Overview of Quantitative Methodologies to Understand Antimicrobial Resistance via Minimum Inhibitory Concentration

Surveillance of Antimicrobial Resistance of Escherichia coli Isolates from Intestinal Contents of Dairy and Veal Calves in the Veneto Region, Northeaster Italy

This surveillance study aimed to estimate the proportion of antimicrobial resistant strains and antimicrobial resistance (AMR) profiles of E. coli isolates detected from the intestinal contents of veal and dairy calves in the Veneto Region, Northeaster Italy. Additionally, we investigated the differences in AMR profiles between dairy and veal calves over the period 2017-2022. Overall 1150 E. coli isolates were tested from calves exhibiting enteric disease, with 868 from dairy and 282 from veal calves. The percentage of resistant isolates to nine antimicrobials was notably higher in veal calves compared to dairy calves, except for ampicillin. Throughout the study period, we observed a significant increase in the proportion of resistant isolates to florfenicol, gentamycin, paromomycin, tetracycline and trimethoprim/sulfamethoxazole in dairy calves, while we did not detect any significant increase in the proportion of resistant isolates among veal calves. A substantial proportion (75.9%) of the isolated E. coli exhibited multi-drug resistance (MDR). The proportion of multi-drug resistant isolates was significantly higher in veal calves (91.7%) compared to dairy calves (74.3%) all through the surveillance period (2017-2022), with no significant variation in MDR proportion among veal calves between 2017 and 2022 but a significant increase among dairy calves.

Longitudinal antimicrobial susceptibility trends of canine Staphylococcus pseudintermedius

Antimicrobial resistance within Staphylococcus pseudintermedius poses a significant risk for the treatment of canine pyoderma and as a reservoir for resistance and potential zoonoses, but few studies examine long-term temporal trends of resistance. This study assesses the antimicrobial resistance prevalence and minimum inhibitory concentration (MIC) trends in S. pseudintermedius (n=1804) isolated from canine skin samples at the Cornell University Animal Health Diagnostic Center (AHDC) between 2007 and 2020. Not susceptible (NS) prevalence, Cochran-Armitage tests, logrank tests, MIC50 and MIC90 quantiles, and survival analysis models were used to evaluate resistance prevalence and temporal trends to 23 antimicrobials. We use splines as predictors in accelerated failure time (AFT) models to model non-linear temporal trends in MICs. Multidrug resistance was common among isolates (47%), and isolates had moderate to high NS prevalence to the beta-lactams, chloramphenicol, the fluoroquinolones, gentamicin, the macrolides/lincosamides, the tetracyclines, and trimethoprim-sulfamethoxazole. However, low levels of NS to amikacin, rifampin, and vancomycin were observed. Around one third of isolates (38%) were found to be methicillin resistant S. pseudintermedius (MRSP), and these isolates had a higher prevalence of NS to all tested antimicrobials than methicillin susceptible isolates. Amongst the MRSP isolates, one phenotypically vancomycin resistant isolate (MIC >16 µg/mL) was identified, but genomic sequence data was unavailable. AFT models showed increasing MICs across time to the beta-lactams, chloramphenicol, the fluoroquinolones, gentamicin, and the macrolides/lincosamides, and decreasing temporal resistance (decreasing MICs) to doxycycline was observed amongst isolates. Notably, ATF modeling showed changes in MIC distributions that were not identified using Cochran-Armitage tests on prevalence, MIC quantiles, and logrank tests. Increasing resistance amongst these S. pseudintermedius isolates highlights the need for rational, empirical prescribing practices and increased antimicrobial resistance (AMR) surveillance to maintain the efficacy of current therapeutic agents. AFT models with non-linear predictors may be a useful, breakpoint-independent, surveillance tool alongside other modeling methods and antibiograms.

