Spread of a single multiresistant methicillin-resistant Staphylococcus aureus clone carrying a variant of staphylococcal cassette chromosome mec type III isolated in a university hospital

The potential of therapeutic hyperthermia to eradicate Staphylococcus aureus bacteria; an in vitro study

Staphylococcus aureus is one of the most common infectious agents, causing morbidity and mortality worldwide. Most pathogenic bacteria are classified in the group of mesophilic bacteria and the optimal growth temperature of these bacteria changes between 33 and 41 °C. Increased temperature can inhibit bacterial growth and mobility, which in turn, can trigger autolysis and cause cell wall damage. Hyperthermia treatment is defined as a heat-mediated treatment method applied using temperatures higher than body temperature. Nowadays, this treatment method is used especially in the treatment of tumours. Hyperthermia treatment is divided into two groups: mild hyperthermia and ablative or high-temperature hyperthermia. Mild hyperthermia is a therapeutic technique in which tumour tissue is heated above body temperature to produce a physiological or biological effect but is often not aimed at directly causing significant cell death. The goal of this method is to achieve temperatures of 40-45 °C in human tissues for up to 2 h. Hyperthermia can be used in the treatment of infections caused by such bacterial pathogens. In addition, using hyperthermia in combination with antimicrobial drugs may result in synergistic effects and reduce resistance issues. In our study, we used two different temperature levels (37 °C and 45 °C). We assessed growth inhibition, some virulence factors, alteration colony morphologies, and antimicrobial susceptibility for several antibiotics with three methods (Kirby-Bauer, E-test and broth microdilution) under hyperthermia. In the study, we observed that hyperthermia affected the urease enzyme, antibiotic sensitivity levels showed synergy with hyperthermia, and changes occurred in colony diameters and affected bacterial growth. We hypothesise that hyperthermia might be a new therapeutic option for infectious diseases as a sole agent or in combination with different antimicrobials.

Nanoformulation of Biogenic Cefotaxime-Conjugated-Silver Nanoparticles for Enhanced Antibacterial Efficacy Against Multidrug-Resistant Bacteria and Anticancer Studies

OBJECTIVES

Due to the expanded bacterial genetic tolerance to antibiotics through different mechanisms, infectious diseases of MDR bacteria are difficult for treatment. Consequently, we synthesized drug conjugated nanoparticles to dissolve this problem. Moreover, the present study aims to display the cell death status treated with cefotaxime-CS-AgNPs and also, apoptosis pathways of human RPE-1 normal cells and human MCF-7 breast cancer cells.

METHODS

Here, we demonstrate the possibility to synthesize AgNPs and conjugate them with cefotaxime to survey the probability of cefotaxime-CS-AgNPs as an antimicrobial agent against cefotaxime-resistant strains E. coli and MRSA.

RESULTS

TEM showed the size of AgNPs, CS-AgNPs and cefotaxime-CS-AgNPs ranged from 7.42 to 18.3 nm, 8.05-23.89 nm and 8.48-25.3 nm, respectively, with a spherical shape. The cefotaxime-CS-AgNPs enhanced the high antimicrobial properties compared to AgNPs or pure antibiotic. The MIC of Cefotaxime-CS-AgNPs ranged from 3 µg/mL to 8 µg/mL against tested E. coli and MRSA bacteria. Consequently, the highest reduction in the MIC of cefotaxime-CS-AgNPs was noted against tested strains ranging from 22% to 96%. Comparing cefotaime-CS-AgNPs to AgNPs we showed that cefotaime-CS-AgNPs have no cytotoxic effect on normal cells at even 12 µg/mL for 24 hrs. The IC50 for the AgNPs and cefotaxime-CS-AgNPs was 12 µg/mL for human RPE-1 normal cells and human MCF-7 breast cancer cell lines. The pro-apoptotic genes p53, p21, and Bax of cancer cell lines significantly upregulated followed by downregulated by anti-apoptotic gene Bcl-2 after 48 hrs at 24 µg/mL, and this concentration represents the most effective dose.

CONCLUSION

Results enhanced the conjugating utility in old unresponsive cefotaxime to AgNPs to restore its efficiency against previous strains and demonstrated potential therapeutic applications of cefotaxime-CS-AgNPs. Moreover, this research gives remarkable insights for designing nanoscale delivery and curative systems that have a pronounced cytotoxic activity on cancer cells and are safe to normal cells.

