Biological counterstrike: antibiotic resistance mechanisms of Gram-positive cocci

Rapid identification and subsequent contextualization of an outbreak of methicillin-resistant Staphylococcus aureus in a neonatal intensive care unit using nanopore sequencing

Outbreaks of methicillin-resistant Staphylococcus aureus (MRSA) are well described in the neonatal intensive care unit (NICU) setting. Genomics has revolutionized the investigation of such outbreaks; however, to date, this has largely been completed retrospectively and has typically relied on short-read platforms. In 2022, our laboratory established a prospective genomic surveillance system using Oxford Nanopore Technologies sequencing for rapid outbreak detection. Herein, using this system, we describe the detection and control of an outbreak of sequence-type (ST)97 MRSA in our NICU. The outbreak was identified 13 days after the first MRSA-positive culture and at a point where there were only two known cases. Ward screening rapidly defined the extent of the outbreak, with six other infants found to be colonized. There was minimal transmission once the outbreak had been detected and appropriate infection control measures had been instituted; only two further ST97 cases were detected, along with three unrelated non-ST97 MRSA cases. To contextualize the outbreak, core-genome single-nucleotide variants were identified for phylogenetic analysis after de novo assembly of nanopore data. Comparisons with global (n=45) and national surveillance (n=35) ST97 genomes revealed the stepwise evolution of methicillin resistance within this ST97 subset. A distinct cluster comprising nine of the ten ST97-IVa genomes from the NICU was identified, with strains from 2020 to 2022 national surveillance serving as outgroups to this cluster. One ST97-IVa genome presumed to be part of the outbreak formed an outgroup and was retrospectively excluded. A second phylogeny was created using Illumina sequencing, which considerably reduced the branch lengths of the NICU isolates on the phylogenetic tree. However, the overall tree topology and conclusions were unchanged, with the exception of the NICU outbreak cluster, where differences in branch lengths were observed. This analysis demonstrated the ability of a nanopore-only prospective genomic surveillance system to rapidly identify and contextualize an outbreak of MRSA in a NICU.

Antibacterial Potential of Novel Acetamide Derivatives of 2-Mercaptobenzothiazole: Synthesis and Docking Studies

2-Mercaptobenzothiazole and its derivatives are widely known for their diverse biological activities, particularly antimicrobial and anticancer potential. In the present study, a series of new hybrid compounds consisting of 2-mercaptobenzothiazole and different aryl amines 2(a-j) were synthesized and characterized by Fourier transform infrared (FTIR), ¹H NMR, and ¹³C NMR spectral data. The synthesized compounds were screened for in vitro antibacterial activities through agar well diffusion assay. Among the series, 2b, 2c, and 2i exhibited significant antibacterial activity comparable to the standard drug levofloxacin. Based on their antibacterial potential, these compounds were further tested for their antibiofilm activity. All of the three compounds showed promising antibiofilm potential, even better than the standard drug cefadroxil at 100 μg/100 μL concentration. Molecular docking studies were performed to explore the antibacterial mechanism of these compounds. Strikingly, the molecule 2i shared the same hydrophobic pockets as those of levofloxacin in case of bacterial kinases and DNA gyrases. In addition, 2i exhibited satisfactory antibiofilm activity in comparison to the standard. Our study therefore suggested that the synthetic compound 2i possesses remarkable antibacterial activity and may serve as a lead molecule for the discovery of potent antibacterial agents.

Antibiotic resistance genes and molecular typing of Streptococcus agalactiae isolated from pregnant women

BACKGROUND

The antibiotic resistance of genital tract colonizing Streptococcus agalactiae in pregnant women is increasing. We aimed to determine the antibiotic resistance genes of different clonal types of this bacterium in pregnant women.

METHODS

Four hundred twenty non-repeated vaginal and rectal specimens were collected from pregnant women and were transferred to the laboratory using Todd Hewitt Broth. The samples were cultured on a selective medium, and the grown bacteria were identified by standard microbiological and biochemical tests. Antimicrobial resistance pattern and inducible clindamycin resistance of the isolates were determined using the disk agar diffusion method. The genomic DNAs of S. agalactiae strains were extracted using an extraction kit, and the antibiotic resistance genes and RAPD types were detected using the PCR method.

RESULTS

The average age of the participants was 30.74 ± 5.25 years. There was a significant relationship between the weeks of pregnancy and the number of positive bacterial cultures (P-value < 0.05). Moreover, 31 pregnant women had a history of abortion, and 18 had a history of membrane rupture. Among 420 specimens, 106 S. agalactiae isolates were detected. The highest antibiotic resistance rate was found against tetracycline (94.33%), and all isolates were susceptible to linezolid. Moreover, 15, 15, 42, and 7 isolates showed an iMLS_B, M-, cMLS_B, and L-phenotype. The ermB was the most prevalent resistance gene in the present study, while 38 (35.84%), 8 (7.54%), 79 (74.52%), 37 (34.9%), and 20 (18.86%) isolates were contained the ermTR, mefA/E, tetM, tetO, and aphA3 gene, respectively.

