Laboratory evaluation of urinary tract infections in an ambulatory clinic

A 4-month evaluation of ambulatory patients with a suspicion of a urinary tract infection was performed. Specific objectives included assessment of five urinary screening methods, reevaluation of the necessity of the phenylethyl alcohol plate (PEA), and cost-effectiveness of screening for low colony count bacteriuria. Urine samples were collected as midstream, clean-caught specimens. A total of 142 samples, 87 from 79 symptomatic patients and 55 negative controls, were evaluated. All urine specimens were cultured using a 0.01 mL loop and a 0.001 mL loop onto Columbia sheep blood agar, MacConkey agar, and PEA agar. Twenty-four specimens (17%) were sterile, 64 (45%) were contaminated, and 54 (38%) were infected. Five urine screening methods were performed. These tests and their associated sensitivity and specificity are as follows. The Chemstrip 9 (Behring, Inc., Somerville, NJ) for leukocyte esterase and nitrate, 67%, 98%; microscopic analysis on spun urine, 79%, 93%; methylene blue stain for pyuria, 60%, 99%; Gram stain for pyuria, 45%, 93%; Gram stain for bacteriuria, 65%, 75%; and the URISCREEN (Analytab Products, Plainview, NY), 92%, 89%. Inclusion of a PEA plate for isolation of gram-positive organisms provided no additional information. Routine culture of urine samples at 10(-2) mL increased the contamination rate by 19%.

Comparative activity of cefepime, alone and in combination, against clinical isolates of Pseudomonas aeruginosa and Pseudomonas cepacia from cystic fibrosis patients

The comparative in vitro activity and synergy of cefepime were evaluated with clinical isolates of Pseudomonas aeruginosa and Pseudomonas cepacia from cystic fibrosis patients. The activity of cefepime, both alone and in combination, was comparable to those of other antibiotics. The clinical efficacy of cefepime in cystic fibrosis patients merits investigation.

In vitro activities of cefoperazone and sulbactam singly and in combination against cefoperazone-resistant members of the family Enterobacteriaceae and nonfermenters

Among 28,000 isolates of the family Enterobacteriaceae and nonfermenters isolated at multiple medical centers, 1,084 (4%) were resistant to cefoperazone (MIC, greater than or equal to 64 micrograms/ml) and 1,711 (6%) exhibited cefoperazone MICs of 2 to 32 micrograms/ml. Ninety-six percent of these 2,795 isolates produced beta-lactamase, as determined by the nitrocefin test. Sulbactam alone (8 micrograms/ml) was inactive against 99.6% of the isolates other than Acinetobacter calcoaceticus and Pseudomonas cepacia. Sulbactam enhanced the activity of cefoperazone against 56% of the isolates of the family Enterobacteriaceae and 44% of the nonfermenters. In the presence of sulbactam concentrations of less than or equal to 8 micrograms/ml, 65% of the cefoperazone-resistant isolates had reductions in cefoperazone MICs of greater than or equal to 2 log2 dilution steps and were susceptible to less than or equal to 32 micrograms/ml. Antagonism was not observed.

In vitro activities of combinations of aztreonam, ciprofloxacin, and ceftazidime against clinical isolates of Pseudomonas aeruginosa and Pseudomonas cepacia from patients with cystic fibrosis

The in vitro activities of two-drug combinations of aztreonam, ciprofloxacin, and ceftazidime were studied in 96 clinical isolates of Pseudomonas aeruginosa and in 20 clinical isolates of Pseudomonas cepacia from cystic fibrosis patients. Some synergy was observed with each combination used against P. aeruginosa, but synergy was rare when the combinations were used against P. cepacia.

Evaluation of four newer antimicrobial agents in the Avantage susceptibility test system

Antimicrobial elution disks containing amoxicillin-clavulanic acid (Augmentin), cefotetan, ciprofloxacin, or norfloxacin were tested in the Avantage automated susceptibility test system. Performance was compared against an agar diffusion procedure in a three-site collaborative study. Results of 1,500 comparison with amoxicillin-clavulanic acid showed a full accord (agreement of both systems) of 93.6% and an essential accord (agreement excluding minor discrepancies) of 97.6%. Results for cefotetan showed a full accord of 95.1% and an essential accord of 98.3% by the two methods. Results for both ciprofloxacin and norfloxacin were in full accord for more than 98% of tests with gram-negative bacilli and staphylococci, but tests with enterococci gave 38 and 26.1% minor discrepancies (the result of one method was resistant or susceptible and the result of the other method was intermediate), respectively. The results indicated that the Avantage test system is accurate and reliable and provides appropriate determination of bacterial susceptibility with the four antibiotics tested.

