A metallo-β-lactamase is responsible for the degradation of ceftiofur by the bovine intestinal bacterium Bacillus cereus P41

Sonolytic degradation kinetics and mechanisms of antibiotics in water and cow milk

Antibiotics (ABX) residues frequently occurred in water and cow milk. This work aims to understand the kinetics and mechanisms of sonolytic degradation of four ABX, i.e. ceftiofur hydrochloride (CEF), sulfamonomethoxine sodium (SMM), marbofloxacin (MAR), and oxytetracycline (OTC) in water and milk. In both water and milk, the sonolytic degradation of ABX follows pseudo-first order (PFO) kinetics well (R2: 0.951-0.999), with significantly faster ABX degradation in water (PFO kinetics constants (k1): 1.5 × 10-3-1.2 × 10-1 min-1) than in milk (k1: 3.5 × 10-4-5.6 × 10-2 min-1). The k1 values for SMM degradation in water increased by 118% with ultrasonic frequency (40-120 kHz), 174% with ultrasonic frequency (80-500 kHz), 649% with ultrasonic power (73-259 W), 22% with bulk temperature (12-40℃), and by 68% with reaction volume (50-250 mL), respectively, in other things being equal. The relevant k1 values in milk increased by 326%, 231%, 122%, 10% as well as 82% with the above same effective factors, respectively. The oxidation by free radicals generated in situ dominates ABX degradation, and the hydrophobic CEF (54.0-971.7 nM min-1) and SMM (39.2-798.4 nM min-1) underwent faster degradation than the hydrophilic MAR (33.9-751.9 nM min-1) and OTC (33.8-545.3 nM min-1) in both water and milk. Adding an extra 0.5 mM H2O2 accelerated SMM degradation by 19% in water and 33% in milk. After 130-150 min sonication of 100 mL of 2.0 mg L-1 (6.62 μM) SMM in various milk with 500 kHz and 259 W, the residue concentrations (52.9-96.3 μg L-1) can meet the relevant maximum residue limit (100 μg L-1).

Insights into the Bacterial Diversity and Detection of Opportunistic Pathogens in Mexican Chili Powder

Chili powder is the most frequently consumed spice in Mexican diets. Thus, the dissemination of microorganisms associated with chili powder derived from Capsicum annuum L. is significant during microbial quality analysis, with special attention on detection of potential pathogens. The results presented here describe the initial characterization of bacterial community structure in commercial chili powder samples. Our results demonstrate that, within the domain Bacteria, the most abundant family was Bacillaceae, with a relative abundance of 99% in 71.4% of chili powder samples, while 28.6% of samples showed an average relative abundance of 60% for the Enterobacteriaceae family. Bacterial load for aerobic mesophilic bacteria (AMB) ranged from 10⁴ to 10⁶ cfu/g, while for sporulated mesophilic bacteria (SMB), the count ranged from 10² to 10⁵ cfu/g. Bacillus cereus sensu lato (s.l.) was observed at ca. ˂600 cfu/g, while the count for Enterobacteriaceae ranged from 10³ to 10⁶ cfu/g, Escherichia coli and Salmonella were not detected. Fungal and yeast counts ranged from 10² to 10⁵ cfu/g. Further analysis of the opportunistic pathogens isolated, such as B. cereus s.l. and Kosakonia cowanii, using antibiotic-resistance profiles and toxinogenic characteristics, revealed the presence of extended-spectrum β-lactamases (ESBLs) and Metallo-β-lactamases (MBLs) in these organisms. These results extend our knowledge of bacterial diversity and the presence of opportunistic pathogens associated with Mexican chili powder and highlight the potential health risks posed by its use through the spread of antibiotic-resistance and the production of various toxins. Our findings may be useful in developing procedures for microbial control during chili powder production.

