Identification of Functional Regulatory Residues of the β -Lactam Inducible Penicillin Binding Protein in Methicillin-Resistant Staphylococcus aureus

Direct Conjugation of Penicillins and Cephalosporins with Proteins for Receptor Assays of Beta-Lactam Antibiotics

Abstract—

Fifteen protein conjugates of penicillins and cephalosporins containing amino- and/or carboxylic groups in the initial structures have been synthesized in the reactions with human serum albumin or ovalbumin using 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) or a combination of EDC and N-hydroxysulfosuccinimide at various ratios of the base reagents. A comparative study of conjugates composition and properties has been carried out by UV spectroscopy, mass spectrometry and a ligand-receptor assay. It was shown that the antibiotic residue content of the macromolecules obtained varied from 1 to 22, the beta-lactam cycle remained intact assuring specific interactions of the conjugates with a penicillin-binding protein. In two developed models of receptor bioanalytic systems, an ampicillin conjugate onto a solid phase binds to penicillin-binding protein complexed with a monoclonal antibody, which was detected by an immunoenzyme label in microplate wells or gold nanoparticles on test strips. Conjugated ampicillin binding to the receptor was competitively inhibited by beta-lactam antibiotics added to the liquid phase, and analytical sensitivities relative to penicillin G were 0.05 and 1 ng/mL for microplate and receptor chromatographic systems, respectively.

Comparative genomic analyses of Bacillus subtilis strains to study the biochemical and molecular attributes of nattokinases

The present research work explores the Nattokinase (NK) producing capacity of five Bacillus subtilis strains (MTCC 2616, MTCC 2756, MTCC 2451, MTCC 1427, and MTCC 7164) using soybean varieties as substrate under solid-state fermentation conditions. Subsequently, the biochemical attributes of NKs were analyzed. Soybean variety didn't affect the production of NK to a significant extent; however, the five strains differed substantially for their NK producing capacity. NK produced by MTCC 2451 (R3) showed a low Kmvalue implying its higher specificity for fibrin but this strain (MTCC 2451) didn't produce NK in sufficient quantity. The low Km of MTCC 2451 NK implicates its potential candidature for treating blood clots in cardiovascular patients. The NK produced by MTCC 2616 (R1) was produced in sufficient quantity and showed good fibrin dissolving potential. The aprN of MTCC 2616 substantially varied from the other four strains. The aprN of MTCC 2756 (R2), MTCC 2451 (R3), MTCC 1427 (R4), and MTCC 7164 (R5) shared > 99% sequence identity, but the encoded NKs had significant variations in their Km values. The biochemical-molecular analyses indicate the co-presence of three critical residues (Thr130, Asp140, and Tyr217) as a quintessential attribute in determining the low Km of NK enzymes, and the absence of any one of the three critical residues may affect (highly increase) the Km.

Impact of Mutation on the Structural Stability and the Conformational Landscape of Inhibitor-Resistant TEM β-Lactamase: A High-Performance Molecular Dynamics Simulation Study

Gain-of-function mutations and structural adjustment toward β-lactamase inhibitors in the TEM-type β-lactamases among the uropathogenic E. coli (UPEC) culminate in treatment complications and demands detailed investigation. In this study, uncharacterized amino acid substitutions, M69L/I84V/W165G/V184A/V262I/N276S, in inhibitor-resistant TEM (IRT) β-lactamase isolated from clinical UPEC were subjected to extensive molecular dynamics (EMD) simulations for 100 ns to estimate parameters such as root-mean-square deviation (RMSD), root-mean-square fluctuation (RMSF), the radius of gyration (R_g), contour plot (R_g/RMSD), secondary structure element (SSE), etc. Residue interaction networks, principal component analysis (PCA), and correlation heatmaps were generated to predict the relation between functionally important atomic motions to uncover the structural stability of the mutants. To avoid the false positive conclusion of the simulation study, we performed three identically parameterize replicas of 100 ns each. Alterations in hydrophobic interactions resulted in conformation changes exhibited as comparable residue interaction networks. Besides, PCA and porcupine plot analysis based on the ensemble of structure from molecular dynamics trajectories revealed the collective atomic motions of the IRT variants that impart structural flexibility to their active site loop. This study conducted on IRT mutants that delineate intricate protein motions contributes to their stability and folding, which is an absolute necessity for designing candidate molecules owing to the clinical threat of emerging resistance against potent β-lactam antibiotics.

Comparison of PCR and phenotypic methods for the detection of methicillin resistant Staphylococcus aureus

Background and Objectives:

Resistance to methicillin in methicillin resistant strains of Staphylococcus aureus (MRSA) is due to the presence of mec-A gene, which encodes a low affinity penicillin binding protein (PBP)-2a or PBP2. Accurate and rapid identification of MRSA in clinical specimens is essential for timely decision on effective treatment. The aim of the study was to compare three different methods for detection of MRSA namely cefoxitin disc diffusion, CHROM agar MRSA and VITEK-2 susceptibility with PCR which is the gold standard reference method and to find the antibiotic susceptibility pattern of these isolates by VITEK-2.

Materials and Methods:

A Total of 100 non-duplicate S. aureus isolates were collected from different clinical samples among both outpatient and inpatients. Detection of MRSA among these isolates was done by cefoxitin disc diffusion, VITEK-2, CHROM agar MRSA and PCR.

Results:

The sensitivity and specificity of cefoxitin disc diffusion and Vitek was found to be 97.2% and 100%, while that of CHROM agar was found to be 100% and 78.6%. The overall prevalence of MRSA in our study by PCR was 72%.

Conclusion:

Based on the findings in our study, isolates which show cefoxitin zone diameter < 22 mm can be reported as MRSA. However, those isolates which have a zone diameter between 22–24 mm, should ideally be confirmed by PCR.

Evaluation of Genotypic and Phenotypic Methods for Detection of Methicillin Resistant Staphylococcus aureus in a Tertiary Care Hospital of Eastern Odisha

INTRODUCTION

Methicillin resistant Staphylococcus aureus has emerged as an important pathogen in nosocomial and community acquired infections. Accurate and rapid identification of MRSA in clinical specimens is essential for timely decision of effective antimicrobial chemotherapy.

AIM

The present study was conducted to compare efficacy of four conventional phenotypic methods, with mec- A based polymerase chain reaction (PCR) for MRSA identification.

MATERIALS AND METHODS

Methicillin resistance was determined in 200 S.aureus isolates by oxacillin disc diffusion, cefoxitin disc diffusion, Oxacillin Resistance Screening Agar and E-test. The results were compared with mec-A based PCR.

RESULTS

Among 200 S.aureus isolates 62 (31%) were positive for mec-A gene by PCR. Cefoxitin disc diffusion, Oxacillin Resistance Screening Agar and E-test showed 100% specificity. Oxacillin disc diffusion had lowest sensitivity (82.5%) and specificity (98.5%) among all. The conventional methods take more time than PCR for diagnosing MRSA. Linezolid, Vancomycin & Dalfopristin were the highly sensitive drugs against MRSA isolates.

CONCLUSION

Cefoxitin disc diffusion, is rapid, simple and cheaper, hence can be used routinely as an alternative to PCR for detection of MRSA in resource constraint laboratories.