Colonization Kinetics of Different Methicillin-Resistant Staphylococcus aureus Sequence Types in Pigs and Host Susceptibilities

Abstract

In this study we investigated the kinetics of colonization, the host susceptibility and transmissibility of methicillin-resistant Staphylococcus aureus (MRSA) after nasal treatment of pigs with three different MRSA strains of distinctive clonal lineages (sequence type 398 [ST398], ST8, and ST9), and origin in weaning piglets. The colonization dose of 5.0 ؋ 10 8 CFU/animal was determined in preliminary animal studies. A total of 57 piglets were randomly divided into four test groups and one control group. Each of three test groups was inoculated intranasally with either MRSA ST8, MRSA ST9, or MRSA ST398. The fourth group was a mixture of animals inoculated with MRSA ST398 and noninoculated "sentinel" animals. Clinical signs, the nasal, conjunctival, and skin colonization of MRSA, fecal excretion, and organ distribution of MRSA, as well as different environmental samples were examined. After nasal inoculation with MRSA piglets of all four test groups showed no clinical signs of an MRSA infection. MRSA was present on the nasal mucosa, skin, and conjunctiva in all four test groups, including sentinel animals. Likewise, fecal excretion and internal colonization of MRSA ST8, ST9, and ST398 could be shown in each group. However, fecal excretion and the colonization rate of the nasal mucosa with MRSA ST9 were significantly lower in the first days after infection than in test groups infected with ST8 and ST398. The results of this study suggest differences in colonization potential of the different MRSA types in pigs. Furthermore, colonization of lymph nodes (e.g., the ileocecal lymph node) with MRSA of the clonal lineage ST398 was demonstrated.

From Pig to Pork: Methicillin-Resistant Staphylococcus aureus in the Pork Production Chain

“…Because staphylococci and their resistant variants can regularly be isolated from porcine intestines (98), transmission from the intestines to muscle tissue can also be expected. Postevisceration spraying with water is used to remove visible contaminants from carcasses before they enter the chiller.…”

Transmission Dynamics of Methicillin-Resistant Staphylococcus aureus in Pigs

“…At present, a number of experimental colonization models have been developed in order to understand colonization and transmission dynamics of LA-MRSA among pigs, with the aim of future use for development of intervention strategies (Table 2) (Moodley et al, 2011b; Broens et al, 2012a; Crombé et al, 2012b; Jouy et al, 2012; Szabó et al, 2012). The experimental design (i.e., inoculation strategy, type and dose of inoculum, age of the animals, strain, and use of antibiotics), the laboratory techniques as well as the pre-defined criteria for colonization of these models differ largely which makes comparison difficult.…”

“…Nasal and nasal-gastrointestinal inoculation with LA-MRSA has been found not to result in successful colonization of piglets in some studies (Moodley et al, 2011b; Broens et al, 2012a), while others achieved colonization using relatively high bacterial inoculum doses (Broens et al, 2012a; Crombé et al, 2012b; Szabó et al, 2012). Unfortunately, in the study of Broens et al (2012a), this high dose led to the development of lethal necrotizing pneumonia in 80% (4/5) of the inoculated animals, making this procedure unsuitable for future experiments.…”

Individual Predisposition to Staphylococcus aureus Colonization in Pigs on the Basis of Quantification, Carriage Dynamics, and Serological Profiles

“…The higher S. aureus prevalence in MRSA-positive farms indicates that certain MRSA clones may be able to spread at higher rates, driven either by selective pressure or by adaptation of these clones to pig farming (28). Others have attempted to compare the colonization kinetics of different lineages in pigs under experimental conditions, showing MRSA ST398 as the most successful (29). The present study did not analyze S. aureus strain diversity, as it was not designed to assess whether differences in S. aureus prevalence between farms were due to specific lineages.…”