Suhail Ahmad - Academia.edu (original) (raw)

Papers by Suhail Ahmad

Annals of Saudi Medicine, 2005

International Journal of Systematic and Evolutionary Microbiology, 2000

The dnaK operon in Gram-positive bacteria includes grpE, dnaJ and, in some members, hrcA as well.... more The dnaK operon in Gram-positive bacteria includes grpE, dnaJ and, in some members, hrcA as well. Both DnaK and DnaJ have been utilized for constructing phylogenetic relationships among various organisms. Multiple copies exist for dnaK and dnaJ genes in some bacterial genera, as opposed to a single gene copy for grpE and for hrcA, according to the currently available data. Here, we present a partial protein-based phylogenetic tree for Grampositive bacteria, derived by using the amino acid sequence identity of GrpE ; the results are compared with the phylogenetic trees generated from 5S rRNA, 16S rRNA, dnaK and dnaJ sequences. Our results indicate three main groupings : two are within low-GMC DNA Gram-positive bacteria comprising Bacillus species and Staphylococcus aureus on the one hand and Streptococcus species/Lactococcus lactis/Enterococcus faecalis/Lactobacillus sakei on the other hand ; the Mycobacterium species and Streptomyces coelicolor, belonging to the high-GMC DNA Gram-positive bacteria, form the third cluster. This hierarchical arrangement is in close agreement with that obtained with 16S rRNA and DnaK sequences but not DnaJ-based phylogeny.

The Indian journal of medical research, 2012

Frequency of resistance-conferring mutations vary among isoniazid- and ethambutol-resistant Mycob... more Frequency of resistance-conferring mutations vary among isoniazid- and ethambutol-resistant Mycobacterium tuberculosis isolates obtained from patients of various ethnic groups. This study was aimed to determine the occurrence of specific rpoB mutations in rifampicin-resistant M. tuberculosis isolates from tuberculosis patients of various ethnic groups in Kuwait. Rifampicin-resistant M. tuberculosis isolates (n=119) from South Asian (n=55), Southeast Asian (n=23), Middle Eastern (n=39) and other (n=2) patients and 107 rifampicin-susceptible isolates were tested. Mutations in rpoB were detected by DNA sequencing. Polymorphisms at katG463 and gyrA95 were detected by PCR-RFLP for genetic group assignment. None of rifampicin-susceptible but 116 of 119 rifampicin-resistant isolates showed rpoB mutation(s). Mutations among isolates from South Asian patients were distributed at rpoB516 (20%), rpoB526 (24%) and rpoB531 (27%) while 78 and 51 per cent of isolates from Southeast Asian and Middl...

Medical mycology case reports, 2014

A case of Malassezia pachydermatis fungemia in a preterm neonate is described. The isolate was id... more A case of Malassezia pachydermatis fungemia in a preterm neonate is described. The isolate was identified by rDNA sequencing and was resistant to fluconazole and flucytosine. Since M. pachydermatis does not require lipid supplementation for growth, it can be misidentified as a Candida species. The report highlights M. pachydermatis as a cause of late onset sepsis in preterm neonates and emphasizes the need for prior antifungal susceptibility testing.

The Journal of antimicrobial chemotherapy, 2015

Resistance to triazoles in Aspergillus fumigatus has emerged in several countries and is usually ... more Resistance to triazoles in Aspergillus fumigatus has emerged in several countries and is usually mediated by mutations in the cyp51A gene. We determined the presence of both itraconazole-susceptible and -resistant A. fumigatus in routine cultures isolated from environmental and clinical samples. A total of 50 environmental and 16 clinical A. fumigatus isolates obtained from single colonies were tested for itraconazole susceptibility by Etest. Serial dilution and plating for selected A. fumigatus cultures were performed to separate triazole-susceptible and -resistant phenotypes. Antifungal drug susceptibility of subcultures to itraconazole, posaconazole and voriconazole was determined by the broth microdilution method. Itraconazole resistance was determined by the presence of tandem repeats in the promoter region and other resistance-conferring mutations by PCR and/or direct DNA sequencing of cyp51A. Genotyping was performed with a panel of nine microsatellite loci. PCR amplification...