Antimicrobial resistance and underlying mechanisms in Staphylococcus aureus isolates

OBJECTIVE

To investigate the antimicrobial susceptibility of 97 clinical Staphylococcus aureus (S. aureus) strains against 14 antimicrobials and corresponding resistance mechanisms.

METHODS

The antimicrobial susceptibility of the isolates was determined using a disk diffusion method and antimicrobial resistance genes were screened by polymerase chain reaction. Mutations responsible for ciprofloxacin and rifampicin resistance were investigated by polymerase chain reaction and DNA sequencing.

RESULTS

All isolates were found to be susceptible to vancomycin. Various rates of resistance to penicillin (83.5%), ampicillin (77.3%), erythromycin (63.9%), tetracycline (16.5%), amoxicillin/clavulanic acid (16.5%), ciprofloxacin (15.5%), trimethoprim/sulfamethoxazole (15.5%), oxacillin (13.4%), fusidic acid (12.4%), rifampin (6.2%), clindamycin (6.2%), gentamicin (6.2%) and mupirocin (5.2%) were determined. In addition, different combinations of resistance genes were identified among resistant isolates. Ciprofloxacin resistant isolates had mutations in codon 84 (Ser84Leu) and 106 (Gly106Asp) in the gyrA gene. Mutations in grlA were mostly related to Ser80Phe substitution. Leu466Ser mutation in the rpoB gene was detected in all rifampin resistant isolates. All methicillin resistant S. aureus isolates were SCCmec type V.

CONCLUSIONS

In conclusion, it was determined that the isolates were resistant to different classes of antimicrobials at varying rates and resistance was mediated by different genetic mechanisms. Therefore, continuous monitoring of resistance in S. aureus strains is necessary to control their resistance for clinically important antimicrobials.

Staphylococcal chromosomal cassettes mec (SCCmec): A mobile genetic element in methicillin-resistant Staphylococcus aureus

Considered to be a potential "superbug", methicillin-resistant Staphylococcus aureus (MRSA) has been one of the major recent infectious pathogens and thus poses a challenge to hospital infection control. The mobile genetic element staphylococcal chromosomal cassette mec (SCCmec) carries both the mecA or mecC gene, encoding for a novel specific penicillin-binding protein (PBP2a), and site-specific recombinase genes ccrAB or/and ccrC. In MRSA, the acquisition of SCCmec leads to the resistance to the β-lactam antibiotics. As SCCmec plays a core role in the antimicrobial resistance characteristics, molecular epidemiology and evolution of MRSA, a thorough summary and comprehensive understanding of the prevalence and structural characteristics of SCCmec may aid in global surveillance, implementation and investigation on MRSA isolates, as well as further development of preventive and therapeutic approaches. Consequently, this review is aimed at describing the history, prevalence, types and subtypes, and current typing methods of SCCmec, with the focus on the typical structures of the SCCmec cassette.

Phenotypic and genotypic detection of methicillin-resistant Staphylococcus aureus in hunting dogs in Maiduguri metropolitan, Borno State, Nigeria

Aim:

To determine the presence of MRSA in hunting dogs in Maiduguri metropolitan.

Materials and Methods:

Phenotypic methods used includes microscopic technique, colony morphology study, catalase-coagulase tests, and the use of mannitol salt agar test, oxacillin resistance screening agar base, and antibiotic susceptibility testing methods. Genotypic approach was used for deoxyribonucleic acid extraction, and the presence of nuc and mecA gene was detected using polymerase chain reaction (PCR) techniques.

Results:

Examination of 416 swab samples from nasal and perineal region of dogs revealed a total of 79.5% of S. aureus, where 62.5% of the isolates were MRSA. Molecular analysis revealed that 7nuc genes specific for S. aureus from 20 presumptive MRSA assay were all mecA PCR negative. The isolates were sensitive to gentamicin and ciprofloxacin but proved resistant to cefoxitin and oxacillin.

Conclusion:

High isolation rate of MRSA was found in hunting dogs. Significant level (p<0.05) of MRSA was isolated in the nasal cavity of hunting dogs than its perineum. Only nuc genes were detected from the MRSA isolates.

