Background

Vegetables are those plants which are consumed in relatively small quantities as a side-dish or as a relish with staple food^[5]. In order to keep them from losing their full turgidity, harvested vegetables often require low temperature and moist environment during storage^[4]. As a result, vegetable in the form of leaves are often sprinkled with water after harvesting and during exposure in the open market. The moist condition of the vegetables fostered by the sprinkling of water together with low temperature condition encourages the growth of microorganisms^[6]. These conditions also facilitate direct contamination by microorganisms through the handlers (buyers and sellers). Indirect contamination may also occur as a result of poor hygienic environment of the market. Consequently, harvested vegetables so soon begin to spoil if not sold immediately. However, cleaning processes reduce the number of microorganisms^[6]. This study of bacteriological quality of vegetables was aimed at estimating the level of bacterial contamination of the vegetables commonly sold in different markets of Calabar metropolis and to determine the safety of the vegetables for human consumption.

Materials And Methods

Study area

Handling and Washing of the Vegetables

Method of Culturing the Washings from the vegetables

Sub culturing of the Cultures

Identification of Various Isolates Obtained in the Cultures

Estimation of Intensity of Contamination

Intensity of contamination was estimated by using the viable count technique. Only plates that showed not less than 30 colonies and not more than 300 colonies were used for this estimation. Colony forming unit (CFU) was used as the standard unit for the estimation and is defined by:

Figure 1

Results

The bacteria isolates from the vegetables in Akim market are shown in table 1. Altogether 53 bacteria isolates were made. Bacillus spp had the highest incidence 34(65.30%) followed by Escherichia coli with 10(20.00%), Lactobacillus acidophilus, Micrococcus spp and Proteus vulgaris recorded the lowest incidence of 1(1.60%) each, while Alcaligen faecalis had an incidence of 2(3.20%).

The bacteria isolates from the vegetable samples from Marian market are shown in table 2. Altogether 52 isolates were made. Again Bacillus spp had the highest incidence 24(45.50%) followed by E.coli 16(30.20%), E. aerogenes 7(14.00%), L. acidophilus 3(5.80%) while P.vulgaris and A.faecalis had the lowest incidence of 1(2.25%) each.

From the Watt market, 48 bacteria isolates were made (table 3). Bacillus spp had the highest incidence of 25(53.50%), followed by Escherichia coli 10(22.00%), Enterobacter aerogenes 4(7.20%), Lactobacillus acidophilus and Alcaligen faecalis 3(6.55%) respectively and Micrococcus spp 1(1.80%).

Table 4 shows a comparison of the bacteria isolates from the three markets of Calabar metropolis. From total of 153 bacteria isolates made from the three markets, 53(34.64%) were from Akim market, 52(33.99%) were from Marian market and 48(31.37%) were Watt market. Although the isolates from Akim and Marian markets were slightly higher than that of Watt market, they were not significantly higher (P>0.05) than that of the Watt market.

Of the seven bacteria species namely Bacillus spp, Micrococcus spp, Escherichia coli, Proteus vulgaris, Enterobacter aerogenes, Lactobacillus acidophilus and Alcaligen faecalis, from the three markets, Bacillus species isolates 83(54.25%) were significantly higher (P<0.05) than other bacteria isolates. In the order of their significance, Bacillus was followed by E. coli 36(23.53%) and Enterobacter aerogenes 15(9.80%). Others were Lactobacillus acidophilus 7(4.56%) Alcaligen faecalis 6(3.92%), Proteus vulgaris 4(2.61%) and Micrococcus species 2(1.31%).

The distribution of individual bacteria isolates on the vegetables is shown in table 5. Of the seven bacteria species, Bacillus species and Eschericha coli were isolated from all the five vegetable groups studied. The highest number of Bacillus isolates 31(37.75%) were from fluted pumpkin leaves while the least 3(3.61%) were from pepper. Also the highest number of E. coli isolates 14(38.8%) were from fluted pumpkin leaves and least 1(2.78%) were from pepper. One isolate each of Micrococcus spp was made from tomatoes and fluted pumpkin. Proteus vulgaris was not isolated from onions and pepper, it has the highest isolate 2(50.0%) from tomatoes and 1(25.0%) from cucumber and pumpkin leaves respectively. Enterobacter acrogens and Alcaligen faecalis were also not isolated from onions and pepper. The highest number of E. aerogenes isolates 8(42.86%) were from fluted pumpkin leaves and the least 3(20.0%) from tomatoes. Also the highest member of A. alcaligen isolate 3(50.0%) were from fluted pumpkin leaves and the least 1(16.67%) was from tomatoes. Lactobacillus acidophilus was not isolated from pepper only. The highest number of L. acidophilus isolates 3(50.0%) were from fluted pumpkin leaves and least number 1(14.29%) were from cucumber and onions. With the exception of P. vulgaris with its highest number of isolates from tomatoes, five bacteria species namely Bacillus spp, E. coli, E. aerogenes, L. acidophilus and A. alcaligens had their highest isolates from fluted pumpkin leaves. An equal number of isolates of Micrococcus species was isolated from tomatoes and fluted pumpkin leaves (one isolate from each). All the seven bacteria isolates were made from fluted pumpkin leaves and tomatoes while only Bacillus spp and E. coli were found in pepper. Onions has only 3 bacteria isolates viz. Bacillus spp, E. coli and L. acidophilus. Cucumber has all the six bacteria isolates with the exception of Micrococcus species.

