Detection and Prevalence of Penicillin-Susceptible Staphylococcus aureus in the United States in 2013.

Using blaZ PCR as the "gold standard," the sensitivities of CLSI penicillin zone edge and nitrocefin-based tests for ß-lactamase production in Staphylococcus aureus were 64.5% and 35.5%, respectively, with specificity of 99.8% for both methods. In 2013, 13.5% of 3,083 S. aureus isolates from 31 U.S. centers were penicillin susceptible.

The molecular epidemiology of Streptococcus pneumoniae with quinolone resistance mutations.

BACKGROUND: The purpose of this study was to determine the prevalence of fluoroquinolone resistance and quinolone resistance-determining region (QRDR) mutations among Streptococcus pneumoniae isolates in the United States during the period of 2001-2002. A second objective was to examine the genetic relatedness of pneumococcal isolates with parC and/or gyrA mutations during the period of 1994-2002. METHODS: Susceptibility testing was performed for 1902 S. pneumoniae isolates collected in the United States during the period of 2001-2002. On the basis of the minimum inhibitory concentration (MIC) of ciprofloxacin, 146 isolates were selected from the 2001-2002 study for QRDR analysis of parC, parE, gyrA, and gyrB genes. The genetic relatedness of isolates with parC and/or gyrA mutations from 2001-2002 (n=55) and from 3 US surveillance studies conducted during 1994-2000 (n=56) was determined by pulsed-field gel electrophoresis (PFGE). RESULTS: Between 1999-2000 and 2001-2002, there was a 2-fold increase in the rate of ciprofloxacin resistance (MIC, >or=4 micro g/mL), from 1.2% to 2.7%, and in the rate of levofloxacin nonsusceptibility (MIC, >or=4 micro g/mL), from 0.6% to 1.3%. The 111 isolates with parC and/or gyrA mutations were assigned to 48 different PFGE types. Forty-four isolates (40%) belonged to 8 PFGE types that were closely related to widespread clones. Fifteen of the 43 levofloxacin-nonsusceptible pneumococci (LNSP) belonged to 4 PFGE types that were closely related to major clones (Spain(23F)-1 [n=6]; Spain(6B)-2 [n=5], Taiwan(19F)-14 [n=2], and Tennessee(23F)-4 [n=2]). CONCLUSION: The population of fluoroquinolone-resistant S. pneumoniae in the United States has increased but remains genetically diverse. However, 35% of LNSP were related to widespread pneumococcal clones, increasing the potential for the rapid spread of quinolone resistance in this species.

A fresh look at the definition of susceptibility of Streptococcus pneumoniae to beta-lactam antibiotics.

Definitions for susceptibility or resistance of Streptococcus pneumoniae to penicillin were not developed until penicillin-resistant pneumococci appeared in South Africa in the late 1970s. The definition that was accepted (which still remains in use) and later definitions of resistance to most other beta-lactam antibiotics were derived from laboratory and clinical data relating to the treatment of meningitis, not otitis media, sinusitis, or pneumonia. An understanding of the origin of these definitions helps to resolve the apparent paradox that infections of the respiratory tract due to seemingly beta-lactam-resistant pneumococci may still respond well to standard doses of these drugs. A recently sanctioned change in the definition of susceptibility to amoxicillin is helpful in eliminating the paradox for this drug, but it may create further confusion by implying that, on a microgram basis, amoxicillin is substantially more effective than penicillin or third-generation cephalosporins. This article examines definitions of susceptibility and resistance of pneumococci, highlighting areas that have led to confusion and proposing a new way of understanding them.

Presumptive evidence for Blastocystis hominis as a cause of colitis.

A patient with persistent diarrhea was found to have biopsy-proved colitis with large numbers of the protozoan Blastocystis hominis present in stool. Extensive evaluation failed to reveal any other potential etiologic agent of acute colitis. Following treatment with a course of metronidazole, the patient became asymptomatic, B hominis was no longer present in stool, and results of a repeated biopsy were normal. These observations are consistent with the role of B hominis as a gastrointestinal pathogen.

Influence of triple-lumen central venous catheters coated with chlorhexidine and silver sulfadiazine on the incidence of catheter-related bacteremia.