The use of aztreonam in the cystic fibrosis patient

Eradication of pulmonary infection by Pseudomonas aeruginosa in cystic fibrosis (CF) patients has long presented a significant challenge to the medical community. Many antimicrobial agents have proved incompletely effective against this persistent pathogen, and even the aminoglycosides, which represent the traditional therapy for such infections, have been associated with considerable toxicity and resistance. The monobactam antibacterial agent aztreonam is used both as single-agent therapy and in combination with other drugs. Several controlled, clinical trials have demonstrated the efficacy of aztreonam in the treatment of CF patients with pulmonary exacerbations caused by P. aeruginosa. The only side effect of aztreonam therapy commonly encountered in these studies was elevation of hepatic transaminase concentrations; this effect was of uncertain significance. It was concluded that aztreonam may offer clinical efficacy comparable to that provided by the combination of tobramycin plus azlocillin. Further, there does not seem to be any appreciable difference in the development of resistance to aztreonam compared with traditional therapies.

Comparative in vitro activity of lomefloxacin (SC 47111 or NY-198) against fresh clinical bacterial isolates

The in vitro antibacterial activity of a new difluorinated quinolone (lomefloxacin) was compared with that of ten selected antibiotics against 744 fresh bacterial isolates representing 32 species. Lomefloxacin was comparable to other quinolones tested against Enterobacteriaceae (MIC90, less than or equal to 0.25 micrograms/ml) and generally more effective than other compounds tested against Staphylococcus spp. and Pseudomonas aeruginosa with MIC90s of less than or equal to 2 and less than or equal to 4 micrograms/ml, respectively.

Changing susceptibility of Pseudomonas aeruginosa isolates from cystic fibrosis patients with the clinical use of newer antibiotics

To detect a change in antibiotic susceptibility patterns in Pseudomonas aeruginosa isolates upon the introduction and clinical use of ciprofloxacin, aztreonam, and ceftazidime, MICs for clinical isolates collected before introduction of the antibiotics, during early clinical use, and later were determined for these and seven other antipseudomonal antibiotics. Concomitant resistance to two or more antibiotics was also studied. Over the three study periods, rates of susceptibility to 9 of the 10 antibiotics decreased. The largest decrease occurred with ceftazidime. Analysis of subsets of isolates from patients treated with ciprofloxacin or aztreonam also showed declining susceptibility to the latter but a stabilization of susceptibility to the former after an initial decline. Concomitant resistance within and among antibiotic classes was common.

The regionalization of laboratory services at the University of Utah Medical Center. Associated Regional and University Pathologists Inc (ARUP)

We feel that now, four years out, we have achieved the interim goals that we set for ourselves. There are some key aspects that we would do differently if we were now starting over, and we have provided that information to those seeking to begin similar off-site ventures who have sought our advice. There is an interesting constellation of factors that must be present for such an operation to succeed, and the individual components of that constellation will differ by institution and location. The rationale and circumstance will vary profoundly, and what is "right" in one setting may be entirely "wrong" in another. I feel compelled to caution the reader about the myriad of determinants and ingredients that must be considered. Study the precedents and seek knowledgeable advice from financial, legal, insurance, human resource (personnel), and laboratory management professionals. Regional laboratories can succeed. Hospitals may well benefit from a strategy of marketing services to physician staff members and the incremental financial and service benefits from added testing volume can be significant. However, the more expansive the business design, the more complicated the management requirements and demands and, potentially, the higher the risks, costs, pressures, and down-side factors. We feel very strongly about our focus of supporting the pathology and medical technology professions. Our value-added services are geared not only to providing technology, management, and financial services support for our clients, but also to not competing with them for local clientele. We have a program of teaching them how to market to that clientele and of providing the support materials to assist them in so doing. We have progressed from being a hospital laboratory to being a hospital laboratory referral laboratory, and now have also become a referral laboratory for other reference laboratories. As a full-service reference laboratory we send out very few tests, and are continually incorporating new tests and technologies. We have referral testing accounts currently in 42 states and we want to be the very best at what we do, namely, esoteric reference testing. Our credo is that quality at ARUP is making best continually better.

