Disseminated Burkholderia gladioli infection in a lung transplant recipient with underlying hypocomplementemic urticarial vasculitis.

Burkholderia gladioli is difficult to definitively identify within the laboratory using phenotypic testing alone. We describe a case of recurrent B. gladioli infection in a lung transplant recipient with underlying hypocomplementemic urticarial vasculitis syndrome, discuss the difficulties encountered with laboratory identification, provide a review of the methodology required for definitive identification, and discuss potential pathophysiologic mechanisms in this patient responsible for the difficulty in treatment.

The contribution of pharmacokinetic-pharmacodynamic modelling with Monte Carlo simulation to the development of susceptibility breakpoints for Neisseria meningitidis.

This study used pharmacokinetic-pharmacodynamic (PK-PD) modelling and MICs of 15 antimicrobial agents, derived from testing a large international culture collection, to assist in the development of interpretative criteria, i.e., breakpoints, for Neisseria meningitidis. PK parameters, protein binding, percentage penetration into cerebrospinal fluid (CSF), and the variability of these values, were extracted from the published literature for the 15 agents. PK-PD parameters have not been developed specifically for N. meningitidis in animal or human studies. Thus, it was necessary to invoke PK-PD targets from other organisms that cause infections at similar sites. The PK-PD targets utilised were: time above the MIC for at least 50% of the dosing interval for all beta-lactams, chloramphenicol, sulphafurazole and trimethoprim-sulphamethoxazole; an AUC/MIC ratio of >or=25 for the tetracyclines and macrolides; and an AUC/MIC ratio of >or=125 for the fluoroquinolones. A 10 000-subject Monte Carlo simulation was designed with the usual dosing regimens of each antimicrobial agent at MIC values of 0.03-64 mg/L in both serum and CSF. The PK-PD breakpoint was defined as the MIC at which the calculated target attainment was >or=95%. Using these assumptions, the proposed PK-PD breakpoints were: azithromycin, 0.125 mg/L; doxycycline, 0.25 mg/L; cefotaxime, ciprofloxacin and levofloxacin, 0.5 mg/L; penicillin G, meropenem, rifampicin, tetracycline and minocycline, 1 mg/L; chloramphenicol and sulphafurazole, 2 mg/L; and ampicillin, ceftriaxone and trimethoprim-sulphamethoxazole, 4 mg/L. Proposed PK-PD breakpoints applicable to CSF were: penicillin and cefotaxime, 0.06 mg/L; rifampicin, 0.125 mg/L; ceftriaxone, meropenem and trimethoprim-sulphamethoxazole, 0.25 mg/L; ampicillin, 0.5 mg/L; and chloramphenicol, 1 mg/L.

Typhoid fever. An epidemic with remarkably few clinical signs and symptoms.

A major common-source, foodborne epidemic of typhoid fever occurred in San Antonio, Tex, in the fall of 1981, involving 80 verified cases. We summarize the clinical course of our 34 patients who had a nonspecific symptom complex that included at the initial examination fever (32 patients, 93%), headache (19 patients, 57%), diarrhea (11 patients, 33%), and anorexia (ten patients, 30%). The most common initial diagnoses were urinary tract and upper respiratory tract infections. The subsequent isolation of Salmonella typhi from blood cultures was usually unexpected. Physical findings were different from two previous series originating in the United States. Hepatomegaly was noted in only 7% (two patients), splenomegaly was noted in 13% (four patients), and rose spots were noted in 5% (two patients) of the patients. Liver function test results, however, were abnormal in 32 (95%) of the 34 patients (mean SGOT, 155 IU/mL). Typhoid fever, as seen in this outbreak, was notable for its nonspecific and mild manifestation and uniformly favorable outcome.

Management of community-acquired pneumonia in the era of pneumococcal resistance: a report from the Drug-Resistant Streptococcus pneumoniae Therapeutic Working Group.

