Somerset Times

Year 7 Science Snippets: What your mother calls a germ – or is it?




Somerset Times Edition

Week 1, Term Three, 2017

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Although Somerset College's Science Week is to be celebrated Week 2, Term Three; the Year 7 Scientists were fortunate to have two preliminary Science Week guest speakers in the last week of Term two. The following is an overview of these lectures.

On the 7 June Dr John Gerrard, Director of Infectious Diseases at Gold Coast Health, came to talk to the Year 7 cohort about microbiology: the study of microscopic life, such as bacteria. He talked about his search for a particular pathogen that eluded him for a decade, causing several infections on the east coast of Australia, and in Texas, USA.

“Hold on. What is a pathogen?” I hear you ask. Well, a pathogen is any form of harmful microbial life such as Salmonella (a bacteria) or Ebola (a virus), or what your mother might call a germ. However, not all bacteria are pathogens – about 70 to 90 per cent of bacteria are harmless (“Good” bacteria) and the remaining 10 to 30 per cent being harmful pathogens (“Bad” bacteria). Some of these good bacteria are even beneficial to human life, helping to aid digestion. The study of microscopic life is truly fascinating and can lead to exciting discoveries.

Dr Gerrard’s interest in microbiology became an obsession with his determination to find the origin of one particular pathogen, Photorhabdus. Samples taken from the abscesses that were found on a man from Murwillumbah was from a genus known as Photorhabdus, which means “light rod” in Greek. It was given this name due to its ability to glow in the dark. In search for possible vessels of the pathogen, Dr Gerrard visited the man’s farm, testing everything from water to soil and even spiders. Alas, these tests showed no results matching the bacteria. Despite the man’s recovery, Dr Gerrard continued his research in finding the origin of Photorhabdus.

In his studies of Photorhabdus, Dr Gerrard found through scholarly literature, there were three species under the genus Photorhabdus: P. luminescens, P. temperata and P. asymbiotica. It was also discovered that all of the Photorhabdus species were in a symbiotic relationship with microscopic nematode worms of the genus Heterorhabditis to gain nutrients. To understand this relationship, a worm’s life cycle is as follows: 1. A worm finds an insect larva. 2. The worm penetrates the larva’s skin and regurgitates (vomits) out Photorhabdus. 3. Photorhabdus kills the larva and preserves its body. 4. The worm lays its eggs and the offspring eat the larva. 5. The offspring exit the larva and move on to find more larva.

Soon, another patient came presented with a similar abscess on his right hand. The wound was deep enough to see the man’s tendons! From consulting the patient, Dr Gerrard found out the man had been building a fence around his house using nothing but his right hand to dig up the soft, sandy soil. Dr Gerrard hypothesised that the nematode worms that lived in the soil had infected the man’s hand when he was digging.

To test his hypothesis, Dr Gerrard visited the patient’s house to collect soil samples from the dug out holes. With the soil samples, Dr Gerrard added mealworms to coax out the nematodes. One week later, the mealworms were dead, but they glowed in the dark! This was a clear sign of Photorhabdus.

Under the microscope, Dr Gerrard saw worms slowly coming out of the larva. At first, there were only one or two. Then ten, twenty. Not before long, there were hundreds, thousands and even tens of thousands of worms! Dr Gerrard’s hypothesis was correct and he had finally discovered the cause of the festering abscesses after ten years of hard work.

Dr Gerrard’s obsession with the nematode worms didn’t stop there. From further research into nematode worms in the USA, it was determined that there was a new species of Heterorhabditis. Scientists decided to name this species after Dr Gerrard for his exemplary effort in researching them – Heterorhabditis gerrardi.

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