scholarly journals Nucleophilic re-activation of the PC1 β-lactamase of Staphylococcus aureus and of the dd-peptidase of Streptomyces R61 after their inactivation by cephalosporins and cephamycins

1987 ◽  
Vol 246 (3) ◽  
pp. 651-658 ◽  
Author(s):  
W S Faraci ◽  
R F Pratt
Keyword(s):  
Staphylococcus Aureus ◽  
Strong Support ◽  
Model Systems ◽  
Elimination Reaction ◽  
Beta Lactam ◽  
Beta Lactamases ◽  
Processing Enzymes ◽  
Leaving Group ◽  
Leaving Groups ◽  
Kinetics Of

It has been shown previously [Faraci & Pratt (1985) Biochemistry 24, 903-910; (1986) Biochemistry 25, 2934-2941; (1986) Biochem. J. 238, 309-312] that certain beta-lactam-processing enzymes form inert acyl-enzymes with cephems that possess good leaving groups at the C-3′ position. These inert species arise by elimination of the leaving group from the initially formed and more rapidly hydrolysing acyl-enzyme, which has the ‘normal’ cephalosporoate structure. The present paper shows that a strong nucleophile, thiophenoxide, can catalyse the re-activation of three examples of these inert acyl-enzymes, generated on reaction of cephalothin and cefoxitin with the PC1 beta-lactamase of Staphylococcus aureus and of cephalothin with D-alanyl-D-alanine transpeptidase/carboxypeptidase of Streptomyces R61. In view of the reversibility of the elimination reaction, demonstrated in model systems [Pratt & Faraci (1986) J. Am. Chem. Soc. 108, 5328-5333], this catalysis is proposed to arise through nucleophilic addition to the exo-methylene carbon atom of the inert acyl-enzyme to regenerate a more rapidly hydrolysing normal cephalosporoate. Strong support for this scenario was obtained through comparison of the kinetics of the catalysed re-activation reaction with those of turnover of the relevant 3′-thiophenoxycephems, thiophenoxycephalothin and thiophenoxycefoxitin. The enzymes appear to stabilize the products of the elimination reaction with respect to the normal cephalosporoate, but more strongly to destabilize the transition states. The effects of other nucleophiles, including cysteine, glycine amide and imidazole, on the above enzymes and on other beta-lactamases can be understood in terms of the model reaction kinetics and thermodynamics.

The Formation of Alkenes by the Thermal Elimination Reaction of N-Methyl-4-alkoxypyridinium Iodides. II. An Investigation of the Mechanism

1972 ◽  
Vol 50 (8) ◽  
pp. 1188-1191
Author(s):  
George H. Schmid ◽  
Aaron W. Wolkoff
Keyword(s):  
Elimination Reaction ◽  
Product Composition ◽  
Thermal Elimination ◽  
Leaving Group ◽  
Elimination Reactions ◽  
Leaving Groups

A comparison of the products from elimination reactions of a number of compounds containing various leaving groups with those containing the N-methyl oxypyridinium leaving group suggests that the elimination is not occurring by means of a simple E1 mechanism. Changing the anion of the salt from iodide to methyl-sulphate and tetrafluoroborate affects the product composition indicating that the anion is taking part in the reaction. The mechanism of this reaction appears to be on the E1-E2 borderline.

scholarly journals Kinetics of penicillin binding to penicillin-binding proteins of Staphylococcus aureus

1994 ◽  
Vol 301 (1) ◽  
pp. 139-144 ◽  
Author(s):  
H F Chambers ◽  
M J Sachdeva ◽  
C J Hackbarth
Keyword(s):  
Staphylococcus Aureus ◽  
Binding Proteins ◽  
Beta Lactam ◽  
Penicillin Binding Proteins ◽  
Structural Modifications ◽  
Drug Concentrations ◽  
Lactam Antibiotic ◽  
Resistant Strains ◽  
The Relationship ◽  
Kinetics Of

Reduced affinity of penicillin-binding proteins (PBPs) for binding penicillin has been proposed as a mechanism of beta-lactam antibiotic resistance in staphylococci. Penicillin binding by PBPs of three penicillin-susceptible and two penicillin-resistant strains of Staphylococcus aureus was studied in kinetic assays to determine rate constants, drug concentrations at which PBPs were bound and the relationship between concentrations that bound PBPs and concentrations that inhibited bacterial growth. PBPs 1 and 2 of the resistant strains exhibited slower acylation and more rapid deacylation than susceptible strains. In contrast PBP 4, a naturally low-affinity PBP, was modified such that it exhibited a lower rate of deacylation. The concentrations of penicillin at which modified PBPs were bound correlated with concentrations that inhibited growth of the resistant strains. Acquisition of penicillin resistance in these strains of S. aureus results, at least in part, from structural modifications affecting binding of multiple PBPs and appears to include recruitment of a non-essential PBP, PBP 4.

