Persistent and Transient Airborne MRSA Colonization of Piglets in a Newly Established Animal Model

Abstract

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) was first found in 2005 and is up to date widespread in animal husbandry reservoir – focusing on pig farming. The regular detectability of MRSA in the air of pigsties as well as in exhaust air of pig farms (mean count: 102 cfu/m3) poses the question whether an airborne spread and, therefore, a MRSA colonization of animals via the airborne route exists. To answer this question, we exposed three groups of nine MRSA-negative tested piglets each to a defined airborne MRSA concentration (102, 104, and 106 cfu/m3) in our aerosol chamber for 24 h. In the following observation period of 21 days, the MRSA status of the piglets was monitored by taking different swab samples (nasal, pharyngeal, skin, conjunctival, and rectal swab). At the end of the experiment, we euthanized the piglets and investigated different tissues and organs for the spread of MRSA. The data of our study imply the presence of an airborne MRSA colonization route: the animals exposed to 106 cfu/m3 MRSA in the air were persistent colonized. The piglets exposed to an airborne MRSA concentration of 104 cfu/m3 were transient, and the piglets exposed to an airborne MRSA concentration of 102 cfu/m3 were not colonized. Consequently, a colonization via the airborne route was proven.

Influence of immune status on the airborne colonization of piglets with methicillin-resistant staphylococcus aureus (MRSA) clonal complex (CC) 398

“…Both groups were exposed to aerosolized MRSA for 24 h using an aerosol chamber. A control group (CG) of 9 piglets (n = 9) was exposed to airborne MRSA alone as described previously [4]. All 3 groups were exposed to an airborne MRSA concentration of 10 4 cfu/m 3 as we previously demonstrated that this dose results in transient MRSA colonization of piglets [4].…”

“…A control group (CG) of 9 piglets (n = 9) was exposed to airborne MRSA alone as described previously [4]. All 3 groups were exposed to an airborne MRSA concentration of 10 4 cfu/m 3 as we previously demonstrated that this dose results in transient MRSA colonization of piglets [4]. Blood samples were taken to investigate the total leucocytes, including differential blood counts and the proliferation capacity of CD 4 + T cells.…”

“…Aerosol Chamber. To expose piglets to MRSA, an aerosol chamber with a base area of 3.2 m 2 and a volume of 7 m 3 was used as described previously [4]. The MRSA suspension was prepared and transported by a perfusion pump with a rate of 9 mL/h to an ultrasonic nebulizer (Broadband Ultrasonic Generator, Sono-Tek) that generated the aerosol.…”

“…Bacterial Strain and Preparation of MRSA Suspension. For our experiments, a MRSA strain (strain ID: BfR 08S00974, ITU 1179) of the sequence type (ST) 398 and the spa type t011 was obtained from the "Federal Institute for Risk Assessment" (BfR) and used as previously reported [4,12]. Briefly, MRSA was streaked out on blood base agar plates (Blood Agar Base No.…”

“…In Germany, an MRSA prevalence between 52% and 96% is reported in pig farming [3]. We recently identified the airborne MRSA concentration of 10 6 colony forming units (cfu)/m 3 as an effective dose for airborne MRSA colonization of piglets [4]. Piglets exposed to this MRSA concentration for 24 h in an aerosol chamber were persistently colonized with MRSA.…”