Biomedical subjects
Publications and source records attributed to J M Boyce.
Clinical isolates of Staphylococcus aureus wee inappropriately categorized as intermediate or resistant to oxacillin on the basis of tests with two lots of oxacillin disks. The potency of one lot was tested and found to be below accepted limits. Routine quality control tests failed to detect the defective disks.
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Of 27 unique clinical isolates of methicillin-resistant Staphylococcus aureus, only 4 were homogeneously resistant, and all 4 produced little or no beta-lactamase. Among heterogeneously resistant strains, those most resistant to beta-lactam antibiotics produced the most beta-lactamase. Similar genes may regulate production of the low-affinity penicillin-binding protein and beta-lactamase.
cdc9 mutants of yeast lack detectable DNA ligase activity at restrictive temperatures. They also appear to be more sensitive than wild-type cells to ultraviolet (u.v.) radiation and it has been assumed that this is because the CDC9 ligase is needed for the final ligation step in excision repair. The fact that single-strand breaks have been demonstrated in u.v.-irradiated cdc9 mutants has been regarded as evidence for this interpretation. However, the kinetics of appearance of nicks in the DNA do not support this since maximal levels of strand breaks appear almost immediately after exposure to u.v. light and not progressively as repair events are initiated. We believe, therefore, that these strand breaks are connected with a u.v.-dependent preincision event, possibly connected with reorganization of chromatin.
Coagulase-positive staphylococci have been isolated from more than 95% of cases of toxic shock syndrome (TSS). Toxic shock syndrome toxin-1 (TSST-1) is produced in more than 90% of cases. A case is described of recurrent TSS in which a coagulase-negative staphylococcus was isolated from the vagina and produced TSST-1. No coagulase-positive staphylococci were isolated. Coagulase-negative staphylococci should be considered as causative agents in cases of TSS. Assay for TSST-1 should be performed on coagulase-negative staphylococci obtained from the appropriate clinical sites if no coagulase-positive staphylococci are isolated.
Some parts of the Guideline are clearly cost-effective. Abandoning routine cultures of respiratory therapy equipment is cost-effective and should be adopted by any hospitals that have not done so already. Other practices such as the use of preoperative and postoperative instructions regarding deep breathing and incentive spirometry, and the policy of never reusing respiratory therapy equipment items that are intended for single use probably warrant further cost-benefit analysis. Finally, there is increasing evidence that changing ventilator tubing every 24 hours is not cost-effective. Changing tubing every 48 hours appears to be safe and can save hospitals substantial sums of money.
We describe what appears to be the first reported case of nosocomial pneumonia caused by Neisseria cinerea. The isolate metabolized glucose when tested in BACTEC Neisseria Differentiation Kits (Johnston Laboratories), but did not produce detectable acid in cystine-Trypticase (BBL Microbiology Systems) agar medium or in modified oxidation-fermentation medium. Clinical laboratories that rely on the BACTEC method for differentiation of pathogenic neisseriae should be aware of the fact that N. cinerea may mimic N. gonorrhoeae when tested in BACTEC Neisseria Differentiation kits. The ability of N. cinerea to grow well on tryptic soy and Mueller-Hinton agars and its inability to grow on modified Thayer-Martin medium are characteristics which help to distinguish N. cinerea from N. gonorrhoeae.
A replicator method for screening Staphylococcus aureus isolates for synergistic hemolytic activity is described. The technique should also be useful for assessing the hemolytic activity of staphylococci and streptococci on different lots or brands of blood agar because the inoculum and the distances between spot inocula are standardized.
Six strains of Neisseria cinerea were tested in BACTEC Neisseria Differentiation kits (Johnston Laboratories, Inc., Towson, Md.), and all yielded positive glucose growth indices and negative maltose and fructose growth indices. These results were similar to those achieved with Neisseria gonorrhoeae. However, most of the N. cinerea isolates tested yielded 3-h glucose growth indices that were lower than those obtained with gonococci. 14C-labeled gas was produced significantly faster (P less than 0.02) by N. gonorrhoeae than by N. cinerea. Additional studies suggested that the 14C-labeled gas produced by N. cinerea was carbon dioxide. N. cinerea strains were similar to Branhamella catarrhalis strains because both species failed to produce detectable acid from glucose, maltose, sucrose, fructose, and lactose in cysteine-tryptic agar media. However, in contrast to N. cinerea strains, B. catarrhalis strains did not metabolize glucose in BACTEC Neisseria Differentiation kits.