In vitro inactivation of aminoglycosides by cephalosporin antibiotics

The in vitro inactivation of aminoglycoside antibiotics by semisynthetic penicillins complicates antibiotic assays. Due to the increasing number of new cephalosporins and use of aminoglycoside-cephalosporin combinations, we determined the in vitro stability of 28 aminoglycoside-cephalosporin combinations (gentamicin sulfate, tobramycin sulfate, netilmicin sulfate [10 micrograms/mL], and amikacin [20 micrograms/mL] in combination with cefazolin sodium, cefoxitin sodium, cefoperazone sodium, cefotaxime sodium, ceftazidime acid pentahydrate, cefsulodin sodium, or cefpiramide sodium at 100, 200, and 300 micrograms/mL). These mixtures were incubated at 37 degrees C and sampled at 0, 8, and 24 hours. Amikacin and tobramycin were most stable and netilmicin was the least stable of the aminoglycosides. Cefoxitin, ceftazidime, and cefotaxime were the least inactivating of the cephalosporins. When combined with first- and second-generation cephalosporins, aminoglycosides are relatively stable, but some laboratory precautions may be necessary when determining aminoglycoside levels in the presence of third-generation cephalosporin compounds.

Absence of rapidly developing resistance during treatment of cystic fibrosis patients with aztreonam

The in vitro activity of aztreonam and 10 other antibiotics was determined for clinical isolates of Pseudomonas aeruginosa from 18 cystic fibrosis patients obtained before, at the end of, and 7-14 days after the completion of therapy with aztreonam. The percent of isolates susceptible to aztreonam at each sampling period were 79%, 78%, and 81% respectively.

In vitro activity of aztreonam combined with tobramycin and gentamicin against clinical isolates of Pseudomonas aeruginosa and Pseudomonas cepacia from patients with cystic fibrosis

The in vitro activity of aztreonam combined with tobramycin and with gentamicin was assessed in 78 clinical isolates of Pseudomonas aeruginosa and 11 clinical isolates of Pseudomonas cepacia from patients with cystic fibrosis. Synergy was detected in 56.4% of P. aeruginosa isolates and 60% of P. cepacia isolates with the aztreonam-tobramycin combination and in 49.3% of P. aeruginosa isolates and 81.8% of P. cepacia isolates with the aztreonam-gentamicin combination. No antagonism was observed. These combinations merit clinical evaluation in the treatment of patients with cystic fibrosis.

Selective and differential medium for recovery of Pseudomonas cepacia from the respiratory tracts of patients with cystic fibrosis

A selective and differential medium, OFPBL (oxidation-fermentation base supplemented with agar, lactose, and two antimicrobial agents), for the isolation of Pseudomonas cepacia from respiratory specimens of patients with cystic fibrosis was developed and tested. Among 725 specimens submitted from seven centers over a 4- to 6-month period, 58 (8%) yielded P. cepacia on OFPBL; only 19 of these were recovered on MacConkey or sheep blood agar (P less than 0.001). No isolate was recovered on MacConkey or sheep blood agar alone. Ranges of recovery rates among centers were 0 to 15% on OFPBL and 0 to 10% on MacConkey or sheep blood agar. Ninety percent of P. cepacia isolates were detected on OFPBL in less than or equal to 3 days. Other nonfermenters and yeasts isolated on OFPBL were distinguished from P. cepacia by failure to acidify the medium. The new medium was clearly superior to MacConkey and sheep blood agars for the isolation of P. cepacia from the respiratory secretions of patients with cystic fibrosis.

In vitro activity in deptomycin (LY-146032) compared with other antimicrobial agents against gram-positive cocci

A comparison was made of the activity of deptomycin (LY-146032) with that of ampicillin, cephalexin, cefamandole, cephalothin, erythromycin, teicoplanin, tetracycline, and vancomycin. The minimal inhibitory concentration (MICs) for greater than or equal to 90% of 356 Gram-positive cocci, against deptomycin, were less than or equal to 2 micrograms/ml. The MICs for the other antimicrobials varied greatly depending on the compound. A slight and unexplained inoculum effect was observed for LY-146032.

Ciprofloxacin versus tobramycin plus azlocillin in pulmonary exacerbations in adult patients with cystic fibrosis

Twenty adult patients with cystic fibrosis who were experiencing acute pulmonary exacerbations were enrolled in a randomized, controlled trial comparing oral ciprofloxacin with intravenous tobramycin plus azlocillin. Efficacy of the two treatments was compared based upon changes in clinical status, pulmonary function tests, white blood cell counts, and quantitative bacteriology of sputum. No statistically significant differences were detected in these parameters of response between the two treatment groups (p greater than 0.05). Ciprofloxacin appears to be therapeutically equivalent to intravenous antibiotics in the treatment of adult patients with cystic fibrosis who are experiencing pulmonary exacerbations associated with susceptible bacteria.

