Disinfection Effects and Clinical Application of Sodium Dichloroisocyanurate Powder on Bacteria

Shijin GUO, Ling LI, Qing LI, Jingjing ZHOU, Chengxin LYU, Lanying GUO, Zhiqiang SHEN

Abstract With the continuous increase of large-scale pig farms， the disinfection of pig farm environment plays an extremely important part in the control and prevention of pig farm diseases in high-density breeding environment. As an important breeding place for pig farms， the farrowing house must be performed with scientific and standardized disinfection. In this paper， different disinfection modes were used to disinfect the empty farrowing houses of pig farms， and the total plate count， Escherichia coli， Staphylococcus aureus， and fungi were used as detection indicators to comprehensively evaluate the disinfection effect of the air microorganisms and the surface of the objects in the empty house after disinfection， with the aim to provide a basis for the establishment of a scientific pig farm environmental disinfection model.

Key words Sodium dichloroisocyanurate powder; Bacteria; Disinfection effect; Pig farm; Clinical application

Received： March 2， 2022  Accepted： May 20， 2022

Supported by the Major Science and Technology Innovation Project of Shandong Province （2019JZZY020606）.

Shijin GUO（1974-）， male， P.R.China， assistant researcher， devoted to the research and development of new veterinary medicine and new feed.

*Corresponding author.

Introduction

Disinfection is the main， efficient and economical countermeasure to prevent infectious diseases. The widespread use of disinfectants has played a great role in improving the efficiency of farms， preventing and controlling the emergence of diseases. However， the large-scale application of disinfectants had led to the resistance in bacteria， which further reduces the disinfection effect. Currently， there are few research reports on this problem， which has brought certain problems to the disinfection of farms. Therefore， investigation on the sensitivity of bacteria to disinfectants is of great significance for selecting high-efficiency disinfectants， improving the efficiency of farm disinfection and deepening disease control and prevention.

Epidemiological Status of Common Bacterial Diseases in Pig Farms

Haemophilus parasuis disease

Haemophilus parasuis targets piglets and nursery pigs before and after weaning， and the affected pigs always have relatively obvious symptoms. Pigs under eight weeks old are relatively susceptible to the disease. In the clinical field， the incidence rate reaches 25%. For pigs under five weeks of age， the main conditions are arthritis and pericarditis， and the mortality rate is as high as 95%. Easy to produce， this pathogen is an opportunistic one， and under the influence of various stress factors， this kind of disease is very easy to appear. In pig herds， pigs affected with PRRS and swine fever tend to be easily drop in their immunity， resulting in the infection of this disease， thereby leading to the increase of morbidity and mortality of pig herds. In addition， the disease also makes it easy to produce mixed infection， especially for porcine respiratory coronavirus， pneumonia virus， resulting in severe porcine respiratory disease syndrome.

Streptococcus suis disease

Streptococcus is easy to come into being in the polluted environment， dust and drinking water process， and it is very easy to infect through the respiratory tract and digestive tract. The susceptibility of large and small pigs is very obvious， and the disease is infectable throughout the year， but most serious from May to November. At present， if affected with Streptococcus， piglets mainly get septicemia and meningitis， and the mortality rate is relatively high， which has exceeded 80%; for middle size pigs， purulent lymphadenitis and arthritis are the common symptoms[1].

Usage of Disinfectants

Disinfection plays a very important role in promoting the healthy development of animal husbandry and maintaining ecological balance. An effective disinfectant should be able to quickly kill most viruses， bacteria and fungi， with long-term activity， no irritating， no toxicity and no  corrosiveness.

Alkali disinfectants have the characteristics of low price， strong penetration ability and stable disinfection. Commonly used alkali disinfectants include caustic soda， quicklime. However， due to their corrosiveness， they cannot be used in pig disinfection. In production， 4% sodium hydroxide solution is generally used to disinfect contaminated houses， troughs and vehicles.

Formaldehyde and glutaraldehyde are the most commonly used aldehyde disinfectants in clinical practice. Formaldehyde is relatively irritating， but its infiltration ability is relatively strong， and it has good effects on bacteria， viruses and even spores. The 37%-40% formaldehyde solution is widely used in the fumigation and disinfection of houses. Glutaraldehyde is mostly used in the disinfection of pig houses or pregnant pigs. The 2% glutaraldehyde solution is commonly used to soak medical equipment， body temperature agents and plastics， and 10% solution can be used to fumigate and disinfect closed spaces at 1.06 ml/m3.

Peroxides are used for disinfection through soaking， spraying， and smearing， and potassium permanganate and peracetic acid are most commonly used. The 0.1% potassium permanganate is often used clinically to clean the breasts， rear parts and perineum of preclinical pigs， as well as to clean the injuries and ulcers of skin and mucous. Moreover， the mixture of potassium permanganate with formalin is often used to carry out fumigation and disinfection of empty houses. With strong bactericidal ability and no side effects on humans and animals， peracetic acid  is the most widely used in pig farms and can be used for disinfection in pig houses. It is often used at a concentration of 0.05%-0.50% to carry out comprehensive disinfection of pig house passages， pens and feeding utensils[2].