CONCLUSIONS

The high-level antibiotic resistance and prevalence of resistance genes may be due to the arbitrarily use, livestock industry consumption, and the preventive use of antibiotics in pregnant women. Thus, the need to re-considering this problem seems to be necessary.

Investigating antibiotic resistance in enterococci in Gabonese livestock

Background and Aim:

The emergence of antibiotic resistance is a major problem worldwide. Antibiotics are often used to prevent or treat infections in livestock. This study aimed to investigate antibiotic resistance in enterococci in Gabonese livestock.

Materials and Methods:

We collected 174 animal samples (46 laying hens, 24 swine, 62 cattle, and 42 sheep) from farms in four provinces of Gabon. Bacterial strains belonging to the genus Enterococcus were obtained using selective media and polymerase chain reaction targeting the tuf gene. Antibiotic susceptibility was determined by the disk diffusion method on Mueller-Hinton agar.

Results:

Enterococci were present in 160 of the samples (97%), distributed as follows: laying hens (100%, 41/41), swine (100%, 22/22), small ruminants (88%, 37/42), and cattle (100%, 60/60). Resistance to cephalothin/cephalexin, streptomycin, and rifampicin (RIF) was high, and resistance to vancomycin (VAN), erythromycin, and tetracycline was moderate. A high diversity of resistance was found in Haut-Ogooué and Estuaire provinces. Laying hens and swine showed moderate levels of resistance to ciprofloxacin and penicillin, while sheep and cattle had high levels of resistance to RIF. All species showed a high level of resistance to VAN. We found various patterns of multiple resistances in the isolates, and the multiple resistance indexes ranged from 0.2 to 0.8.

Conclusion:

This study shows that livestock in Gabon can be considered potential reservoirs of resistance.

New Insights on Streptococcus dysgalactiae subsp. dysgalactiae Isolates

Streptococcus dysgalactiae subsp. dysgalactiae (SDSD) has been considered a strict animal pathogen. Nevertheless, the recent reports of human infections suggest a niche expansion for this subspecies, which may be a consequence of the virulence gene acquisition that increases its pathogenicity. Previous studies reported the presence of virulence genes of Streptococcus pyogenes phages among bovine SDSD (collected in 2002-2003); however, the identity of these mobile genetic elements remains to be clarified. Thus, this study aimed to characterize the SDSD isolates collected in 2011-2013 and compare them with SDSD isolates collected in 2002-2003 and pyogenic streptococcus genomes available at the National Center for Biotechnology Information (NCBI) database, including human SDSD and S. dysgalactiae subsp. equisimilis (SDSE) strains to track temporal shifts on bovine SDSD genotypes. The very close genetic relationships between humans SDSD and SDSE were evident from the analysis of housekeeping genes, while bovine SDSD isolates seem more divergent. The results showed that all bovine SDSD harbor Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas IIA system. The widespread presence of this system among bovine SDSD isolates, high conservation of repeat sequences, and the polymorphism observed in spacer can be considered indicators of the system activity. Overall, comparative analysis shows that bovine SDSD isolates carry speK, speC, speL, speM, spd1, and sdn virulence genes of S. pyogenes prophages. Our data suggest that these genes are maintained over time and seem to be exclusively a property of bovine SDSD strains. Although the bovine SDSD genomes characterized in the present study were not sequenced, the data set, including the high homology of superantigens (SAgs) genes between bovine SDSD and S. pyogenes strains, may indicate that events of horizontal genetic transfer occurred before habitat separation. All bovine SDSD isolates were negative for genes of operon encoding streptolysin S, except for sagA gene, while the presence of this operon was detected in all SDSE and human SDSD strains. The data set of this study suggests that the separation between the subspecies "dysgalactiae" and "equisimilis" should be reconsidered. However, a study including the most comprehensive collection of strains from different environments would be required for definitive conclusions regarding the two taxa.

