Antibiotic resistance in Enterobacter cloacae strains with derepressed/partly derepressed/inducible AmpC and extendedspectrum beta-lactamases in Zenica-Doboj Canton, Bosnia and Herzegovina
Abstract
This is an accepted article with a DOI pre-assigned that is not yet published.
Aim: To investigate the prevalence of derepressed/partly derepressed/inducible and ESBL/AmpC-producing Enterobacter cloacae isolates and treatment options for infections associated with those isolates.
Methods: Antibiotic susceptibility was determined by disc diffusion and broth microdilution according to CLSI guidelines. Doubledisk synergy test (DDST) was performed in order to screen for ESBLs and combined disk test with phenylboronic acid to detect AmpC ?-lactamases. PCR was used to detect bla ESBL /bla carb genes. Genetic relatedness of the strains was determined by pulsed-fieldgel-electrophoresis (PFGE).
Results: Among 14 isolates with the ESBL positive E. cloaceae producing isolates, four (28.6%), nine (64.3%) and one (7.1%) isolates were derepressed/partly derepressed and inducible AmpC producers. Eleven (out of 14) isolates were resistant to cefotaxime, ceftazidime, ceftriaxone, aminoglycosides and fluoroquinolones. All isolates were susceptible to imipenem and meropenem, 79% to cefepime. Five (out of 14; 35.7%) isolates (four derepressed and one inducible AmpC carrying E. cloaceae) were negative in phenotypic test for ESBLs, but positive for broad spectrum TEM-1 ?-lactamase. One (out of four derepressed) also produced CMY-2 ?-lactamase. Four (out of nine) partly derepressed isolates were positive with the DDST, but did not yield PCR products with primers targeting TEM, SHV and CTX-M beta-lactamases. Four positive partly derepressed isolates carried a bla CTX-M-1 gene, two bla OXA-1 one bla CTX-M-15, OXA-1 and one bla CTX-M-28, OXA-1 (n=1).
Conclusion: Microbiology laboratories must be able to detect and recognize AmpC-carrying isolates in a timely manner, especially those that are falsely susceptible in vitro to drugs that may be considered for therapy of infected patients.
Keywords: chromosomal AmpC, ESBL, antibiotic resistance