In order to prevent and combat animal diseases, livestock facilities and their surroundings must be disinfected on a regular basis.
The Flemish Research Institute for Agriculture, Fisheries & Food (ILVO) recently reported that there are some indications, based on laboratory tests, that disinfectant use can lead to bacterial resistance to not only the disinfectant but also antibiotics.
However, this is not true if the correct dose of disinfectant is used, according to researcher Helder Maertens with ILVO and the University of Ghent in Belgium.
For her doctoral research, Maertens carried out a large series of field experiments to determine the effective risk of the formation of resistance under practical conditions.
She determined that no resistance to the disinfectant or to antibiotics occurs by using disinfectants according to the prescribed application method and the recommended dosage by the manufacturer. However, the use of lower concentrations of disinfectant than prescribed does cause problems, Maertens added.
Maertens worked with a large set of data available from DGZ-Vlaanderen, the Flemish veterinarian association. She analyzed data from hygiograms (hygiene scores based on microbiological analyses) collected in the poultry sector between 2007 and 2014, ILVO said in its announcement.
She looked for a link between the applied cleaning and disinfection protocol and the hygiene score determined afterwards. Over the years, the average hygiene score decreased, indicating better hygiene, ILVO said.
Hygiene turned out to be better when using a cleaning product than when cleaning with water alone, Maertens reported, and when two different disinfection products were used instead of one, scores also improved. This was also the case when the disinfection was carried out by an external company compared to by the farmer.
Sensitivity of E. coli bacteria
Maertens conducted a survey of no fewer than 25 broiler farms and 21 pig farms on their applied cleaning and disinfection protocol. On each farm, samples were taken from the barn environment (broiler house and piglet nursery) 24 hours after disinfection. This was done in order to collect Escherichia coli bacteria and test the sensitivity to antibiotics and disinfectants.
Maertens said these tests showed that the bacteria collected in the poultry house did not show any resistance to the disinfectants. Furthermore, the researcher found no evidence of increased antibiotic resistance through the use of disinfectants.
In a subsequent trial, three common disinfectants were used in several animal housing units (broiler house and piglet nursery) during five consecutive rounds of production. Maertens studied the effects of repeated use of these disinfectants on the sensitivity of bacteria to both disinfectants and antibiotics to see whether antimicrobial resistance developed.
The E. coli bacteria did not show any differences in sensitivity, depending on the choice of disinfectant. There was also no change in sensitivity with respect to the disinfection products based on the time elapsed in the observation period.
In other words, she said there was no buildup of disinfectant resistance with repeated use. There also was no development of antibiotic resistance.
Under-dosage of disinfection
During two laboratory tests, Maertens studied the consequences of disinfection at a lower dosage than prescribed by the manufacturer. Bacteria can survive at this concentration, although there are also bacteria that get into an "intermediate" state between life and death as a result, she said.
Such bacteria, which have undergone a suboptimal disinfection, appear to react less sensitively to an antibiotic treatment. It is not the case that bacteria under the influence of a suboptimal disinfection are able to transfer their antibiotic resistance genes to other bacteria.
There is now scientific clarity on the effect of the types of disinfectants used in the primary animal sector and their (nonexistent) link with antimicrobial resistance, Maertens said.
On the basis of these results from field trials, the researcher concluded that there is no reason for concern about antimicrobial resistance selection through the use of disinfectants in animal husbandry, albeit under the important condition that the disinfectants are correctly applied.