Mechanistic insights into translation inhibition by aminoglycoside antibiotic arbekacin

How aminoglycoside antibiotics limit bacterial growth and viability is not clearly understood. Here we employ fast kinetics to reveal the molecular mechanism of action of a clinically used, new-generation, semisynthetic aminoglycoside Arbekacin (ABK), which is designed to avoid enzyme-mediated deactivation common to other aminoglycosides. Our results portray complete picture of ABK inhibition of bacterial translation with precise quantitative characterizations. We find that ABK inhibits different steps of translation in nanomolar to micromolar concentrations by imparting pleotropic effects. ABK binding stalls elongating ribosomes to a state, which is unfavorable for EF-G binding. This prolongs individual translocation step from ∼50 ms to at least 2 s; the mean time of translocation increases inversely with EF-G concentration. ABK also inhibits translation termination by obstructing RF1/RF2 binding to the ribosome. Furthermore, ABK decreases accuracy of mRNA decoding (UUC vs. CUC) by ∼80 000 fold, causing aberrant protein production. Importantly, translocation and termination events cannot be completely stopped even with high ABK concentration. Extrapolating our kinetic model of ABK action, we postulate that aminoglycosides impose bacteriostatic effect mainly by inhibiting translocation, while they become bactericidal in combination with decoding errors.

Kinetic Analysis Suggests Evolution of Ribosome Specificity in Modern Elongation Factor-Tus from "Generalist" Ancestors

It has been hypothesized that early enzymes are more promiscuous than their extant orthologs. Whether or not this hypothesis applies to the translation machinery, the oldest molecular machine of life, is not known. Efficient protein synthesis relies on a cascade of specific interactions between the ribosome and the translation factors. Here, using elongation factor-Tu (EF-Tu) as a model system, we have explored the evolution of ribosome specificity in translation factors. Employing presteady state fast kinetics using quench flow, we have quantitatively characterized the specificity of two sequence-reconstructed 1.3- to 3.3-Gy-old ancestral EF-Tus toward two unrelated bacterial ribosomes, mesophilic Escherichia coli and thermophilic Thermus thermophilus. Although the modern EF-Tus show clear preference for their respective ribosomes, the ancestral EF-Tus show similar specificity for diverse ribosomes. In addition, despite increase in the catalytic activity with temperature, the ribosome specificity of the thermophilic EF-Tus remains virtually unchanged. Our kinetic analysis thus suggests that EF-Tu proteins likely evolved from the catalytically promiscuous, “generalist” ancestors. Furthermore, compatibility of diverse ribosomes with the modern and ancestral EF-Tus suggests that the ribosomal core probably evolved before the diversification of the EF-Tus. This study thus provides important insights regarding the evolution of modern translation machinery.

Ugly bugs in healthy guts! Carriage of multidrug-resistant and ESBL-producing commensal Enterobacteriaceae in the intestine of healthy Nepalese adults

Background

Fecal carriage of multidrug-resistant and extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae is one of the important risk factors for infection with antibiotic-resistant bacteria. In this report, we examined the prevalence of multidrug-resistant and ESBL-producing common enterobacterial strains colonizing the intestinal tract of apparently healthy adults in Kathmandu, Nepal.

Methods

During a 6-month period (February-July 2016), a total of 510 stool specimens were obtained from apparently healthy students of Manmohan Memorial Institute of Health Sciences, Kathmandu, Nepal. Stool specimens were cultured, and the most common enterobacterial isolates (Escherichia coli and Klebsiella species) were subjected to antimicrobial susceptibility tests according to the standard microbiologic guidelines. Multidrug-resistant isolates were selected for ESBL confirmation by combined disk test and E-test methods. Molecular characterization of plasmid-borne ESBL genes was performed by using specific primers of cefotaximase Munich (CTX-M), sulfhydryl variant (SHV), and temoniera (TEM) by polymerase chain reaction.

Results

Among 510 bacterial strains, E. coli (432, 84.71%) was the predominant organism followed by Klebsiella oxytoca (48, 9.41%) and K. pneumoniae (30, 5.88%). ESBLs were isolated in 9.8% of the total isolates including K. oxytoca (29.17%), E. coli (7.87%), and K. pneumoniae (6.67%). Among ESBLs, bla-TEM was the predominant type (92%) followed by bla-CTX-M (60%) and bla-SHV (4%).

Conclusion

Multidrug-resistant and ESBL-producing enterobacterial commensal strains among healthy individuals are of serious concern. Persistent carriage of ESBL organisms in healthy individuals suggests the possibility of sustained ESBL carriage among the diseased and hospitalized patients. We recommend similar types of epidemiologic surveys in larger communities and in hospital settings to ascertain the extent of ESBL resistance.