Tackling Multidrug Resistance in Streptococci - From Novel Biotherapeutic Strategies to Nanomedicines

The pyogenic streptococci group includes pathogenic species for humans and other animals and has been associated with enduring morbidity and high mortality. The main reason for the treatment failure of streptococcal infections is the increased resistance to antibiotics. In recent years, infectious diseases caused by pyogenic streptococci resistant to multiple antibiotics have been raising with a significant impact to public health and veterinary industry. The rise of antibiotic-resistant streptococci has been associated to diverse mechanisms, such as efflux pumps and modifications of the antimicrobial target. Among streptococci, antibiotic resistance emerges from previously sensitive populations as result of horizontal gene transfer or chromosomal point mutations due to excessive use of antimicrobials. Streptococci strains are also recognized as biofilm producers. The increased resistance of biofilms to antibiotics among streptococci promote persistent infection, which comprise circa 80% of microbial infections in humans. Therefore, to overcome drug resistance, new strategies, including new antibacterial and antibiofilm agents, have been studied. Interestingly, the use of systems based on nanoparticles have been applied to tackle infection and reduce the emergence of drug resistance. Herein, we present a synopsis of mechanisms associated to drug resistance in (pyogenic) streptococci and discuss some innovative strategies as alternative to conventional antibiotics, such as bacteriocins, bacteriophage, and phage lysins, and metal nanoparticles. We shall provide focused discussion on the advantages and limitations of agents considering application, efficacy and safety in the context of impact to the host and evolution of bacterial resistance.

Occurrence of antimicrobial agents, drug-resistant bacteria, and genes in the sewage-impacted Vistula River (Poland)

Antimicrobial agents (antimicrobials) are a group of therapeutic and hygienic agents that either kill microorganisms or inhibit their growth. Their occurrence in surface water may reveal harmful effects on aquatic biota and challenge microbial populations. Recently, there is a growing concern over the contamination of surface water with both antimicrobial agents and multidrug-resistant bacteria. The aim of the study was the determination of the presence of selected antimicrobials at specific locations of the Vistula River (Poland), as well as in tap water samples originating from the Warsaw region. Analysis was performed using the liquid chromatography-electrospray ionization-tandem mass spectrometry method. In addition, the occurrence of drug-resistant bacteria and resistance genes was determined using standard procedures. This 2-year study is the first investigation of the simultaneous presence of antimicrobial agents, drug-resistant bacteria, and genes in Polish surface water. In Poland, relatively high concentrations of macrolides are observed in both surface and tap water. Simultaneous to the high macrolide levels in the environment, the presence of the erm B gene, coding the resistance to macrolides, lincosamides, and streptogramin, was detected in almost all sampling sites. Another ubiquitous gene was int1, an element of the 5'-conserved segment of class 1 integrons that encode site-specific integrase. Also, resistant isolates of Enterococcus faecium and Enterococcus faecalis and Gram-negative bacteria were recovered. Multidrug-resistant bacteria isolates of Gram-negative and Enterococcus were also detected. The results show that wastewater treatment plants (WWTP) are the main source of most antimicrobials, resistant bacteria, and genes in the aquatic environment, probably due to partial purification during wastewater treatment processes.

Detection of antibiotic resistant Escherichia Coli bacteria using infrared microscopy and advanced multivariate analysis

DeterminingE. colibacteria susceptibility by analyzing their FTIR spectra using multivariate analysis.

Synthesis and antimicrobial activity of new piperazine-based heterocyclic compounds

The hydrazide

Presence of the optrA Gene in Methicillin-Resistant Staphylococcus sciuri of Porcine Origin

A total of 57 methicillin-resistant Staphylococcus aureus (MRSA) isolates and 475 methicillin-resistant coagulase-negative staphylococci (MRCoNS) collected from pigs in the Guangdong province of China in 2014 were investigated for the presence of the novel oxazolidinone-phenicol resistance gene optrA The optrA gene was detected in 6.9% (n = 33) of the MRCoNS, all of which were Staphylococcus sciuri isolates, but in none of the MRSA isolates. Five optrA-carrying methicillin-resistant (MR) S. sciuri isolates also harbored the multiresistance gene cfr Pulsed-field gel electrophoresis (PFGE) and dru typing of the 33 optrA-carrying MR S. sciuri isolates revealed 25 patterns and 5 sequence types, respectively. S1 nuclease PFGE and Southern blotting confirmed that optrA was located in the chromosomal DNAs of 29 isolates, including 1 cfr-positive isolate. The remaining four isolates harbored a ∼35-kb pWo28-3-like plasmid on which optrA and cfr were located together with other resistance genes, as confirmed by sequence analysis. Six different types of genetic environments (types I to VI) of the chromosome-borne optrA genes were identified; these types had the optrA gene and its transcriptional regulator araC in common. Tn558 was found to be associated with araC-optrA in types II to VI. The optrA gene in types II and III was found in close proximity to the ccr gene complex of the respective staphylococcal cassette chromosome mec element (SCCmec). Since oxazolidinones are last-resort antimicrobial agents for the control of serious infections caused by methicillin-resistant staphylococci in humans, the location of the optrA gene close to the ccr complex is an alarming observation.

