Gram-positive infections: lessons learnt and novel solutions

A High Level of Antimicrobial Resistance in Gram-Positive Cocci Isolates from Different Clinical Samples Among Patients Referred to Arsho Advanced Medical Laboratory, Addis Ababa, Ethiopia

Background

Gram-positive cocci are clinically important pathogens that cause infections and their development of antibiotic resistance continues to pose a severe threat to public health. Therefore, this study aims to investigate the level of antimicrobial resistance among Gram-positive cocci isolated from different clinical samples among patients referred to Arsho Advanced Medical Laboratory, Addis Ababa, Ethiopia.

Methods

From January to April 2018, a cross-sectional study was conducted at Arsho Advanced Medical Laboratory. Seven hundred ninety-two (792) different clinical samples were obtained from 792 individuals and inoculated into blood culture bottles and Blood Agar base. Bacterial identification was done using the number, type, and morphology of colonies, as well as Gram staining, catalase testing, and coagulase test after isolation of pure growth on culture media using the standard operating procedure. VITEK 2 compact system was used for bacterial identification and drug susceptibility testing. The information entry and analysis were performed by using SPSS version 20.

Results

Out of 792 clinical samples cultured, the prevalence of Gram-positive cocci was 12.6% (n=100/792). The most frequent one is S. aureus 54% (n=54/100) followed by coagulase-negative Staphylococcus species 42% (n=42/100), S. agalactiae 1% (n=1/100) and E. faecalis 3% (n=3/100). Penicillin showed the highest resistance rate 85% (n=85/100), followed by sulfamethoxazole/trimethoprim (47%), and oxacillin (38%); however, highest sensitivity was seen towards linezolid 97% (n=97/100) and vancomycin 94% (n=94/100). The total multi-drug resistance (MDR) Gram-positive cocci were 44% (n=44/100).

Conclusion

This study demonstrated high antimicrobial resistance and multi-drug resistance. This suggests that the importance of continuous monitoring of antimicrobial resistance patterns is crucial for selecting the suitable drug for treatment and infection prevention.

Nasal carriage of resistant Staphylococcus aureus in a medical student community

Staphylococcus aureus can cause a variety of infections due to its high transmissibility, high pathogenic potential and resistance to multiple drugs, factors that contribute to the relevance of infections in healthcare services. The aim of this study was to document phenotypic and genotypic resistance factors of Staphylococcus aureus strains, isolated from nasal mucosa of medical students. A nasal swab was collected from the nares (nostrils) of 222 medical students. After collection, the samples were submitted to isolation and identification procedures. From 204 valid samples, 20.6% (42 samples) were positive for S. aureus. For the assessment of phenotypic resistance by disk-diffusion technique, from 42 samples, 95.2% showed resistance to erythromycin, 42.8% to clindamycin, 16.6% to cephoxitin and 9.5% to oxacillin. The D test showed that 26.2% of samples were resistant to macrolides, lincosamides and streptogramin B. A PCR assay allowed for the evaluation of a genotypic resistance profile, in which 16.6% of the samples were positive for the mecA gene, 35.7% positive for the ermC gene or ermA gene and 28.5% were positive for both genes. These results demonstrate that medical students can enter the healthcare service previously colonized by multidrug resistant strains and become potential spreaders in the hospital environment.

Anti-infective drug development for MRSA

Staphylococcus aureus is an important pathogen linked to serious infections both in the hospital and the community settings. The challenge to treat infections caused by S. aureus has increased because of the emergence of multidrug-resistant strains such as methicillin-resistant S. aureus (MRSA). A limited spectrum of antibiotics is available to treat MRSA infections. This chapter reviews antimicrobial agents currently in use for the treatment of MRSA infections as well as agents that are in various stages of development. This chapter also reviews the alternate approaches that are being explored for the treatment of staphylococcal infections.

MRSA distribution and epidemiological procedures evaluation at two hospitals in Northern Poland

In the present study we have analyzed the impact of modified MRSA screening of carriers and patients on epidemiological situation of MRSA during 2008-2010, comparing two regional hospitals with similar bed numbers and similar ward profiles in Northern Poland. In 2008 the proportion of MRSA to all S. aureus isolates was 14.4% resp. 6.0%, in 2009 8.3% resp. 4.7% and in 2010 6.5% in both hospitals. Independent of the different prevention and intervention strategy in both hospitals the different MRSA incidence seems to be due to regional epidemic settings.

Current diagnostic tools for methicillin-resistant Staphylococcus aureus infections

Methicillin-resistant Staphylococcus aureus (MRSA) is a common pathogen responsible for a wide spectrum of healthcare-associated and community-acquired infections. Infections with MRSA strains that are resistant to beta-lactams and other types of antibiotics are a serious therapeutic problem - first, because in such cases only a limited spectrum of antibiotics can be used; and second, because such infections require prolonged hospitalization and result in economic losses. Therefore, in order to limit the overspread of pathogens, the development of diagnostic tools enabling rapid identification of carriers and infected patients, as well as proper identification of drug-resistance mechanisms to enable development of more targeted clinical treatment, are vital. This article reviews the current knowledge concerning prospective diagnostics of MRSA infections.

Group a Streptococcus: a loser in the battle with autophagy

Autophagy is an intracellular bulk degradation/recycling system for turning over cellular constituents. In one of the more remarkable findings among the recent developments in the field of autophagy, it was found that autophagy can also eliminate bacteria that invade host cells. The first evidence of this phenomenon came from an analysis of group A Streptococcus (GAS), the etiological agent underlying diverse human diseases. This bacterium is often internalized into nonphagocytic cells via the endocytic pathway, and then escapes from endosomes into the cytoplasm by secreting streptolysin O. The bacteria that escape into the cytoplasm induce and are captured by a unique membranous structure, which shares characteristics and molecular machinery with canonical autophagosomes but has some distinctions, including its large size. Subsequent fusion with lysosomes causes the death of most intracellular GAS. These findings have opened up a new field of innate immunity: the intracellular immune system against pathogens that penetrate the first defense of the endocytic pathway. The role of autophagy in Staphylococcus aureus infection is also discussed.

