David A. Bruckner

Increased Vancomycin MICs for Staphylococcus aureus Clinical Isolates from a University Hospital during a 5-Year Period

ABSTRACT Staphylococcus aureus is one of the most commonly isolated organisms in nosocomial infections. While the prevalence of methicillin-resistant S. aureus (MRSA) continues to increase worldwide, there is concern about an increase in vancomycin MICs among S. aureus strains. The prevalence of MRSA and vancomycin MIC trends in S. aureus from patients in a university hospital were analyzed. Clinical Laboratory Standards Institute (CLSI, formerly NCCLS) reference broth microdilution MIC testing was performed on all clinically relevant S. aureus isolates from January 2000 through December 2004. A total of 6,003 S. aureus isolates were analyzed. No vancomycin-resistant S. aureus isolates were detected. One MRSA isolate had a vancomycin MIC of 8 μg/ml and was confirmed as vancomycin-intermediate S. aureus. Among the 6,002 remaining isolates, a shift in vancomycin MICs from ≤0.5 to 1.0 μg/ml was observed during the 5-year period. The percentage of S. aureus isolates with a vancomycin MIC of 1 μg/ml in 2004 was significantly higher than the percentage of isolates in 2000 (70.4% versus 19.9%; P < 0.01). This vancomycin MIC shift was more notable in methicillin-susceptible S. aureus. Our 5 years of routine testing of clinical isolates using the CLSI reference broth microdilution MIC method demonstrated a tendency toward decreasing susceptibility to vancomycin in S. aureus.

Nomenclature for Aerobic and Facultative Bacteria

The following lists represent our update of the current nomenclature, taxonomy, and classification of various microbial agents. We will update these lists every two years. The primary purpose of nomenclature is to permit us to know as exactly as possible what another clinician, microbiologist, epidemiologist, or investigator is referring to when describing an organism responsible for infecting individuals or for causing an outbreak.

Outbreak of Stenotrophomonas maltophilia Bacteremia in Allogenic Bone Marrow Transplant Patients: Role of Severe Neutropenia and Mucositis

From March 1997 through November 1997, 8 allogenic bone marrow transplant (BMT) patients developed Stenotrophomonas maltophilia bacteremia on the hematology service at UCLA Medical Center (Los Angeles). Five of these patients had undergone transplantation during the same hospitalization that S. maltophilia bacteremia was detected (case patients). Compared with 7 concurrently hospitalized allogenic BMT patients (control patients), the 5 case patients were more likely to have been hospitalized in room A (P=.045), to have severe neutropenia on the culture date (P=.028), to have a longer duration of severe neutropenia (P=.05), to have severe mucositis (P=. 028), and to have received total parenteral nutrition (P=.028). Pulsed-field gel electrophoresis revealed that 2 of 3 isolates from case patients hospitalized in room A were identical. In allogenic BMT patients, severe neutropenia and severe mucositis may promote infection with S. maltophilia by impairing host defenses.

Clearance of Cellulosimicrobium cellulans bacteremia in a child without central venous catheter removal.

ABSTRACT Cellulosimicrobium cellulans (formerly known as Oerskovia xanthineolytica) rarely causes human infection. Infections have been reported in immunocompromised hosts or in patients with foreign bodies, such as catheters, where treatment has generally involved removal of the foreign body. We report on a case in which the organism was isolated in multiple blood cultures from a 13-year-old male. After initial therapy failed, treatment with vancomycin and rifampin resulted in infection clearance without removal of the central venous catheter.

DNA probe reactivity of Mycobacterium avium complex isolates from patients without AIDS.

Mycobacterium avium complex isolates from 27 patients without AIDS and from 76 patients with AIDS were analyzed with the Gen-Probe Rapid Diagnostic System for Mycobacterium avium complex, and a retrospective chart review was performed to determine clinical significance of the isolates. While 87% of isolates from AIDS patients reacted only with the M. avium probe, only 37% from non-AIDS patients were M. avium probe positive (p less than 0.001). This pattern among non-AIDS patients was also observed among the 13 patients from whom isolates were considered to be clinically significant. Reactivity to both probes occurred with three isolates, two from non-AIDS patients that were not clinically significant and one from an AIDS patient. Results of further testing suggested that these represented dual infection with two coexisting strains. Awareness of the differences in DNA probe reactivity between isolates from AIDS and non-AIDS patients may influence testing strategies in the clinical laboratory.

Multicenter Evaluation of the BD Phoenix Automated Microbiology System for Antimicrobial Susceptibility Testing of Streptococcus Species

