Salmonella infantis is a highly prevalent bacterium in fattening poultry farms, which in recent years has shown great capacity to generate resistance to antibiotics. It is a potentially zoonotic bacterium that causes enteritis in humans, and reports of illnesses related to this bacterium have increased in recent years.

The reduction of S. infantis in broilers has a favorable impact on food safety and public health, since contamination of poultry products for human consumption is prevented.

An assay carried out with a specific natural antimicrobial for the control of Salmonella infantis in broilers is presented below.

Aim of the trial

1. To evaluate the bactericidal effect of the natural microbiocide in chickens challenged by Salmonella infantis.
2. Compare the efficacy of the natural microbicide against the use of formaldehyde (a chemical product used to control Salmonella with various disadvantages such as its high toxicity and its irritating effect on the mucous membranes of the digestive and respiratory tracts).

Experimental design

A total of 216 Cobb 500 male broilers raised to 35 days of age were used. At the beginning of the trial, the weight was 40 ± 2.5 grams, and the birds were distributed in 4 batches, with 54 chickens per treatment. 3 replicates per treatment and 18 chickens per replicate were established.

Evaluated parameters:

1. Final weight (g)
2. Accumulated intake (g/bird)
3. Conversion rate
4. Homogeneity (%)
5. Daily mortality (%)
6. Stool moisture (%)
7. Number of birds positive for infantis
8. Quantification of infantis in positive samples (UFC/g)
9. Birds with gross intestinal lesions

Treatments

• T1 Negative control (CN): Standard basal diet (SBD) without antibiotics or microbicidal products
• T2 Positive Control (PC): SBD + challenge
• T3 Natural Microbiocide (NAT): SBD + NAT 0.5 kg/t throughout the trial + challenge.
• T4 Formaldehyde (FOR)*: SBD + FOR at 2 kg/t throughout the test + challenge.

*Commercial product with a composition of 33% formaldehyde and 9% propionic acid 

Challenge 

The challenge with S. infantis was carried out on day 21, administering the bacteria at 2×10⁸ CFU/bird directly in the crop.

The food was withdrawn 4 hours and the water 2-3 hours before inoculation to favor the proliferation of the bacteria in the mucosa of the digestive tract.

Results

Regarding the final weight, the NAT batch obtained 51.5 grams more than the CP batch and 43.54 grams more than the FOR batch, these differences being statistically significant. This improvement in weight is related to better intestinal well-being (graph 1).

Regarding the accumulated intake (g/bird), the NAT group obtained slightly lower values than the rest of the trial bacthes. With a difference of 60.73 g less in relation to the CP batch and 51.3 g less compared to the FOR batch on day 35 (graph 2).

Analyzing the conversion rates, there were significant differences (graph 3); it is observed that the NAT batch was more efficient in the use of feed: the chickens from this batch consumed less feed and gained more weight than the rest of the batches, even the CN batch.

The homogeneity was significantly higher in the batch supplemented with NAT, since it obtained 9.22% more than the CP batch, 4.11% more than the CN batch (even though it did not receive a challenge) and 6.11% more than the FOR batch (graph 4).

Regarding mortality (%), the NAT batch obtained the best result, obtaining a 2.08% mortality, only on day 14 of the trial, even better than the CN batch, which obtained 4.17% on the same day. The FOR batch and the CP batch obtained very high mortalities throughout the trial and very similar between them (graph 5).

Stool moisture

The NAT batch obtained significantly lower percentages of moisture in feces, together with the CN batch.

This is indicative of better digestive well-being. The challenged control batch and the batch supplemented with formaldehyde presented higher humidity (graph 6).

Isolation of S. infantis

S. infantis was isolated from 6 chickens/treatment from mucosal swabs from each intestinal segment on days 15, 28 and 35.

Isolation of S. infantis (Number of positive birds) on day 15

Results from day 15 (before challenge) showed that S. infantis was not present in the intestines of birds from any of the batches (table 1).

Isolation of S. infantis (Number of positive birds) on day 28

In relation to day 28, the CP and FOR batches presented 4 and 2 birds positive for S. infantis only in the ileus. The CN and NAT batches obtained 0 positive birds in all segments of the intestine even though the second was challenged with S. infantis on day 21 (table 2).

Isolation of S. infantis (Number of positive birds) at day 35

At day 35, there was an increase in the number of birds positive for S. infantis in the CP and FOR batches of birds positive in various segments of the intestine. On the other hand, both the CN batch and the NAT batch obtained 0 positive birds on day 35 in all segments of the intestine, even when the NAT batch was challenged with S. infantis (table 3).

S. infantis quantification (UFC/g)

From the samples obtained to isolate S. infantis, CFU/g) quantifications were performed in the ileus. The CP and FOR batches obtained counts of 1.9×106 and 6.9×104 on day 28 and 3.3×106 and 5.1×104 on day 35, respectively.

Macroscopic intestinal lesions

Macroscopic lesions at the intestinal level of 6 birds/batch were evaluated on days 15, 28 and 35. Birds from the NAT batch did not present lesions, while in the FOR and CP batches macroscopic lesions were observed (graph: 8).

Conclusions

The natural microbiocide was shown to effectively control the presence of S. infantis in birds, a bacterium that poses a danger to public health. The natural microbiocide was able to control Salmonella infantis more effectively than formaldehyde, even though the latter is often used for Salmonella control.

• All birds were negative for S. infantis in the batch with the natural microbiocide.
• The formaldehyde batch and the positive control had higher colony counts.

The administration of the natural microbiocide also allows an improvement of the productive parameters: better weight (+51.5 g/bird) and conversion rate (3.4% improvement). This improvement is due to a better balance of the digestive microflora, which is observed with a reduction in the humidity of the feces and in lesions at the digestive level.