Safia Ahmed

Biological degradation of plastics: a comprehensive review.

Lack of degradability and the closing of landfill sites as well as growing water and land pollution problems have led to concern about plastics. With the excessive use of plastics and increasing pressure being placed on capacities available for plastic waste disposal, the need for biodegradable plastics and biodegradation of plastic wastes has assumed increasing importance in the last few years. Awareness of the waste problem and its impact on the environment has awakened new interest in the area of degradable polymers. The interest in environmental issues is growing and there are increasing demands to develop material which do not burden the environment significantly. Biodegradation is necessary for water-soluble or water-immiscible polymers because they eventually enter streams which can neither be recycled nor incinerated. It is important to consider the microbial degradation of natural and synthetic polymers in order to understand what is necessary for biodegradation and the mechanisms involved. This requires understanding of the interactions between materials and microorganisms and the biochemical changes involved. Widespread studies on the biodegradation of plastics have been carried out in order to overcome the environmental problems associated with synthetic plastic waste. This paper reviews the current research on the biodegradation of biodegradable and also the conventional synthetic plastics and also use of various techniques for the analysis of degradation in vitro.

Combined efficacy of biologically synthesized silver nanoparticles and different antibiotics against multidrug-resistant bacteria.

Biological synthesis of nanoparticles is a growing innovative approach that is relatively cheaper and more environmentally friendly than current physicochemical processes. Among various microorganisms, fungi have been found to be comparatively more efficient in the synthesis of nanomaterials. In this research work, extracellular mycosynthesis of silver nanoparticles (AgNPs) was probed by reacting the precursor salt of silver nitrate (AgNO3) with culture filtrate of Aspergillus flavus. Initially, the mycosynthesis was regularly monitored by ultraviolet-visible spectroscopy, which showed AgNP peaks of around 400–470 nm. X-ray diffraction spectra revealed peaks of different intensities with respect to angle of diffractions (2θ) corresponding to varying configurations of AgNPs. Transmission electron micrographs further confirmed the formation of AgNPs in size ranging from 5–30 nm. Combined and individual antibacterial activities of the five conventional antibiotics and AgNPs were investigated against eight different multidrug-resistant bacterial species using the Kirby–Bauer disk-diffusion method. The decreasing order of antibacterial activity (zone of inhibition in mm) of antibiotics, AgNPs, and their conjugates against bacterial group (average) was; ciprofloxacin + AgNPs (23) . imipenem + AgNPs (21) > gentamycin + AgNPs (19) > vancomycin + AgNPs (16) > AgNPs (15) . imipenem (14) > trimethoprim + AgNPs (14) > ciprofloxacin (13) > gentamycin (11) > vancomycin (4) > trimethoprim (0). Overall, the synergistic effect of antibiotics and nanoparticles resulted in a 0.2–7.0 (average, 2.8) fold-area increase in antibacterial activity, which clearly revealed that nanoparticles can be effectively used in combination with antibiotics in order to improve their efficacy against various pathogenic microbes.

Physicochemical characterization and Bioremediation perspective of textile effluent, dyes and metals by indigenous Bacteria

Physicochemical and bacteriological status of a local textile mill effluent showed considerably high values of temperature (40 degrees C), pH (9.50), EC (3.57mus/m), BOD (548mgl(-1)), COD (1632mgl(-1)), TSS (5496mgl(-1)), TDS (2512mgl(-1)), heavy metals ions (0.28-6.36mgl(-1)) and color above the prescribed fresh water limits. However, a considerable decline in almost all pollution indicators from source to sink indicated signs of natural remediation. Ten bacteria strains isolated from effluent showed comparatively higher resistance (MRL) (mgl(-1)) (average) for 10 heavy metals than against four structurally different dyes tested on solid media of mineral salt. Overall bacterial resistance was quite high against Fe(3+) (2820), Cr(3+) (1203), Zn(2+) (1122), Mn(2+) (804) and Pb(2+) (435), whereas, it varied amid 300-500 in four dyes. Bacterial decolorization/degradation of dyes indicated on solid media was confirmed through experiments carried out in liquid broth.

