Equine Methicillin-Resistant Sequence Type 398 Staphylococcus aureus (MRSA) Harbor Mobile Genetic Elements Promoting Host Adaptation

Abstract

Continuing introduction of multi-drug resistant, zoonotic pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) in horse clinics challenges the biosafety of employees and animal patients. This study was aimed to determine the occurrence of mobile genetic elements facilitating survival in the early stages of invasive infection in different host species, including humans and horses, in MRSA carried by equine patients admitted to a large horse clinic. A total of 341 equine patients were investigated for carriage of MRSA by hygiene screening directly at hospital admission. MRSA were further investigated by antimicrobial susceptibility testing, whole-genome sequencing and genomic composition, including virulence factors involved in immune evasion and host adaption. From a total of 340 validated specimens from equine nostrils, 3.5% yielded positive results for MRSA. All MRSA were found to be closely related belonging to sequence type (ST) 398_t011 with up to four additional antimicrobial resistances. All MRSA harbored a specific Staphylococcal Pathogenicity Island (SaPIbov5) involved in facilitating survival in ruminant and equine plasma. Moreover, a β-hemolysin (hlb) converting ΦSa3 phage encoding the human-specific Immune Evasion Cluster (IEC) was present in 72% of the isolates. An equid-specific leukotoxin encoded by a further temperate phage (Saeq1) was only rarely detected (22%). Despite the absence of β-hemolysin production for all IEC-positive ST398, a prominent hemolysis zone was demonstrable on sheep blood agar. Thus, IEC might remain undetected among the ST398 lineage, since the presence of IEC is commonly associated with reduction of hemolysis in S. aureus belonging to other genetic backgrounds. Here we describe MRSA-ST398 harboring different mobile genetic elements encoding variants of immune evasion factors and toxins previously shown to contribute to S. aureus invasive diseases in specific host species or ecologic niches. We suggest these combinations contribute to the adaptation of MRSA belonging to ST398 with respect to epidemic spread across different habitats and hosts, and may therefore confer a host “generalist” phenotype.

The role of rpoS in the regulation of Vibrio alginolyticus virulence and the response to diverse stresses

“…Haemolysin is a chief virulence factor of many Vibrio and other bacteria (Syed et al, ; Walther et al., ). Tan, Liu, Oliver, and Wong () suggested that haemolysin is regulated by the rpoS gene and expressed in cells under low salinity in Vibrio vulnificus .…”

Silence as a way of niche adaptation: mecC-MRSA with variations in the accessory gene regulator (agr) functionality express kaleidoscopic phenotypes

“…Methicillin-resistant Staphylococcus aureus (MRSA) is among the leading causes of opportunistic infectious diseases in human and veterinary medicine worldwide 1 , 2 . Mobile genetic elements (MGEs) originally denominated as staphylococcal cassette chromosome mec (SCC mec ) cause horizontal spread of methicillin resistance among staphylococci 3 , with either mec A or mec C 4 , 5 as the resistance-mediating gene.…”

“…Mechanisms enabling opportunistic bacteria to cross species barriers, to infect a new host or to enhance their viability in the environment are still poorly understood. Changes expected to be involved in (niche) adaptation processes of S. aureus encompass (among others) alterations of metabolic pathways 17 , escape of host defence mechanisms 1 , biofilm formation 18 , iron acquisition abilities 19 , generation of pseudogenes 20 , 21 or nucleotide changes altering promoter structures 22 . In addition, production of cytotoxins 23 , 24 and other virulence factors as well as their regulation circuits might have a strong influence on host adaptation 23 , 25 , 26 .…”

“…In this study, complementary phenotypical methods including colony spreading and haemolysin production were employed to investigate the activity of the agr system. Synergistic production of different haemolysins (SPDH) on columbia agar plates (Oxoid, Germany) supplemented with 5% sheep blood (SBA) was investigated by cross-streaking tested bacteria perpendicularly to laboratory strain S. aureus RN4220 as described before 1 . RN4220 is characterized by a strong β-haemolysin production while α-haemolysin secretion is missing and PSM α peptides are produced only at non-considerable amounts 35,67,68 .…”

“…A modified CAMP test for verification of β-haemolysin production was performed using Streptococcus agalactiae (ATCC12386) and the β-haemolysin producing S. aureus strain ATCC25923 (positive control) as described recently 1 . Briefly, staphylococci of interest were streaked perpendicularly to CAMP-factor producing ATCC12386.…”