Key Role of Disinfection

With the rapid development of contemporary breeding industry， and various new breeding skills and methods， the stocking density of livestock has increased to a certain extent. While bringing rich benefits to farmers， it has also increased the infection possibility of various diseases. Under such environmental background， there is a more and more urgent need for pig breeding to carry out high-quality breeding environment control operations， and it is necessary to pay attention to the scientific and efficient disinfection of various sessions.

In order to achieve this goal and greatly reduce the occurrence of various swine epidemics and various infectious diseases， it is not only necessary to combine a variety of technical measures for comprehensive prevention， but also to give full play to the effectiveness of disinfection. The detection and analysis of disinfection effect should be carried out to identify the weaknesses of the work， and adopt targeted countermeasures to further maintain the healthy growth and development of pigs[3].

Disinfection Effect of Sodium Dichloroisocyanurate Powder

After determining the content of available chlorine in 20% sodium dichloroisocyanurate， investigation was made to find out its disinfection effect on the environment of the empty houses of the pig farm so as to explore the feasible disinfection mode. The methods were as follows： sodium thiosulfate indirect iodometric method was used to determine the content of available chlorine in sodium dichloroisocyanurate， and different disinfection modes were used to disinfect the empty farrowing houses of pig farms， followed by the analysis on total plate count， E. coli， S. aureus and fungi were analyzed.

Test materials

Test equipment： 301 electric heating constant temperature incubator， from Longkou Xianke Instrument Co.， Ltd.; XC-30 colony counting equipment; SJ-CJ ultra-clean workbench， from Suzhou Zuoyou Purification Technology Co.， Ltd.; HDS7-16C Special cleaning and disinfection high-pressure cleaner for pig farms， from Haibeng Cleaning Equipment Co.， Ltd.; high-pressure steam sterilizer， from Ailaibao Technology Co.， Ltd.; electronic balance， from Shanghai Sartorius Instrument Equipment Co.， Ltd.; burette， 100 ml Graduated cylinder， 1 000 ml graduated cylinder， dish （diameter： 90 mm）， sampling holder.

Drugs and reagents： 20% sodium dichloroisocyanurate （Shandong Lvdu Ante Animal Pharmaceutical Co.， Ltd.， batch number 21030901）， purified water （Shandong Lvdu Ante Animal Pharmaceutical Co.， Ltd.， batch number 21030911）; potassium iodide， sulfur sodium sulfate， sulfuric acid， soluble starch， formaldehyde， and hydrochloric acid， all analytically pure; potassium iodide starch test paper; quicklime （Shijiazhuang Huilu Building Materials Co.， Ltd.）.

Test medium： Nutrient agar medium， BP agar medium （Baird-Parer medium）， violet red bile agar medium （VRBA agar medium）， Sabouraud agar medium， all purchased from Beijing Wanjia Biological Technology Co.， Ltd.

Research Methods and Results Analysis

Test methods

（1） Content determination method. The solution used for the test was prepared as follows：

Sodium thiosulfate titration solution （0.1 mol/L）： first， take 26 g of sodium thiosulfate solution and 0.20 g of anhydrous sodium carbonate solution， which was then added with appropriate amounts of freshly boiled cold water; after dissolving， the mixture was diluted to 1 000 ml; after shaking well， the solution was laid stand for a month before filtering.

Starch indicator solution： first， 0.5 g of soluble starch was taken and added with 5 ml of water， and after stirring， the mixture was slowly added to 100 ml of boiling water， accompanied with continuous stir; after boiling for 2 min， the solution was ready to use after cooling.

Sulfuric acid （1→5） solution： 20 ml of sulfuric acid was taken and set to constant volume  of 100 ml， which was ready to use after well stirring.

Diluted hydrochloric acid： 234 ml of hydrochloric acid was taken and diluted to 1 000 ml by adding water， and then the solution was ready.

Determination method： an accurate amount of sample was taken by weighing （approximately equivalent to 0.1g of available chlorine）， and put it in a 250ml iodine bottle， which was added with 100 ml of water. After dissolving， 3 g of potassium iodide was added， followed by shake to dissolve. Then， after adding 20 ml of sulfuric acid solution （1→5）， the mixture was sealed tightly and placed in the dark for 5 min after shaking. Then， 5 ml of water was used to wash the bottle stopper and the inner wall of the bottle， and sodium thiosulfate titration solution （0.1 mol/L） was used to titrate the solution. When the titration was near to the end， 2 ml of starch indicator soluation was added until blue disappeared， and the titration results were corrected with a blank test.

Content equivalent to labelled content （%）=V×T×CrW×Cs×1 000×100%

Where， V is the volume of titrant consumed by the test product （ml）; T is the titer of the titrant according to the substance to be tested; W is the sample mass （mg）; Cs is the standard concentration of titrant; Cr is the actual concentration of the titrant.

There is a certain deviation between the two parallel determination results， but not more than 0.3%.

