Whole genome-based antimicrobial resistance, virulence, and phylogenetic characteristics of Trueperella pyogenes clinical isolates from humans and animals.

Trueperella pyogenes is an opportunistic zoonotic bacterial pathogen, whose antimicrobial resistance, virulence, and genetic relatedness between strains from animals and humans are barely studied. These characteristics were therefore analyzed for clinical T. pyogenes strains from 31 animals of 11 different species and 8 humans determining their complete circular genome sequence and antimicrobial susceptibility. The MICs of 19 antimicrobials including 3 antiseptics correlated to the resistance genes identified in silico within the genomes revealing a predominance of resistance to streptomycin (aadA9), sulfamethoxazole (sul1), and tetracycline (tet(33), tet(W/N/W)) among strains from humans and cattle. Additional resistance genes (erm(X), erm(56), cmx, drfA1, aadA1, aph(3'')-Ib (strA), aph(6)-Id (strB), aac(3)-IVa, aph(4)-Ia) were found only sporadically. The resistance genes were localized on genetic elements integrated into the chromosome. A cgMLST-based phylogenetic analysis revealed two major clusters each containing genetically diverse strains. The human strains showed the closest relatedness to strains from cattle. Virulence genes coding for fimbriae (fimA, fimC), neuroamidase (nanP, nanH), pyolysin (plo), and collagen binding protein (cbpA) were identified in strains from different hosts, but no correlation was observed between virulence factors and strain origin. The existence of resistance genes typically found in Gram-negative bacteria within the Gram-positive T. pyogenes indicates a wider capacity to adapt to antimicrobial selective pressure. Moreover, the presence of similar antimicrobial resistance profiles found in cattle and human strains as well as their closest relatedness suggests common zoonotic features and cattle as the potential source for human infections.

Antimicrobial efficiency of bromhexine hydrochloride against endometritis-causing Escherichia coli and Trueperella pyogenes in bovines.

In this study, the main agents associated with endometritis in cows in the state of Santa Catarina, Brazil, were identified and the resistance profile and virulence mechanisms of the bacterial isolates were evaluated. Isolates of Escherichia coli and Trueperella pyogenes were tested for their biofilm forming ability and the antimicrobial action of bromhexine hydrochloride in combination with other antimicrobials. A total of 37 uterine lavage samples were collected from cows with endometritis. Of the 55 bacteria isolated, 25.4% were identified as T. pyogenes and 16.3% as E. coli. The bacterial isolates showed greater resistance to sulfamethoxazole + trimethoprim (58.2%) and tetracycline (56.3%). Among the species, E. coli showed the highest resistance rates, with 100% of isolates showing resistance to amoxicillin, streptomycin, and gentamicin. The results of the minimum inhibitory concentration for the T. pyogenes isolates showed that 91.6% of the isolates were resistant to enrofloxacin and tetracycline, and 75% were resistant to ceftiofur and sulfamethoxazole + trimethoprim. All E. coli and T. pyogenes isolates showed biofilm forming ability. The plo, fimA, and nanH genes were identified in 100% of T. pyogenes isolates. In parallel, 100% of E. coli isolates had the fimH gene, and 11.1% had the csgD gene. Bromhexine hydrochloride showed antimicrobial activity against 100% of E. coli isolates and 66.6% of T. pyogenes isolates. Furthermore, when associated with antimicrobials, bromhexine hydrochloride has a synergistic and additive effect, proving to be an option in the treatment of endometritis in cows and an alternative for reducing the use of antimicrobials.

An in vitro comparison of antimicrobial efficacy and cytotoxicity between povidone-iodine and chlorhexidine for treating clinical endometritis in dairy cows.

