en Infectious disease (Molecular and Cellular aspects) Infectious disease (Molecular and Cellular aspects) Original Article Original Article <span style="line-height:200%"><span arial="" style="font-family:">The opportunistic pathogen </span><i><span arial="" style="font-family:">Pseudomonas aeruginosa</span></i><span arial="" style="font-family:"> (<i>Pa</i>) is a </span><span arial="" style="font-family:">major</span><em> </em><em><span arial="" style="font-family:"><span style="font-style:normal">concern for immunocompromised </span></span></em><em><span arial="" style="font-family:"><span style="font-style:normal">and </span></span></em><em><span arial="" style="font-family:"><span style="font-style:normal">cystic fibrosis patients.</span></span></em><em> </em><em><span arial="" style="font-family:"><span style="font-style:normal">Chronic</span></span></em><em> </em><span arial="" style="font-family:">lung infections caused by </span><i><span arial="" style="font-family:">Pa</span></i><span arial="" style="font-family:"> are generally considered incurable, in part, due to the bacteria&rsquo;s ability to form persister cells</span><i><span arial="" style="font-family:">.</span></i><span arial="" style="font-family:"> These variants are categorized as being phenotypically dormant and highly tolerant to antibiotic treatment. Currently, the mechanisms involved in</span><i> </i><i><span arial="" style="font-family:">Pa</span></i><i> </i><span arial="" style="font-family:">persister cell formation is poorly understood</span><span arial="" style="font-family:">. One promising candidate is the </span><i><span arial="" style="font-family:"><span style="color:#222222">Pa </span></span></i><span arial="" style="font-family:"><span style="color:#222222">filamentation induced by cAMP (FIC) domain containing toxin (</span></span><span arial="" style="font-family:">PaFicT), which like other <span style="color:black">FIC toxins</span> transiently inhibits cell growth.<b> </b>Genetic knockout and complementation by single copy chromosomal insertion was used to </span><span arial="" style="font-family:">characterize <i>paficT</i> </span><span arial="" style="font-family:">involvement in <i>Pa</i> </span><span arial="" style="font-family:">persister cell formation</span><span arial="" style="font-family:">. Toxicity and the PaFicT active site were examined by overexpression of wild-type and mutant protein variants. Antibiotic tolerance of PaFicT-induced <i>Pa </i>persister cells, was measured by minimum inhibitory concentration (MIC) analysis and compared to parental mostly non-persister populations. Deletion of <i>paficT</i> resulted in a 7.2-fold reduction in<i> </i>persister cell formation, which was fully complemented by re-insertion of the gene. Expression of PaFicT significantly increased persister cell formation by 5.9-fold, and this phenotype required a functional FIC active site motif. Unlike growing cell populations, PaFicT-induced persister cells were unaffected by 4 h treatment with 10 &times; MIC meropenem and showed an increased survival of 6.2 &times; 10⁵-fold to tobramycin under the same conditions. Alternatively, survival of both persisters and parental, mostly non-persister, populations were below detectable levels following amikacin treatment.&nbsp;</span></span><span style="line-height:200%"><span arial="" style="font-family:">Results indicate a potential major involvement of PaFicT in </span><i><span arial="" style="font-family:">Pa</span></i><i> </i><span arial="" style="font-family:">persister cell formation and multidrug tolerance. </span><b><span style="font-family:"Arial","sans-serif""></span></b></span><br> &nbsp; Drug resistance, Pseudomonas, cystic fibrosis 277 287 http://ijmcmed.org/browse.php?a_code=A-10-4499-1&slc_lang=en&sid=1 Dawson Fogen dfogen@hawaii.edu 100319475328460023519 100319475328460023519 Yes Department of Microbiology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA.