Tarek A Ahmad - Academia.edu (original) (raw)

Papers by Tarek A Ahmad

Scientific Reports, 2019

Genital chlamydia infection in women causes complications such as pelvic inflammatory disease and... more Genital chlamydia infection in women causes complications such as pelvic inflammatory disease and tubal factor infertility, but it is unclear why some women are more susceptible than others. Possible factors, such as time of day of chlamydia infection on chlamydial pathogenesis has not been determined. We hypothesised that infections during the day, will cause increased complications compared to infections at night. Mice placed under normal 12:12 light: dark (LD) cycle were infected intravaginally with Chlamydia muridarum either at zeitgeber time 3, ZT3 and ZT15. Infectivity was monitored by periodic vaginal swabs and chlamydiae isolation. Blood and vaginal washes were collected for host immunologic response assessments. The reproductive tracts of the mice were examined histopathologically, and fertility was determined by embryo enumeration after mating. Mice infected at ZT3 shed significantly more C. muridarum than mice infected at ZT15. This correlated with the increased genital tract pathology observed in mice infected at ZT3. Mice infected at ZT3 were less fertile than mice infected at ZT15. The results suggest that the time of day of infection influences chlamydial pathogenesis, it indicates a possible association between complications from chlamydia infection and host circadian clock, which may lead to a better understanding of chlamydial pathogenesis. Genital chlamydia infection, a sexually transmitted infection (STI), which is caused by the bacteria C. trachoma-tis, is the most commonly reported bacterial STI in the United States. In the female reproductive tract, genital chlamydia infection is manifested in several ways such as pelvic inflammatory disease (PID), Salpingitis and tubal factor infertility 1-3. A high number of chlamydia infection cases go unreported because they are asymptomatic, and this has been estimated to be about 70% of the cases in women 2,3. There are varying levels of severity among women who do develop complications such as cervicitis, PID, uterine fibrosis and tubal factor infertility (TFI) regardless of how many times they have been exposed or have become reinfected 4,5. A better understanding of how some women develop genital disease (PID alone, PID with Salpingitis, TFI or are asymptomatic) following chlamydia infection, while others do not, and the underlying mechanisms 6,7 will enhance a search for prevention measures. Circadian rhythms, the body's internal clock, describe the endogenous oscillation in organisms that are observed in approximate association with the Earth's daily rotation 8. Circadian rhythms are governed by the light-dark cycle and allows organisms to anticipate changes in the environment 8. In mammals, circadian rhythms are regulated by the molecular clock of the suprachiasmatic nucleus (SCN) of the hypothalamus and by circa-dian clocks found in most peripheral tissues 9. The molecular clock consists of several transcription factors that function in an autoregulatory transcription-translation feedback loop 8. The circadian genes, Clock and

Reports of Biochemistry and Molecular Biology, 2018

Pasteurellosis is one of the most important respiratory diseases facing economically valuable far... more Pasteurellosis is one of the most important respiratory diseases facing economically valuable farm animals such as poultry, rabbit, cattle, goats and pigs. It causes severe economic loss due to its symptoms that range from primary local infection to fatal septicemia. Pasteurella multocida is the responsible pathogen for this contagious disease. Chemotherapeutic treatment of Pasteurella is expensive, lengthy, and ineffective due to the increasing antibiotics resistance of the bacterium, as well as its toxicity to human consumers. Though, biosecurity measures played a role in diminishing the spread of the pathogen, the immunization methods were always the most potent preventive measures. Since the early 1950s, several trials for constructing and formulating effective vaccines were followed. This up-to-date review classifies and documents such trials. A section is devoted to discussing each group benefits and defects.

