Stephen D. Allen

Bacteremia with Upper Gastrointestinal Endoscopy

Fifty patients undergoing upper gastrointestinal fiberoptic endoscopy were studied prospectively for the development of bacteremia by aerobic and anerobic blood cultures obtained before, during, and at 5 and 30 minutes after the procedure. Forty-six patients were culture negative; four had positive cultures at 5 or 30 minutes after the procedure, or at both times. The level of bacteremia as estimated by pour plates was very low. Bacteremia did not correlate with the performance of biopsy or the type of mucosal abnormality found. It is concluded that only very high-risk patients should receive antimicrobial prophylaxis before this procedure. The minor risk of this low-level bacteremia should not be considered a contraindication to the performance of upper gastrointestinal endoscopy.

Multicenter Evaluation of the LightCycler Methicillin-Resistant Staphylococcus aureus (MRSA) Advanced Test as a Rapid Method for Detection of MRSA in Nasal Surveillance Swabs

ABSTRACT The rate of methicillin-resistant Staphylococcus aureus (MRSA) infection continues to rise in many health care settings. Rapid detection of MRSA colonization followed by appropriate isolation can reduce transmission and infection. We compared the performance of the new Roche LightCycler MRSA advanced test to that of the BD GeneOhm MRSA test and culture. Double-headed swabs were used to collect anterior nasal specimens from each subject. For both tests, DNA was extracted and real-time PCR was performed according to manufacturers instructions. For culture, one swab of the pair was plated directly to CHROMagar MRSA. The swab paired with the BD GeneOhm MRSA test was also placed into an enrichment broth and then plated to CHROMagar MRSA. Colonies resembling staphylococci were confirmed as S. aureus by standard methods. Discrepant specimens had further testing with additional attempts to grow MRSA as well as sample amplicon sequencing. Agreement between results for the two swabs was 99.3% for those with valid results. A total of 1,402 specimens were tested using direct culture detection of MRSA as the gold standard; 187 were culture positive for MRSA. The LightCycler MRSA advanced test had relative sensitivity and specificity of 95.2% (95% confidence interval [CI]: 91.1% to 97.8%) and 96.4% (95% CI: 95.2% to 97.4%), respectively. The BD GeneOhm assay had relative sensitivity and specificity of 95.7% (95% CI: 91.7% to 98.1%) and 91.7% (95% CI: 90.0% to 93.2%), respectively. Following discrepancy analysis, the relative sensitivities of the LightCycler MRSA advanced test and the BD GeneOhm MRSA assay were 92.2 and 93.2%, respectively; relative specificities were 98.9 and 94.2%, respectively. Specificity was significantly better (P < 0.001) with the LightCycler MRSA advanced test. The sensitivity of direct culture was 80.4%. The LightCycler MRSA advanced test is a useful tool for sensitive and rapid detection of MRSA nasal colonization.

Piperacillin/tazobactam (YTR 830) combination: Comparative antimicrobial activity against 5889 recent aerobic clinical isolates and 60 Bacteroides fragilis group strains

Piperacillin combined with tazobactam (formerly YTR 830) was tested at a ratio of 8:1 against 5889 aerobic isolates and 50 strains from the Bacteroides fragilis group. Imipenem was the most active agent tested against Enterobacteriaceae (99.3% at less than or equal to 4 micrograms/ml), ceftazidime was most effective against nonenteric Gram-negative bacilli (80.7% at less than or equal to 8 micrograms/ml), and piperacillin/tazobactam possessed a superior spectrum against Gram-positive cocci (92.2% at less than or equal to 16/2 micrograms/ml). Against all aerobic strains, piperacillin/tazobactam had a spectrum (90.3% at less than or equal to 16/2 micrograms/ml) comparable to imipenem (93.6% at less than or equal to 4 micrograms/ml) and was distinctly greater than that of ticarcillin/clavulanic acid (73.3% at less than or equal to 16/2 micrograms/ml) and ceftazidime (75.5% at less than or equal to 8 micrograms/ml). Against the B. fragilis group isolates, all piperacillin/tazobactam MICs were less than or equal to 64/8 micrograms/ml. This activity was superior to piperacillin alone (MIC:50, 8-64 micrograms/ml) and cefoxitin (MIC50, 4-64 micrograms/ml). Piperacillin/tazobactam appears to be a promising parenteral antimicrobial combination, with a spectrum effective against a wide variety of clinical pathogens.

