Comparison of Short-Term Therapeutic Effects between Amoxicillin-Clavulanic Acid and Ceftriaxone Sodium on Febrile Urinary Tract Infections in Children under Five Years Old.

BACKGROUND: Febrile urinary tract infections in children are typically treated with a standard 10-day course of antibiotics. However, prolonged antibiotic use can lead to increased bacterial resistance, underscoring the need to explore shorter treatment regimens. This study aimed to compare the short-term therapeutic effects of amoxicillin-clavulanic acid and ceftriaxone sodium in children under five years old with febrile urinary tract infections. METHODS: Clinical data from 109 children under five years old diagnosed with febrile urinary tract infections between August 2022 and December 2023 were retrospectively analyzed. Among them, 52 children received ceftriaxone sodium (group A), and 48 children received amoxicillin-clavulanic acid (group B). Clinical symptoms, laboratory indicators, clinical efficacy, and adverse reactions were compared between the two groups. RESULTS: Children from group B showed significantly shorter improvement times for fever, dysuria, and urinary frequency compared to those in group A (p < 0.05). Initially, there were no significant differences in the levels of white blood cell counts, squamous epithelial cells, bacteria, interleukin-6, interleukin-8, and neutrophil gelatinase-associated lipocalin between the two groups (p > 0.05). However, after treatment, group B exhibited significantly lower levels of white blood cell counts, squamous epithelial cells, bacteria, interleukin-6, interleukin-8, and neutrophil gelatinase-associated lipocalin compared to group A (p < 0.05). Moreover, the total effective rate was significantly higher in group B (95.83%) than in group A (80.77%) (p < 0.05). There was no significant difference in the incidence of adverse reactions between groups B (10.42%) and A (13.45%) (p > 0.05). CONCLUSIONS: Amoxicillin-clavulanic acid demonstrated superior short-term therapeutic efficacy for febrile urinary tract infections in children under five years old compared to ceftriaxone sodium. It effectively reduced cure times, mitigated inflammatory responses, and improved treatment outcomes, suggesting its potential for broader clinical application and adoption.

Incidence, antimicrobial susceptibility & out of pocket expenditure of severe enteric fever in Chandigarh, north India.

Background & objectives Burden estimates of enteric fever are required to make policy decisions on introducing typhoid vaccine in India. Incidence, antimicrobial susceptibility, and out-of-pocket expenditure (OOPE) of enteric fever are estimated in Chandigarh, India. Methods A hybrid (facility and community-based) surveillance system was set up at a secondary care hospital to enrol patients above six months of age, hospitalized with fever, from a defined catchment population from May 2018 to March 2020. Blood samples were collected and cultured using an automated system (BD BACTECTM blood culture system). The Salmonella Typhi and S. Paratyphi isolates were characterized for antimicrobial susceptibility. OOPE was recorded after 14 and 28 days of discharge. Results Blood samples were collected from 97 per cent of the 1650 study participants enrolled. The incidence of enteric fever was 226.8 per 1,00,000 person-years (PY), severe typhoid fever 156.9 per 1,00,000 PY, and severe paratyphoid fever 69.9 per 1,00,000 PY. Salmonella was highly susceptible to ampicillin, azithromycin, and ceftriaxone (99.25%) and least susceptible to ciprofloxacin (11.3%). The OOPE due to hospitalization of individuals infected with S. Paratyphi [INR 8696.6 (USD 116)] was significantly higher than the individuals infected with S. Typhi [INR 7309 (USD 97.5), P=0.01], and among cases who were hospitalized for more than seven days [INR 12,251 (USD 163.3)] as compared with those with a stay of 3-7 days [INR 8038.2 (USD 107.2)] or less than three days [INR 5327.8 (USD 71), P<0.001]. Interpretation & conclusions There was a high incidence of enteric fever, high OOPE, and resistance to ciprofloxacin.

Genomic epidemiology of ceftriaxone-resistant non-typhoidal Salmonella enterica strain in China.

