Cockroaches: Nature's petri dish

© COURTESY OF THE CDC

If the sight of a cockroach scuttling across your kitchen floor is enough to trigger paroxysms of disgust, then you'd be well advised to take a deep breath before browsing through "Cockroaches in the Home, Cockroaches Everywhere!!!" This exceptionally well-named publication was written by a team led by Sesai Mpuchane, associate professor of biological sciences at the University of Botswana, and it is meant to be scary. Its purpose is to raise awareness among householders, street vendors, and other groups of the biology of these reviled creatures, in the hope that they can be better controlled.

The booklet's 73 pages are crammed with illustrations showing some of the approximately 4,000 species of cockroaches that populate the planet, plus their feces, eggs, and nymphs. It also reports the findings of a study Mpuchane and her colleagues conducted a few years ago to survey the cockroach population of Gaborone, the capital of Botswana (see p. 44 ). Armed with scores of sticky traps to capture their quarry, Mpuchane's group sampled for the presence of adult cockroaches, their egg cases, and nymphs in kitchens, bathrooms, bedrooms, and larders throughout the city.

The results make for unpleasant reading. In the 50 houses they chose, scattered through four districts, they found thousands of cockroaches, predominantly the small "German" cockroach, Blattella germanica, and its larger cousin, the American cockroach, Periplaneta americana.

Like many cities, Gaborone is home to people from a wide range of economic groups, but wealth didn't seem to be a factor in the presence of these unwelcome visitors. In a group of houses occupied by university staff, for example, the researchers captured more than 7,000 per week. "Even in some very clean-looking homes cockroaches were trapped," Mpuchane points out.

The true horror emerged, however, when the researchers began subjecting the bugs to microbiological studies. Nestled into the roaches' rough body surfaces, and secreted away in their gut contents, the Botswana scientists found species of Bacillus, Enterobacter, Escherichia, Klebsiella, Pseudomonas, Serratia, Staphylococcus, Shigella, and Xanthomonas, as well as other coliforms.

Several species of yeasts were also routinely found, plus molds such as Aspergillus, Cladosporium, Fusarium, and others. Dozens of crisp electron micrographs produced at the university illustrate the copious microbes growing across the cockroaches' wings, legs, and antennae. In one picture, a bacteria-laden residue of cockroach vomitus is helpfully illustrated with a nice white arrow.

If the implications of all this weren't clear, Mpuchane's team spell them out. "They feed on human food and on feces. They drop their feces on human dwellings. They regurgitate some of their partially digested food."

Over lunch in a Gaborone restaurant recently, Mpuchane elaborates on those findings. "Not only were the cockroaches carrying organisms," she says, "but in some cases they were resistant to antimicrobials. They were therefore carrying integrons for resistance, which they could have been spreading."

The fact that some cockroaches are carrying drug-resistant pathogenic microbes across our bench-tops, she says, should motivate health authorities to prioritize control efforts. She advises the use of an integrated approach, combining sanitation, chemical control, insecticides, and other methods.

It doesn't look like the general public will need much convincing. The booklet lists dozens of the most popular roach sprays in Botswana. Their names - Fast Kill, Raid, Doom, and Blue Death among them - suggest householders already consider the problem a matter of life and death.