Antibiotic resistance in the absence of selective pressure

ESBL Displace: A Protocol for an Observational Study to Identify Displacing Escherichia coli Strain Candidates from ESBL-Colonized Travel Returners Using Phenotypic, Genomic Sequencing and Metagenome Analysis

Introduction: Invading extended-spectrum beta-lactamase-producing Escherichia coli (ESBL-PE), non-ESBL E. coli, and other bacteria form a complex environment in the gut. The duration and dynamics of ESBL-PE colonization varies among individuals. Understanding the factors associated with colonization may lead to decolonization strategies. In this study, we aim to identify (i) single E. coli strains and (ii) microbiome networks that correlate with retention or decline of colonization, and (iii) pan-sensitive E. coli strains that potentially could be used to displace ESBL-PE during colonization. Methods and analysis: We recruit healthy travellers to Southeast Asia for a one-year prospective observational follow-up study. We collect and biobank stool, serum, and peripheral blood mononuclear cells (PBMCs) at predefined timepoints. Additional information is collected with questionnaires. We determine the colonization status with ESBL-PE and non-ESBL E. coli and quantify cell densities in stools and ratios over time. We characterize multiple single bacterial isolates per patient and timepoint using whole genome sequencing (WGS) and 16S/ITS amplicon-based and shotgun metagenomics. We determine phylogenetic relationships between isolates, antimicrobial resistance (AMR; phenotypic and genotypic), and virulence genes. We describe the bacterial and fungal stool microbiome alpha and beta diversity on 16S/ITS metagenomic data. We describe patterns in microbiome dynamics to identify features associated with protection or risk of ESBL-PE colonization. Ethics and dissemination: The study is registered (clinicaltrials.gov; NCT04764500 on 09/02/2019) and approved by the Ethics Committee (EKNZ project ID 2019-00044). We will present anonymized results at conferences and in scientific journals. Bacterial sequencing data will be shared via publicly accessible databases according to FAIR principles.

Growth kinetics and fitness of fluoroquinolone resistant and susceptible Campylobacter jejuni strains of cattle origin

Human enterocolitis is frequently caused by the Gram-negative microaerobic bacterium Campylobacter jejuni. Macrolides (e.g., erythromycin) and fluoroquinolones (FQs) (e.g., ciprofloxacin) are the preferred antibiotics for the treatment of human campylobacteriosis. Rapid emergence of FQ-resistant (FQ-R) Campylobacter during treatment with FQ antimicrobials is well known to occur in poultry. Cattle is also an important reservoir of Campylobacter for humans, and FQ-R Campylobacter from cattle has become highly prevalent in recent years. Even though the selection pressure may have contributed to the expansion of FQ-R Campylobacter, the actual impact of this factor appears to be rather low. In this study, we examined the hypothesis that the fitness of FQ-R Campylobacter may have also played a role in the rise seen in FQ-R Campylobacter isolates by employing a series of in vitro experiments in MH broth and bovine fecal extract. First, it was shown that FQ-R and FQ-susceptible (FQ-S) C. jejuni strains of cattle origin had comparable growth rates when individually cultured in both MH broth and the fecal extract with no antibiotic present. Interestingly, FQ-R strains had small but statistically significant increases over FQ-S strains in growth in competition experiments performed in mixed cultures with no antibiotic present. Lastly, it was observed that FQ-S C. jejuni strains developed resistance to ciprofloxacin more readily at high initial bacterial cell density (10⁷ CFU/mL) and when exposed to low levels of the antibiotic (2-4 μg/mL) compared with that at a low level of initial bacterial cell density (10⁵ CFU/mL) and exposure to a high level of ciprofloxacin (20 μg/mL) in both MH broth and the fecal extract. Altogether, these findings indicate that even though FQ-R C. jejuni of cattle origin may have a slightly higher fitness advantage over the FQ-S population, the emergence of FQ-R mutants from susceptible strains is primarily dictated by the bacterial cell density and the antibiotic concentration exposed under in vitro condition. These observation may also provide plausible explanations for the high prevalence of FQ-R C. jejuni in cattle production due to its overall fit nature in the absence of antibiotic selection pressure and for the paucity of development of FQ-R C. jejuni in the cattle intestine in response to FQ-treatment, as observed in our recent studies.

Heavy metal-induced selection and proliferation of antibiotic resistance: A review

Antibiotic resistance is recognized as a global threat to public health. The selection and evolution of antibiotic resistance in clinical pathogens was believed to be majorly driven by the imprudent use of antibiotics. However, concerns regarding the same, through selection pressure by a multitude of other antimicrobial agents, such as heavy metals, are also growing. Heavy metal contamination co-selects antibiotic and metal resistance through numerous mechanisms, such as co-resistance and cross-resistance. Here, we have reviewed the role of heavy metals as antimicrobial resistance driving agents and the underlying concept and mechanisms of co-selection, while also highlighting the scarcity in studies explicitly inspecting the process of co-selection in clinical settings. Prospective strategies to manage heavy metal-induced antibiotic resistance have also been deliberated, underlining the need to find specific inhibitors so that alternate medicinal combinations can be added to the existing therapeutic armamentarium.

Shotgun metagenomics reveals a heterogeneous prokaryotic community and a wide array of antibiotic resistance genes in mangrove sediment

Saline tolerant mangrove forests partake in vital biogeochemical cycles. However, they are endangered due to deforestation as a result of urbanization. In this study, we have carried out a metagenomic snapshot of the mangrove ecosystem from five countries to assess its taxonomic, functional and antibiotic resistome structure. Chao1 alpha diversity varied significantly (P < 0.001) between the countries (Brazil, Saudi Arabia, China, India and Malaysia). All datasets were composed of 33 phyla dominated by eight major phyla covering >90% relative abundance. Comparative analysis of mangrove with terrestrial and marine ecosystems revealed the strongest heterogeneity in the mangrove microbial community. We also observed that the mangrove community shared similarities to both the terrestrial and marine microbiome, forming a link between the two contrasting ecosystems. The antibiotic resistant genes (ARG) resistome was comprised of nineteen level 3 classifications dominated by multidrug resistance efflux pumps (46.7 ± 4.3%) and BlaR1 family regulatory sensor-transducer disambiguation (25.2 ± 4.8%). ARG relative abundance was significantly higher in Asian countries and in human intervention datasets at a global scale. Our study shows that the mangrove microbial community and its antibiotic resistance are affected by geography as well as human intervention and are unique to the mangrove ecosystem. Understanding changes in the mangrove microbiome and its ARG is significant for sustainable development and public health.

