Antibiotics was discovered in 1928 by Alexander Fleming, which is responsible for synthesis of thousands of antibiotics and saved millions of lives from various pathogenic bacteria. Antibiotics are among the best-selling medicines worldwide, playing a critical role in treating bacterial infections and saving countless lives. Globally, there was increased in antibiotic consumption by 36% during 2000 (54 billion) to 2010 (73 billion), particularly in countries like Brazil, Russia, India, China and South Africa, indicating the growing demand for these drugs (Van Boeckel et al., 2015). The use of antibiotics in veterinary and animal husbandry constituted 50–75% of the total antibiotic consumed (Steinfeld et al., 2006). The consumption of antibiotic in livestock was projected to increase by 67–200% in 2030 (Van Boeckel et al., 2015). World antibiotic consumption rate increased from 9.8 (in 2000) to 14.3 (in 2018) define daily dose (DDD) per 1,000 population per day (Browne et al., 2021). However, the extensive use of antibiotic risk the environment, and the effects of these compounds on the host require realistic assessments. Among the various antibiotics, the most used antibiotics in human medicine consisted of penicillin, macrolides, and fluoroquinolones while penicillin, tetracyclines, and sulfonamides are commonly used in animal husbandry for treatment, prevention of infectious diseases and supplemented as growth promoter in feed for animals (Chopra and Robert, 2001). Ampicillin is a penicillin group drug used during pregnancy against Group B staphylococcus as an intrapartum prophylactic drug (Aloisio et al., 2014). The nature of the toxicity varies based on the compounds in the antibiotics, routes, pathways, and targeted gene/population (Arnold et al., 2013). During antibiotic administration, some portions are released as residues into the soil, water, flora, and fauna. Around, 25–75% of antibiotics administered are released into the environment which facilitates the proliferation of antibiotic resistant bacteria. The residue of antibiotic like ampicillin persistently exists in the environment due to its hydrophobic nature. Ultimately, it possesses a potential risk on the host organisms, which includes both humans and animals. The consumption of contaminated water or food products has impact on human health. In several cases, exposure to diclofenac via food web leads to near-extinction of vultures (Oaks et al., 2004) and estrogen-exposure increases femininization of the fish population (Kidd et al., 2007). Even though antibiotics are targeted on pathogenic bacteria and the unexpected detrimental effects on non-target organisms have been continuously reported but no clear mode of action in higher organisms has been mentioned in earlier studies so far. The shifting of gut microbiota varies with the antibiotic used i.e., amoxicillin and azithromycin reduce Lactobacillus johnsonii abundances while cefactor enriched the GM in rat model (Khan et al., 2016). Antibiotics can alter gut microbiota including functional attributes of the microbiota formation, reduction of microbial diversity and selection of antibiotic resistance strains. Evidence suggests that rich species diversity and balance microbiota composition are essential for optimal function of the host health (Heiman & Greenway, 2016) whereas imbalance or reduce diversity leads to intestinal illness in infant’s gut (Volkova et al., 2021; Milani et al., 2017). Induced change in gut microbiota during pregnancy also correlates with metabolic disorder in germ mice (Koren et al., 2012). Broad-spectrum antibiotics eliminate beneficial microbes (Blaser, 2011) and reduce diversity in gut microbes (Dubourg et al., 2014) with deleterious effects on the host. Maternal antibiotic uptakes during pregnancy transformed the microbial composition in offspring according to the antibiotic type (Coker et al., 2020; Azad et al., 2016). Also, increases the chance of allergy and asthma in the offspring (Stokholm et al., 2014). The levels of bifidobacterial were reduced in infants due to maternal ampicillin treatment during pregnancy against streptococcus infection (Aloisio et al., 2014).
The ubiquity and importance of microbes have been appreciated in the past few decades with utmost attention on pathogenic bacteria. The bacterial symbiont composition plays a beneficial role in the lives of the host. It is more evident that intestinal and extra intestinal disorders are link with gut microbiome (Cani, 2018). Several studies reveal the link of human gut microbiome and gastrointestinal disorders viz. colorectal cancer (Tilg et al., 2016), chronic liver diseases (Tilg et al., 2018; Trebicka et al., 2021), intestinal bowel diseases (IBDs) (Lloyd et al., 2019), pancreatic disorders (Adoplph et al., 2019; Riquelme et al., 2019), irritable bowel syndrome (IBS) (Mars et al., 2020), coeliac disease (Leonard et al., 2021). Gut symbionts of many insects are essential for core host, survival, physiology, and ecological adaptation (Brune, 1998; Janson et al., 2008; Hosokawa et al., 2006). They can serve as a barrier against invading pathogens by competing for resources or producing antimicrobial compounds. It can also interact directly with the host's immune system, influencing its response to pathogens. Disruptions to the gut microbiota can weaken this defense mechanism, making the host more susceptible to infections or altering the outcome of pathogenic interactions. Experimental evidence from insect gut showed the role of microbes in mediating interactions between the host and potential pathogens (Broderick et al., 2006). Kaufman and Klug (1991) suggested that the presence of GM in insect may not be necessary for their basic survival. However, GM plays a vital role in several physiological processes and can significantly affect the overall phenotype of the host.
Drosophila melanogaster is a well-known model of host-microbiome interactions, host physiology, pathology with simpler bacterial community in gut (Martino et al., 2017; Broderick and Lemaitre, 2012). Bacteria affects the life span, gut homeostasis, interaction with pathogens and behaviour of fly (Ryu et al., 2008; Wong et al., 2017). Commensal and non-pathogenic intestinal microbes actively suppress the immune response and community homeostasis in the flies (Lhocine et al., 2008). Similarly, downregulation of caudal significantly increased the rare bacteria (Ryu et al., 2008). The dominance of one gut microbe eventually leads to apoptosis, host mortality and affects the health and fitness of the host e.g., Gluconobacter sp. strain EW707, (Ryu et al., 2008). Drosophila gut microbes help in the production of antimicrobial peptides (AMPs) as well as microbial reactive oxygen species (ROS) and activate the host antimicrobial defense (Ha et al., 2005; Ryu et al., 2006). Despite the important roles of the gut microbiota in the host, so far, the constituent of gut microbes are still an open question. Very few microbes viz., Acenetobacter sp. and Lactobacillus sp. were reported from the laboratory-associated flies (Staubach et al., 2013; Ryu et al., 2008) while the natural environment flies harbours more diverse population in addition (Chandler et al., 2011; Staubach et al., 2013).
In our study, we focus on the impact of ampicillin on gut microbiota in D. melanogaster model and its effect on the host in terms of metabolic and enzymatic activities. The change in diversity and richness of D. melanogaster gut microbe was analysed through 16S amplicon sequencing.