Susceptibilities of Corynebacterium bovis and Corynebacterium amylocolatum isolates from bovine mammary glands to 15 antimicrobial agents

Antibiotic Treatment of Corynebacterium bovis-associated Clinical Disease in NSG Mice

Depending on the strain of immunodeficient mice, Corynebacterium bovis infection can be asymptomatic or cause transient or prolonged skin disease. C. bovis infection of NOD. Cg- Prkdcscid Il2rgtm1Wjl /SzJ (NSG) mice results in clinical skin disease that progresses in severity. Amoxicillin metaphylaxic and prophylaxic therapy prevents transmission and infection of mice after exposure to C. bovis and inhibits the growth of C. bovis isolates at therapeutic doses that are clinically achievable in mice. Amoxicillin is not efficacious for treatment of transient clinical skin disease in athymic nude mice, but the efficacy of amoxicillin treatment has not previously been characterized in C. bovis -infected NSG mice. In the current study, NSG mice were treated with amoxicillin beginning at 5 wk after exposure to C. bovis, at which time they had well-established clinical signs of disease. Clinical signs were scored to assess disease progression, regression, and reappearance. Our results showed that amoxicillin treatment for 3 or 6 wk reduced the clinical scores of NSG mice with C. bovis -associated clinical disease. In addition, withdrawal of treatment led to the recurrence of clinical signs. Collectively, our data suggest that amoxicillin treatment is effective in alleviating the clinical signs associated with C. bovis infection for the duration of treatment in NSG mice. Clinical intervention with antibiotics for C. bovis -infected NSG mice can be an option for management of C. bovis -related clinical disease either before or during facility-wide remediation efforts.

Effect of Antimicrobial Prophylaxis on Corynebacterium bovis Infection and the Skin Microbiome of Immunodeficient Mice

Corynebacterium bovis is an opportunistic pathogen of the skin of immunodeficient mice and is sensitive to oral antibiotics that reach therapeutic blood concentrations. However, prophylactic antibiotics are considered to be ineffective at preventing C. bovis infection. In addition, the effect of C. bovis on the skin microbiome (SM) of common immunodeficient mouse strains has yet to be characterized. Consequently, we evaluated whether oral prophylactic antibiotics prevent C. bovis infection after inoculation. An infectious dose of C. bovis was applied to the skin of Hsd:Athymic Nude (nude) and NOD. Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice. Mice were then housed individually and assigned randomly to receive either untreated drinking water (Cb+Abx-group) or prophylactic amoxicillin-clavulanic acid in the drinking water (0.375 mg/mL) for 14 d (Cb+Abx+group). A third treatment group of each mouse strain was uninoculated and untreated (Cb-Abx-group). Mice from all groups were serially sampled by using dermal swabs to monitor C. bovis infection via quantitative real-time PCR and the SM via 16S rRNA sequence analysis. Fourteen days of prophylactic antibiotics prevented the perpetuation of C. bovis skin infection in both strains. Only the combination of C. bovis inoculation and oral antibiotics (Cb+Abx+) significantly affected the SM of NSG mice at day 14; this effect resolved by the end of the study (day 70). In mice that did not receive antibiotics, C. bovis significantly altered the SM of nude mice but not NSG mice at days 14 and 70. These findings demonstrate the potential benefit of prophylactic antibiotics for prevention of C. bovis infection. However, indirect effect of antibiotics on commensal bacteria and potential effects on xenograft models must be considered.

Minimum inhibitory concentrations of chlorhexidine- and lactic acid-based teat disinfectants: An intervention trial assessing bacterial selection and susceptibility

Teat disinfection is a recommended preventive tool to improve udder health and to prevent new intramammary infections. However, side effects are discussed, such as bacterial selection of less-susceptible bacteria with the application of certain teat disinfectants. The objective of this study was to assess the species composition and bacterial in vitro susceptibility by means of an interventive trial. For this purpose, 3 different postmilking teat treatments (disinfection with 0.215% chlorhexidine or 3.5% lactic acid, or control group with no dipping) were applied to 28 cows in a 6-d intervention approach using a split-udder design. Milk samples were taken before and after intervention. Bacteria were cultured and differentiated to species or genus level by MALDI-TOF mass spectrometry. Minimum inhibitory concentrations (MIC) were determined, and MIC changes over time were recorded. Susceptibilities to chlorhexidine and lactic acid were compared between species of the genera Staphylococcus, Streptococcus, Corynebacterium, and others. Species composition changed during the intervention. Under the treatment of chlorhexidine and lactic acid, the proportion of coagulase-negative staphylococci (CNS) decreased. An increased proportion of species belonging to the genus Corynebacterium was observed especially under the application of lactic acid. Although both teat disinfectants were basically effective, isolates differed in their susceptibility to both teat disinfectants. Populations of CNS, Staphylococcus aureus, and Corynebacterium spp. showed significantly lower absolute MIC values for chlorhexidine. Compared with other species, Corynebacterium spp. showed the lowest susceptibility for chlorhexidine as well as for lactic acid. A significant increase in MIC values after 6 d of intervention was observed with the lactic acid treatment in all isolates, as well as in CNS. This increase can be interpreted as either adaptation of isolates or displacement of more-susceptible species by less-susceptible species. Further studies using long-term intervention might reveal more pronounced effects on MIC values and species composition.