Antibacterial products of marine organisms

Marine organisms comprising microbes, plants, invertebrates, and vertebrates elaborate an impressive array of structurally diverse antimicrobial products ranging from small cyclic compounds to macromolecules such as proteins. Some of these biomolecules originate directly from marine animals while others arise from microbes associated with the animals. It is noteworthy that some of the biomolecules referred to above are structurally unique while others belong to known classes of compounds, peptides, and proteins. Some of the antibacterial agents are more active against Gram-positive bacteria while others have higher effectiveness on Gram-negative bacteria. Some are efficacious against both Gram-positive and Gram-negative bacteria and against drug-resistant strains as well. The mechanism of antibacterial action of a large number of the chemically identified antibacterial agents, possible synergism with currently used antibiotics, and the issue of possible toxicity on mammalian cells and tissues await elucidation. The structural characteristics pivotal to antibacterial activity have been ascertained in only a few studies. Demonstration of efficacy of the antibacterial agents in animal models of bacterial infection is highly desirable. Structural characterization of the active principles present in aqueous and organic extracts of marine organisms with reportedly antibacterial activity would be desirable.

Marine bacteria: potential sources for compounds to overcome antibiotic resistance

Methicillin-resistant Staphylococcus aureus (MRSA) is the most problematic Gram-positive bacterium in the context of public health due to its resistance against almost all available antibiotics except vancomycin and teicoplanin. Moreover, glycopeptide-resistant S. aureus have been emerging with the increasing use of glycopeptides. Recently, resistant strains against linezolid and daptomycin, which are alternative drugs to treat MRSA infection, have also been reported. Thus, the development of new drugs or alternative therapies is clearly a matter of urgency. In response to the antibiotic resistance, many researchers have studied for alternative antibiotics and therapies. In this review, anti-MRSA substances isolated from marine bacteria, with their potential antibacterial effect against MRSA as potential anti-MRSA agents, are discussed and several strategies for overcoming the antibiotic resistance are also introduced. Our objective was to highlight marine bacteria that have potential to lead in developing novel antibiotics or clinically useful alternative therapeutic treatments.

Detection and fate of antibiotic resistant bacteria in wastewater treatment plants: a review

Antibiotics are among the most successful group of pharmaceuticals used for human and veterinary therapy. However, large amounts of antibiotics are released into municipal wastewater due to incomplete metabolism in humans or due to disposal of unused antibiotics, which finally find their ways into different natural environmental compartments. The emergence and rapid spread of antibiotic resistant bacteria (ARB) has led to an increasing concern about the potential environmental and public health risks. ARB and antibiotic resistant genes (ARGs) have been detected extensively in wastewater samples. Available data show significantly higher proportion of antibiotic resistant bacteria contained in raw and treated wastewater relative to surface water. According to these studies, the conditions in wastewater treatment plants (WWTPs) are favourable for the proliferation of ARB. Moreover, another concern with regards to the presence of ARB and ARGs is their effective removal from sewage. This review gives an overview of the available data on the occurrence of ARB and ARGs and their fate in WWTPs, on the biological methods dealing with the detection of bacterial populations and their resistance genes, and highlights areas in need for further research studies.

Genetic characterization of antimicrobial resistance in coagulase-negative staphylococci from bovine mastitis milk

Coagulase-negative staphylococci (CNS; n=417) were isolated from bovine milk and identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Nineteen different species were identified, and Staphylococcus xylosus, Staphylococcus chromogenes, Staphylococcus haemolyticus, and Staphylococcus sciuri were the most prevalent species. Resistance to oxacillin (47.0% of the isolates), fusidic acid (33.8%), tiamulin (31.9%), penicillin (23.3%), tetracycline (15.8%), streptomycin (9.6%), erythromycin (7.0%), sulfonamides (5%), trimethoprim (4.3%), clindamycin (3.4%), kanamycin (2.4%), and gentamicin (2.4%) was detected. Resistance to oxacillin was attributed to the mecA gene in 9.7% of the oxacillin-resistant isolates. The remaining oxacillin-resistant CNS did not contain the mecC gene or mecA1 promoter mutations. The mecA gene was detected in Staphylococcus fleurettii, Staphylococcus epidermidis, Staph. haemolyticus, and Staph. xylosus. Resistance to tetracycline was attributed to the presence of tet(K) and tet(L), penicillin resistance to blaZ, streptomycin resistance to str and ant(6)-Ia, and erythromycin resistance to erm(C), erm(B), and msr. Resistance to tiamulin and fusidic acid could not be attributed to an acquired resistance gene. In total, 15.1% of the CNS isolates were multidrug resistant (i.e., resistant to 2 or more antimicrobials). The remaining CNS isolates were susceptible to antimicrobials commonly used in mastitis treatment. Methicillin-resistant CNS isolates were diverse, as determined by mecA gene sequence analysis, staphylococcal cassette chromosome mec typing, and pulsed-field gel electrophoresis. Arginine catabolic mobile element types 1 and 3 were detected in both methicillin-resistant and methicillin-susceptible Staph. epidermidis and were associated with sequence types ST59 and ST111. Because this study revealed the presence of multidrug-resistant CNS in a heterogeneous CNS population, we recommend antibiogram analysis of CNS in persistent infections before treatment with antimicrobials.