This study aimed to assess the in vitro antimicrobial effects of chlorhexidine (CHX) and povidone-iodine (PI) on clinical isolates of Escherichia coli (E. coli) and Trueperella pyogenes (T. pyogenes) from the vaginal discharge of dairy cows, as well as to compare the cytotoxicity effects of CHX and PI on bovine endometrial epithelial cells (BEnEpC). In Experiment 1, 12 E. coli and 10 T. pyogenes were isolated from the vaginal discharge of cows with a uterine infection. The MIC and MBC against CHX and PI were analyzed in vitro. In Experiment 2, the cytotoxicity effects of CHX and PI on BEnEpC were analyzed using a Viability/Cytotoxicity Kit, wound scratch healing assay, and the expression of pro-inflammatory cytokine genes (IL-6, IL-8, and TNF-α). In Experiment 1, the MIC and MBC values of CHX against E. coli were 0.0002% and 0.0002 to 0.00025%, respectively. The MIC and MBC values of PI were 1.25 to 2.5% and 1.25 to 5%, respectively. For T. pyogenes, the MIC and MBC values of CHX were 0.00002%. The MIC and MBC values of PI were 1.25%. In Experiment 2, the cell viability significantly decreased, and wound closures were significantly inhibited after treatment with ≥ 0.002% CHX and ≥ 0.025% PI. The expression of IL-6, IL-8, and TNF-α significantly increased after treatment with PI. Only IL-6 showed a significant increase after cells were treated with 0.00002% and 0.0002% CHX. The results suggested that both CHX and PI had high antibacterial effects. However, veterinarians and farmers should be aware of their cytotoxicity, which decrease viability of endometrial epithelial cells and inhibit wound healing in vitro.

Luteolin increases susceptibility to macrolides by inhibiting MsrA efflux pump in Trueperella pyogenes.

Trueperella pyogenes (T. pyogenes) is an opportunistic pathogen associated with a variety of diseases in many domestic animals. Therapeutic treatment options for T. pyogenes infections are becoming limited due to antimicrobial resistance, in which efflux pumps play an important role. This study aims to evaluate the inhibitory activity of luteolin, a natural flavonoid, on the MsrA efflux pump and investigate its mechanism. The results of antimicrobial susceptibility testing indicated that the susceptibility of msrA-positive T. pyogenes isolates to six macrolides increased after luteolin treatment, while the susceptibility of msrA-negative isolates showed no change after luteolin treatment. It is suspected that luteolin may increase the susceptibility of T. pyogenes isolates by inhibiting MsrA activity. After 1/2 MIC luteolin treatment for 36 h, the transcription level of the msrA gene and the expression level of the MsrA protein decreased by 55.0-97.7% and 36.5-71.5%, respectively. The results of an affinity test showed that the equilibrium dissociation constant (KD) of luteolin and MsrA was 6.462 × 10-5 M, and hydrogen bonding was predominant in the interaction of luteolin and MsrA. Luteolin may inhibit the ATPase activity of the MsrA protein, resulting in its lack of an energy source. The current study illustrates the effect of luteolin on MsrA in T. pyogenes isolates and provides insight into the development of luteolin as an innovative agent in combating infections caused by antimicrobial-resistant bacteria.

Septic hip abscess due to Fusobacterium nucleatum and Actinomyces turicensis in an immunocompetent SARS-CoV-2 positive patient.

A 42-year-old man was referred to the Department of Orthopedic Surgery with pain over his right greater trochanter and signs of systemic infection. CT showed an enhanced mass in his gluteus maximus as well as gas in the biceps femoris over the underlying hip joint. Tissue biopsy yielded Fusobacterium nucleatum and Actinomyces turicensis. The patient was successfully treated for 6 weeks with amoxicillin/clavulanic acid 875mg/125mg and metronidazole 500mg.

Effect of intramolecular disulfide bond of bovine lactoferricin on its molecular structure and antibacterial activity against Trueperella pyogenes separated from cow milk with mastitis.

