virulence determinants are also discussed. We conclude with proposals for the applications of these models and recombinant technology to the development of diagnostic, control, and therapeutic measures.

Antibacterial therapy for Crohn's disease: a review emphasizing therapy directed against mycobacteria

The most commonly used antibiotics in Crohn's disease are nitroimidazoles and macrolides often combined with corticosteroids or sulfasalazine. There has been interest in a mycobacterial involvement in Crohn's disease since its earliest description. It is not recognized that Mycobacterium avium subspecies paratuberculosis, a proven but uncommon cause of human disease, is widespread in the human food chain especially in dairy products and beef. M. paratuberculosis has been identified in tissues from a higher proportion of Crohn's disease patients than controls, suggesting that it may be one of the causes of Crohn's disease. We review the large number of antibiotic trials in Crohn's disease. Although studies have been performed with many different protocols and variations in the definition of success, preliminary reports of multiple drug therapies are encouraging. Nevertheless, large-well designed preferably placebo-controlled studies are needed before one could recommend such therapy.

Development of a transposon mutagenesis system for Mycobacterium avium subsp. paratuberculosis

Mycobacterium avium subspecies paratuberculosis, a slow-growing Mycobacterium, is the causative agent of Johne's disease. Although M. paratuberculosis is difficult to manipulate genetically, our laboratory has recently demonstrated the ability to introduce DNA into these bacteria by transformation and phage infection. In the current study we develop the first transposon mutagenesis system for M. paratuberculosis using the conditionally replicating mycobacteriophage phAE94 to introduce the mycobacterial transposon Tn5367. Southern blotting and sequence analysis demonstrated that the transposon insertion sites are distributed relatively randomly throughout the M. paratuberculosis genome. We constructed a comprehensive bank of 5620 insertion mutants using this transposon. The transposition frequency obtained using this delivery system was 1.0 x 10(-6) transposition events per recipient cell. Auxotrophic mutants were observed in this library at a frequency of 0.3%.