OBJECTIVE: To provide recommendations for the management of community-acquired pneumonia and the surveillance of drug-resistant Streptococcus pneumoniae (DRSP). METHODS: We addressed the following questions: (1) Should pneumococcal resistance to beta-lactam antimicrobial agents influence pneumonia treatment? (2) What are suitable empirical antimicrobial regimens for outpatient treatment of community-acquired pneumonia in the DRSP era? (3) What are suitable empirical antimicrobial regimens for treatment of hospitalized patients with community-acquired pneumonia in the DRSP era? and (4) How should clinical laboratories report antibiotic susceptibility patterns for S pneumoniae, and what drugs should be included in surveillance if community-acquired pneumonia is the syndrome of interest? Experts in the management of pneumonia and the DRSP Therapeutic Working Group, which includes clinicians, academicians, and public health practitioners, met at the Centers for Disease Control and Prevention in March 1998 to discuss the management of pneumonia in the era of DRSP. Published and unpublished data were summarized from the scientific literature and experience of participants. After group presentations and review of background materials, subgroup chairs prepared draft responses, which were discussed as a group. CONCLUSIONS: When implicated in cases of pneumonia, S pneumoniae should be considered susceptible if penicillin minimum inhibitory concentration (MIC) is no greater than 1 microg/mL, of intermediate susceptibility if MIC is 2 microg/ mL, and resistant if MIC is no less than 4 microg/mL. For outpatient treatment of community-acquired pneumonia, suitable empirical oral antimicrobial agents include a macrolide (eg, erythromycin, clarithromycin, azithromycin), doxycycline (or tetracycline) for children aged 8 years or older, or an oral beta-lactam with good activity against pneumococci (eg, cefuroxime axetil, amoxicillin, or a combination of amoxicillin and clavulanate potassium). Suitable empirical antimicrobial regimens for inpatient pneumonia include an intravenous beta-lactam, such as cefuroxime, ceftriaxone sodium, cefotaxime sodium, or a combination of ampicillin sodium and sulbactam sodium plus a macrolide. New fluoroquinolones with improved activity against S pneumoniae can also be used to treat adults with community-acquired pneumonia. To limit the emergence of fluoroquinolone-resistant strains, the new fluoroquinolones should be limited to adults (1) for whom one of the above regimens has already failed, (2) who are allergic to alternative agents, or (3) who have a documented infection with highly drug-resistant pneumococci (eg, penicillin MIC > or =4 microg/mL). Vancomycin hydrochloride is not routinely indicated for the treatment of community-acquired pneumonia or pneumonia caused by DRSP.

Amikacin therapy of patients with multiply antibiotic-resistant Serratia marcescens infections: development of increasing resistance during therapy.

Over a recent 22 month period, 222 patients in two adjacent hospitals became infected with a multiply antibiotic-resistant strain of Serratia marcescens; 13 were bacteremic. Nineteen patients with clinically significant infections received amikacin. Nine of 11 patients with urinary tract infections were cured. In contrast, only one of eight patients with pneumonia or other deep tissue infections was cured and four died. These eight patients were severely ill; many had infections with multiple microorganisms. In four of five patients in whom the infection failed to clear promptly. Serratia strains became increasingly resistant to amikacin during therapy and these strains contributed to the death of two of these patients. Amikacin proved useful in treating patients with infections due to gentamicin-resistant S. marcescens organisms, especially urinary tract infections. However, the capacity of some strains of S. marcescens to develop resistance to amikacin may limit the usefulness of this antibiotic in the treatment of deep tissue infections which involve this microorganism.

Mechanisms of methicillin resistance in Staphylococcus aureus and methods for laboratory detection.

Three distinctly different mechanisms of methicillin resistance have been described in Staphylococcus aureus. The best-documented and probably most important mechanism is production of a unique, low affinity penicillin-binding protein, PBP 2a. Strains possessing PBP 2a are resistant to methicillin, oxacillin, and probably all other currently available beta-lactam antibiotics. Two additional mechanisms of reduced susceptibility to methicillin have been described. Borderline resistance (BORSA) to the semi-synthetic penicillins has been attributed to the hyperproduction of normal staphylococcal beta-lactamase. A third mechanism has recently been advanced that describes an intermediate level of resistance to methicillin due to production of modified, normal PBPs with reduced affinity for beta-lactams (MODSA). Little is known regarding the prevalence or clinical significance of the BORSA and MODSA strains. The most reliable in vitro susceptibility test methods for detecting MRSA (strains possessing PBP 2a) include the microdilution minimum inhibitory concentration (MIC) test (with 2% NaCl supplemented broth), the oxacillin agar screen plate test (incorporating 6 micrograms/ml oxacillin in 4% NaCl supplemented agar), and the National Committee for Clinical Laboratory Standards (NCCLS) disk diffusion test with oxacillin. All three methods use direct inoculum preparation and incubation of tests at 35 degrees C for a full 24 hours.

Association of antibiotic utilization measures and control of multiple-drug resistance in Klebsiella pneumoniae.

