DIAGN MICROBIOL INFECT DIS 1992;15:277-280
277
BACTERIOLOGY
Assessment of Gelatin-Supplemented BACTEC Blood Culture Medium in a Pediatric Hospital Jane C. McDonald, Kathleen Knowles, Simon Sorger, and Geoffrey K. Richards
Sodium polyanetheolesulfonate (SPS), an anticoagulant used in blood culture media, adversely affects the isolation of Neisseria meningitidis. The addition of gelatin appears to counteract this effect. Studies using the radiometric BACTECsystem, however, have noted a lower isolation rate of other bacteria from gelatin-supplemented media. We wished to evaluate the effect of the addition of gelatin (1.2%) to a nonradiometric BACTECaerobic medium (NR6A) on the recovery of N. meningitidis and other pathogens. The NR6A medium with gelatin (NR6A analogue) also contained a lower concentration of SPS (0.025% vs 0.035%). We did 6045 paired comparisons of blood cultured in routine NR6A medium and the
NR6A analogue. Eight isolates of N. meningitidis were recovered, five only from the gelatin-supplemented medium and three from both bottles. There was no statistically significant difference in total recovery of aerobic and facultative bacteria or Candida species from both bottles. Haemophilus influenzae was detected earlier in the nonsupplemented NR6A medium. We conclude that the use of the NR6A analogue medium appeared to increase the yield of N. meningitidis without adversely affecting the recovery of other common pathogens, although the recovery of H. influenzae was slightly delayed.
INTRODUCTION
SPS on the g r o w t h of N. meningitidis could be neutralized in vitro by the addition of gelatin (1.2%) to culture media. Pai a n d Sorger (1981) s h o w e d that the addition of gelatin to blood culture media enh a n c e d the recovery of N. meningitidis from blood cultures in a pediatric hospital. Against SPS toxicity for N. gonorrheae (Staneck a n d Vincent, 1981), 2% gelatin or 1% h e m o g l o b i n have similar protective effects. As N. meningitidis is a significant p a t h o g e n in pediatrics, it is i m p o r t a n t to maximize its recovery from blood cultures. We studied the effect of the addition of gelatin and a lower SPS concentration to blood culture bottles in a modified n o n r a d i o m e t r i c BACTEC NR730 system on the yield and speed of recovery of microorganisms.
Sodium p o l y a n e t h o l e s u l f o n a t e (SPS) is routinely incorporated into almost all commercial blood culture media as an anticoagulant. As well as its anticoagulant properties, it is k n o w n to inhibit phagocytosis, complement, and lysozyme, a n d to inactivate aminoglycoside antibiotics, thus e n h a n c i n g the rate of recovery of most organisms from blood cultures (Eng, 1975). The addition of SPS, however, has been shown to have an adverse effect u p o n the isolation of Neisseria meningitidis (Eng a n d Ivelard, 1975) and Neisseria gonorrhoeae (Staneck a n d Vincent, 1981) from blood cultures. Eng and H o l t e n (1977) r e p o r t e d that the effect of From the Department of Microbiology, Montreal Children's Hospital, McGill University, Montreal, Quebec, Canada. Address reprint requests to Dr. J. C. McDonald, Department of Microbiology, Room C-1339, Montreal Children's Hospital, 2300 Tupper Street, Montreal, PQ H3H 1P3, Canada. Received 2 October 1990; revised and accepted 1 July 1991. © 1992 Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010 0732-8893/92/$5.00
MATERIALS AND METHODS C o l l e c t i o n of S a m p l e s From A u g u s t 1988 to A u g u s t 1989, all blood cultures from patients seen at the Montreal Children's Hos-
278
pital were inoculated into two 30-ml BACTECbottles: one aerobic NR6A medium (tryptic soy broth base containing 0.035% SPS) and the same medium (NR6A analogue), but with 0.025% SPS and 1.2% gelatin (prepared by Johnston Laboratories). Blood cultures were obtained after preparation of the skin with povidone iodine and isopropyl alcohol. The protocol includes equal division of the blood obtained into the two bottles.