Efficacy of aztreonam in pulmonary exacerbations of cystic fibrosis

A noncomparative pilot study was conducted to assess the potential usefulness of aztreonam in pulmonary exacerbations of cystic fibrosis. Of 27 patients initially enrolled 25 received sufficient courses of aztreonam therapy to be evaluable. All patients received 200 mg/kg/day of aztreonam in 4 equally divided doses administered intravenously. Of 57 isolates of Pseudomonas aeruginosa from pretherapy sputum cultures, 48 were susceptible to aztreonam in vitro as were 11 of 18 strains isolated at the conclusion of therapy. With treatment colony counts of P. aeruginosa in sputum were reduced by 3 log10 or more in 15 patients. It was totally (but temporarily) eradicated in 11 of these patients. Clinical scores and white blood cell counts improved significantly (P less than 0.05). Side effects of aztreonam were limited to transient elevations of liver enzymes occurring in 16 patients. Aztreonam merits further evaluation in a randomized, comparative trial with standard antibiotic therapy for cystic fibrosis.

Group B streptococcal breast abscess

A 22-year-old women was admitted to the hospital with a large, tender supraareolar mass of her right breast. Cultures of the purulent aspirate yielded beta-hemolytic group B streptococcus. Surgical incision and drainage, together with therapy with erythromycin ethylsuccinate in this penicillin-allergic patient, resulted in cure. This is the first report, to our knowledge, of group B streptococcus causing human breast abscess.

Use of the Bac-T-Screen to predict bacteriuria from urine specimens held at room temperature

Results from the Bac-T-Screen (BTS) of fresh urine specimens were compared with the BTS results obtained when the same urine specimens had been held at room temperature for 24 h. Of the 246 specimens studied, 43 were initially BTS positive, 11 were false-negative, and 39 had greater than or equal to 10(5) CFU/ml. After 24 h at room temperature an additional 60 specimens had greater than or equal to 10(5) CFU/ml, of which only 16 were BTS positive; 10 specimens still gave false-negative results, and the number of false-positive specimens increased by only 6.5% of all specimens. For significant specimens (containing greater than or equal to 10(5) CFU of probable pathogens per ml), the predictive value of a negative test changed by only 0.1% (99.5 to 99.4%), whereas the sensitivity of the test remained at 96.4% for incubated specimens. Of those specimens that developed greater than or equal to 10(5) CFU/ml in vitro, 85% contained gram-negative bacilli. Neither bacteria grown in vitro nor urine specimens from normal females containing greater than or equal to 10(5) CFU/ml were positive with the BTS. For reasons not entirely understood, the BTS system may be unique in its ability to discriminate between bacteria which represent true bacteriuria and those which are present because of contamination, possibly due to other cellular elements present in infection-related bacteriuria, namely leukocytes and sloughed bladder epithelial cells.

Review of urine microscopy for bacteriuria

Urine microscopy for bacteriuria remains a useful and valid technique for the evaluation of urinary tract infection; however, established interpretive criteria are not agreed on. Our own data and a review of the literature demonstrate that reliable data can be obtained by enumerating the organisms observed in stained or unstained centrifuged and stained uncentrifuged urine specimens. Criteria are given for the interpretation of urine microscopy for maximum sensitivity and specificity for each method reviewed. For clinicians desiring to perform urine microscopy, we recommend the use of oil-immersion microscopy of Gram-stained centrifuged urine sediment and suggest that observing at least one organism per oil-immersion field corresponds with 95% sensitivity and that observing more than five organisms corresponds with 95% specificity for bacteriuria at a level of 10(5) or more colony-forming units per milliliter. Further testing will be required on any negative specimen from a symptomatic patient.

Pyrolysis mass spectrometry of bacteria from infected human urine. I. Influence of culturing and antibiotics

Curie-point pyrolysis mass spectrometry was performed on three bacterial isolates obtained from infected human urine using a novel, direct isolation method. Bacterial samples were analysed directly after isolation, as well as after free growth in broth and after exposure to solutions containing penicillin and gentamicin. The spectra of bacteria directly from urine showed no detectable contamination from urinary constituents. Discriminant analysis indicated genetic strain differences to be greater than the combined variances due to sample preparation or the growth phase. Characteristic biochemical changes related to growth or non-growth were detectable after only 2 h of incubation. The potential usefulness of pyrolysis mass spectrometry techniques for rapid susceptibility testing is discussed.

Comparison of visual and photometric Bac-T-Screen results

The Bac-T-Screen (Marion Laboratories, Kansas City, MO) was used to screen 826 urine specimens. Of these, 85 either pigmented or clogged the Bac-T-Screen filter and could not be evaluated. Results for the remaining 741 specimens were examined both visually and photometrically by a newly developed photometric card reader. The results were then compared. Screening results for all urines containing greater than or equal to 10(5) pathogens/mL were equivalent for both methods, with sensitivity and predictive negative values of greater than 98% and greater than 99%, respectively. The predictive values of positive tests were also equivalent at 57.5% for visual and 59.6% by photometry. The overall agreement varied with the card reader value used because the photometric card-reader procedure allows the user to select desired sensitivity and specificity levels.

