Phenotypic and genotypic characterization of antimicrobial resistance profiles in Streptococcus dysgalactiae isolated from bovine clinical mastitis in 5 provinces of China.

Bovine mastitis is among the most prevalent and costly diseases of dairy animals and is caused by a variety of bacterial pathogens including Streptococcus dysgalactiae. However, comprehensive studies reporting the prevalence and antimicrobial resistance profiles of S. dysgalactiae isolated from bovine mastitis are scarce. Therefore, this study was to investigate the occurrence of S. dysgalactiae associated with bovine clinical mastitis, to assess their antimicrobial resistance profiles, and to analyze the phenotypic and genotypic profiling of resistant isolates. In total, 1,180 milk samples were collected from dairy cows with clinical mastitis belonging to 74 commercial dairy herds located in 14 provinces of China from January 2014 to May 2016. Overall S. dysgalactiae isolates were recovered from 88 (7.5%) of the mastitic milk samples. The antimicrobial susceptibility of these isolates was tested against 8 antimicrobial agents by using minimum inhibitory concentrations. Results showed that 82 (93.2%) isolates expressed resistance to more than one antimicrobial agent. Antimicrobial resistance was highest against kanamycin (89.8%), sulfonamide (83.0%), and streptomycin (58.0%), which can be attributed to the intrinsic resistance for most of Streptococcus spp. against those antimicrobial substances. Strikingly, 30 (34.1%) and 12 (13.6%) isolates were found resistant to cephalexin and ceftriaxone, respectively. BlaTEM, ermB, and tetM were the most prevalent resistance genes. All isolates carried at least one of all tested resistance genes. Also, 1.1, 12.5, 18.2, 36.4, and 31.8% of isolates were positive for at least one tested resistance gene in 1, 2, 3, 4, or 5 classes of antimicrobials. Survival analysis showed a significant association between ermB and survival of the S. dysgalactiae isolates at increasing erythromycin concentrations. No other statistically significant associations were observed between the phenotypic and genotypic resistance profiles. This study concludes a considerable prevalence of S. dysgalactiae associated with bovine mastitis in dairy herds of China and these isolates exhibited high resistance rates to tested antimicrobials, coupled with high occurrence of resistance genes. Both the prevalence of S. dysgalactiae and their antimicrobial resistance profiles strongly varied among dairy herds, demonstrating the need for antimicrobial susceptibility surveillance at the herd level to ensure optimal therapeutic results.

Zhang S ，Piepers S ，Shan R ，Cai L ，Mao S ，Zou J ，Ali T ，De Vliegher S ，Han B ... -  《-》

Antimicrobial resistance in Staphylococcus aureus, Streptococcus uberis and Streptococcus dysgalactiae from dairy cows with mastitis.

McDougall S ，Hussein H ，Petrovski K 《NEW ZEALAND VETERINARY JOURNAL》

Antimicrobial resistance and virulence genes of Streptococcus isolated from dairy cows with mastitis in China.

Streptococcus is a major mastitis-causing pathogen in dairy cows. To investigate the prevalence, antimicrobial resistance and virulence gene of Streptococcus in mastitic milk, a total of 735 mastitic raw milk samples from dairy cows in 11 provinces of China were collected and tested. Antimicrobial resistance of Streptococcus isolates was determined by disc diffusion against 8 classes 29 antimicrobial agents, and Streptococcus resistant genes and virulence genes were determined by PCR and agarose gel electrophoresis. A total of 64 (8.71%) isolates of Streptococcus were isolated and identified using biochemical profiling, including 22 isolates of Streptococcus agalactiae, 13 isolates of Streptococcus dysgalactiae, and 29 isolates of Streptococcus uberis. Out of 64 resistant Streptococcus isolates, all isolates (100%) were resistant to 3 or more antimicrobials. The most frequency (n = 18, 28.12%) of the isolates were multi-resistant to 5-7 antimicrobials and the highest multi-resistant number was 29 (n = 1, 1.56%). Streptococcus isolates had the highest resistance rate to tetracycline (98.44%) and oxacillin (98.44%), followed by penicillin G (96.88%) and doxycycline (96.88%), and the lowest resistance was observed with respect to ciprofloxacin (1.56%). A total of 16 antimicrobials resistance genes with 25 combination patterns were detected in the isolates. The gene combination of Sul1/Sul2/Sul3 + gyrA/parC + cat1/cat2 was the most common pattern (12.5%). The correlation between resistant phenotypes and resistance genes in Streptococcs was 35.87%. A total of 7 virulence genes were detected and 59 (92.19%) isolates harbored at least one gene. Twenty-four classes of gene patterns were found in the isolates and the patterns of bca (9.38%) and cfb (9.38%) were the most prevalent form. In conclusion, the issue of drug resistance of Streptococcus is still a great concern in cattle health in China.