OBJECTIVE: To study the association of antibiotic-utilization measures and control of multidrug-resistant (MDR) Klebsiella pneumoniae after emergence in two hospitals in our medical center. DESIGN AND SETTING: Rates of MDR K. pneumoniae at two hospitals were compared before and after acute interventions, including emphasis on Contact Precautions and education in antibiotic utilization. Antipseudomonal beta-lactam antibiotic use was measured before and after the interventions at both hospitals. Pulsed-field gel electrophoresis of whole cell DNA was used as a marker of strain identity. RESULTS: Clonal strain dissemination was the major mechanism of emergence at hospital A; emergence was polyclonal at hospital B. Antibiotic-utilization interventions at both institutions included physician education regarding the association of ceftazidime use and MDR K. pneumoniae. At hospital A, ceftazidime use decreased from 4,301 g in the preintervention period, to 1,248 g in the postintervention period. Piperacillin-tazobactam use increased from 12,455 g to 17,464 g. Ceftazidime resistance in K. pneumoniae decreased from 110 (22%) of 503 isolates to 61 (15%) of 407 isolates (P<.05); piperacillin-tazobactam resistance decreased from 181 (36%) of 503 to 77 (19%) of 407 isolates (P<.05). At hospital B, ceftazidime use decreased from 6,533 g in the preintervention period to 4,792 g in the postintervention period. Piperacillin-tazobactam use increased from 58,691 g to 67,027 g. Ceftazidime resistance in K. pneumoniae decreased from 42 (10%) of 415 isolates to 19 (5%) of 383 isolates (P<.05). Piperacillin-tazobactam resistance decreased from 91 (22%) of 415 isolates to 54 (14%) of 383 isolates (P<.05). Follow-up data showed continued decrease in piperacillin-tazobactam resistance despite increased use at both hospitals. CONCLUSIONS: Antibiotic-use measures may be particularly important for control of MDR K. pneumoniae, whether emergence is clonal or polyclonal.

Limulus lysate assay for early detection of certain Gram-negative corneal infections.

The limulus endotoxin assay has been previously demonstrated to be the most sensitive method available for detection of bacterial endotoxin. A commercially available form of limulus amoebocyte lysate was used in this study for detection of Gram-negative corneal infections in both experimental animals and in a group of nine patients. The limulus assay enabled rapid detection of Gram-negative infections in both the experimentally induced ulcers in rabbits and in the patients studied. False-positive reactions did not occur in corneal infections due to either Gram-positive bacteria, fungi, or herpes simplex keratitis. The limulus test proved to be more sensitive than examination of Gram-stained smears of corneal scrapings and became positive earlier than bacterial cultures. The limulus test was helpful in the diagnosis of partially antibiotic-treated corneal infections but could not be used to assess the response to antimicrobial therapy, since endotoxin persisted in the corneal scrapings for some time after initiation of therapy.

Rapid bioassay for chloramphenicol in the presence of other antibiotics.

A simple, rapid bioassay for the measurement of chloramphenicol in serum or cerebrospinal fluid was developed using a multiply antibiotic-resistant strain of Escherichia coli. The agar diffusion system involved the addition of patients' specimens and three standard concentrations of chloramphenicol to 7.5 mm diameter wells cut in agar seeded with the test organism. Assays of chloramphenicol using this system could be read routinely in three to four hours and allowed determinations of levels of 5-60 micrograms/ml. Chloramphenicol could be measured accurately in the presence of a variety of beta-lactam, aminoglycoside, sulfonamide, and tetracycline antimicrobial agents, but not cefoxitin or trimethoprim-sulfamethoxazole. Repetitive assays of sera containing known concentrations of chloramphenicol indicated a coefficient of variation of 8%. Seeded assay plates could be stored at 2-8 degrees C for up to five days prior to use.

Comparative evaluation of the Limulus assay and the direct Gram stain for detection of significant bacteriuria.

A double-blind study comparing the Limulus in-vitro endotoxin assay with the direct Gram stain of uncentrifuged urine for detection of significant bacteriuria was performed. One-thousand seventy-seven urine specimens were examined by the two methods and the results compared with results of quantitative urine cultures. Two hundred three samples produced growth of greater than 10-5 organisms per ml. urine. The Limulus assay detected 86.2% of these specimens, and 98.8% of urines that contained greater than 10-5 Gram-negative bacilli per ml. The Gram stain procedure detected only 69.5% of urines containing greater than 10-5 organisms per ml. and 74.5% of specimens with greater than 10-5 Gram-negative bacteria per ml. urine. The Limulus assay demonstrated both greater sensitivity and greater specificity than the Gram stain procedure. Moreover, the Limulus test is much less susceptible to errors of interpretation than methods involving microscopy.

