|Year : 2001 | Volume
| Issue : 2 | Page : 44-50
Culture of body fluids using the bact/alert system
Department of Microbiology, Nizamís Institute of Medical Sciences, Punjagutta, Hyderabad - 500 082, India
Department of Microbiology, Nizamís Institute of Medical Sciences, Punjagutta, Hyderabad - 500 082, India
The BacT/Alert system was evaluated for its utility to recover clinically significant bacteria from several sterile body fluids, other than blood. Of the1500 specimens processed, 530 (35.33%) cultures were recorded positive by the BacT/Alert bottles while only 379 (25%) cultures were recovered on the plate cultures. The mean time to detection was <12 hours for Gram-negative organisms and 12 - 16 hours for the Gram-positive organisms. The rapid detection of important pathogens like Streptococcus pneumoniae, Streptococcus pyogenes and Salmonella typhi, within 12 hours of inoculation, is of particular interest especially in serious infections like deep-seated abscesses. This enabled the treating physician to start the specific and appropriate antibiotics early and facilitated a better prognosis in the patient. The system is also very efficient in the early detection of anaerobes from the clinical specimens.
|How to cite this article:|
Lakshmi V. Culture of body fluids using the bact/alert system. Indian J Med Microbiol 2001;19:44-50
One of the important responsibilities of a Clinical Microbiologist is to optimize culture techniques for rapid isolation and detection of the specific etiological agent(s) from clinical specimen. Several automated systems, which can efficiently detect bacterial growth earlier than the conventional culture methods, have been developed in the recent years. One such system is the BacT/Alert (Organon Teknika), an automated system for blood cultures. Although the BacT/Alert system has been extensively evaluated for culture of blood,  (only a limited number of studies have reported the utility of this system for the culture of other sterile body fluids.,,
This study was designed to evaluate the ability of the BacT/Alert system to recover microorganisms from several types of sterile body fluids (other than blood and urine). The mean time to detection was compared with that of the standard culture methods using solid plated media. The ability of the BacT/Alert to recover more number of organisms than the solid media was also assessed.
| ~ Materials and Methods|| |
1500 clinical specimen collected from patients attending the hospital services at the Nizam's Institute of Medical Sciences, Hyderabad, were included in the study. Fluid specimen collected by aspiration were included in this study. The number of each specimen type is listed in [Table - 1]. The pus specimens were purulent aspirates collected from lesions in the skin and subcutaneous tissues (wounds and open ulcers excluded) and abscesses in the internal organisms. All the fluids were transported immediately to the laboratory after collection. The specimens were processed for culture within 30 minutes of receipt in the laboratory, both by conventional plate methods and by using the BacT/Alert standard anaerobic bottles.
| ~ Conventional Method|| |
The samples were inoculated on 7 % blood agar and MacConkey agar and incubated at 370 C for 48 hours and observed for bacterial colonies. Identification of the positive cultures was performed as per standard protocols of bacterial identification. The cultures were declared sterile if there was no growth on the plates after 48 hours of incubation.
Anaerobic culture of all the specimens were also performed on blood agar using the gas pack anaerobic system and incubated for 48 hours at 37 O C.
| ~ Bact/Alert System|| |
5 ml of specimen was inoculated into Bact/Alert standard anaerobic bottles and incubated in the system. The inoculated bottles were loaded into the BacT/Alert Incubator and incubated for a maximum period of 5 days. Standard BacT/Alert software was used for recording the results. Bottles flagged as positive by the BacT/Alert instrument were subcultured both for aerobic and anaerobic organisms. The organisms were identified as per standard protocols.
| ~ Results|| |
Of the1500 specimens, 530 (35.33%) cultures were recorded positive by the BacT/Alert bottles while only 379 (25%) cultures were recovered on the plate cultures.
