Clonal features of community-acquired methicillin-resistant Staphylococcus aureus in children

Antimicrobial evaluation of thiadiazino and thiazolo quinoxaline hybrids as potential DNA gyrase inhibitors; design, synthesis, characterization and morphological studies

A series of thiadiazino[5,6-b]quinoxaline and thiazolo[4,5-b]quinoxaline derivatives was designed and synthetized from the reaction of 2,3-dichloro-6-(morpholinosulfonyl)quinoxaline (2) with thiosemicarbazide or thiocarbohydrazide and thiourea derivatives to give nineteen quinoxaline derivatives 3-16. All the synthesized compounds were evaluated for in vitro antimicrobial potential against various bacteria and fungi strains that showed considerable antimicrobial activity against tested microorganisms. The most potent compounds 2, 7, 9, 10, 12 and 13c were exhibited bactericidal activity, in addition to fungistatic activity by dead live assay. Moreover, these compounds showed a significant result against all multi-drug resistance (MDRB) used especially compound 13c that displayed the best results with MICs of MDRB (1.95, 3.9, 2.6, 3.9 µg/mL) for stains used in this study, compared with Norfloxacin (1.25, 0.78, 1.57, 3.13 µg/mL). Also, cytotoxicity on normal cell (Vero cells ATCC CCL-81) by MTT assay was performed with lower toxicity results. Additionally, morphological studies, immunostimulatory potency and DNA gyrase inhibition assay of most active compounds was done. A molecular docking study has also been carried out to support the effective binding of the most promising compounds at the active site of the target enzyme S. aureus DNA gyrase (2XCT).

Pharmacological evaluation of poly(3-methylthiophene) and its titanium(IV)phosphate nanocomposite: DNA interaction, molecular docking, and cytotoxic activity

Cancer and pathogenic microbial diseases have terribly affected human health over a longer period of time. In response to the increasing casualties due to cancer and microbial diseases, unique poly(3-methylthiophene) and poly(3-methylthiophene)-titanium(IV)phosphate composite were prepared via in-situ oxidative chemical polymerization in this work. The poly(3-methylthiophene) and poly(3-methylthiophene)-titanium(IV)phosphate composite were well characterized by Fourier transform infrared spectroscopy and field emission scanning electron microscopy. DNA binding studies by UV-Visible and fluorescence spectroscopic investigations indicated strong binding affinities of poly(3-methylthiophene) and poly(3-methylthiophene)-titanium(IV)phosphate nanocomposite; leading to structural damage of DNA. Poly(3-methylthiophene)-titanium(IV)phosphate nanocomposite showed stronger interactions with DNA as compared to poly(3-methylthiophene) and from dye displacement assay it was confirmed that mode of binding of both the formulations was intercalative. The antimicrobial screening revealed that polymer and its composite displayed stronger antibacterial effects than ampicillin against Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa and Salmonella typhimurium. Besides, the poly(3-methylthiophene) and poly(3-methylthiophene)-titanium(IV)phosphate nanocomposite showed dose dependent effects towards estrogen receptor positive breast cancer (MCF-7) and estrogen receptor negative breast cancer (MDA-MB-231) cell lines; with poly(3-methylthiophene)-titanium(IV)phosphate nanocomposite showing better activities against both cell lines. In all in-vitro biological investigations, poly(3-methylthiophene)-titanium(IV)phosphate composite showed superior properties to that of the pure poly(3-methylthiophene), which encouraged us to suggest its potential as future therapeutic gear in drug delivery and other allied fields.

Geographic variability and anti-staphylococcal activity of the chrysophaentins and their synthetic fragments

Drug-resistant Staphylococcus aureus is a continuing public health concern, both in the hospital and community settings. Antibacterial compounds that possess novel structural scaffolds and are effective against multiple S. aureus strains, including current drug-resistant ones, are needed. Previously, we have described the chrysophaentins, a family of bisdiarylbutene macrocycles from the chrysophyte alga Chrysophaeum taylori that inhibit the growth of S. aureus and methicillin-resistant S. aureus (MRSA). In this study we have analyzed the geographic variability of chrysophaentin production in C. taylori located at different sites on the island of St. John, U.S. Virgin Islands, and identified two new linear chrysophaentin analogs, E2 and E3. In addition, we have expanded the structure activity relationship through synthesis of fragments comprising conserved portions of the chrysophaentins, and determined the antimicrobial activity of natural chrysophaentins and their synthetic analogs against five diverse S. aureus strains. We find that the chrysophaentins show similar activity against all S. aureus strains, regardless of their drug sensitivity profiles. The synthetic chrysophaentin fragments indeed mimic the natural compounds in their spectrum of antibacterial activity, and therefore represent logical starting points for future medicinal chemistry studies of the natural products and their analogs.

Synthesis and antibacterial activity of a novel series of acylides active against community acquired respiratory pathogens

A novel series of acylides 4 were designed to overcome antibacterial resistance and evaluated for in vitro and in vivo activity. This series of acylides was designed from clarithromycin by changing the substitution on the desosamine nitrogen, followed by conversion to 3-O-acyl and 11,12-carbamate. These compounds showed significantly potent antibacterial activity against not only Gram-positive pathogens, including macrolide-lincosamide-streptogramin B (MLS(B))-resistant and efflux-resistant strains, but also Gram-negative pathogens such as Haemophilus influenzae. These acylides also showed better activity against telithromycin resistant Streptococcus pneumoniae strains.

