Antimicrobial resistance of Streptococcus dysgalactiae, Streptococcus agalactiae, and Streptococcus canis in quarter milk samples from Bavaria, Southern Germany, between 2012 and 2022.

The objective of this study was to analyze the in vitro antimicrobial resistance (AMR) of Streptococcusdysgalactiae, Strep. agalactiae, and Strep. canis over a 10-yr period from 2012 to 2022 against the most commonly used antimicrobial agents. For this purpose, all quarter milk samples (QMS) submitted to the milk laboratory of the Bavarian Animal Health Service were analyzed. Each QMS was tested using the California Mastitis Test and categorized as negative, subclinical, or clinical mastitis if the milk character was abnormal. Samples with Strep. dysgalactiae, Strep. agalactiae, or Strep. canis were included and a subset of isolates were further tested for in vitro AMR by breakpoint analysis with broth microdilution. Streptococcus dysgalactiae (61%, n = 65,750) was the most abundant pathogen among those 3 species, followed by Strep. agalactiae (28%, n = 30,486), and Strep. canis (11%, n = 11,336). All 3 species showed the highest resistance to the same 4 antimicrobial agents: erythromycin, marbofloxacin, pirlimycin, and cefalexin/kanamycin with varying degrees of resistance. Throughout the study period, Strep. dysgalactiae, Strep. agalactiae, and Strep. canis were largely susceptible to the remaining antimicrobial agents tested (penicillin, amoxicillin-clavulanate, oxacillin, cefazolin, cefoperazone, cefquinome). Only less than 14% of isolates of Strep. dysgalactiae and Strep. canis were resistant against any of the antimicrobials tested. Streptococcus agalactiae was the species with the highest percentage of resistant isolates. Although the percentage of resistant isolates from Strep. canis and Strep. dysgalactiae decreased, the percentage of resistant Strep. agalactiae isolates increased after 2017. In summary, most isolates were not resistant to the most commonly used antimicrobial agents for mastitis therapy, including β-lactam antibiotics and penicillin should remain the first-choice therapy against streptococcal mastitis.

Bechtold V ，Petzl W ，Huber-Schlenstedt R ，Gangl A ，Sorge US ... -  《-》

Short communication: Streptococcus species isolated from mastitis milk samples in Germany and their resistance to antimicrobial agents.

Mastitis is one of the most frequent infectious diseases in dairy cattle and is a reason for antimicrobial drug usage in dairy cows. The bacteria involved in bovine mastitis are mainly Streptococcus spp., Staphylococcus spp., and coliforms. The aim of this study was to determine antimicrobial resistance among Streptococcus spp. isolated from bovine mastitis milk. Antimicrobial resistance in Strep. uberis (n=227), Strep. dysgalactiae (n=49), and Strep. agalactiae (n=3) was determined for 9 antimicrobial agents using the broth microdilution method in accordance with Clinical and Laboratory Standards Institute recommendations. Of all Streptococcus spp., 13% were multidrug resistant. The rate of multidrug resistance was higher among Strep. uberis (15%) than among Strep. dysgalactiae (6%) and Strep. agalactiae (0%). Resistance to tetracycline was the most common, followed by resistance to erythromycin, pirlimycin, and gentamicin. Resistance rates were higher on farms with more than 80 cows compared with those with fewer than 20 cows. β-Lactams should remain the drugs of choice in the treatment of streptococcal mastitis. The slightly elevated minimum inhibitory concentrations determined for these antibiotics may indicate, however, the emergence of resistant streptococci. To identify such changes in susceptibility as early as possible, antimicrobial resistance in streptococci should be surveyed regularly.

Minst K ，Märtlbauer E ，Miller T ，Meyer C ... -  《-》

Changes in antimicrobial resistance of Staphylococcus aureus in bovine quarter milk samples from southern Germany between 2012 and 2022.

The objective of this study was to describe the in vitro resistance of Staphylococcus aureus from bovine quarter milk samples obtained by the udder health laboratory of the Bavarian Animal Health Services between 2012 and 2022. All S. aureus samples were tested for β-lactamase production and only forwarded to further microbroth susceptibility testing either if the β-lactamase result was positive or upon explicit request by the submitter. The growth of most S. aureus isolates was inhibited at the lowest evaluated minimum inhibitory concentration (MIC) of tested antimicrobials, with the MIC50 and MIC90 (the MIC where 50% and 90% of isolates were inhibited by the tested antibiotics, respectively) mostly beneath the respective breakpoint. On average, about one-fourth (24%, n = 5,718) of tested isolates was resistant to erythromycin. However, the prevalence of resistant isolates dropped from 53% (n = 1,018) in 2012 to 8% (n = 113) in 2022. The second highest prevalence of in vitro resistance was to penicillin (17%, of all isolates tested for β-lactamase production, n = 28,069). Less than 14% of isolates were resistant to the remaining assessed antimicrobial agents (cefoperazone, pirlimycin, kanamycin-cefalexin, marbofloxacin, amoxicillin-clavulanate, cefquinome, or cefazolin, respectively). Over the years, 4% (n = 959) of the S. aureus isolates selected for microbroth susceptibility testing (and 0.8% (n = 1,392) of all submitted S. aureus isolates) were methicillin-resistant S. aureus, and 5% (n = 1,162) of S. aureus isolates were multidrug resistant. However, there was an overall trend toward fewer resistant isolates. These findings are consistent with those of several European monitoring programs that reported a slight decrease of antimicrobial resistance (AMR) of bovine S. aureus in countries where antibiotic use in veterinary medicine was reduced. Notably, isolates of clinical mastitis cases were consistently less likely to express in vitro resistance than isolates obtained from milk of healthy cows or subclinical mastitis cases. In conclusion, AMR of S. aureus was decreasing and penicillin should remain the first-choice antimicrobial in the attempt of treating S. aureus intramammary infections in Bavaria.

Karell J ，Petzl W ，Gangl A ，Huber-Schlenstedt R ，Sorge US ... -  《-》

Molecular characterization and antimicrobial susceptibility pattern of Streptococcus agalactiae isolated from clinical mastitis in dairy cattle.

Tomazi T ，de Souza Filho AF ，Heinemann MB ，Dos Santos MV ... -  《PLoS One》

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 ... -  《-》