The increasing resistance of many microbial strains to antibiotics, delayed laboratory results, a... more The increasing resistance of many microbial strains to antibiotics, delayed laboratory results, and side effects of many chemotherapeutics has raised the need to search for sensitive diagnostics and new pro-phylactic strategies especially prevention by vaccination. Understanding the epitope/antibody interaction is the key to constructing potent vaccines and effective diagnostics. B-cell epitope mapping is a promising approach to identifying the main antigenic determinants of microorganisms, in special concern the discontinuous conformational ones. Epitope-based vaccines have remarkable privilege over the conventional ones since they are specific, able to avoid undesirable immune responses, generate long lasting immunity, and are reasonably cheaper. This up-to-date review discusses and compares the different physical, computational, and molecular methods that have been used in epitope mapping. The role of each method in the identification of potent epitopes in viruses, bacteria, fungi, parasites, as well as human diseases are tagged and documented. Simultaneously, frequent combinatorial methods are highlighted. The article aims to assist researchers to design the most suitable protocol for mapping their B-cell epitopes.

Acinetobacter baumannii has recently crossed all lines once considered harmless, pushing its way ... more Acinetobacter baumannii has recently crossed all lines once considered harmless, pushing its way as a nosocomial pathogen. It had acquired resistance to almost all available chemotherapies and mainly targets intensive care residents; causing pneumonia and major outbreaks with high mortality rates. This urged the need for preventive methods, which include infection control, non-specific immune-therapy,
passive, and active immunization in order to offer vulnerable immune-compromised patients a flare in the dark. Several attempts were done for constructing effective vaccines with promising results. These are precisely classified, documented, and discussed in this up-to-date review.

Klebsiella pneumoniae is the most common cause of nosocomial respiratory tract and premature inte... more Klebsiella pneumoniae is the most common cause of nosocomial respiratory tract and premature intensive
care infections, and the second most frequent cause of Gram-negative bacteraemia and urinary tract
infections. Drug resistant isolates remain an important hospital-acquired bacterial pathogen, add significantly
to hospital stays, and are especially problematic in high impact medical areas such as intensive
care units. Many investigations worldwide proved the increasing resistance of such pathogen, resulting
in an average rate of 1.63 outbreak every year. A variety of preventive measures were applied to reduce
such incidences. Immunotherapy and passive immunization researches as well found their way to the
treatment of Klebsiella. During the last 40 years, many trials for constructing effective vaccines were followed.
This up-to-date review classifies such trials and documents them in a progressive way. A following
comment discusses each group benefits and defects

ioassay-directed screening of compounds and extracts is the initial step in the discovery process... more ioassay-directed screening of compounds and extracts is the initial step in the discovery process for new natural chemicals of potential usefulness as antibacterial agents. In the current research, lipophilic and water soluble extracts of three fresh water macrophytes (Ceratophyllum demersum, Lemna gibba and Potamogeton pectinatus) and a marine macroalga (Enteromorpha prolifera) were screened for antibacterial activity by the single disk method against a group of enteric and sewage bacteria. The tested bacteria included three Gram negative bacteria (Escherichia coli, Proteus vulgaris and Pseudomonas aeruginosa) and three Gram positive bacteria, (Bacillus sp, Staphylococcus aureus and Enterococcus faecalis). Cluster analysis indicated that the best results were obtained from extracts of the marine alga against most of the tested bacterial species. Bacillus sp. was profoundly affected by all plant extracts, while the other bacteria were affected to a lesser extent. The results indicated a great potential for finding new bioactive agents from aquatic plants and the antibacterial substances present in the tested aquatic plant extracts could be used to inhibit the growth of some human pathogens. Further investigations on the analysis and fractionation of such bioactive agents are recommended.

Immunization is usually performed against foreign substances that enter the living body, in order... more Immunization is usually performed against foreign
substances that enter the living body, in order to enable
the immune system to remove them. Those substances
vary from being bacterial cells, viruses, fungi, parasites,
toxins or even irregular cells such as cancer cells. The
development of immunization is a story that dates back
long time ago. It depends on the previous researcher’s
trials and errors. The development is often a specific case
for each vaccine. Some vaccines give a protective immune
response when produced by simple first generations
procedures, while others profited from the advancement
in design and preparation techniques.
The design of vaccines –itself– is now an independent
science. It starts usually by the investigation of the 2
heroes of the vaccination process, the pathogen and the
patients. The study of the previous trials to construct that
vaccine offers a rich database to understand the pathogen
and disfavor the continuation in the same way of the
previous failures. The review of the literature of vaccine’s
research sometimes revives the misevaluated hidden
solutions to construct a vaccine. Computational, physical
and binding techniques are powerful tools to identify
the appropriate building-blocks for vaccine production
whereas biotechnology is the key science to produce
vaccines.
The field of vaccine’s research starting from the call
to prevent a specific pathogen, going through its design, production, evaluation and trials on human’s models
exclusively requires the experience and methods of
variable set of sciences. Therefore, it necessitates the
cooperation of several scientific disciplines. It is always
a rich and interesting field for research and innovation
since diseases always emerge, older vaccines require
development, and up-to-date techniques evolve to
produce better vaccines. This editorial article displays
the development of immunization trials and offers a
simple understanding for the development concepts.
Simultaneously, it proposes calls for further research and
documentations.

