Isolation of a Capnophilic and an Extended-Spectrum-β-Lactamase-Producing Proteus mirabilis Isolate with Inability to Grow under pH-Indicator Dyes from the Urine of an Octogenarian Male-Patient with Acute Pyelonephritis.

A capnophilic Gram-negative rod was recovered from the urine of an octogenarian male patient with acute pyelonephritis. The isolate also demonstrated to produce CTX-M-2-type- extended-spectrum-β-lactamase. Interestingly, the isolate failed to grow on modified Drigalski (BTB) and MacConkey agars even in the CO2 -enriched atmosphere. The investigation of this phenomenon revealed that the pH-indicator dyes, bromothymol-blue and/or crystal-violet, incorporated into the agars should serve to inhibit the growth of the isolate. Although routine identification with Vitek® 2 Compact systems was unsuccessful, the isolate was finally identified as Proteus mirabilis by sequencing the 16S rRNA genes and by the MALDI-TOF MS analysis. The carbonic anhydrase (CA) region, responsible for the CO2 requirement, could not be amplifiable from approximately 2,000bp upstream to 2,000bp downstream. This could possibly be ascribed to the large-scale deletion or mutation of the DNA sequences containing the CA gene region. In fact, no revertant with ability to grow under the atmosphere without addition of CO2 emerged. However, the revertant, capable of growing both on BTB and MacConkey agars, emerged at frequencies less than 10-9 . Therefore, the genes responsible for the highly sensitive reactions to pH-indicator dyes might not be linked to those of the CA genes.