Prevalence and characterization of methicillin-resistant Staphylococcus aureus carrying mecA or mecC and methicillin-susceptible Staphylococcus aureus in dairy sheep farms in central Italy

Abstract

Between January and May 2012, a total of 286 bulk tank milk samples from dairy sheep farms located in central Italy were tested for the presence of Staphylococcus aureus. One hundred fifty-three samples were positive for S. aureus (53.5%), with an average count of 2.53 log cfu/mL. A total of 679 S. aureus colonies were screened for methicillin resistance by the cefoxitin disk diffusion test, and 104 selected cefoxitin-susceptible isolates were also tested for their susceptibility to other antimicrobials representative of the most relevant classes active against Staphylococcus spp. by using the Kirby-Bauer disk diffusion method. Two methicillin-resistant Staphylococcus aureus (MRSA) isolates, carrying respectively the mecA and the mecC genes, were detected in 2 samples from 2 different farms (prevalence 0.7%). The mecA-positive MRSA isolate was blaZ positive, belonged to spa type t127, sequence type (ST)1, clonal complex (CC)1, carried a staphylococcal cassette chromosome mec (SCCmec) type IVa, and was phenotypically resistant to all the β-lactams tested and to erythromycin, streptomycin, kanamycin, and tetracycline. The mecC-positive MRSA isolate was negative for the chromosomally or plasmid-associated blaZ gene but positive for the blaZ allotype associated with SCCmec XI (blaZ-SCCmecXI), belonged to spa type 843, ST(CC)130, carried a SCCmec type XI, and was resistant only to β-lactams. Both MRSA were negative for the presence of specific immune-evasion and virulence genes such as those coding for the Panton-Valentine leucocidin, the toxic shock syndrome toxin 1, and the immune evasion cluster genes. Regarding the presence of the major S. aureus enterotoxin genes, the mecC-positive MRSA tested negative, whereas the ST (CC)1 mecA-positive MRSA harbored the seh gene. Among the 104 methicillin-susceptible S. aureus isolates examined for antimicrobial susceptibility, 63 (60.58%) were susceptible to all the antimicrobials tested, and 41 (39.42%) were resistant to at least 1 antimicrobial. In particular, 23 isolates (22.12%) were resistant to tetracycline, 16 (15.38%) to sulfonomides, 14 (13.46%) to trimethoprim and sulfamethoxazole, and 9 (8.65%) to ampicillin, whereas only 1 isolate was resistant to both fluoroquinolones and aminoglycosides. The high prevalence of S. aureus found in bulk tank milk samples and the isolation of MRSA, although at a low prevalence, underlines the importance of adopting control measures against S. aureus in dairy sheep farms to minimize the risks for animal and public health. Moreover, this study represents the first report of mecC-positive MRSA isolation in Italy and would confirm that, among livestock animals, sheep might act as a mecC-MRSA reservoir. Although this lineage seems to be rare in dairy sheep (0.35% of farms tested), because mecC-positive MRSA are difficult to detect by diagnostic routine methods employed for mecA-positive livestock-associated MRSA, diagnostic laboratories should be aware of the importance of searching for the mecC gene in all the mecA-negative S. aureus iso...

Prevalence and Characterization of Staphylococcus aureus Cultured From Raw Milk Taken From Dairy Cows With Mastitis in Beijing, China

“…In the present study, 46.2% (90/195) of raw milk samples taken from dairy cows with mastitis were positive for S. aureus . This prevalence is similar to a recent report in China and other reports in Brazil and Italy (Cavicchioli et al, 2015 ; Li et al, 2015 ; Giacinti et al, 2017 ). However, another recent study reported that the prevalence of S. aureus in raw milk of health cows in Beijing was 22.0% (Liu et al, 2017 ).…”

Prevalence and Antibiotic-Sensitivity of Methicillin-Resistant Staphylococcus aureus (MRSA) in Pyogenic Skin Affections of Animals and Human

“…Meanwhile, despite the high number of sheep and goat with skin abscesses subjected to this study, the estimated prevalence of MRSA was low (3.0%). This finding came in agreement with other investigations carried out on small ruminants (Giacinti et al, 2017;Caruso et al, 2015;Cortimiglia et al, 2015) in Italy, (Ariza-Miguel et al, 2014) in Spain and (Pexara et al, 2005) in Greece, who reported prevalence rates ranged from 0-2%.…”

Identification of Methicillin-Resistant Staphylococcus aureus in Bulk Tank Milk

“…On the current study, a high rate of mecA MRSA strains was detected in bulk tank milk samples. Researchers from several countries have reported the rate of MRSA in milk as 50%, 13%, 9.7%, 4.4%, 2.5%, and 0.7% (Kreausukon et al, 2012;Jamali et al, 2015;Parisi et al, 2016;Giacinti et al, 2017;Asiimwe et al, 2017;Tenhagen et al, 2018). Previous studies from Turkey have indicated lower rates than the current study: Ektik et al (2017) 14.28%, Sayin et al (2016) 18.6%, Siiriken et al (2016) 13.3% and Buyukcangaz et al (2013) 15.8%.…”