Neisseria cinerea and Neisseria gonorrhoeae may occur at the same body sites and may have similar colony morphologies. Ideally, systems used for rapid identification of N. gonorrhoeae should be able to differentiate N. cinerea from gonococci. We tested seven N. cinerea strains using the Gonochek II (Du Pont Diagnostics), Minitek (BBL Microbiology Systems), RapID-NH (Innovative Diagnostics, Inc.), RIM-N (American Microscan), and Phadebact (Pharmacia Diagnostics) systems. We found that the reactions produced by N. cinerea in Gonochek II, Minitek, and RapID-NH kits could be confused with the results produced by some strains of N. gonorrhoeae. The susceptibility of N. cinerea to colistin, its ability to grow on tryptic soy or Mueller-Hinton agar, and its inability to grow on modified Thayer-Martin medium help differentiate it from gonococci.
To reevaluate the ability of the disk diffusion method to detect methicillin-resistant Staphylococcus aureus, 73 such isolates from 13 cities were tested for antimicrobial susceptibility with the standardized disk diffusion test. Duplicate plates were incubated at 30 and 35 degrees C and read after 18, 24, and 48 h. After incubation at 35 degrees C for 24 h, 97% of isolates appeared resistant to methicillin, and 99% appeared resistant to oxacillin. A significantly smaller proportion of isolates appeared resistant to cephalothin (P less than 0.001) and cefamandole (P less than 0.001). Isolates from some cities had no zones of inhibition around methicillin and oxacillin disks, whereas those from other cities had measurable zones of inhibition, with light growth inside the zones. Patterns of growth around cephalothin and cefamandole disks also varied among isolates from different cities. Incubation at 30 degrees C for 24 h did not result in better detection of methicillin or oxacillin resistance. All study isolates appeared resistant to methicillin and oxacillin after 48 h of incubation at 35 degrees C. The results suggest that methicillin-resistant S. aureus strains from many areas will be detected if standardized disk diffusion tests are incubated at 35 degrees C for 24 h.
To determine whether methicillin-resistant (MR) Staphylococcus aureus from different geographic areas are detected reliably by various commercially available microdilution broth and disk elution systems, 73 such isolates obtained from hospitals in 13 cities were tested by a reference method (agar dilution) and by the Microscan, API 3600S, Autobac I, and MS-2 systems. Both Eugonic broth and Low Thymidine Eugonic broth were used in the evaluation of the Autobac I, and two versions of the MS-2 were used. The proportions of isolates categorized as MR by the various methods were: agar dilution method, 99%; Microscan, 100% (if the suggested cut-off of the manufacturer was used); API 3600S, 96%; Autobac I, 84 to 93%; and MS-2, 54 to 68%. With the MS-2 system, isolates from Jackson, Miss., were classified as susceptible to methicillin more often than were strains from other cities. With the Autobac I (Eugonic broth), only 55% of isolates from Houston, Tex., were classified as MR, whereas 89% of isolates from all other cities were correctly classified as MR. With the API 3600S, strains from some cities were categorized as nafcillin susceptible, whereas strains from other cities were classified as resistant to nafcillin. The results of this study suggest that future evaluations of antimicrobial susceptibility testing systems should include MR strains of S. aureus from several geographic areas.
During a 3 1/2-year period (January 1978 through June 1981), 245 patients in a university hospital became colonized or infected with methicillin-resistant Staphylococcus aureus. During the first 18 months, the incidence of colonization and infection was only 0.05%. After a focal outbreak of methicillin-resistant S aureus in the burn unit, acquisition of the organism by patients on other wards increased significantly. Nonburn patients acquired the organism more often during time periods when newly admitted burn patients acquired methicillin-resistant S aureus. After the burn unit was closed, acquisition of the organism among nonburn patients on adult surgical and medical services decreased significantly. A questionnaire survey of other institutions disclosed that large outbreaks of this infection occurred more frequently in hospitals with burn units. These studies suggest that the occurrence of methicillin-resistant S aureus infections in burn units may lead to increased transmission of the organism to nonburn patients and that control of the infection in such units may reduce spread of the organism to patients without burns.
