Antimicrobial resistance, virulence gene profile and molecular typing of Staphylococcus aureus isolates from dairy cows in Xinjiang Province, northwest China.

Staphylococcus aureus (SA) is a major pathogen causing dairy cow mastitis and endometritis. Recently, animal-derived SA strains pose a serious public-health threat. However, little is known about antimicrobial resistance and virulence factors of SA isolated from dairy cows in Xinjiang, China. In this study, antimicrobial resistance, virulence gene profiles and genotypes of SA from clinical mastitis and endometritis in dairy cows were investigated. A total of 337 clinical samples (186 milk samples from clinical mastitis cases and 151 endometritis swab samples) were collected from 15 large-scale dairy farms and were screened for SA. All SA isolates were subjected to antimicrobial susceptibility testing, detection of virulence genes and molecular typing. A total of 155 SA strains were isolated; 22 (14.2%) were methicillin-resistant S. aureus (MRSA). Resistance of MRSA isolates was significantly higher than that of methicillin-susceptible S. aureus (MSSA). The percentage of virulence genes varied between MSSA and MRSA. The strains could be divided into two SCCmec types (I and IVa), three agr types (I, II and III) and four spa types (t779, t2883, t13751 and t1939). MLST identified 14 sequence types, among which ST1 and ST9 had relatively high detection rates. These findings revealed that ST9-t1939-agrI was the main genotype of MSSA, whilst ST1-SCCmecI-t1939-agrI was the main genotype of MRSA from dairy cows. More significantly, a novel ST (STX) was identified for the first time. The majority of SA strains from dairy cows were multidrug-resistant and carried multiple virulence genes, posing a potential public-health risk.

Dan M ，Yehui W ，Qingling M ，Jun Q ，Xingxing Z ，Shuai M ，Kuojun C ，Jinsheng Z ，Zibing C ，Zaichao Z ，Xuepeng C ... -  《-》

Molecular Characteristics of Staphylococcus aureus Causing Bovine Mastitis between 2014 and 2015.

Li T ，Lu H ，Wang X ，Gao Q ，Dai Y ，Shang J ，Li M ... -  《Frontiers in Cellular and Infection Microbiology》

Molecular characterization and clonal diversity of methicillin-susceptible Staphylococcus aureus in milk of cows with mastitis in Brazil.

Mastitis is an important disease for the dairy industry worldwide, causing economic losses and reducing milk quality and production. Staphylococcus aureus is a worldwide agent of this intramammary infection, which also causes foodborne diseases. The objective of this study was to determine the frequency of methicillin-susceptible Staphylococcus aureus (MSSA) isolates in milk of mastitis cows in Brazil and to analyze the genetic lineages and the content of antimicrobial resistance genes and virulence factors among these isolates. Fifty-six MSSA isolates were recovered from 1,484 milk samples (positive for the California mastitis test) of 518 cows from 11 different farms in Brazil (representing 51% of total Staph. aureus obtained), and they were further characterized. Methicillin-susceptible Staphylococcus aureus were isolated from 3.7% of California mastitis test-positive tested milk samples and from 6.2% of tested mastitic cows. Methicillin-susceptible Staphylococcus aureus isolates were characterized by spa typing, agr typing, and multilocus sequence typing, and resistance and virulence traits were investigated by PCR. Seven spa types were identified among MSSA (% of isolates): t127 (44.6), t605 (37.5), t002, t1784, t2066 (1.8), and 2 new ones: t10856 (10.7) and t10852 (1.8). Five distinct sequence types (ST) were detected (% of isolates): ST1 (46.4), ST126 (37.5), ST133 (10.7), ST5 (3.6), and a novel ST registered as ST2493 (1.8). Resistances were detected for streptomycin, chloramphenicol, and tetracycline. One strain contained the chloramphenicol resistance gene (fexA; included within transposon Tn558) and 3 strains contained the tetracycline resistance gene [tet(K)]. Methicillin-susceptible Staphylococcus aureus strains were susceptible to most of the antibiotics studied and lacked the virulence genes of Panton-Valentine leukocidin (lukF/S-PV), toxic shock syndrome toxin 1 (tst), exfoliative toxin A (eta), and exfoliative toxin B (etb), as well as the genes of the immune evasion cluster. Methicillin-susceptible Staphylococcus aureus isolates were detected in a relatively low proportion of cows with mastitis (6.2%) and recovered isolates presented high diversity of genetic lineages, with CC1 and CC126 the predominant clonal complexes, and CC133 also being detected. Larger epidemiological studies with molecular characterization of isolates are required to deepen the knowledge on the circulating genetic lineages among the cow population with mastitis.

Silva NCC ，Guimarães FF ，Manzi MP ，Budri PE ，Gómez-Sanz E ，Benito D ，Langoni H ，Rall VLM ，Torres C ... -  《-》

Genetic characterisation of Staphylococcus aureus isolated from milk and nasal samples of healthy cows in Tunisia: First report of ST97-t267-agrI-SCCmecV MRSA of bovine origin in Tunisia.

This study aimed to screen for and characterise methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) in nasal swabs and milk from healthy cows from different regions in Tunisia. A total of 141 Staphylococcus spp. isolates were recovered from milk and nasal samples of cows. S. aureus isolates were further characterised by determining their antimicrobial susceptibilities, genes encoding antimicrobial resistance and virulence factors, biofilm production, agr type and PFGE. spa and SCCmec typing and MLST were also performed for the MRSA isolate. Twenty-seven isolates (19.1%) were identified as S. aureus, of which 26 were MSSA and 1 was MRSA. The MSSA isolates were resistant to penicillin (73.1%), fusidic acid (61.5%), clindamycin (34.6%) and erythromycin (34.6%). The MRSA isolate, from a milk sample, was resistant to cefoxitin, penicillin, fusidic acid, amikacin and clindamycin. Twenty-five isolates (92.6%) had at least one enterotoxin gene. Only four isolates (14.8%) were positive for the tsst-1 gene. Genes encoding the exfoliative toxins D and A were detected in 9 (33.3%) and 6 (22.2%) isolates, respectively. The single MRSA isolate and 22 MSSA isolates were biofilm-producers on Congo red agar plates. Twelve pulsotypes were identified amongst 25 MSSA isolates revealing the clonal diversity of these isolates; however, one MSSA isolate was identified as CC398. The MRSA isolate was PVL-negative and was typed as ST97-t267-agrI-SCCmecV. Contamination of milk with S. aureus, especially enterotoxin- and TSST-1-positive strains, poses a potential public-health threat. This is the first report of MRSA of bovine origin in Tunisia.

Khemiri M ，Abbassi MS ，Couto N ，Mansouri R ，Hammami S ，Pomba C ... -  《-》

Molecular Characterization and Clonal Diversity of Methicillin-Resistant and -Susceptible Staphylococcus aureus Isolates of Milk of Cows with Clinical Mastitis in Tunisia.

Klibi A ，Jouini A ，Gómez P ，Slimene K ，Ceballos S ，Torres C ，Maaroufi A ... -  《-》