Knowledge, Attitudes, and Practices of Antimicrobial Uses and Resistance Among Public University Students in Bangladesh

Background

Antibiotics are lifesaving drugs, and inappropriate uses lead to the resistance that renders them ineffective. This study aims to understand knowledge, attitude, and practice (KAP) concerning antibiotic use and resistance among university students in Bangladesh.

Methods

A cross-sectional study was performed from January to April 2020 among students at Jahangirnagar University (JU), Bangladesh. Purposive sampling was conducted through an in-person interview using a structured questionnaire. Students from the faculties of biological sciences and non-biology background were included. The univariate ordinal regression technique was used to analyze the relationship between predictors and good knowledge about the antibiotics. A two-tailed p-value was calculated to determine statistical association.

Results

Out of 205 study participants, 92 and 113 responders were from biological science faculty and non-biology disciplines, respectively. Less than half of the students (42.4%) showed a good knowledge level (scores higher than 80%). Biology-background students possess better knowledge than non-biology students [odds ratio (OR) = 4.44, 95% confidence level (CL) (2.56, 7.70), p < 0.001]. A better attitude was noticed among all students. The self-medication rate was quite low, and more than 90% of students were found to consume antibiotics according to the physician’s prescription. Lack of treatment adherence was recorded, and students admitted to stop-taking antibiotics when symptoms disappeared (48.67% biology and 36.26% non-biology). Multivariate regression analysis was unable to detect any significant association between self-medication and gender, student category or the level of knowledge about antibiotics.

Conclusion

Students of biological science background possessed better knowledge indicating the importance of appropriate curriculum imparted in knowledge buildup. Introducing a short course about the risk and development of antibiotic resistance will grow the students’ awareness to avoid the resistance phenomenon.

Evolution of drug-resistant and virulent small colonies in phenotypically diverse populations of the human fungal pathogen Candida glabrata

Antimicrobial resistance frequently carries a fitness cost to a pathogen, measured as a reduction in growth rate compared to the sensitive wild-type, in the absence of antibiotics. Existing empirical evidence points to the following relationship between cost of resistance and virulence. If a resistant pathogen suffers a fitness cost in terms of reduced growth rate it commonly has lower virulence compared to the sensitive wild-type. If this cost is absent so is the reduction in virulence. Here we show, using experimental evolution of drug resistance in the fungal human pathogen Candida glabrata, that reduced growth rate of resistant strains need not result in reduced virulence. Phenotypically heterogeneous populations were evolved in parallel containing highly resistant sub-population small colony variants (SCVs) alongside sensitive sub-populations. Despite their low growth rate in the absence of an antifungal drug, the SCVs did not suffer a marked alteration in virulence compared with the wild-type ancestral strain, or their co-isolated sensitive strains. This contrasts with classical theory that assumes growth rate to positively correlate with virulence. Our work thus highlights the complexity of the relationship between resistance, basic life-history traits and virulence.

Antibiotic Resistant Pseudomonas Spp. Spoilers in Fresh Dairy Products: An Underestimated Risk and the Control Strategies

Microbial multidrug resistance (MDR) is a growing threat to public health mostly because it makes the fight against microorganisms that cause lethal infections ever less effective. Thus, the surveillance on MDR microorganisms has recently been strengthened, taking into account the control of antibiotic abuse as well as the mechanisms underlying the transfer of antibiotic genes (ARGs) among microbiota naturally occurring in the environment. Indeed, ARGs are not only confined to pathogenic bacteria, whose diffusion in the clinical field has aroused serious concerns, but are widespread in saprophytic bacterial communities such as those dominating the food industry. In particular, fresh dairy products can be considered a reservoir of Pseudomonas spp. resistome, potentially transmittable to consumers. Milk and fresh dairy cheeses products represent one of a few "hubs" where commensal or opportunistic pseudomonads frequently cohabit together with food microbiota and hazard pathogens even across their manufacturing processes. Pseudomonas spp., widely studied for food spoilage effects, are instead underestimated for their possible impact on human health. Recent evidences have highlighted that non-pathogenic pseudomonads strains (P. fluorescens, P. putida) are associated with some human diseases, but are still poorly considered in comparison to the pathogen P. aeruginosa. In addition, the presence of ARGs, that can be acquired and transmitted by horizontal genetic transfer, further increases their risk and the need to be deeper investigated. Therefore, this review, starting from the general aspects related to the physiological traits of these spoilage microorganisms from fresh dairy products, aims to shed light on the resistome of cheese-related pseudomonads and their genomic background, current methods and advances in the prediction tools for MDR detection based on genomic sequences, possible implications for human health, and the affordable strategies to counteract MDR spread.

Antibiotic resistant bacteria and commensal fungi are common and conserved in the mosquito microbiome

The emerging and increasing prevalence of bacterial antibiotic resistance is a significant public health challenge. To begin to tackle this problem, it will be critical to not only understand the origins of this resistance but also document environmental reservoirs of antibiotic resistance. In this study we investigated the possibility that both colony and field caught mosquitoes could harbor antibiotic resistant bacteria. Specifically, we characterized the antibiotic resistant bacterial populations from colony-reared Aedes aegypti larvae and adults and two field caught mosquito species Coquillettidia perturbans and Ochlerotatus canadensis. The cultured bacterial populations were dominated by isolates belonging to the class Gammaproteobacteria. Among the antibiotic resistant populations, we found bacteria resistant to carbenicillin, kanamycin, and tetracycline, including bacteria resistant to a cocktail of all three antibiotics in combination. The antibiotic resistant bacteria were numerically rare, at most 5% of total cell counts. Isolates were characterized by 16S rRNA gene sequencing, and clustering into Operational Taxonomic Units (OTUs; 99% sequence identity). 27 antibiotic resistant OTUs were identified, although members of an OTU did not always share the same resistance profile. This suggests the clustering was either not sensitive enough to distinguish different bacteria taxa or different antibiotic resistant sub-populations exist within an OTU. Finally, the antibiotic selection opened up a niche to culture mosquito-associated fungi, and 10 fungal OTUs (28S rRNA gene sequencing) were identified. Two fungal OTUs both classified to the class Microbotryomycetes were commonly identified in the field-caught mosquitoes. Thus, in this study we demonstrate that antibiotic resistant bacteria and certain fungi are common and conserved mosquito microbiome members. These observations highlight the potential of invertebrates to serve as vehicles for the spread of antibiotic resistance throughout the environment.

