Peptide Deformylase (def) is essential in Mycobacterium smegmatis, but the essentiality is compensated by inactivation of methionine formylation.

BACKGROUND: Co-translational processes in bacteria are attractive drug targets, but while some processes are essential, others are not. The essentiality of Peptide Deformylase (PDF, def) for vitality of mycobacteria was speculated, but never unequivocally proven. RESULTS: Here we show by targeted deletion experiments that def can only be deleted from M. smegmatis when an additional copy is present; that prior deletion of tRNAfMet-Formyl Transferase (FMT, encoded by fmt) renders def completely dispensable; and that re-introduction of fmt into a Δdef mutant is not possible - constituting a definitive proof for the essentiality of def in mycobacteria. CONCLUSIONS: Peptide deformylase is essential in M. smegmatis, but the fact that inactivation of fmt renders the gene completely dispensable, and thus any inhibitor of def useless, casts doubt on the usefulness of PDF as a drug-target in mycobacteria.

Comparison of Isogenic Strains Shows No Evidence of Altered Nosocomial Transmission-Competency of Rough, GPL-Negative Mycobacterium abscessus Strains.

Mycobacterium abscessus is an emerging pathogen causing severe pulmonary infections. While environmental in origin, in the clinical setting M. abscessus often changes to a Rough phenotype associated with severe non-remitting infections. Clinical isolates baring mutations in glycopeptidolipid-synthesis genes, leading to the Rough phenotype, were suggested to have increase bacterial virulence while possibly showing reduced transmissibility on fomites. We set to determine whether an isolated glycopeptidolipid (GPL) defect affects transmissibility. We used transposon technology to create a fully isogenic Rough (GPL-defective) (Tn_4099c) and compare it to the isogenic parent strain (ATCC 19977). Survival on fomites was determined by spotting, drying, and retrieving the isolates at designated time points. This was repeated as a competition experiment using a mixture of differentially fluorescent M. abscessus 19977 (Smooth) and the Tn_4099c mutant (Rough). Survival ability in chlorhexidine solution (Septal Scrub Teva) was performed using a disinfectant killing-assay for mycobacteria. Despite significant bacterial killing in all assays, we found no survival advantage to either GPL-defected Rough or GPL-reserved Smooth morphotype-both on fomites and in chlorhexidine. Our findings suggest that while transmission fitness may be altered due to some within-host evolutionary changes, decreased transmissibility of clinical strains cannot be attributed to the GPL-synthesis defect alone. Further studies are needed to determine the effect of other mutations on the transmission potential of M. abscessus in the clinical setting. IMPORTANCE Mycobacterium abscessus is an emerging pathogen causing severe pulmonary infections. In the clinical setting, M. abscsssus undergoes molecular and genetic changes associated with increased virulence. Specifically, bacterial defects in glycopeptidolipid (GPL) synthesis, creating the "Rough" colony phenotype, have been associated with increased virulence, yet were also presumably observed to have decreased survival on fomites, leading to reduced transmissibility. We set to determine whether GPL-synthesis defects are indeed responsible for reduced transmissibility of clinical isolates. We compared fully isogenic GPL-disrupted versus GPL-preserved strains, and demonstrated no survival advantage for either strain on fomites. Additionally, neither isolate had a survival advantage in chlorhexidine, a widely used disinfectant in health care settings. Our findings suggest that reduced transmissibility of clinical isolates, should it be found, cannot be attributed to GPL-synthesis mutations. While clinical isolates may show changes in transmission potential, more studies are needed to investigate the mechanisms leading to these phenotypic changes.