ABSTRACT This multicenter study evaluated the BD Phoenix Automated Microbiology System STREP panel (BD Diagnostic Systems). Antimicrobial susceptibility testing (AST) with 13 agents was performed on 2,013 streptococci (938 Streptococcus pneumoniae isolates; 396 group B streptococci [GBS]; 369 viridans group streptococci [VGS]; 290 beta-hemolytic streptococcus groups A, C, and G; and 20 other streptococci) with the Phoenix system and a broth microdilution reference method. Clinical and challenge isolates were tested against cefepime, cefotaxime (CTX), ceftriaxone (CTR), clindamycin (CLI), erythromycin (ERY), gatifloxacin, levofloxacin, linezolid, meropenem, penicillin (PEN), tetracycline (TET), trimethoprim-sulfamethoxazole, and vancomycin. Clinical isolates with major errors or very major errors (VMEs) were retested in duplicate by both methods. The final results for clinical isolates showed the following trends. For all of the organism-antimicrobial agent combinations tested, categorical agreement (CA) was 92 to 100%, with one exception—VGS-PEN (87% CA; all errors were minor). For S. pneumoniae, there was one major error with CLI (0.1%) and one or two VMEs with CTX (4%), CTR (4.5%), ERY (0.9%), and TET (0.7%). For groups A, C, and G, the CA was 97 to 100% and the only VMEs were resolved by additional reference laboratory testing. For GBS, there was only one VME (TET, 0.3%) and D-zone testing of 23 isolates with CLI major errors (one isolate unavailable) revealed inducible CLI resistance. For VGS, the major error rates were 0 to 3% and VMEs occurred with seven agents (3.5 to 7.1%). The mean times required for organism groups to generate results ranged from 8.4 to 9.4 h. The Phoenix system provided reliable and rapid AST results for most of the organism-antimicrobial agent combinations tested.

Mycobacterium avium: A pathogen of patients with acquired immunodeficiency syndrome

Mycobacterium avium complex has been isolated with increasing frequency from humans during the last few decades. Thirteen patients admitted to the UCLA Medical Center with the diagnosis of acquired immunodeficiency syndrome (AIDS), in addition to having Kaposis sarcoma, Pneumocystis pneumonia, and other opportunistic infections, also had M. avium complex isolated from a variety of tissues and fluids submitted for culture. Of these patients, 10 had histologic and bacteriologic evidence of disseminated mycobacterial infection, and M. avium complex was isolated from the blood of 5. The organisms were isolated from routine bacteriologic and diphasic fungal blood culture bottles. Periodic cultures of sputum, urine, and other body fluids and tissues should be performed for mycobacterial infections in all such patients. Routine blood cultures should be kept for at least 8 weeks to check for the presence of acid-fast bacteria in general and for M. avium complex in particular from all patients with immune deficiencies.

Serologic and Intradermal Tests for Parasitic Infections

For years, the diagnosis of most parasitic diseases has depended upon the direct demonstration of the parasite or its cysts, eggs, or larvae in specimens. In some infections, direct demonstration of the causative agent or its stages is almost impossible. In such cases, indirect techniques, such as serologic methods, have been found to be more practical and sensitive than are direct methods. Most serologic methods have been devised to detect antibodies. Tests for the detection of antigen are just beginning to be utilized; however, the practicality and under what situations antigen detection tests can be used await further testing. The majority of the serum antibody tests employ a heterogeneous mixture of antigens. Antigens derived from whole adult or larval stages usually result in tests with poor specificity and/or sensitivity. The necessity for better purified and standardized antigens cannot be over emphasized. Although there have been many major advances in the serodiagnosis of parasitic infections, a major drawback to routine use of parasitic serologies is the lack of commercially available reliable test kits. For the diagnosis of most parasitic diseases, one must rely upon specialty laboratories or public health laboratories. Before any laboratory begins to offer parasitic test serologies, they should contact their local or state public health laboratory or the Parasitic Serologic Section of the Centers for Disease Control to determine the pros and cons of these tests. Information of this type should be used to inform the physician of the limitations of the test in the differential diagnosis.

Enzyme-linked immunoabsorbent assays in the detection of Chlamydia trachomatis: How valid are they?

Two enzyme-linked immunoabsorbent assays (Chlamydiazyme, Abbott Laboratories, North Chicago, IL, and IDEIA, Boots-CellTech Diagnostics Inc., East Hanover, NJ) specific for the detection of Chlamydia trachomatis antigen were used to assess 451 cervical specimens. All specimens obtained from the subjects were also simultaneously cultured for Chlamydia. Both assays identified 90.9% (20/22) of the culture positive cases. Chlamydiazyme identified two and IDEIA three additional specimens as positive. Of these additional positive tests, one of two Chlamydiazyme and three of three IDEIA specimens were confirmed as positive by the direct fluorescent antibody technique (MicroTrak, Syva Co., Palo Alto, CA). Given the inexpense, availability, ease of performance, high sensitivity (91%), and specificity (99%) of these tests, both should become valuable tools to objectively assess women at risk for this common sexually transmitted disease.

Incidence of Cryptosporidium in all patients submitting stool specimens for ova and parasite examination: Monoclonal antibody IFA method

The development of a monoclonal antibody to Cryptosporidium oocysts provides a more sensitive detection method than that seen using other diagnostic techniques. Incidence reports on this organism have been based on earlier, less-sensitive methods. In order to determine the numbers of positive patients and stool specimens, every stool specimen submitted for an ova and parasite examination was tested using the Merifluor IFA system (Meridian Diagnostics, Inc). Over a 12-mo period, 2,786 specimens were tested (1,516 patients). Positive specimens (23) were from nine known immunosuppressed patients and from four symptomatic immunocompetent patients. This represents an overall positive rate of 0.86% (patients). In those patients who were not suspected of having cryptosporidiosis (immunocompetent), diagnosis of this infection would not have been accomplished without the use of a sensitive screening method. This data, obtained over a 12-mo period, provides information for those laboratories considering the clinical relevance of screening all stool specimens for this infection. With the development of therapy, early detection of Cryptosporidium will become more important.