In vitro inactivation of aminoglycosides by apalcillin

Apalcillin, at concentrations of 75, 150, 300, and 600 micrograms/ml, was combined in vitro with amikacin, gentamicin, netilmicin, or tobramycin. Incubation at 37 degrees C resulted in an apalcillin concentration-dependent and time-dependent decrease of aminoglycoside activity of up to 60%. Amikacin was the most stable and tobramycin was the least stable aminoglycoside under the conditions tested.

Pharmacokinetics and dosage requirements of netilmicin in cystic fibrosis patients

The pharmacokinetics of netilmicin were determined in 10 patients with cystic fibrosis. Mean (+/- standard error of the mean) values for total body clearance and volume of distribution were 2.62 (+/- 0.18) ml/min per kg of body weight and 0.38 (+/- 0.01) liter/kg, respectively, and were considerably larger than the same parameters reported for patients without cystic fibrosis.

Means to facilitate physician acceptance and use of rapid test results

Rapid testing methods can have a positive impact on patient care and help ease the mounting economical pressures facing clinical microbiology laboratories. Rapid test reporting, the validation of rapid test procedures and results, and physician acceptance and use of these tests are among the 10 categorical measures outlined to help laboratories optimize productivity, efficiency, and economic and patient-care impact.

Effect of urine preservation on urine screening and organism identification

Three urine preservation-transport methods were examined for their effect on rapid urine-screening procedures. Results from fresh urine specimens, screened for bacteriuria by leukocyte esterase, nitrate, Autobac, Bac-T-Screen, Auto Microbic System (AMS), and bioluminescence procedures, were compared with urine-screen results from urine specimens held for 24 hours at room temperature in chemical preservatives. Quantitative discrepancies ranged from 0%, for urine preserved with glycerin-boric acid-sodium formate and tested by AMS or leukocyte esterase, to 21% for urines in the same preservative tested by bioluminescence or nitrate. Up to 62% of the organism identifications made from preserved urine specimens tested by the AMS urine card were in error. These data suggest that it may be inadvisable to use weak organic acid-based urine preservation systems in conjunction with these urine-screen procedures.

False susceptibility of enterococci to aminoglycosides with blood-enriched Mueller-Hinton agar for disk susceptibility testing

Disk diffusion susceptibility tests for enterococci are frequently modified by adding 5% sheep blood (SB) to Mueller-Hinton agar; the performance standards from the National Committee for Clinical Laboratory Standards sanction this addition. Susceptibility testing of aminoglycoside antibiotics is not recommended for enterococci; in actual practice, however, some laboratories do include aminoglycoside antibiotics routinely, and others may test upon request or in selected situations. In examining 50 clinical isolates of enterococci, SB-enriched Mueller-Hinton agar frequently gave enlarged zone sizes that falsely indicated susceptibility (72% for gentamicin and tobramycin), with the average increase in zone size being 6.3 and 7.6 mm, respectively. Comparison agar dilution MICs demonstrated uniform resistance, with or without added SB. The effect was shown to be caused by heme in concentrations as low as 0.03 micrograms/ml, which, when combined with aminoglycoside antibiotics, caused a synergistic growth inhibition of the enterococci, resulting in larger aminoglycoside antibiotic zones. We postulate that the heme effect is related to a catalytic cleavage of intracellular H2O2 and resultant lipid peroxidation. No other organism or antimicrobial agent tested demonstrated a similar effect, although other investigators have shown a similar phenomenon with the broad-spectrum cephalosporins. Because enterococci grow well and give accurate susceptibility results on Mueller-Hinton agar without SB supplementation and because of the spectrum of definable problems with a number of antimicrobial agents, we recommend that enterococci routinely be tested without SB.

Packaged commercial bacterial identification systems

The authors attempt to provide a useful and current guide for clinical microbiologists who are seeking a review of the available packaged commercial systems for bacterial identification. Each system is outlined according to test principle, laboratory procedures, turn-around time, and limitations. Selected peer evaluations and references for many of the systems are also cited.

