Unicellular organisms such as yeast have served as tractable models to probe the molecular biology of eukaryotes, whereas most major human pathogens are prokaryotes.
Over one century of extensive efforts directed towards investigating the immune response and the immuno-protection associated with sexually transmitted infections have failed to produce any effective vaccines against most of the major pathogens, among them Neisseria gonorrhea, herpes simplex virus type 2, and Chlamydia trachomatis.
First, most major classes of pathogens have evolved agents that are capable of being transmitted by blood-feeding arthropods: viruses (e.g., yellow fever virus, Rift Valley fever virus), rickettsiae (Rickettsia rickettsii, R. typhi), bacteria (Borrelia burgdorferi, Francisella tularensis), protozoa (genera Plasmodium and Leishmania), and helminths (Onchocerca volvulus, Wuchereria bancrofti).
Gram-negative bacteria, most commonly pseudomonas, are the major pathogens.
The most frequently observed PNC mastitis pathogens (major pathogens) are Streptococcus uberis, Strep.
Among the major pathogens causing BSI, most often fatal within the first 28 days was K pneumoniae infection (40%) followed by S pneumoniae (9.6%), S aureus (8%) and E coli (5%; χ=39.1, 4df; p<0.001).
Most cases of OM are caused by three major pathogens: S. pneumoniae (30 40%), nontypeable Haemophilus influenzae (NTHi, 30%) and M. catarrhalis (20%) [ 1, 2].
Major pathogens were identified in 49% of patients, most commonly methicillin-resistant Staphylococcus aureus (14.8%) and Pseudomonas aeruginosa (14.3%).
The causative agents for most major infectious diseases have been well characterized, and so identification of archaeal pathogens, if they exist, is more likely given this bias.
They are believed not to be based on pathogen recognition systems, as it is the case with most major R genes, but the possibility cannot be excluded [ 27].