The percentage distribution of the isolates on the vegetables is represented in figure 1. Of the 153 bacteria isolates, 61(39.87%) were from fluted pumpkin leaves, 42(27.45%) from cucumber, 38(24.84%) from tomatoes, 8(5.23%) from onions and 4(2.61%) from pepper. The distribution of the isolates on the different vegetable was statistically significant (P<0.05). Fluted pumpkin had the highest number of isolates followed by cucumber, tomatoes, onions and pepper.

The viable bacteria counts from the different vegetables bought from markets of Calabar metropolis were shown in figure 2. Telfairia occidentalis (fluted pumpkin) recorded very high bacteria counts in all the three markets in Calabar metropolis with 5.0x10⁷ cfu/ml, 6.2x10⁷ cfu/ml and 9.3x10⁷ cfu/ml respectively in Akim, Marian and Watt Markets. Cucumis sativus (cucumber) recorded its highest count of 9.0x10⁷ cfu/ml in Watt market while Lycopersicon esculentum (tomatoes) had its highest count of 4.8x10⁷ cfu/ml in Akim market. Allium cepa (onions) recorded its highest bacteria count 3.0x10⁷ cfu/ml in Marian market while Capsicum annuum (pepper) had the highest bacteria count 1.8x10⁷ cfu/ml in Marian market.

Figure 2

TABLE 1: BACTERIA ISOLATES FROM AKIM MARKET SAMPLES

Figure 3

TABLE 2: BACTERIA ISOLATES FROM MARAIN MARKET SAMPLES.

Figure 4

TABLE 3: BACTERIA ISOLATES FROM WATT MARKET SAMPLES.

Figure 5

TABLE 4: COMPARISON OF BACTERIA ISOLATES FROM THE MARKETS IN CALABAR METROPOLIS

Figure 6

TABLE 5: THE NUMBER AND PERCENTAGE DISTRIBUTION OF INDIVIDUAL BACTERIA SPECIES ON THE FIVE DIFFERENT VEGETABLES

Figure 7

FIGURE 1: PERCENTAGE FREQUENCY DISTRIBUTION OF THE BACTERIA ISOLATES ON THE VEGETABLES.

Figure 8

FIGURE 2: SHOWING VIABLE BACTERIA COUNTS (cfu/ml) FROM THE VEGETABLES

Discussion

In Calabar Markets, the commonly sold vegetables such as Lycopersicum esculentum, Telfairia occidentalis, cucumis sativus, Allium cepa and Capsicum annuum were found to be contaminated with bacteria. This contamination could be as a result of poor processing methods which may involve washing with faecal contaminated stream water and spraying the vegetable with water. Though spraying with water gives fresh appearance to the vegetables and delays decomposition but it could add microorganisms, especially, psychrotrophs from water or ice^[3]. This spray method provides moist surface that encourages bacteria growth on longer storage. Also vegetables are subject to contamination by containers unless adequately sanitized^[2].

The bacteria isolates from the vegetable samples were Bacillus species, Micrococcus species, Escherichia coli, Proteus vulgaris, Enterobacter aerogenes, Lactobacillus acidophilus and Alcaligen faecalis. The distribution of these isolates varied with different vegetables. Bacillus species was found to have high count in Telfairia occidentalis while low count was recorded in Capsicum annuum. Escherichia coli ranked next to Bacillus spp in high count and it was recorded in T. occidentalis. Micrococcus species was the isolate with the least count. The low bacteria count in Allium cepa and Capsicum annuum may be due to anti-microbial compounds in them which are inhibitory to multiplication of microorganisms^[7]. Distribution of bacteria isolates also differed in the different markets. Akim market recorded the highest bacteria count in Bacillus species while Marian market recorded the least count in this isolate. No isolate of Micrococcus was found in Marian market samples but Akim and Watt markets yielded very low count for micrococcus species.

The higher incidences of Bacillus species over others may be due to its spores which could resist killing by high temperature of ultra-violet sun rays which may kill and reduce the bacteria load in vegetables during exposure and display for sale. High incidence of Escherichia Coli may probably be due to handling by buyers and sellers whose hands may have been contaminated with faecal matters or they may have been contaminated from the farm yards when fertilized with human and animal manures. Bacillus species has been implicated as one of the common contaminants of vegetables^[1]. The presence of Enterobacter aerogenes and Alcaligen faecalis could probably be due to washing of these vegetables with water contaminated with faecal matter. Low incidences of Lactobacillus acidophilus may be attributed to their inability to produce spores like Bacillus species. Being acidophilic, their survival and multiplication require acidic and relatively anaerobic conditions, which are not provided for on these vegetables.

All the bacteria isolated were opportunistic pathogens, in that; they usually cause infection if suitable opportunity arises. This suitable opportunity could be seen in a person with weak natural immunity probably due to poor health, malnutrition, infection with HIV or drug therapy.

Conclusion

Adequate care should be taken in processing these vegetables to destroy the microorganisms before they enter inside the human body and obtain favourable conditions which could support their increase in number; thereby causing food-borne disease or food poisoning to the detriment of the human health.