Mathematical modelling of the agr operon in Staphylococcus aureus

Staphylococcus aureus is a pathogenic bacterium that utilises quorum sensing (QS), a cell-to-cell signalling mechanism, to enhance its ability to cause disease. QS allows the bacteria to monitor their surroundings and the size of their population, and S. aureus makes use of this to regulate the production of virulence factors. Here we describe a mathematical model of this QS system and perform a detailed time-dependent asymptotic analysis in order to clarify the roles of the distinct interactions that make up the QS process, demonstrating which reactions dominate the behaviour of the system at various timepoints. We couple this analysis with numerical simulations and are thus able to gain insight into how a large population of S. aureus shifts from a relatively harmless state to a highly virulent one, focussing on the need for the three distinct phases which form the feedback loop of this particular QS system.

Is an increase of MRSA in Oslo, Norway, associated with changed infection control policy?

OBJECTIVES

The objective was to describe the prevalence of MRSA in Oslo, Norway, before and after introduction of a new National MRSA Control Guideline.

METHODS

From 1993 to 2006, we prospectively collected clinical and microbiological data on all MRSA cases in Oslo, Norway. Two MRSA guidelines; a strict Ullevål Standard MRSA Guideline and a less strict National MRSA Control Guideline were compared.

RESULTS

During 1993-2006, 358 MRSA cases were registered in Oslo; 43.9% detected in Ullevål University Hospital, 21.2% in nursing homes, and 18.7% in primary healthcare. One out of three (30.4%) were import-associated, and one out of ten (11.2%) were healthcare personnel. From 2004 on, a new National MRSA Control Guideline was introduced in primary healthcare, served by the community infection control. From 2004 on, there was a 4-6-fold increase of MRSA in primary healthcare (p = 0.038) and nursing homes (p = 0.005). Increase of MRSA cases at Ullevål (p < 0.001) was import-associated or from outbreaks in primary healthcare. There was no increase of internal spread in the hospital.

CONCLUSION

These data indicate that perhaps a less strict national MRSA infection control guideline in Norway may be associated with the 4-6-fold increase of MRSA cases in the community after 2003.

Structure of the scientific community modelling the evolution of resistance

Faced with the recurrent evolution of resistance to pesticides and drugs, the scientific community has developed theoretical models aimed at identifying the main factors of this evolution and predicting the efficiency of resistance management strategies. The evolutionary forces considered by these models are generally similar for viruses, bacteria, fungi, plants or arthropods facing drugs or pesticides, so interaction between scientists working on different biological organisms would be expected. We tested this by analysing co-authorship and co-citation networks using a database of 187 articles published from 1977 to 2006 concerning models of resistance evolution to all major classes of pesticides and drugs. These analyses identified two main groups. One group, led by ecologists or agronomists, is interested in agricultural crop or stock pests and diseases. It mainly uses a population genetics approach to model the evolution of resistance to insecticidal proteins, insecticides, herbicides, antihelminthic drugs and miticides. By contrast, the other group, led by medical scientists, is interested in human parasites and mostly uses epidemiological models to study the evolution of resistance to antibiotic and antiviral drugs. Our analyses suggested that there is also a small scientific group focusing on resistance to antimalaria drugs, and which is only poorly connected with the two larger groups. The analysis of cited references indicates that each of the two large communities publishes its research in a different set of literature and has its own keystone references: citations with a large impact in one group are almost never cited by the other. We fear the lack of exchange between the two communities might slow progress concerning resistance evolution which is currently a major issue for society.

The state of play in the battle against antimicrobial resistance: a general practitioner perspective

This article summarizes personal reflections from the perspective of general practice on developments with regard to antibiotic resistance and the containment of antibiotic prescribing during the lifetime of the Specialist Advisory Committee on Antimicrobial Resistance in England. These reflections concern the entry of antibiotics into the food chain, recent extensions of prescribing responsibilities and developments towards improved surveillance and reduced antibiotic prescribing. A large gap remains between the scientific appreciation of the risks from antimicrobial resistance and effective means to measure it and thereby hopefully control it.

Novel approaches to developing new antibiotics for bacterial infections

Antibiotics are an essential part of modern medicine. The emergence of antibiotic-resistant mutants among bacteria is seemingly inevitable, and results, within a few decades, in decreased efficacy and withdrawal of the antibiotic from widespread usage. The traditional answer to this problem has been to introduce new antibiotics that kill the resistant mutants. Unfortunately, after more than 50 years of success, the pharmaceutical industry is now producing too few antibiotics, particularly against Gram-negative organisms, to replace antibiotics that are no longer effective for many types of infection. This paper reviews possible new ways to discover novel antibiotics. The genomics route has proven to be target rich, but has not led to the introduction of a marketed antibiotic as yet. Non-culturable bacteria may be an alternative source of new antibiotics. Bacteriophages have been shown to be antibacterial in animals, and may find use in specific infectious diseases. Developing new antibiotics that target non-multiplying bacteria is another approach that may lead to drugs that reduce the emergence of antibiotic resistance and increase patient compliance by shortening the duration of antibiotic therapy. These new discovery routes have given rise to compounds that are in preclinical development, but, with one exception, have not yet entered clinical trials. For the time being, the majority of new antibiotics that reach the marketplace are likely to be structural analogues of existing families of antibiotics or new compounds, both natural and non-natural which are screened in a conventional way against live multiplying bacteria.