MRSA strains have become increasingly prevalent in the United States and are now an important cause of nosocomial infections in many large, medical school-affiliated hospitals. In affected institutions, from a few percent to 50% of all hospital-acquired S aureus infections are caused by MRSA strains. It has been suggested that the overall incidence of nosocomial S aureus infections may not increase in hospitals where MRSA strains have become epidemic or endemic and that MRSA strains merely replace methicillin-susceptible strains as a cause of hospital-acquired infections. Several recent studies lend support to this theory. Thompson et al [1] reported that the overall incidence of nosocomial S aureus-associated bacteremias and postoperative wound infections in a university hospital did not increase during a period when MRSA strains caused a significantly greater proportion of such infections. Similarly, Linnemann et al [2] found that the overall incidence of nosocomial S aureus-associated bacteremias did not change during a four-year period when the incidence of MRSA-associated bacteremias increased appreciably. At the University of Mississippi Medical Center, MRSA strains have been recovered from patients with increased frequency since an outbreak of MRSA infections occurred in the burn unit in June 1979 [3]. Continuing surveillance has revealed that the incidence of nosocomial MRSA infections was significantly higher in 1980-1982 than during 1979 (P = 0.002 by Mann-Whitney U test). MRSA strains accounted for 11% of nosocomial S aureus infections in 1979, 38% in 1980, 50% in 1981, 36% in 1982, and 32% in early 1983.(ABSTRACT TRUNCATED AT 250 WORDS)
This study was designed to determine if lidocaine inhibited growth of Blastomyces dermatitidis and thereby reduced recovery of the fungus from bronchoscopy specimens. Case records of 36 patients with pulmonary blastomycosis showed that when the fungus was present at microscopy, whether the specimen was sputum or bronchial washings, culture of the bronchoscopic specimen was more frequently negative than the culture of the sputum specimen (p less than .05). In addition, lidocaine was shown to inhibit growth of B dermatitidis in vitro, with the inhibition depending on the concentration of the drug and the duration of exposure (p less than .01). High concentrations of lidocaine for topical anesthesia appear to adversely affect the recovery of B dermatitidis from bronchoscopic specimens.
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We compared the antimicrobial susceptibility results obtained with the Cathra replicator and reference methods when Staphylococcus aureus strains were tested by using agar dilution techniques. The Cathra replicator and the 0.001-ml calibrated loop gave results that fell within +/- 1 log2 dilution for greater than or equal to 95% of isolates when methicillin and cefamandole were tested.
The MS-2 system (Abbott Diagnostics, Division of Abbott Laboratories, Dallas, Tex.) is an automated system capable of rapid antimicrobial susceptibility testing. However, the short incubation periods used by the device may adversely affect its ability to detect slowly growing resistant organisms. Shortly after the introduction of the MS-2 system into the University of Mississippi Medical Center clinical microbiology laboratory, we noted discrepancies between the MS-2 and the disk diffusion susceptibility reports when methicillin-resistant Staphylococcus aureus isolates were tested. Subsequently, we determined the susceptibilities of 75 such isolates by the MS-2 and Kirby-Bauer disk diffusion methods and measured the minimum inhibitory concentrations of methicillin, oxacillin, and cephalothin for 33 of the 75 isolates by standardized agar dilution techniques. There was only 47% overall agreement between the MS-2 and disk diffusion methods when methicillin was tested and 15% agreement when cephalothin was the test drug. There was 93% or more overall agreement between the two methods when other antimicrobial agents were tested. The minimum inhibitory concentration of methicillin was greater than or equal to 16 micrograms/ml for all 33 isolates evaluated by the agar dilution method. A comparison of the MS-2 and agar dilution results revealed an overall agreement of 49% when the susceptibilities to methicillin were determined. The MS-2 system reported that multiple methicillin-resistant S. aureus isolates obtained from a single patient were either resistant, intermediate, or sensitive to methicillin. Inconsistent results were also obtained when a single isolate was tested simultaneously in 10 cuvette cartridges. We conclude that the MS-2 system does not reliably detect methicillin and cephalothin resistance among S. aureus.