Corynebacterium pseudodiphteriticum has been considered a very
infrequent respiratory pathogen. We report three cases of pneumonia
due to C. pseudodiphteriticum, describing their clinical and microbiological
features. There were two patients with pre-existing chronic
respiratory disease, one of their with steroidal therapy, and other
associated with endotracheal intubation. The diagnostic was made by
Gram stain and quantitative cultures from respiratory tract specimens.
All patients were cured after treatment with amoxicillin-clavulanate,
ceftriaxone and vancomycin respectively. C. pseudodiphteriticum
must be consider as a possible causal agent of pneumonia in
patients with underlying respiratory disease or endotracheal intubation.
Antimicrobial susceptibility testing of C. pseudodiphteriticum
may be useful for correct treatment of infected patients, but beta-lactam
antibiotics are an appropriate therapeutic option against this
bacteria.

Strains cultivated had a pattern of susceptibility to antimicrobials common, with in vitro resistance to macrolides and lincosamides and, on two occasions, also to ciprofloxacin, being sensitive to penicillin, cephalosporins and glycopeptides. Possibly in cases 1 and 3, treatment with levofloxacin favored selection in the bronchial tree of C. pseudodiphteriticum resistant to quinolones. In the three reported cases the therapeutic response was good after adjusting the treatment to the antibiogram, using beta-lactams in the cases 1 and 2 and vancomycin in the third.

In conclusion, the possibility of infection should be considered
respiratory infection by C. pseudodiphteriticum especially in those
patients with chronic respiratory disease,
some type of immune compromise or have undergone
repeated endotracheal intubation. Gram stain of the
respiratory samples will initially guide the diagnostic suspicion
and treatment, confirming with quantitative cultures
and the study of antimicrobial susceptibility of the isolate.
In any case, given the sensitivity profile so
constant offered by C. pseudodiphteriticum, beta-lactams
as 3rd generation cephalosporins and amoxicillin-clavulanate
seem to be the most appropriate therapeutic group to treat
infections caused by this bacteria.