Genetics and roadblocks of drug resistant tuberculosis

Considering the extensive evolutionary history of Mycobacterium tuberculosis, anti-Tuberculosis (TB) drug therapy exerts a recent selective pressure. However, in a microorganism devoid of horizontal gene transfer and with a strictly clonal populational structure such as M. tuberculosis the usual, but not sole, path to overcome drug susceptibility is through de novo mutations on a relatively strict set of genes. The possible allelic diversity that can be associated with drug resistance through several mechanisms such as target alteration or target overexpression, will dictate how these genes can become associated with drug resistance. The success demonstrated by this pathogenic microbe in this latter process and its ability to spread is currently one of the major obstacles to an effective TB elimination. This article reviews the action mechanism of the more important anti-TB drugs, including bedaquiline and delamanid, along with new findings on specific resistance mechanisms. With the development, validation and endorsement of new in vitro molecular tests for drug resistance, knowledge on these resistance mechanisms and microevolutionary dynamics leading to the emergence and fixation of drug resistance mutations within the host is highly important. Additionally, the fitness toll imposed by resistance development is also herein discussed together with known compensatory mechanisms. By elucidating the possible mechanisms that enable one strain to reacquire the original fitness levels, it will be theoretically possible to make more informed decisions and develop novel strategies that can force M. tuberculosis microevolutionary trajectory down through a path of decreasing fitness levels.

Mycobacterium tuberculosis Subculture Results in Loss of Potentially Clinically Relevant Heteroresistance

Multidrug-resistant tuberculosis (TB) presents a major public health dilemma. Heteroresistance, the coexistence of drug-resistant and drug-susceptible strains or of multiple drug-resistant strains with discrete haplotypes, may affect accurate diagnosis and the institution of effective treatment. Subculture, or passage of cells onto fresh growth medium, is utilized to preserve Mycobacterium tuberculosis cell lines and is universally employed in TB diagnostics. The impact of such passages, typically performed in the absence of drug, on drug-resistant subpopulations is hypothesized to vary according to the competitive costs of genotypic resistance-associated variants. We applied ultradeep next-generation sequencing to 61 phenotypically rifampin-monoresistant (n = 17) and preextensively (n = 41) and extensively (n = 3) drug-resistant isolates with presumptive heteroresistance at two time points in serial subculture. We found significant dynamic loss of minor-variant resistant subpopulations across all analyzed resistance-determining regions, including eight isolates (13%) whose antibiogram data would have transitioned from resistant to susceptible for at least one drug through subculture. Surprisingly, some resistance-associated variants appeared to be selected for in subculture.

Use of phenotype microarrays to study the effect of acquisition of resistance to antimicrobials in bacterial physiology

It is widely accepted that the acquisition of resistance to antimicrobials confers a fitness cost. Different works have shown that the effect of acquiring resistance in bacterial physiology may be more specific than previously thought. Study of these specific changes may help to predict the outcome of resistant organisms in different ecosystems. In addition to changing bacterial physiology, acquisition of resistance either increases or reduces susceptibility to other antimicrobials. In the current article, we review recent information on the effect of acquiring resistance upon bacterial physiology, with a specific focus on studies using phenotype microarray technology.

The Beneficial Effect of Equisetum giganteum L. against Candida Biofilm Formation: New Approaches to Denture Stomatitis

Equisetum giganteum L. (E. giganteum), Equisetaceae, commonly called “giant horsetail,” is an endemic plant of Central and South America and is used in traditional medicine as diuretic and hemostatic in urinary disorders and in inflammatory conditions among other applications. The chemical composition of the extract EtOH 70% of E. giganteum has shown a clear presence of phenolic compounds derived from caffeic and ferulic acids and flavonoid heterosides derived from quercitin and kaempferol, in addition to styrylpyrones. E. giganteum, mainly at the highest concentrations, showed antimicrobial activity against the relevant microorganisms tested: Escherichia coli, Staphylococcus aureus, and Candida albicans. It also demonstrated antiadherent activity on C. albicans biofilms in an experimental model that is similar to dentures. Moreover, all concentrations tested showed anti-inflammatory activity. The extract did not show cytotoxicity in contact with human cells. These properties might qualify E. giganteum extract to be a promising alternative for the topic treatment and prevention of oral candidiasis and denture stomatitis.

Effects of in-feed copper and tylosin supplementations on copper and antimicrobial resistance in faecal enterococci of feedlot cattle

AIMS

The objective was to investigate whether in-feed supplementation of copper, at elevated level, co-selects for macrolide resistance in faecal enterococci.

METHODS AND RESULTS

The study was conducted in cattle (n = 80) with a 2 × 2 factorial design of copper (10 or 100 mg kg(-1) of feed) and tylosin (0 or 10 mg kg(-1) of feed). Thirty-seven isolates (4·6%; 37/800) of faecal enterococci were positive for the tcrB and all were Enterococcus faecium. The prevalence was higher among cattle fed diets with copper and tylosin (8·5%) compared to control (2·0%), copper (4·5%) and tylosin (3·5%) alone. All tcrB-positive isolates were positive for erm(B) and tet(M) genes. Median copper minimum inhibitory concentrations (MICs) for tcrB-positive and tcrB-negative enterococci were 20 and 4 mmol l(-1) , respectively.

CONCLUSIONS

Feeding of elevated dietary copper and tylosin alone or in combination resulted in an increased prevalence of tcrB and erm(B)-mediated copper and tylosin-resistant faecal enterococci in feedlot cattle.

SIGNIFICANCE AND IMPACT OF THE STUDY

In-feed supplementation of elevated dietary copper has the potential to co-select for macrolide resistance. Further studies are warranted to investigate the factors involved in maintenance and dissemination of the resistance determinants and their co-selection mechanism in relation to feed-grade antimicrobials' usage in feedlot cattle.

Rational design of antibiotic treatment plans: a treatment strategy for managing evolution and reversing resistance

The development of reliable methods for restoring susceptibility after antibiotic resistance arises has proven elusive. A greater understanding of the relationship between antibiotic administration and the evolution of resistance is key to overcoming this challenge. Here we present a data-driven mathematical approach for developing antibiotic treatment plans that can reverse the evolution of antibiotic resistance determinants. We have generated adaptive landscapes for 16 genotypes of the TEM β-lactamase that vary from the wild type genotype “TEM-1” through all combinations of four amino acid substitutions. We determined the growth rate of each genotype when treated with each of 15 β-lactam antibiotics. By using growth rates as a measure of fitness, we computed the probability of each amino acid substitution in each β-lactam treatment using two different models named the Correlated Probability Model (CPM) and the Equal Probability Model (EPM). We then performed an exhaustive search through the 15 treatments for substitution paths leading from each of the 16 genotypes back to the wild type TEM-1. We identified optimized treatment paths that returned the highest probabilities of selecting for reversions of amino acid substitutions and returning TEM to the wild type state. For the CPM model, the optimized probabilities ranged between 0.6 and 1.0. For the EPM model, the optimized probabilities ranged between 0.38 and 1.0. For cyclical CPM treatment plans in which the starting and ending genotype was the wild type, the probabilities were between 0.62 and 0.7. Overall this study shows that there is promise for reversing the evolution of resistance through antibiotic treatment plans.