Processing of Samples Both bottles were incubated in a shaking air incubator within 30 min of sampling, shaken for the first 48 hr of incubation, and incubated aerobically for a total of 7 days. All bottles were examined macroscopically and read by infrared spectrophotometry (BACTEC NR730 system) twice daily for the first 2 days and then once daily through day 7. Blind subcultures of all bottles onto chocolate agar were made at 24 hr and incubated in 5% CO2 for 48 hr. Bottles with a growth index of 15 or more or an increase of 10 or more index units between consecutive readings were examined by Gram stain and subcultured. The companion bottle was always subcultured and placed back in the tray to complete the protocol. All microorganisms isolated were identified by standard procedures.
Analysis of Data Isolation rates were evaluated by the McNemar modification of the X2 test (McNemar, 1962) and times to positivity were evaluated by paired t test.
RESULTS During the study period, 6045 blood culture sets were received. A total of 396 (6.5%) were positive in either the NR6A and/or the NR6A analogue medium. Clinically important bacteria and fungi were isolated in 370 (6.1%). Of these, 230 (62.2%) isolates grew in both, 80 (21.6%) grew in the NR6A medium only, and 60 (16.2%) grew in the NR6A analogue only. A comparison of the frequency of isolation of these organisms from the two media is shown in Table 1. Of particular note is the finding that N. meningitidis was isolated more frequently in the NR6A analogue than in the NR6A medium. Only three of eight isolates grew in the NR6A medium, whereas all eight isolates grew in the NR6A analogue. Thus there is a trend for better isolation in the media with gelatin (X2 = 3.2, p = 0.07). This did not reach statistical significance probably because of the small numbers. There was no significant difference in the eventual recovery of other bacteria or of Candida species.
J.C. McDonald et al.
Charts of all cases with positive meningococcal isolates were reviewed. It was apparent that the isolation of the organism was important in at least one instance where meningococcemia was not suspected clinically. This patient presented with a 2-day history of headache and fever. He had no rash, and a lumbar puncture showed no white blood cells. He was discharged from emergency after a blood culture was drawn with a diagnosis of probable viral infection. The patient was contacted when the NR6A analogue blood culture was reported as positive on day 1, admitted, and treated with penicillin for 7 days. He subsequently developed a reactive arthritis of his left knee. In two other patients, meningococcal infection was not suspected because of the absence of a typical rash or clinical signs on presentation. These two patients had positive blood cultures only in NR6A analogue. However, as the cerebrospinal fluid from these patients also grew meningococci, the blood culture results did not influence the final management. Table 2 shows the speed of detection of blood culture isolates in the two media by growth index flagging. It should be noted that the growth of Haemophilus influenzae was significantly delayed in the NR6A analogue medium at 24 hr.
DISCUSSION
Hemophilus influenzae and N. meningitidis are important pathogens in the pediatric age group. The rapid isolation of these organisms with the BACTECsystem has in the past been relatively poor. Delayed yield of these organisms was shown by Meadow and Schwartz (1986) with only 12% of 33 N. meningitidis isolates and 7% of 289 H. influenzae isolates detected by 24 hr in a radiometric BACTEC system. Schnur et al. (1989) demonstrated that the nonradiometric BACTEC NR730 blood culture system using bottles with and without SPS, but no gelatin supplement, was also poor in the early detection (24 hr) of N. meningitidis. Interestingly, this did not appear to be related to the presence or absence of SPS in the culture medium in that study. The mechanism whereby gelatin seems to counter the effect of SPS on the recovery of Neisseria spp. in blood culture medium is not fully understood. It may be related to interference with complement inactivation by the SPS or to protective stabilization of the cell membrane. A study by Weinstein et al. (1987), which did not include any isolates of N. meningitidis, reported a lower yield and slower growth of several aerobic and facultative bacteria in 1% gelatin-supplemented, 0.025% SPS BACTECmedia used in a radiometric system. Another study by the same group (Stratton et al., 1988) did not show a difference in