Short term evolution of a highly transmissible methicillin-resistant Staphylococcus aureus clone (ST228) in a tertiary care hospital

Staphylococcus aureus is recognized as one of the major human pathogens and is by far one of the most common nosocomial organisms. The genetic basis for the emergence of highly epidemic strains remains mysterious. Studying the microevolution of the different clones of S. aureus is essential for identifying the forces driving pathogen emergence and spread. The aim of the present study was to determine the genetic changes characterizing a lineage belonging to the South German clone (ST228) that spread over ten years in a tertiary care hospital in Switzerland. For this reason, we compared the whole genome of eight isolates recovered between 2001 and 2008 at the Lausanne hospital. The genetic comparison of these isolates revealed that their genomes are extremely closely related. Yet, a few more important genetic changes, such as the replacement of a plasmid, the loss of large fragments of DNA, or the insertion of transposases, were observed. These transfers of mobile genetic elements shaped the evolution of the ST228 lineage that spread within the Lausanne hospital. Nevertheless, although the strains analyzed differed in their dynamics, we have not been able to link a particular genetic element with spreading success. Finally, the present study showed that new sequencing technologies improve considerably the quality and quantity of information obtained for a single strain; but this information is still difficult to interpret and important investments are required for the technology to become accessible for routine investigations.

Novel dendrimeric lipopeptides with antifungal activity

A series of new cationic lipopeptides containing branched, amphiphilic polar head derived from (Lys)Lys(Lys) dendron and C(8) or C(12) chain at C-end were designed, synthesized and characterized. Antimicrobial in vitro activity expressed as minimal inhibitory concentration (MIC) was evaluated against Gram-positive and Gram-negative bacteria and yeasts from the Candida genus. A significant enhancement of antimicrobial potency along with increased selectivity against Candida reference strains was detected for derivatives with the C(12) residue. Several compounds were characterized by a low hemotoxicity. The antifungal activity of branched lipopeptides is multimodal and concentration dependent. Several compounds, studied in detail, induced potassium leakage from fungal cells, caused morphological alterations of fungal cells and inhibited activity of candidal β(1,3)-glucan synthase.

The accessory genome of Pseudomonas aeruginosa

Pseudomonas aeruginosa strains exhibit significant variability in pathogenicity and ecological flexibility. Such interstrain differences reflect the dynamic nature of the P. aeruginosa genome, which is composed of a relatively invariable "core genome" and a highly variable "accessory genome." Here we review the major classes of genetic elements comprising the P. aeruginosa accessory genome and highlight emerging themes in the acquisition and functional importance of these elements. Although the precise phenotypes endowed by the majority of the P. aeruginosa accessory genome have yet to be determined, rapid progress is being made, and a clearer understanding of the role of the P. aeruginosa accessory genome in ecology and infection is emerging.

Antimicrobial susceptibility of canine and human Staphylococcus aureus collected in Saskatoon, Canada

Staphylococcus aureus is one of the most common causes of infection in people and is increasingly recognized in dogs. The increasing prevalence of methicillin resistant S. aureus (MRSA) is complicating the treatment of these infections. Panton Valentine leukocidin (PVL), a toxin involved in the pathogenesis of necrotic syndromes in people may be partially responsible for the rise of MRSA. Canine and human S. aureus from the same geographic area are genetically similar, indicating a common population and likely transmission. The implications of increasing antimicrobial resistance complicated by interspecies transmission, necessitates including both dogs and humans in S. aureus resistance surveillance studies. A collection of 126 S. aureus isolates from people (n = 99) and dogs (n = 27) were included, minimum inhibitor concentrations to a panel of 33 antimicrobials used in human and veterinary medicine were determined. No resistance to vancomycin, linezolid, daptomycin, quinupristin/dalfopristin or nitrofurantoin was found. A wide range of antibiograms were found; including resistance to 0-12 drugs (0-6 drug classes). Outstanding antibiograms included a canine MRSA resistant to rifampin and a human MRSA resistant to chloramphenicol. Inducible clindamycin resistance was found among 78% and 4% of canine and human MRSA and 17% and 25% of canine colonizing and human methicillin susceptible S. aureus (MSSA), respectively. Resistance to mupirocin was only found among human isolates including 20% of MRSA and 4% of MSSA. While no canine isolates were PVL positive, 39% of human MRSA and 2% of MSSA carried the gene. The bidirectional transmission of S. aureus between people and dogs necessitates the inclusion of isolates from both species in future studies.

