ENTEROBACTERIACAE, PRODUCING ESBLS AND METALLO-β-LACTAMASE NDM-1, ISOLATED IN HOSPITALS OF BALTIC REGION COUNTRIES

Abstract. We studied the prevalence of K. pneumoniae and E. coli resistance to extended spectrum cephalosporins and carbapenems, isolated from patients of eight hospitals in St-Petersburg from January to May, 2012. Prevalence of cephalosporin resistant isolates varied in different hospitals: E. coli – from 7,8 to 50%, K. pneumoniae – from 25,4 to 88,4%. Isolates produced extended spectrum beta-lactamases СТХ-М, mainly СТХ-М-1, also СТХ-М-2 and СТХ-М-9. Twenty two carbapenem-resistant K. pneumoniae strains (also resistant to other antimicrobials) were isolated in three hospitals. MALDI-TOF MS showed that carbapenem resistance was caused by carbapenemase. Carbapenemases of all isolates belonged to metallo-β-lactamases according to results of the ROSCO Diagnostica tests. The gene coding production of New Delhi metallo-β-lactamase (blaNDM-1) were detected in all strains. Our data confirmed that the main cephalosporin resistance mechanism of E. coli и K. pneumoniae in Baltic region (including Russia, St-Petersburg) is CTX-M-1 production. For the first time in Russia K. pneumoniae strains  producing metallo-β-lactamases NDM-1 were isolated in several hospitals of St-Petersburg

Topological constraints of structural elements in regulation of catalytic activity in HDV-like self-cleaving ribozymes

Self-cleaving ribozymes fold into intricate structures, which orient active site groups into catalytically competent conformations. Most ribozyme families have distinct catalytic cores stabilized by tertiary interactions between domains peripheral to those cores. We show that large hepatitis delta virus (HDV)-like ribozymes are activated by peripheral domains that bring two helical segments, P1 and P2, into proximity – a “pinch” that results in rate acceleration by almost three orders of magnitude. Kinetic analysis of ribozymes with systematically altered length and stability of the peripheral domain revealed that about one third of its free energy of formation is used to lower an activation energy barrier, likely related to a rate-limiting conformational change leading to the pre-catalytic state. These findings provide a quantitative view of enzyme regulation by peripheral domains and may shed light on the energetics of allosteric regulation