BACKGROUND: Lactoferricin (Lfcin) is an antimicrobial activity center of lactoferrin, produced by hydrolysis from the N-terminal of lactoferrin. It was hypothesized that the intramolecular disulfide bond in Lfcin could affect its antibacterial function through influencing its molecular structure. To prove this hypothesis, bovine Lfcin (bLfcin) and its two derivatives, bLfcin with an intramolecular disulfate bond (bLfcin DB) and bLfcin with a mutation C36G (bLfcin C36G), were synthesized, purified, and identified. The circular dichroism spectra of the peptides were detected in solutions with different ionic and hydrophobic strength. The antibacterial activity of the peptides against Trueperella pyogenes, separated from cow milk with mastitis, were determined. RESULTS: The secondary structure of bLfcin DB showed more ß-turn and less random coil than the other peptides in H2O, similar ratios of secondary structures with bLfcin and bLfcin C36G under ionic conditions, and close percentages of secondary structure with bLfcin under hydrophobic conditions. The synthetic peptides exhibited strong antimicrobial activity against T. pyogenes isolates, T. pyogenes ATCC 19,411, and E. coli ATCC 25,922. The antimicrobial activities of the three peptides were greater against T. pyogenes than against E. coli, and bLfcin DB exhibited higher antibacterial activity compared with its derivatives. CONCLUSIONS: The intramolecular disulfide bond could change the molecular structure of bLfcin under alternative ionic strengths and hydrophobic effects, and the formation of the disulfide bond is beneficial to executing the antibacterial function of bLfcin.

New Determinants of Aminoglycoside Resistance and Their Association with the Class 1 Integron Gene Cassettes in Trueperella pyogenes.

Trueperella pyogenes is an important opportunistic animal pathogen. Different antimicrobials, including aminoglycosides, are used to treat T. pyogenes infections. The aim of the present study was to evaluate aminoglycoside susceptibility and to detect aminoglycoside resistance determinants in 86 T. pyogenes isolates of different origin. Minimum inhibitory concentration of gentamicin, streptomycin, and kanamycin was determined using a standard broth microdilution method. Genetic elements associated with aminoglycoside resistance were investigated by PCR and DNA sequencing. All studied isolates were susceptible to gentamicin, but 32.6% and 11.6% of them were classified as resistant to streptomycin and kanamycin, respectively. A total of 30 (34.9%) isolates contained class 1 integrons. Class 1 integron gene cassettes carrying aminoglycoside resistance genes, aadA11 and aadA9, were found in seven and two isolates, respectively. Additionally, the aadA9 gene found in six isolates was not associated with mobile genetic elements. Moreover, other, not carried by gene cassettes, aminoglycoside resistance genes, strA-strB and aph(3')-IIIa, were also detected. Most importantly, this is the first description of all reported genes in T. pyogenes. Nevertheless, the relevance of the resistance phenotype to genotype was not perfectly matched in 14 isolates. Therefore, further investigations are needed to fully explain aminoglycoside resistance mechanisms in T. pyogenes.

Antimicrobial susceptibility of Trueperella pyogenes isolated from food-producing ruminants.

A total of 96 Trueperella pyogenes isolates, an opportunistic pathogen of food-producing ruminants, obtained from cattle (n = 34), sheep (n = 35) and goats (n = 27), and identified by Real Time PCR (qPCR), were analysed to determine the susceptibility to 12 antimicrobials commonly used in livestock, using a broth microdilution. The Minimal Inhibitory Concentration (MIC) distribution was unimodal for half of the antimicrobials tested with the exception of apramycin, gentamicin, streptomycin, oxytetracycline, tylosin, and erythromycin all of which showed bimodal MIC distributions. Low MIC90 values for penicillin, amoxicillin, ceftiofur, enrofloxacin, and gentamicin (<1 µg/ml) were obtained, suggesting that these antimicrobials would be the most effective first line empiric treatment for T. pyogenes infections in livestock. Furthermore, according to the specific T. pyogenes breakpoints for penicillin, sulfamethoxazole/trimethoprim and erythromycin, 93.7 % of isolates were susceptible to penicillin and 77.2 % to erythromycin, whereas 92.7 % were non-susceptible to sulfamethoxazole/trimethoprim. Significant differences were observed in the MIC distribution of almost all antimicrobials, except enrofloxacin, tylosin and erythromycin against cattle, sheep or goat isolates, although all antimicrobials showed similar MIC90 values, except apramycin and oxytetracycline that showed higher values when tested against cattle isolates. These data provide interesting information on the antimicrobials of choice for the treatment of infections caused by T. pyogenes in ruminants.

Genomic island type IV secretion system and transposons in genomic islands involved in antimicrobial resistance in Trueperella pyogenes.

