Antibiogram Of Gram Negative Bacteria Isolated From Fresh Vegetables

Project and Seminar Material for Microbiology

Antibiogram Of Gram Negative Bacteria Isolated From Fresh Vegetables


This study was carried out on the antibiogram of gram negative bacteria isolated from fresh vegetables. There has been an unusual increase in the emergence of antimicrobial resistance to most of the commonly used antibiotics particularly in the developing countries. In this study, five bacteria species tentatively named NC1-5 were isolated from these vegetables: Corchorus olitorius (L.), Celosia caracas, Vernonia amydalina and Abelmoschus esculentus and the irrigation water in Ado-Odo Ota, Nigeria. The isolates were characterized culturally, morphologically and biochemically. The organisms were compared with standard reference organisms and were proposed to be species of Escherichia coli, Chromobacterium violaceum, Micrococcus luteus, Shigella and Salmonella. These bacteria species were tested for their susceptibility to standard Gram positive and Gram negative antibiotics by agar disk diffusion method. The tested antibiotics at different concentrations include: cotrimazole, cloxacillin, erythromycin, gentamycin, augmentin, streptomycin, tetracycline and chloramphenicol. Chromobacterium violaceum exhibited 100% susceptibility to all antibiotics tested, while other bacteria species showed different susceptibility patterns ranging from susceptible, intermediate resistant and resistant patterns. From this study, vegetables can be an avenue for transferring antibiotic resistant genes in community settings. Hence it is necessary to monitor and understand the critical points in the control of antibiotic resistance among the developing countries.

Chapter One


1.1 Background of the study

Vegetables include the leafy, fruit, seed or root vegetables that are fit for human consumption (Obetta et al., 2011). These parts are consumed whole or in part, raw or cooked as a supplement to other food crops. Nowadays, there has been an increase in fresh vegetables consumption due to health benefits in eating natural, healthy and functional foods. Consequently, consumers are seeking for vegetables products that maintain its natural nutrition and other aesthetic qualities such as flavor, texture and color properties. In the developing countries, vegetables are comparatively cheap and easy to grow (Nwachukwu et al., 2008). Thus, most rural women rely on these vegetables as source of income. Despite the numerous benefits of vegetables, it could be a medium for the spread of bacterial, parasitic, viral pathogens and antimicrobial resistance mechanisms. As a consequence, the production and distribution of fresh vegetables could be a huge challenge to the food industry.

Water is one of the principal agents for the spread of various enteric diseases. Some researchers have stated that water from contaminated sources can propagate harmful microorganisms that can affect the safety of such vegetables (Moses et al., 2016). Since most of the populations that grow vegetables are from rural areas, majority of them cannot afford expensive technologies, such as use of chlorinated water to rinse their vegetables. Accordingly, they adopt locally-available and cheap technologies such as rinsing with ordinary water from rivers and shallow wells without recourse about the safety of the vegetables.

Food borne outbreaks associated with vegetables that are partially processed or consumed naturally have increased over the years (Ehimemen et al., 2019). This rise in the food-borne outbreaks from vegetables is due to the favorable conditions that the vegetables provide consequently encouraging the growth and survival of many types of microorganisms. Some of the favorable conditions include nutrient rich internal tissues-comprising polysaccharides (starch), pectin, hemicelluloses and cellulose. Enteropathogens such as Escherichia coli and Salmonella are among the greatest concerns with food-borne outbreaks. In 2007, these organisms were implicated in food-borne outbreaks in UK that resulted in the recalling of bagged lettuce. Such recalls damage the consumer’s confidence and hampers economically the income and corporate image of such food processing industry involved with the sale and distribution of such products. The enteropathogens Escherichia coli and Salmonella have been implicated in cases of diarrhea and typhoid fever following consumption of contaminated vegetables (Nasiru et al., 2015). In most developing countries, street vending of fresh vegetables are on the increase and as such precautionary measures on the safety of the vegetables are not considered. Consequently, such vegetables could be a repository for various organisms that can severely affect the welfare of the consumers, shelf-life and nutritional worth of the vegetables.
In this study, selected vegetables popularly grown and consumed in the Ado-Odo Ota, Nigeria were assessed for epiphytic bacteria species associated with it and their antibiotics susceptibility patterns. The selected vegetables include: Corchorus olitorius (L.), Vernonia amydalina Delile, Abelmoschus esculentus and Celosia caracas. The selection of these vegetables were based on the huge culinary and medicinal benefits they offer the population when consumed raw or lightly cooked. For instance Corchorus olitorius when boiled or mashed as fresh leaves serves as rich sources of vitamins A, C and methionine. Also, Vernonia amydalina. Delile is known for its antimalaria, antihelmenthic, antitumorigenic properties as well as antioxidant properties.

