Epidemiological characteristics and drug resistance analysis of multidrug-resistant Acinetobacter baumannii in a China hospital at a certain time

Multidrug-resistant Acinetobacter baumannii is an important bacterium causing nosocomial infections; A. baumannii infections have increased in our hospital since 2009. However, multidrug-resistant A. baumannii, which was mainly isolated from patients in each intensive care unit (ICU), rapidly increased from December 2012 to January 2013. Therefore, we described the molecular characteristics of A. baumannii by pulsed-field gel electrophoresis (PFGE). We also detected resistance genes for β-lactam, aminoglycosides, and plasmid-mediated quinolones. Disinfectant-resistant genes were also detected in the clinical isolates of blaOXA-51-positive multidrug-resistant A. baumannii. The conjugative test was performed to detect whether or not resistance genes can be transferred to different strains. Carbonyl cyanide m-chlorophenylhydrazone (CCCP) inhibition test was conducted to analyze the factors influencing the resistance of A. baumannii to imipenem, meropenem, ceftazidime, levofloxacin, and tigecycline. PFGE profiles contained 12 strains, including 20 type C strains (47.6%), 4 type D strains (9.5%), and 1 to 3 strains of other types; 38 strains were distributed in patients in each ICU. In our test samples, the presence of blaOXA-23 was closely related to carbapenem resistance. The 16S rRNA methylase gene armA was associated with resistance to amikacin, gentamicin, and tobramycin. The multidrug-resistant A. baumannii was closely related to various resistance genes. These results indicated that multidrug-resistant A. baumannii with type C strains was predominant in our hospital in this period.

Avoidable antibiotic exposure for uncomplicated skin and soft tissue infections in the ambulatory care setting

BACKGROUND

Uncomplicated skin and soft tissue infections are among the most frequent indications for outpatient antibiotics. A detailed understanding of current prescribing practices is necessary to optimize antibiotic use for these conditions.

METHODS

This was a retrospective cohort study of children and adults treated in the ambulatory care setting for uncomplicated cellulitis, wound infection, or cutaneous abscess between March 1, 2010 and February 28, 2011. We assessed the frequency of avoidable antibiotic exposure, defined as the use of antibiotics with broad gram-negative activity, combination antibiotic therapy, or treatment for 10 or more days. Total antibiotic-days prescribed for the cohort were compared with antibiotic-days in 4 hypothetical short-course (5-7 days), single-antibiotic treatment models consistent with national guidelines.

RESULTS

A total of 364 cases were included for analysis (155 cellulitis, 41 wound infection, and 168 abscess). Antibiotics active against methicillin-resistant Staphylococcus aureus were prescribed in 61% of cases of cellulitis. Of 139 cases of abscess where drainage was performed, antibiotics were prescribed in 80% for a median of 10 (interquartile range, 7-10) days. Of 292 total cases where complete prescribing data were available, avoidable antibiotic exposure occurred in 46%. This included use of antibiotics with broad gram-negative activity in 4%, combination therapy in 12%, and treatment for 10 or more days in 42%. Use of the short-course, single-antibiotic treatment strategies would have reduced prescribed antibiotic-days by 19% to 55%.

CONCLUSIONS

Approximately half of uncomplicated skin infections involved avoidable antibiotic exposure. Antibiotic use could be reduced through treatment approaches using short courses of a single antibiotic.