Non-typhoidal Salmonella (NTS) is one of the top causes of diarrhea worldwide. Ceftriaxone is commonly recommended as the initial treatment option for Salmonella infections due to its antibacterial effectiveness. The objective of this study was to investigate the molecular epidemiological characteristics of NTS and to compare the phenotypic and genotypic profiles of antimicrobial resistance in multidrug-resistant Salmonella strains by sequencing 329 NTS strains collected from a county-level hospital between 2018 and 2021. Multi-locus sequence typing (MLST), antimicrobial resistance genes and plasmid types were identified by BacWGSTdb 2.0 webserver. Phylogenetic analysis of all NTS strains was carried out using Snippy and Gubbins software. The transferability of ceftriaxone resistant plasmids was confirmed through plasmid conjugation assays, and verified by S1-PFGE-Southern blot assays. The predominant serotypes among all NTS strains were Typhimurium (161/329), Enteritidis (49/329) and London (45/329). The most common sequence type observed was ST34 (86/329), followed by ST19 (72/329) and ST11 (47/329). The antimicrobial resistance of Salmonella to a wide range of antimicrobials showed an overall increase. Out of these 37 (11.24%) ceftriaxone-resistant strains, with the majority of them (33/37) being blaCTX-M. The predominant plasmid types identified were IncHI2 (14/21) and IncI1 (6/21), ranging in size from 70 kb to 360 kb. The conjugation efficiency was calculated with the high conjugation efficiency of 1.1 × 10- 5 to 9.3 × 10- 2. The strains varied widely, ranging from 3 to 45,024 single nucleotide polymorphisms (SNPs). There are close linkages observed among the predominant lineage, with an average of 78 SNPs between each pair of ST34 strains. The findings contribute to our understanding of the transmission and resistance mechanisms of multidrug-resistant Salmonella, thereby facilitating the development of effective control strategies.

Sensorineural hearing loss in Lyme neuroborreliosis.

BACKGROUND: Sensorineural hearing loss (SNHL) has been suggested to occur in patients with Lyme neuroborreliosis (LNB); however, a clear association has never been documented. The present study prospectively investigated the development of SNHL in patients admitted for treatment of LNB using distortion-product-oto-acoustic emissions (DPOAE) as a measure of cochlear function. METHODS: DOAE were measured in patients with LNB on the day of diagnosis, during treatment, and 30-60 days after discharge. Frequencies were categorized as Low (1, 1.5, 2 kHz), Mid (3, 4, 5 kHz), Mid-high (6, 7, 8 kHz), and High (9, 10 kHz). Pure Tone Audiometry (PTA3) was performed at discharge and 60 days after. Patients were treated with i.v. ceftriaxone or oral doxycycline for 14 days according to guidelines. RESULTS: DPOAE measurements were obtained in 25 patients with LNB at admission and in 18 patients at follow-up. Median age was 56 years (IQR, 48-64 years), and 16 (67%) were men. Fourteen (78%) of 18 patients showed improvement in Emission Threshold Levels (ETL) from admission to follow-up in low, mid-, and mid-high frequency categories, where ETLs increased by median levels of 3.2 (-4.1 to 8.3), 7.5 (-2.8 to 9.8), and 4.7 dB (-4.3 to 10.1). A decline was observed in the high frequency category, median -3.3 dB (-9.1 to 6.7). SNHL defined by pure tone average (PTA3) >20 dB was present in 11 out of 23 (48%) at discharge and in 9 out of 16 patients (56%) 60 days after discharge, which differed significantly from matched controls (Mann-Whitney test, p = 0.036). CONCLUSION: LNB can lead to cochlear outer-hair cell dysfunction, resulting in temporary and long-term SNHL.

Adverse Drug Reactions Resulting From the Use of Chiral Medicines Amoxicillin, Amoxicillin-Clavulanic Acid, and Ceftriaxone: A Mixed Prospective-Retrospective Cohort Study.