scholarly journals The kinetics of non-stoichiometric bursts of β-lactam hydrolysis catalysed by class C β-lactamases

1993 ◽  
Vol 295 (1) ◽  
pp. 295-304 ◽  
Author(s):  
M G P Page
Keyword(s):  
Beta Lactam ◽  
Beta Lactamases ◽  
Beta Lactam Antibiotics ◽  
Steady State Rate ◽  
State Rate ◽  
Rate Of Hydrolysis ◽  
Class C ◽  
Burst Kinetics ◽  
Kinetics Of ◽  
Hydrolysis Of

Class C beta-lactamases from Pseudomonas aeruginosa and several species of the Enterobacteriaceae have been observed to undergo a rapid burst in hydrolysis of beta-lactam antibiotics before relaxation to a steady-state rate of hydrolysis. The amplitude of the burst corresponds to the hydrolysis of between 1 and 10,000 mol of the substrate per mol of enzyme. The decay of the rate of hydrolysis in the burst phase comprises two exponential reactions, which indicates that there are three different reactive states of the enzymes. Examination of the kinetics of acylation by slowly reacting beta-lactams suggests that there are three forms of the free enzyme in slow equilibrium. Thus it would appear that the burst kinetics exhibited by class C enzymes can be attributed to redistribution of the enzyme between different conformations induced by the reaction with substrate.

scholarly journals Staphylococcus aureus methicillin-resistance mechanisms

2008 ◽  
Vol 65 (5) ◽  
pp. 377-382
Author(s):  
Ljiljana Petrovic-Jeremic ◽  
Nada Kuljic-Kapulica ◽  
Veljko Mirovic ◽  
Branislava Kocic
Keyword(s):  
Staphylococcus Aureus ◽  
Methicillin Resistance ◽  
Resistance Mechanisms ◽  
Dilution Method ◽  
Agar Dilution Method ◽  
Beta Lactam ◽  
Disk Diffusion Test ◽  
Beta Lactamases ◽  
Significant Difference ◽  
The Difference

Background/Aim. In many hospitals in the world and in our country, the spread of methicillin-resistant Staphylococcus aureus (MRSA) is so wide that nowdays vancomycin is recommended for empiric treatment of staphylococcal life threatening infections (sepsis, pneumonia) instead of beta-lactam antibiotics. The aim of this study was to determine the production of beta-lactamases in hospital and community isolates of staphyloococus aureus, i. e. hospital associated MRSA (HA-MRSA) and community associated MRSA (CA-MRSA), the presence of homogeneous and heterogeneous type of methicillin resistance, and border-line resistance in Staphylococcus aureus (BORSA). The aim of this study was also to determine if there was a statistically significant difference between mechanisms of resistance in HA-MRSA and CA-MRSA. Methods. A total 216 clinical Staphylococcus aureus isolates from the General Hospital in the town of Cuprija and 186 ambulance Staphylococcus aureus isolates from the community were examined for the presence of methicillin-resistance using disk-diffusion test with penicillin disk (10 ij), oxacillin disk (1 ?g) and cefoxitin disk (30 ?g). Betalactamases production was detected by nitrocefin disk and betalactamase tablets. Determination of oxacillin minimum inhibitory concentracion (MIC) was done by agar-dilution method. Results. The prevalence of HA-MRSA was 57.4%, and CA-MRSA was 17.7% (p < 0.05). There was a higher rate of heterogeneous type of resistance among clinical MRSA isolates (11.1%) compared with ambulance ones (3.8%) (p < 0.05). The rates of beta-lactamases production were similar among hospital associated isolates (97.5%), as well as in the community associated isolates (95.5%) (p > 0.05). There were 4.6 % of BORSA hospital isolates and 3.3 % of BORSA ambulance isolates (p > 0.05). Conclusion. The frequency of MRSA isolates in hospital was significantly higher than in community, as well as the heterogeneous type of resistance. The frequency of BORSA isolates and production of betalactamases were higher among hospital Staphylococcus aureus isolates, but the difference is not significant.

scholarly journals Kinetic studies and predictions on the hydrolysis and aminolysis of esters of 2-S-phosphorylacetates

2010 ◽  
Vol 6 ◽  
pp. 732-741 ◽  
Author(s):  
Milena Trmčić ◽  
David R W Hodgson
Keyword(s):  
Reaction Times ◽  
Kinetic Studies ◽  
Cross Linking ◽  
Significant Difference ◽  
Leaving Group ◽  
Leaving Groups ◽  
Phosphoryl Groups ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Acid Esters