A treatment plant receiving waste water from multiple bulk drug manufacturers is a reservoir for highly multi-drug resistant integron-bearing bacteria

The arenas and detailed mechanisms for transfer of antibiotic resistance genes between environmental bacteria and pathogens are largely unclear. Selection pressures from antibiotics in situations where environmental bacteria and human pathogens meet are expected to increase the risks for such gene transfer events. We hypothesize that waste-water treatment plants (WWTPs) serving antibiotic manufacturing industries may provide such spawning grounds, given the high bacterial densities present there together with exceptionally strong and persistent selection pressures from the antibiotic-contaminated waste. Previous analyses of effluent from an Indian industrial WWTP that processes waste from bulk drug production revealed the presence of a range of drugs, including broad spectrum antibiotics at extremely high concentrations (mg/L range). In this study, we have characterized the antibiotic resistance profiles of 93 bacterial strains sampled at different stages of the treatment process from the WWTP against 39 antibiotics belonging to 12 different classes. A large majority (86%) of the strains were resistant to 20 or more antibiotics. Although there were no classically-recognized human pathogens among the 93 isolated strains, opportunistic pathogens such as Ochrobactrum intermedium, Providencia rettgeri, vancomycin resistant Enterococci (VRE), Aerococcus sp. and Citrobacter freundii were found to be highly resistant. One of the O. intermedium strains (ER1) was resistant to 36 antibiotics, while P. rettgeri (OSR3) was resistant to 35 antibiotics. Class 1 and 2 integrons were detected in 74/93 (80%) strains each, and 88/93 (95%) strains harbored at least one type of integron. The qPCR analysis of community DNA also showed an unprecedented high prevalence of integrons, suggesting that the bacteria living under such high selective pressure have an appreciable potential for genetic exchange of resistance genes via mobile gene cassettes. The present study provides insight into the mechanisms behind and the extent of multi-drug resistance among bacteria living under an extreme antibiotic selection pressure.

Mechanism of action-based classification of antibiotics using high-content bacterial image analysis

Image-based screening has become a mature field over the past decade, largely due to the detailed information that can be obtained about compound mode of action by considering the phenotypic effects of test compounds on cellular morphology. However, very few examples exist of extensions of this approach to bacterial targets. We now report the first high-throughput, high-content platform for the prediction of antibiotic modes of action using image-based screening. This approach employs a unique feature segmentation and extraction protocol to quantify key size and shape metrics of bacterial cells over a range of compound concentrations, and matches the trajectories of these metrics to those of training set compounds of known molecular target to predict the test compound's mode of action. This approach has been used to successfully predict the modes of action of a panel of known antibiotics, and has been extended to the evaluation of natural products libraries for the de novo prediction of compound function directly from primary screening data.

A docking-based receptor library of antibiotics and its novel application in predicting chronic mixture toxicity for environmental risk assessment

As organisms are typically exposed to chemical mixtures over long periods of time, chronic mixture toxicity is the best way to perform an environmental risk assessment (ERA). However, it is difficult to obtain the chronic mixture toxicity data due to the high expense and the complexity of the data acquisition method. Therefore, an approach was proposed in this study to predict chronic mixture toxicity. The acute (15 min exposure) and chronic (24 h exposure) toxicity of eight antibiotics and trimethoprim to Vibrio fischeri were determined in both single and binary mixtures. The results indicated that the risk quotients (RQs) of antibiotics should be based on the chronic mixture toxicity. To predict the chronic mixture toxicity, a docking-based receptor library of antibiotics and the receptor-library-based quantitative structure-activity relationship (QSAR) model were developed. Application of the developed QSAR model to the ERA of antibiotic mixtures demonstrated that there was a close affinity between RQs based on the observed chronic toxicity and the corresponding RQs based on the predicted data. The average coefficients of variations were 46.26 and 34.93 % and the determination coefficients (R (2)) were 0.999 and 0.998 for the low concentration group and the high concentration group, respectively. This result convinced us that the receptor library would be a promising tool for predicting the chronic mixture toxicity of antibiotics and that it can be further applied in ERA.