Novel C-4'' modified azithromycin analogs with remarkably enhanced activity against erythromycin-resistant Streptococcus pneumoniae: the synthesis and antimicrobial evaluation

Three novel structural series of C-4'' modified azithromycin analogs with two amide groups, which were connected by different alkyl linkage, were designed, prepared and evaluated for their in vitro antibacterial activity against seven phenotypes of respiratory pathogens. Among them, 7d, 8j and 9j, as representatives of corresponding series, exhibited remarkably improved activity against erythromycin-resistant Streptococcus pneumoniae expressing the erm gene, the mef gene, and the erm and mef genes. In addition, 7a-c, 7f-h, 7j, 8d, 8g, 8i, 9a-b and 9i displayed favorable efficacy against erythromycin-resistant S. pneumoniae A22072 expressing the mef gene.

Synthesis and antibacterial activity of novel 4''-O-carbamoyl erythromycin-A derivatives

Novel 4''-O-carbamoyl erythromycin-A derivatives were designed, synthesized, and evaluated for their in-vitro antibacterial activities. All of the 4''-O-carbamoyl derivatives showed excellent activity against erythromycin-susceptible Staphylococcus aureus ATCC25923, Streptococcus pyogenes, and Streptococcus pneumoniae ATCC49619. Most of the 4''-O-arylalkylcarbamoyl derivatives displayed potent activity against erythromycin-resistant S. pneumoniae encoded by the mef gene and greatly improved activity against erythromycin-resistant S. pneumoniae encoded by the erm gene or the erm and mef genes. In particular, the 4''-O-arylalkyl derivatives 4c-4e and 4g were found to possess the most potent activity against all the tested erythromycin-susceptible strains, which were comparable to those of erythromycin, clarithromycin, or azithromycin. 4''-O-Arylalkyl derivatives 4e and 4g were the most effective against erythromycin-resistant S. pneumoniae encoded by the mef gene (0.25 and 0.25 microg/mL). 4''-O-Arylalkyl derivatives 4a and 4b exhibited significantly improved activity against erythromycin-resistant S. pneumoniae encoded by the erm gene. In contrast, the 4''-O-alkylcarbamoyl derivatives hardly showed improved activity against all the tested erythromycin-resistant strains.

Synthesis and antibacterial evaluation of novel clarithromycin derivatives with C-4″ elongated arylalkyl groups against macrolide-resistant strains

Novel clarithromycin derivatives with C-4″ elongated arylalkyl groups were designed, synthesized and evaluated to probe the effect of different lengths of their C-4″ side chains on the activity against resistant bacterial strains. These derivatives had excellent activity against erythromycin-susceptible Streptococcus pneumoniae, Streptococcus aureus or Streptococcus pyogenes and some of them exhibited greatly improved activity against erythromycin-resistant strains. Compounds 18 and 16, which had the C-4″ elongated arylalkyl groups with eight atoms from the 4″-oxygen atom to the terminal benzene ring, were the most effective against S. pneumoniae expressing the erm gene and the erm and mef genes. In contrast, the most potent compounds 3, 5, 9, 17 and 18 against S. pneumoniae expressing the mef gene had C-4″ elongated arylalkyl groups with three to eight atoms between the 4″-oxygen atom and the terminal aromatic ring.

Community-associated methicillin-resistant Staphylococcus aureus: epidemiology and clinical consequences of an emerging epidemic

Staphylococcus aureus is an important cause of skin and soft-tissue infections (SSTIs), endovascular infections, pneumonia, septic arthritis, endocarditis, osteomyelitis, foreign-body infections, and sepsis. Methicillin-resistant S. aureus (MRSA) isolates were once confined largely to hospitals, other health care environments, and patients frequenting these facilities. Since the mid-1990s, however, there has been an explosion in the number of MRSA infections reported in populations lacking risk factors for exposure to the health care system. This increase in the incidence of MRSA infection has been associated with the recognition of new MRSA clones known as community-associated MRSA (CA-MRSA). CA-MRSA strains differ from the older, health care-associated MRSA strains; they infect a different group of patients, they cause different clinical syndromes, they differ in antimicrobial susceptibility patterns, they spread rapidly among healthy people in the community, and they frequently cause infections in health care environments as well. This review details what is known about the epidemiology of CA-MRSA strains and the clinical spectrum of infectious syndromes associated with them that ranges from a commensal state to severe, overwhelming infection. It also addresses the therapy of these infections and strategies for their prevention.

Staphylococcus aureus: a community pathogen

Staphylococcus aureus is a common human pathogen. S aureus infections most commonly clinically manifest as skin infections. There has been much interest in S aureus infections in the community over the past decade because of the rise of community-associated methicillin-resistant S aureus (CA-MRSA) infections, which have emerged globally over a relatively short period of time. In contrast to health care-associated methicillin resistant S aureus (HA-MRSA), circulating strains of CA-MRSA have characteristic pathogenesis, strain characteristics, epidemiology, and clinical manifestations that are distinct from HA-MRSA. In fact, CA-MRSA probably behaves more like community-associated methicillin-sensitive S aureus (MSSA). This article reviews current knowledge of the epidemiology and clinical manifestations of community-associated S aureus and CA-MRSA infections.

