What Is Bacterial Contamination?

Bacterial pollution indicators are a series of indicators used to determine whether the water source is contaminated by bacteria and describe the degree of pollution. Humans often come into contact with pathogenic bacteria in water through drinking, contacting and other ways, which are harmful to human health. The most common diseases include cholera, typhoid fever, and dysentery.

The ideal indicator bacteria as an indicator of bacterial contamination should have the following conditions: ^[1]

(1) Bacterial pollution index (1) Total number of colonies

The total number of colonies is used as one of the indicators to judge the degree of pollution of water quality. The increase in the total number of colonies measured indicates that the water is contaminated by microorganisms, but it cannot explain the source of the pollution. The source and safety level of water pollution must be judged in conjunction with indicator bacteria of fecal contamination ^[2] .

(2) Bacterial pollution index (2) Total coliform

Total coliform is the most common and most abundant type of bacteria in the intestine. It can be detected in the feces of humans and warm-blooded animals, and a few species can be detected in the external environment. It has strong resistance to stress, and the amount in the water is related to intestinal pathogens. Fermentation of lactose to produce acid and gas, aerobic and facultative anaerobic, Gram-negative Acinetobacter at 35 ° C within 48 hours, mainly composed of the following four genus: Escherichia, Klebsiella Genus, Enterobacteriaceae, and acid bacteria. Because the identification method of Escherichia coli is more complicated, in 1973, HE Jordan (Jordon H.E) proposed that TC should be used instead of E. coli. This suggestion has attracted the attention of scholars from various countries, and gradually replaced E.coli with TC as an indicator of food and water contamination with feces. A new definition of total coliform was added to the 2006 "Sanitary Standards for Drinking Water", that is, total coliform refers to filtering water samples with a microporous filter with a pore diameter of 0.45pm, and attaching the filter to a selective medium Above, the group of bacteria that can produce -galactosidase to decompose ONPG and make the colony yellow is the total coliform group defined by this method. According to this definition, the detection time of total coliforms was shortened to 18-24 hours ^[2] .

(3) Bacterial pollution index (3) Fecal coliform

The fecal coliform is similar to the total coliform, except that the culture temperature needs to be raised to 44.5 ° C, and the total coliform microorganisms can still ferment lactose to produce acid and gas. The quantity directly indicates the degree of fecal contamination of the water body. It is an internationally used indicator bacteria for monitoring the quality of water contaminated by feces. It is suitable for general water quality monitoring of rivers, lakes, wastewater treatment systems, outdoor bath water and seawater. Research findings in recent years. TC and FC are quite different from many pathogenic microorganisms indicated by them in terms of ecology, prevalence and resistance to external stimuli. With increasing requirements for the sensitivity and accuracy of indicator bacteria, in order to better detect fecal contamination in water, Escherichia coli, Enterococcus, Clostridium perfringens, etc. have better indicating capabilities 2. Indicator microorganisms that are more closely related to pathogenic microorganisms in polluted water bodies have been widely used ^[2] .

(4) Indicators of bacterial contamination (4)

Eichrichia was first isolated in 1885, and Theobald Smith pointed out in 1893 that Escherichia coli is commonly found in the intestines of humans and animals and cannot survive in natural water for a long time. When found in the environment, it can be considered to be contaminated by human and animal feces. Due to the complex identification, it has not been used much before. But in recent years, with the establishment of new methods for determination. E.coli is increasingly used as an indicator of fecal contamination. For example, in the detection method of TC and E.coli for drinking water and recreational water promulgated by the US Environmental Protection Agency in 2000, the glucose protease produced by E.coli was used to decompose the indole gluconoside and produce colored substances, thus making E.coli. The coli colonies developed color, and the E. coli 'number was measured (enzyme substrate method). China's 2006 edition of the "Standard Method of Sanitary Drinking Water Inspection" also adopted this method as the standard inspection method. Escherichia coli can be a good indicator of intestinal pathogenic microorganism contamination, and it is a better indicator of fecal contamination. The most significant detection is ^[2] .

(5) Indicators of bacterial contamination (5) Enterococcus

Enterococci belong to the D serogroup of Streptococcus. Enterococcus is one of the normal flora in the intestines of humans and warm-blooded animals. It has different contents in humans and animals. The number of enterococci that mainly inhabit the intestines of animals is more than that of E.coli. Less, the proportion of human feces is less than E.col, about 10 to the 5th power per gram of feces. Generally judge the source of pollution based on the ratio of the two. The ratio of FC to Enterococcus is greater than 4.1, and the source of pollution can be considered to be human feces; less than 0.7, the source of pollution can be considered to be animal feces; in between, it can be considered to be mixed pollution of human and animal feces. Enterococci are more resistant to harsh environments such as cold, heat, and alkali. They are more resistant to chlorinated disinfectants than TC. Their fertility in nutrient-rich water is lower than that of coliform bacteria. Conditions ^[2] .

(6) Indicators of bacterial contamination (6) Clostridium perfringens

Clostridium perfringens is one of the normal intestinal flora. It is a Gram-positive, obligate anaerobic, bud-embedded intestinal condition pathogenic bacteria. The survival time of its pods in water is similar to some parasites. For example, Giardia and Cryptosporidium sacs and oocysts survive in water for an equivalent period of time, so they can be used to indicate the contamination of these parasites. Clostridium perfringens also exists in soils and rivers in tropical areas at relatively low concentrations. When polluted by sewage or feces, their numbers increase greatly, so they can also be used to detect tropical water pollution. Because Clostridium perfringens has a strong resistance to the outside world and can survive in the environment for a long time, it can better predict the possible pollution in the past. The combined use of Escherichia coli and Clostridium perfringens can simultaneously detect recent and past possible fecal contamination in small-volume water environments such as streams and lakes ^[2] .