Seitz filtration of fluids: After passing a fluid through a Seitz filter, which of the following organisms would be present in the filtrate (i.e., retained in the fluid) under proper use?

Introduction:
Depth filters such as the classic Seitz filter (historically asbestos/cellulose) are used to remove bacteria from heat-sensitive fluids. Understanding what remains in the filtrate versus what is retained on the filter is crucial for interpreting sterility assurance in laboratory and pharmaceutical settings.

Given Data / Assumptions:

• Assume correct assembly and use of a Seitz filter with appropriate pre-wetting and flow rates.
• Question asks which organisms would be present in the filtrate (i.e., pass through into the fluid after filtration).
• Choices include common vegetative bacteria and spores.

Concept / Approach:
Seitz filters are designed to retain bacteria on the filter matrix; the filtrate should be free of vegetative bacteria and most spores. While viruses and certain bacterial toxins can pass due to smaller size, the listed organisms (Proteus, Staphylococcus, Clostridium) are bacteria/spores that are retained on the filter under proper conditions. Therefore, none should be present in the filtrate.

Step-by-Step Solution:
Clarify terminology: “retained in the fluid” means present in filtrate after filtration. Match typical pore retention: vegetative bacteria are captured by Seitz filters. Conclude that properly filtered fluid contains none of the listed bacteria.

Verification / Alternative check:
Filtration sterilization is a standard for heat-labile solutions; sterility testing confirms absence of cultivable bacteria in filtrate.

Why Other Options Are Wrong:

• Proteus / Staphylococcus / Clostridium / Mycobacterium: All are retained on the filter matrix under correct procedure.

Common Pitfalls:
Confusing what the filter retains (on the pad) with what remains in the filtrate (the collected fluid). Also, assuming virus removal; Seitz filtration does not reliably remove viruses.

Final Answer:
None of these organisms should be present in the filtrate after correct Seitz filtration.