Comparison of virulence in community-associated methicillin-resistant Staphylococcus aureus pulsotypes USA300 and USA400 in a rat model of pneumonia

BACKGROUND

The predominant genetic background of community-associated methicillin-resistant Staphylococcus aureus has transitioned from USA400 to USA300 in most US communities. The explanation for this shift is unclear. We hypothesized that USA300 must be more pathogenic--specifically, that USA300 would have increased virulence when compared with USA400 in an animal model.

METHODS

Rats were inoculated intratracheally with 1 of 6 S. aureus isolates from the USA300 and USA400 backgrounds. We assessed mortality, in vivo bacterial growth, and histopathology. We assessed the in vitro expression of capsule and of selected genes believed to be important in virulence in S. aureus, including agr, saeRS, sarA, alpha-toxin (hla), and Panton-Valentine leukocidin (pvl).

RESULTS

USA300 isolates were more lethal, produced more severe pneumonia, and had higher in vivo bacterial density in the lung than did USA400 isolates. In vitro expression of agr, saeRS, sarA, hla, and pvl were greater in USA300 isolates. USA300 isolates were unencapsulated, whereas 2 of 3 USA400 isolates produced capsule.

CONCLUSIONS

USA300 isolates were more virulent than USA400 isolates in a model of necrotizing pneumonia. The explanation for this is unclear, but it likely results from increased expression of S. aureus regulatory systems (e.g., agr, saeRS, and sarA) and the resultant upregulation of key virulence factors including alpha-toxin and PVL.

Changing trends in acute osteomyelitis in children: impact of methicillin-resistant Staphylococcus aureus infections

BACKGROUND

Staphylococcus aureus remains the most common etiologic agent of acute osteomyelitis in children. Recently, methicillin-resistant S. aureus (MRSA) has emerged as a major pathogen.

METHODS

Records of all children admitted with acute osteomyelitis from January 1999 to December 2003 were reviewed. For the comparative analysis, the study population was evenly distributed in 2 periods: period A, January 1999 to June 2001; n = 113; and period B, July 2001 to December 2003; n = 177. In addition, clinical findings of MRSA osteomyelitis were compared with non-MRSA osteomyelitis, including methicillin-sensitive S. aureus infections.

RESULTS

Two hundred ninety children (60% male subjects) with acute osteomyelitis were identified. Median (25th-75th percentile) age at diagnosis was 6 years (range, 2-11 years). Significant clinical findings included the following: localized pain (84%), fever (67%), and swelling (62%). Affected bones included the following: foot (23%), femur (20%), tibia (16%), and pelvis (7%). Thirty-seven percent of blood cultures were positive, and a bacterial isolate was obtained in 55% of cases. Bacteria most frequently isolated included the following: methicillin-sensitive S. aureus (45%) (57% in period Avs 40% in period B), MRSA (23%) (6% in A vs 31% in B; P < 0.001), Streptococcus pyogenes (6%), and Pseudomonas aeruginosa (5%). Children with MRSA compared with those with non-MRSA osteomyelitis had significantly greater erythrocyte sedimentation rate and C-reactive protein values on admission and increased length of hospital stay, antibiotic therapy, and overall rate of complications. We observed significant changes in antibiotic therapy related to increased use of agents with activity against MRSA.

CONCLUSIONS

Methicillin-resistant S. aureus was isolated more frequently in the second study period and was associated with worse clinical outcomes.

Synthesis and biological evaluation of new N-linked 5-triazolylmethyl oxazolidinones

A new series of oxazolidinones bearing N-linked 5-triazolylmethyl group have been synthesized and their in vitro antibacterial activities (MIC) were evaluated against a spectrum of resistant and susceptible Gram-positive organisms. Some of the analogues in this series displayed activity superior to linezolid and vancomycin. Furthermore, in vivo efficacies and pharmacokinetic properties of the selected compounds were also disclosed herein; the selected compounds showed reasonable bioavailability as well as in vivo efficacy comparable to that of linezolid.

Synthesis and antibacterial activity of oxazolidinones containing triazolyl group

A new series of oxazolidinones containing triazolyl group has been synthesized and tested for in vitro antibacterial activity by MIC determination against a panel of resistant and susceptible Gram-positive organisms. Most of the analogs in this series displayed activity superior to linezolid and vancomycin in vitro. Further, in vivo efficacies of the selected oxazolidinones were also disclosed herein.

Antibacterial Effects of Moxifloxacin and Levofloxacin Simulating Epithelial Lining Fluid Concentrations against Community-Acquired Methicillin-Resistant Staphylococcus aureus

BACKGROUND AND OBJECTIVE

Current North American guidelines advocate the use of respiratory fluoroquinolones for the empirical management of community-acquired pneumonia (CAP). While community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged as a pathogen frequently encountered in skin and skin structure infections, it has also now been recognised as a causative pathogen in CAP. Since fluoroquinolones may be used empirically to treat unsuspected CA-MRSA pneumonia, the objective of this study was to evaluate the antibacterial properties of levofloxacin and moxifloxacin using human simulated drug exposures in epithelial lining fluid (ELF).