Agreement between capillary and arterial serum gentamicin concentrations in neonates

Due to inherent difficulties in blood sampling in neonates, specimens for laboratory analyses are often obtained by heel puncture technique. While agreement between venous or arterial and capillary concentrations of some substances has been reported, that for gentamicin, when obtained by heel stick, has not. Simultaneously obtained heel stick (capillary) and umbilical artery (arterial) serum samples were analyzed for gentamicin concentrations in 20 preterm neonates. Further, 14 subjects underwent manual manipulation of the heel to encourage blood flow before sampling to test the effect of such manipulation on gentamicin concentration. The agreement between capillary and arterial serum concentrations of gentamicin was found to be excellent in infants greater than 1000 g body weight. Manipulation of the heel had no effect on this agreement.

A five-year analysis of antimicrobial susceptibility testing profiles for beta-lactam antimicrobials, with inter-hospital and susceptibility method comparisons within a medical school affiliated hospital system

A comparative study of antimicrobial susceptibility patterns was performed for a five-year period in four hospitals affiliated with the University of Utah School of Medicine due to concern that susceptibility testing method and results differences between hospital units might complicate training and comprise initial antimicrobial therapy. Few significant pattern changes were detected within or between the individual hospitals during the five-year period, and variances between hospitals were in general no greater than variances demonstrated within individual service units within the University Hospital.

The spot indole test for identification of swarming Proteus

The authors evaluated the use of the spot indole test for rapid speciation of swarming Proteus from the primary isolation plate. One hundred seventy-two consecutive isolates of swarming Proteus were studied, 163 Proteus mirabilis and nine Proteus vulgaris. One hundred fifty-six isolates (95.7%) of Proteus mirabilis gave a negative spot indole. Seven (4.3%) gave a positive spot indole test, but all seven isolates were from cultures in which other indole-producing organisms also were present. If only isolates representing single gram-negative strains in the specimens were tested, the predictive value was greater than 99%. Eight of the nine (88.9%) Proteus vulgaris isolates gave a positive spot indole test; one (11.1%) gave a negative result. This isolate also failed to produce indole by conventional methods but was ornithine decarboxylase negative, and additional biochemical testing was consistent with the Proteus vulgaris identification. All Proteus vulgaris isolates were resistant to ampicillin, and 94.2% of the Proteus mirabilis tested were ampicillin susceptible. The spot indole test is a rapid, accurate, simple, and cost-effective means of speciating swarming Proteus strains isolated as the only gram-negative bacilli in a specimen. The spot indole test should be used in conjunction with an ampicillin susceptibility test result or other confirmatory test information if other gram-negative bacilli are present in the culture.

Purchasing instrumentation for the microbiology laboratory

Though the decision of whether or not to purchase instrumentation for clinical microbiology depends on the circumstances in the individual laboratory, the author believes that a knowledge of the proper perspective and some general rules will make decision making easier. In this article he presents a list of guidelines.

Evaluation of cost-effectiveness and rationale for use of a selective culture plate for isolation of Staphylococcus aureus from stool specimens

An assessment was made of the necessity of performing routine screening for Staphylococcus aureus in stool specimens. A total of 527 stool specimens were evaluated. Because of the rare incidence of staphylococcal enterocolitis and the high ($2.50) screening cost, the results of this evaluation suggest that such a screening need not be performed routinely.

Disk diffusion testing, quality control guidelines, and antimicrobial spectrum of HR810, a fourth-generation cephalosporin, in clinical microbiology laboratories

HR810 is a new, very broad-spectrum cephalosporin with significant activity against members of the family Enterobacteriaceae, pseudomonads, gram-positive cocci, and anaerobes that is generally greater than the third-generation cephalosporins (99.6% of 4,128 clinical facultative enteric isolates were inhibited by less than or equal to 8.0 micrograms of HR810 per ml). Tests and statistical methods to establish in vitro antimicrobial susceptibility test criteria favor tentative breakpoints of greater than or equal to 18 mm (less than or equal to 8.0 micrograms/ml) as susceptible and less than or equal to 14 mm (greater than or equal to 32 micrograms/ml) as resistant. This provides a 93.7 to 98.3% absolute interpretive accuracy. Several preliminary ranges for zone sizes obtained with quality control organisms are proposed for the 30-micrograms HR810 disk diffusion test used during the clinical trials.