The use of chiral medicines (possessing center(s) of asymmetric carbon) may cause adverse drug reactions (ADRs). The safety assurance of these medicines is critical. We aimed to evaluate registered and commonly used anti-infective chiral medicines circulating in the Tanzanian market to establish their safety profile to protect public health. A mixed prospective-retrospective cohort study was conducted to assess the safety profile of amoxicillin, amoxicillin-clavulanic acid and ceftriaxone injection. ADRs causality assessment was conducted by using World Health Organization (WHO)-Algorithm criteria. Data were collected from 7 tertiary hospitals: Muhimbili National Hospital (MNH), Kilimanjaro Christian Medical Centre (KCMC), Bugando Medical Centre (BMC), Ligula Referral-Regional Hospital (LRRH), Kitete Referral-Regional Hospital (KRRH), Dodoma Referral-Regional Hospital (DRRH), and Mbeya Zonal-Referral Hospital (MZRH). Data were supplemented by those recorded in the WHO-Vigiflow/VigiLyze database within the same monitoring period. Data were analyzed using STATA version-15. The results were considered statistically significant when P < .05. A total of 2522 patients were enrolled in hospitals: MNH (499), KCMC (407), BMC (396), LRRH (387), KRRH (345), DRRH (249), and MZRH (239). Among those, 1197 (47.5%) were treated with ceftriaxone, 585 (23.2%) amoxicillin and 740(29.3%) amoxicillin-clavulanic acid. Out of those, 102 (4.5%) experienced adverse events (AEs), 49 (48%) were due to ceftriaxone, 37 (36.3%) amoxicillin-clavulanic acid and 16 (15.7%) amoxicillin (P-value .012). A total of 443 participants from the enrolled and WHO-Vigiflow/VigiLyze database were experienced with ADRs. The ADRs affected mainly gastro-intestinal system 234 (53%), skin and subcutaneous tissue 85 (19%), nervous system 49 (11%), respiratory thoracic 22 (5%), and general disorders 18(4%). In this study, approximately 90% of reported AEs were ADRs possible-related to the monitored medicines, with few plausible and certain. Ceftriaxone injection caused more ADRs. Amoxicillin-clavulanic acid was associated with more ADRs than amoxicillin alone. The safety profile of these medicines is still maintained; however, comprehensive monitoring of ADRs is recommended to improve patient safety and enhance overall treatment outcomes.

Blood infection of Capnocytophaga canimorsus etiology following a dog bite: case report and review of the available literature. / Zakazenie krwi o etiologii Capnocytophaga canimorsus po pogryzieniu przez psa - opis przypadku i analiza dostepnej literatury.

We present the case of a 71-year-old man who developed sepsis caused by Capnocytophaga canimorsus as a result of being bitten by his own dog. Positive blood cultures were obtained, but due to difficulties in determining the bacterial species, the patient was treated empirically with ceftriaxone and levofloxacin. After using the recommended empirical therapy, the patient's condition improved. Capnocytophaga canimorsus is difficult to identify, among others, due to its long growth time and specific development conditions (capnophiles). These Gram-negative bacilli cause a number of diseases in humans, ranging from infections of the skin and subcutaneous tissue, through peritonitis, to sepsis. The portal of infection with these bacteria is most often a wound caused by an animal bite. Additional risk factors that increase the risk of developing a severe infection and even death include older age, concomitant chronic diseases, and immunosuppression.

Antibiotic prescription patterns in the emergency department of a tertiary healthcare center in Nepal: a descriptive cross-sectional study.

OBJECTIVE: To describe antibiotic prescription patterns in the emergency department (ED) of a tertiary healthcare center in Nepal. METHODS: This was a descriptive cross-sectional study of hospital records of patients who visited the ED. RESULTS: Of the 758 ED patients included in the study, 384 (50.6%) received a total of 536 antibiotic prescriptions. Common indications for antibiotic prescriptions included respiratory infection (37.5%), gastrointestinal infection (19.3%), urinary infection (10.4%), and prophylaxis (29.9%). Antibiotics listed as essential in the National List of Essential Medicines (NLEM) and generic formulations were used in 77.1% and 61.9% of the antibiotic prescriptions, respectively. Injectable antibiotics were prescribed to 54.9% of the 384 patients. Frequently prescribed antibiotics included ceftriaxone (34.1%), metronidazole (18.5%), amoxicillin + clavulanic acid (15.9%), and cefixime (14.3%). Bacterial culture testing was performed in 15.1% of the patients who received antibiotics. CONCLUSIONS: This study showed that overuse of antibiotics, prescription of branded antibiotics, prescription of antibiotics not listed in the NLEM, prophylactic use of antibiotics, and empirical treatment of suspected infections without isolation of pathogens were all prevalent. We recommend more research to determine the causes underlying these practices and develop interventions to limit such practices.

Irreversible neurological manifestations in undiagnosed disseminated gonococcal infection.

Neisseria gonorrhoeae causes a common sexually transmitted infection with manifestations ranging from asymptomatic to urethritis and pelvic inflammatory disease to disseminated infections including septic arthritis. Serious complications may arise in unrecognised or inappropriately treated infections.We report a young, healthy woman who developed fever and joint pain and was diagnosed with an inflammatory arthritis. After starting immune suppressing treatments, she experienced right wrist drop and progressive muscle atrophy, joint contractures and sensory loss. Electrodiagnostic studies showed patchy, mixed neurogenic and myopathic features. Areas of muscle oedema on extremity MRI led to a right brachioradialis biopsy, which showed only nonspecific changes. Other testing, including lumbar puncture and MRI of the brain/spine was noncontributory. Additional history revealed unprotected intercourse with a new partner prior to symptom onset. Urine gonorrhoeae PCR was positive, and right shoulder arthrocentesis confirmed septic arthritis. After intravenous antibiotic treatment with ceftriaxone, she demonstrated slow, incomplete symptomatic improvement.