Gelatin-Supplemented Blood Culture Medium
TABLE 1
279
C o m p a r i s o n of Yield of Clinically I m p o r t a n t Bacteria a n d Fungi f r o m BACTEC N R 6 A M e d i u m a n d A n a l o g u e M e d i u m (with Gelatin) No. Isolates Recovered by
Organism Streptococcus groups A and B Enterococcus Streptococcus pneumoniae Haemophilus influenzae Neisseria meningitidis Staphylococcus aureus Coagulase-negative staphylococci Escherichia coli Klebsiella Enterobacter Salmonella Pseudomonas aeruginosa Bacteroides fragilis Candida albicans
Total
TABLE 2
Total No. Isolated
Analogue Only
Both
NR6A Only
5
3
1
1
6 38 25 8 13 132
4 23 20 3 6 64
1 6 2 5 2 28
1 9 3 0 5 40
27 21 9 10 18 1 47
17 18 8 5 15 0 36
4 3 0 2 0 1 4
6 0 1 3 3 0 7
370
230
60
80
C o m p a r i s o n of Detection Times for Clinically Significant M i c r o o r g a n i s m s Isolated f o r m BACTEC NR6A M e d i u m a n d A n a l o g u e M e d i u m (Gelatin) No. Isolates Detected by
Microogranism Streptococcus groups A and B Streptococcus pneumoniae Enterococcus Haemophilus influenza Neisseria meningitidis Staphylococcus aureus Coagulase-negative staphylococci Escherichia coli Klebsiella Enterobacter Salmonella Pseudomonas aeruginosa Pseudomonas maltophilia Candida albicans
Total
Total No. Isolates in Both Bottles
NR6A + Analogue at Same Time
NR6A Earlier
Analogue Earlier
3
2
1
0
23 4 20 3 6 64
21 4 9 1 5 50
0 0 11 0 1 4
2 0 0" 2 0 10
17 18 8 5 15 2 36
16 15 7 3 10 2 28
1 0 0 2 4 0 4
0 3 1 0 1 0 4
230
178
29
23
aSignificantly increased time to positivity (15.61 hr; 95% confidence intervals, 9.63, 20.69 hr).
280
the recovery of N. meningitidis (seven isolates) w h e n comparing 1.2% gelatin and V-factor-supplemented versus n o n s u p p l e m e n t e d BACTEC media (6B) for the radiometric system (SPS concentration, 0.025%). In this study, more aerobic and facultative bacteria and Candida albicans were r e c o v e r e d earlier from the nons u p p l e m e n t e d m e d i u m . H o w e v e r , H. influenzae was recovered earlier in the gelatin and V-factor-supplemented medium. The n u m b e r of meningococcal isolates in our study is small, but a trend was f o u n d in favor of better recovery from the NR6A analogue m e d i u m containing 1.2% gelatin and 0.025% SPS than from the NR6A routine m e d i u m w i t h o u t gelatin, but with 0.035% SPS. The lower concentration of SPS in this m e d i u m might have contributed to this effect. Unlike the other studies cited, in our s t u d y the addition of gelatin did not significantly affect the recovery of other bacteria or yeasts. H o w e v e r , the detection of H. influenzae was delayed in the NR6A analogue m e d i u m
J.C. McDonald et al.
at 24 hr, although the eventual rate of recovery was not different. This was not o b s e r v e d in the previous s t u d y by Pal and Sorger (1981) As H. influenzae is an i m p o r t a n t pediatric p a t h o g e n , a delay in detection of e v e n 1 day is significant. Therefore we do not advocate using NR6A analogue m e d i u m blood culture media alone, and our institution continues to use both a regular BACTEC NR6A m e d i u m and a gela t i n - s u p p l e m e n t e d analogue for the collection of routine blood cultures. More studies are n e e d e d to establish the efficacy of gelatin in the recovery of N. meningitidis and its effect on the recovery of other p a t h o g e n s from blood cultures using the a u t o m a t e d BACTEC system.
We thank the laboratory staff for their technological support, and Ms. Carole Fisher for her expert assistance in the preparation of the manuscript.