Use of and cost savings with morphologic criteria and the spot indole test as a routine means of identification of Escherichia coli

The use of primary isolation plate colonial morphologic criteria (CMC) of a flat, nonmucoid, lactose-fermenting, gram-negative rod on MacConkey agar and the spot indole (SI) test from the sheep blood agar plate was evaluated as a means for identification of Escherichia coli in comparison to kit (Micro-ID, API-20E) and conventional biochemical testing. In this preliminary phase of comparison of accuracy, 427 isolates of E. coli (69.8%) from a total of 612 isolates of lactose-fermenting gram-negative rods were evaluated. Of these E. coli isolates, 357 (83.6%) fit the CMC and were SI positive; 3 (less than 1% error rate) were not E. coli. In the second phase of the evaluation, using CMC and SI alone as a means for identification of E. coli, 472 (57.6%) E. coli isolates from a total of 820 Enterobacteriaceae isolates were assessed. Of these E. coli isolates, 326 could be identified using only CMC and SI (69.1% of the E. coli isolates and 39.8% of all Enterobacteriaceae isolates); 146 (30.9%) required additional biochemical testing because of atypical colonial morphology, because of the investigator's inability to differentiate colony types on both media or lack of isolated colonies on either of the two required media, or because as isolates from sterile body sites they were processed directly to Micro-ID kits. A minimum of 40% savings on Enterobacteriaceae identification schemes without compromising accuracy was calculated. As of November 1983, a direct (labor and materials) cost savings of approximately +200.80 per 100 Enterobacteriaceae identifications was projected.

Differential primary plating medium for enhancement of pigment production by Pseudomonas aeruginosa

A cost-effective and more rapid means of detection of Pseudomonas aeruginosa in cultures from clinical specimens would be very advantageous. We have developed a modified MacConkey agar (MMA), which enhances pigment production of P. aeruginosa and which, if pyocyanin pigment is present, provides a relatively rapid and very cost-effective identification. The MMA medium inhibits the gram-positive organisms, while lactose- and non-lactose-fermenting gram-negative rods are easily distinguishable from pigment-producing pseudomonads. Organisms that produce pyocyanin, pyoverdin, or pyorubin, or both pyocyanin and pyoverdin, are easily recognized on the medium. Pyocyanin production is clearly distinguishable from other Pseudomonas pigments on MMA. In a comparative study, MMA identified 97% of the P. aeruginosa strains 24 h earlier than routine laboratory biochemical methods. Highly mucoid strains which did not produce detectable pigments on standard biochemicals produced detectable pigments on the MMA within 48 h. This medium can provide a very practical, reliable, and cost-effective means for early characterization of P. aeruginosa.

Azlocillin pharmacokinetics in patients with cystic fibrosis

The pharmacokinetics of azlocillin were studied in 10 cystic fibrosis patients, ranging in age from 11 to 28 years. The patients received a 9- to 23-day course of 350 mg of azlocillin per kg in four or six divided daily doses in combination with am aminoglycoside. Blood and urine samples were collected at specified times after the last dose of the course of azlocillin therapy and then assayed for azlocillin content. Pharmacokinetic parameters were determined by noncompartmental analysis. Mean values for serum half-life (1.74 h), disposition constant (0.41 h-1), total body clearance (123 ml/kg per h), and renal clearance (58 ml/kg per h) were determined. All patients exhibited improvement with respect to clinical and laboratory parameters and displayed no adverse reactions. The pharmacokinetic analysis offers further evidence of the dose-dependent nature of azlocillin elimination, but elimination did not appear to be altered in cystic fibrosis patients.

Collaborative clinical evaluation of the Autobac IDX system for identification of gram-negative bacilli

The Autobac IDX system (General Diagnostics, Warner-Lambert Co., Morris Plains, N.J.) for rapid, semiautomated identification of gram-negative bacilli was compared with the identification methods in routine use in four laboratories. The study included 1,515 organisms representing 30 species of enteric and nonenteric bacteria. Discrepancies between the results of the IDX system and routine methods were resolved by classical biochemical testing at a reference center. Overall, 98% of the organisms were correctly identified by the routine methods, and 93% were correctly identified by the IDX systems. After adjustment for frequency of clinical occurrence of the organisms tested, the IDX system performed with 95% accuracy. Results with the IDX system were available in 3 to 6 h. Results with the comparative methods were available in 4 to 48 h. A wide variety of organisms, including oxidase positive, oxidase negative, fermentative, and nonfermentative, were identified by a single system by using Autobac. Three or more systems were required to identify the 30 species by the comparative methods. Overall, the results indicate the Autobac IDX system is useful for the rapid identification of enteric and nonfermentative gram-negative bacilli.

Evaluation of a rapid bacteriuria screening instrument

A newly modified, semiautomated instrument (Bacteriuria detection device (BDD] designed to detect the presence of bacteriuria in less than 3 min was compared to quantitative urine culture plating techniques. The instrument consists of a self-enclosed vacuum-filtration-staining system in which a 1-ml urine filtrate is stained on a filter. The resulting color determines the quantitation. Of the total of 525 clinical urine specimens tested, 66 (12.6%) were uninterpretable due to pigment deposition or inability to complete the filtering process (clogging of the filter). Of the remaining 459 specimens, 93 (20.3%) had a plate quantitation colony count of 10(5) colony-forming units (CFU)/ml or more. The BDD detected 94.2% of these positive specimens if only significant pathogens were included (85% if specimens that were probably contaminated were also included). For specimens containing significant pathogens at 10(4)-10(5) CFU/ml, the BDD detection rate was 41%. The device detected most (94.3%) gram-negative bacilli and enterococci at colony counts of 10(5) CFU/ml or more. In addition, the BDD accurately detected 95.6% of specimens with no growth or fewer than 10(4) CFU/ml. With several proposed modifications, these results suggest that this instrument is potentially useful as a urine screening device in a select population.