Microbial & Comparative Genomics, 1999

The dnaK gene region of Bacillus sphaericus was cloned as a 3.8 kb HindIII fragment and an overla... more The dnaK gene region of Bacillus sphaericus was cloned as a 3.8 kb HindIII fragment and an overlapping 1.7 kb EcoRI fragment by using an internal B. sphaericus specific dnaK gene probe generated by polymerase chain reaction (PCR). Complete DNA sequencing of the two fragments revealed three complete open reading frames (ORFs). These ORFs exhibited a high degree of identity to the grpE dnaK, and dnaJ heat shock genes from other gram-positive bacteria. The order of the genes was found to be grpE-dnaK-dnaJ. Additionally, the 5'-end and 3'-end contained amino acid sequences that were homologous to the C-terminal sequence of the hrcA gene and the N-terminal sequence of ORF35 (yqeT), respectively, from Bacillus subtilis. The entire hrcA gene from B. sphaericus was then isolated by high-fidelity PCR and completely sequenced. A transcription stop site is located between the dnaK and dnaJ genes but not after the dnaJ gene. Consistent with this observation, the dnaJ gene is immediately followed by an ORF that shows a high degree of identity to ORF35 from B. subtilis, Staphylococcus aureus, and Clostridium acetobutylicum. The presence of ORF35 is not indicated in other genera representing the gram-positive bacteria. The amino acid sequence of ORF35 exhibited nearly 30% identity with the methyltransferase for large subunit ribosomal protein L11 from gram-negative Proteobacteria and the related protein from cyanobacteria, other gram-negative bacteria, and Archaea, suggesting the presence of the gene for this protein in the common ancestor of Bacteria and Archaea. The absence of the ORF35 gene in Mycobacterium tuberculosis and other gram-positive bacteria indicates that the loss of this gene must have occurred in an ancestor of other gram-positive bacteria following their divergence from the ancestor of Bacillus/Clostridium/staphylococcus lineage.

Advances in Structural Engineering, 2014

finite element analysis of composite structures based on mesoscale random fields of material prop... more finite element analysis of composite structures based on mesoscale random fields of material properties, Comput.

Volume 1: Offshore Technology; Ocean Space Utilization, 2003

ABSTRACT Present study investigates the non-linear dynamic behavior of Double Hinged Articulated ... more ABSTRACT Present study investigates the non-linear dynamic behavior of Double Hinged Articulated Tower (DHAT) under long crested random Sea and directional random sea. The non-linearities due to time wise variation of submergence, buoyancy, added mass, instantaneous tower orientation and resulting hydrodynamic loading have been taken into account for modeling the forcing functions of equation of motion which is derived by Largrangian approach. A long crested random sea has been modeled by Monte-Carlo Simulation using P-M spectrum. The non-linear equations of motion are solved by an iterative time integration scheme using Newmark’s β integration scheme. Various important parameters such as heel angles, deck displacements, base share for double hinged articulated tower under long and short crested random sea are compared and presented in the form of time-histories and their respective PSDFs. Statistical studies of random time histories have been carried out and important characteristics like mean, maxima, minima, standard deviations etc. have been analyzed. The dynamic behaviors have been investigated in detail in terms of various parametric combinations. Effect of current, and significant wave height are also studied. Sub and super harmonic excitations are highlighted through power spectra. A multi-hinged articulated tower is found to be economical and suitable for various offshore activities in adverse environmental and deep sea conditions.

Clinical Pharmacology and Therapeutics, 1985

The kinetics of oral ketoconazole in serum and peritoneal fluid were studied in six patients with... more The kinetics of oral ketoconazole in serum and peritoneal fluid were studied in six patients with renal failure receiving peritoneal dialysis A dose of 400 mg ketoconazole resulted in a maximum blood concentration of 2.3 :1_-1.7 Rg/m1 (X-± SD), which occurred 3.3-± 1.6 hours after dosing. The serum was 2.4-± 0.8 hours. Peritoneal clearance values were <1 ml/min, and peritoneal penetration reached 3.4% of the serum concentration by 5 hours. Protein binding studies were also performed. Compared with healthy controls, patients receiving peritoneal dialysis have significantly less ketoconazole serum protein binding. Fifty to eighty percent of the drug is protein bound in the peritoneal fluid, and the unbound concentration is in the same range as that in the serum of healthy individuals with "therapeutic" total ketoconazole levels of 1 to 2 jig/ml. (CLIN PHARIVIACOL THER 37:325-329, 1985.