OBJECTIVE: To evaluate the efficacy of triple-lumen central venous catheters coated with a combination product of chlorhexidine and silver sulfadiazine (CSS) in reducing the incidence of local catheter infection and catheter-related bacteremia. DESIGN: Randomized, controlled trial. SETTING: The surgical intensive care units in a university hospital. PATIENTS: All patients who needed central venous catheterization were randomized to receive either an uncoated triple-lumen catheter (n = 157) or a catheter coated with CSS (n = 151). MAIN OUTCOME MEASURE: Catheters were removed when no longer needed or suspected as a cause of infection. The tip and a 5-cm segment of the intradermal portion of the catheter were cultured semiquantitatively. Blood cultures were obtained when clinically indicated. The remaining segment of catheters coated with CSS were cut and incubated on an agar plate with strains of Staphylococcus aureus and Enterococcus. Zone of inhibition was determined 24 hours later. Data were analyzed by survival and logistic multivariate regression methods. RESULTS: Catheters coated with CSS were effective in reducing the rate of significant bacterial growth on either the tip or intradermal segment (40%) compared with control catheters (52%; P = .04). However, there was no difference in the incidence of catheter-related bacteremia (3.8% [uncoated] vs 3.3% [coated]; P = .81). In vitro activity of catheters with CSS against S aureus was evident up to 25 days but activity against Enterococcus dissipated more quickly over time and was absent by day 4. The most common colonizing organisms were coagulase-negative staphylococcus and enterococcus. Variables that were associated with a significant amount of growth on the tip or intradermal segment were a duration of catheterization of longer than 7 days, jugular insertion site, and the absence of a CSS coating. The use of a guidewire when the catheter was removed was associated with a lower risk of significant bacterial growth. CONCLUSIONS: The use of CSS reduces the incidence of significant bacterial growth on either the tip or intradermal segments of coated triple-lumen catheters but has no effect on the incidence of catheter-related bacteremia. In this patient population, catheters coated with CSS provide no additional benefit over uncoated catheters.

The molecular epidemiology of penicillin-resistant Streptococcus pneumoniae in the United States, 1994-2000.

The genetic relatedness of 672 penicillin-resistant isolates of Streptococcus pneumoniae (PRSP) recovered during national surveillance studies conducted in the United States during the periods of 1994-1995, 1997-1998, and 1999-2000 was determined by use of pulsed-field gel electrophoresis (PFGE). Overall, 104 different PFGE types were elucidated. For all study periods combined, the 12 most prevalent PFGE types included >75% of all isolates, and 5 types were closely related to widespread clones (Spain(23F)-1, France(9V)-3, Spain(6B)-2, Tennessee(23F)-4, and Taiwan(19F)-14). From 1994-1995 to 1999-2000, 3 major PFGE types (not closely related to 16 recognized clones) increased in prevalence. Multidrug resistance was identified among 96%-100% of the isolates in 9 of 12 predominant PFGE types. The prevalence of erythromycin resistance increased within 4 major PFGE types. These observations support the hypothesis that the dominant factor in the emergence of PRSP in the United States during the 1990s has been human-to-human spread of relatively few clonal groups that harbor resistance determinants to multiple classes of antibiotics.

Branhamella catarrhalis: phenotypic characteristics.

PURPOSE: This review provides a comprehensive description and discussion of recognized phenotypic characteristics of Branhamella catarrhalis. An emphasis is placed on attributes of this organism that are relevant to its recovery and identification in the clinical microbiology laboratory. In addition, characteristics useful in determining strain identity for use in epidemiologic investigations are addressed. Finally, factors are discussed that may account for the infection-causing potential of B. catarrhalis or at least are of potential consequence to investigations of the pathogenesis of Branhamella disease. CONCLUSIONS: B. catarrhalis is readily isolated from human clinical specimens and can be easily identified using simple, rapid laboratory techniques. Restriction endonuclease analysis of chromosomal deoxyribonucleic acid has proven to be a useful tool in epidemiologic studies. Beta-lactamase isoelectric focusing is of limited value because of the small number of distinct patterns. The lipopolysaccharide and outer membrane proteins of B. catarrhalis have been characterized and found to be relatively non-varying among different strains. Circumstantial evidence exists in support of the hypothesis that the B. catarrhalis beta-lactamase is a virulence determinant.