In Vitro Antibacterial Activity of Microbial Natural Products against Bacterial Pathogens of Veterinary and Zoonotic Relevance

Antimicrobial resistance (AMR) is considered one of the greatest threats to both human and animal health. Efforts to address AMR include implementing antimicrobial stewardship programs and introducing alternative treatment options. Nevertheless, effective treatment of infectious diseases caused by bacteria will still require the identification and development of new antimicrobial agents. Eight different natural products were tested for antimicrobial activity against seven pathogenic bacterial species (Brachyspira sp., Chlamydia sp., Clostridioides sp., Mannheimia sp., Mycobacterium sp., Mycoplasma sp., Pasteurella sp.). In a first pre-screening, most compounds (five out of eight) inhibited bacterial growth only at high concentrations, but three natural products (celastramycin A [CA], closthioamide [CT], maduranic acid [MA]) displayed activity at concentrations <2 µg/mL against Pasteurella sp. and two of them (CA and CT) also against Mannheimia sp. Those results were confirmed by testing a larger collection of isolates encompassing 64 Pasteurella and 56 Mannheimia field isolates originating from pigs or cattle, which yielded MIC90 values of 0.5, 0.5, and 2 µg/mL against Pasteurella and 0.5, 4, and >16 µg/mL against Mannheimia for CA, CT, and MA, respectively. CA, CT, and MA exhibited higher MIC50 and MIC90 values against Pasteurella isolates with a known AMR phenotype against commonly used therapeutic antimicrobial agents than against isolates with unknown AMR profiles. This study demonstrates the importance of whole-cell antibacterial screening of natural products to identify promising scaffolds with broad- or narrow-spectrum antimicrobial activity against important Gram-negative veterinary pathogens with zoonotic potential.

Antimicrobial Resistance in Bacteria from Meat and Meat Products: A One Health Perspective

According to the 2030 Agenda of the United Nations, one of the sustainable development goals is to ensure sustainable consumption and production patterns. The need to ensure food safety includes, other than microbiological hazards, concerns with antimicrobial-resistant (AMR) bacteria. The emergence of resistant bacteria in the food industry is essentially due to the abusive, and sometimes incorrect, administration of antimicrobials. Although not allowed in Europe, antimicrobials are often administered to promote animal growth. Each time antimicrobials are used, a selective pressure is applied to AMR bacteria. Moreover, AMR genes can be transmitted to humans through the consumption of meat-harbouring-resistant bacteria, which highlights the One Health dimension of antimicrobial resistance. Furthermore, the appropriate use of antimicrobials to ensure efficacy and the best possible outcome for the treatment of infections is regulated through the recommendations of antimicrobial stewardship. The present manuscript aims to give the current state of the art about the transmission of AMR bacteria, particularly methicillin-resistant S. aureus, ESBL-producing Enterobacteriaceae, and vancomycin-resistant Enterococcus spp., along with other ESKAPE bacteria, from animals to humans through the consumption of meat and meat products, with emphasis on pork meat and pork meat products, which are considered the most consumed worldwide.

Silver-cored Ziziphus spina-christi extract-loaded antimicrobial nanosuspension: overcoming multidrug resistance

Aims: To synthesize a silver-cored nanosuspension utilizing Ziziphus spina-christi fresh-leaf extract and evaluate their antimicrobial activity against multidrug-resistant pathogenic microbes. Materials and Methods: The prepared nanosuspension was analyzed by spectro-analytical techniques and tested for antimicrobial activity and resistance to biofilm formation. The leaf extract and nanosuspension were tested separately and together as a mixture. Results: Constituent nanoparticles were average-sized (∼34 nm) and were active against both Gram-positive and Gram-negative microbes and yeast. Candida albicans showed a 24.50 ± 1.50 mm inhibition zone, followed by Escherichia coli and Staphylococcus aureus. Increased bioactivity with the highest multifold increments, 150%, for erythromycin against all tested microbes was observed. Carbenicillin and trimethoprim showed 166%- and 300%-fold increments for antimicrobial activity against Pseudomonas aeruginosa, respectively. Conclusion: The nanosuspension exhibited strong potential as an antimicrobial agent and overcame multidrug resistance.

Serotype distribution and antibiogram of Streptococcus parauberis isolated from fish in South Korea