Antimicrobial resistance: a global view from the 2013 World Healthcare-Associated Infections Forum

Antimicrobial resistance (AMR) is now a global threat. Its emergence rests on antimicrobial overuse in humans and food-producing animals; globalization and suboptimal infection control facilitate its spread. While aggressive measures in some countries have led to the containment of some resistant gram-positive organisms, extensively resistant gram-negative organisms such as carbapenem-resistant enterobacteriaceae and pan-resistant Acinetobacter spp. continue their rapid spread. Antimicrobial conservation/stewardship programs have seen some measure of success in reducing antimicrobial overuse in humans, but their reach is limited to acute-care settings in high-income countries. Outside the European Union, there is scant or no oversight of antimicrobial administration to food-producing animals, while evidence mounts that this administration leads directly to resistant human infections. Both horizontal and vertical infection control measures can interrupt transmission among humans, but many of these are costly and essentially limited to high-income countries as well. Novel antimicrobials are urgently needed; in recent decades pharmaceutical companies have largely abandoned antimicrobial discovery and development given their high costs and low yield. Against this backdrop, international and cross-disciplinary collaboration appears to be taking root in earnest, although specific strategies still need defining. Educational programs targeting both antimicrobial prescribers and consumers must be further developed and supported. The general public must continue to be made aware of the current scale of AMR's threat, and must perceive antimicrobials as they are: a non-renewable and endangered resource.

Fitness factors in vibrios: a mini-review

Vibrios are Gram-negative curved bacilli that occur naturally in marine, estuarine, and freshwater systems. Some species include human and animal pathogens, and some vibrios are necessary for natural systems, including the carbon cycle and osmoregulation. Countless in vivo and in vitro studies have examined the interactions between vibrios and their environment, including molecules, cells, whole animals, and abiotic substrates. Many studies have characterized virulence factors, attachment factors, regulatory factors, and antimicrobial resistance factors, and most of these factors impact the organism's fitness regardless of its external environment. This review aims to identify common attributes among factors that increase fitness in various environments, regardless of whether the environment is an oyster, a rabbit, a flask of immortalized mammalian cells, or a planktonic chitin particle. This review aims to summarize findings published thus far to encapsulate some of the basic similarities among the many vibrio fitness factors and how they frame our understanding of vibrio ecology. Factors representing these similarities include hemolysins, capsular polysaccharides, flagella, proteases, attachment factors, type III secretion systems, chitin binding proteins, iron acquisition systems, and colonization factors.

Antimicrobial resistance and virulence: a successful or deleterious association in the bacterial world?

Hosts and bacteria have coevolved over millions of years, during which pathogenic bacteria have modified their virulence mechanisms to adapt to host defense systems. Although the spread of pathogens has been hindered by the discovery and widespread use of antimicrobial agents, antimicrobial resistance has increased globally. The emergence of resistant bacteria has accelerated in recent years, mainly as a result of increased selective pressure. However, although antimicrobial resistance and bacterial virulence have developed on different timescales, they share some common characteristics. This review considers how bacterial virulence and fitness are affected by antibiotic resistance and also how the relationship between virulence and resistance is affected by different genetic mechanisms (e.g., coselection and compensatory mutations) and by the most prevalent global responses. The interplay between these factors and the associated biological costs depend on four main factors: the bacterial species involved, virulence and resistance mechanisms, the ecological niche, and the host. The development of new strategies involving new antimicrobials or nonantimicrobial compounds and of novel diagnostic methods that focus on high-risk clones and rapid tests to detect virulence markers may help to resolve the increasing problem of the association between virulence and resistance, which is becoming more beneficial for pathogenic bacteria.

In vitro activity of tigecycline against Acinetobacter baumannii isolates from a teaching hospital in Malaysia

The In vitro susceptibility of clinical and environmental isolates of Acinetobacter baumannii to tigecycline and other antibiotics was determined by disk diffusion method. The E-test was used to determine the minimum inhibitory concentration (MIC). The growth curves of tigecycline treated environmental and clinical strains were established. Fifty-seven percent and 75% of the clinical and environmental isolates were MDR strains, respectively. Ninety-five percent of the clinical isolates were susceptible to tigecycline and 5% showed intermediate resistance with MIC ranging between 0.032 and 3 mg/l. Tigecycline susceptible and intermediate resistance among the environmental isolates were 40% and 60%, respectively, with a significantly lower MIC range of 0.5-4 mg/l. The bacterial growth curves demonstrated the higher ability of the environmental strains to tolerate the antibiotic effects than the clinical strains. The relatively high resistance profile among the environmental isolate suggests an insidious emergence of tigecycline resistance amongst A. baumannii. Strict infection control procedures are imperative to prevent the dissemination of tigecycline-resistant A. baumannii strains in the hospital environment.

Low dose aerosol fitness at the innate phase of murine infection better predicts virulence amongst clinical strains of Mycobacterium tuberculosis

Background

Evaluation of a quick and easy model to determine the intrinsic ability of clinical strains to generate active TB has been set by assuming that this is linked to the fitness of Mycobacterium tuberculosis strain at the innate phase of the infection. Thus, the higher the bacillary load, the greater the possibility of inducting liquefaction, and thus active TB, once the adaptive response is set.

Methodology/Principal Findings

The virulence of seven clinical Mycobacterium tuberculosis strains isolated in Spain was tested by determining the bacillary concentration in the spleen and lung of mice at weeks 0, 1 and 2 after intravenous (IV) inoculation of 10⁴ CFU, and by determining the growth in vitro until the stationary phase had been reached. Cord distribution automated analysis showed two clear patterns related to the high and low fitness in the lung after IV infection. This pattern was not seen in the in vitro fitness tests, which clearly favored the reference strain (H37Rv). Subsequent determination using a more physiological low-dose aerosol (AER) inoculation with 10² CFU showed a third pattern in which the three best values coincided with the highest dissemination capacity according to epidemiological data.

Conclusions/Significance

The fitness obtained after low dose aerosol administration in the presence of the innate immune response is the most predictive factor for determining the virulence of clinical strains. This gives support to a mechanism of the induction of active TB derived from the dynamic hypothesis of latent tuberculosis infection.