Antimicrobial Susceptibility of Corynebacterium bovis Isolates from Immunodeficient Rodents

Corynebacterium bovis, the causative agent of hyperkeratotic dermatitis in immunodeficient mice, is a significant problem in preclinical oncology research. Infection results in lifelong skin colonization and a decrease in successful engraftment of patient-derived xenograft tumor models. The use of antimicrobial agents for C. bovis is controversial in light of reports of poor efficacy and the possibility of selection for resistant strains. The purpose of this study was to describe the antimicrobial susceptibilities of C. bovis isolates obtained exclusively from immunodeficient rodents in order to aid in antimicrobial dose determination. Between 1995 and 2018, 15 isolates were collected from 11 research institutions across the United States. Antimicrobial susceptibility testing was performed for 24 antimicrobials commonly used against gram-positive bacteria. Our results provide an updated understanding of the susceptibility profiles of rodent C. bovis isolates, indicating little variability between geographically and temporally distant isolates. These results will facilitate appropriate antimicrobial use to prevent and treat C. bovis infections in immunodeficient rodents.

Metaphylactic Antibiotic Treatment to Prevent the Transmission of Corynebacterium bovis to Immunocompromised Mouse Offspring

Current methods for eradicating Corynebacterium bovis, such as depopulation, embryo transfer, and cesarean rederivation followed by cross fostering, are expensive, complex, and time-consuming. We investigated a novel method to produce immunocompromised offspring free of C. bovis from infected NOD. Cg-PrkdcscidIl2rgtm1Wgl/SzJ (NSG) breeding pairs. Adult NSG mice were infected with C. bovis, paired, and randomly assigned to either a no-antibiotic control group (NAB, n = 8) or a group that received amoxicillin-clavulanic acid (0.375 mg/mL) in their drinking water for a mean duration of 7 wk (AB group, n = 7), spanning the time from pairing of breeders to weaning of litters. The AB group also underwent weekly cage changes for 3 wk after pairing to decrease intracage C. bovis contamination, whereas the NAB mice received bi-weekly cage changes. Antibiotics were withdrawn at the time of weaning. All litters (n = 7) in the AB group were culture- and qPCR-negative for C. bovis and remained negative for the duration of the study, whereas all litters in the NAB group (n = 6) remained C. bovis positive. A single adult from each breeding pair was sampled at weaning and at 5 and 10 wk after weaning to confirm the maintenance of (NAB) or to diagnose the reemergence (AB) of C. bovis infection. By the end of the study, C. bovis infection had returned in 3 of the 7 (43%) tested AB adults. Our data suggest that metaphylactic antibiotic use can decrease viable C. bovis organisms from adult breeder mice and protect offspring from infection. However, using antibiotics with frequent cage changing negatively affected breeding performance. Nevertheless, this technique can be used to produce C. bovis-free NSG offspring from infected adults and may be an option for salvaging infected immunocompromised strains of mice that are not easily replaced.

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., β-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 β-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.

Isolation and characterization of Corynebacterium spp. from bulk tank raw cow's milk of different dairy farms in Germany

We detected Corynebacterium spp. in raw milk samples of three farms by means of a selective, tellurite-containing medium. The isolated strains were identified based on full 16S rRNA gene sequences and partial rpoB gene sequences as C. xerosis, C. variabile, C. lactis, C. callunae, C. confusum, C. glutamicum and C. crudilactis. The identification based on 16S rRNA and rpoB sequences was not reliable for isolates of C. xerosis. Chemotaxonomic markers of the isolates, fatty acids, acyl type of peptidoglycan, presence and length of mycolic acids, quinone patterns, and polar lipids, were in accord with the known characteristics of these species. Biochemical profiles, analyzed with the API Coryne system, were able to differentiate all groups, but were unable to identify the strains due to an inappropriate database for raw-milk associated corynebacteria. Most of the tested isolates showed a single-substance resistance against oxacillin, but three single isolates were classified as multidrug resistant.

Strategies to prevent, treat, and provoke Corynebacterium-associated hyperkeratosis in athymic nude mice

Athymic nude mice infected with Corynebacterium bovis typically exhibit transient hyperkeratotic dermatitis. Our vivarium experienced an increased incidence of disease characterized by persistent skin lesions and increased mortality, leading to this study. For detection of infection, skin and buccal swab methods showed comparable sensitivities in nude mice. Various prevention, treatment, and eradication strategies were evaluated through clinical assessment, microbiology, and histopathology. In experimentally naïve athymic nude mice, a 2-wk course of prophylactic amoxicillin-containing diet (1200 ppm amoxicillin; effective dose, 200 mg/kg) was ineffective at preventing infection or disease. There was also no significant difference in disease duration or severity in athymic nude mice that received amoxicillin diet or penicillin-streptomycin topical spray (penicillin, 2500 U/mL; streptomycin, 2500 μg/mL). Prolonged treatment with 4 or 8 wk of amoxicillin diet cleared only a small number of athymic nude mice that had subclinical C. bovis infections. Antibiotic sensitivity of C. bovis isolates demonstrated a small colony isolate with less susceptibility to all antibiotics compared with a large colony isolate. Resistance did not appear to develop after prolonged treatment with amoxicillin. Provocation testing by administration of cyclophosphamide (50 mg/kg i.p. every 48 to 72 h for 90 d) to subclinically infected athymic nude mice resulted in prolonged clinical disease that waxed and waned without progression to severe disease. Our findings suggest that antibiotic prophylaxis and treatment of clinical disease in experimentally naïve mice is unrewarding, eradication of bacterial infection is difficult, and severe disease associated with C. bovis is likely multifactorial.