Journal of Civil Engineering and Management, 2013

Spar platforms are treated as cost-effective and resourceful type of offshore structure in deep w... more Spar platforms are treated as cost-effective and resourceful type of offshore structure in deep water. With increasing depth there are significant changes in its structural behaviour due to coupling of spar hull-mooring line along with radical influence of mooring line damping. So these phenomena should be precisely counted for accurate motion analysis of spar mooring system. In present study, spar platform are configured as a single fully coupled integrated model in ABAQUS/AQUA. Non-linear dynamic analysis in time domain is performed adopting Newmark-β automatic time incrementation technique. Non-linearities due to geometric, loading and boundary conditions are duly considered. Displacement and rotational responses of spar and mooring tensions are obtained during long-duration storm. spar responses get significantly modified and mean position of oscillations gets shifted after longer wave loading. The surge, heave and pitch responses are predominantly excited respectively. The ener...

Procedia Engineering, 2011

The paper presents a numerical Analysis of deep water Steel Catenary Riser (SCR) under random sea... more The paper presents a numerical Analysis of deep water Steel Catenary Riser (SCR) under random sea loads. A finite element method is implemented in the time domain using Newmark's-Beta method. The response analysis is based on a simulation technique which duly considers the various non-linear effects such as relative velocity squared drag force, variable added mass due to variable submergence and nonlinearity due to large excursions. It also accounts for variable tension in riser due to variable submergence, variable buoyancy and wave forces. Results are presented which illustrates the effects of nonlinearities, long term drift oscillations and current velocity on the bending stress in the marine risers. The bending stress response time histories are obtained and presented in terms of bending stress envelopes and spectra showing contribution of various harmonics which is significant because of a non-linear system.

Toxicological & Environmental Chemistry, 1993

... 0.59 0.87 1.01 0.40 Page 4. 136 S. MALIK, M. KENNY AND S. AHMAD Pre and post-dialysis DEHP le... more ... 0.59 0.87 1.01 0.40 Page 4. 136 S. MALIK, M. KENNY AND S. AHMAD Pre and post-dialysis DEHP levels In 4 hemodialysis patients Scrum DEHP, ug/ml 1.2 - 1 - 0.8 - ... 117-81-7), Technical Report Series No. 217, NIH, Bethesda (1982). 7. DE Moody and JK Reddy, Toxicol. App. ...

European Journal of Biochemistry, 1995

ABSTRACT 5-Enolpyruvylshikimate-3-phosphate synthase of Bacillus subtilis has been cloned, expres... more ABSTRACT 5-Enolpyruvylshikimate-3-phosphate synthase of Bacillus subtilis has been cloned, expressed and purified to near homogeneity. Clustal alignment of the amino acid sequences from different bacteria revealed several conserved residues located in the N-terminal, middle and C-terminal domains. The role of conserved Arg24, Pro105, and His385 residues has been examined by site-directed mutagenesis. Steady-state kinetic analysis of the native synthase exhibited allosteric behaviour, a feature thought to be unique amongst bacterial and plant 5-enolpyruvylshikimate-3-phosphate synthase enzymes investigated so far. Both substrates, phosphoenolpyruvate (P-pyruvate) and shikimate 3-phosphate have multiple interaction sites. There are two sites for P-pyruvate binding, catalytic and non-catalytic. Glyphosate (N-phosphonomethyl glycine) competes for binding at the catalytic site and does not interact at the secondary site. Glyphosate in the absence of ammonium ions increases cooperativity of P-pyruvate binding and favors dimerization of the enzyme through an interaction between P-pyruvate-binding sites. The ammonium-ion-activated 5-enolpyruvylshikimate-3-phosphate synthase displays no cooperativity with respect to P-pyruvate. Absence of ammonium ions decreases affinity for substrates and introduces cooperativity. Cooperativity was also introduced in the enzyme by point mutations, Arg24-->Asp and His385-->Lys. The latter mutant of the native enzyme exists as a dimer and aggregates to a tetrameric form in the presence of glyphosate. The occurrence of multimeric forms of the synthase has been demonstrated by staining for the enzyme activity on the native gel and by resolving purified enzyme preparations on a sucrose density gradient. A model describing the alteration in the aggregation status of the enzyme by the inhibitor, activator and the substrates has been proposed.

