Basic microbiologic support for hospital epidemiology.

The laboratory plays a major role in the epidemiology program's efforts to minimize nosocomial infections in healthcare institutions. This article will describe some of the interactions between the laboratory and the epidemiology program, and will identify resources and procedures that the laboratory needs to achieve epidemiologic goals.

Penicillin-resistant pneumococci--an emerging threat to successful therapy.

Pneumococci highly resistant to penicillin G [minimum inhibitory concentration (MIC) > or = 2 mg L-1] have become prevalent in many parts of the world since their emergence and spread in the late 1970s. In the USA, such organisms are seen primarily in two populations: infants and children, and adults with AIDS. Surveys in both rural and urban areas have revealed presence of these organisms, as well as an increasing frequency of Streptococcus pneumoniae strains relatively resistant to penicillin (MIC 0.1-1.0 mg L-1--now defined by some as 'intermediate' resistance). Predisposing factors are not yet clear. Prior antimicrobial therapy was given to some of the children and most of the adults who are colonized or infected with resistant strains. Prior or concurrent use of cotrimoxazole prophylaxis for Pneumocystis carinii pneumonia has been frequent in our cases in adults, most of whom had a concurrent diagnosis of AIDS. Children with disease often have a history of long-term prophylaxis with a beta-lactam drug (for sickle cell disease, etc). Many strains are also resistant to newer cephalosporins like cefotaxime and ceftriaxone (MIC > or = 2 mg L-1). The organisms are frequently multi-resistant, with high MIC values common as well for chloramphenicol and variable for tetracycline, macrolides, cotrimoxazole, and fluoroquinolones. Only to vancomycin are the organisms consistently susceptible. These findings raise alarms about the future of pneumococcal disease in both community and nosocomial disease. Increasing prevalence in otitis and pneumonia in children and in community-acquired pneumonia in adults may lead to use of vancomycin as empirical therapy for these clinical situations. This would increase the selective pressure for emergence of vancomycin-resistant organisms, whether S. pneumoniae or others. Moreover, the pneumococcus was a common cause of hospital infection prior to the introduction of penicillin. The potential now exists for nosocomial pneumococcal infection again to become a feared and ominous occurrence.

Determination of growth value thresholds for BACTEC PLUS aerobic blood culture vials.

Growth value thresholds used to identify positive blood culture vials can be defined by users for each BACTEC NR-660 bacteremia detection instrument. Growth values were compared with the recovery of organisms from vials flagged as positive during the testing of 3.056 high-volume vials containing aerobic (BACTEC PLUS 26) medium over a 2-month period. Results showed that optimal threshold values for our use of these vials varied from those recommended by the manufacturer; if the thresholds defined from these data had been used during the study period, total vials flagged as positive from which no organisms were recovered (false alarms) would have been reduced from 181 (5.9/100 vials tested) to 71 (2.3/100 vials tested), with a minimal decrease in the identification of vials containing usual or occasional pathogens (hits). Adjustments of growth value thresholds by the individual user can make the use of BACTEC instruments more efficient by decreasing further processing of vials from which no organisms are recovered.

The impact of a clinic for adults with HIV infection on the microbiology laboratory.

The Infectious Diseases Clinic (IDC) discussed serves adults who are seropositive for human immunodeficiency virus. The authors reviewed the outpatient and inpatient microbiology tests of a three-month period during 1989 for a systematic sample of IDC patients. The 249 patients in the sample had 682 microbiology tests performed during the period (mean 2.7 tests per patient). Tests most frequently requested were mycobacterial culture, routine blood culture, and cryptococcal antigen determination. Patients with acquired immunodeficiency syndrome (43% of IDC patients) accounted for 63% of the requested IDC tests. IDC patients comprised about 2.4% of patients served but accounted for 3.9% of the requested microbiology tests and 6.6% of the microbiology work load for reported tests. Using Centers for Disease Control case projections, the authors estimated that services to IDC patients in 1993 would comprise 6.6% of all microbiology tests and 10.6% of the microbiology work load. The implications of these data for microbiology probably also apply to other laboratory testing and emphasize the need for more efficient ways to use and perform diagnostic studies required by patients with HIV infection.

Microplate phosphocellulose binding assay for aminoglycoside-modifying enzymes.

We modified the phosphocellulose binding assay for aminoglycoside-modifying enzymes (AMEs) by use of microdilution plates and a multichannel micropipette. Batteries of aminoglycoside substrates for screening organisms for the presence of AMEs as well as for subclassifying enzymes were prepared and stored in microdilution plates. When tested in parallel with the conventional tube reaction assay, the microplate assay yielded comparable radioactive counts and therefore equally correct identifications of AMEs in 32 isolates representing nine bacterial species. Other modifications, such as multichannel dispensing of crude enzyme preparations and radioisotopic precursors, provided a more rapid, convenient, and less expensive means of examining large collections of organisms for AMEs.