Effective degradation of Chlortetracycline using dual bio catalyst

Chlortetracycline (CTC) degradation using potential microbial consortia or individual bacterial strains was useful method for improving bioremediation potential. The co-culture (Klebsiella pneumoniae CH3 and Bacillus amyloliquefaciens CS1) of bacterial strains have the ability to degrade chlortetracycline (91.8 ± 1.7%), followed by sulfamethoxazole (62.1 ± 1.2%) and amoxicillin (73.9 ± 3.3%). It was observed that the degradation potential was maximum after 10 days incubation, 8-10% inoculum, pH 7.5, and antibiotic concentration ranged from 150 to 200 mg/L. The initial concentrations of CTC significantly affected CTC degradation. In strain CH3, maximum biodegradation of CTC (99.4 ± 2.3%) was observed at 200 mg/L initial CTC concentrations. In CS1, maximum biodegradation of CTC was obtained at 150 mg/L concentration (80.5 ± 3.2%) after 10 days of culture. Alkaline pH was found to be suitable for the degradation of antibiotic than acidic range. After initial optimization by one factor at a time approach in free cells, the bacterial strains (CH3 and CS1) were co-immobilized. The co-immobilized bacterial cells showed improved degradation potential than free cells. To determine the biodegradation potential of immobilized cells, the selected strains were immobilized in polymer beads and treated with CTC with 175 mg/L initial concentration. The experimental results revealed that after 3 days of treatment the residual CTC concentration was 150.1 ± 3.2 mg/L and it decreased as 1.28 ± 0.01 mg/L after 10 days of treatment. The present study confirmed the effectiveness and feasibility of biodegradation ability of K. pneumoniae CH3 and B. amyloliquefaciens CS1 immobilized for CTC degradation in wastewater.

Mechanism for biodegradation of sulfamethazine by Bacillus cereus H38

Degradation of sulfonamides (SAs) by microorganisms has become a focus of current research. Sulfamethazine (SMZ) is a type of SA widely used in the livestock and poultry industry. However, understanding the intermediate products, degradation pathways and mechanism of SMZ biodegradation is limited at present. In this study, a SMZ degrading bacterium Bacillus cereus H38, which can use SMZ as its only carbon source, was isolated from farmland soil. The bacterium was gram-positive with rod-shaped cells. The effects of initial SMZ concentration, pH, temperature and amount of inoculation on the biodegradation of SMZ were investigated by a single factor experiment. The results showed that the maximum degradation rate of SMZ was achieved in the environmental conditions at an initial SMZ concentration of 5 mg/L, pH of 7.0, temperature of 25 °C and inoculation amount of 5%. Under these optimum degradation conditions, strain H38 can completely degrade SMZ within 3 days. The effects of intracellular enzymes, extracellular enzymes and periplasmic enzymes on the SMZ degradation process were compared. It was found that intracellular enzymes contributed the most to the biodegradation of SMZ, and the degradation rate approached 70%. Three possible intermediates were identified by LC-MS/MS, and two degradation pathways were proposed. Whole genome sequencing results showed that the genome size of strain H38 was 5,477,631 bp, including 5599 coding sequences (CDSs), and the GC content was 35.21%. In addition, functional annotation of CDSs was performed to analyze the metabolic pathways of nitrogen and sulfur in strain H38 combining genomics and bioinformatics. This study proposes new insights into the mechanism for biodegradation of SAs and will inform future research.

Detection of Bacillus cereus sensu lato Isolates Posing Potential Health Risks in Mexican Chili Powder

The potential presence of spore-forming bacteria related to the Bacillus cereus group in Mexican chili powder elaborated from Capsicum annuum L. is of commercial and clinical interest, because chili powder is an essential spice in the Mexican diet and in diets around the globe. To facilitate detection and isolation of members of this group of spore-forming bacteria from Mexican chili powder samples, we identified colonies that grew on agar medium selective for Bacillus cereus sensu lato, supplemented with polymyxin B (10 µg/mL) and ampicillin (10 to 100 µg/mL). The presumptive B. cereus (s.l.) isolates were tested using a tRNA^Cys-PCR-based approach and the results identified species related phylogenetically to B. cereus, B. thuringiensis, and B. toyonensis. Their toxigenic potential was assessed by serological tests to detect enterotoxins (Nhe and Hbl) and by PCR targeting the hemolysin BL (hbl) component C (hblC) and non-hemolytic enterotoxin component A (nheA). The antibiotic profiles of the isolates showed a high resistance to β-lactams (100% of the isolates), trimethoprim-sulfamethoxazole (100%), tetracycline (90%), erythromycin (77%), clindamycin (74%), and chloramphenicol (42%). Our results indicate the presence of B. cereus s.l. with toxigenic characteristics in Mexican chili powder. Because of the potential for these organisms to cause disease through their production of various toxins, and resistance to antibiotics, we recommend that a microbiological risk assessment must be considered in the Mexican regulatory requirements.

