Resistance to dicloxacillin, methicillin and oxacillin in methicillin-susceptible and methicillin-resistant Staphylococcus aureus detected by dilution and diffusion methods

A total of 54 Staphylococcus aureus strains of varying methicillin resistance were investigated for their resistance to methicillin, oxacillin and dicloxacillin by different diffusion tests. Inhibition zones were measured around locally prepared paperdiscs with 10 micrograms methicillin, 5 and 10 micrograms oxacillin, 5 and 10 micrograms dicloxacillin, PDM paperdiscs with 10 micrograms methicillin or oxacillin and Neo-sensitabs tablets with methicillin or oxacillin. All diffusion tests were performed both with Mueller-Hinton agar and Danish Blood agar as well as at 37 degrees C and 30 degrees C and read after overnight incubation. Differences in zone diameter under different conditions were found to be independent of the susceptibility level of the strains. Seventeen of the strains were detected as methicillin-resistant (MRSA) by two methods including high inoculum and prolonged incubation at 30 degrees C. The minimum inhibitory concentration (MIC) of the 54 strains was determined by a plate dilution method at 30 degrees C and 37 degrees C. A 10 micrograms locally prepared methicillin disc detected all MRSA strains with no false reactions either at 37 degrees C or 30 degrees C on Mueller-Hinton agar. Investigations with oxacillin discs had to be performed at 30 degrees C or with a 5 microgram disc in order to detect correctly. PDM paperdiscs gave reactions identical to the corresponding locally prepared discs. Methicillin Neo-sensitabs detected all MRSA strains but also included a few susceptible strains among the resistant ones. Addition of blood increased the number of not-detected MRSA strains. All 17 MRSA strains were susceptible to dicloxacillin by the dilution method, and the disc diffusion test showed similar results. Dicloxacillin discs therefore did not detect the presence of MRSA strains. The implications of replacement of the methicillin/oxacillin disc by a dicloxacillin disc are discussed.     

Antimicrobial susceptibility and epidemiology of a worldwide collection of Chryseobacterium spp: report from the SENTRY Antimicrobial Surveillance Program (1997-2001)

Limited data are available on Chryseobacterium spp. leading to an evaluation of the patient demographics and susceptibility patterns for Chryseobacterium spp. collected in the first 5 years of the SENTRY Antimicrobial Surveillance Program (1997 to 2001). Fifty isolates (24 Chryseobacterium meningosepticum, 20 Chryseobacterium indologenes, two Chryseobacterium gleum, and 4 Chryseobacterium spp. isolates) were collected. The highest Chryseobacterium prevalence was detected among the elderly. The most active antimicrobials were the newer quinolones (garenoxacin, gatifloxacin, and levofloxacin, each with a MIC at which 90 percent of the isolates are inhibited [MIC(90)] of 1 micro g/ml and 98.0% susceptibility) followed by rifampin (MIC(90), 2 microg/ml and 85.7% susceptibility). Trimethoprim-sulfamethoxazole, ciprofloxacin, and piperacillin-tazobactam also showed reasonable activity; vancomycin showed poor potency.     

Comparison of tests to detect oxacillin resistance in Staphylococcus intermedius, Staphylococcus schleiferi, and Staphylococcus aureus isolates from canine hosts

Multiple tests were compared to the reference standard PBP2a latex agglutination test for detection of mecA-mediated oxacillin resistance in canine staphylococci. Cefoxitin disk diffusion, using breakpoints for human isolates of coagulase-negative Staphylococcus spp., had low sensitivity for detection of oxacillin resistance in members of the Staphylococcus intermedius group.     

Strain relatedness of meticillin-resistant Staphylococcus aureus isolates recovered from patients with repeated bacteraemia

Information on the relatedness of isolates causing repeated meticillin-resistant Staphylococcus aureus (MRSA) bacteraemia is limited. An observational study of 177 patients with MRSA bacteraemia, admitted to the emergency department of National Taiwan University Hospital, was conducted from January 2001 to June 2006. Among these patients, 28 had a previous episode of MRSA bacteraemia and 59 died during the index episode of bacteraemia. Until December 2007, among the 118 patients who survived the index episode (101 without previous bacteraemia and 17 with previous bacteraemia), 24 (20.3%) had repeated MRSA bacteraemia. The duration from discontinuation of antimicrobial therapy to repeat episodes was in the range 35–854 days (median 86 days). Eight patients (33.3%) died as a result of the second bacteraemic episode. Clinical characteristics associated with repeated bacteraemia included the diagnosis of infective endocarditis and active malignancy. Pulsed-field gel electrophoresis and multilocus sequence typing analysis were performed for 32 pairs of available isolates recovered from patients with repeated bacteraemia and revealed that 29 of them (90.6%) were genetically closely-related strains. The majority of patients with repeated MRSA bacteraemia had recurrent infections and a high mortality rate.     