Trends in antimicrobial susceptibility of bacterial pathogens of the respiratory tract.

Rates of antimicrobial resistance have been increasing in bacteria responsible for community-acquired lower respiratory tract infections in the United States. Nearly 100% of clinical isolates of Moraxella catarrhalis now produce beta-lactamase, an enzyme that renders this pathogen resistant to such agents as penicillin, ampicillin, and amoxicillin. However, this organism remains nearly uniformly susceptible to alternative oral antimicrobials, such as cephalosporins, macrolides, tetracyclines, beta-lactamase inhibitor combinations, and the combination of trimethoprim/sulfamethoxazole. The susceptibility of M. catarrhalis to these agents is not expected to change markedly in the next few years. A linear increase in the prevalence of beta-lactamase-mediated ampicillin resistance has been evident among isolates of nontypeable Haemophilus influenzae during the past decade in the United States. By the year 2000, 45-50% of isolates are likely to produce beta-lactamase. Although the susceptibility of this organism to alternative oral antimicrobials varies, rates of resistance to cefuroxime axetil, cefpodoxime, cefixime, azithromycin, and perhaps clarithromycin remain < 1%. The rate of penicillin resistance among isolates of Streptococcus pneumoniae, which has increased steadily in recent years, currently stands at approximately 25% in the United States and will likely reach 40-50% during the next 5-10 years. Because of cross-resistance, in general all beta-lactam antimicrobials have reduced activity against penicillin-resistant strains of S. pneumoniae. A 1994-1995 survey found that 3.4% of S. pneumoniae isolates were highly resistant to cefotaxime, and 4-8% were resistant to chloramphenicol, tetracycline, and the macrolides. Resistance to these antimicrobials has usually followed the emergence of penicillin resistance in other countries. Therefore, S. pneumoniae resistance to these drugs is expected to increase markedly during the next few years in the United States.

Resistance among problem respiratory pathogens in pediatrics.

During the past two decades, the prevalence of beta-lactamase production with nontypable strains of Haemophilus influenzae has increased to about 35%. Fortunately, rates of resistance to other oral antimicrobials have not developed at a comparable pace. Amoxicillin/clavulanate, cefuroxime and cefpodoxime remain nearly uniformly active whereas rates of resistance to tetracycline, trimethoprim/sulfamethoxazole, chloramphenicol, cefaclor, loracarbef, cefprozil, azithromycin and clarithromycin remain low (1 to 5%). Virtually all clinical isolates of Moraxella catarrhalis produce beta-lactamase and are probably resistant to ampicillin and amoxicillin. However, alternative oral antimicrobials are almost always active. A compelling problem facing pediatricians today is the emergence of penicillin resistance with clinical isolates of Streptococcus pneumoniae. Currently, 15 to 25% of pneumococcal isolates in the United States have either intermediate (10 to 20%) or complete (3 to 5%) penicillin resistance caused by alterations in penicillin-binding proteins. Loss of activity of other beta-lactams is observed with penicillin-resistant S. pneumoniae. Third generation cephalosporins retain sufficient activity to warrant use in selected pneumococcal infections, even those caused by completely penicillin-resistant strains. Unfortunately, strains of S. pneumoniae with further alterations in penicillin-binding proteins have emerged such that even extended spectrum third generation cephalosporins lack activity. Rates of resistance to non-beta-lactam agents are also changing. The consequence of these changing patterns of resistance is that therapeutic options for pneumococcal infections in some patients are becoming increasingly limited.

Genetic relatedness of multidrug-resistant, methicillin (oxacillin)-resistant Staphylococcus aureus bloodstream isolates from SENTRY Antimicrobial Resistance Surveillance Centers worldwide, 1998.