Recently, efforts have been devoted to prolonging the shelf life of vegetables, however, the determination of the antibiotic susceptibility patterns of the bacteria species associated with these vegetables have been scarcely reported. Therefore, the present study attempted to evaluate the presence of bacteria species associated with the selected local vegetables and their antibiogram to standard antibiotics.

1.2 Statement of the problem

Vegetables spoilage can result to changes or hydrolysis or decomposition of matrices by microorganisms resulting in unpleasant disorder of the vegetable due to toxic substances released in the vegetable material resulting in pigmentation, degeneration and discoloration of the vegetable materials (Afolabi et al., 2015). These physical abnormalities can make the vegetables inedible and unacceptable to the public or in some cases may pose a public health risk to consumers due to the high microbial load or pathogens associated with spoiled vegetables. In Nigeria, vegetables are chewed raw or heated lightly in order to retain its organoleptic properties. This has in most cases been responsible for food– borne infections, because in the process of harvesting, disease-causing microorganisms may contaminate these vegetables through contact with organic wastes such as faecal matter, organic manure, sewages, untreated irrigation water or surface waters used as nutrients or composts to improve soil quality (Afolabi et al., 2015).

The water sprinkled on the vegetables to keep them fresh may also be a source of microbial contamination depending on the source of the water used. Antinutritional factors such as hydrogen cyanide, phytates and oxalates are able to influence the metabolic processes needed for the increase and bioavailability of nutrients in vegetables. Most vegetables are used as nutrients in flavoring soups and sauces. Vegetables have pleasant aroma when added to soups and sauces, also contribute to the protein and essential minerals. Subjecting them to heat in the form of cooking in soups and sauces increases their digestibility. Their presence or use in foods preparation introduces a variety in the flavors obtained from the same foodstuff and enhances nutritional value of the food. Therefore, vegetables have great potential as key protein and mineral sources which are basic ingredients for food supplementation.

1.3 Objectives of the study

The main objective of the study is to examine the antibiogram of gram negative bacteria isolated from fresh vegetables. Specifically, the study sought to:

  1. Examine the bacteria species occurring in the samples.
  2. Examine the physiological characteristics of the isolated organisms.
  3. Examine the antibiotics susceptibility pattern of the bacteria species.
  4. Examine the zones of inhibition (mm) of antibiogram patterns of the bacteria isolates.

1.4 Justification of the study

Vegetables were selected in this study because they are often eaten raw. resistant bacteria could colonize vegetables for a number of reasons: the direct use of antibiotics during cultivation, the use of contaminated fertilizers or irrigation water, or some unknown non-human selection pressure. To this knowledge very little research has been done on the antibiogram of gram negative bacteria isolated from fresh vegetables, therefore, the need to carry out this research.

Chapter Five


In conclusion, this study has revealed that although local vegetables could provide huge culinary and health benefits for mans sustenance and development, it could also harbor antimicrobial resistance genes that could be transferred to the consumers causing widespread resistance to the usual antibiotics. Given the significance of this study to the public health managers it is advocated that irrigation water supplies should be properly screened before use in other to eliminate/reduce minimally contaminations and antibiotic resistance gene transfers. In addition, safe wash water for the vegetables is advocated among the rural areas rather than the use of untreated and unsafe water that will negatively affect the community health.

Presence of pathogenic organism, Staphylococcus aureus, Escherichia coli, salmonella spp., in most vegetables and fruits reflects poor sanitary condition adopted during cultivation, harvesting, transportation, storage and utilization or preparation process ranging from peeling, slicing, trimming, packaging, handling and marketing. For example, salmonella spp. are associated with humans gastrointestinal disorders, fever, abdominal cramp, vomiting and diarrhea due to food poisoning, while enteropathogenic Escherichia coli are also implicated in diarrhea originating from poor sanitary conditions and virulent factors. This is of a public health concern, which calls for caution to be exercised by consumers and venders. Proper implementation of the above recommendations would go a long way in curtailing microbial risk associated with fruits and vegetable consumption in Nigeria.

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