Low prevalence of livestock‐associated methicillin‐resistantStaphylococcus aureusclonal complex 398 andmecCMRSA among human isolates in North‐West England

Abstract

Aims Livestock‐associated methicillin‐resistant Staphylococcus aureus (LA‐MRSA) is an important public health problem in many countries. Despite reports of such isolates being found in both animals and humans in the United Kingdom few data are available on the prevalence in humans of such isolates. A prevalence study was therefore undertaken in the north‐west of England. Methods and Results One thousand two hundred and forty‐two human MRSA isolates collected during 2015 were screened by PCR to detect two of the major forms of LA‐MRSA: clonal complex (CC)398 and mecC MRSA. Isolates identified were further characterized by antimicrobial susceptibility testing and whole‐genome sequencing using HiSeq technology. A single mecC MRSA isolate and three CC398 LA‐MRSA were identified among the isolates screened. All four isolates were from MRSA screening. A phylogenetic analysis, including previously sequenced isolates from the United Kingdom, provided strong evidence for the genomic and epidemiological linkage between a pair of animal and human isolates of CC398 LA‐MRSA in England. These data are indicative of animal and humans isolates of CC398 LA‐MRSA being involved in the same transmission network and is the first demonstration of such closely linked animal and human isolates of this lineage in the UK. Conclusions The study indicates there is a low prevalence of CC398 LA‐MRSA and mecC MRSA among MRSA isolates in the sampled population. Significance and Impact of the Study While the study demonstrates that LA‐MRSA were rare among human MRSA isolates in the sampled population, the data provide a baseline for the future surveillance of what is a significant public health challenge in some regions. The demonstration of linked human and animal isolates of CC398 LA‐MRSA, supported by genomic and epidemiological data, reinforces the need for such surveillance and for continued awareness of the risks that LA‐MRSA may pose in the UK.

Human mecC-Carrying MRSA: Clinical Implications and Risk Factors

“…Several studies did not identify any mecC -positive S. aureus among included human isolates/samples ( Table 2 ) [ 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 ]. In studies in which this gene was detected ( Table 1 ), the prevalence identified, considering the total number of isolates/samples included, was < 1% in most of the cases [ 24 , 27 , 28 , 29 , 32 , 33 , 37 , 40 , 41 , 42 , 43 ], similar to that identified in the first study in which mecC was discovered (approximately 0.04%) [ 16 ]. In a few studies, the prevalence was > 1% but, in all of these, only a small number of initial isolates (<400 isolates) was used; this ma...…”

“…Since then, several retrospective and prospective studies using human S. aureus isolates/samples were carried out in order to search for mecC -MRSA isolates ( Table 1 and Table 2 ) [ 16 , 18 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 ,…”

“…Importantly, the criteria chosen for the selection of the initial isolates/samples varied significantly. While all S. aureus isolates were collected in some studies [ 29 , 38 , 45 ], only MRSA isolates were included in others [ 24 , 26 , 27 , 28 , 32 , 33 , 36 , 41 , 42 ]. Moreover, several studies were more restrictive and only used isolates that showed characteristics suspected of carrying the mecC gene such as spa types associated with mecC -positive clonal lineages previously described, mecA -negative MRSA isolates, isolates with antimicrobial susceptibility suspected to be mecC -positive or pvl -negative MRSA isolates [ 25 , 26 , 37 , 69 ] ( Table S1 ).…”

“…The time and host in which CC130 MSSA isolates acquired the mecC resistance gene remain unknown today. In order to establish a possible human or animal origin for the detected mecC -MRSA isolates in human samples, several studies analyzed the presence of IEC (immune evasion cluster) genes [ 17 , 24 , 26 , 31 , 33 , 36 , 41 , 42 , 78 , 81 ] ( Table 1 and Table 3 ). In all cases, human mecC -MRSA isolates were negative for sak , chp and scn except for one ST1945 (CC130) isolate obtained from a screen swab from a patient in the UK that was positive for sak and scn (IEC type E), suggesting a possible human origin [ 41 ].…”

“…The newest human mecC -MRSA isolates detected so far in Europe were obtained in 2015, one of them in Germany [ 27 ], and the other in England [ 42 ]. Both strains showed similarities to those identified in the first studies [ 16 , 17 ] and both belonged to CC130.…”