Maximum levels of cross-contamination for 24 antimicrobial active substances in non-target feed. Part 1: Methodology, general data gaps and uncertainties

The European Commission requested EFSA to assess, in collaboration with EMA, the specific concentrations of antimicrobials resulting from cross-contamination in non-target feed for food-producing animals below which there would not be an effect on the emergence of, and/or selection for, resistance in microbial agents relevant for human and animal health, as well as the levels of the antimicrobials which could have a growth promotion/increase yield effect. The assessment was performed for 24 antimicrobial active substances, as specified in the mandate. This scientific opinion describes the methodology used, and the main associated data gaps and uncertainties. To estimate the antimicrobial levels in the non-target feed that would not result in emergence of, and/or selection for, resistance, a model was developed. This 'Feed Antimicrobial Resistance Selection Concentration' (FARSC) model is based on the minimal selective concentration (MSC), or the predicted MSC (PMSC) if MSC for the most susceptible bacterial species is unavailable, the fraction of antimicrobial dose available for exposure to microorganisms in the large intestine or rumen (considering pharmacokinetic parameters), the daily faecal output or rumen volume and the daily feed intake. Currently, lack of data prevents the establishment of PMSC and/or FARSC for several antimicrobials and animal species. To address growth promotion, data from an extensive literature search were used. Specific assessments of the different substances grouped by antimicrobial classes are addressed in separate scientific opinions. General conclusions and recommendations were made.

Faecal concentrations of ceftiofur metabolites in finisher pigs administered intramuscularly with ceftiofur

The objective of this study was to determine the effects of dietary fibre level and source on faecal ceftiofur metabolites concentrations after intramuscular administration of therapeutic ceftiofur hydrochloride in finisher pigs. Pens of finisher pigs (n = 36), with an equal number of barrows and gilts, were randomly assigned to 1 of 3 dietary treatment groups: basal diet composed of corn grain and soy bean meal with no supplement and formulated to contain 8.7% neutral detergent fibre (NDF), supplemented with 20% distillers dried grains with solubles (a byproduct of the ethanol production from corn grain) formulated to contain 13.6% NDF, primarily insoluble fibre or supplemented with 14.5% sugar beet pulp formulated to contain 13.6% NDF. Faecal samples were collected 6–8 hr after ceftiofur injection from treated and untreated pen‐mate pigs on days 1 and 3 of the 3‐day treatment regimen. Faecal concentrations of ceftiofur metabolites, including the major metabolite, desfuroylceftiofur, were analysed by reverse‐phase high pressure liquid chromatography with ultraviolet detection. Overall, the faecal concentrations of ceftiofur metabolites did not differ significantly between the dietary treatments. The mean concentrations of metabolites tended to be lower (p = .1) on day 3 compared to day 1 of the 3‐day treatment regimen. Faecal concentrations of metabolites were not affected by the gender of the finisher pigs. The concentrations of ceftiofur metabolites in the faeces are likely reflective of the microbial activity in the hindgut. Our data suggest that the fibre level and source used in the study did not affect the faecal concentrations of ceftiofur metabolites.