Magnetic Resonance Imaging Evaluation of Musculoskeletal Diseases of Ankle and Foot

Background Ankle and foot pain is a common clinical problem, that may be due to a variety of soft tissue and osseus abnormalities. Magnetic resonance imaging plays vital role for diagnosing internal derangement of the ankle joint, assessing soft tissue structures around the ankle such as tendons, ligaments, nerves and osseus structures. Method Retrospective magnetic resonance imaging evaluation of the ankle and foot was done in 100 patients using 0.3T and 1.5T magnetic resonance imaging. Clinical history included pain, swelling of the ankle and foot, trauma, twisting injury, palpable mass and difficulty in walking. Result Fifty two patients were male and 48 patients female aged 6 months to 70 years. Ligaments tear were the commonest and seen in 22% patients. Tenosynovitis found in 17%, Pigmented villonodular synovitis (PVNS) in 3%, Achilles tendon abnormality in 8%, stress fracture-9%, osteomyelitis-8%, soft tissue vascular malformation in 5%, soft tissue and bone tumor-4%, marrow edema-20%, osteoarthritis-10%, Osteochondral lesion of talus-8%, sinus tarsi syndrome-3%, posterior impingement-5%, plantar fasciitis-2%, Sever disease-2%, peroneus tendon split-2%. The commonest clinical presentation was pain and swelling of the ankle in 42 patients, twisting/inversion injury of the ankle in 23 patients followed by traumatic injury with difficulty in walking in 20 patients and palpable mass in 8 patients. Ligaments injury were mostly associated with inversion/twisting injury. Conclusion Magnetic resonance imaging is advantageous for assessing soft tissue structures around the ankle and foot, such as tendons, ligaments, nerves, masses and occult osseus lesions. It provides a quick, non-invasive tool for the diagnosis of related injuries and guide for the further treatment planning.

Epidemiology of device-associated infections in an intensive care unit of a teaching hospital in Nepal: A prospective surveillance study from a developing country

BACKGROUND

Device-associated health care-acquired infections (DA-HAIs) in intensive care unit patients are a major cause of morbidity, mortality, and increased health care costs.

METHODS

A prospective, structured clinicomicrobiological surveillance was carried out for 3 common DA-HAIs: ventilator-associated pneumonia (VAP), central line-associated bloodstream infection (CLABSI), and catheter-associated urinary tract infection (CAUTI) present in the patients of an intensive care unit of a teaching hospital in Nepal. DA-HAIs were identified using the Centers for Disease Control and Prevention definitions, and their rates were expressed as number of DA-HAIs per 1,000 device-days.

RESULTS

Overall incidence rate of DA-HAIs was 27.3 per 1,000 patient-days occurring in 37.1% of patients. The device utilization ratio for mechanical ventilation, central line catheter, and urinary catheter was 0.83, 0.63, and 0.78, respectively. The rates of VAP, CLABSI, and CAUTI were 21.40, 8.64, and 5.11 per 1,000 device-days, respectively. Acinetobacter spp (32.7%), Klebsiella spp (23.6%), Burkholderia cepacia complex (12.7%), and Escherichia coli (10.9%) were the common bacterial pathogens. Most of the bacterial isolates associated with DA-HAIs were found to be multidrug-resistant.

CONCLUSIONS

Incidence of DA-HAIs in the study intensive care unit was high compared with that of developed countries. Formulation and implementation of standard infection control protocols, active surveillance of DA-HAIs, and antimicrobial stewardship are urgently needed in our country.

High burden of antimicrobial resistance among gram negative bacteria causing healthcare associated infections in a critical care unit of Nepal

Background

Healthcare associated infections (HCAI) and antimicrobial resistance are principal threats to the patients of intensive care units and are the major determining factors for patient outcome. They are associated with increased morbidity, mortality, excess hospitalization and financial costs. The present study is an attempt to investigate the spectrum and antimicrobial resistance of bacterial isolates involved in healthcare associated infections (HCAI) in the patients of a critical care unit at a tertiary care university hospital in Kathmandu, Nepal.

Methods

A laboratory based study was conducted over the period of 15 months (January 2014 to March 2015) among the patients of intensive care unit of Tribhuvan University Teaching Hospital, Kathmandu, Nepal. Clinical specimens from patients with suspected healthcare-associated infection were processed and bacterial isolates were identified with standard microbiological methods. Antimicrobial susceptibilities of the isolated strains were determined according to the CLSI guidelines and β-lactamases (ESBL, AmpC, MBL and KPC) were detected by various phenotypic tests.

