Besides microbes, there are other parts of nature in which the exact
same natural processes can produce results which are perceived "good" or
"evil," depending upon circumstances and perspective. The clever
beavers' dams change the local ecology, favoring some plants and
animals, harming others. Rain is good, but lots of rain causes
destructive flooding. Is one inch of rain good but ten inches evil?
(You can't make a sharp dividing line at, say, five inches.) In the
insect world, we find a spectrum from "beautiful" symbiosis to "ugly"
parasitism -- but the exact same natural processes of adaptation make
both possible. A similar spectrum is there for microbes in our bodies.
There's a multi-paragraph quote, on the subject of "natural evil," from
John Polkinghorne's "Science and Providence" in the archives at
(about 2/3 of the way down the file) that might be worth perusing.
In discussing lethal microbes with your students at Bethel College, I'd
recommend teaching them some of the biological processes which these
microbes take advantage of. Cell membrane traffic regulation and gene
transcription are totally cool and awe-inspiring processes. I'd
describe (as much as possible, for non-science-majors) how they work
"normally" in the body, and maybe give some examples of some "good"
(symbiotic) microbes in our bodies, and then describe how the lethal
microbes take advantage of those systems. Understanding something of
the good (and amazing) natural processes going on does much to give
perspective on the occasional "natural evil." The students should learn
that there are all manner of microbes ranging from nice to naughty and
everything in between. Maybe include examples of how human activity
(e.g. poor water management or over-use of antibiotics) can push
relatively benign bugs to develop lethal varieties. And, as Ralph
Winter's article suggests, restraining "natural evil" where we can
(through flood management or microbe hunting) may be a task some of us
are called to do.
Is there any possibility you'll have your lecture notes on computer, and
can share them when the class is finished?