Antibiotics in the Soil Environment-Degradation and Their Impact on Microbial Activity and Diversity

Antibiotics play a key role in the management of infectious diseases in humans, animals, livestock, and aquacultures all over the world. The release of increasing amount of antibiotics into waters and soils creates a potential threat to all microorganisms in these environments. This review addresses issues related to the fate and degradation of antibiotics in soils and the impact of antibiotics on the structural, genetic and functional diversity of microbial communities. Due to the emergence of bacterial resistance to antibiotics, which is considered a worldwide public health problem, the abundance and diversity of antibiotic resistance genes (ARGs) in soils are also discussed. When antibiotic residues enter the soil, the main processes determining their persistence are sorption to organic particles and degradation/transformation. The wide range of DT50 values for antibiotic residues in soils shows that the processes governing persistence depend on a number of different factors, e.g., physico-chemical properties of the residue, characteristics of the soil, and climatic factors (temperature, rainfall, and humidity). The results presented in this review show that antibiotics affect soil microorganisms by changing their enzyme activity and ability to metabolize different carbon sources, as well as by altering the overall microbial biomass and the relative abundance of different groups (i.e., Gram-negative bacteria, Gram-positive bacteria, and fungi) in microbial communities. Studies using methods based on analyses of nucleic acids prove that antibiotics alter the biodiversity of microbial communities and the presence of many types of ARGs in soil are affected by agricultural and human activities. It is worth emphasizing that studies on ARGs in soil have resulted in the discovery of new genes and enzymes responsible for bacterial resistance to antibiotics. However, many ambiguous results indicate that precise estimation of the impact of antibiotics on the activity and diversity of soil microbial communities is a great challenge.

Cephalosporin antibiotics in the aquatic environment: A critical review of occurrence, fate, ecotoxicity and removal technologies

Due to their widespread occurrence in the aquatic environment, human and veterinary cephalosporin antibiotics have been studied as water pollutants. In order to characterize environmental risks of this compound class, this review evaluates relevant data about physicochemical properties, occurrence, ecotoxicity and degradation of cephalosporins. Although application of cephalosporins is rather low compared to other antibiotics and their environmental life-time is believed to be short (i.e. days), the available data is insufficient to draw conclusions on their environmental relevance. Few studies concerning the fate of cephalosporins in soil are available, while hydrolysis and photo-degradation are suggested as the main attenuation processes in the aquatic environment. Cephalosporins have been detected in different aqueous matrices in concentrations ranging from 0.30 ng L^-1 to 0.03 mg L^-1, with sewage and wastewater being the main matrices with positive findings. For wastewater treatment purposes, several technologies have been tested for the abatement of cephalosporins, including photolysis and adsorption. In most cases, the technology employed led to complete or significant removal (>95%) of parental drugs but few authors reported on cephalosporins' metabolites and transformation products. Furthermore, the present ecotoxicological data are insufficient for comprehensive ecological risk quotient calculations. Considering the total of 53 cephalosporins, effective values (EC, LC, NOAEC, NOAEL, etc.) are only available for around 30% of parental drugs and are very scarce for cyanobacteria, which is considered to be the most sensitive group of organisms to antibiotics. Furthermore, it has been demonstrated that cephalosporins' transformation products can be more toxic and more persistent than the parental drugs. Few investigations considering this possibility are available. Consequently, more effort on ecotoxicological data generation and verification of biological inactivation of cephalosporins-related products is needed. Likewise, the lack of natural depletion rates and knowledge gaps on mixture effects for cephalosporins' degradation and toxicity have to be overcome.

Detection of the iron complexes with hydrolysis products of cephalexin and cefradine upon high-performance liquid chromatography/electrospray ionization mass spectrometry analysis

RATIONALE

Cephalosporins (e.g. cephalexin, cefradine) are a major group of widely used β-lactam antibiotics. Hydrolysis of the β-lactam ring is an important reaction (often undesired) which leads to deactivation of β-lactams. To the best of our knowledge there is no electrospray ionization mass spectrometry (ESI-MS) data reported concerning the products of hydrolysis of cephalosporins.

METHODS

The hydrolysis of cephalexin and cefradine was performed in aqueous NaOH solutions. After the process the solutions were analyzed by high-performance liquid chromatography (HPLC)/ESI-MS. The elemental compositions of the ions discussed were confirmed by the accurate mass measurements on a quadrupole time-of-flight (QTOF) mass spectrometer.