Results

One hundred and forty nine clinical specimens received from 135 patients suspected of HCAI (out of 491 patients) were found with significant bacterial growth. Specimens were from patients suspected of hospital-acquired pneumonia (16%, 79/491), bloodstream infections (5.7%, 28/491), surgical site infections (4.7%, 23/491), and urinary tract infections (3.9%, 19/491). Acinetobacter spp., Klebsiella spp., Escherichia coli and Burkholderia cepacia were the leading bacterial pathogens. Extremely high level of drug resistance (95.8%) along with the production of β-lactamases (ESBL; 43.7%, AmpC; 27.5%), MBL; 50.2% and KPC; 4.2%) was observed among Gram negative bacterial isolates.

Conclusion

Healthcare associated infections are very common in our ICU. Gram negative bacterial pathogens are major culprits associated with these infections and there is alarming state of drug resistance among these isolates. Continuous surveillance and establishment of preventive and control measures of healthcare associated infections are urgently needed in our setting.

High rates of multidrug resistance among uropathogenic Escherichia coli in children and analyses of ESBL producers from Nepal

Background

Emergence of Extended-spectrum beta-lactamase producing Escherichia coli causing urinary tract infections (UTI) among pediatric patients is an increasing problem worldwide. However, very little is known about pediatric urinary tract infections and antimicrobial resistance trend from Nepal. This study was conducted to assess the current antibiotic resistance rate and ESBL production among uropathogenic Escherichia coli in pediatric patients of a tertiary care teaching hospital of Nepal.

Methods

A total of 5,484 urinary tract specimens from children suspected with UTI attending a teaching hospital of Nepal over a period of one year were processed for the isolation of bacterial pathogens and their antimicrobial susceptibility testing. Escherichia coli (n = 739), the predominant isolate in pediatric UTI, was further selected for the detection of ESBL-production by phenotypic combination disk diffusion test.

Results

Incidence of urinary tract infection among pediatric patients was found to be 19.68% and E coli (68.4%) was leading pathogen involved. Out of 739 E coli isolates, 64.9% were multidrug resistant (MDR) and 5% were extensively drug resistant (XDR). Extended spectrum beta lactamase (ESBL) was detected in 288 (38.9%) of the E coli isolates.

Conclusion

Alarming rate of drug resistance among pediatric uropathogens and high rate of ESBL-producing E. coli was observed. It is extremely necessary to routinely investigate the drug resistance among all isolates and formulate strict antibiotics prescription policy in our country.

Bacteremia caused by a rare pathogen - Chromobacterium violaceum: a case report from Nepal

Chromobacterium violaceum is a gram negative saprophytic bacterium, prevalent in tropical and subtropical climates. Infections caused by C. violaceum are very uncommon, yet it can cause severe systemic infections with higher mortality when entered into the bloodstream through open wound. A case of symptomatic bacteremia in a woman caused by C. violaceum was identified recently at a tertiary care teaching hospital in Nepal. Timely diagnosis by microbiological methods and rapid administration of antimicrobials led to a successful treatment of this life-threatening infection in this case. From this experience, we suggest to include this bacterium in the differential diagnosis of sepsis, especially when abraded skin is exposed to soil or stagnant water in tropical areas. The precise antimicrobial selection and timely administration should be considered when this infection is suspected.

Distally based sural faciocutaneous and fascial (adipofascial) flap for reconstruction of distal leg, ankle and foot defects

BACKGROUND

Any soft tissue defect in distal leg, ankle and hind foot is still a challenging problem. There are various options for coverage of such defects, but the distally based sural neurocutaneous and neurofascial flap based on the sural nerve and superficial sural artery has been an important option.

OBJECTIVE

To evaluate the efficacy of distally based sural flap in reconstruction of the distal leg, ankle and hind foot soft tissue defects.

METHOD

Seventeen patients with soft tissue defects over distal leg, ankle and hind foot were included in this study. All patients were treated with distally based sural flap. Most of the cases were due to trauma (16 cases) which compromised tendon and bone. One case was of malignant melanoma of sole of hind foot which required wide excision and soft tissue reconstruction with sural flap.

RESULT

In all cases defects were successfully covered. Three showed venous congestion and partial necrosis. One developed secondary infection. One flap failed completely. Mean follow up of patients was 20 months (6-36 months).

CONCLUSION

Sural flap is a good option for reconstruction of distal leg, ankle and foot defects.