Isolation of airborne oxacillin-resistant Staphylococcus aureus from culturable air samples of urban residences

Culturable single-stage impactor samples were collected onto nutrient agar in kitchen and bedroom areas of eight urban and four suburban residences in Philadelphia, Pennsylvania. Staphylococcus aureus colonies were identified by replica plating of the original impactor samples onto Chapman Stone medium followed by isolation of up to eight colonies for coagulase testing. Kirby-Bauer disk diffusion method was utilized to evaluate S. aureus resistance to both oxacillin and cefaclor. The median concentrations of total culturable bacteria observed in bedrooms and trash areas were 300 CFU/m(3) and 253 CFU/m(3), respectively. Median culturable Staphylococcus spp. concentrations in bedrooms and trash areas were 142 CFU/m(3) and 204 CFU/m(3), respectively. A total of 148 individual S. aureus colonies were isolated and tested for antibiotic resistance. Cefaclor resistance was encountered among only 6 of the 148 (4%) colonies. Nearly one-quarter of all S. aureus isolates tested displayed resistance (n = 30) or intermediate resistance (n = 5) to oxacillin. Twenty-six percent (n = 20) of trash area isolates and 21% (n = 15) of bedroom isolates displayed resistance or intermediate resistance to oxacillin. The median difference in percent resistance between trash and bedroom areas was 10% (p = 0.1). Results suggest that there may be a systematic difference in bacterial populations between downtown and suburban residences. Storage of household waste and handling of food may contribute to presence of the organism in the air of residences.

LmrS is a multidrug efflux pump of the major facilitator superfamily from Staphylococcus aureus

A multidrug efflux pump designated LmrS (lincomycin resistance protein of Staphylococcus aureus), belonging to the major facilitator superfamily (MFS) of transporters, was cloned, and the role of LmrS in antimicrobial efflux was evaluated. The highest relative increase in MIC, 16-fold, was observed for linezolid and tetraphenylphosphonium chloride (TPCL), followed by an 8-fold increase for sodium dodecyl sulfate (SDS), trimethoprim, and chloramphenicol. LmrS has 14 predicted membrane-spanning domains and is homologous to putative lincomycin resistance proteins of Bacillus spp., Lactobacillus spp., and Listeria spp.

Institutional Experience with Daptomycin Treatment in Patients with Gram-Positive Infections

Purpose

Daptomycin was originally approved for the treatment of complicated skin and skin-structure infections caused by gram-positive bacteria, and recently, its indications were expanded to include bacteremia and right-sided infective endocarditis caused by Staphylococcus aureus. This retrospective chart review examines outcomes and costs for individuals treated with daptomycin at a tertiary care medical center.

Methods

During an 11-month period, records of patients treated with daptomycin at the institution were reviewed. Cases for which complete cost data were available were included in the analysis. Outcomes were assigned to 4 categories: cured, improved, failed, or unevaluable. Hospital stay details were recorded, and antibiotic and total hospital treatment costs were calculated.

Results

Thirty-five patients representing 37 cases were included in the review. Of those cases, 89% (33 of 37) involved documented infections with gram-positive bacteria, 22% involved confirmed methicillin-resistant S. aureus infections, and 32% involved confirmed vancomycin-resistant enterococcus infections. Most cases (27 of 37; 73%) involved infections with multiple bacterial isolates for which previous therapy had failed. Of all clinically evaluable cases, 54% were classified as cured and 42% as improved after daptomycin therapy. Median and mean ± standard deviation (SD) total cost of hospitalization were $46,730 and $111,604 ± $137,138, respectively. Overall median duration of therapy for all 37 cases was 14 days (range, 1 to 143; mean ± SD duration, 25.5 ± 32 days).

Conclusion

Daptomycin cured or improved most evaluable gram-positive infections. The results of this study suggest that daptomycin may be considered a therapeutic option for treatment of drug-resistant gram-positive infections.

Antimicrobial resistance in bacteria

The development of antimicrobial resistance by bacteria is inevitable and is considered as a major problem in the treatment of bacterial infections in the hospital and in the community. Despite efforts to develop new therapeutics that interact with new targets, resistance has been reported even to these agents. In this review, an overview is given of the many therapeutic possibilities that exist for treatment of bacterial infections and how bacteria become resistant to these therapeutics.