METHODS

An in vitro model was used to simulate the ELF concentrations, previously determined in older adults receiving multiple doses, of levofloxacin 500 mg once daily and moxifloxacin 400mg once daily. Four CA-MRSA isolates were studied at a starting inoculum of 10(6) colony-forming units (CFU)/mL; selected isolates were also studied at 10(8) CFU/mL. Bacterial density and resistance were quantitatively assessed over 48 hours. Drug exposure (area under the concentration-time curve [AUC]) was confirmed using validated drug assays.

RESULTS

At a standard 10(6) starting inoculum, sustained bacterial kill (3.6-4.5 log) with both fluoroquinolones was noted for CA-MRSA isolates 27 and 44 (AUC/minimum inhibitory concentration [MIC] = 383-3923). Despite an MIC of 8 microg/mL (AUC/MIC = 25) for isolate 3, levofloxacin displayed a 2.8 log kill, while moxifloxacin (MIC 1 microg/mL) sustained a 4.5 log kill (AUC/MIC = 207) over 48 hours. Against isolate 59, levofloxacin displayed no antibacterial effect (AUC/MIC = 3), while moxifloxacin with an MIC of 8 microg/mL (AUC/MIC = 31) killed 4.6 log. At a high inoculum (10(8)), both fluoroquinolones showed 5.2-5.6 log kill for the susceptible isolate (44), while moxifloxacin showed no antibacterial activity against isolate 59. Drug exposure (AUC/MIC) appeared to correlate well (r(2) = 0.99) with the change in log CFU/mL. Maximal activity was observed for both drugs at an AUC/MIC of approximately 30.

CONCLUSION

When evaluated at human simulated ELF concentrations, both levofloxacin and moxifloxacin appeared to demonstrate sustained antibacterial activity for CA-MRSA isolates with MICs <or=8 microg/mL at a starting inoculum of 10(6). Use of a high inoculum (10(8)) appeared to compromise the antimicrobial activity of the fluoroquinolones when the MIC was 8 microg/mL, but did not mitigate antibacterial kill for susceptible isolates.

Synthesis and antibacterial activity of novel oxazolidinones bearing N-hydroxyacetamidine substituent

Novel oxazolidinone antibacterials containing N-hydroxyacetamidine moiety are synthesized with the diversity at C-5 terminus. These compounds have been evaluated against a panel of clinically relevant gram-positive and gram-negative pathogens. Most of the analogs in this series displayed activity superior to Linezolid and in vivo efficacies of selected oxazolidinones are also disclosed herein.

Three-year surveillance of community onset health care-associated staphylococcus aureus infections in children

BACKGROUND

Staphylococcus aureus causes skin and soft tissue or invasive infections in children in the community, in the hospital or in other ways associated with the health care system (HCA).

METHODS

Prospective community-acquired S. aureus infection surveillance at Texas Children's Hospital was initiated on August 1, 2001. Community onset HCA (CO HCA) infections were identified. Demographic and clinical data were collected. Antibiotic susceptibilities were determined. Data were analyzed by chi or Student's t test. CO HCO-isolates were characterized by pulsed field gel electrophoresis and staphylococcal chromosomal cassette carrying the mecA methicillin-resistant gene (SCCmec) typing.

RESULTS

From August 1, 2001 to July 31, 2004, 61.5% of 322 in year 1, 62.9% of 259 in year 2 and 56.9% of 318 in year 3 of CO HCA isolates were methicillin-resistant S. aureus (MRSA). Among the CO HCA-MRSA isolates, 8.9% of 542 were from children with invasive infections compared with 24.1% of 357 CO HCA-methicillin-susceptible S. aureus (MSSA; P < 0.001). Sixty-six percent of children with CO HCA-S. aureus isolates were admitted to the hospital. Clindamycin resistance increased over the 3 years (CO HCA-MRSA, from 3.5% to 18.8%, P < 0.001; CO HCA-MSSA, from 3.2% to 10.2%, P = 0.053). Thirty-three of 35 (94.3%) CO HCA-MRSA carried SCCmecIV; 30 were USA300. Only 3 of 35 MSSA were related to USA300 by pulsed field gel electrophoresis.

CONCLUSIONS

CO HCA-S. aureus infections remained steady over the 3-year study at Texas Children's Hospital. Clindamycin resistance increased >4-fold for CO HCA-S. aureus isolates over the 3 years and is no longer appropriate for empiric treatment of invasive infections suspected to be caused by CO HCA-MRSA at our hospital. In our setting, CO HCA-MRSA infections are steady in number despite substantial increases in community-acquired MRSA infections and both being related to the same clone.