Tian XY ，Zheng N ，Han RW ，Ho H ，Wang J ，Wang YT ，Wang SQ ，Li HG ，Liu HW ，Yu ZN ... -  《-》

Phenotypic antimicrobial susceptibility and occurrence of selected resistance genes in gram-positive mastitis pathogens isolated from Wisconsin dairy cows.

In the United States, few intramammary antimicrobials exist that are approved for treatment of bovine mastitis; thus, ensuring judicious use of these products is a priority. The objectives of this study were to determine phenotypic susceptibility and presence of selected antimicrobial resistance genes from staphylococci, streptococci, and streptococcal-like organisms recovered from cases of clinical mastitis occurring in cows on large Wisconsin farms. Staphylococcus aureus (n=35 from 19 herds), coagulase-negative staphylococci (n=51 from 30 herds), Streptococcus spp. (n=78 from 36 herds), and streptococcal-like organisms (n=31 from 19 herds) were used in this study. All Staphylococcus spp. were susceptible to ceftiofur, cephalothin, and the combination of penicillin and novobiocin. Of all staphylococci, only a single Staphylococcus epidermidis exhibited phenotypic resistance to oxacillin. Phenotypic susceptibility to erythromycin was observed in only 8.6 and 15.7% of Staphylococcus aureus and coagulase-negative staphylococci, respectively. Approximately 20% of staphylococci and 13 to 22% of streptococci and streptococcal-like organisms exhibited phenotypic resistance to pirlimycin. All Streptococcus spp. exhibited phenotypic susceptibility to ceftiofur, cephalothin, and oxacillin. The proportion of isolates exhibiting phenotypic susceptibility to pirlimycin and sulfadimethoxine differed among Streptococcus dysgalactiae and Streptococcus uberis. All streptococcal-like organisms exhibited phenotypic susceptibility to ceftiofur, cephalothin, oxacillin, penicillin, and the combination of penicillin and novobiocin. Of all organisms tested, 36.9% did not carry any of the resistance genes (ermC, blaZ, tetK, or tetM), 35.4% carried 1 gene, and 27.7% carried multiple genes (usually blaZ in combination with a tet gene). Eighteen (51.4%) Staph. aureus and 12 (48.0%) Staphylococcus chromogenes carried multiple resistance genes. Six (12.2%) Strep. dysgalactiae and no Strep. uberis carried multiple resistance genes. Results indicate that most gram-positive mastitis organisms were susceptible to most antimicrobials used for intramammary administration, but some resistance to drugs used for systemic treatment of mastitis was noted. The presence of selected resistance genes was not proportional to the occurrence of phenotypic resistance.

Ruegg PL ，Oliveira L ，Jin W ，Okwumabua O ... -  《-》

Antimicrobial resistance and virulence-related genes of Streptococcus obtained from dairy cows with mastitis in Inner Mongolia, China.

Ding Y ，Zhao J ，He X ，Li M ，Guan H ，Zhang Z ，Li P ... -  《-》