Streptococcus parauberis is the dominant etiological agent of streptococcosis, the most devastating bacterial disease in the olive flounder farming industry in South Korea. In this study, the distribution of serotypes, antimicrobial susceptibility, and presence of antimicrobial resistance genes (ARGs) in S. parauberis isolates obtained between 1999 and 2021 was thoroughly investigated to gain insight into the dynamics of their presence and the relationship between serotypes and antimicrobial resistance. Disk diffusion testing of 103 isolates against 10 antimicrobial agents was performed, and epidemiological cut-off values generated through normalized resistance interpretation analysis were used to classify wild-type (WT) and non-wild-type (NWT) populations. Principal component analysis and hierarchical clustering were implemented to achieve an understanding on the relationship between serotypes and antimicrobial resistance patterns. PCR-based serotyping showed that serotype Ia (67.1%) was the most prevalent in South Korea, followed by serotypes Ib/Ic (25.2%) and II (7.7%). The highest proportion of isolates was assigned to NWT against amoxicillin (80.6%), followed by oxytetracycline (77.7%) and erythromycin (48.5%). The time-scale data showed that recently obtained serotypes Ib/Ic and II isolates tended to be categorized as NWT populations resistant to more antibiotics, possibly due to microbial adaptation to antibiotic pressure. ARGs responsible for resistance to oxytetracycline and erythromycin were found only in NWT populations in serotype Ia [tet(S) and erm(B), respectively], and serotype II [tet(M) and mef(J)-msr(I), respectively]. We also found that the mef-msr gene pair in S. parauberis serotype II might be involved in low-level resistance to erythromycin. IMPORTANCE This study presents serotype distribution and antimicrobial susceptibility data along with the antimicrobial resistance genes (ARGs) of Streptococcus parauberis, which is an important bacterial fish pathogen worldwide. In particular, almost all oxytetracycline and erythromycin non-wild-type (NWT) populations harbored tet(S) or tet(M), and erm(B) or mef(J)-msr(I), respectively. Interestingly, these ARGs were distributed in a highly serotype-dependent manner, resulting in a clear correlation between the antibiogram and serotype distribution. Moreover, recent isolates belonging to serotypes Ib/Ic and II tended to be more frequently categorized as NWT against antimicrobials, including amoxicillin and cefalexin compared to old isolates, while a dramatic decrease in erythromycin and clindamycin NWT frequencies was observed in recent serotype Ia isolates, which lacked erm(B). These variations might be attributed to shifts in the antibiotics employed in South Korean aquaculture over time. The overall findings would provide important background knowledge for understanding the epidemiology of S. parauberis infection in aquaculture.

Effect of Group Housing of Preweaned Dairy Calves: Health and Fecal Commensal Antimicrobial Resistance Outcomes

The objectives of this study were to investigate the effects of group housing (three calves per group) on bovine respiratory disease (BRD), diarrhea and antimicrobial resistance (AMR) to fecal commensal Escherichia coli (EC) and enterococci/streptococci (ES). Our study comprised two arms, one experimental and one observational. In the experimental arm, preweaned calves on a California dairy were randomized to either individual (IND; n = 21) or group (GRP; n = 21) housing, using a modified California-style wooden hutch. The study period lasted from birth to 56 days of age, during which calves were health scored daily. Cumulative incidence and hazard ratios were estimated for disease. Antimicrobial resistance outcomes were assessed using a prospective cohort design; feces were collected from each calf three times per week and EC and ES were evaluated for AMR using the broth microdilution method against a panel of 19 antimicrobial drugs (AMD). Analysis of treatment records was used to select calves that had been exposed (EXP) to an AMD-treated calf. In GRP, exposure occurred when a calf was a hutchmate with an AMD-treated calf. In IND, exposure occurred when a calf was a neighbor with an AMD-treated calf (TRT). Age-matched unexposed calves (UNEXP) were then selected for comparison. Proportions of AMR in fecal commensals among EXP, UNEXP, and TRT calves were compared between GRP and IND. Accelerated failure time survival regression models were specified to compare differences in minimum inhibitory concentration (MIC) of fecal commensals between EXP and UNEXP calves within each of GRP and IND calves separately. Group calves had a BRD hazard 1.94 times greater that of IND calves (p = 0.03), using BRD treatment records as the outcome. For AMR in EC isolates, higher resistance to enrofloxacin was detected in enrofloxacin-EXP GRP isolates compared with enrofloxacin-EXP IND isolates, and UNEXP GRP calves had lower resistance to ceftiofur compared with enrofloxacin-EXP and enrofloxacin-TRT calves. A significant housing-by-time interaction was detected for EC ceftiofur MIC in EXP GRP calves at 4-14 days post exposure to enrofloxacin (MIC EXP-UNEXP: µg/mL (95% CI): 10.62 (1.17, 20.07)), compared with UNEXP calves. The findings of this study show an increase in BRD hazard for group-housed calves and an increase in ceftiofur resistance in group-housed calves exposed to an enrofloxacin-treated calf.