Modeling of Dissolving Microneedle-Based Transdermal Drug Delivery: Effects of Dynamics of Polymers in Solution.

Dissolving microneedle (DMN)-assisted transdermal drug delivery (TDD) has received attention from the scientific community in recent years due to its ability to control the rate of drug delivery through its design, the choice of polymers, and its composition. The dissolution of the polymer depends strongly on the polymer-solvent interaction and polymer physics. Here, we developed a mathematical model based on the physicochemical parameters of DMNs and polymer physics to determine the drug release profiles. An annular gap width is defined when the MN is inserted in the skin, accumulating interstitial fluid (ISF) from the surrounding skin and acting as a boundary layer between the skin and the MN. Poly(vinylpyrrolidone) (PVP) is used as a model dissolving polymer, and ceftriaxone is used as a representative drug. The model agrees well with the literature data for ex vivo permeation studies, along with the percent height reduction of the MN. Based on the suggested mathematical model, when loading 0.39 mg of ceftriaxone, the prediction indicates that approximately 93% of the drug will be cleared from the bloodstream within 24 h. The proposed modeling strategy can be utilized to optimize drug transport behavior using DMNs.

Acute hepatitis as a manifestation of secondary syphilis: a case report and literature review.

This is the case of a 25-year-old patient, with the notion of unprotected sexual relations with multiple partners consulted for cholestatic icterus with pruritus evolving for 2 months. The general examination found an intense mucocutaneous icterus. The examination of the lymph nodes revealed multiple lymph nodes. A thoracic-abdominal-pelvic scanner showed peri-portal edema and adenopathies above and below the diaphragm without suspicious lesions. Biologically, there was acute cytolysis with ASAT at 1612IU/L, ALAT at 1506IU/L, and icteric cholestasis, the acute viral serologies and other autoantibodies were all negative. Given the presence of adenopathy and sexual risk factors, a syphilis serology was requested and was positive: a TPHA at 2560UI/L, and a VDRL at 1/32 UI/L. A liver biopsy was performed, which showed the presence, on immunohistochemistry, of anti-treponemal-pallidum antibodies. After eliminating all etiologies of cytolytic hepatitis, we retained the diagnosis of syphilitic hepatitis. Therapeutically, we started a treatment based on ceftriaxone 2g/dl with spectacular biological improvement at H48 of the beginning of treatment.

Assessing novel partner antimicrobials to protect ceftriaxone against gonococcal resistance: An in vitro evaluation.

BACKGROUND: The emergence of ceftriaxone-resistant Neisseria gonorrhoeae poses a significant threat to existing treatment regimens. Our study aimed to assess the efficacy of antimicrobials that could be combined with ceftriaxone to reduce the probability of ceftriaxone resistance emerging and spreading in N. gonorrhoeae. METHODS AND RESULTS: Broth microdilution was used to determine the minimal inhibitory concentrations (MICs) for a panel of ceftriaxone-resistant (WHO X, Y, Z) and ceftriaxone-susceptible (WHO L, N, P) N. gonorrhoeae WHO reference strains for the following antimicrobials: ceftriaxone, doxycycline, azithromycin, zoliflodacin, fosfomycin, pristinamycin, ramoplanin, gentamicin and NAI-107. The MICs for zoliflodacin and pristinamycin for all strains were lower than or equal to the available breakpoints. A checkerboard assay was used to determine the drug-drug combination effect, which showed either an indifferent or an additive effect for all the combinations tested with ceftriaxone. CONCLUSIONS: The low MICs of zoliflodacin and pristinamycin for the three ceftriaxone-resistant strains suggest that these antimicrobials could be used as partner drugs with ceftriaxone to reduce the probability of ceftriaxone resistance spreading in areas with a high prevalence of ceftriaxone resistance.

A case of drug fever in the treatment of Brucella arthritis in a child: a case report.