Spontaneous emergence of multiple drug resistance in tuberculosis before and during therapy

The emergence of drug resistance in M. tuberculosis undermines the efficacy of tuberculosis (TB) treatment in individuals and of TB control programs in populations. Multiple drug resistance is often attributed to sequential functional monotherapy, and standard initial treatment regimens have therefore been designed to include simultaneous use of four different antibiotics. Despite the widespread use of combination therapy, highly resistant M. tb strains have emerged in many settings. Here we use a stochastic birth-death model to estimate the probability of the emergence of multidrug resistance during the growth of a population of initially drug sensitive TB bacilli within an infected host. We find that the probability of the emergence of resistance to the two principal anti-TB drugs before initiation of therapy ranges from 10⁻⁵ to 10⁻⁴; while rare, this is several orders of magnitude higher than previous estimates. This finding suggests that multidrug resistant M. tb may not be an entirely “man-made” phenomenon and may help explain how highly drug resistant forms of TB have independently emerged in many settings.

Protein-protein interaction networks suggest different targets have different propensities for triggering drug resistance

Emergence of drug resistance is a major problem in the treatment of many diseases including tuberculosis. To tackle the problem from a wholistic perspective, it is essential to understand the molecular mechanisms by which bacteria acquire drug resistance using a systems approach. Availability of genome-scale data of expression profiles under different drug exposed conditions and protein-protein interactions, makes it feasible to reconstruct and analyze systems-level models. A number of proteins involved in different resistance mechanisms, referred to as the resistome are identified from literature. The interaction of the drug directly with the resistome is unable to explain most resistance processes adequately, including that of increased mutations in the target's binding site. We recently hypothesized that some communication might exist from the drug environment to the resistome to trigger emergence of drug resistance. We report here a network based approach to identify most plausible paths of such communication in Mycobacterium tuberculosis. Networks capturing both structural and functional linkages among various proteins were weighted based on gene expression profiles upon exposure to specific drugs and betweenness centrality of the interactions. Our analysis suggests that different drug targets and hence different drugs could trigger the resistome to different extents and through different routes. The identified paths correlate well with the mechanisms known through experiment. Some examples of the top ranked hubs in multiple drug specific networks are PolA, FadD1, CydA, a monoxygenase and GltS, which could serve as co-targets, that could be inhibited in order to retard resistance related communication in the cell.

Effects of diet and Aspergillus oryzae extract or Saccharomyces cervisiae on growth and carcass characteristics of lambs and steers fed to meet requirements of natural markets

Two studies were conducted to determine the effects of diet and feed additive on growth and carcass characteristics of lambs and cattle destined for all natural markets. In Exp. 1, 48 Dorset × Hampshire lambs (initial BW 29.4 ± 0.1 kg) were used in a randomized complete block experiment to determine the effects of Aspergillus oryzae extract, Amaferm (AMF) supplementation (1 g/d) in an 85% concentrate diet on growth and carcass characteristics. Lambs were allotted to 12 pens (4 lambs per pen), and blocked by sex and BW. Lambs were fed until the average BW of each pen reached a target BW (55.4 kg for wethers and 50.0 kg for ewes), at which time the entire pen of lambs was slaughtered. Amaferm resulted in a greater (P=0.07) G:F. In Exp. 2, 168 crossbred steers (initial BW 300 ± 0.7 kg) were used in a trial with a 3 × 2 factorial arrangement of treatments to examine the effects of 0.5 g/d of Saccaromyces cervisiae boulardii CNCM 1079-Levucell SB (LEV), or 3 g/d of AMF with 2 corn sources, dry whole-shelled corn or high moisture corn, on growth and carcass characteristics. Neither LEV nor AMF improved (P>0.10) carcass characteristics compared with control or non-feed-supplemented steers. Addition of LEV to high-concentrate, corn-based diets did not improve (P>0.10) growth performance of feedlot steers. However, addition of AMF to a diet composed of dry whole-shelled corn resulted in an improvement (P<0.05) in G:F (0.208 vs. 0.194). Results indicate that at the amounts fed, AMF may improve G:F for lambs and steers fed dry corn-based finishing diets.

Peritoneal fluid culture in appendicitis: review in changing times

Appendicectomy is one of the commoner operations with a lifetime risk as high as 12% or 23% in males or females, respectively. Since the 1940s intra-operative intra-peritoneal swabs have commonly been taken from the appendix site, the spectrum of infecting organisms and their antibiotic sensitivity may be gauged from the culture results. This approach remains common but in recent years, studies have claimed that intra-peritoneal swabs are unnecessary; however, they relied upon retrospective patient groups predating wider use of laparoscopic appendicectomy, increasing numbers of immunocompromised people at risk of appendicitis and the clinical/medicolegal significance of increasing risk of antibiotic-associated Clostridium difficile colitis. Therefore, a key-word literature research was done to identify relevant publications from 1930 to June 2009. Newer features relating to intra-peritoneal swabs in appendicectomy have been discussed against this background information for periabdominal appendicectomy with or without appendicular perforation, laparoscopic appendicectomy and appendicectomy in the growing numbers of immunocompromised patients. All studies questioning the use of intra-peritoneal swabs were open, non-randomised, and retrospective with incompletely matched control groups, non-standardised swab collection techniques, and consequently lacked power to inform surgical practice. They concluded that an appropriately powered randomised, blinded, prospective, controlled clinical trial is needed to test for absolute efficacy in the use of peritoneal swabs in patient management. Until controlled trial data becomes available, it may be wise to continue peritoneal swabs at least in high-risk patients to decrease clinical and medicolegal risk.

Capacity of serotype 19A and 15B/C Streptococcus pneumoniae isolates for experimental otitis media: Implications for the conjugate vaccine

Non-vaccine Streptococcus pneumoniae serotypes are increasingly associated with disease. We evaluated isolates of the same sequence type (ST199) but different serotypes (15B/C, 19A) for growth in vitro, and pathogenic potential in a chinchilla otitis media model. We also developed a quantitative PCR (qPCR) assay to quantitatively assess each isolate, circumventing the need for selectable markers. In vitro studies showed faster growth of serotype 19A over 15B/C. Both were equally capable of colonization and middle ear infection in this model. Serotype 19A is included in new conjugate vaccine formulations while serotype 15B/C is not. Non-capsular vaccine targets will be important in disease prevention efforts.

