Establishment of a Pathogenicity Index for One-day-old Broilers to Pasteurella multocida Strains Isolated from Clinical Cases in Poultry and Swine

Abstract

Although Pasteurella multocida is a member of the respiratory microbiota, under some circumstances, it is a primary agent of diseases , such as fowl cholera (FC), that cause significant economic losses. Experimental inoculations can be employed to evaluate the pathogenicity of strains, but the results are usually subjective and knowledge on the pathogenesis of this agent is still limited. The objective of this study was to establish a new methodology for classifying the pathogenicity of P. multocida by formulating a standard index. Strains isolated from FC cases and from swine with respiratory problems were selected. One hundred mL of a bacterial culture of each strain, containing 10 6 CFU, was inoculated in 10 one-day-old broilers. Mortality after inoculation, time of death (TD), and the presence of six macroscopic lesions were evaluated over a period of seven days post-inoculation (dpi). A Pathogenicity Index Per Bird (IPI), ranging 0 to 10, was calculated. Liver and heart fragments were collected to reisolate the bacteria. Blood was collected from the surviving birds, and an ELISA test was carried out to detect specific antibodies. The median of the pathogenicity indices, the number of lesions and the rate of bacteria reisolation were significantly different (p<0.05) among the origins of the isolates (p<0.05). The pathogenicity index developed in this study allows the classification of Pasteurella multocida pathogenicity and may be an alternative to the pathogenicity models currently used for screening.

Evaluation of the biofilm formation capacity of Pasteurella multocida strains isolated from cases of fowl cholera and swine lungs and its relationship with pathogenicity

“…Following the evaluation of biofilm formation and grouping of the samples, the analyzed strains were compared to their respective PIs (Table 4), which were previously obtained by an in vivo study (Pilatti et al 2016). The mean PI of the P. multocida strains classified as non-biofilm producers differed significantly (p˂0.05) from the mean PI of moderate biofilm producer strains (Fig 1).…”

“…The degree of biofilm formation was compared with the PI obtained for the same strain, which can be considered a measure of the in vivo pathogenicity of the isolate (Pilatti et al 2016). Pathogenicity is related to the characteristics of a microorganism that are involved in the capacity to cause infection, whereas virulence determines the level of disease caused by a specific pathogenic microorganism (Kubatzky 2012).…”

“…This relationship was not possible to evaluate statistically in this study due to the presence of only a single strong biofilm producing strain. In addition, the lesions evaluated through the experimental inoculation (Pilatti et al 2016) involve mechanisms and virulence factors previously surveyed ) that are not directly related to biofilm formation. For example, the widespread petechiae on serosal and epicardial surfaces of the inoculated animals were an indication of the consumptive coagulopathy common to endotoxemia .…”

“…The pathogenicity indices (PIs) of the 94 strains were associated with biofilm formation capacity at 37°C. The PIs were previously established by Pilatti et al (2016). In this preliminary study, the strains were classified into three groups of pathogenicity (high, intermediate, low) on a scale from 0 to 10, calculated from the experimental inoculation of one--day-old chicks.…”

“…In this preliminary study, the strains were classified into three groups of pathogenicity (high, intermediate, low) on a scale from 0 to 10, calculated from the experimental inoculation of one--day-old chicks. The high-pathogenicity group comprised strains with PIs ranging from 8 to 10, the intermediate-pathogenicity group had PIs between 4 and 7, and the low-pathogenicity group included strains with indices from 0 to 3 (Pilatti et al 2016).…”