Trueperella pyogenes (T. pyogenes) is a well-known opportunistic pathogen of many animal species. It can cause a variety of suppurative infections. The objective of this research was to get insight into the gene context and the location of the antimicrobial resistance determinants in the two multi-resistant T. pyogenes isolates TP3 and TP4. Comparative analysis of key factors leading to antimicrobial resistance was performed. Both isolates were resistant to erythromycin, azithromycin and tetracycline, and susceptible to ciprofloxacin, enrofloxacin, cefazolin and florfenicol. In addition, TP4 was resistant to amikacin and gentamicin. Whole-genome analyses revealed that both TP3 and TP4 contained two different genomic islands (TP3-GI1, TP3-GI5, TP4-GI5 and TP4-GI8) involved in multi-drug resistance. There is a common region in TP3-GI1 and TP4-GI5, containing the tetracycline resistance gene tet(W) and a series of genes involved in type IV secretion systems. Several genes located on TP3-GI5 and TP4-GI8 are highly homologous. Tetracycline-resistance gene tet(33) was potentially acquired by horizontal gene transfer via IS6100 located on 57,936 bp TP3-GI5. The macrolide resistance gene erm(X) was located near the end of the TP3-GI5. The sequence analysis of TP4-GI8 showed that two copies of erm(X) and two IS1634 elements located in the same orientation may have formed a composite transposon. GI-type T4SS, transposons and multiple resistance genes located on GIs play a key role in multiple drug resistance of TP3 and TP4.

Chemical composition and antibacterial activity of essential oils against pathogens often related to cattle endometritis.

INTRODUCTION: Endometritis is a condition marked by inflammation of the endometrium that affects dairy cows from 21 days after parturition, causing damage to herd fertility and economic losses on farms. The use of active compounds obtained from plant sources has gained importance as disease treatment agents in farm animals due to the high resistance rates currently observed against traditional antibiotics commonly used. The study was carried out to examine the chemical composition and to investigate the antibacterial activity of rosemary, cinnamon, cloves, eucalyptus, lemon, oregano and thyme essential oils against the reference strain of Escherichia coli (ATCC 25922), Fusobacterium necrophorum (ATCC 25286), Trueperella pyogenes (ATCC 19411) and Staphylococcus aureus (ATCC 29213), considered as typical bacteria causing endometritis. METHODOLOGY: The chemical composition of the seven essential oils were analyzed by GC-MS and their antibacterial activity was evaluated by the disc diffusion method. RESULTS: Thirty-six components were identified in total using GC-MS analyzes. The main compounds were cinnamaldehyde (86.5% for cinnamon essential oil), eugenol (85.7% for clove essential oil), 1,8-cineol (80% for eucalyptus and 47.8% rosemary essential oils), limonene (65.5% for lemon essential oil), carvacrol (72.1% for oregano essential oil) and thymol (48.8% for thyme essential oil). The disc diffusion assay revealed that cinnamon, clove, oregano, and thyme essential oils showed the best results compared to the other three essential oils, showing the largest zone of inhibition against all bacteria evaluated. CONCLUSIONS: These findings indicated that essential oils are a potential agent to be used as an alternative for bovine endometritis treatment.

Multidrug resistance genes are associated with a 42-kb island TGI1 carrying a complex class 1 integron in Trueperella pyogenes.

OBJECTIVES: This research was conducted to ascertain the context and location of the antibiotic resistance determinants in a multiple antibiotic-resistant Trueperella pyogenes isolate TP1. METHODS: The genome was sequenced using PacBio RS II, and the filtered data were assembled using Canu. Sequences were annotated on the basis of those in GenBank, and the genomic island (GI) of the TP1 was predicted by IslandPath-DIMOB. RESULTS: TP1 as a multiple antibiotic-resistant isolate was recovered at Jilin Province (China) in 2017 from a dairy cow with pneumonia. TP1 exhibited resistance to aminoglycosides (gentamicin and amikacin), macrolides (erythromycin), lincosamides (clindamycin), sulfonamides (sulfamonomethoxine), tetracyclines (tetracycline and doxycycline) and chloramphenicols (chloramphenicol and florfenicol). An antibiotic resistance gene clustered together with the aadB, aadA1, cmlA5 and cmlA6 resistance genes located on a 7-kilobase (kb) multidrug-resistant (MDR) region, constituting a complex class 1 integron. The MDR region was located at one end of a 42-kb GI, and IS6100Δ1 mediated a genetic rearrangement with the complex class 1 integron-like SGI1 and formed a composite transposon. Furthermore, the tetW gene was located outside the four GIs consistent with tetracycline and doxycycline resistance. The ermD gene positioned in the front end of the 42-kb GI played an important role in mediating acquired erythromycin and clindamycin resistance. CONCLUSIONS: Multiple resistance genes are located in a complex class 1 integron within a 42-kb T. pyogenes genomic island (TGI1), leading to TP1 multiple drug resistance. In comparison with SG1 families, TGI1 possesses versatile gene distribution and specific gene context for it upstream and downstream, and it represents a new lineage of genomic resistance islands.