We reviewed Staphylococcus aureus bloodstream infection isolates from SENTRY centers worldwide during 1998 to evaluate the molecular epidemiology of multiply drug-resistant methicillin (oxacillin)-resistant S. aureus (MDR-MRSA). MDR-MRSA was defined as a S. aureus isolate with a MIC for oxacillin at >2 microg/ml and with four or more additional resistances. A total of 325 unique patient isolates of MDR-MRSA from five continents were analyzed using ribotyping and pulsed-field gel electrophoresis (PFGE). The frequency of MDR-MRSA among all S. aureus BSI isolates ranged from only 2.2% in Canada to 35.6% in the Asia-Pacific region. Forty-eight ribotypes (RT) were distinguished, but over 80% of the isolates were contained within the 10 most prevalent RTs. The most common RT, RT 184.5, which included 30% of all MDR-MRSA, was found on four of five continents. PFGE provided superior discrimination and identified numerous clusters of possible clonal dissemination of MDR-MRSA within individual medical centers and between institutions that are in geographic proximity. In four instances, strains with indistinguishable PFGE patterns were found on more than one continent. The predominant PFGE subtype in South America (RT 893.5/Ia) was isolated from patients at centers in Brazil, Argentina, and Portugal, and closely related subtypes were isolated in Chile and Italy. There is great geographic variation in rates of methicillin- and multidrug-resistance among S. aureus bloodstream isolates worldwide. Although many MDR-MRSA strains group geographically, a few closely related epidemic strains have wide regional and even global range.

Clinical impact of rapid susceptibility testing.

The clinical impact of susceptibility testing in general, and rapid same-day susceptibility tests in particular, was assessed from two perspectives: does the performance of susceptibility testing in the laboratory influence the clinical use of antibiotics? Does laboratory susceptibility testing affect the outcome of patients with infectious diseases? The following conclusions were derived from this investigation. In vitro susceptibility testing does significantly influence antibiotic usage, but it is difficult to demonstrate a direct relationship between the results of the susceptibility tests and disease outcome. There is little objective evidence to support the contention that rapid susceptibility tests have a greater clinical impact than traditional overnight procedures. Additional studies directed at addressing this issue are clearly necessary, however; in the absence of such studies, routine performance of same-day susceptibility testing should be considered only if the cost of such testing is less than the cost of overnight procedures, or if cost is not a limiting consideration.

Clinically expedient reporting of rapid diagnostic test information.

With the development of rapid diagnostic tests in the clinical microbiology laboratory has come an awareness of the importance of rapid results reporting. Clearly, the potential clinical impact of rapid diagnostic tests is dependent on expeditious reporting. Traditional manual reporting systems are encumbered by the necessity of transcription of test information onto hard copy reports and then the subsequent distribution of such reports into the hands of the user. Laboratory computers when linked directly to CRTs located in nursing stations, ambulatory clinics, or physician's offices, both inside and outside of the hospital, permit essentially instantaneous transfer of test results from the laboratory to the clinician. Computer-assisted results reporting, while representing a significant advance over manual reporting systems is not, however, without problems. Concerns include validation of test information, authorization of users with access to test information, mechanical integrity, and cost. These issues notwithstanding, computerized results reporting will undoubtedly play a central role in optimizing the clinical impact of rapid diagnostic tests.

In vitro activity of ceftibuten against Haemophilus influenzae and Branhamella catarhallis.

The in vitro activity of ceftibuten, a new orally administered cephalosporin, was assessed against clinical isolates of Haemophilus influenzae and Branhamella catarrhalis. The activity of ceftibuten was compared to that of ampicillin, amoxicillin-clavulanic acid, and three oral cephalosporins, cefaclor, cefuroxime, and cefixime. With the exception of rare beta-lactamase-negative ampicillin-resistant strains of H. influenzae, resistance to ceftibuten was not observed with any of the study isolates. Ceftibuten was more active than amoxicillin/clavulanic acid for beta-lactamase-positive and -negative strains of H. influenzae; it was less active than this combination for B. catarrhalis. Ceftibuten was essentially equivalent in activity to cefixime against both Haemophilus and Branhamella but more active than cefaclor and cefuroxime against these two organisms.

The in vitro activity of cefotaxime versus bacteria involved in selected infections of hospitalized patients outside of the intensive care unit.

