Dear Evan

A collaboration from our ASM communications ambassadors Binod Rayamajhee and Umme Laila Urmi, PhD Candidates, School of Optometry & Vision Science, Faculty of Medicine & Health, UNSW; Dr Melinda Ashcroft, Postdoctoral Research Fellow, Department of Infectious Diseases, Central Clinical School, Monash University, and Xavi Bertran Forga, PhD Candidate, QUT.

A great opportunity came up last week for our new ASM communications ambassadors when we received an email from a Year 6 student, Evan, asking some questions about microbiology. Together some of our ambassadors collaborated on the questions, along with input from one of our past Presidents Professor Roy Robins-Browne.

What do good bacteria do for us every day?

Good bacteria are also known as commensal bacteria and have pl functions depending on the type of bacteria and where they are found in or on the body. For example, commensal bacteria have a role in protecting us from bad/harmful (otherwise known as pathogenic) bacteria. Commensals can outcompete pathogenic bacteria, limiting their growth and preventing infections. Additionally, commensals can stimulate our immune system to fight against pathogenic bacteria that make us sick and reduce inflammation. Commensals also have a large role in digestion (known as the gut microbiota), where they live in our digestive system and help us break down the food we eat. They assist in breaking down fibres and substances that our own bodies cannot process, which then allows us to absorb these essential nutrients and vitamins [1].

How could I try to stay healthy and avoid bacteria?

Although it is impossible to completely evade bacteria as they are present everywhere, there are steps you can take to maintain good health and reduce the likelihood of harmful bacterial infections. Here, we should prioritise our general health by obtaining a good amount of sleep daily, eating healthy, and exercising regularly. We should also maintain good hygiene practices such as hand washing, washing fruits and vegetables, cooking meats, and ensuring foods are stored at appropriate temperatures (for example, food poisoning bacteria grow best at temperatures between 5-60°C, which is known as the temperature danger zone [2]).

An interesting fact is that our phones tend to accumulate incredibly high amounts of pathogenic bacteria [3], so washing your phone screens from time to time is a good habit to have.

It is crucial to note that it is neither possible, nor recommended to completely avoid all bacteria, as many bacteria are commensals and serve significant functions in our bodies and the world around us.

https://unsplash.com/@mrsmaria

When is the most common season to get sick?

Bacterial infections can occur at any time of the year, and there isn't a specific season that is universally associated with a higher risk of bacterial infections. The prevalence of bacterial infections is influenced by various factors, including the type of bacteria, geographical location, and individual behaviours.

Certain bacterial infections, such as respiratory tract infections caused by bacteria like Streptococcus pneumoniae or Haemophilus influenzae, can occur more frequently during the colder months. This increase in infections in colder months is typical because people tend to spend more time indoors and are in close proximity to others, with low levels of ventilation [4]. However, it's important to note that viral respiratory infections, such as those causing colds, the flu, and COVID-19 are generally more common than bacterial ones during colder months.

Other bacterial infections, such as foodborne illnesses caused by bacteria like Salmonella or Campylobacter, can occur throughout the year, but the risk may increase during warmer months when food is often prepared and consumed outdoors, and there is a higher likelihood of improper food handling or inadequate refrigeration.

In summary, the seasonality of bacterial infections varies depending on the specific type of infection and various environmental and behavioural factors. It's important to maintain good hygiene practices, handle food safely, and seek appropriate medical care if you suspect a bacterial infection, regardless of the season.

How long should I grow bacteria for?

This really depends on the bacteria, as they all have different growth requirements. Temperature, the type of media they are grown in/on and requirements of oxygen exposure are also important.

Some facultative anaerobic bacteria can take up to 48-72 hours at their optimum temperature to grow, whereas some aerobic bacteria grow faster requiring only 12-24 hours to grow. Some bacteria such as those from the Mycobacterium genus are very slow growing and can take up to 6-8 weeks to grow [5].

How do we measure the intensity of bacteria?

There are several different ways to determine bacterial growth.

One of the most common methods for monitoring the growth and proliferation of bacteria is a growth curve measurement based on optical density (measuring the turbidity or cloudiness of the culture). This is related to the number of bacterial cells which are measured in small glass or plastic containers called cuvettes at a wavelength of 600 nm using a spectrophotometer [6]. The size of the population could be measured by counting cells directly or by first diluting the original sample (serial dilution), spreading the diluted sample on agar and then counting the number of cells (colonies) that grow. The result is then multiplied to give a population density per cm3 of culture [6]. There are many other methods including direct counting of cells from under a microscope, measurements of growth rates based on metabolic activity, measuring single cells using fluidics etc.

What intake of E. coli O:157H:7 can we take without getting sick?

We asked Medical Microbiology expert Professor Roy Robins-Browne:

As someone with an interest in E. coli O157:H7, I can say the answer is “not very many” (i.e., <100), but it’s highly variable, as data from outbreaks show [7].

References

[1] A. Adak and M.R. Khan. Cell Mol Life Sci (2019). 76(3): 473-493

[2] Temperature danger zone. NSW Government. https://www.foodauthority.nsw.gov.au/media/1356

[3] M. Olsen, et al. Travel Med Infect Dis (2020). 35: 101704

[4] L. Willem et al. PLoS One. 7(11): e48695

[5] L.B. Reller, et al. Clin Infect Dis (2001). 33(6): 834-46

[6] N. Parker et al. How Microbes Grow. OpenStax: Microbiology (2016). Open Educational Resources Collection. 3. https://openstax.org/details/books/microbiology

[7] L.W. Riley, et al. N England J M (1983). 308(12): 681-5