Brucellosis, a zoonotic ailment induced by the Brucella and some patients may present with joint involvement. This report describes a pediatric patient diagnosed with Brucella arthritis, presenting with swelling and pain in the right knee. The patient had a reoccurrence of fever due to sulfamethoxazole-trimethoprim allergy during treatment. Symptoms improved after adjusting the antimicrobial regimen to ceftriaxone and rifampicin. This case emphasizes the importance of the need for brucellosis as a differential diagnosis for arthralgia and fever in brucellosis- endemic areas. Furthermore, it emphasizes the importance of timely recognition that recurrent fever after effective anti-infective therapy must be considered as a possibility of drug fever.

Rapid detection of ceftriaxone-resistant Salmonella by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry combined with the ratio of optical density.

BACKGROUND: The increased resistance rate of Salmonella to third-generation cephalosporins represented by ceftriaxone (CRO) may result in the failure of the empirical use of third-generation cephalosporins for the treatment of Salmonella infection in children. The present study was conducted to evaluate a novel method for the rapid detection of CRO-resistant Salmonella (CRS). METHODS: We introduced the concept of the ratio of optical density (ROD) with and without CRO and combined it with matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS) to establish a new protocol for the rapid detection of CRS. RESULTS: The optimal incubation time and CRO concentration determined by the model strain test were 2 h and 8 µg/ml, respectively. We then conducted confirmatory tests on 120 clinical strains. According to the receiver operating characteristic curve analysis, the ROD cutoff value for distinguishing CRS and non-CRS strains was 0.818 [area under the curve: 1.000; 95% confidence interval: 0.970-1.000; sensitivity: 100.00%; specificity: 100%; P < 10- 3]. CONCLUSIONS: In conclusion, the protocol for the combined ROD and MALDI-TOF MS represents a rapid, accurate, and economical method for the detection of CRS.

Neisseria gonorrhoeae isolates resistant to extended spectrum cephalosporins and macrolides isolated from symptomatic men in western Kenya.

BACKGROUND: We characterized the antimicrobial resistance (AMR) profiles of Neisseria gonorrhoeae (NG) isolated from symptomatic men at a sexually transmitted infection clinic in Kisumu, Kenya. METHODS: Two urethral swabs were obtained from symptomatic men between 2020 and 2022, one for Gram's stain and the other inoculated directly onto modified Thayer-Martin media containing 1% VCNT and 1% IsoVitaleX enrichment. Culture results were confirmed by colony morphology, Gram's stain and oxidase test. Duplicate isolates were shipped to Uniformed Services University for confirmation and characterization. Susceptibility to eight drugs was assessed by E-test. Agar dilution confirmed resistance to ceftriaxone, cefixime, and azithromycin. Susceptibility, intermediate resistance (IR), and resistance (R) were determined according to published criteria. RESULTS: Of 154 enrolled participants, 112 were culture-positive for NG. Agar dilution results in 110 (98.2%) showed the following: azithromycin-R (1.8%), and 4.5% R or IR to ceftriaxone or cefixime: ceftriaxone-R (0.9%), ceftriaxone-IR (2.7%), and cefixime-IR (2.7%). By E-test, most isolates were IR or R to tetracycline (97.2%), penicillin (90.9%), and ciprofloxacin (95.4%). CONCLUSIONS: We detected NG with resistance to azithromycin and ceftriaxone, indicating a growing threat to the current Kenyan dual syndromic treatment of urethritis with cephalosporin plus macrolides. Ongoing AMR surveillance is essential for effective drug choices.

The HtrA chaperone monitors sortase-assembled pilus biogenesis in Enterococcus faecalis.

Sortase-assembled pili contribute to virulence in many Gram-positive bacteria. In Enterococcus faecalis, the endocarditis and biofilm-associated pilus (Ebp) is polymerized on the membrane by sortase C (SrtC) and attached to the cell wall by sortase A (SrtA). In the absence of SrtA, polymerized pili remain anchored to the membrane (i.e. off-pathway). Here we show that the high temperature requirement A (HtrA) bifunctional chaperone/protease of E. faecalis is a quality control system that clears aberrant off-pathway pili from the cell membrane. In the absence of HtrA and SrtA, accumulation of membrane-bound pili leads to cell envelope stress and partially induces the regulon of the ceftriaxone resistance-associated CroRS two-component system, which in turn causes hyper-piliation and cell morphology alterations. Inactivation of croR in the OG1RF ΔsrtAΔhtrA background partially restores the observed defects of the ΔsrtAΔhtrA strain, supporting a role for CroRS in the response to membrane perturbations. Moreover, absence of SrtA and HtrA decreases basal resistance of E. faecalis against cephalosporins and daptomycin. The link between HtrA, pilus biogenesis and the CroRS two-component system provides new insights into the E. faecalis response to endogenous membrane perturbations.