Extended-Spectrum β-Lactamases (ESBLs): Characterization, Epidemiology and Detection

β-lactamases of Enterobacteriaceae are the most important mechanism of resistance against β-lactam drugs. Two types of β-lactamases can confer resistance against 3rd generation cephalosporins. Chromosomally mediated β-lactamases are inducible and are not inhibited by clavulanic acid. Resistance due to these enzymes is non-transferable. The 2nd type of enzyme is plasmid-mediated β-lactamases, which are inhibited by clavulanic acid. These enzymes are more important clinically as these can be transferred between various species of Enterobacteria ceae. These enzymes are called extended-spectrum β-lactamases (ESBLs). ESBL-producing Enterobacteriaceae have been responsible for numerous outbreaks of infection throughout the world and pose challenging infection control issues. Antibacterial choice is often complicated by multi-resistance. ESBLs can confer resistance against all β-lactam drugs except carbapenems and cephamycins. Nursing home patients may be an important reservoir of ESBL-containing multiple antibiotic-resistant organisms. Use of broad-spectrum oral antibiotics and probably poor infection control practices may facilitate spread of this plasmid-mediated resistance. In addition to known populations at risk, ambulatory patients with chronic conditions represent another patient population that may harbor ESBL-producing organisms. Various methods can be used for detection of ESBLs in the laboratory. These tests include double disc diffusion test, Vitek ESBL test, E Tests, MIC Determination, genetic method, and isoelectric focusing (IEF).

Biological characterization and phylogenetic analysis of a novel genetic group of Newcastle disease virus isolated from outbreaks in commercial poultry and from backyard poultry flocks in Pakistan.

Newcastle disease (ND) is a contagious viral disease of many avian species particularly domestic poultry, and is responsible for devastating outbreaks in the poultry industries around the globe. In spite of its importance and endemicity in Southern Asia, data on the genetic nature of the viruses and epizootiological information of the disease is scarce. In this study, six isolates from an emerging wave of ND outbreaks in the north of Pakistan and two isolates from healthy poultry flocks were biologically and genetically characterized. Based on pathogenicity indices such as intracerebral pathogenicity index (ICPI), mean death time (MDT) and cleavage motifs in the fusion protein, all these isolates were classified as virulent. Phylogenetic analysis of the fusion (F), hemagglutinin-neuraminidase (HN) and matrix (M) genes indicated the emergence of a novel genetic group within lineage 5, distinct from isolates previously reported in the region. Several mutations in the neutralizing epitopes and functionally important motifs of the F and HN genes pose a need for re-evaluation of the currently used vaccine and vaccination practices. The characteristics of Newcastle disease virus (NDV) as virulent (F protein cleavage site, ICPI and MDT) in apparently healthy backyard poultry (BYP) explain that BYP can play crucial role in the epizootiology and spread of the disease. The present investigation provides essential information on the genetic nature of NDV circulating in Pakistan and its implication on disease diagnosis and control. Furthermore, these investigations emphasize the importance of continuous surveillance of ND in developing countries.

Degradation of petroleum hydrocarbons by oil field isolated bacterial consortium

A mixed consortium was prepared with 15 bacteria isolated by enrichment technique from the sample collected from an oil contaminated site. This consortium was incubated with crude oil to investigate the metabolic capability of bacteria. The degradation efficiency of the isolates in consortium was checked with 2% crude oil by shake flask transformation in mineral salt medium, at 37°C for 24 days. Total removal of aliphatic and aromatics was 94.64% and 93.75% respectively. Among the various components of the crude oil degradation by the bacterial consortium, the biotic removal of alkanes was maximum, 90.96% for tridecane (C 13 ) followed by pentadecane (C 15 ) at 77.95%, octadecane (C 18 ) at 74.1%, while other alkanes showed 56 to 69% after 24 days of incubation. The aromatics (benzene, toluene and xylene) were vaporized in the 4th day of incubation, while the efficiency on polyaromatic fractions (anthracene, phenanthrene and pyrene) was 46.17 to 55.3% after 24 days. The ability of degrading long chain n-alkanes and crude oil at high concentrations makes the consortium potentially useful for bioremediation and microbial enhanced oil recovery. Key words : Consortium, petroleum hydrocarbons, crude oil, aliphatics, aromatics.

Influence of calcium in extracellular DNA mediated bacterial aggregation and biofilm formation.