Antibiotic resistance determinants of multidrug-resistant Acinetobacter baumannii clinical isolates in Algeria

Antibiotic susceptibility testing was performed on 71 Acinetobacter baumannii clinical isolates, and presence of antibiotic resistance genes was screened for by PCR amplification and sequencing. Resistance rates were very high for aminoglycosides (22-80%), fluoroquinolones (>90%), and cephalosporins (>90%) but remained low for rifampin (2.8%) or null for colistin. Antibiotic resistance encoding genes detected were as follows: blaTEM-128 gene (74.6%), aph(3')-VI (50.7 %), aadA (63.4%), ant(2″)-I (14.1%), aac(3)-Ia (91.1%), aac(6')-Ib (4.2%), mutation Ser83Leu in gyrA (94.4%), double mutations Ser83Leu and Ser80Leu (or Ser84Leu) in gyrA and parC (69.0%), and mutation I581N in RRDR of the rpoB gene.

Benzene, coumarin and quinolinone derivatives from roots of Citrus hystrix

Two coumarins, hystrixarin (1) and (+)-hopeyhopin (2); a benzenoid derivative, hystroxene-I (3) and a quinolinone alkaloid, hystrolinone (4), along with 33 known compounds were isolated from the crude acetone extract of the roots of Citrus hystrix. Their structures were determined by analysis of 1D and 2D NMR spectroscopic data. The antioxidant, anti-HIV and antibacterial activities of the isolated compounds were also evaluated.

Structures and properties of naturally occurring polyether antibiotics

Polyether ionophores represent a large group of natural, biologically active substances produced by Streptomyces spp. They are lipid soluble and able to transport metal cations across cell membranes. Several of polyether ionophores are widely used as growth promoters in veterinary. Polyether antibiotics show a broad spectrum of bioactivity ranging from antibacterial, antifungal, antiparasitic, antiviral, and tumour cell cytotoxicity. Recently, it has been shown that some of these compounds are able to selectively kill cancer stem cells and multidrug-resistant cancer cells. Thus, they are recognized as new potential anticancer drugs. The biological activity of polyether ionophores is strictly connected with their molecular structure; therefore, the purpose of this paper is to present an overview of their formula, molecular structure, and properties.

[The problem of growing resistance of microorganisms to antibiotic therapy and prospects for Helicobacter pylori eradication]

The problem of growing resistance of microorganisms to antibiotic therapy acquires increasingly greater significance as threatening the loss of endosymbiotic bacteria. The causes, mechanisms, and consequences of this phenomenon are considered. Several groups of modern antibiotic drugs are characterized along with the methods for improving their efficacy and preventing side effects. The schemes for Helicobacter pylori eradication as recommended by the Maastricht consensus are discussed in conjunction with major mistakes accounting for marked reduction of their effectiveness. Terminological issues are briefly considered.

Antimicrobial drugs

Antibiotics play a vital role in dental practice for managing orofacial infections. They are used to manage existing infection and they are also used as prophylaxis for certain medical conditions and surgical procedures. This article will review pharmacological and therapeutic considerations for the proper use of these agents for dental infections.

Class IIa bacteriocins: diversity and new developments

Class IIa bacteriocins are heat-stable, unmodified peptides with a conserved amino acids sequence YGNGV on their N-terminal domains, and have received much attention due to their generally recognized as safe (GRAS) status, their high biological activity, and their excellent heat stability. They are promising and attractive agents that could function as biopreservatives in the food industry. This review summarizes the new developments in the area of class IIa bacteriocins and aims to provide uptodate information that can be used in designing future research.

Antibacterial activity in adhesive dentistry: a literature review

This literature review summarizes the published research regarding the antibacterial agents used in adhesive dentistry. This article provides information about the clinical applications, beneficial effects, and possible disadvantages of antibacterials when used in various bonding situations.

Metallo-beta-lactamase producing gram-negative bacterial isolates

BACKGROUND

The global emergence of metallo-β-lactamase (MBL) producing bacterial isolates causing lower respiratory tract infection (LRTI) has resulted in fewer therapeutic options in treatment modalities. However, to our knowledge no studies regarding MBLs had been done so far in Nepal. Therefore, this study was carried out to assess the current level of MBL producing bacterial isolates in our setup.