StaphVar-DNA microarray analysis of accessory genome elements of community-acquired methicillin-resistant Staphylococcus aureus

OBJECTIVES

Approximately 75% of the genome of Staphylococcus aureus (the 'core' genome) is highly conserved between strains, whereas the remaining 25% (the 'accessory' genome) is composed of mobile genetic elements (MGEs), containing virulence and resistance genes. We developed a composite microarray focused on resistance and virulence genes located on the accessory or core-variable genome to characterize a collection of Belgian community-acquired methicillin-resistant S. aureus (CA-MRSA) strains.

METHODS

Oligonucleotide probes targeting 403 genes encoding antimicrobial resistance (35%), virulence (28%) and adhesion (31%) factors were designed among eight S. aureus sequenced genomes. The StaphVar Array was validated by testing five of the strains used for the design and utilized to characterize 13 CA-MRSA strains representative of the multilocus sequence typing (MLST) sequence types circulating in Belgium.

RESULTS

Analysis of the gene content of the five reference strains by the StaphVar Array matched 90% to 97% of the theoretical results. Analysis of CA-MRSA strains showed that 54.4% of the genes tested were strain-dependent. Strains presented specific exotoxin, enterotoxin, cytolysin and adhesin gene profiles by MLST lineage. One exception to these 'lineage-specific' profiles was the variable presence of the arginine catabolic mobile element (characteristic of the USA300 clone) within ST8 strains.

CONCLUSIONS

The StaphVar Array enables the characterization of approximately 400 variable resistance and virulence determinants in S. aureus. CA-MRSA strains displayed extensive diversity in virulence and resistance profiles. The presence of the USA300 clone in Belgium was confirmed. Although mainly located on MGEs, associations of virulence genes were highly conserved within strains of the same MLST lineage.

Metallo-beta-lactamase gene bla(IMP-15) in a class 1 integron, In95, from Pseudomonas aeruginosa clinical isolates from a hospital in Mexico

During 2003, 40 carbapenem-resistant Pseudomonas aeruginosa clinical isolates collected in a Mexican tertiary-care hospital were screened for metallo-beta-lactamase production. Thirteen isolates produced IMP-15, and 12 had a single pulsed-field gel electrophoresis pattern. The bla(IMP-15) gene cassette was inserted in a plasmid-borne integron with a unique array of gene cassettes and was named In95.

Antimicrobial activities of tigecycline and other broad-spectrum antimicrobials tested against serine carbapenemase- and metallo-beta-lactamase-producing Enterobacteriaceae: report from the SENTRY Antimicrobial Surveillance Program

A total of 104 carbapenemase (serine- and metallo-beta-lactamase [MbetaL])-producing strains of the Enterobacteriaceae family collected from 2000 to 2005 in medical centers distributed worldwide were tested against tigecycline and 25 comparators by reference broth microdilution methods. The most frequent carbapenemase was KPC-2 or -3 (73 strains), followed by VIM-1 (14), IMP-1 (11), SME-2 (5), and NMC-A (1). All serine carbapenemases were detected in the United States, while MbetaL-producing strains were isolated in Europe. Carbapenemase-producing Enterobacteriaceae showed high rates of resistance to most antimicrobial agents tested. The rank order of in vitro activity against these strains was as follows: tigecycline (100.0% susceptible) > polymyxin B (88.1%) > amikacin (73.0%) > imipenem (37.5%). Tigecycline was very active (MIC(90), 1 microg/ml) against this significant, contemporary collection of well-characterized strains and appears to be an excellent option compared to the polymyxins for treatment of infections caused by these multidrug-resistant Enterobacteriaceae.

Screening methods used to determine the anti-microbial properties of Aloe vera inner gel

The emergence of antibiotic resistant bacterial strains is a growing problem and is an important concern for patients, physicians, healthcare managers, and policymakers as it results in poorer health and economic outcomes. This has led to an urgent global call for new antimicrobial drugs, particularly from natural resources. We have been studying the antimicrobial properties of the inner leaf gel component of Aloe barbadensis Miller and have used a number of different, simple in vitro assays to establish a scientific basis for the potential use of Aloe vera on a range of clinically relevant bacteria. The bacteria used include Shigella flexneri, Methicillin-Resistant Staphylococcus aureus (MRSA), Enterobacter cloacae and Enterococcus bovis. In this paper, we compare standard methods recommended by the Clinical and Laboratory Standards Institute (CLSI) with a microtitre assay using a metabolic colour indicator Alamar blue. All the techniques described have shown that Aloe vera has an antimicrobial effect, however, the microtitre assay enables high throughput screening, under similar conditions and is less wasteful of plant material.