Cefotaxime, a parenteral third-generation cephalosporin in broad clinical use since the early 1980s, continues to possess extensive in vitro activity versus a variety of bacteria that are frequent causes of selected infections that commonly occur in hospitalized patients. Currently, bacteria with cefotaxime minimum inhibitory concentrations (MICs) of < or = 8 micrograms/ml are considered to be susceptible, and therefore amenable to treatment with cefotaxime at dosages of 2 g intravenously (IV) every 6 or 8 h when causing monomicrobic infections in immunocompetent patients in whom adequate delivery of the drug to site(s) of infection can be assured. In fact, many common bacterial causes of infection typically have cefotaxime MICs 64 to 256-fold lower than the 8 micrograms/ml break point for susceptible. It is likely that selected monomicrobic infections in immunocompetent hospitalized patients due to such highly susceptible organisms could be treated with lower dosages of cefotaxime or with longer dosing intervals (e.g.,I g IV every 8-12 h or 2 g IV every 12 h. Examples of such infections include Gram-negative pneumonia outside of the intensive care unit setting, community-acquired pneumonia, skin and-soft tissue infections, pyelonephritis, and uncomplicated lower urinary tract infections.

In vitro activity of BAY v 3522, a new oral cephalosporin tested against Haemophilus influenzae and Branhamella catarrhalis.

The in vitro activity of BAY v 3522, a new orally absorbed cephalosporin, was assessed against 150 clinical isolates each of Haemophilus influenzae and Branhamella catarrhalis. The MIC90S for beta-lactamase-positive and -negative strains of H. influenzae were 8 and 2 micrograms/ml, respectively. For beta-lactamase-positive and -negative strains of B. catarrhalis, the BAY v 3522 MIC90S were 4 and 0.25 micrograms/ml, respectively. In general, BAY v 3522 was less active against H. influenzae than amoxicillin/clavulanic acid and cefixime, equivalent in activity to cefuroxime, and more active than cefaclor. BAY v 3522 had activity most similar to cefuroxime and cefaclor for B. catarrhalis but was less active than amoxicillin/clavulanic acid and cefixime.

Susceptibility of Haemophilus influenzae to amoxicillin/clavulanic acid, erythromycin, cefaclor, and trimethoprim/sulfamethoxazole.

A total of 126 strains of Haemophilus influenzae were examined for susceptibility to amoxicillin/clavulanic acid, trimethoprim/sulfamethoxazole, cefaclor, and erythromycin by an agar dilution procedure. Fifty strains (eight type B, 42 non-type B), all with ampicillin minimal inhibitory concentrations (MIC) of greater than or equal to 6.2 micrograms/ml, produced beta-lactamase. The remaining 76 strains (18 type B, 59 non-type B) were beta-lactamase-negative. All of these strains had ampicillin MICs of less than or equal to 0.8 micrograms/ml. The combination of amoxicillin and clavulanic acid (2:1) was highly active against all strains tested. With the exception of two strains with amoxicillin/clavulanic acid MICs of 1.6/0.8 ug/ml, all strains were inhibited by concentrations of less than or equal to 0.8/0.4 ug/ml. Trimethoprim/sulfamethoxazole was also found to be highly active (MICs uniformly less than or equal to 0.1/1.9 ug/ml). Cefaclor and erythromycin were the least active of the agents tested. Fourteen strains (10.6%) had cefaclor MICs of greater than 32 ug/ml. Forty-seven strains (35.6%) had erythromycin MICs of greater than 8 micrograms/ml. With the exception of amoxicillin/clavulanic acid beta-lactamase production did not seem to influence the activity of any of the antimicrobials tested. Minimum inhibitory concentrations of amoxicillin/clavulanic acid, although still well within achievable serum levels, were approximately one twofold dilution higher with beta-lactamase-producing H. influenzae type B strains than with beta-lactamase-negative strains.

In vitro susceptibility test practices with Haemophilus influenzae among College of American Pathologists survey participants in the United States.

