The phrase "a primary agent" is correct and usable in written English.
It can be used in contexts where you are referring to a main or principal individual or entity that has a significant role or influence in a particular situation or process.
Example: "In the study of social dynamics, a primary agent can significantly impact the behavior of the group."
Alternatives: "a key player" or "a main contributor".
Biomechanical forces, such as those produced during mastication, are considered a primary agent in stimulating craniofacial growth and development.
The research is focused on developing a heat pipe heat exchanger for domestic hot water and thermal agent preparation, preheating / heating the air from ventilation systems in buildings, using as a primary agent the return of the existing heating system.
Typically, you name a primary agent and a backup agent (say, your eldest child and your second eldest), in case the first can't or won't take on the duty.
Typically, when you sign a financial power, you name a primary agent and a backup agent (say, your eldest child and second eldest) in case the first can't or won't take on the duty.
Example: A widow might name one adult child as a primary agent able to make routine decisions but require that another child (the backup agent) sign off, too, before property is given away or sold.
Informal interaction between students and faculty has been identified as a primary agent of college culture, and has an important influence on the attitudes, interests, and values of college students (Chickering & Reisser, 1993; Lambert, Terinzini, & Lattuca, 2007; Pascarella, 1980b; Pascarella & Terenzini, 1991, 2005; Thompson, 2001).
Knowing that the disease has a single primary agent will simplify the work of developing accurate and sensitive diagnostic tests that are key to slowing the spread of the disease, said Klaus Stöhr, who is helping to coordinate the WHO effort against SARS.
In 39 cases it was not possible to determine the MRDD; this was primarily due to absent weight data, but in 3 dogs prescription of multiple systemic antimicrobial agents concurrently prevented assessment of a single primary agent.
They also found significantly more E. coli isolates in affected sheep than in unaffected animals, but since the prevalence rate was low (7,5%) they considered this agent not to be a primary causal agent.
Citrate capped silver nanoparticles (AgNPs were synthesized from silver nitrate (AgNO3) using sodium borohydride as a primary reducing agent and trisodium citrate acting as both a reducing and capping agent to obtain the diameter of ~10 nm. 2 mM of sodium citrate and 2 mM sodium borohydride were mixed using a magnetic stirrer for 30 minutes at 60 °C.
In summary, of the bacterial respiratory pathogens evaluated, M. ovipneumoniae was the only agent for which the data consistently met the criteria for a primary etiologic agent across all outbreaks.