Antimicrobial susceptibility and genetic characterization of Trueperella pyogenes isolates from pigs reared under intensive and extensive farming practices.

Trueperella pyogenes is an opportunistic pathogen associated with a variety of diseases and responsible for important economic losses for pig production. Minimal Inhibitory Concentration (MIC) and Pulsed Field Gel Electrophoresis (PFGE) typing analysis were used to determine the MIC distribution and to genetically characterize a total of 180 T. pyogenes isolates obtained from slaughtered pigs reared under intensive (TpIN, n = 89) and extensive (TpEX, n = 91) farming practices. Low MIC90 values for penicillin and amoxicillin (0.008 and 0.06 µg/ml, respectively), ceftiofur, gentamicin and enrofloxacin (1 µg/ml, respectively) were obtained, so they could be of choice for the empiric treatment of T. pyogenes infections. Except for the penicillin, amoxicillin and ceftiofur, a statistically significant difference was observed in the MIC distribution of all antimicrobials analysed between TpIN and TpEX isolates. Also, MIC90 values were higher in TpIN than in TpEX isolates for neomycin and streptomycin (32 µg/ml vs 8 µg/ml), sulfamethoxazole/trimethoprim (30.4/1.6 µg/ml vs 1.90/0.10 µg/ml) and tylosin (≥1024 µg/ml vs 1 µg/ml). A relatively lower genetic diversity was detected in TpIN in comparison with TpEX isolates (GD 0.42 and GD 0.47, respectively). All isolates were distributed in three clusters (A, B, C). TpIN isolates were statistically associated with cluster A (P = 0.0002; OR 3.21; CI95 1.74-5.93), whereas the TpEX were distributed throughout the dendrogram, showing more genetic diversity. These data suggest that the antimicrobial susceptibility and genetic variability of the T. pyogenes isolates could be influenced by the management systems.

Luteolin Showed a Resistance Elimination Effect on Gentamicin by Decreasing MATE mRNA Expression in Trueperella pyogenes.

Trueperella pyogenes is a common inhabitant of mucosal surfaces in animals and causes a variety of infections, including endometritis, mastitis, and liver abscessation, in dairy cows. Many antimicrobial agents are used for treatment of infections caused by T. pyogenes; however, antibiotic resistance has recently become a serious problem. The objective of this study was to characterize the effect of the efflux pump-encoding multidrug and toxic compound extrusion (MATE) gene on antibiotic resistance in T. pyogenes isolates from cows with signs of endometritis. As a compound from plants, luteolin showed antimicrobial activities in Escherichia coli and Staphylococcus aureus; therefore, we also investigated whether luteolin can eliminate antibiotic resistance. We constructed a MATE deletion mutant in BM-H06-3 to identify the function of MATE in antibiotic resistance. MATE mRNA expression was measured to identify the mechanism of luteolin in gentamicin resistance elimination effect in T. pyogenes. The T. pyogenes isolate BM-H06-3 became susceptible to gentamicin, amikacin, streptomycin, erythromycin, and roxithromycin after MATE deletion. No synergistic effect between luteolin and gentamicin was observed in eight isolates, which were randomly selected from 34 T. pyogenes isolates, but the isolates became susceptible to gentamicin after luteolin treatment at a subinhibitory concentration (1/4 minimum inhibitory concentration [MIC]) for 36 hr. Furthermore, luteolin can decrease MATE mRNA expression after luteolin treatment at a subinhibitory concentration (1/4 MIC). We found that the MATE gene was involved in antibiotic resistance and that luteolin induces a resistance elimination effect in T. pyogenes. Therefore, luteolin may be a potential agent to inhibit efflux pumps in multidrug-resistant T. pyogenes.

