Genotyping and Antimicrobial Susceptibility Profiling of Streptococcus uberis Isolated from a Clinical Bovine Mastitis Outbreak in a Dairy Farm.

Valentina Monistero,Paola Cremonesi,Bianca Castiglioni,Renata Piccinini,Clara Locatelli,M Filippa Addis,Stefano Morandi,Desiree C K Lassen,Lærke B Astrup,Paolo Moroni,Antonio Barberio,Valerio Bronzo

doi:10.3390/antibiotics10060644

Abstract

Streptococcus uberis, an environmental pathogen responsible also for contagious transmission, has been increasingly implicated in clinical mastitis (CM) cases in Europe. We described a 4-month epidemiological investigation of Strep. uberis CM cases in an Italian dairy farm. We determined molecular characteristics and phenotypic antimicrobial resistance of 71 Strep. uberis isolates from dairy cows with CM. Genotypic variability was investigated via multiplex PCR of housekeeping and virulence genes, and by RAPD-PCR typing. Antimicrobial susceptibility was assessed for 14 antimicrobials by MIC assay. All the isolates carried the 11 genes investigated. At 90% similarity, two distinct clusters, grouping 69 of the 71 isolates, were detected in the dendrogram derived from the primer ERIC1. The predominant cluster I could be separated into two subclusters, containing 38 and 14 isolates, respectively. Strep. uberis strains belonging to the same RAPD pattern differed in their resistance profiles. Most (97.2%) of them were resistant to at least one of the drugs tested, but only 25.4% showed a multidrug resistance phenotype. The highest resistance rate was observed for lincomycin (93%), followed by tetracycline (85.9%). This study confirmed a low prevalence of β-lactam resistance in Strep. uberis, with only one isolate showing resistance to six antimicrobial classes, including cephalosporins.

Highlights

Streptococcus uberis is primarily classified as an environmental pathogen causing about one-third of all intramammary infection (IMI) cases in lactating and nonlactating cows worldwide [1,2]
The 71 Strep. uberis isolates were characterized by RAPD-PCR analysis with primer ERIC1
Strep. uberis isolated from clinical mastitis (CM) carried a combination of virulence genes, that might be linked to strains with a greater probability of causing clinical infections

Summary

Introduction

Streptococcus uberis is primarily classified as an environmental pathogen causing about one-third of all intramammary infection (IMI) cases in lactating and nonlactating cows worldwide [1,2]. Uberis strains show a contagious transmission mode [8,9], deserving further investigation. Uberis has a nonclonal population structure but clonal strains in different cows have been detected [13]. This latter technique was shown to be reliable in typing Strep. Uberis and identifying clonal strains in different cows within herds [15]. Uberis strains share the same combination of highly conserved virulence genes (hasA, hasB, hasC, oppF, pauA, sua) [16,17,18], strongly associated with the pathogenesis of IMI. The two multiplex PCR (mPCR) assays developed by Calonzi and collaborators [19] allow the detection of these genes for a rapid characterization of Strep. The lbp-producing iron-binding protein aids in adherence to and internalization into bovine mammary epithelial cells [20]

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Results

Discussion

Conclusion