Clinical evaluation of a lysis-centrifugation technique for the detection of septicemia

A commercially available lysis-centrifugation blood culture system was compared with a two-bottle broth-culture system employing 100 mL of broth and 10 mL of blood per bottle to analyze 1,913 blood specimens. Of 154 clinically significant isolates, 89% were detected by the lysis-centrifugation technique, and 73% were detected by the broth-culture method. Twenty-seven percent of the organisms were detected only by the lysis-centrifugation technique, and 11% were detected only by the broth system. Fifteen polymicrobial cultures were encountered; the lysis-centrifugation technique detected 93% of the organisms in these cultures, while the broth-culture method detected only 20%. Isolated colonies of clinically important organisms were available 30 hours earlier with the lysis-centrifugation technique. These results suggest that the lysis-centrifugation technique may provide a substantial improvement over conventional methods for blood cultures.

Viability of organisms held in the isolator blood culture system for 15 h and their rapid detection by acridine orange staining

Sets of three Isolator blood culture tubes were seeded with low numbers of 96 strains of 26 bacterial species (fresh and stock clinical isolates). One tube was processed immediately, and the other two were held at 22 and 34 degrees C for 15 h before processing. Organism recovery was 99, 99, and 98%, respectively. Organism numbers increased at both 22 degrees C (60% of strains) and 34 degrees C (79% of strains). Especially notable was that the increases were seen with most strains of Staphylococcus aureus, streptococcal species, Pseudomonas, and all of the Enterobacteriaceae tested. Seven strains, including Streptococcus pneumoniae and Haemophilus influenzae, although viable, were recovered with a decreased number of organisms at each temperature. Acridine orange staining detected organisms in 53% of those Isolator tubes being held and 71% of those demonstrating a numerical increase, after incubation at 34 degrees C. In addition, it was noted that after processing, 48% of the strains that had increased in number while being held at 34 degrees C resulted in visible growth on agar media in 6 h. The results suggest that up to a 15-h delay in processing Isolator tubes may be possible and that acridine orange staining for the rapid detection of positive cultures may be useful in such a circumstance.

Lack of relationship of Clostridium difficile to antibiotic-associated diarrhea in children

We studied prospectively the conversion rate to Clostridium difficile-positive stool cultures in 31 children receiving oral antibiotics for common infections and looked for a possible association of C. difficile colonization with diarrhea. The incidence of pretreatment positive stool cultures was 35% with the majority of positive findings in infants less than 1 year of age. After treatment with oral antibiotics C. difficile was cultured from the stool of 42% of the children. Eleven children developed diarrhea during antibiotic therapy. Seven of these children had at least one stool culture positive for C. difficile and four had persistently negative cultures. Oral antibiotic treatment of common infections in otherwise healthy children does not appear to predispose to stool colonization with C. difficile, nor is the presence of C. difficile in stools in these children significantly associated with the onset of antibiotic-associated diarrhea.

Cefoperazone pharmacokinetics in preterm infants

The elimination pharmacokinetics of cefoperazone, a new cephalosporin, were studied in 15 preterm infants ranging in gestational age from 32 to 36 weeks and in postnatal age from 1 to 6 days. The infants received a single dose of either 50 or 250 mg of cefoperazone per kg by intravenous infusion. Blood samples were collected at specified times after completion of the drug infusion and then assayed for cefoperazone. Pharmacokinetic parameters were determined by noncompartmental analysis. Mean values for plasma half-life, elimination rate constant, apparent steady-state volume of distribution, and total body clearance were 5.53 h, 0.15 h-1, 124 ml/kg, and 36 ml/h per kg, respectively, for the group receiving a 50-mg/kg dose and 5.76 h, 0.14 h-1, 111 ml/kg, and 35 ml/h per kg, respectively, for the group receiving a 250-mg/kg dose. Positive correlations between gestational age and clearance and elimination rate were detected. A 50-mg/kg dose every 12 h ensured adequate serum levels for most of the common neonatal pathogens. Other than a transient rise in eosinophils in four subjects, no adverse effects were noted.