Treatment considerations for potential uropathogens detected by precision microbiological testing.

PURPOSE: The clinical and microbiological data for urinary tract infections (UTIs) for 6 organisms detected by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) at community health systems were examined. SUMMARY: The use of precision microbiological diagnostic testing such as MALDI-TOF and real-time quantitative polymerase chain reaction has increased the ability to detect a wider spectrum of organisms. This has raised questions of the clinical relevance of infrequently encountered organisms, especially when cultured from urine. This article reviews clinical and microbiological data for UTIs for 6 organisms detected by MALDI-TOF at community health systems (Actinotignum schaalii, Chryseobacterium indologenes, Aerococcus urinae, Aerococcus sanguinicola, Corynebacterium riegelii, and Corynebacterium urealyticum). Since little information currently exists, most of the data associating the aforementioned organisms with UTIs were derived from case reports. Although these organisms are more readily identified using precision microbiological diagnostic testing methods, infection should not be assumed based on culture results alone since asymptomatic bacteriuria has been reported. Similar to more common urinary pathogens, clinical correlation is essential. To facilitate treatment, we provide a table of empirical options likely to achieve clinical success based on in vivo and in vitro data. If available, pathogen-specific susceptibility data should be used to direct therapy. CONCLUSION: Clinical and microbiological data and potential treatment options were presented for 6 traditionally underrecognized organisms that are increasingly being found from urinary specimens. The treatment recommendations should be interpreted cautiously as they were devised through the use of very limited data.

Hamuramicins A and B, 22-membered macrolides, produced by an endophytic actinomycete Allostreptomyces sp. K12-0794.

Two new compounds, designated as hamuramicins A (1) and B (2), were isolated from the cultured broth of an endophytic actinomycete Allostreptomyces sp. K12-0794 by silica gel column chromatography and HPLC. The structures of 1 and 2 were elucidated as 22-membered macrolide containing triene and trienone with an alkyl side chain by spectroscopic analyses including NMR experiments. Both compounds showed growth inhibition activity against Kocuria rhizophia and Xanthomonas oryzae pv. oryzae as well as human cell line toxicity.

Quorum-sensing molecules N-acyl homoserine lactones inhibit Trueperella pyogenes infection in mouse model.

Trueperella pyogenes is a gram-positive opportunistic pathogen normally causes mastitis, liver abscesses and pneumonia of economically important livestock. It has been suggested that gram-negative bacteria can suppress the growth and virulence of T. pyogenes in vitro by using the quorum-sensing (QS) signal molecules and cause the transition of predominant species. However, whether these QS signals can be used as potential anti-virulence drugs against T. pyogenes infection is unclear. In this study, the in vivo inhibitory effect N-acyl homoserine lactones (AHLs) from Escherichia coli and Pseudomonas aeruginosa on T. pyogenes was tested by using mouse model. Mice were first peritoneally infected with T. pyogenes followed by intravenous injection of N-Octanoyl-DL-homoserine lactone (C8HSL) or N-(3-oxododecanoyl) homoserine-l-lactone (C12HSL). The results showed that C8HSL and C12HSL significantly reduced bacterial load and increased the survival rate of mice against T. pyogenes challenge. Additionally, the treatment of AHLs promoted the secretion of IL-1ß, IL-6, IL-8 and TNF-α in mouse peritoneal fluid, and significantly decreased the expression levels of virulence genes of residual T. pyogenes. Importantly, murine macrophages rapidly phagocytosed bacteria when they were treated with AHLs compared to untreated cells. Collectively, our findings provide a major advance in understanding the inhibitory effect of AHLs in vivo and a promise for developing new clinical or veterinary treatments of T. pyogenes-related infection.

Minimum inhibitory concentrations of frequently used antibiotics against Escherichia coli and Trueperella pyogenes isolated from uteri of postpartum dairy cows.