RESULTS

Unexpectedly, complexes between the hydrolysis products of cephalexin and cefradine (CFL_h and CFR_h ) and iron cation were detected upon HPLC/ESI-MS analysis, namely the ions [(CFL_h -H)₂ +Fe]⁺ and [(CFR_h -H)₂ +Fe]⁺ , although iron was not added to the analyzed solutions or to the mobile phase. These ions were found to be very stable in the gas phase.

CONCLUSIONS

The detection of the complexes between the hydrolysis products of cephalosporins and iron may have a positive impact on the sensitivity and specificity of HPLC/ESI-MS analyses of the hydrolysis products of some cephalosporins.

Biodegradation of the veterinary antibiotics enrofloxacin and ceftiofur and associated microbial community dynamics

Fluoroquinolones and cephalosporins are two classes of veterinary antibiotics arising as pollutants of emerging concern. In this work, the microbial degradation of two representative antibiotics of both these classes, enrofloxacin (ENR) and ceftiofur (CEF), is reported. Biodegradation of the target antibiotics was investigated by supplementing the culture medium with ENR and CEF, individually and in mixture. Microbial inocula were obtained from rhizosphere sediments of plants derived from experimental constructed wetlands designed for the treatment of livestock wastewaters contaminated with trace amounts of these antibiotics. Selected microbial inocula were acclimated during a period of 5months, where the antibiotics were supplemented every three weeks at the concentration of 1mgL^-1, using acetate as a co-substrate. After this period, the acclimated consortia were investigated for their capacity to biodegrade 2 and 3mgL^-1 of ENR and CEF. Complete removal of CEF from the inoculated culture medium was always observed within 21days, independently of its concentration or the concomitant presence of ENR. Biodegradation of ENR decreased with the increase in its concentration in the culture medium, with defluorination percentages decreasing from ca. 65 to 4%. Ciprofloxacin and norfloxacin were detected as biodegradation intermediates of ENR in the microbial cultures supplemented with this antibiotic, indicating that defluorination of at least part of ENR in these cultures is not an immediate catabolic step. Abiotic mechanisms showed high influence in the removal of CEF, affecting less ENR degradation. The acclimation process with the target antibiotics led to significant shifts in the structure and diversity of the microbial communities, predominantly selecting microorganisms belonging to the phyla Proteobacteria (e.g. Achromobacter, Variovorax and Stenotrophomonas genera) and Bacteroidetes (e.g. Dysgonomonas, Flavobacterium and Chryseobacterium genera). The results presented in this study indicate that biodegradation can be an important mechanism for the environmental removal of the tested compounds.

Pharmacokinetics of enrofloxacin and ceftiofur in plasma, interstitial fluid, and gastrointestinal tract of calves after subcutaneous injection, and bactericidal impacts on representative enteric bacteria

This study's objectives were to determine intestinal antimicrobial concentrations in calves administered enrofloxacin or ceftiofur sodium subcutaneously, and their impact on representative enteric bacteria. Ultrafiltration devices were implanted in the ileum and colon of 12 steers, which received either enrofloxacin or ceftiofur sodium. Samples were collected over 48 h after drug administration for pharmacokinetic/pharmacodynamic analysis. Enterococcus faecalis or Salmonella enterica (5 × 10(5) CFU/mL of each) were exposed in vitro to peak and tail (48 h postadministration) concentrations of both drugs at each location for 24 h to determine inhibition of growth and change in MIC. Enrofloxacin had tissue penetration factors of 1.6 and 2.5 in the ileum and colon, while ciprofloxacin, an active metabolite of enrofloxacin, was less able to cross into the intestine (tissue penetration factors of 0.7 and 1.7). Ceftiofur was rapidly eliminated leading to tissue penetration factors of 0.39 and 0.25. All concentrations of enrofloxacin were bactericidal for S. enterica and significantly reduced E. faecalis. Peak ceftiofur concentration was bactericidal for S. enterica, and tail concentrations significantly reduced growth. E. faecalis experienced growth at all ceftiofur concentrations. The MICs for both organisms exposed to peak and tail concentrations of antimicrobials were unchanged at the end of the study. Enrofloxacin and ceftiofur achieved intestinal concentrations capable of reducing intestinal bacteria, yet the short exposure of ceftiofur in the intestine may select for resistant organisms.