Background: Heterobifunctional cross-linking agents are useful in both protein science and organic synthesis. Aminolysis of reactive esters in aqueous systems is often used in bioconjugation chemistry, but it must compete against hydrolysis processes. Here we study the kinetics of aminolysis and hydrolysis of 2-S-phosphorylacetate ester intermediates that result from displacement of bromide by a thiophosphate nucleophile from commonly used bromoacetate ester cross-linking agents. Results: We found cross-linking between uridine-5′-monophosphorothioate and D-glucosamine using N-hydroxybenzotriazole and N-hydroxysuccinimde bromoacetates to be ineffective. In order to gain insight into these shortfalls, 2-S-(5′-thiophosphoryluridine)acetic acid esters were prepared using p-nitrophenyl bromoacetate or m-nitrophenyl bromoacetate in combination with uridine-5′-monophosphorothioate. Kinetics of hydrolysis and aminolysis of the resulting p- and m-nitrophenyl 2-S-(5′-thiophosphoryluridine)acetates were determined by monitoring the formation of phenolate ions spectrophotometrically as a function of pH. The p- and m-nitrophenyl 2-S-(5′-thiophosphoryluridine)acetates showed similar reactivity profiles despite the significant difference in the pK aH values of their nitrophenolate leaving groups. Both were more reactive with respect to hydrolysis and aminolysis in comparison to their simple acetate progenitors, but their calculated selectivity towards aminolysis vs hydrolysis, while reasonable, would not lead to clean reactions that do not require purification. Extrapolations of the kinetic data were used to predict leaving group pK a values that could lead to improved selectivity towards aminolysis while retaining reasonable reaction times. Conclusions: Both p- and m-nitrophenyl 2-S-(5′-thiophosphoryluridine)acetates show some selectivity towards aminolysis over hydrolysis, with the m-nitrophenolate system displaying slightly better selectivity. Extrapolation of the data for hydrolysis and aminolysis of these esters suggests that the use of readily accessible trifluoroethyl 2-S-(5′-thiophosphoryluridine)acetate with a leaving group pK aH of 12.4 should afford better selectivity while maintaining reasonable reaction times. Kinetically, p- and m-nitrophenyl 2-S-(5′-thiophosphoryluridine)acetates show similar properties to o-nitrophenyl 2-S-ethylacetate, and show no evidence for intramolecular catalysis of hydrolysis or aminolysis by the phosphoryl groups.

Molecular Characterization of Methicillin Resistant and Extended Spectrum β-Lactamase Staphylococcus aureus Isolated from Burn Patients

2020 ◽  
pp. 145-151
Author(s):  
Shawnm Ahmed Aziz
Keyword(s):  
Staphylococcus Aureus ◽  
Methicillin Resistance ◽  
Vancomycin Resistance ◽  
World Health ◽  
Molecular Technique ◽  
Burn Patients ◽  
Beta Lactamase ◽  
Beta Lactam ◽  
Extended Spectrum Beta Lactamase ◽  
Extended Spectrum

Antibiotic resistance has become a major world health challenge and has limited the ability of physician's treatment. Staphylococcus aureus the most notorious pathogens causes morbidity and mortality especially in burn patients. However, Staphylococcus aureus rapidly acquired resistance to multiple antibiotics. Vancomycin, a glycopeptide antibiotic remains a drug of choice for treatment of severe Methicillin Resistance S. aureus infections. This study aimed to detect the emergence of beta-lactam and glycopeptide resistance genes. 50 clinical specimens of S. aureus collected from burn patients in burn and plastic surgery units in Sulaimani-Iraq city. All specimens were confirmed to be positive for S. aureus. All the isolates were assessed for their susceptibility to different antibiotics depending on NCCL standards, followed by Extended Spectrum Beta Lactamase detection by double disk diffusion synergy test. The production of β- lactamases was evaluated in the isolated strains by several routine methods and polymerase chain reaction. Among the isolates 94% were Methicillin resistance and 34.28% were Extended Spectrum Beta Lactamase producer. PCR based molecular technique was done for the bla genes related to β- lactamase enzymes by the specific primers, as well as genes which related to reduced sensitivity to Vancomycin were detected. The results indicated that all isolated showed the PBP1, PBP2, PBP3, PBP4, trfA and trfB, graSR, vraS except the vraR gene and the prolonged therapy of Methicillin resistance infection with teicoplanin have been associated with progress of resistance and the rise of tecoplanin resistance may be a prologue to evolving Vancomycin resistance. In conclusion, beta-lactam over taking can rise Vancomycin- Intermediate S. aureus strains leading to appearance of Vancomycin resistance although the treatment of Vancomycin resistant infections is challenging.