Inducible clindamycin resistance and molecular epidemiologic trends of pediatric community-acquired methicillin-resistant Staphylococcus aureus in Dallas, Texas

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infection occurs commonly in children. Clindamycin resistance may be inducible or constitutive, and the rates of inducible resistance in CA-MRSA that could produce clindamycin treatment failures vary worldwide. The double-disk test was performed in 197 erythromycin-resistant and clindamycin-susceptible CA-MRSA strains from children in Dallas, Texas, from 1999 to 2002 to determine inducible clindamycin resistance. Resistance mechanisms were studied by PCR; epidemiologic trends were studied by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Inducible resistance was demonstrated in 28 (93%+/-6%) of 30 tested isolates in 1999, 21 (64%, +/-11%) of 33 in 2000, 12 (23%+/-7%) of 52 in 2001, and 6 (7%+/-3%) of 82 in 2002. All noninducible strains had the msr(A) gene. Among inducible resistant strains, 31 had erm(B), 24 had erm(C), and 12 had erm(A) genes. Two distinct pulsed types were the most prevalent; one of them was the most common pulsed type in 1999, whereas in 2002 a different pulsed type was prevalent. MLST analyses determined that ST-8 was the most common type, with 76%+/-5% found in 2002. All but one of these clindamycin-susceptible, erythromycin-resistant ST-8 strains showed no induction of clindamycin resistance. We conclude that, among erythromycin-resistant, clindamycin-susceptible CA-MRSA strains isolated from children in Dallas, inducible methylase resistance became less common from 1999 to 2002 (P<0.001). The phenotype of strains was associated with their sequence type. Our results demonstrate a clonal shift in CA-MRSA in Dallas children from 1999 to 2002.

Emergence of a predominant clone of community-acquired Staphylococcus aureus among children in Houston, Texas

BACKGROUND

Community-acquired (CA), methicillin-resistant Staphylococcus aureus (MRSA) infections among children are increasing in the United States. At Texas Children's Hospital (TCH), surveillance has been in place since August 2001. The objectives of this study were to describe the distribution of CA S. aureus among patients at TCH and to study genomic relationships of isolates collected between August 2001 and July 2003.

METHODS

Genomic relationships were determined with repetitive element-polymerase chain reaction (PCR). Multilocus sequence typing was performed for selected strains representing major clones. Molecular characterization of CA-MRSA was performed with PCR, including staphylococcal cassette chromosome (SCCmec), pvl (lukS-PV plus lukF-PV), hla, hlb and selected microbial surface components recognizing adhesive matrix molecule genes, ie, cna, clfA, fnbA and fnbB.

RESULTS

A 62% increase was observed in CA S. aureus infections from year 1 (2001-2002) to year 2 (2002-2003), whereas the annual number of hospital admissions was unchanged. CA methicillin-sensitive S. aureus isolates were more likely to be associated with invasive infections than were CA-MRSA isolates (P < 0.01). TCH clone A, sequence type (ST) 8, was responsible for approximately 94% of all CA-MRSA isolated from children in the greater Houston area. Clone A differed from clones B (ST30) and C (ST1) by lacking the cna gene while carrying the fnbB gene.

CONCLUSIONS

One CA-MRSA clone, TCH clone A, has become the predominant cause of CA S. aureus infections among children in the Houston area. It causes a wide spectrum of diseases, including complicated pneumonia.

Emergence and spread of community-associated methicillin-resistant Staphylococcus aureus in rural Wisconsin, 1989 to 1999

We investigated the emergence and spread of community-associated strains of methicillin-resistant Staphylococcus aureus (CA-MRSA) in central and northern Wisconsin by determining the temporal and clonal relationships and geographic expansion among 581 of 956 clinical isolates of MRSA collected between 1989 and 1999. Based on EcoRI plasmid profiles (PP), two types, PP-11 and PP-13, were highly stable over time and were consistently associated with multidrug-sensitive strains recovered from outpatients treated at Native American community clinics. Pulsed-field gel electrophoresis (PFGE) yielded six major clonal groups (MCGs) and 19 minor clonal groups. The six MCGs represented 82% of the isolates. All strains with either PP-11 or -13 were present in MCG-2. Eighty-nine percent of the isolates in MCG-2 originated from Native American clinics, and 90% belonged to two PFGE types (19 and 20), the types associated with an outbreak of MRSA in a Native American community in 1992. MCG-2 isolates were multidrug sensitive, harbored type IVa staphylococcal cassette chromosome mec, and were very closely related by PFGE to the Midwestern CA-MRSA strain MW2. MCG-2 strains were mostly obtained from skin infections and affected patients with a mean age of 24 (+/-18.0) years. MCG-2 strains spread to four additional Native American communities and 20 other communities. Our findings suggest that CA-MRSA in Wisconsin likely originated in Native American communities in the early 1990s and since has become widespread throughout the state. Two early CA-MRSA strains (WI-33 and WI-34) in Wisconsin represent progenitors of the MW2 strain, based on their almost indistinguishable genotypic characteristics.

Risk factors for community-associated methicillin-resistant Staphylococcus aureus infections in an outbreak of disease among military trainees in San Diego, California, in 2002

An outbreak of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) skin infections was observed in a population of U.S. military trainees in the summer of 2002. A questionnaire was developed and administered to 206 trainees, 22 of whom had MRSA infections. Factors associated with infection were described by multivariable logistic regression modeling and included having a roommate in training with a prior skin infection (odds ratio [OR] = 3.44) or having a family member or friend who worked in a health care setting (OR = 2.79). Previous antibiotic use, hospitalization, or health problems were not associated with MRSA infection. This outbreak of MRSA skin infections in an otherwise-healthy, well-defined, military population provided an opportunity to describe risk factors for CA-MRSA which may help focus prevention efforts in this and other communities.