Questionnaire results from 5233 clinical microbiology laboratories participating in the College of American Pathologists (CAP) survey program in the United States were used to establish current standards of practice with respect to in vitro susceptibility testing of Haemophilus influenzae. The results of this CAP survey indicated that the recently developed National Committee for Clinical Laboratory Standards (NCCLS) guidelines for H. influenzae susceptibility tests have been widely adopted, particularly with regard to the medium used to perform susceptibility tests. Haemophilus test medium (HTM) is now the most commonly used medium and there exists a general level of satisfaction (approximately 80%) with medium performance. Specific methodologic recommendations of the NCCLS, however, are often not being followed, for example, length and atmosphere of incubation and means of preparing inocula. beta-Lactamase assays constitute a very commonly employed means of assessing ampicillin activity. Among susceptibility test methods, disk diffusion (82.2%) is much more commonly used compared with broth microdilution (17.8%) procedures. Data are provided regarding the most commonly tested antimicrobials as well as some of the problems encounted when using current NCCLS methods for susceptibility tests with H. influenzae. Finally, the CAP survey questionnaire revealed that many laboratories have applied HTM to susceptibility tests with other fastidious bacteria such as pathogenic Neisseria sp., streptococci, and Moraxella catarrhalis.

Comparison of MRC-5 and A-549 cells in conventional culture tubes and shell vial assays for the detection of varicella-zoster virus.

A-549 and MRC-5 cells were compared for the detection of varicella-zoster virus (VZV) by conventional tube cell culture and by shell vial assay using fresh specimens. VZV was detected in 33 (32.4%) of 102 specimens by one or all of these methods. In conventional tube culture, seven (21.2%) of 33 were positive in MRC-5 cells and 24 (72.7%) of 33 were positive in A-549 cells, a threefold increase in sensitivity. In shell vial assay, 30 (90.9%) of 33 were positive in MRC-5 cells and 31 (93.9%) of 33 were positive in A-549 cells. The samples tested by A-549 shell vial assay had more positives showing plaque formation. The two shell vial procedures gave the highest levels of sensitivity. A-549 cells provided a more sensitive method of detecting VZV in clinical specimens in both conventional tubes and shell vial assays than did MRC-5 cells.

Determination of biotypes of Haemophilus influenzae and Haemophilus parainfluenzae a comparison of methods and a description of a new biotype (VIII) of H. parainfluenzae.

A total of 180 strains of Haemophilus influenzae and 119 strains of Haemophilus parainfluenzae were characterized with respect to biotype (i.e., production of indole, urease, and ornithine decarboxylase) using conventional biochemical methods and two commercially available biotyping systems: Trio-Tube Haemophilus system (Carr Microbiologicals) and the Rapid NH System (Inovative Diagnostic Systems). Concordance between the results of the Trio-Tube system and conventional biochemicals was achieved with 294 of the 299 test organisms (98.3%). With the Rapid NH System, concordance with the results of conventional biochemical tests was observed with 275 of the 299 tests strains (92.0%). One previously unrecognized biotype of H. parainfluenzae, designated biotype VIII, is described. Typical reactions of this biotype include indole production but no production of urease or ornithine decarboxylase.

A comparison of commercially available monoclonal antibodies for direct and indirect immunofluorescence culture confirmation and direct detection of parainfluenza viruses.

Two commercially available immunofluorescence monoclonal antibody (MAB) reagents (Bartels, Baxter Healthcare, Issaquah, WA; and Symex, Broken Arrow, OK) were evaluated as a means for detecting parainfluenza virus (PIV) both in shell-vial cultures and directly in clinical specimens. Bartels reagents are used in an indirect immunofluorescence assay (IFA) format and exist as MABs reactive with all three PIV serotypes, individually and in a pool. Symex reagents, also available individually and in a trivalent pool, are used in a direct immunofluorescence assay (DFA) format. Among a total of 299 respiratory specimens, 24 yielded PIV. In a shell-vial culture confirmation test, both the individual and pooled monoclonal antibody reagents from both Bartels and Symex detected all 24 PIV isolates. There were three apparent false-positive results with the Bartels pooled IFA reagents. Of the 299 specimens, 160 were also tested directly for the presence of PIV. There were 13 positive specimens among these 160. The Bartels and Symex monoclonal antibody reagents detected similar percentages of positive samples when used for direct detection (that is, 78.6-85.7). No false-positive results were obtained with any of the reagents in the direct-detection format.