The objective of this study was to determine minimum inhibitory concentrations (MIC) of frequently used antimicrobials for Escherichia coli and Trueperella pyogenes isolated from postpartum bovine uteri of cows with acute puerperal metritis (APM, n = 67), cows suspected to have APM (n = 37), and healthy cows (n = 37) and to evaluate possible differences in MIC according to clinical signs. Cows with APM had reddish-brown, fetid vaginal discharge and rectal temperature (RT) ≥39.5°C within 21 d in milk; cows suspected to have APM had either reddish-brown, fetid vaginal discharge or RT ≥39.5°C within 21 d in milk; and healthy cows had neither fetid discharge nor RT ≥39.5°C. Samples were collected from cows on commercial dairy herds (n = 7) using the cytobrush technique. A total of 37 T. pyogenes isolates and 85 E. coli isolates were tested. Ceftiofur, a third-generation cephalosporin that is often used to treat APM, was the focus of analysis. Trueperella pyogenes and E. coli were isolated more often from samples of cows with APM (46 and 90%, respectively) compared with samples from healthy cows (19 and 54%, respectively). Regarding cows suspected to have APM, T. pyogenes and E. coli were numerically more often isolated (30 and 70%, respectively) than in healthy cows (19 and 54%, respectively). Minimum inhibitory concentrations of ceftiofur were low. For T. pyogenes and E. coli, MIC50 (concentration that inhibited growth of 50% of isolates) were 0.25 and 0.5 µg/mL and MIC90 (concentration that inhibited growth of 90% of isolates) were 0.5 and 1 µg/mL, respectively. Although ceftiofur inhibited all T. pyogenes at the highest concentration tested (64 µg/mL), the growth of 5.9% of E. coli was not impaired. Recently, ampicillin has been suggested as an alternative treatment for APM. Although the T. pyogenes isolates exhibited low MIC in general (MIC50 ≤0.015 µg/mL and MIC90 = 0.06 µg/mL) and 81.1% of all T. pyogenes could be inhibited at the lowest ampicillin concentration tested, 11.8% of the E. coli isolates were not impaired at the highest concentration (64 µg/mL) tested in this study. The MIC50 and MIC90 of E. coli were 4 and ≥128 µg/mL, respectively. We detected no difference in the MIC distributions of ceftiofur or ampicillin among isolates from the 3 APM groups. In summary, E. coli with high MIC against ceftiofur as well as against ampicillin were found in this study.

Antimicrobial Resistance in Corynebacterium spp., Arcanobacterium spp., and Trueperella pyogenes.

There is currently only limited information on the antimicrobial susceptibility and resistance of Corynebacterium spp., Arcanobacterium spp., and Trueperella pyogenes from animals. The comparability of the data is hampered by the use of different antimicrobial susceptibility testing methods and interpretive criteria. To date, standard broth microdilution methods and clinical breakpoints that are approved by the Clinical and Laboratory Standards Institute and are applicable to Corynebacterium spp., Arcanobacterium spp., and T. pyogenes are available. The lack of species-specific clinical breakpoints for the different animal species reduces the explanatory power of the data. Among the isolates of the three genera, elevated MICs for different classes of antimicrobial agents (e.g., ß-lactams, macrolides, lincosamides, tetracyclines, aminoglycosides, phenicols, sulfonamides/diaminopyrimidines, and fluoroquinolones) have been described. The most comprehensive data set is available for T. pyogenes, which also includes information about genes and mutations involved in antimicrobial resistance. In T. pyogenes isolates, the macrolide-lincosamide-streptogramin B resistance genes erm(B) and erm(X) were identified. Tetracycline resistance in T. pyogenes was based on the resistance genes tet(W), tet(Z), and tet(33), whereas the aminoglycoside resistance genes aacC, aadA1, aadA2, aadA5, aadA24, and aadB have been described in T. pyogenes. So far, only single genes conferring either phenicol resistance (cmlA6), trimethoprim resistance (dfrB2a), or ß-lactam resistance (blaP1) are known to occur in T. pyogenes isolates. Various 23S rRNA mutations, including A2058T, A2058G, and G2137C, were identified in macrolide/lincosamide-resistant T. pyogenes.