[Table - 2] and [Figure:1] show the comparison of the number of culture positive by both methods. There were 20 anaerobic isolates in all, which have been excluded while calculating the recovery rate on plate media. It is evident that 151 / 1500 (10%) cultures had been missed by the plate media and could be isolated only through the BacT/Alert bottles. [Figure:1] shows the comparative results between the two systems in the recovery of Gram-positive and Gram-negative organisms. In general, Gram-negative organisms grew faster and recovered more in number than the gram positives. The mean time detection was less than 12 hours for the Gram-negatives, while that for the Gram- positives was about 12 - 16 hours.
[Table - 3] through 8 summarize the mean time to detection and the range of significant isolates from the various specimen types. However, there was not much significant difference between the specimen types with respect to the time to detection and number of organisms recovered by the BacT/Alert bottles.
Our results indicate that the recovery of organisms is much faster, especially the Gram-negatives, by the BacT/Alert than plate method. This enabled us to inform the culture results to the clinician on the same day itself in majority of cases. The final report was ready by the next day morning (within 24 hours of specimen collection) as against that of the conventional method of 48 -72 hours, thereby enabling an early initiation of therapy. Also, the number of isolates recovered was more with the BacT/Alert bottle than on the plates. The superior performance of BacT/Alert over the conventional system for Gram-positive organism like Streptococcus pyogenes d Streptococcus pneumoniae is of particular interest especially in serious infections like deep-seated abscesses. In addition, significant organisms like Salmonella More Details typhi were recovered earlier in the bottles than on the plates. This enabled the treating physician to start the specific and appropriate antibiotics early and facilitated a better prognosis of the patient. We encountered false positive signals from the BacT/Alert in 44 samples. On analysis, the samples had high counts of lymphocytes and no organisms were seen on Gram stain and on subculture from the bottles. Clinically also the patient did not have any significant infection or morbidity.
| ~ Discussion|| |
Early information on the causative organism(s) is of significant importance to the patient as well as to the clinician. Availability of such early information helps the clinician to initiate early and specific treatment and reduced lengths of stay of the patients in the hospital.
An important responsibility of a clinical microbiology laboratory is to meet this demand and to provide accurate information about the presence and type of the infecting microorganisms in a given clinical specimen in as little time as possible. The generation time for most clinically relevant bacteria is about 20 - 30 minutes. Many conventional methods require 18 - 24 hours of incubation or longer before the test results can be accurately interpreted. Although this is the standard approach in clinical and diagnostic microbiology, the desire to produce results and identification in a more timely fashion has resulted in development of automated system that can detect bacterial growth earlier than the routine methods. Automated systems have thus become an integral part of many clinical microbiology laboratories in recent times .
One such automated systems is the BacT/Alert. Culture of a large volume of the fluid (5 - 10ml), sustained agitation and continuous monitoring of the incubated culture by the BacT/Alert system allows higher yields and decreased detection time for the various organisms, as compared to the conventional method. Reports on the use of the BacT/Alert for peritoneal and CAPD fluids have been well documented. In these studies, the FAN aerobic bottles were used for inoculating the fluids.,, However, we used the standard anaerobic bottle, to recover both facultative anaerobic and strict anaerobic organisms. All the bottles were directly inoculated with the fluids or aspirates without any centrifugation step thereby reducing the burden on the technicians. We tested the system only for large volume specimens, using 5 mL of the specimen and excluded the smaller volume fluids like the cerebrospinal fluid in this study. Fluid volumes up to 10 ml have been used by other workers.,, However, as suggested in an earlier report, the optimum fluid to broth ratio has to be assessed to determine its effect on the rate of isolation. In an earlier study, we attempted to determine the performance of the BacT/Alert to recover organisms from vitreous fluids. However, as the volume of the fluid available for inoculation was very minimal (<0.5 ml), the sensitivity of the system was low as compared to the conventional plate cultures.
In conclusion, our study indicates that the BacT/Alert system is a reliable, very efficient rapid system and a less labour-intensive approach to the early detection of clinically significant microorganisms in large volume aspirates and body fluids.
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