Antimicrobial resistance and molecular epidemiology of Staphylococcus aureus from Ulaanbaatar, Mongolia

This study aimed to characterize Staphylococcus aureus (S. aureus) strains isolated from human infections in Mongolia. Infection samples were collected at two time periods (2007–08 and 2011) by the National Center for Communicable Diseases (NCCD) in Ulaanbaatar, Mongolia. S. aureus isolates were characterized using polymerase chain reaction (PCR) for mecA, PVL, and sasX genes and tested for agr functionality. All isolates were also spa typed. A subset of isolates selected by frequency of spa types was subjected to antimicrobial susceptibility testing and multilocus sequence typing. Among 251 S. aureus isolates, genotyping demonstrated methicillin resistance in 8.8% of isolates (22/251). Approximately 28% of the tested S. aureus isolates were observed to be multidrug resistant (MDR). Sequence type (ST) 154 (spa t667) was observed to be a strain with high virulence potential, as all isolates for this spa type were positive for PVL, had a functional agr system and 78% were MDR. S. aureus isolates of ST239 (spa t037) were observed to cause infections and roughly 60% had functional agr system with a greater proportion being MDR. Additionally, new multilocus sequence types and new spa types were identified, warranting continued surveillance for S. aureus in this region.

Community-acquired methicillin-resistant Staphylococcus aureus: community transmission, pathogenesis, and drug resistance

Methicillin-resistant Staphylococcus aureus (MRSA) is able to persist not only in hospitals (with a high level of antimicrobial agent use) but also in the community (with a low level of antimicrobial agent use). The former is called hospital-acquired MRSA (HA-MRSA) and the latter community-acquired MRSA (CA-MRSA). It is believed MRSA clones are generated from S. aureus through insertion of the staphylococcal cassette chromosome mec (SCCmec), and outbreaks occur as they spread. Several worldwide and regional clones have been identified, and their epidemiological, clinical, and genetic characteristics have been described. CA-MRSA is likely able to survive in the community because of suitable SCCmec types (type IV or V), a clone-specific colonization/infection nature, toxin profiles (including Pantone-Valentine leucocidin, PVL), and narrow drug resistance patterns. CA-MRSA infections are generally seen in healthy children or young athletes, with unexpected cases of diseases, and also in elderly inpatients, occasionally surprising clinicians used to HA-MRSA infections. CA-MRSA spreads within families and close-contact groups or even through public transport, demonstrating transmission cores. Re-infection (including multifocal infection) frequently occurs, if the cores are not sought out and properly eradicated. Recently, attention has been given to CA-MRSA (USA300), which originated in the US, and is growing as HA-MRSA and also as a worldwide clone. CA-MRSA infection in influenza season has increasingly been noted as well. MRSA is also found in farm and companion animals, and has occasionally transferred to humans. As such, the epidemiological, clinical, and genetic behavior of CA-MRSA, a growing threat, is focused on in this study.

Evolution of MRSA during hospital transmission and intercontinental spread

Current methods for differentiating isolates of predominant lineages of pathogenic bacteria often do not provide sufficient resolution to define precise relationships. Here, we describe a high-throughput genomics approach that provides a high-resolution view of the epidemiology and microevolution of a dominant strain of methicillin-resistant Staphylococcus aureus (MRSA). This approach reveals the global geographic structure within the lineage, its intercontinental transmission through four decades, and the potential to trace person-to-person transmission within a hospital environment. The ability to interrogate and resolve bacterial populations is applicable to a range of infectious diseases, as well as microbial ecology.

Population structure of a hybrid clonal group of methicillin-resistant Staphylococcus aureus, ST239-MRSA-III

The methicillin-resistant Staphylococcus aureus (MRSA) clonal group known as ST239-MRSA-III is notable for its hybrid origin and for causing sustained hospital epidemics worldwide since the late 1970s. We studied the population structure of this MRSA clonal group using a sample of 111 isolates that were collected over 34 years from 29 countries. Genetic variation was assessed using typing methods and novel ascertainment methods, resulting in approximately 15 kb of sequence from 32 loci for all isolates. A single most parsimonious tree, free of homoplasy, partitioned 28 haplotypes into geographically-associated clades, including prominent European, Asian, and South American clades. The rate of evolution was estimated to be approximately 100× faster than standard estimates for bacteria, and dated the most recent common ancestor of these isolates to the mid-20th century. Associations were discovered between the ST239 phylogeny and the ccrB and dru loci of the methicillin resistance genetic element, SCCmec type III, but not with the accessory components of the element that are targeted by multiplex PCR subtyping tools. In summary, the evolutionary history of ST239 can be characterized by rapid clonal diversification that has left strong evidence of geographic and temporal population structure. SCCmec type III has remained linked to the ST239 chromosome during clonal diversification, but it has undergone homoplasious losses of accessory components. These results provide a population genetics framework for the precise identification of emerging ST239 variants, and invite a re-evaluation of the markers used for subtyping SCCmec.