Geographic variations in species distribution and echinocandin and azole antifungal resistance rates among Candida bloodstream infection isolates: report from the SENTRY Antimicrobial Surveillance Program (2008 to 2009)

Antifungal testing results from the SENTRY Antimicrobial Surveillance Program (2008 to 2009) were analyzed for regional variations of invasive Candida species infections. Among 2,085 cases from the Asian-Pacific (APAC) (51 cases), Latin American (LAM) (348 cases), European (EU) (750 cases), and North American (NAM) (936 cases) regions, Candida albicans predominated (48.4%), followed by C. glabrata (18.0%), C. parapsilosis (17.2%), C. tropicalis (10.5%), and C. krusei (1.9%). Resistance to echinocandins (anidulafungin [2.4%] and micafungin [1.9%]) and azoles (3.5 to 5.6%) was most prevalent among C. glabrata isolates, as determined using recently established CLSI breakpoint criteria. C. glabrata isolates were more common in NAM (23.5%), and C. albicans isolates were more common in APAC (56.9%), with C. parapsilosis (25.6%) and C. tropicalis (17.0%) being more prominent in LAM. Emerging resistance patterns among C. glabrata cases in NAM require focused surveillance.     

Changing antimicrobial susceptibility patterns among Streptococcus pneumoniae and Haemophilus influenzae from Brazil: Report from the SENTRY Antimicrobial Surveillance Program (1998-2004)

Although antimicrobial resistance rates among Streptococcus pneumoniae and Haemophilus influenzae have increased significantly in most countries in the last years, most studies from Brazil report relatively low resistance rates among these pathogens. In this study, we analyzed the susceptibility patterns of S. pneumoniae and H. influenzae from Brazil during a 7-year period. A total of 829 S. pneumoniae and 718 H. influenzae consecutively collected from 1998 to 2004, mainly from respiratory tract and bloodstream infections, were susceptibility tested by broth microdilution methods against >30 drugs and the results were analyzed by year. Overall, 77.8% of S. pneumoniae strains were considered susceptible (MIC, < or =0.06 microg/ml) to penicillin. Resistance to penicillin (MIC, > or =2 microg/ml) and ceftriaxone (MIC, > or =4 microg/ml) were detected in 7.5 and 0.5% of strains, respectively. The fluoroquinolones, levofloxacin (MIC90) 1 microg/ml) and gatifloxacin (MIC90, 0.5 microg/ml), were active against 99.8% of the isolates tested. Among the other non-beta-lactam drugs tested, the rank order of susceptibility rates was chloramphenicol (98.9%) > clindamycin (96.4%) > erythromycin (90.6%) > tetracycline (69.8%) > trimethoprim/sulfamethoxazole (36.7%). Resistance to penicillin has increased markedly among S. pneumoniae isolates over 7 years (from 2.9 to 11.0%). Additionally, resistance rates against erythromycin, clindamycin, and tetracycline decreased among pneumococcal strains during the same period. S. pneumoniae recovered from pediatric patients (< or =5 years) showed increased penicillin and trimethoprim/sulfametroxazole resistance rates compared to older populations. The rate of ampicillin resistance among H. influenzae was 14.0%, which also corresponds with the beta -lactamase production rate. All H. influenzae isolates were susceptible to amoxicillin/clavulanate (MIC90, 1 microg/ml), ceftriaxone (MIC90, < or =0.008 microg/ml), cefepime (MIC90, 0.12 microg/ml), ciprofloxacin (MIC90, < or = 0.12microg/ml), levofloxacin (MIC90, < or =0.5 microg/ml), and gatifloxacin (MIC90, < or =0.03 microg/ml). Resistance to the antimicrobials tested remained very stable among H. influenzae isolates during the 7-year study period. The continued emerging antimicrobial resistances found in these pathogens (mainly S. pneumoniae) highlight the need for alternative agents for the treatment of infections caused by these species.     

Comparative analysis of multidrug-resistant,non-multidrug-resistant,and archaic methicillin-resistant Staphylococcus aureus isolates from Central Sydney,Australia

In this study, the phenotypic and genotypic characteristics of 50 methicillin-resistant Staphylococcus aureus (MRSA) isolates (43 contemporary and 7 archaic strains from the mid-1960s) from four Sydney hospitals in the central Sydney area were compared. Phenotypic analysis based on antibiotic profiles and phage typing patterns categorized the MRSA isolates into three major groups: multidrug resistant (mMRSA), non-multidrug resistant (nmMRSA), and archaic. The nmMRSA isolates could be further subdivided into nmMRSA group 1, which was phage typeable and similar to the archaic group; nmMRSA group 2, which was non-phage typeable and only resistant to ciprofloxacin; and nmMRSA group 3, which was also nontypeable and generally resistant to other antibiotics. The characterization of all five phenotypic groups was then extended by genetic analysis. Restriction fragment length polymorphism (RFLP) analysis showed the 50 isolates could be sorted into 20 group-specific pulsotypes. mecI gene deletions and mutations at various percentages among the five MRSA groups were detected by sequencing. Several mec promoter mutations were also found. The overall findings indicated that nmMRSA strains may have independently acquired mec DNA and are more likely to be newly emergent strains than nmMRSA variants.     

Study of methicillin resistant S. aureus (MRSA) isolates from high risk patients

MRSA is an important hospital pathogen, the incidence of which is increasing every year especially in high risk groups. The present study was performed in high risk patients admitted in burns and orthopaedic units of LN hospital to study the infection rate of MRSA from these units. The proportion of MRSA amongst S. aureus isolates was found to be 51.6% and these isolates were multidrug resistant. Phage typing of these isolates gave a typeability of 41.8% using the MRSA set of phages. Biotyping of these isolates could divide them into four groups. The study shows a high incidence of MRSA from burns and orthopaedic units with a high level of antibiotic resistance amongst these isolates.     

Epidemiology and susceptibility of 3,051 Staphylococcus aureus isolates from 25 university hospitals participating in the European SENTRY study

A total of 3,051 methicillin-susceptible Staphylococcus aureus (MSSA) isolates and methicillin-resistant S. aureus (MRSA) isolates in Europe were compared. MRSA isolates constituted 25% of all isolates and were more prevalent in southern Europe. MRSA isolates appeared to be more prevalent in intensive care units than in outpatient departments. Only a small minority of MSSA isolates were multidrug resistant, whereas the majority of MRSA isolates were multidrug resistant.     

Molecular characterization of resistance to mupirocin in methicillin-susceptible and -resistant isolates of Staphylococcus aureus from nasal samples

A total of 15 of 101 (14.8%) nasal methicillin-resistant Staphylococcus aureus (MRSA) isolates exhibited mupirocin resistance (Mup(r)) compared with 1 of 154 (0.6%) methicillin-susceptible Staphylococcus aureus isolates. A total of 14 (93%) isolates exhibiting high-level Mup(r) belonged to a single clone. Horizontal plasmid transfer and transmission of Mup(r) strains contribute to a high incidence of Mup(r) MRSA at our institution.     

Changing molecular epidemiology of methicillin-resistant Staphylococcus aureus bloodstream isolates from a teaching hospital in Northern Taiwan

A changing molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) bloodstream isolates from a university-affiliated hospital in Taiwan during a 4-year interval was demonstrated. The changing epidemiology is due to the introduction of a new epidemic clone (sequence type 5) and a local community clone (sequence type 59) of MRSA into the hospital.     

Occurrence and characterization of carbapenemase-producing Enterobacteriaceae: report from the SENTRY Antimicrobial Surveillance Program (2000-2004)

Emergence and dissemination of Enterobacteriaceae isolates harboring carbapenemases in various geographic regions represents a significant threat to the management of nosocomial infections. Enterobacteriaceae isolates from the SENTRY Antimicrobial Surveillance Program (2000-2004) demonstrating decreased susceptibility to imipenem and meropenem (minimum inhibitory concentration [MIC], > or =2 mg/L) were evaluated for the production of metallo-beta-lactamases and serine carbapenemases using disk approximation and polymerase chain reaction (PCR) tests. Carbapenemase-producing strains were epidemiologically typed by automated riboprinting and pulsed-field gel electrophoresis (PFGE) to establish clonality. Among 37,557 Enterobacteriaceae (5 genus groups) evaluated, 119 (0.32%) had increased carbapenem MIC values, and a carbapenemase was identified in 51 (42.9%) of these strains. KPC-2 and KPC-3 were the most frequently occurring carbapenemases (24 isolates, 20.2%) in the United States and were detected in Klebsiella spp, Citrobacter spp., Enterobacter spp., and Serratia marcescens strains isolated in New York, Arkansas, and Virginia. SME-2-producing S. marcescens were isolated in the New York City area, Texas, and Ohio, while NMC-A was found in one E. cloacae strain from New York. In contrast, metallo-beta-lactamases were prevalent in Europe. IMP-1-producing E. cloacae (11 isolates) were detected in Turkey, while VIM-1-producing strains were found in Italy (Enterobacter spp.) and Greece (Klebsiella pneumoniae). Clonal dissemination of carbapenemase-producing strains was observed in several medical centers on both continents. The occurrence of carbapenemases in various Enterobacteriaceae remains rare but appears to be spreading geographically (not in Latin America), mainly with metallo-beta-lactamases being found in Mediterranean Europe and KPC enzymes in the New York City area.     

Comparison of the Vitek Gram-Positive Susceptibility 106 card and the MRSA-screen latex agglutination test for determining oxacillin resistance in clinical bloodstream isolates of Staphylococcus aureus

The Vitek automated susceptibility testing system with a modified Gram-Positive Susceptibility (GPS) 106 Card (bioMerieux Vitek, Inc., Hazelwood, Mo.) and a rapid slide latex agglutination test (MRSA-Screen; Denka Seiken Co., Ltd., Tokyo, Japan) were evaluated for their ability to detect oxacillin resistance in Staphylococcus aureus. The oxacillin-salt agar screen (OS) test, the reference broth microdilution method, and the detection of the mecA gene by PCR were compared with the commercial products. A total of 200 contemporary (1999) bloodstream infection isolates were collected from the SENTRY Antimicrobial Surveillance Program, representing diverse geographic areas throughout the world. Among the 99 mecA-positive isolates, 3 isolates were found negative by the MRSA-Screen. Another two isolates did not grow on OS plates and had MICs of 0.5 and 2 microg/ml with the Vitek GPS card. All 101 mecA-negative isolates were also found negative by the MRSA-Screen and were categorized as susceptible by the GPS card. Overall, the MRSA-Screen, GPS card, and OS test had sensitivities of 96.9, 98.0, and 98.0% and specificities of 100.0, 100.0, and 98.0%, respectively. MRSA-Screen was a rapid (相似文献   

Molecular characterization of nasal methicillin resistant Staphylococcus aureus isolates from workers of an automaker company in southeast Iran

Colonization of methicillin resistant Staphylococccus aureus (MRSA) can occur more commonly in healthy people who live in close together or are in close physical contact with each other. Having knowledge about the molecular characteristics of these strains provides considerable discernment into the epidemiology of this important microorganism. A total of 806 nasal swabs were collected from healthy workers of an automaker company in the southeast of Iran and were analyzed to detect MRSA isolates. Multilocus sequence typing (MLST), spa typing, and detection of staphylococcal cassette chromosome mec (SCCmec) were performed. The presence of genes encoding Panton‐Valentine Leukocidin (PVL) and Arginine Catabolic Mobile Element (ACME) were also investigated. Carriage rate of S. aureus was 20%. Among 10 identified MRSA, no acme was found while high prevalence of pvl (60%) was of great concern. Seven different spa types including five new ones were identified. The most frequent sequence type was the novel one; ST 3373 (n = 3), followed by each of ST22, ST88, ST859 (n = 2) and ST1955 (n = 1). MRSA isolates were clustered into two main clonal complexes; CC22 (n = 6) and CC88 (n = 4). Low genetic diversity with the dominance of CC22, SCCmecIV was found. Distribution of previously found hospital‐associated MRSA was demonstrated among our isolates.     

Antimicrobial susceptibility of bacteria causing urinary tract infections in Latin American hospitals: results from the SENTRY Antimicrobial Surveillance Program (1997)

Objectives: To evaluate the antimicrobial susceptibility patterns among 469 pathogens isolated as a significant cause of urinary tract infections in 10 Latin American medical centers.
Methods: Consecutively collected isolates were susceptibility tested by broth microdilution methods, and selected isolates were characterized by molecular typing methods.
Results: Escherichia coli and Klebsiella spp. isolates revealed high rates of resistance to broad-spectrum penicillins and to fluoroquinolones. Ceftazidime MICs of ≥2 mg/L, suggesting the production of extended-spectrum β-lactamases (ESBLs), were observed in 37.7% of K. pneumoniae and 8.3% of Escherichia coli isolates. Enterobacter spp. isolates were characterized by high resistance rates to ciprofloxacin (35%) and to ceftazidime (45%), but they generally remained susceptible to cefepime (95% susceptible). Pseudomonas aeruginosa and Acinetobacter spp. were highly resistant to ciprofloxacin and ceftazidime. Imipenem was active against 80% of P. aeruginosa and 93% of Acinetobacter spp. isolates.
Conclusions: Our results demonstrate a high level of resistance to various classes of antimicrobial agents among isolates causing nosocomial urinary tract infections in Latin American hospitals. Clonal dissemination of ESBL-producing K. pneumoniae strains was infrequent.     