Respiratory Medicine, 2009

Tuberculosis (TB) is a major infectious disease killing nearly two million people, mostly in deve... more Tuberculosis (TB) is a major infectious disease killing nearly two million people, mostly in developing countries, every year. The increasing incidence of resistance of Mycobacterium tuberculosis strains to the most-effective (first-line) anti-TB drugs is a major factor contributing to the current TB epidemic. Drug-resistant strains have evolved mainly due to incomplete or improper treatment of TB patients. Resistance of M. tuberculosis to anti-TB drugs is caused by chromosomal mutations in genes encoding drug targets. Multidrug-resistant (resistant at least to rifampin and isoniazid) strains of M. tuberculosis (MDR-TB) evolve due to sequential accumulation of mutations in target genes. Emergence and spreading of MDR-TB strains is hampering efforts for the control and management of TB. The MDR-TB is also threatening World Health Organization's target of tuberculosis elimination by 2050. Proper management of MDR-TB relies on early recognition of such patients. Several diagnostic methods, both phenotypic and molecular, have been developed recently for rapid identification of MDR-TB strains from suspected patients and some are also suitable for resource-poor countries. Once identified, successful treatment of MDR-TB requires therapy with several effective drugs some of which are highly toxic, less efficacious and expensive. Minimum treatment duration of 18e24 months is also long, making it difficult for health care providers to ensure adherence to treatment. Successful treatment has been achieved by supervised therapy with appropriate drugs at institutions equipped with facilities for culture, drug susceptibility testing of MDR-TB strains to second-line drugs and regular monitoring of patients for adverse drug reactions and bacteriological and clinical improvement.

Molecular and Cellular Probes, 2004

Mutations at embB gene codons 306 and 497 and iniA gene codon 501 occur frequently in ethambutol ... more Mutations at embB gene codons 306 and 497 and iniA gene codon 501 occur frequently in ethambutol (EMB)-resistant Mycobacterium tuberculosis strains worldwide. The identification of these mutations in resistant strains has been achieved by labor-intensive DNA sequencing or by tedious amplification protocols followed by restriction endonuclease digestion. In this report, we describe PCR-restriction fragment length polymorphism (RFLP)-based methods for determining substitutions at embB codons 306 and 497 and iniA codon 501 directly in BACTEC cultures of M. tuberculosis isolates. The wild-type and mutant alleles are revealed by easily interpretable and different RFLP patterns. The methods optimized initially on reference strains were tested directly on BACTEC cultures of 25 randomly selected clinical M. tuberculosis isolates, seven of which were determined to contain EMB-resistant strains by phenotypic drug susceptibility testing. The PCR-RFLP methods identified mutations in four of seven EMB-resistant strains with three isolates containing mutated embB codon 306 and one isolate containing mutated embB codon 497. The results of PCR-RFLP were confirmed by DNA sequencing. The worldwide prevalence figures for mutations at embB codons 306 and 497 and iniA codon 501 suggest that nearly half of EMB-resistant M. tuberculosis strains could be identified within one working day even in developing countries equipped with simple PCR technology instead of weeks required for phenotypic drug susceptibility testing. Further, since EMB resistance is also associated with multiple-drug resistance from some geographical locations, detection of EMB resistance may also lead to rapid identification of multidrug-resistant strains of M. tuberculosis.

Medical Principles and Practice, 2004

Objective: To perform molecular fingerprinting for strain relatedness among isoniazid-resistant M... more Objective: To perform molecular fingerprinting for strain relatedness among isoniazid-resistant Mycobacterium tuberculosis isolates recovered from tuberculosis (TB) patients in the United Arab Emirates (UAE). Materials and Methods: Thirty-two consecutive isoniazid-resistant M. tuberculosis strains isolated from TB patients (4 natives and 28 expatriates) at Rashid Hospital, Dubai, UAE were analyzed. The typing was carried out by touchdown double-repetitive-element PCR (DRE-PCR). The status of R463 or L463 polymorphism and the presence of S315T mutation in the katG gene were also determined for isolates exhibiting cluster pattern in DRE-PCR. Results: All the 32 isolates (28 from expatriate patients and 4 from UAE nationals) exhibited 21 distinct patterns in DRE-PCR with 20 of 32 isolates exhibiting unique patterns and the remaining 12 exhibiting cluster ‘A’ pattern. All the isolates (19 of 19) yielding two or more DNA fragments in DRE-PCR were unique strains. The genotypic heterogenei...