Application of continuous culture for measuring the effect of environmental stress on mutation frequency in Mycobacterium tuberculosis

The ability of all pathogens to survive within the host is key to their success in establishing disease. Environmental conditions that affect the growth of a pathogen in the host include nutrient status, environmental pH, oxygen availability, and host defences. Studying the response of Mycobacterium tuberculosis (M. tuberculosis) exposed to these relevant host conditions in vitro will further increase our understanding of how these environments have an impact on the molecular mechanisms M. tuberculosis adopts to combat the effects of external influences such as antimycobacterials. The methods presented here are used to investigate the effect of environmental factors on the development of drug-resistant M. tuberculosis. Cultures grown under controlled conditions in continuous culture are sampled and the frequency with which resistant mutants develop are determined. These studies provide data that aid our understanding of the complex interaction between the host environment and invading bacterium that allow resistant strains to develop and continue to cause disease.

Methods to determine fitness in bacteria

Acquisition of antibiotic resistance may be associated with a physiological cost for the bacterium. Determination of growth rate and generation time is often used to measure fitness costs associated with antibiotic resistance. However, fitness costs may be small and difficult to quantify and multiple models are required. Available in vitro models that can be used to measure fitness include quantification of biofilm growth, survival in water, resistance to drying, and measurement of planktonic growth rates. The use of growth curve techniques to determine generation time is laborious, time-consuming, and can introduce sampling error. We have described the use of a semi-automated liquid culture system to estimate generation time in Burkholderia cepacia complex bacteria. We have also used the BacT/ALERT system to determine generation time and enumerate bacterial numbers in Mycobacterium tuberculosis. We describe methods for measuring biofilm growth and environmental survival in Burkholderia cepacia complex bacteria. These methods can be adapted for use with other organisms.

Little evidence for reversibility of trimethoprim resistance after a drastic reduction in trimethoprim use

OBJECTIVES

The worldwide rapid increase in antibiotic-resistant bacteria has made efforts to prolong the lifespan of existing antibiotics very important. Antibiotic resistance often confers a fitness cost in the bacterium. Resistance may thus be reversible if antibiotic use is discontinued or reduced. To examine this concept, we performed a 24 month voluntary restriction on the use of trimethoprim-containing drugs in Kronoberg County, Sweden.

METHODS

The intervention was performed on a 14 year baseline of monthly data on trimethoprim resistance and consumption. A three-parameter mathematical model was used to analyse the intervention effect. The prerequisites for reversion of resistance (i.e. fitness cost, associated resistance and clonal composition) were studied on subsets of consecutively collected Escherichia coli from urinary tract infections.

RESULTS

The use of trimethoprim-containing drugs decreased by 85% during the intervention. A marginal but statistically significant effect on the increase in trimethoprim resistance was registered. There was no change in the clonal composition of E. coli and there was no measurable fitness cost associated with trimethoprim resistance in clinical isolates. The frequency of associated antibiotic resistances in trimethoprim-resistant isolates was high.

CONCLUSIONS

A lack of detectable fitness cost of trimethoprim resistance in vitro together with a strong co-selection of other antibiotics could explain the rather disappointing effect of the intervention. The result emphasizes the low possibility of reverting antibiotic resistance once established and the urgent need for the development of new antibacterial agents.

Decrease in bacterial load versus resistance selection of pneumococcal subpopulations by beta-lactam physiological concentrations over time: an in vitro pharmacodynamic simulation

To investigate beta-lactam effects on Streptococcus pneumoniae-mixed cultures, a computerized pharmacodynamic model simulating over 24-hr concentrations obtained after several beta-lactam regimens was used. Strain 1 (no penicillin binding protein [PBP] mutations) and strain 2 (mutation in pbp1a) were penicillin/amoxicillin susceptible. Strain 3 (mutations in pbp1a, pbp2x, and pbp2b) and strain 4 (mutations in pbp1a, pbp2x, and pbp2b [10 changes]) were penicillin/amoxicillin resistant. Initial inoculum was approximately 6 x 10(6) CFU (colony forming units)/ml (with a 1:1:1:1 proportion of each strain). Population analysis profile was performed pre- and post-simulations. Strain 1 exhibited the best fitness (growth over 24 hr) in individual cultures, and strain 2 did so in mixed cultures in antibiotic-free simulations. In antibiotic simulations with the mixed inocula, penicillin/amoxicillin-susceptible strains were eradicated with all study drugs (time that concentrations exceed the minimal inhibitory concentration [T>MIC >or= 43%]). Penicillin-resistant strains showed different evolution depending on the antibiotic: (a) cefditoren produced >2 log(10) reduction of initial inocula at 12-24 hr (T>MIC >or=45%), with a remaining population growing in plates with >or=4 mg/L amoxicillin; (b) cefuroxime, cefixime, and cefaclor did not decrease initial inocula at 12-24 hr (T>MIC=0%), with minor subpopulations growing in plates with 4 mg/L amoxicillin; (c) amoxicillin produced 2.6 log(10) decrease of initial inocula at 12 hr (T>MIC=47.5%), but 1.1 log(10) increase of initial inocula at 24 hr, with a significant population growing in plates with 4 mg/L amoxicillin. Antibiotic activity against mixed inocula (susceptible and resistant strains) depends on intrinsic activity (as well as its subsequent pharmacodynamic activity: T>MIC against resistant strains), and on possible selection of intra-strain-resistant subpopulations.

Effect of subtherapeutic administration of antibiotics on the prevalence of antibiotic-resistant Escherichia coli bacteria in feedlot cattle

Antibiotic-resistant Escherichia coli in 300 feedlot steers receiving subtherapeutic levels of antibiotics was investigated through the collection of 3,300 fecal samples over a 314-day period. Antibiotics were selected based on the commonality of use in the industry and included chlortetracycline plus sulfamethazine (TET-SUL), chlortetracycline (TET), virginiamycin, monensin, tylosin, or no antibiotic supplementation (control). Steers were initially fed a barley silage-based diet, followed by transition to a barley grain-based diet. Despite not being administered antibiotics prior to arrival at the feedlot, the prevalences of steers shedding TET- and ampicillin (AMP)-resistant E. coli were >40 and <30%, respectively. Inclusion of TET-SUL in the diet increased the prevalence of steers shedding TET- and AMP-resistant E. coli and the percentage of TET- and AMP-resistant E. coli in the total generic E. coli population. Irrespective of treatment, the prevalence of steers shedding TET-resistant E. coli was higher in animals fed grain-based compared to silage-based diets. All steers shed TET-resistant E. coli at least once during the experiment. A total of 7,184 isolates were analyzed for MIC of antibiotics. Across antibiotic treatments, 1,009 (13.9%), 7 (0.1%), and 3,413 (47.1%) E. coli isolates were resistant to AMP, gentamicin, or TET, respectively. In addition, 131 (1.8%) and 143 (2.0%) isolates exhibited potential resistance to extended-spectrum beta-lactamases, as indicated by either ceftazidime or cefpodoxime resistance. No isolates were resistant to ciprofloxacin. The findings of the present study indicated that subtherapeutic administration of tetracycline in combination with sulfamethazine increased the prevalence of tetracycline- and AMP-resistant E. coli in cattle. However, resistance to antibiotics may be related to additional environmental factors such as diet.