Standardized disk-diffusion susceptibility test for Haemophilus influenzae.

The emergence of ampicillin-resistant strains of Haemophilus influenzae has emphasized the need for an improved practical method for routine susceptibility testing of clinical isolates. We have previously described a simplified medium for quantitative dilution susceptibility testing that is composed of Mueller-Hinton medium plus Supplement C (Difco). In the present study, paired broth-dilution and disk-diffusion susceptibility tests with ampicillin and chloramphenicol were performed on 100 strains of Haemophilus (95 H. influenzae and five H. parainfluenzae), including 30 strains with previously documented ampicillin resistance. Disk-diffusion tests were performed in exactly the same manner as the standardized Kirby-Bauer procedure used for less fastidious organisms, except that supplemented Mueller-Hinton agar plates were incubated in an increased-CO2 atmosphere. Using this method, ampicillin-susceptible strains of Haemophilus produced zone diameters of 22 mm or more, while ampicillin-resistant strains produced zones of 18 mm or less. All strains were chloramphenicol-susceptible and produced zone diameters of 30 mm or more. This method would allow routine disk-diffusion testing of isolates of H. influenzae by hospital diagnostic laboratories, using a clear medium that closely resembles unsupplemented Mueller-Hinton agar.

Bacteremia and postmortem microbiology in burned children.

During a three-year period, Staphylococcus aureus and Pseudomonas aeruginosa were the organisms most commonly isolated from blood cultures of burned children. Microorganisms were considered to contribute to the cause of death in 17 of 20 patients who died from various complications of thermal injuries. Pseudomonas aeruginosa was involved in eight deaths, whereas other Gram-negative bacilli or fungi, or both, were involved in the deaths of the remaining nine patients. The microbiologic examination of cardiac blood and pulmonary tissue correlated reasonably well with clinical and anatomic judgments of cause of death, as well as with the defining of some cases of "terminal sepsis".

A rapid paper-disc test for penicillinase.

A practical acidimetric assay for penicillinase production using penicillin and phenol red impregnated in paper discs was developed. Blank discs were first impregnated with buffered penicillin G and, after drying, with 1% phenol red. For use, a disc was added to a bacterial suspension made in saline solution. A yellow color within 1 to 30 min of incubation indicated penicillinase production. These discs were tested against Staphylococcus aureus, Haemophilus influenzae, and Neisseria gonorrhoeae, and the assay was found to be a simple, rapid, and accurate method for detection of penicillinase.

Comparison of automated and rapid manual methods for the same-day identification of Enterobacteriaceae.

The Vitek AMS automated instrument method for identification of Enterobacteriaceae was compared with two rapid manual methods intended for the same purpose, the Micro ID System and the API 20E Same-Day procedure, on a series of 400 consecutive fresh clinical isolates. Results were compared with identifications obtained using the API 20E System with overnight incubation and supplemental tube biochemicals (when needed). Both the final (8-hour) and a manually requested, presumptive 5-hour result from the AMS were compared with the 4-hour results provided by the Micro ID and the 5-hour results provided by the API. The Micro ID system proved to be the most rapid and accurate of the three test systems by correctly identifying 96.8% (387/400) of isolates. The API 20E using 5-hour readings identified 90.7% (363/400) of isolates, although 96.8% (387/400) could be identified if supplemental overnight tests were employed to separate profile codes with "good likelihood, but low selectivity." The AMS correctly identified 88.8% (355/400) isolates after 5 hours, and 95.0% (380/400) following 8 hours incubation.

The pharmacokinetics of prophylactic antibiotics administered by intraoperative irrigation at the time of cesarean section.

Thirty patients at term undergoing cesarean section received intraoperative irrigation with either cefamandole, cephalothin, or ampicillin to prevent postoperative infection. Serum drug levels were measured at 15, 60 and 120 minutes after completion of irrigation. Serum levels at each sampling interval were highest for cefamandole and lowest for cephalothin. Les than 2% of the total drug dose was excreted in the urine during the first 2 postoperative hours. In most patients, maximum serum antibiotic concentrations exceeded minimal inhibitory concentrations for several recognized pelvic pathogens. It is concluded that the mechanism of action of intraoperative irrigation may in part be due to systemic absorption of antibiotic and not simply to a local effect on the endometrium. Moreover, the degree of systemic absorption may be sufficient to cause allergic drug reactions and to exert selective pressures for the emergence of drug-resistant microorganisms.