Rational protein engineering in action: the first crystal structure of a phenylalanine tRNA synthetase from Staphylococcus haemolyticus

In this article, we describe for the first time the high-resolution crystal structure of a phenylalanine tRNA synthetase from the pathogenic bacterium Staphylococcus haemolyticus. We demonstrate the subtle yet important structural differences between this enzyme and the previously described Thermus thermophilus ortholog. We also explain the structure-activity relationship of several recently reported inhibitors. The native enzyme crystals were of poor quality--they only diffracted X-rays to 3-5A resolution. Therefore, we have executed a rational surface mutagenesis strategy that has yielded crystals of this 2300-amino acid multidomain protein, diffracting to 2A or better. This methodology is discussed and contrasted with the more traditional domain truncation approach.

CP5484, a novel quaternary carbapenem with potent anti-MRSA activity and reduced toxicity

A new series of 1beta-methyl carbapenems possessing a 6,7-disubstituted imidazo[5,1-b]thiazol-2-yl group directly attached to the C-2 position of the carbapenem nucleus was prepared, and the activities of these compounds against methicillin-resistant Staphylococcus aureus (MRSA) were evaluated. To study the effect of basic moieties on anti-MRSA activity, we introduced an amino, or imino, or amidino group at the 6-position of imidazo[5,1-b]thiazole in place of the carbamoylmethyl moiety of CP5068. Anti-MRSA activities of almost all basic group-substituted carbapenems were improved, though some of the compounds showed stronger acute toxicity in mice than IPM. In order to decrease the toxicity without decreasing the activity, we introduced various additional functionalities around the basic moiety. Finally, we obtained CP5484, which has excellent anti-MRSA activity and low acute toxicity.

Carbapenemases: the versatile beta-lactamases

Carbapenemases are beta-lactamases with versatile hydrolytic capacities. They have the ability to hydrolyze penicillins, cephalosporins, monobactams, and carbapenems. Bacteria producing these beta-lactamases may cause serious infections in which the carbapenemase activity renders many beta-lactams ineffective. Carbapenemases are members of the molecular class A, B, and D beta-lactamases. Class A and D enzymes have a serine-based hydrolytic mechanism, while class B enzymes are metallo-beta-lactamases that contain zinc in the active site. The class A carbapenemase group includes members of the SME, IMI, NMC, GES, and KPC families. Of these, the KPC carbapenemases are the most prevalent, found mostly on plasmids in Klebsiella pneumoniae. The class D carbapenemases consist of OXA-type beta-lactamases frequently detected in Acinetobacter baumannii. The metallo-beta-lactamases belong to the IMP, VIM, SPM, GIM, and SIM families and have been detected primarily in Pseudomonas aeruginosa; however, there are increasing numbers of reports worldwide of this group of beta-lactamases in the Enterobacteriaceae. This review updates the characteristics, epidemiology, and detection of the carbapenemases found in pathogenic bacteria.

Modes and modulations of antibiotic resistance gene expression

Since antibiotic resistance usually affords a gain of function, there is an associated biological cost resulting in a loss of fitness of the bacterial host. Considering that antibiotic resistance is most often only transiently advantageous to bacteria, an efficient and elegant way for them to escape the lethal action of drugs is the alteration of resistance gene expression. It appears that expression of bacterial resistance to antibiotics is frequently regulated, which indicates that modulation of gene expression probably reflects a good compromise between energy saving and adjustment to a rapidly evolving environment. Modulation of gene expression can occur at the transcriptional or translational level following mutations or the movement of mobile genetic elements and may involve induction by the antibiotic. In the latter case, the antibiotic can have a triple activity: as an antibacterial agent, as an inducer of resistance to itself, and as an inducer of the dissemination of resistance determinants. We will review certain mechanisms, all reversible, that bacteria have elaborated to achieve antibiotic resistance by the fine-tuning of the expression of genetic information.

The use of calcium hydroxide, antibiotics and biocides as antimicrobial medicaments in endodontics

Bacteria have been implicated in the pathogenesis and progression of pulp and periapical diseases. The primary aim of endodontic treatment is to remove as many bacteria as possible from the root canal system and then to create an environment in which any remaining organisms cannot survive. This can only be achieved through the use of a combination of aseptic treatment techniques, chemomechanical preparation of the root canal, antimicrobial irrigating solutions and intracanal medicaments. The choice of which intracanal medicament to use is dependent on having an accurate diagnosis of the condition being treated, as well as a thorough knowledge of the type of organisms likely to be involved and their mechanisms of growth and survival. Since the disease is likely to have been caused by the presence of bacteria within the root canal, the use of an antimicrobial agent is essential. Many medicaments have been used in an attempt to achieve the above aims but no single preparation has been found to be completely predictable or effective. Commonly used medicaments include calcium hydroxide, antibiotics, non-phenolic biocides, phenolic biocides and iodine compounds. Each has advantages and disadvantages, and further research is required to determine which is best suited for root canal infections.