Metoclopramide to Prevent Pneumonia in Patients With Stroke and a Nasogastric Tube: Data From the PRECIOUS Trial.

BACKGROUND: A randomized trial suggested that treatment with metoclopramide reduces the risk of pneumonia in patients with acute stroke and a nasogastric tube. We assessed whether this finding could be replicated in a post hoc analysis of the randomized PRECIOUS trial (Prevention of Complications to Improve Outcome in Elderly Patients With Acute Stroke). METHODS: PRECIOUS was an international, 3×2 partial-factorial, randomized controlled, open-label clinical trial with blinded outcome assessment assessing preventive treatment with metoclopramide, paracetamol, and ceftriaxone in patients aged ≥66 years with acute ischemic stroke or intracerebral hemorrhage and a National Institutes of Health Stroke Scale score ≥6. In the present study, we analyzed patients who had a nasogastric tube within 24 hours after randomization. Patients who were allocated to metoclopramide (10 mg TID) were compared with patients who were not. Treatment was started within 24 hours after symptom onset and continued for 4 days or until discharge if earlier. The primary outcome was pneumonia in the first week after stroke. The score on the modified Rankin Scale after 90 days was a secondary outcome and analyzed with ordinal logistic regression. RESULTS: From April 2016 through June 2022, a total of 1493 patients were enrolled with 1376 included in this analysis, of whom 1185 (86%) had ischemic stroke and 191 (14%) had intracerebral hemorrhage. The first day after randomization, 329 (23.9%) patients had a nasogastric tube, of whom 156 were allocated to metoclopramide and 173 to standard care. Metoclopramide was not associated with a reduction of pneumonia (41.0% versus 35.8%; adjusted odds ratio, 1.35 [95% CI, 0.79-2.30]) or with poor functional outcome (adjusted odds ratio, 1.07 [95% CI, 0.71-1.61]). CONCLUSIONS: In patients with stroke who had a nasogastric tube shortly after stroke onset, metoclopramide for 4 days did not reduce pneumonia or have an effect on the functional outcome.

Ischaemic apoplexy caused by syphilis.

Syphilis is a sexually transmitted disease caused by the spirochaete Treponema pallidum. Patients with untreated syphilis can develop meningovascular syphilis at any stage of the disease. This is a case report of a 44-year-old man displaying two instances of acute vertigo and lateralized paraesthesia. MRI showed infarctions in the left thalamus and capsula interna. Subsequent investigations including cerebral spinal fluid analysis revealed a diagnosis of neurosyphilis. The patient was treated intravenously with benzylpenicillin and ceftriaxone with complete clinical remission.

Molecular Basis of Influence of A501X Mutations in Penicillin-Binding Protein 2 of Neisseria gonorrhoeae Strain 35/02 on Ceftriaxone Resistance.

The increase in the resistance of mutant strains of Neisseria gonorrhoeae to the antibiotic ceftriaxone is pronounced in the decrease in the second-order acylation rate constant, k2/KS, by penicillin-binding protein 2 (PBP2). These changes can be caused by both the decrease in the acylation rate constant, k2, and the weakening of the binding affinity, i.e., an increase in the substrate constant, KS. A501X mutations in PBP2 affect second-order acylation rate constants. The PBP2A501V variant exhibits a higher k2/KS value, whereas for PBP2A501R and PBP2A501P variants, these values are lower. We performed molecular dynamic simulations with both classical and QM/MM potentials to model both acylation energy profiles and conformational dynamics of four PBP2 variants to explain the origin of k2/KS changes. The acylation reaction occurs in two elementary steps, specifically, a nucleophilic attack by the oxygen atom of the Ser310 residue and C-N bond cleavage in the ß-lactam ring accompanied by the elimination of the leaving group of ceftriaxone. The energy barrier of the first step increases for PBP2 variants with a decrease in the observed k2/KS value. Submicrosecond classic molecular dynamic trajectories with subsequent cluster analysis reveal that the conformation of the ß3-ß4 loop switches from open to closed and its flexibility decreases for PBP2 variants with a lower k2/KS value. Thus, the experimentally observed decrease in the k2/KS in A501X variants of PBP2 occurs due to both the decrease in the acylation rate constant, k2, and the increase in KS.