Bloodstream Infections by AmpC-Producing Enterobacterales: Risk Factors and Therapeutic Outcome.

Bloodstream infections associated with AmpC-producing Enterobacterales are severe medical conditions which, without prompt and effective treatment, may have dire ramifications. This study aimed to assess whether certain comorbidities and previous surgical procedures coincide with resistance determinants of AmpC-producing Enterobacterales associated with bloodstream infections. Antibiotic resistance patterns and therapy outcome were also determined. The patients' data obtained revealed that the prevalence of recent surgical procedures, solid organ tumors, metabolic diseases, kidney and liver failure, and hematological malignancies do not differ between resistant and susceptible isolates of AmpC-producing Enterobacterales. Furthermore, no difference was reported in mortality rates. Regarding antibiotic resistance, 34.52% of isolates were confirmed to be resistant (AmpC hyperproduction, ESBL, or carbapenemase). More than one in five AmpC hyperproducers were reported amid Providencia spp., K. aerogenes, E. cloacae, and C. freundii. strains. Carbapenemases were mostly noted in Providencia spp. followed by M. morganii and K. aerogenes strains. Serratia marcescens had the highest proportion of ESBLsof ESBLs. Resistance to expanded-spectrum cephalosporins of Providencia spp. and K. aerogenes strains exceeded 50%, and resistance to meropenem over 10% was observed only in C. freundii strains. Enterobacterales' ever-growing resistance to antibiotics is becoming quite a challenge for clinicians and new treatment options are required.

Emergence and Spread of Enterobacterales with Multiple Carbapenemases after COVID-19 Pandemic.

Resistance to carbapenems in Enterobacterales has become a matter of the highest concern in the last decade. Recently, Enterobacterales harboring multiple carbapenemases were detected in three hospital centers in Croatia and in the outpatient setting, posing a serious therapeutic challenge for clinicians. In this study, we analyzed eight Klebsiella pneumoniae and two Enterobacter cloacae complex isolates with multiple carbapenemases, with regard to antibiotic susceptibility, ß-lactamase production and plasmid content. The isolates demonstrated uniform resistance to amoxicillin/clavulanate, piperacillin/tazobactam, cefuroxime, ceftazidime, cefotaxime, ceftriaxone and ertapenem. Among novel ß-lactam/inhibitor combinations, ceftazidime/avibactam exhibited moderate activity, with 50% of isolates susceptible. All isolates demonstrated resistance to imipenem/cilastatin/relebactam, and all but one to ceftolozane/tazobactam. Four isolates exhibited a multidrug-resistant phenotype (MDR), whereas six were allocated to an extensively drug-resistant phenotype (XDR). OKNV detected three combinations of carbapenemases: OXA-48+NDM (five isolates), OXA-48+VIM (three isolates) and OXA-48+KPC (two isolates). Inter-array testing identified a wide variety of resistance genes for ß-lactam antibiotics: blaCTX-M-15, blaTEM, blaSHV, blaOXA-1, blaOXA-2, blaOXA-9, aminoglycosides: aac6, aad, rmt, arm and aph, fluoroquinolones: qnrA, qnrB and qnrS, sulphonamides: sul1 and sul2 and trimethoprim: dfrA5, dfrA7, dfrA14, dfrA17 and dfrA19. mcr genes were reported for the first time in Croatia. This study demonstrated the ability of K. pneumoniae and E. cloacae to acquire various resistance determinants under the selection pressure of antibiotics widely used during the COVID-19 pandemic. The novel inter-array method showed good correlation with OKNV and PCR, although some discrepancies were found.

FALSE POSITIVE PHENOTYPIC DETECTION OF METALLO-BETA-LACTAMASES IN ACINETOBACTER BAUMANNII.

Phenotypic detection of metallo-ß-lactamases (MBLs) in Acinetobacter (A.) baumannii is a serious challenge to clinical microbiologists. MBLs are inhibited by metal chelators such as ethylenediaminetetraacetic acid) (EDTA). Production of MBLs cannot be recognized based on resistance phenotype. Therefore, phenotypic tests using EDTA are recommended. The aim of this study was to investigate the sensitivity and specificity of inhibitor based tests (EDTA) for detection of MBL. A total of 172 A. baumannii strains (123 carbapenemase positive and 49 carbapenemase negative) were analyzed. Phenotypic detection of MBLs was performed by the combined disk test with EDTA (CDT-EDTA) and EPI-dilution test (EPI-DT). Both tests were positive in all 11 isolates possessing VIM-1 MBL, showing 100% sensitivity. However, false positive results were observed in strains with class D carbapenemases using both tests, i.e. all OXA-23 and OXA-24/40 producing organisms and most OXA-58 positive strains (77% with CDT-EDTA vs. 65% with EPI-DT). False positive results can occur because oxacillinases are converted to a less active state in the presence of EDTA, leading to augmentation of the inhibition zone around the carbapenem disk or reduction of carbapenem minimum inhibitory concentrations. This study showed high sensitivity but low specificity of phenotypic methods in the detection of MBLs.

In vitro synergy and postantibiotic effect of colistin combinations with meropenem and vancomycin against Enterobacteriaceae with multiple carbapenem resistance mechanisms.

AIM: The aim of the study was to determine in vitro synergy and postantibiotic effect of colistin alone and combined with meropenem or vancomycin against Enterobacteriaceae producing multiple carbapenemases; combinations of two metallo-ß-lactamases (MBL) or MBL with OXA-48. Colistin-resistant strain positive for OXA-48 was also included in the study. METHODS: The antibiotic susceptibility was tested by broth microdilution method. Synergy was tested by chequerboard, time-kill and 2-well method. PAE was determined by viable counting. RESULTS: The chequerboard analysis revealed synergy for colistin combination with meropenem in all isolates with FICI values ranging from 0.12 to 0.24. FICI values for combinations with vancomycin were below 0.5 indicating synergy in two out of four isolates. K. pneumoniae 609815 positive for OXA-48 and colistin resistant showed the most pronounced and consistent synergy effect with meropenem in both chequerboard and time-kill method. Synergy effect in time-kill curves, was observed for K pneumoniae 145846 with two MBLs and colistin resistant K. pneumoniae 609815 positive for OXA-48, with both combinations including meropenem and vancomycin. Colistin alone exhibited short postantibiotic effect (PAE) against all tested isolates. Meropenem markedly prolonged the PAE in two isolates in contrast to vancomycin which did not demonstrate significant effect on the duration of PAE. CONCLUSIONS: The synergy effect and the duration of PAE was strain and antibiotic dependent but not related to the resistance gene content.