P1473 Wild-type Klebsiella pneumoniae contains a persister subpopulation causing heteroresistance to carbapenems and some other beta-lactams Julia Guzmán-Puche *1, Cristina Elias-Lopez1, Carmen María Medina Ruíz1, Luis Martinez-Martinez1

1 Microbiology Unit, Reina Sofia University Hospital-IMIBIC-University of Córdoba, Córdoba, Spain Background: Heteroresistance (HR) can be related to the selection of resistant mutants (stable increment of the minimum-inhibitory-concentration, MIC) or the presence of persisters (organisms can survive the lethal action of antibiotics without a MIC change). HR has been more often studied in multiresistant organisms. Here, we have evaluated if Klebsiella pneumoniae strains resistant only to aminopenicillins (wild-type; Wt-Kpn) express HR to antibiotics of clinical interest. Materials/methods: Eight Wt-Kpn strains isolated from clinical samples of different patients have been evaluated. HR to 16 antibiotics was tested by disk diffusion, using inocula prepared with bacteria grown for 4h, 24h, 48h, 3 and 5 days on blood agar and in tryptic soy broth. HR was defined when colonies appeared inside the inhibition zones; up to 10 of those colonies were cultured in antibiotic-free medium and tested again by disk diffusion to classify them as stable mutants [ decreased (≥5mm) inhibition zone] or persisters (<5mm of the inhibition zone). A population-analysis-profile (PAP) was performed with imipenem and meropenem for 6 of the tested isolates. Results: The 8 isolates corresponded to ST29, ST34, ST875, ST1825, ST2436, ST1628, ST3477 and ST3478. HR to imipenem, meropenem, ertapenem, mecillinam (PBP2 inhibitor), ceftazidime, cefepime, amoxicillin/clavulanic-acid and ceftazidime/avibactam was detected when using inocula of bacteria grown in solid medium for 48h-3d-5d. With bacteria from liquid medium (any time) or from solid medium (4-24h), HR was only observed with imipenem and ceftazidime. HR to imipenem and meropenem was documented in the 6 studied strains by PAP, with colonies (always persisters) growing up to 32-64xMIC (imipenem) and 1-8xMIC (meropenem). HR was never detected with aztreonam (PBP3 inhibitor), cefotaxime, ceftriaxone, amikacin, gentamicin and ciprofloxacin. Conclusions: Wt-Kpn can generate a subpopulation of persisters to carbapenems, most cephalosporins and mecillinam, but not to aztreonam, cefotaxime, ceftriaxone, aminoglycosides or ciprofloxacin. Detection of those persisters depends on the bacteria incubation time and the type of culture medium. Differences in beta-lactams behavior suggests that PBPs (but not SHV-1/11) may have a relevant role in HR due to the emergence of persisters.

3337 48H PLACA-LIQUIDO.jpg Image. Heteroresistance detection in Kpn-Wt_HURS_3337(ST3477). IMI-imipenem, ETP-ertapenem, MER- meropenem, FOT-fosfomycin, FEP-cefepime, CTX-cefotaxime, CIP-ciprofloxacin, Ak-amikacin, NA-nalidixic acid, CN-gentamicin.

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