Serum gentamicin levels in patients with post-cesarean endomyometritis.

Serum gentamicin levels were measured by agar diffusion bioassay in 38 patients undergoing treatment with clindamycin-gentamicin for post-cesarean endomyometritis. Patients received intravenous gentamicin in a dose of 1 mg/kg actual body weight every eight hours. All trough levels were less than 1 microgram/ml. The mean 30-minute postinfusion level was 5.78 +/- 2.43 micrograms/ml (mean +/- SD). The range of postinfusion concentrations was 1 to 12 micrograms/ml. Postinfusion concentrations were less than 5 micrograms/ml in 13 patients, but none of these individuals experienced a clinical failure of antimicrobial therapy. There were no statistically significant differences in mean age, weight, hematocrit, serum creatinine, estimated creatinine clearance, or administered dose in patients with therapeutic gentamicin levels and patients with apparent subtherapeutic levels. The authors conclude that postinfusion gentamicin concentrations fluctuate widely in obstetric patients receiving 1 mg/kg/dose and that apparent subtherapeutic postinfusion levels still may be clinically efficacious, depending upon the antimicrobial susceptibility of the infecting microorganisms.

Antimicrobial susceptibility testing of bacteria that grow aerobically.

This article focuses on susceptibility testing methods for aerobic and fastidious bacteria that may be tested using standard dilution or agar diffusion methods. Also discussed are those bacteria that may be tested by use of an automated or nontraditional methodology.

Laboratory issues in the detection and reporting of antibacterial resistance.

The emergence of antimicrobial resistance among several common bacterial pathogens requires that clinical microbiology laboratories have the ability to promptly and accurately recognize resistance in patients' isolates. Laboratories have several options for performing routine susceptibility testing, including the broth microdilution procedure (with or without instrumentation for test reading), automated instrument systems that provide rapid results, antibiotic gradient diffusion, and disk diffusion procedures. In addition, there are definitive screening tests capable of recognizing resistance to drugs of choice among several common bacterial species based on single drug concentration tests or rapid spot tests. The likely emergence of still newer resistance mechanisms will provide a challenge to clinical microbiologists to devise accurate, yet cost-effective strategies for use in the future.

Selection of antimicrobial agents for routine testing in a clinical microbiology laboratory.

Each clinical microbiology laboratory must establish its own standard battery of antimicrobial agents to be tested routinely on clinical isolates of various organism groups. Some choices are based upon the intrinsic activities of antimicrobial agents for a particular group of organisms, for example, agents primarily active against either Gram-positive or Gram-negative bacteria. For final selection of limited batteries of agents for routine testing, however, it is necessary to use additional criteria based upon physician prescribing patterns and the availability of antimicrobial agents in a particular institution. A fundamental principle in the selection process should be routine testing and reporting of those antimicrobial agents that physicians actually use, that is, the institution's formulary agents. Testing of the most appropriate drugs for an institution may be complicated by lack of availability of some antimicrobial agents among the standard panels offered by automated instrument or commercial test system manufacturers. The laboratory should develop its final test batteries in consultation with the infectious disease and pharmacy services and the pharmacy and therapeutics and infection-control committees of the medical staff. These choices should not be made based upon the most convenient selection of drugs from the laboratory's perspective or based upon pharmaceutical industry promotional efforts.

Rapid methods in clinical microbiology. Clinical situations in which rapid methods may best be applied.

Utilization of rapid microbiologic methods could improve both the quality of patient care and help to reduce patient health care costs through more efficient patient management. Medically urgent situations such as meningitis, endocarditis, bacteremia, some soft tissue infections, ocular infections, and pneumonia in immunocompromised hosts are obvious areas for application of rapid methods. However, efficient management of outpatient infections such as group A streptococcal pharyngitis, bacteriuria, diarrhea, and sexually transmitted diseases could also benefit from rapid test results. Rapid methods for detection of slow growing or unculturable microorganisms represent a promising area for development of new test methodologies. Realization of the potential of various rapid microbiology tests, however, requires that several difficult questions be addressed. Acceptable test rapidity and accuracy must be established by concensus of microbiologists and clinicians. Moreover, new approaches to reduce total test turn-around time and novel means to facilitate physician use of rapid test results must be sought in the immediate future.