Genome sequence of a recently emerged, highly transmissible, multi-antibiotic- and antiseptic-resistant variant of methicillin-resistant Staphylococcus aureus, sequence type 239 (TW)

The 3.1-Mb genome of an outbreak methicillin-resistant Staphylococcus aureus (MRSA) strain (TW20) contains evidence of recently acquired DNA, including two large regions (635 kb and 127 kb). The strain is resistant to a wide range of antibiotics, antiseptics, and heavy metals due to resistance genes encoded on mobile genetic elements and also mutations in housekeeping genes.

Integrative and sequence characteristics of a novel genetic element, ICE6013, in Staphylococcus aureus

A survey of chromosomal variation in the ST239 clonal group of methicillin-resistant Staphylococcus aureus (MRSA) revealed a novel genetic element, ICE6013. The element is 13,354 bp in length, excluding a 6,551-bp Tn552 insertion. ICE6013 is flanked by 3-bp direct repeats and is demarcated by 8-bp imperfect inverted repeats. The element was present in 6 of 15 genome-sequenced S. aureus strains, and it was detected using genetic markers in 19 of 44 diverse MRSA and methicillin-susceptible strains and in all 111 ST239 strains tested. Low integration site specificity was discerned. Multiple chromosomal copies and the presence of extrachromosomal circular forms of ICE6013 were detected in various strains. The circular forms included 3-bp coupling sequences, located between the 8-bp ends of the element, that corresponded to the 3-bp direct repeats flanking the chromosomal forms. ICE6013 is predicted to encode 15 open reading frames, including an IS30-like DDE transposase in place of a Tyr/Ser recombinase and homologs of gram-positive bacterial conjugation components. Further sequence analyses indicated that ICE6013 is more closely related to ICEBs1 from Bacillus subtilis than to the only other potential integrative conjugative element known from S. aureus, Tn5801. Evidence of recombination between ICE6013 elements is also presented. In summary, ICE6013 is the first member of a new family of active, integrative genetic elements that are widely dispersed within S. aureus strains.

Comparison of different methods for detecting methicillin resistance in MRSA isolates belonging to international lineages commonly isolated in the American continent

The aim of the present paper was to compare different methods for detecting methicillin resistance in Staphylococcus aureus. Among the isolates analyzed, 52 belonged to MRSA international lineages commonly detected in the American continent and 14 to sporadic MRSA clones. Both 30 microg-cefoxitin disk and PBP2a had 100% sensibility/specificity when the low-level heterogeneous isolates were tested and, thus, are highly recommended.

A novel type-III staphylococcal cassette chromosome mec (SCCmec) variant among Indian isolates of methicillin-resistant Staphylococcus aureus

We identified a novel type-III staphylococcal cassette chromosome mec (SCCmec) element carried by eight methicillin-resistant Staphylococcus aureus (MRSA) strains from different wards and patients in an Indian hospital. Although the pulsed-field gel electrophoresis pattern and spa types of eight strains were identical and clonally related to other nosocomial Indian isolates that belonged to sequence type (ST) 239 and spa type t037, the minimum inhibitory concentration (MIC) of these eight variants was noticeably low compared with the typical type-III isolates from the same hospital, and we were unable to identify ccrC and hsdR by multiplex PCR, although mer operon and transposases A, B, and C of Tn554 were amplified. By amplifying the entire SCCmec region by long-range PCR and determining parts of the nucleotide sequences of one isolate (V14), we found that the strain carried a novel SCCmec element containing a 422 bp sequence, which is highly homologous to that identified in strain CCR1-9583, mer operon and plasmid pT181 integrated in tandem via IS431 in the J3 region. It also carried a cassette chromosome, previously reported to be an SCC-like element, downstream of type-III SCCmec. Because PCR amplification of representative genes showed that these eight strains carried the same genetic elements, they belong to a novel MRSA clone that differs from most nosocomial clones carrying type-III SCCmec and SCCmercury, despite belonging to the ST239 genotype.