Technical note: Occurrence in fecal microbiota of genes conferring resistance to both macrolide-lincosamide-streptogramin B and tetracyclines concomitant with feeding of beef cattle with tylosin

Development of antimicrobial resistance in food animals receiving antimicrobials has been well documented among bacterial isolates, especially pathogens, but information on development of antimicrobial resistance at the microbial community level during long-term feeding of antimicrobials is lacking. The objective of this study was to examine the association between inclusion of tylosin in feed and occurrence of resistance to macrolide-lincosamide-streptogramin B (MLS(B)) in the entire fecal microbial communities of beef cattle over a feeding study of 168 d. A completely randomized design included 6 pens housed together in 1 barn, with each pen housing 10 to 11 steers. The control and tylosin groups each had 3 pens, with the former receiving no antimicrobial whereas the latter received both tylosin and monensin (11 and 29.9 mg/ kg of feed, respectively, DM) in feed. The abundance of genes conferring resistance to MLS(B) (erm genes) and tetracyclines (tet genes) were quantified using class-specific, real-time PCR assays. The abundances of erm and tet genes were analyzed with pens as experimental units using the MIXED procedure of SAS. Correlations between abundance of different resistance genes were calculated using the CORR procedure of SAS. We identified 4 classes (B, F, T, and X) of erm genes in fresh fecal samples collected at wk 2, 17, and 21 of feeding. From wk 2 to 17, the abundance of erm(T) and erm(X) increased (P < 0.05), whereas that of erm(B) and erm(F) did not. The abundance of the erm genes did not further change from wk 17 to 21. The tet(A/C), tet(G), and tet gene variants encoding ribosomal protection proteins (including classes M, O, P, Q, S, T, and W) appeared to be co-selected by tylosin feeding. Such co-selection of multiresistance at community level by one antimicrobial drug used in animals has the important implication that future studies should examine resistance to not only the antimicrobials used in animals, but also other antimicrobials, especially those used in human medicine, to fully assess the potential risk associated with antimicrobial use in animals. Both the erm and tet genes appeared to be disseminated among the microbial populations in all steers housed together.

Genetic constraints on protein evolution

Evolution requires the generation and optimization of new traits ("adaptation") and involves the selection of mutations that improve cellular function. These mutations were assumed to arise by selection of neutral mutations present at all times in the population. Here we review recent evidence that indicates that deleterious mutations are more frequent in the population than previously recognized and that these mutations play a significant role in protein evolution through continuous positive selection. Positively selected mutations include adaptive mutations, i.e. mutations that directly affect enzymatic function, and compensatory mutations, which suppress the pleiotropic effects of adaptive mutations. Compensatory mutations are by far the most frequent of the two and would allow potentially adaptive but deleterious mutations to persist long enough in the population to be positively selected during episodes of adaptation. Compensatory mutations are, by definition, context-dependent and thus constrain the paths available for evolution. This provides a mechanistic basis for the examples of highly constrained evolutionary landscapes and parallel evolution reported in natural and experimental populations. The present review article describes these recent advances in the field of protein evolution and discusses their implications for understanding the genetic basis of disease and for protein engineering in vitro.

Evaluation of differential gene expression in susceptible and resistant clinical isolates of Klebsiella pneumoniae by DNA microarray analysis

DNA microarray technology was used to evaluate differential gene expression in a susceptible Klebsiella pneumoniae isolate and a resistant clinical derivative. Nineteen genes were up-regulated in the resistant isolate when compared with the susceptible isolate. An ABC transporter-related gene, ycjV, was strongly over-expressed, suggesting the existence of a novel active efflux mechanism. Approximately half of the up-regulated genes coded for ribosomal proteins, or proteins involved in tRNA metabolism. Among 33 downregulated genes, almost one-third were related to nitrogen metabolism. A possible role of fitness in the development of antimicrobial resistance is suggested.

Fitness of antimicrobial-resistant Campylobacter and Salmonella

Campylobacter and Salmonella are the most commonly reported bacterial causes of human foodborne infections, and increasing proportions of these pathogens become resistant to medically important antimicrobial agents, imposing a burden on public health. Acquisition of resistance to antibiotics affects the adaptation and evolution of Salmonella and Campylobacter in various environments. Many resistance-conferring mutations entail a biological fitness cost, while others (e.g. fluoroquinolone resistance in Campylobacter) have no cost or even enhanced fitness. In Salmonella, the fitness disadvantage due to antimicrobial resistance can be restored by acquired compensatory mutations, which occur both in vitro and in vivo. The compensated or even enhanced fitness associated with antibiotic resistance may facilitate the spread and persistence of antimicrobial-resistant Salmonella and Campylobacter in the absence of selection pressure, creating a significant barrier for controlling antibiotic-resistant foodborne pathogens.

A proteomic analysis of penicillin resistance in Streptococcus pneumoniae reveals a novel role for PstS, a subunit of the phosphate ABC transporter

Resistance to penicillin is widespread in the Gram-positive bacterium Streptococcus pneumoniae, and while several mutations are known to be implicated in resistance other mechanisms are likely to occur. We used a proteomic screen of two independent mutants in which resistance was selected in vitro. We found a number of differentially expressed proteins including PstS, a subunit of the phosphate ABC transporter of S. pneumoniae. This protein was increased in both mutants, a phenotype correlated to increased RNA expression of the entire phosphate ABC transporter operon. Inactivation of the pstS gene led to increased susceptibility to penicillin in the wild-type strain. To further link the expression of the ABC phosphate transporter with penicillin resistance, we looked at pstS mRNA levels in 12 independent clinical isolates sensitive and resistant to penicillin and found an excellent correlation between resistance and increased expression of pstS. Inactivation of pstS in one of the clinical isolates significantly reduced penicillin resistance. Global approaches are ideally suited for the discovery of novel factors in the biology of resistance.

Novel mechanism of resistance to oxazolidinones, macrolides, and chloramphenicol in ribosomal protein L4 of the pneumococcus

Two clinical Streptococcus pneumoniae isolates, identified as resistant to macrolides and chloramphenicol and nonsusceptible to linezolid, were found to contain 6-bp deletions in the gene encoding riboprotein L4. The gene transformed susceptible strain R6 so that it exhibited such resistance, with the transformants also showing a fitness cost. We demonstrate a novel bacterial mechanism of resistance to chloramphenicol and nonsusceptibility to linezolid.

