Utilization of a ts-sacB selection system for the generation of a Mycobacterium avium serovar-8 specific glycopeptidolipid allelic exchange mutant

BACKGROUND: Mycobacterium avium are ubiquitous environmental organisms and a cause of disseminated infection in patients with end-stage AIDS. The glycopeptidolipids (GPL) of M. avium are proposed to participate in the pathogenesis of this organism, however, establishment of a clear role for GPL in disease production has been limited by the inability to genetically manipulate M. avium. METHODS: To be able to study the role of the GPL in M. avium pathogenesis, a ts-sacB selection system, not previously used in M. avium, was employed as a means to achieve homologous recombination for the rhamnosyltransferase (rtfA) gene of a pathogenic serovar 8 strain of M. avium to prevent addition of serovar-specific sugars to rhamnose of the fatty acyl-peptide backbone of GPL. The genotype of the resultant rtfA mutant was confirmed by polymerase chain reaction and southern hybridization. Disruption in the proximal sugar of the haptenic oligosaccharide resulted in the loss of serovar specific GPL with no change in the pattern of non-serovar specific GPL moieties as shown by thin layer chromatography and gas chromatography/mass spectrometry. Complementation of wild type (wt) rtfA in trans through an integrative plasmid restored serovar-8 specific GPL expression identical to wt serovar 8 parent strain. RESULTS: In this study, we affirm our results that rtfA encodes an enzyme responsible for the transfer of Rha to 6d-Tal and provide evidence of a second allelic exchange mutagenesis system suitable for M. avium. CONCLUSION: We report the second allelic exchange system for M. avium utilizing ts-sacB as double-negative and xylE as positive counter-selection markers, respectively. This system of allelic exchange would be especially useful for M. avium strains that demonstrate significant isoniazid (INH) resistance despite transformation with katG. Through the construction of mutants in GPL or other mycobacterial components, their roles in M. avium pathogenesis, biosynthesis, or drug resistance can be studied in a consistent manner

Pathogenic nontuberculous mycobacteria resist and inactivate cathelicidin: implication of a novel role for polar mycobacterial lipids

Includes bibliographic references.Nontuberculous mycobacteria (NTM) are a large group of environmental organisms with worldwide distribution, but only a relatively few are known to be pathogenic. Chronic, debilitating lung disease is the most common manifestation of NTM infection, which is often refractory to treatment. The incidence and prevalence of NTM lung disease are increasing in the United States and in many parts of the world. Hence, a more complete understanding of NTM pathogenesis will provide the foundation to develop innovative approaches to treat this recalcitrant disease. Herein, we domonstrate that several species of NTM show broad resistance to the antimicrobial peptide, cathelicidin (LL-37). Resistance to LL-37 was not significantly different between M. avium that contain serovar-specific glycopeptidolipid (GPL, M. aviumˢˢᴳᴾᴸ) and M.avium that do not (M. aviumᐞˢˢᴳᴾᴸ). Similarly, M. Abscessus containing non-specific GPL (M. abscessusⁿˢᴳᴾᴸ⁽⁺⁾) or lacking nsGPL (M. abscessusⁿˢᴳᴾᴸ⁽⁻⁾) remained equally resistant to LL-37. These findings would support the notion that GPL are not the components responsible for NTM resistance to LL-37. Unexpectedly, the growth of M. abscessusⁿˢᴳᴾᴸ⁽⁻⁾ increased with LL-37 or scrambled LL-37 peptide in a dose-dependent fashion. We also discovered that LL-37 exposed to NTM had reduced antimicrobial activity, and initial work indicates that this is likely due to inactivation of LL-37 by lipid component(s) of the NTM cell envelope. We conclude that pathogenic NTM resist and inactivate LL-37. The mechanism by which NTM circumvent the antimicrobial activity of LL-37 remains to be determined

A Review of Microbiology: an Evolving Science

<p><strong>Review of: </strong><em>Microbiology: an Evolving Science. </em> 1^st ed. Joan L. Slonczewski and John W. Foster; (2008) . W.W. Norton and Company, New York. 1280 pages.</p

snr-1 Gene Is Required for Nitrate Reduction in Pseudomonas aeruginosa PAO1

Pseudomonas aeruginosa is able to use nitrate for both assimilation and anaerobic respiration. One set of genes, designated snr (for “shared nitrate reduction”), have been recently cloned and partially characterized. In this study, we demonstrate that the snr-1 gene encodes a predicted 52.5-kDa protein that is 82% similar to a unique cytochrome c of Desulfomonile tiedjei DCB-1. Importantly, the Snr-1 protein sequence of P. aeruginosa differed from that of the cytochrome c of D. tiedjei primarily in the first 25 amino acids, which are required for membrane attachment in D. tiedjei. In P. aeruginosa, the Snr-1 protein hydropathy profile indicates that it is a soluble protein. An isogenic snr-1::Gm insertional mutant was unable to grow aerobically with nitrate as a sole nitrogen source or anaerobically with nitrate as an electron acceptor. Complementation of the snr-1::Gm mutant with the snr-1 gene restored the wild-type phenotypes. Interestingly, anaerobic growth rates were significantly higher in the snr-1 mutant harboring a multicopy plasmid containing snr-1. In contrast, aerobic growth rates of the restored mutant using nitrate as the sole nitrogen source were similar to those of the wild type. Transcriptional lacZ fusions demonstrated that snr-1 was not regulated by molybdate, oxygen, or nitrate

ssGPL does not contribute to the resistance of <i>M</i>. <i>avium</i> to LL-37.

<p>CFU determination of <i>M</i>. <i>avium</i>^ssGPL and <i>M</i>. <i>avium</i>^ΔssGPL serovar 8 after incubation with 0, 10, 25, and 100 μg/ml LL-37 and 20 μg/ml gentamicin. ***p<0.0001. Data are the mean ± SEM of 3 independent experiments.</p

Loss of LL-37 activity after exposure to NTM or NTM-derived lipids.

<p><i>E</i>. <i>coli bioassays</i> were used to evaluate LL-37 activity. (A) LL-37 remaining in NTM (but not <i>Mtb</i>) culture supernatant no longer kills <i>E</i>. <i>coli</i>. (B) <i>E</i>. <i>coli</i> survives in untreated or boiled NTM culture supernatants to which fresh LL-37 was added. (C) <i>E</i>. <i>coli</i> survival following incubation with <i>M</i>. <i>abscessus</i> or <i>M</i>. <i>intracellulare</i> derived cell fractions. CM = cell membrane, CW = cell wall, ICW = insoluble cell wall fraction.</p

LL-37 demonstrates broad-spectrum antimicrobial activity.

<p>Log₁₀ CFU after 1–8 hours of incubation of a (A) laboratory isolate of <i>Salmonella enteriditis</i> or clinical isolates of (B) <i>Salmonella enteriditis</i> (Uganda) or (C) <i>Salmonella non-typhi</i> (Nairobi) with 0–50 μg/ml of LL-37. *p< 0.01; **p< 0.001; ***p<0.0001. Data are the mean ± SEM of 3–6 independent experiments. (D) <i>Mtb</i> H37Rv were incubated with 10 μg/ml LL-37 and the percent change in CFU calculated after 96 hours incubation. n = 3 independent experiments.</p