Antibacterial screening of plants used in Iranian folkloric medicine

Fifty methanolic plant extracts belonging to 44 plant species of 33 families finding use in Iranian folkloric medicine were screened for antibacterial activity. Thirty samples, including 28 species in 20 families, had antibacterial activity against at least on one of the bacteria. Among the active plants, 32.6% were active against G(-), 62% against G(+), and 47.3% against both G(-) and G(+) bacteria. Dianthus coryophyllus was active against all tested G(-) and G(+) bacteria except Micrococcus luteus. Most susceptible G(-) bacteria were Klebsiella pneumoniae and Bordetella bronchiseptica and least susceptible G(-) bacterium was Escherichia coli. In G(+) bacteria, most and least susceptible were Staphylococcus aureus and M. luteus, respectively. The least MIC, as 0.62 mg/ml, belonged to Myrtus communis seeds against S. aureus, Bacillus cereus and B. bronchiseptica, and to Terminalia chebula ripe seeds against S. aureus.

Hospital Transmission of Community-Acquired Methicillin-Resistant Staphylococcus aureus among Postpartum Women

Infections caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) are being increasingly observed in patients who lack traditional risk factors. We described 8 postpartum women who developed skin and soft-tissue infections caused by MRSA at a mean time of 23 days (range, 4-73 days) after delivery. Infections included 4 cases of mastitis (3 of which progressed to breast abscess), a postoperative wound infection, cellulitis, and pustulosis. The outbreak strains were compared with the prototype CA-MRSA strain MW2 and found to be indistinguishable by pulsed-field gel electrophoresis. All were spa type 131, all contained the staphylococcal chromosomal cassette mec type IV, and all expressed Panton-Valentine leukocidin and staphylococcal enterotoxins C and H. The route of transmission was not discovered: the results of surveillance cultures of samples obtained from employees of the hospital, the hospital environment, and newborns were negative for the outbreak strain. We report that MW2, which was previously limited to the midwestern United States, has spread to the northeastern United States and has become a health care-associated pathogen.

Severe Staphylococcus aureus infections caused by clonally related community-acquired methicillin-susceptible and methicillin-resistant isolates

We investigated the genetic relatedness of 5 community-acquired (CA) Staphylococcus aureus isolates obtained from 4 consecutive pediatric patients presenting with sepsis syndrome and severe pneumonia during a 3-week period in 2000. Two patients were infected with methicillin-susceptible S. aureus (MSSA), and 2 were infected with methicillin-resistant S. aureus (MRSA). The pulsed-field gel electrophoresis patterns for the 2 CA-MRSA isolates were identical to each other, as were the patterns for the 3 CA-MSSA isolates. A 2-band difference reflecting the presence of a staphylococcal cassette chromosome mec (SCCmec) element distinguished the CA-MRSA isolates from the CA-MSSA isolates. The small, mobile type IV SCCmec element was present in the CA-MRSA isolates. These data suggest that an insertion or, less likely, a deletion of the SCCmec type IV element occurred in a highly virulent S. aureus background. Staphylococcal toxin genes sea, seh, lukS-PV, and lukF-PV were detected in all isolates. Also, in all isolates, was a partial homolog of seo (seo'). The relationship among these patient isolates strengthens the assumption that CA-MRSA infections may be caused by isolates closely related to MSSA isolates.

Tratamento e prevenção das infecções e da colonização por Staphylococcus aureus

The number of Staphylococcus aureus (S. aureus) community and nosocomial acquired infections have increased in the last twenty years. Between 1990 and 1992, this pathogen has become the most frequent source of nosocomial infections 1,2. On the other hand, as result of antibiotherapy selection pressure, we observe a dramatic increase in the methicillin-resistant S. aureus (MRSA) infections 3,4. With the recent emergence of multiresistant strains, including glycopeptides resistance, the treatment of these infections became still more difficult 2,4-6. It's important to prevent resistant strains emergence. To prevent further emergence of resistant strains, the use of antibiotherapy must be optimised, laboratory methods for the detection of resistant pathogens must be enhanced and strict precautions should be taken following of the infection or colonization of patients 6-10. In this paper, we review anti-staphylococci history evolution and point out the present recommendations for the treatment and prevention of Staphylococcus aureus infections and colonization.

Prevalence of and risk factors for colonization with methicillin-resistant Staphylococcus aureus at the time of hospital admission

OBJECTIVES

To determine the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) colonization among patients presenting for hospital admission and to identify risk factors for MRSA colonization.

DESIGN

Surveillance cultures were performed at the time of hospital admission to identify patients colonized with S. aureus. A case-control study was performed to identify risk factors for MRSA colonization.

SETTING

A tertiary-care academic medical center.

PATIENTS

Adults presenting for hospital admission (N = 974).

RESULTS

S. aureus was isolated from 205 (21%) of the patients for whom cultures were performed. Methicillin-sensitive S. aureus was isolated from 179 (18.4%) of the patients, and MRSA was isolated from 26 (2.7%) of the patients. All 26 MRSA-colonized patients had been admitted to a healthcare facility in the preceding year, had at least one chronic illness, or both. In multivariate analyses comparing MRSA-colonized patients with control-patients, admission to a nursing home (odds ratio [OR], 16.5; 95% confidence interval [CI95], 1.4 to 192.1; P = .025) or a hospitalization of 5 days or longer during the preceding year (OR, 3.91; CI95, 1.1 to 13.9; P = .035) were independent predictors of MRSA colonization.