Clostridium clostridioforme: a mixture of three clinically important species

Clostridium clostridioforme shows much variability in phenotypic and antimicrobial susceptibility tests, suggesting it may be more than a single species even though all strains share unique morphology. This study was designed to determine if there are multiple species and, if so, to demonstrate the differences that exist between them. A total of 107 strains of C. clostridioforme were investigated by sequencing of the 16S rRNA gene, phenotypic studies, and antimicrobial susceptibility testing. In addition, clinical data from patients whose infections yielded an organism identified as C. clostridioforme was reviewed. Data from the above studies revealed three principal species in what has been called C. clostridioforme: Clostridium bolteae, C. clostridioforme, and Clostridium hathewayi. Each species may be distinguished by certain phenotypic tests. All three species were involved in infections, including bacteremia. C. clostridioforme appears to be associated with more serious or invasive human infections than the other two species in the group. Resistance to penicillin G is common and is due to β-lactamase production. Resistance to clindamycin and moxifloxacin is also seen. The three species differ in terms of virulence and antimicrobial resistance. “C. clostridioforme” actually represents three distinct species that are different in terms of 16S rRNA sequences, phenotypic characteristics, and antimicrobial susceptibility. It is important for microbiology laboratories to distinguish between these species and for clinicians to be aware of the differences between them.

Antimicrobial activity of cefpirome an update compared to five third-generation cephalosporins against nearly 6000 recent clinical isolates from five medical centers☆

Cefpirome, cefotaxime, ceftazidime, cefoperazone, ceftizoxime, and ceftriaxone were tested against approximately 6000 fresh clinical isolates from five medical centers. For 3031 strains of Enterobacteriaceae tested, cefpirome consistently had the lowest MIC50s and lowest percentage of resistant strains. Cefpirome was also the most active agent against the 2138 Gram-positive cocci tested; Staphylococcus haemolyticus was uniformly resistant to all agents tested. Against 791 nonenteric Gram-negative bacilli, the activity of cefpirome was most comparable to that of cefoperazone and slightly less active than ceftazidime. Among the current third-generation cephalosporins, cefotaxime and cefoperazone emerged as having better overall balanced activity. Ceftazidime displayed poorest coverage against Enterobacteriaceae and Gram-positive organisms. Ceftizoxime also provided compromised coverage of staphylococci and nonenteric Gram-negative bacilli. Cefpirome remains as active as originally described in 1984 and possesses a slightly wider spectrum of activity against contemporary aerobic pathogens compared to currently marketed third-generation cephalosporins.

Pathogenic Differences between North American and Latin American Strains of Histoplasma capsulatum var. capsulatum in Experimentally Infected Mice

ABSTRACT Clinical differences in histoplasmosis between North America and Brazil prompted investigation of experimental infection with representative strains. Mortality was higher with Latin American strains, and lung pathology showed large necrotizing granuloma with prominent neutrophilic infiltration. Chronic disease was unique to the North American strain.

Comparison of the Next-Generation Xpert MRSA/SA BC Assay and the GeneOhm StaphSR Assay to Routine Culture for Identification of Staphylococcus aureus and Methicillin-Resistant S. aureus in Positive-Blood-Culture Broths

ABSTRACT A bloodstream infection with Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), is a serious condition that carries a high mortality rate and is also associated with significant hospital costs. The rapid and accurate identification and differentiation of methicillin-susceptible S. aureus (MSSA) and MRSA directly from positive blood cultures has demonstrated benefits in both patient outcome and cost-of-care metrics. We compare the next-generation Xpert MRSA/SA BC (Xpert) assay to the GeneOhm StaphSR (GeneOhm) assay for the identification and detection of S. aureus and methicillin resistance in prospectively collected blood culture broths containing Gram-positive cocci. All results were compared to routine bacterial culture as the gold standard. Across 8 collection and test sites, the Xpert assay demonstrated a sensitivity of 99.6% (range, 96.4% to 100%) and a specificity of 99.5% (range, 98.0% to 100%) for identifying S. aureus, as well as a sensitivity of 98.1% (range, 87.5% to 100%) and a specificity of 99.6% (range, 98.3% to 100%) for identifying MRSA. In comparison, the GeneOhm assay demonstrated a sensitivity of 99.2% (range, 95.2% to 100%) and a specificity of 96.5% (range, 89.2% to 100%) for identifying S. aureus, as well as a sensitivity of 94.3% (range, 87.5% to 100%) and a specificity of 97.8% (range, 96.1% to 100%) for identifying MRSA. Five of six cultures falsely reported as negative for MRSA by the GeneOhm assay were correctly identified as positive by the Xpert assay, while one culture falsely reported as negative for MRSA by the Xpert assay was correctly reported as positive by the GeneOhm assay.