Operative fixation of displaced middle third clavicle (Edinburg Type 2) fracture with superior reconstruction plate osteosynthesis

BACKGROUND

Conservative management of middle third clavicle fracture has been recently reported with suboptimal outcomes. Despite higher nonunion rates in initial open reduction and internal fixation, understanding the problem better and taking in accounts of previous shortcomings, such fractures can be optimally treated by open reduction and internal fixation with reconstruction plate.

OBJECTIVE

To study the outcome of middle third clavicle fracture treated with superior reconstruction plating in terms of function using Constant shoulder score, union time and rate, complications and patient satisfaction.

METHODS

Twenty patients with displaced middle third clavicle fracture (Edinburg type 2) treated with open reduction and internal fixation with reconstruction plate implanted in superior surface were prospectively followed for at least one year after surgery.

RESULTS

There were 20 patients, 16 males and 4 females. The mean age of the patients was 31.5 years with SD 11.5 years (range 15-60 years) and 5 patients (25%) had associated injuries. All fractures united in 16 weeks or less in near anatomic position with complication in 2 (5%) patients, one deep infection and one frozen shoulder which on subsequent management recovered well. There was no nonunion or implant failure. The average Constant score was 97.45 in one year follow up and the patients were relatively satisfied with the treatment.The most common indication (25%) for hardware removal was young age of the patient, hardware prominence and occasional discomfort.

CONCLUSION

This small series shows that displaced midshaft clavicle fracture can be optimally treated with operative fixation implanting the reonstruction plate in superior surface with six cortical purchases on either side and supervised physiotherapy, although subsequent surgery for implant removal might be necessary.

Scaphoid Fracture: Functional Outcome Following Fixation with Herbert Screw

Background Most scaphoid fractures though heal uneventfully with cast treatment, immobilization with cast is associated with complication like wrist stiffness. Open reduction and fixation with Herbert Screw though technically demanding procedure can yield excellent results and prevents complication like nonunions and loss of wrist function. Objectives To assess clinical outcome and radiological union of scaphoid fracture after operative management following Herbert screw fixation in patient attending Dhulikhel Hospital. Methods All scaphoid fracture, treated from Feb 2007 till Feb 2011, were retrospectively studied in Dhulikhel Hospital, Kathmandu University Hospital. Fifteen patients with scaphoid fractures were treated with Herbert screw. Fourteen were males and one was female. Serial radiographs were taken to assess radiographic union and functional outcome was assessed using Modified Mayo wrist score. Results Out of 15 patients, 13 scaphoid had waist fractures and two had proximal pole factures. All scaphoid were treated with open reduction and Herbert screw fixation either by volar approach or by dorsal approach. All fractures maintained good alignment post operatively. Nine (60%) patients had excellent results with normal wrist range of motion, five (33.3%) patients had good results and one (6.7%) patient had poor outcome. In 14 (93.3%) patients good radiological union was seen at final follow up at six months time. Conclusion Fixation with Herbert screw for scaphoid fracture is an effective and convenient way of treatment with satisfactory functional outcome and less complication.DOI: http://dx.doi.org/10.3126/kumj.v9i4.6342 Kathmandu Univ Med J 2011;9(4):267-73

Intramedullary nailing for paediatric diaphyseal forearm bone fracture

BACKGROUND

Though most of the pediatric diaphyseal forearm bone fracture can be treated with closed reduction and cast application, indications for operative intervention in pediatric both-bone forearm fractures include open fractures, irreducible fractures, and unstable fractures. Controversy exists as to what amount of angulation, displacement, and rotation constitutes an acceptable reduction.

OBJECTIVE

To review union time and functional outcome of pediatric diaphyseal forearm bone fracture managed with intramedullary rush pin by closed or open reduction.

METHODS

Fifty patients with both bone fracture of forearm were treated with intramedullary rush pin by closed or open reduction were included in the study and followed up for minimum six months for radiological and functional outcome.

RESULTS

Out of 50 patients, 31 underwent closed reduction and 19 underwent open reduction. All fractures maintained good alignment post operatively. Forty seven patients had excellent results with normal elbow range of motion and normal forearm rotation and three patients had good results. In all patients good radiological union was seen in three months time. Eight patients had minor complications including skin irritation over prominent hardware, backing out of ulnar pin, superficial skin break down with exposed hardware. Twenty-three (46%) patients had undergone implant removal at an average of 6 months (range 4-8 months) under regional or general anesthesia.

CONCLUSION

Fixation with intramedullary rush pin for forearm fracture is an effective, simple, cheap, and convenient way for treatment in pediatric age group.