Coccidiosis is a major intestinal disease affecting economically valuable livestock animals such ... more Coccidiosis is a major intestinal disease affecting economically valuable livestock animals such as chickens and turkeys. Economic losses are associated with decreased productivity in afflicted animals. The different Eimeria spp. are the main etiologic agents for that virulent disease. The usefulness of prophylactic and therapeutic anticoccidial compounds has decreased in recent years due to the emergence of drug resistance in Eimeria, together with their possible toxic effect to the human consumers. Despite that, biosecurity and disinfection measures are the cornerstone to control the emergence of the pathogen, the immunization methods proved to be more practical and promising to prevent outbreaks due to coc-cidia. Since the early 1950s, several attempts were followed to formulate commercial immunotherapies, but up till now none proved to be sufficient. This review summarizes, classifies, and evaluates the trials performed to prevent avian coccidiosis, thereafter introduces an out of frame scientific strategy to find a solution for that emerging parasite.

Infectious Disease Reports, 2012

Klebsiella pneumoniae is a major cause of nosocomial pneumonia, septicemia and urinary tract infe... more Klebsiella pneumoniae is a major cause of nosocomial pneumonia, septicemia and urinary tract infections, especially in newborns, blood cancer patients, and other immunocompromised candidates. The control of K. pneumoniae is a complicated issue due to its tight pathogenesis. Immuno-prophylactic preparations, especially those directed toward the bacterium O-antigen, showed to be the most successful way to prevent the infection incidence. However, all previously proposed preparations were either of limited spectrum or non-maternal, and hence not targeting the main Klebsiella patients. Moreover, all preparations were directed only to prevent the respiratory diseases due to that pathogen. This article addresses the development of a method originally used to purify the non-capsular bacterial-endotoxins, as a new and easy method for vaccine production against K. pneumoniae. The application of this method was preceded by a biotechnological control of capsular polysaccharide production in K. pneumoniae. The new produced natural conjugate between the bacterial O-antigen and its outer membrane proteins was evaluated by physicochemical and immunological methods to investigate its purity, integrity, safety and immunogenicity. It showed to be pure, stable, safe for use, and able to elicit a protective immunoglobulin titer against different Klebsiella infections. This immune-response proved to be transferable to the offspring of the vaccinated experimental rabbits via placenta.

Vaccine, 2012

The success of vaccines may lie in their association with selected adjuvants.

International Journal of Immunological Studies, 2012

ABSTRACT Abstract: K. pneumoniae is the most common cause of nosocomial respiratory tract and pre... more ABSTRACT Abstract: K. pneumoniae is the most common cause of nosocomial respiratory tract and premature intensive care infections, and the second most frequent cause of Gram-negative bacteraemia and urinary tract infections. Although immuno-prophylactic preparations appeared to offer the most suitable control, no vaccine trials were directed to prevent Klebsiella in all patient’s groups. Therefore, the screening for universal protein epitopes in all types of Klebsiella infections is the corner-stone to produce potent vaccines. Western blot was used for such purpose and highlighted five proteins produced in sufficient amounts, shared by all isolates and exerted a clear immunogenic response in different groups of infected patients. Literature review and further purification of outer membrane proteins (OMPs) revealed that those bands are the main OMP’s of Klebsiella. The conjugation of those OMPs to the main Klebsiella O-antigens would be the building block of a new potent vaccine.