CONCLUSIONS

Patients colonized with MRSA admitted to this hospital likely acquired the organism during previous encounters with healthcare facilities. There was no evidence that MRSA colonization occurs commonly among low-risk individuals in this community. These data suggest that evaluation of recent healthcare exposures is essential if true community acquisition of MRSA is to be confirmed.

Spread of methicillin-resistant Staphylococcus aureus (MRSA) among household contacts of individuals with nosocomially acquired MRSA

OBJECTIVE

To determine the frequency with which methicillin-resistant Staphylococcus aureus (MRSA) is spread from colonized or infected patients to their household and community contacts.

DESIGN

Retrospective cohort study.

SETTING

University hospital.

PARTICIPANTS

Household and community contacts of MRSA-colonized or -infected patients for whom MRSA screening cultures were performed.

RESULTS

MRSA was isolated from 25 (14.5%) of 172 individuals. Among the contacts of index patients who had at least one MRSA-colonized contact, those with close contact to the index patient were 7.5 times more likely to be colonized (53% vs 7%; 95% confidence interval, 1.1 to 50.3; P = .002). An analysis of antimicrobial susceptibility and DNA fingerprint patterns suggested person-to-person spread.

CONCLUSIONS

MRSA colonization occurs frequently among household and community contacts of patients with nosocomially acquired MRSA, suggesting that transmission of nosocomially acquired MRSA outside of the healthcare setting may be a substantial source of MRSA colonization and infection in the community.

Infection control recommendations for patients with cystic fibrosis: microbiology, important pathogens, and infection control practices to prevent patient-to-patient transmission

Infection Control Recommendations for Patients With Cystic Fibrosis: Microbiology, Important Pathogens, and Infection Control Practices to Prevent Patient-to-Patient Transmissionupdates, expands, and replaces the consensus statement,Microbiology and Infectious Disease in Cystic Fibrosispublished in 1994. This consensus document presents background data and evidence-based recommendations for practices that are intended to decrease the risk of transmission of respiratory pathogens among CF patients from contaminated respiratory therapy equipment or the contaminated environment and thereby reduce the burden of respiratory illness. Included are recommendations applicable in the acute care hospital, ambulatory, home care, and selected non-healthcare settings. The target audience includes all healthcare workers who provide care to CF patients. Antimicrobial management is beyond the scope of this document.

Identification of phenylisoxazolines as novel and viable antibacterial agents active against Gram-positive pathogens

A new and promising group of antibacterial agents, collectively known as the oxazolidinones and exemplified by linezolid (PNU-100766, marketed as Zyvox), have recently emerged as important new therapeutic agents for the treatment of infections caused by Gram-positive bacteria. Because of their significance, extensive synthetic investigations into the structure-activity relationships of the oxazolidinones have been conducted at Pharmacia. One facet of this research effort has focused on the identification of bioisosteric replacements for the usual oxazolidinone A-ring. In this paper we describe studies leading to the identification of antibacterial agents incorporating a novel isoxazoline A-ring surrogate. In a gratifying result, the initial isoxazoline analogue prepared was found to exhibit in vitro antibacterial activity approaching that of the corresponding oxazolidinone progenitor. The synthesis and antibacterial activity profile of a preliminary series of isoxazoline analogues incorporating either a C-C or N-C linkage between their B- and C-rings will be presented. Many of the analogues exhibited interesting levels of antibacterial activity. The piperazine derivative 54 displayed especially promising in vitro activity and in vivo efficacy comparable to the activity and efficacy of linezolid.

Community-acquired methicillin-resistant Staphylococcus aureus: a meta-analysis of prevalence and risk factors

Reports suggest that carriage of methicillin-resistant Staphylococcus aureus (MRSA) among persons without health care-associated risks has increased. A meta-analysis of studies reporting the prevalence of community-acquired MRSA (CA-MRSA) among MRSA isolates from hospitalized patients or the prevalence of MRSA colonization among community members was conducted. The CA-MRSA prevalence among hospital MRSA was 30.2% in 27 retrospective studies and 37.3% in 5 prospective studies; 85% of all patients with CA-MRSA had > or =1 health care-associated risk. The pooled MRSA colonization rate among community members was 1.3% (95% confidence interval [CI], 1.04%-1.53%), but there was significant heterogeneity among study populations. Community members from whom samples were obtained in health care facilities were more likely to be carrying MRSA than were community members from whom samples were obtained outside of the health care setting (relative risk, 2.35; 95% CI, 1.56-3.53). Among studies that excluded persons with health care contacts, the MRSA prevalence was 0.2%. Moreover, most persons with CA-MRSA had > or =1 health care-associated risk, which suggests that the prevalence of MRSA among persons without risks remains low (< or =0.24%). Effective control of dissemination of MRSA throughout the community likely will require effective control of nosocomial MRSA transmission.

Clindamycin treatment of methicillin-resistant Staphylococcus aureus infections in children

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) with a narrower antibiotic resistance pattern have emerged. There is a risk for the appearance of resistance during clindamycin therapy of erythromycin-resistant MRSA infections because of the linked resistance mechanisms.