The effect of steric size of leaving group on rates of the competing syn- and anti-pathways in biomolecular elimination

1980 ◽  
Vol 45 (8) ◽  
pp. 2171-2178
Author(s):  
Jiří Závada ◽  
Magdalena Pánková
Keyword(s):  
Comparative Analysis ◽  
Homologous Series ◽  
Leaving Group ◽  
Leaving Groups

Approximate rates of the competing syn- and anti-pathways have been determined in t-C4H9OK-t-C4H9OH promoted elimination from two homologous series of tosylates: I-OTs trans-III (R = H, CH3, C2H5, n-C3H7, i-C3H7, t-C4H9) and II-OTs trans-IV (R = CH3, C2H5, n-C3H7, i-C3H7, t-C4H9). A comparison has been made with rates of the same processes in the (+) elimination of the corresponding trimethylammonium salts I-N(CH3)3 trans-III and (+) II-N(CH3)3 trans-IV. The title effect is demonstrated by a comparative analysis of the rate patterns obtained for the two leaving groups.

scholarly journals Predominance of PVL-negative community-associated methicillin-resistant Staphylococcus aureus sequence type 8 in newly diagnosed HIV-infected adults, Tanzania

2021 ◽  
Author(s):  
Joel Manyahi ◽  
Sabrina J. Moyo ◽  
Said Aboud ◽  
Nina Langeland ◽  
Bjørn Blomberg
Keyword(s):  
Staphylococcus Aureus ◽  
Hiv Infection ◽  
Diffusion Method ◽  
Molecular Characteristics ◽  
People Living With Hiv ◽  
Newly Diagnosed ◽  
Beta Lactam ◽  
Disk Diffusion Method ◽  
Methicillin Resistant ◽  
Inducible Clindamycin Resistance

AbstractDifficult-to-treat infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are of concern in people living with HIV infection as they are more vulnerable to infection. We aimed to identify molecular characteristics of MRSA colonizing newly diagnosed HIV-infected adults in Tanzania. Individuals newly diagnosed with HIV infection were recruited in Dar es Salaam, Tanzania, from April 2017 to May 2018, as part of the randomized clinical trial CoTrimResist (ClinicalTrials.gov identifier: NCT03087890). Nasal/nasopharyngeal isolates of Staphylococcus aureus were susceptibility tested by disk diffusion method, and cefoxitin-resistant isolates were characterized by short-reads whole genome sequencing. Four percent (22/537) of patients carried MRSA in the nose/nasopharynx. MRSA isolates were frequently resistant towards gentamicin (95%), ciprofloxacin (91%), and erythromycin (82%) but less often towards trimethoprim-sulfamethoxazole (9%). Seventy-three percent had inducible clindamycin resistance. Erythromycin-resistant isolates harbored ermC (15/18) and LmrS (3/18) resistance genes. Ciprofloxacin resistance was mediated by mutations of the quinolone resistance-determining region (QRDR) sequence in the gyrA (S84L) and parC (S80Y) genes. All isolates belonged to the CC8 and ST8-SCCmecIV MRSA clone. Ninety-five percent of the MRSA isolates were spa-type t1476, and one exhibited spa-type t064. All isolates were negative for Panton-Valentine leucocidin (PVL) and arginine catabolic mobile element (ACME) type 1. All ST8-SCCmecIV-spa-t1476 MRSA clones from Tanzania were unrelated to the globally successful USA300 clone. Carriage of ST8 MRSA (non-USA300) was common among newly diagnosed HIV-infected adults in Tanzania. Frequent co-resistance to non-beta lactam antibiotics limits therapeutic options when infection occurs.

Copper(II) complexes with tridentate halogen‐substituted Schiff base ligands: synthesis, crystal structures and investigating the effect of halogenation, leaving group and ligand flexibility on antiproliferative activities

2021 ◽  
Author(s):  
Nazanin Kordestani ◽  
Hadi Amiri Rudbari ◽  
Alexandra R Fernandes ◽  
Luís R Raposo ◽  
André Luz ◽  
...  
Keyword(s):  
Schiff Base ◽  
Anticancer Activity ◽  
Crystal Structures ◽  
Copper Complexes ◽  
Schiff Base Ligands ◽  
Leaving Group ◽  
Leaving Groups ◽  
Tridentate Schiff Base ◽  
Antiproliferative Activities

To investigate the effect of different halogen substituents, leaving groups and the flexibility of ligand on the anticancer activity of copper complexes, sixteen copper(II) complexes with eight different tridentate Schiff-base...

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