An investigation of the antimicrobial activity of essential oils against antibiotic resistant foodborne pathogens related to diarrhoea

Thesis (Master: Health Sciences: Environmental Health)--Central University of Technology

Infections that cause diarrhoea, which is a persistent health problem globally, are some of the most prevalent causes of mortality in children under the age of five. This health issue is also known to have caused as many as 500 000 deaths annually around the world (Najim et al., 2019). In children under the age of five, diarrhoea is known to spread through contaminated food, lack of access to safe drinking water, poor hygiene by mothers when handling paediatrics, non-breastfeeding or delayed breast-feeding, socio-economic status, and malnutrition (Akinyemi et al., 2018; Kuhn, 2019). Additionally, the Global Enteric Multicentre Study (GEMS) indicates that the rate of children presenting with diarrhoea which results in morbidity and mortality in developing countries is high (Liu et al., 2016 Aljamali, 2021). Most food poisoning reports (Aljamali, 2021) are associated with pathological defilement, especially among members of Gram-negative microbes like Salmonella typhimurium, Escherichia coli and Pseudomonas aeruginosa (Mostafa et al., 2018). Gram-positive bacteria such as Staphylococcus aureus and Bacillus cereus have also been identified as causal agents of foodborne illnesses (Mostafa et al., 2018). As severe diarrhoea has been categorised as life-threatening, scientists have endeavoured to discover antibiotic treatments to manage this threat. Initially, antibiotics were effective and reduced diarrhoeal cases among paediatric patients (Mantegazza et al., 2018; Najim et al., 2019). However, most microorganisms have developed resistance to antibiotics such as Cephalosporin, Methicillin, Tetracycline and Ampicillin, resulting in more problems in the medical field (Church & McKillip, 2021). Researchers have thus begun to search for alternative strategies to augment the effect of currently used antibiotics, and one such alternative is the use of essential oils (Gibson et al., 2015; Chandra, 2017). The current investigation focused on the use of essential oils to address the effects of pathogens that cause diarrhoeal infection in children under the age of five. A point of departure was that antimicrobials with plant origins such as essential oils (EOs) are less likely to be associated with adverse side effects as they are natural products. Moreover, many such preparations have been used in foods such as spices and flavour enhancers and have been shown to have therapeutic potential to heal infectious diseases (Mehdi et al., 2018; et al., 2021). To identify the constituents of the essential oils (also referred to as aromatic oils) that were used in the study, a gas chromatography-mass spectrometry (GC-MS) analysis was performed. The antimicrobial activities of the selected essential oils (Helichrysum splendidum, Mentha piperita, Tagetes minuta, and Pelargonium graveolens) that were used on the selected bacteria (Escherichia coli, Clostridium difficile, Salmonella enterica, and Staphylococcus aureus) were evaluated by using the bioassay and minimum inhibition concentration (MIC) methods. The analyses revealed that all four the selected oils contained components that are known to have antimicrobial effects on bacteria. However, the EOs that were tested affected bacterial cells differently per bacteria because of the difference in the bacterial cells of the microorganisms. For instance, Tagetes minuta and Pelargonium graveolens were the most effective oils as they showed greater zones of inhibition against the organisms. It is thus argued that these two oils show great promise for use as alternative antimicrobial agents.