METHODS

This was a cross-sectional study conducted over a period of six months (June to November 2008) at Bacteriology laboratory of a teaching hospital. A total of 1120 specimens representing lower respiratory tract (sputum, endotracheal secretion and bronchial washing) were processed from outpatients and inpatients, with suspected LRTI, at TUTH. The specimens were collected and processed according to the standard methodology. Combination disk method and Double disk synergy test methods were used for the detection of MBL producing isolates.

RESULTS

Respiratory pathogens were recovered from 497 (44.4%) of suspected cases. Among these, gram-negative bacteria were observed in 448 (84.0%). Multidrug resistance (MDR) was found in 286 (53.7%) of the total bacterial isolates. MBL was present in 6 (1.3%) of the total 448 gram-negative isolates. MBL was detected by both DDST and CD methods in 3 isolates each of Pseudomonas aeruginosa and Acinetobacter spp. from inpatients. All MBL producers were MDR.

CONCLUSIONS

MBL-producing gram negative bacteria were detected from LRTI isolates in this study and this data can be used as base-line information of this novel type of β-lactamase in our setup.

Antimicrobial susceptibility patterns of Salmonella typhi and Salmonella paratyphi A in a tertiary care hospital

BACKGROUND

Enteric fever is still an important public health problem in developing countries including Nepal. A changing antibiotic susceptibility pattern of Salmonella typhi and Salmonella paratyphi A and emergence of multi drug resistance has increased to a great concern. Aim of the study was to investigate the antibiotic susceptibility pattern of Salmonella typhi and Salmonella paratyphi A.

METHODS

Study was carried out at the department of microbiology in Kathmandu Medical College. Blood culture samples were collected from suspected enteric fever patient and tested microbiologically by standard procedure. Antibiotic susceptibility test was performed by Kirby-Bauer disc diffusion method and results were interpreted by National Committee for Clinical Laboratory (NCCLS) guideline.

RESULTS

Of total 78 (2.0%) Salmonella serotype isolated from 3,980 blood culture samples, in which 47 (60.3%) were S. typhi and 31 (39.7%) were S. paratyphi A. Isolates were from all age group median age being the 25 years. Among the tested antibiotics S. typhi was susceptible towards Ciprofloxacin (100%) followed by Gentamicin (97.9%), Ofloxacine (95.7%), Ceftriaxone (95.7%) and Chloramphenicol (93.6%). In case of S. paratyphi A most of the tested antibiotics showed high percentage of susceptibility and least susceptible antibiotic for S. paratyphi A was Ampicillin (25.8%). Three isolates of S. typhi showed multidrug resistance.

CONCLUSIONS

A considerable variation was observed in the antimicrobial susceptibility pattern of S.typhi and S. paratyphi A. Hence antibiotic susceptibility test must be sought before instituting appropriate therapy to prevent from further emergence of drug resistance.

A bacterial reporter panel for the detection and classification of antibiotic substances

The ever-growing use of pharmaceutical compounds, including antibacterial substances, poses a substantial pollution load on the environment. Such compounds can compromise water quality, contaminate soils, livestock and crops, enhance resistance of microorganisms to antibiotic substances, and hamper human health. We report the construction of a novel panel of genetically engineered Escherichia coli reporter strains for the detection and classification of antibiotic substances. Each of these strains harbours a plasmid that carries a fusion of a selected gene promoter to bioluminescence (luxCDABE) reporter genes and an alternative tryptophan auxotrophy-based non-antibiotic selection system. The bioreporter panel was tested for sensitivity and responsiveness to diverse antibiotic substances by monitoring bioluminescence as a function of time and of antibiotic concentrations. All of the tested antibiotics were detected by the panel, which displayed different response patterns for each substance. These unique responses were analysed by several algorithms that enabled clustering the compounds according to their functional properties, and allowed the classification of unknown antibiotic substances with a high degree of accuracy and confidence.