Prevalence and Genetic Mechanisms of Antimicrobial Resistance in Staphylococcus Species: A Multicentre Report of the Indian Council of Medical Research Antimicrobial Resistance Surveillance Network

Purpose: Routine surveillance of antimicrobial resistance (AMR) is an essential component of measures aimed to tackle the growing threat of resistant microbes in public health. This study presents a 1-year multicentre report on AMR in Staphylococcus species as part of Indian Council of Medical Research-AMR surveillance network. Materials and Methods: Staphylococcus species was routinely collected in the nodal and regional centres of the network and antimicrobial susceptibility testing was performed against a panel of antimicrobials. Minimum inhibitory concentration (MIC) values of vancomycin (VAN), daptomycin, tigecycline and linezolid (LNZ) against selected methicillin-resistant Staphylococcus aureus (MRSA) isolates were determined by E-test and MIC creep, if any, was determined. Resistant genotypes were determined by polymerase chain reaction for those isolates showing phenotypic resistance. Results: The prevalence of MRSA was found to be range from moderate (21%) to high (45%) among the centres with an overall prevalence of 37.3%. High prevalence of resistance was observed with commonly used antimicrobials such as ciprofloxacin and erythromycin in all the centres. Resistance to LNZ was not encountered except for a single case. Full-blown resistance to VAN in S. aureus was not observed; however, a few VAN-intermediate S. aureus isolates were documented. The most common species of coagulase negative staphylococci (CoNS) identified was Staphylococcus haemolyticus and Staphylococcus epidermidis. Resistance among CoNS was relatively higher than S. aureus. Most phenotypically resistant organisms possessed the corresponding resistance genes. Conclusion: There were localised differences in the prevalence of resistance between the centres. The efficacy of the anti-MRSA antimicrobials was very high; however, almost all these antimicrobials showed evidence of creeping MIC.     

Trends in antifungal susceptibility of Candida spp. isolated from pediatric and adult patients with bloodstream infections: SENTRY Antimicrobial Surveillance Program, 1997 to 2000

From 1 January 1997 through 31 December 2000, 2,047 bloodstream infections (BSIs) due to Candida spp. were reported from hospitals in the United States, Canada, Latin America, and Europe participating in the SENTRY Antifungal Surveillance Program. Among individuals in four age groups (< or =1, 2 to 15, 16 to 64, and > or =65 years) Candida albicans was the most common species, causing 60, 55, 55, and 50% of infections, respectively. C. glabrata caused 17 to 23% of BSIs in those ages 16 to 64 and > or = 65 years, whereas it caused only 3% of BSIs in the individuals in the two younger age groups (P < 0.001). C. parapsilosis (which caused 21 to 24% of BSIs) and C. tropicalis (which caused 7 to 10% of BSIs) were more common than C. glabrata in individuals ages < or =1 year and 2 to 15 years. Isolates of Candida spp. showed a trend of decreasing susceptibility to fluconazole, itraconazole, and amphotericin B with increasing patient age (P < or = 0.01). None of the C. glabrata isolates from individuals < or =1 year old were resistant to fluconazole, whereas they made up 5 to 9% of isolates from individuals ages 16 to 64 and > or =65 years. Isolates of C. tropicalis from patients < or =1 year old were more susceptible to flucytosine (MIC at which 90% of isolates are inhibited [MIC(90)], 0.5 microg/ml; 0% resistant isolates) than those from patients > or =65 years old (MIC(90), 32 microg/ml; 11% resistant isolates). The investigational triazoles posaconazole, ravuconazole, and voriconazole were all highly active against all species of Candida from individuals in all age groups. These data demonstrate differences in the species distributions of pathogens and differences in antifungal resistance among isolates from individuals in the pediatric and adult age groups. Ongoing surveillance will enhance efforts to limit the extent of antifungal resistance in individuals in various age groups.