Epidemiological cut-off values for a 96-well broth microdilution plate for high-throughput research antibiotic susceptibility testing of M. tuberculosis

Drug susceptibility testing of M. tuberculosis is rooted in a binary susceptible/resistant paradigm. While there are considerable advantages in measuring the minimum inhibitory concentrations (MICs) of a panel of drugs for an isolate, it is necessary to measure the epidemiological cut-off values (ECOFF/ECVs) to permit comparison with qualitative data. Here we present ECOFF/ECVs for 13 anti-tuberculosis compounds, including bedaquiline and delamanid, derived from 20 637 clinical isolates collected by 14 laboratories based in 11 countries on five continents. Each isolate was incubated for 14 days on a dry 96-well broth microdilution plate and then read. Resistance to most of the drugs due to prior exposure is expected and the MIC distributions for many of the compounds are complex, and therefore a phenotypically wild-type population could not be defined. Since a majority of samples also underwent genetic sequencing, we defined a genotypically wild-type population and measured the MIC of the 99th percentile by direct measurement and via fitting a Gaussian using interval regression. The proposed ECOFF/ECVs were then validated by comparing with the MIC distributions of high-confidence genetic variants that confer resistance and with qualitative drug susceptibility tests obtained via the Mycobacterial Growth Indicator Tube (MGIT) system or Microscopic-Observation Drug Susceptibility (MODS) assay. These ECOFF/ECVs will inform and encourage the more widespread adoption of broth microdilution: this is a cheap culture-based method that tests the susceptibility of 12-14 antibiotics on a single 96-well plate and so could help personalise the treatment of tuberculosis.

3D-Printed Dip Slides Miniaturize Bacterial Identification and Antibiotic Susceptibility Tests Allowing Direct Mastitis Sample Analysis

The early detection of antimicrobial resistance remains an essential step in the selection and optimization of antibiotic treatments. Phenotypic antibiotic susceptibility testing including the measurement of minimum inhibitory concentration (MIC) remains critical for surveillance and diagnostic testing. Limitations to current testing methods include bulky labware and laborious methods. Furthermore, the requirement of a single strain of bacteria to be isolated from samples prior to antibiotic susceptibility testing delays results. The mixture of bacteria present in a sample may also have an altered resistance profile to the individual strains, and so measuring the susceptibility of the mixtures of organisms found in some samples may be desirable. To enable simultaneous MIC and bacterial species detection in a simple and rapid miniaturized format, a 3D-printed frame was designed for a multi-sample millifluidic dip-slide device that combines panels of identification culture media with a range of antibiotics (Ampicillin, Amoxicillin, Amikacin, Ceftazidime, Cefotaxime, Ofloxacin, Oxytetracycline, Streptomycin, Gentamycin and Imipenem) diluted in Muëller-Hinton Agar. Our proof-of-concept evaluation confirmed that the direct detection of more than one bacterium parallel to measuring MIC in samples is possible, which is validated using reference strains E. coli ATCC 25922, Klebsiella pneumoniae ATCC 13883, Pseudomonas aeruginosa ATCC 10145, and Staphylococcus aureus ATCC 12600 and with mastitis milk samples collected from Reading University Farm. When mixtures were tested, a MIC value was obtained that reflected the most resistant organism present (i.e., highest MIC), suggesting it may be possible to estimate a minimum effective antibiotic concentration for mixtures directly from samples containing multiple pathogens. We conclude that this simple miniaturized approach to the rapid simultaneous identification and antibiotic susceptibility testing may be suitable for directly testing agricultural samples, which is achieved through shrinking conventional tests into a simple "dip-and-incubate" device that can be 3D printed anywhere.

Implications of Veterinary Medicine in the comprehension and stewardship of antimicrobial resistance phenomenon. From the origin till nowadays

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Antibiotic resistance is a well-known phenomenon with several implications

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The contribution of Veterinary Medicine is underestimated.

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It was believed that only livestock was responsible for antibiotic resistance.

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Companion animals, wild animals and environment are more involved than estimated.

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Educational tools for public and more veterinary specialists are needed.

Antimicrobial resistance (AMR) is defined by the entire scientific community as the major threat for human health and it is responsible for an increase in morbidity and mortality rates. The reasons behind this phenomenon are complex and the solution is achievable only considering the One Health approach, that encompasses the integration and implementation of human health, veterinary medicine and environmental status. Authors aimed to write this review to summarize to readers the three milestones of One-Health, underlying the most important topics in which veterinary medicine is mostly involved. Therefore, a short introduction about the history of AMR in veterinary medicine is provided, then more detailed aspects about the impact of AMR related to pets, food producing animals, wild animals and environment are discussed. Finally, some critical aspects about current and future issues are considered.