Medical Mycology, 2011

A pre-term female baby delivered at 29 weeks and weighing 1,285 g developed respiratory distress ... more A pre-term female baby delivered at 29 weeks and weighing 1,285 g developed respiratory distress soon after birth and needed continuous positive airway pressure support for 24 h. She was the fi rst baby born to a healthy mother following initiation of spontaneous labor. The newborn was admitted to the special neonatal care unit and started receiving normal nutrition on day 3. On day 13, she developed clinical signs of sepsis and required ventilator support. Blood culture yielded Enterobacter cloacae , which was initially treated with amikacin and tazobactam. Two days later, based on the susceptibility results, she was switched to meropenem and amikacin, and tazobactam was withdrawn. This treatment regimen continued for 21 days. She was transferred to the special care ward in good condition. On day 32, she developed Staphylococcus epidermidis sepsis and hence was readmitted to the neonatal intensive care unit and received treatment with vancomycin. Since she continued to remain febrile, a repeat blood culture (BACTEC Peds Plus/F; Becton Dickinson Diagnostic Systems, Sparks, MD, USA) was performed and yielded a yeast on day 37, which was subsequently identifi ed as K. ohmeri by the Vitek 2 yeast identifi cation system (YST: bioM é rieux, Marcy-l ' Etoile, France) with 90% probability. The same yeast species was isolated in a subsequent blood culture. The patient was started on intravenous amphotericin B (1.5 mg/kg) through a peripheral long line and treated

Kidney International, 1982

Acetate and bicarbonate fluctuations and acetate intolerance during dialysis. Plasma bicarbonate ... more Acetate and bicarbonate fluctuations and acetate intolerance during dialysis. Plasma bicarbonate losses during acetate dialysis were prevented by using a combination of acetate and bicarbonate in the dialysate. In 21 patients who were treated with combination dialysate, the fall in mean blood pressure (MBP), and frequency of symptoms, and post-dialysis task performance were all similar to that observed during dialysis with acetate alone. Furthermore, dialysis performed with bicarbonate dialysate resulted in significantly smaller MBP drops, fewer symptoms, and an improved task performance compared to either an acetate or a combination dialysis. These findings indicate that the presence of acetate, rather than a bicarbonate loss, was responsible for the patients' intolerance to acetate dialysis. Patients symptomatic on acetate dialysis had a similar ultrafiltration rate, weight loss, MBP drops, and postdialysis serum acetate levels; they were similar in age and weight to symptom-free patients. Thus, the toxic effect of acetate n'étaient pas simplement moms tolérants a Ia dialyse en soi mais différaient des malades asymptomatiques par leur reponse a Ia presence d'acétate.

Kidney International, 2003

Effect of ␤ 2-microglobulin adsorption column on dialysis-related amyloidosis. Background. ␤ 2-mi... more Effect of ␤ 2-microglobulin adsorption column on dialysis-related amyloidosis. Background. ␤ 2-microglobulin (␤ 2-m) is considered a major pathogenic factor in dialysis-related amyloidosis (DRA), often seen in long-term dialysis patients. No effective therapy for this severely debilitating disease is currently available. Lixelle, an adsorption column, has been developed for the elimination of ␤ 2-m; the efficacy of this column has been evaluated in this study. Methods. Seventeen hemodialysis patients with DRA were first treated with high-flux dialysis for a minimum of 1 year. This was followed by 1-year treatment with Lixelle column connected in series to the high-flux dialyzer. Treatments were used three times a week for both phases of this study. During the study period, ␤ 2-m, pinch strength, motor terminal latency, and activities of daily living were evaluated. Results. After 1-year treatment with high-flux dialysis the ␤ 2-m level remained unchanged; however, after 1-year treatment with the addition of the Lixelle column, ␤ 2-m level decreased significantly from 34.5 Ϯ 8.4 mg/L to 28.8 Ϯ 7.3 mg/L (P Ͻ 0.05). After 1 year of Lixelle column use, the pinch strength increased from 6.8 Ϯ 4.7 pounds to 9.1 Ϯ 5.5 pounds (P Ͻ 0.01), and the median motor terminal latency was significantly reduced from 5.1 Ϯ 1.0 mseconds to 4.5 Ϯ 1.1 mseconds. A significant improvement was also observed in the activities of daily living score of the upper extremities. Conclusion. These results suggest that the addition of Lixelle to the high-flux dialyzer is associated with a significant clinical improvement in DRA patients. Dialysis-related amyloidosis (DRA) is one of the major complications seen in long-term hemodialysis patients [1]. It is associated with excruciating and debilitating pain and deterioration in quality of life and activities of daily living of dialysis patients. The major pathogenesis

Kidney International, 1990