The Controversy of Combination vs Monotherapy in the Treatment of Hospitalized Community-Acquired Pneumonia

BACKGROUND

The majority of community-acquired pneumonia (CAP) patients (about 80%) will be treated as outpatients, because therapy with a single agent will work. For the remaining 20% of patients requiring hospitalization, there is some growing debate regarding the efficacy of different management approaches. For hospitalized patients, monotherapy with a respiratory fluoroquinolone agent seems to be gaining popularity, but dual therapy combining a beta-lactam and an advanced macrolide still represents a good choice. Indeed, this regimen was recommended for all of the inpatient categories in the latest Infectious Disease Society of America CAP guidelines in 2003.

AIM

The purpose of this review was to examine the current clinical evidence to support one option or the other by gathering all of the available published literature. We will review the existing controversies in terms of microbiology, immunology, and clinical outcomes comparing dual therapy (ie, with any combination of beta-lactams, macrolides, or fluoroquinolones) with monotherapy in the treatment of CAP.

RESULTS

For the vast majority of patients with CAP (ie, outpatients and inpatients on medical wards), the type of antibiotic regimen prescribed does not have any significant impact. For patients with severe pneumonia, for which there is no accepted definition so far, the controversy remains alive. Mortality from pneumococcal pneumonia has been reduced over the last decades, but despite improved medical care, bacteremic pneumococcal pneumonia is still as lethal as ever, probably because of the aging population, the greater number of immunocompromised patients, and the number of patients with frequent comorbid conditions. Worldwide, the increasing rates of resistance of Streptococcus pneumoniae to antibiotics are also a serious concern, and the clinical implications are not always obvious. Although limited in number, the four studies showing the importance of adding a macrolide to a beta-lactam regimen for the treatment of bacteremic S pneumoniae pneumonia are retrospective and nonblinded, the findings are consistent, and they point to a trend that has to be explored more thoroughly. Studies published in the last few years suggest that combination therapy may be superior for bacteremic S pneumoniae pneumonia.

CONCLUSION

In the meantime, for practical purposes, patients hospitalized with a diagnosis of severe CAP may benefit from a dual antibiotic therapy combining a third-generation cephalosporin and a macrolide. For the majority of hospitalized patients with CAP who are not severely ill, fluoroquinolone monotherapy remains an approved, tested, and reliable option. Indeed, the time for more aggressive outpatient fluoroquinolone therapy may reduce the number of patients who are hospitalized with CAP. Independent prospective studies comparing combination therapy with standard monotherapy are urgently required for hospitalized patients with severe CAP.

Relative fitness of fluoroquinolone-resistant Streptococcus pneumoniae

Fluoroquinolone resistance in Streptococcus pneumoniae is primarily mediated by point mutations in the quinolone resistance–determining regions of gyrA and parC. Antimicrobial resistance mutations in housekeeping genes often decrease fitness of microorganisms. To investigate the fitness of quinolone-resistant S. pneumoniae (QRSP), the relative growth efficiencies of 2 isogenic QRSP double mutants were compared with that of their fluoroquinolone-susceptible parent, EF3030, by using murine nasopharyngeal colonization and pneumonia models. Strains containing the GyrA: Ser81Phe, ParC: Ser79Phe double mutations, which are frequently seen in clinical QRSP, competed poorly with EF3030 in competitive colonization or competitive lung infections. However, they efficiently produced lung infection even in the absence of EF3030. The strain containing the GyrA: Ser81Phe, ParC: Ser79Tyr double mutations, which is seen more frequently in laboratory-derived QRSP than in clinical QRSP, demonstrated reduced nasal colonization in competitive or noncompetitive lung infections. However, the strain was equally able to cause competitive or noncompetitive lung infections as well as EF3030.

Do physiological roles foster persistence of drug/multidrug-efflux transporters? A case study

Drug and multidrug resistance have greatly compromised the compounds that were once the mainstays of antibiotic therapy. This resistance often persists despite reductions in the use of antibiotics, indicating that the proteins encoded by antibiotic-resistance genes have alternative physiological roles that can foster such persistence in the absence of selective pressure by antibiotics. The recent observations that Tet(L), a tetracycline-efflux transporter, and MdfA, a multidrug-efflux transporter, both confer alkali tolerance offer a striking case study in support of this hypothesis.

Genetic relatedness of antibiotic-resistant pneumococci isolated during case clusters

Multilocus sequence typing of Streptococcus pneumoniae associated with two case clusters of disease is reported here for the first time. Isolates from the first cluster were serotype 19F, resistant to penicillin and erythromycin, and were characterized as ST 320. Isolates from the second cluster were serogroup 4, resistant to ciprofloxacin, and were characterized as ST 206. Therefore, the isolates from these clusters were antibiotic-resistant, of serotypes infrequently isolated, and of uncommon sequence types.

Antibiotic resistance may affect alkali decontamination of specimens containing mycobacteria

The influence of genetic modification on the decontamination process of mycobacteria was investigated using a wild type Mycobacterium bovis BCG Pasteur and its isogenic mutant strain. The result showed that the killing effect of sodium hydroxide (NaOH) progressively increased with prolonged incubation (up to 20 minutes), and the deteriorating effect of NaOH was more severe on the genetically modified strain.

Antibiotic Resistance in Streptococcus pneumoniae: What Does the Future Hold?

The recent emergence of strains of drug-resistant Streptococcus pneumoniae (DRSP) is a serious clinical and public health problem. Several interventions have been proposed to limit the further emergence and spread of DRSP, including campaigns for appropriate antibiotic use and the introduction of pneumococcal conjugate vaccines. Whether the current epidemic of drug resistance in S. pneumoniae is sustainable or will succumb to current efforts to limit its spread will be decided by an interaction of factors related to the pathogen (i.e., the relative fitness of the resistant strains), to the prescription of antibiotic treatment (i.e., changes in selection pressure), and to the host (i.e., the ability to slow the transmission of DRSP). Much investigation is still needed to better ascertain how maintenance of DRSP strains in the community at large is influenced by each factor and affected by current interventions that are based on these factors.

Can better prescribing turn the tide of resistance?

In the wake of concerns about the level of antibiotic resistance, governments worldwide are pressing for reduced antibiotic use, hoping thereby to reverse resistance trends. Is success likely? The evidence is mixed, and expectations should be tempered by the growing realization that many resistant bacteria are biologically fit, making them difficult to displace. If resistance is unlikely to be reduced significantly by changing prescription practices, how can clinicians outpace increased resistance, particularly when much of 'big pharma' is abandoning antibiotic development?