Comparative antimicrobial activity of piperacillin-tazobactam tested against more than 5000 recent clinical isolates from five medical centers a reevaluation after five years

Piperacillin combined with tazobactam at a fixed concentration (4 micrograms/ml) and a ratio (8:1) was tested against 5,029 aerobic isolates and 447 fastidious organisms, including anaerobes. Among the Enterobacteriaceae, > 95% inhibition was shared only by imipenem (99.1% at < or = 4 micrograms/ml), and some newer cephalosporins (95.1% - 99.8% at < or = 8 micrograms/ml), and piperacillin-tazobactam (95.8% at < or = 16/4 micrograms/ml). Piperacillin-tazobactam was the most active agent tested against nonenteric Gram-negative bacilli (93.5% at < or = 8 micrograms/ml). Ampicillin-sulbactam was the most active agent against staphylococci (95.0% at < or = 8 micrograms/ml), followed by imipenem (91.8%), piperacillin-tazobactam (89.3% at < or = 8/4 micrograms/ml), and cefepime (86.2% at < or = 8 micrograms/ml). Against the enterococci, only ampicillin (93.0% at < or = 8 micrograms/ml) with or without sulbactam, piperacillin (91.0% at < or = 16 micrograms/ml) with or without tazobactam, and imipenem (91.0%) had acceptable activity. Piperacillin-tazobactam and imipenem were the most active drugs tested against all aerobic isolates, inhibiting 93.5% of isolates each. Piperacillin-tazobactam inhibited all fastidious isolates tested, including Haemophilus influenzae (MIC90, 0.094/4 micrograms/ml), Moraxella catarrhalis (MIC90, 0.064/4 micrograms/ml), Neisseira gonorrhoeae (MIC90, < or = 0.016/4 micrograms/ml), and Streptococcus pneumoniae (all MICs, < or = 4/4 micrograms/ml). Against the anaerobic isolates, the most broad-spectrum antimicrobial agents tested were imipenem (100.0%), piperacillin-tazobactam (99.5% at < or = 32/4 micrograms/ml), metronidazole (98.4% at < or = 8 micrograms/ml), and ticarcillin-clavulanic acid (95.1% at < or = 32/2 micrograms/ml). These results are nearly identical to a previous study involving the same five medical centers in 1989. Piperacillin-tazobactam appears to remain a highly effective beta-lactamase inhibitor combination with a wide empiric spectrum and potency in teaching hospitals.

Multilaboratory evaluation of the in vitro activity of 13 β-lactam antibiotics against 1474 clinical isolates of aerobic and anaerobic bacteria

The in vitro activity of 13 beta-lactam antibiotics against 1474 recent clinical isolates was evaluated in a multilaboratory study. The most active antibiotic tested in this study was imipenem (98.5% of the strains were susceptible), followed by ticarcillin-clavulanate (91.4%), cefoperazone (90.0%), ceftazidime (87.9%), cefotaxime (87.7%), ceftriaxone (87.0%), ceftizoxime (86.3%), cefotetan (78.5%), ampicillin-sulbactam (77.9%), cefoxitin (73.5%), cefuroxime (70.9%), cefonicid (64.5%), and cefazolin (57.9%).

Multicenter comparison of the high volume (10 ml) NR BACTEC PLUS system and the standard (5 ml) NR BACTEC system

This multicenter study was designed to compare the new BACTEC PLUS system (nonradiometric), which utilizes an 8- to 10-ml blood inoculum in a resin-containing medium, to the standard BACTEC (nonradiometric) without resins and 5-ml blood inoculum. There were 12,341 compliant sets studied, yielding 1331 positives, with 1099 sets deemed clinically significant. Overall the BACTEC PLUS showed an enhanced recovery of 33% (p less than 0.001) over its standard counterpart, with significant yield increased in the staphylococci (p less than 0.001), streptococci (p less than 0.002), pseudomonads (p less than 0.002), Enterobacteriaceae (p less than 0.001), and other aerobic Gram negatives (p less than 0.02). The enhanced performance increased to 53% if the patient was receiving any antibiotics at the time the blood was cultured. In patients known to be free of antibiotics at the time of blood draw, there was still an increased yield of 18%. The new system detected positivity at least one reading sooner than twice as often as the converse, and confirmed septic episodes significantly more often (21% overall) (41% on antibiotics) (15% no antibiotics). The BACTEC PLUS has distinct advantages over its low blood volume, nonresin counterpart.