Virulence profiles of Klebsiella pneumoniae isolated from 2 large dairy farms in China

摘要

We recently reported on the diversity of Klebsiellapneumoniae isolated from dairy herds in China. Inour previous work, isolates from subclinical mastitis(SCM) had lower indices of diversity when comparedwith bacteria from other sources, possibly due to acontagious-like spread of udder adapted strains. Herewe explored the virulence profile and capsular typesof K. pneumoniae isolated from different sources on2 dairy farms in China. Our overarching goal was togain insights on the role of virulence genes toward theseverity of mastitis caused by K. pneumoniae. A totalof 1,484 samples were collected from clinical mastitis(CM; n = 355), SCM (n = 561), bulk tank milk (BTM;n = 130), and environmental and extramammary (EE)sites (n = 438). From those, 431 K. pneumoniae isolateswere obtained, including 129, 77, 66, and 159 isolatesfrom CM, SCM, BTM, and EE samples, respectively.Polymerase chain reactions were used to determine thecapsular types and to detect potential virulence genesin all isolates. No significant farm effects were observedwhen comparing the distribution of most virulencegenes in K. pneumoniae isolated from each source. K57was the most prevalent capsular type in K. pneumoniaefrom all sources, but with increased detection rate inisolates from CM. entB, kfu, fimH1, mrkD, and β-dlacZwere frequently detected in K. pneumoniae fromall sources. β-d-lacZ, entB, and ituA were more prevalentin isolates from CM, whereas kfu, allS, and nif weremore frequently detected in isolates from SCM. ybtS,aerobactin, and rpmA had increased prevalence in K.pneumoniae from BTM when compared with bacteriafrom other sources. No association was detected betweenvirulence genes and the severity of CM. K57 and the nifgene had the highest discriminatory power to classifyisolates from CM and SCM, respectively. Based on ourfindings, it is likely that K57 is the dominant capsulartype in K. pneumoniae causing CM in large Chinesedairy herds. Likewise, we demonstrated that β-d-lacZis disseminated in K. pneumoniae isolated from largeChinese dairy farms, irrespectively of the source of bacteria.Our results also suggest a low contribution of thevirulence profile of K. pneumoniae toward CM severity.Finally, the role of nif in increasing the adaptability tothe udder and promoting a contagious-like spread of K.pneumoniae warrants further investigation.