METHODS

We analyzed clindamycin-susceptible MRSA organisms from children (1987 to 2000) along with clinical data. Antibiotic susceptibilities of organisms were tested, pulsed field gel electrophoresis (PFGE) was done and the linked resistance mechanism was detected by the D test.

RESULTS

An average of 11 clindamycin-susceptible MRSA per year were obtained from children since 1993. Of 88 isolates 33 (38%) were erythromycin-resistant. The latter were less often community-acquired (45% vs. 69%), more often from infants <1 month of age (24% vs. 4%) and less likely to be in the community acquisition-associated PFGE Group 1 (62% vs. 87%) than those that were susceptible. The D test was positive in 31 of 33 erythromycin-resistant isolates. A 9-month-old boy with pneumonia/empyema caused by a clindamycin-susceptible, erythromycin-resistant, D test-positive MRSA developed a PFGE-identical clindamycin-resistant isolate and clinical relapse during clindamycin treatment. In contrast a 12-year-old girl with abscesses caused by a similar MRSA developed another abscess after clindamycin therapy, but the organism was unchanged in susceptibility.

CONCLUSIONS

Erythromycin resistance was present in 38% of clindamycin-susceptible MRSA in children, and clindamycin resistance was detected during treatment in one child. Clindamycin remains a treatment option if the clinician is notified of the risk by the microbiology laboratory and the clinical situation is suitable.

Controversies in isolation and general infection control practices in pediatrics

Current controversies in pediatric isolation and infection control include correct application of standard precautions, importance of providing adequate staffing levels in intensive care units to prevent transmission of infectious agents, use of rapid diagnostic testing and best precautions to prevent transmission of respiratory syncytial virus, best methods to prevent transmission of multidrug-resistant organisms in acute care settings, and preventing transmission of infections to pregnant healthcare workers. Recommendations are evidence-based.

Microbial epidemiology patterns of surgical infection pathogens

Resistance, as assessed in vitro, has a number of serious consequences in clinical situations. Treatment failures are common when an inappropriate drug has been prescribed and this, in turn, may lead to hospitalization of patients who normally would have been treated on an outpatient basis, as well as to longer hospital stay for inpatients and to the use of alternative drugs, which may be more expensive and more toxic. These factors all contribute to increased health care costs, morbidity and mortality. Microbiological procedures may identify the causative pathogen and provide the appropriate susceptibility pattern to the physician, thus reducing the chances of therapeutic failures. However, for a number of reasons including cost--even in hospitals--not to mention general practice, infections are seldom diagnosed on an etiological basis. From what has been stated, the knowledge of bacterial epidemiology and resistance represents basic support for correct therapeutic decision-making.

Epidemiology and clonality of community-acquired methicillin-resistant Staphylococcus aureus in Minnesota, 1996-1998

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged among patients in the general population who do not have established risk factors for MRSA. Records from 10 Minnesota health facilities were reviewed to identify cases of MRSA infection that occurred during 1996-1998 and to identify which cases were community acquired. Susceptibility testing and pulsed-field gel electrophoresis (PFGE) subtyping were performed on available isolates. A total of 354 patients (median age, 16 years) with community-acquired MRSA (CAMRSA) infection were identified. Most case patients (299 [84%]) had skin infections, and 103 (29%) were hospitalized. More than 90% of isolates were susceptible to all antimicrobial agents tested, with the exception of beta-lactams and erythromycin. Of 334 patients treated with antimicrobial agents, 282 (84%) initially were treated with agents to which their isolates were nonsusceptible. Of 174 Minnesota isolates tested, 150 (86%) belonged to 1 PFGE clonal group. CAMRSA infections were identified throughout Minnesota; although most isolates were genetically related and susceptible to multiple antimicrobials, they were generally nonsusceptible to initial empirical therapy.

Increasing threat of Gram-positive bacterial infections in the intensive care unit setting

The effects of resistance are being noted on an increasing scale in the intensive care unit (ICU). Around the world, new epidemiologic patterns of ICU occurrence are being observed for Gram-positive multidrug-resistant organisms. Current problems include the appearance of insusceptibility to vancomycin and other glycopeptides in Staphylococcus aureus organisms that are virulent enough to cause infection in patients with normal host defenses. In addition, multidrug-resistant organisms like methicillin-resistant S.aureus are spreading from healthcare to community settings, and community organisms like Streptococcus pneumoniae are spreading to healthcare settings. Focal persistence and subsequent worldwide spread of enterococci resistant to vancomycin and other glycopeptides and multiple-resistance mechanisms in the same organism also require attention. Strategies such as multidisciplinary management of infections, appropriate infection control measures, and surveillance of resistance patterns are necessary to address the problem of resistance. Intensivists have been prominent in research and control efforts in this field and should continue to lead future efforts.

Evolving antimicrobial chemotherapy for Staphylococcus aureus infections: Our backs to the wall

Staphylococcus aureus is responsible for many nosocomial and community-acquired infections. Its evolving resistance to traditional antimicrobial chemotherapy and emerging prevalence outside of the healthcare environment are serious concerns. This review of the changing epidemiology of methicillin-resistant S. aureus, the emergence of vancomycin (glycopeptide)-resistant isolates, and the mechanisms of resistance to beta-lactams and glycopeptides provides an update for clinicians regarding effective strategies for treatment.