Antimicrobial Resistance Profiles and Genes in Streptococcus uberis Associated With Bovine Mastitis in Thailand

Streptococcus uberis is recognized as an environmental mastitis pathogen in dairy cattle. The varied success rate of antibiotic treatment for S. uberis intramammary infection may be associated with the antimicrobial resistance (AMR) of these bacteria. This observational study aimed to analyze 228 S. uberis strains associated with bovine mastitis in northern Thailand from 2010 to 2017. AMR and AMR genes were determined by the minimum inhibitory concentration (MIC) using a microdilution method and polymerase chain reaction, respectively. The majority of S. uberis strains were resistant to tetracycline (187/228, 82.02%), followed by ceftiofur (44/228, 19.30%), and erythromycin (19/228, 8.33%). The MIC50 and MIC90 of ceftiofur in 2017 were 2–4-fold higher than those in 2010 (P < 0.01). Resistance to tetracycline and ceftiofur significantly increased between 2010 and 2017 (P < 0.05). The most common gene detected in S. uberis was tetM (199/228, 87.28%), followed by ermB (151/228, 66.23 %) and blaZ (15/228, 6.58 %). The association between tetracycline resistance and tetM detection was statistically significant (P < 0.01). The detection rates of tetM significantly increased, while the detection rates of tetO and ermB significantly decreased during 2010–2017. AMR monitoring for bovine mastitis pathogens, especially S. uberis, is necessary to understand the trend of AMR among mastitis pathogens, which can help create an AMR stewardship program for dairy farms in Thailand.

Bioprospecting of endophytic microorganisms for bioactive compounds of therapeutic importance

Presently, several drug discovery investigations on therapeutic management of human health are aimed at bioprospecting for microorganisms, especially endophytic microbes of biotechnological importance. This review investigates the benefits of endophytes, especially in producing bioactive compounds useful in modern medicine by systematically reviewing published data from 12 databases. Only experimental studies investigating either or both bacterial and fungal endophytes and within the scope of this review were selected. The published data from the last 2 decades (2000-2019) revealed diverse endophytes associated with different plants produce a broad spectrum of bioactive compounds with therapeutic benefits. Notably, antibacterial, followed by anticancer and antifungal activities, were mostly reported. Only three studies investigated the anti-plasmodial activity. The variation observed in the synthesis of bioactive compounds amongst endophytes varied with host type, endophyte species, and cultivation medium. Fungal endophytes were more investigated than bacterial endophytes, with both endophytes having species diversity amongst literature. The endophytes were predominantly from medicinal plants and belonged to either Ascomycota (fungi) or Proteobacteria and Firmicutes (bacteria). This review presents excellent prospects of harnessing endophytes and their unique bioactive compounds in developing novel and effective compounds of medicinal importance.

Antimicrobial Resistance Risk Assessment Models and Database System for Animal-Derived Pathogens

(1) Background: The high use of antibiotics has made the issue of antimicrobial resistance (AMR) increasingly serious, which poses a substantial threat to the health of animals and humans. However, there remains a certain gap in the AMR system and risk assessment models between China and the advanced world level. Therefore, this paper aims to provide advanced means for the monitoring of antibiotic use and AMR data, and take piglets as an example to evaluate the risk and highlight the seriousness of AMR in China. (2) Methods: Based on the principal component analysis method, a drug resistance index model of anti-E. coli drugs was established to evaluate the antibiotic risk status in China. Additionally, based on the second-order Monte Carlo methods, a disease risk assessment model for piglets was established to predict the probability of E. coli disease within 30 days of taking florfenicol. Finally, a browser/server architecture-based visualization database system for animal-derived pathogens was developed. (3) Results: The risk of E. coli in the main area was assessed and Hohhot was the highest risk area in China. Compared with the true disease risk probability of 4.1%, the result of the disease risk assessment model is 7.174%, and the absolute error was 3.074%. Conclusions: Taking E. coli as an example, this paper provides an innovative method for rapid and accurate risk assessment of drug resistance. Additionally, the established system and assessment models have potential value for the monitoring and evaluating AMR, highlight the seriousness of antimicrobial resistance, advocate the prudent use of antibiotics, and ensure the safety of animal-derived foods and human health.