（2） Disinfection of empty farrowing houses of pig farms. First， farrowing house conditions： a medium-sized pig farm in Binzhou City， Shandong Province was used as the test site. There were 550 sows in stock and ten farrowing buildings each with 24 beds arranged in the south-to-north-direction. With good ventilation， the farrowing houses covered an area of about 45 m×35 m， and the facilities and equipment in the delivery room were all available.

Second， test grouping： 8 empty farrowing houses were randomly selected and divided into 4 groups evenly， with 2 buildings in each group， and then disinfection was carried out according to the steps shown in Table 1.

Third， sampling environment： during the sampling process， the doors and windows needed to be closed for 15 to 30 min， and the number of indoor personnel， temperature and humidity should be recorded.

Fourth， sampling method： 2 samples were collected in parallel at each collection point. One was the air microorganisms， which was collected as follows：

The natural sedimentation method was adopted， which refers to that with nutrient agar plate exposed in the air， the microorganisms naturally settle on the plate according to the action of gravity， and the colony count is obtained after being cultivated in the laboratory， which is based on Chapter 3： air microorganism collection （GB/T18204.3-2013）.

Three sampling points were evenly selected along the long axis of the pig house， and two points were selected on a diagonal line of the pig house equidistant from the center of the pig house， totally 5 sampling points. A medium plate was placed at 50-60 cm above the ground at each sampling point， and with cover open， the medium was exposed to the air for 10 min to collect the air microorganisms （ total plate count， E. coli， S. aureus and fungi ）[4].

The other sample was collected from the floors， walls and railings.

After infiltrated with neutralizer， the cotton swab was used to wipe an area of 25 cm2 （length and width of 5 cm） with constant change of the swab surface， and then the cotton end of the swab was put into the sampling solution and stored at low temperature for later use.

Fifth， colony count： the collected samples were cultured （Table 2）， and the mediums used were all for test. The 4 measurement indicators were then performed with related counts， including total plate count， the number of E. coli， the number of S. aureus， and the number of fungi， so as to identify the sterilization status of microorganisms in idle pig houses by different disinfection methods. The counting method of the total plate count was determined according to "Determination of the total number of colonies" （GB 4789.36-2016）; the counting method of E. coli adopted the plate counting method of "Escherichia coli counting" （GB 4789.38-2008）; the counting method of S. aureus followed "Staphylococcus aureus Detection Technology" （GB 4789.37-2008）; fungi count method according to "Agar Plate Viable Count" （GB 4789.39-2008）.

Results and Analysis

The detection and analysis of the disinfection effect of pig farms is an efficient countermeasure to determine the real pollution situation of pig farms. It is beneficial to strengthen the disinfection operation of pig farms and the internal objects， air with a clearer purpose， so as to give full play to the effectiveness of disinfection， and reduce the occurrence of various pig diseases and infectious diseases.

The effectiveness of pig farm disinfection has been explored through relevant testing models. Among them， edimentation method is used to perform the air collection， and it has found that the total plate count also shows great differences according to the differential influence of the location， frame and nearby natural environment elements of the pig farm. Even for the same farm， the total plate count in differentiated pig houses is different， and the number in the house is widely higher than that outside the house. Some researchers believe that when each part of the epidemic prevention operation is carried out in detail， the effect of disinfection is also significantly different. Specifically speaking， the number of bacteria in the air rises very fast， and compared with the two ends of the pig house， the number of bacteria there is relatively small. It is difficult to effectively clarify the effect of disinfection of feed troughs and drinking water facilities. Therefore， during epidemic prevention， it is necessary to carry out disinfection measures and systems with clear goals， which is conducive to more effectively exerting the effectiveness of disinfection[5].

For one thing， the effective use of microbial inspection is conducive to better exerting the practical significance of pig house disinfection， and is highly economical and convenient to operate. Measures for the detection of objects inside the pig house can be used during disinfection operations on the human body and mucous membranes. At present， most pig farmers are accustomed to using natural sedimentation and cotton swab detection methods in large-scale pig farming. However， the latter has poor standardization of sampling. Thus， the volume of cotton swabs should be reduced， and attention should be paid to the reasonable control of smearing and beating strength， which is conducive to improving the accuracy of test results. The natural sedimentation is economical and easy to operate， and thus it is generally used in the primary level.

For another， the objects and air in the pig farm are all carried out through disinfection operations. Whether disinfection is achieved or not can only be known through testing. The effectiveness of disinfection plays an important role in the disinfection of pig farms， and it is closely related to the economic interests of pig farms.

Conclusion

To sum up， the mode of effective detection and analysis of various equipment and facilities in pig farms as well as the effectiveness of air disinfection can identify the effectiveness of the disinfection， thereby determining whether it is necessary to re-disinfect the operation or carry out related work to deepen the effectiveness， which has a positive role in giving full play to the effectiveness and practical value of disinfection. High-quality disinfection is conducive to reducing the occurrence and outbreak of a variety of pig diseases and infectious diseases， and has an important impact on maintaining the healthy growth of pigs and the economic performance of pig farmers.

References

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Editor： Na LI  Proofreader： Xinxiu ZHU