Calcium (Ca2+) has an important structural role in guaranteeing the integrity of the outer lipopolysaccharide layer and cell walls of bacterial cells. Extracellular DNA (eDNA) being part of the slimy matrix produced by bacteria promotes biofilm formation through enhanced structural integrity of the matrix. Here, the concurrent role of Ca2+ and eDNA in mediating bacterial aggregation and biofilm formation was studied for the first time using a variety of bacterial strains and the thermodynamics of DNA to Ca2+ binding. It was found that the eDNA concentrations under both planktonic and biofilm growth conditions were different among bacterial strains. Whilst Ca2+ had no influence on eDNA release, presence of eDNA by itself favours bacterial aggregation via attractive acid-base interactions in addition, its binding with Ca2+ at biologically relevant concentrations was shown further increase in bacterial aggregation via cationic bridging. Negative Gibbs free energy (ΔG) values in iTC data confirmed that the interaction between DNA and Ca2+ is thermodynamically favourable and that the binding process is spontaneous and exothermic owing to its highly negative enthalpy. Removal of eDNA through DNase I treatment revealed that Ca2+ alone did not enhance cell aggregation and biofilm formation. This discovery signifies the importance of eDNA and concludes that existence of eDNA on bacterial cell surfaces is a key facilitator in binding of Ca2+ to eDNA thereby mediating bacterial aggregation and biofilm formation.

Molecular characterization of serotype Asia-1 foot-and-mouth disease viruses in Pakistan and Afghanistan; emergence of a new genetic Group and evidence for a novel recombinant virus

Foot-and-mouth disease (FMD) is endemic in Pakistan and Afghanistan. The FMD virus serotypes O, A and Asia-1 are responsible for the outbreaks in these countries. Diverse strains of FMDV, even within the same serotype, co-circulate. Characterization of the viruses in circulation can facilitate appropriate vaccine selection and tracing of outbreaks. The present study characterized foot-and-mouth disease serotype Asia-1 viruses circulating in Pakistan and Afghanistan during the period 1998-2009. Phylogenetic analysis of FMDV type Asia-1 revealed that three different genetic Groups of serotype Asia-1 have circulated in Pakistan during this time. These are Group-II, -VI and, recently, a novel Group (designated here as Group-VII). This new Group has not been detected in neighbouring Afghanistan during the study period but viruses from Groups I and -II are in circulation there. Using near complete genome sequences, from FMD viruses of serotypes Asia-1 and A that are currently circulating in Pakistan, we have identified an interserotypic recombinant virus, which has the VP2-VP3-VP1-2A coding sequences derived from a Group-VII Asia-1 virus and the remainder of the genome from a serotype A virus of the A-Iran05(AFG-07) sub-lineage. The Asia-1 FMDVs currently circulating in Pakistan and Afghanistan are not efficiently neutralized by antisera raised against the Asia-1/Shamir vaccine strain. Thus, new Asia-1 vaccine strains may be required to block the spread of the current Asia-1 viruses.

Genetic diversity of foot-and-mouth disease virus serotype O in Pakistan and Afghanistan, 1997-2009.

Foot-and-mouth disease (FMD) is endemic in Pakistan and Afghanistan; serotypes O, A and Asia-1 of the virus are responsible for the outbreaks in these countries with FMDV type O usually being the most common. In the present study, the nucleotide sequences encoding the FMDV capsid protein VP1 from virus samples were determined. Phylogenetic analysis of the serotype O FMD viruses circulating in Pakistan and Afghanistan between 1997 and 2009 revealed the presence of at least three different lineages within the ME-SA (Middle East South Asia) topotype. The three lineages detected in this study are Pak98, Iran2001 and PanAsia. The PanAsia lineage is currently dominant in the area and is evolving with time as revealed by the appearance of distinct variants e.g. PanAsia-II and a new variant designated here as PanAsia-III. The rates of evolution of the O-PanAsia-II and III sublineages prevalent in the region were found to be 6.65 × 10(-3) (95% CI=5.49-7.80 × 10(-3)) and 7.80 × 10(-3) (95% CI=6.72-8.89 × 10(-3)) substitutions per nucleotide per year, respectively. The present study reveals the presence of multiple (sub-)lineages of FMDV serotype O co-circulating in the region and that significant new variants are frequently emerging.

Degradation of polyurethane by novel bacterial consortium isolated from soil

The present study describes the isolation of bacteria from soil with the ability to degrade plastic polyurethane (PU). Bacterial strains attached on the polyurethane film, after soil burial for 6 months, were isolated and identified asBacillus sp. AF8,Pseudomonas sp AF9,Micrococcus sp. 10,Arthrobacter sp. AF11, andCorynebacterium sp. AF12. In plate assay, zones of hydrolysis were visualised around the bacterial colonies on mineral salt agar plates containing polyurethane as a sole carbon source. The results of the Sturm test for degradability showed more CO2 production in the test than in control. The production of esterase was detected in the presence of polyurethane as a substrate. The Scanning Electron Microscopy and Fourier Transform Infrared Spectroscopy showed certain changes on the surface of PU film and formation of some new intermediate products after polymer breakdown.