REFERENCES Eng J (1975) Effect of sodium polyanetholesulfonate in blood cultures. J Clin Microbiol 1:119-123. Eng J, Ivelard H (1975) Inhibitory effect in vitro of sodium polyanetholesulfonate on the growth of Neisseria meningitidis. J Clin MicrobioI 1:444-447. Eng J, Holton E (1977) Gelatin neutralization of the inhibitory effect of sodium polyanetnol sulfonate on Neisseria meningitidis in blood culture media. J Clin Microbiol 6:13. McNemar Q (1962) Psychological Statistics, 3rd ed. New York: John Wiley and Sons, pp 209-239. Meadow W, Schwartz 1 (1986) Time course of radiometric detection of positive blood cultures in childhood. Pediatr Infect Dis J 5:333-336. Pai CH, Sorger S (1981) Enhancement of recovery of Neisseria meningitidis by gelatin in blood culture media. J Clin Microbiol 14:20-23. Reller LB, Murray PR, MacLowery JD (1982) Cumitech 1A
Blood Culture II. Coord ed, JA Washington II. Washington, DC: American Society for Microbiology. Schnur ER, Azini PH, Bilchis DA (1989) Poor performance of the BACTECNR730 blood culture system in early detection of Neisseria meningitidis. J Clin Microbiol 27:654656. Staneck JL, Vincent S (1981) Inhibition of Neisseria gonorrhea by sodium polyanetholesulfonate. J Clin Microbiol 13:463-467. Stratton CW, Weinstein MP, Mirrett S, Paisley J, Lauer BA, Reller LB (1988) Controlled evaluation of blood culture medium containing gelatin and V-factor-analog for detection of septicemia in children. J Clin Microbiol 26:747-749. Weinstein MP, Reller LB, Mirrett S, Reisner LG, Wang WL, Stratton CW (1987) Controlled evaluation of modified radiometric blood culture medium supplemented with gelatin for detection of bacteremia and fungemia. J Clin Microbiol 25:1373-1375.
277
BACTERIOLOGY
Assessment of Gelatin-Supplemented BACTEC Blood Culture Medium in a Pediatric Hospital Jane C. McDonald, Kathleen Knowles, Simon Sorger, and Geoffrey K. Richards
Sodium polyanetheolesulfonate (SPS), an anticoagulant used in blood culture media, adversely affects the isolation of Neisseria meningitidis. The addition of gelatin appears to counteract this effect. Studies using the radiometric BACTECsystem, however, have noted a lower isolation rate of other bacteria from gelatin-supplemented media. We wished to evaluate the effect of the addition of gelatin (1.2%) to a nonradiometric BACTECaerobic medium (NR6A) on the recovery of N. meningitidis and other pathogens. The NR6A medium with gelatin (NR6A analogue) also contained a lower concentration of SPS (0.025% vs 0.035%). We did 6045 paired comparisons of blood cultured in routine NR6A medium and the
NR6A analogue. Eight isolates of N. meningitidis were recovered, five only from the gelatin-supplemented medium and three from both bottles. There was no statistically significant difference in total recovery of aerobic and facultative bacteria or Candida species from both bottles. Haemophilus influenzae was detected earlier in the nonsupplemented NR6A medium. We conclude that the use of the NR6A analogue medium appeared to increase the yield of N. meningitidis without adversely affecting the recovery of other common pathogens, although the recovery of H. influenzae was slightly delayed.
INTRODUCTION
SPS on the g r o w t h of N. meningitidis could be neutralized in vitro by the addition of gelatin (1.2%) to culture media. Pai a n d Sorger (1981) s h o w e d that the addition of gelatin to blood culture media enh a n c e d the recovery of N. meningitidis from blood cultures in a pediatric hospital. Against SPS toxicity for N. gonorrheae (Staneck a n d Vincent, 1981), 2% gelatin or 1% h e m o g l o b i n have similar protective effects. As N. meningitidis is a significant p a t h o g e n in pediatrics, it is i m p o r t a n t to maximize its recovery from blood cultures. We studied the effect of the addition of gelatin and a lower SPS concentration to blood culture bottles in a modified n o n r a d i o m e t r i c BACTEC NR730 system on the yield and speed of recovery of microorganisms.
Sodium p o l y a n e t h o l e s u l f o n a t e (SPS) is routinely incorporated into almost all commercial blood culture media as an anticoagulant. As well as its anticoagulant properties, it is k n o w n to inhibit phagocytosis, complement, and lysozyme, a n d to inactivate aminoglycoside antibiotics, thus e n h a n c i n g the rate of recovery of most organisms from blood cultures (Eng, 1975). The addition of SPS, however, has been shown to have an adverse effect u p o n the isolation of Neisseria meningitidis (Eng a n d Ivelard, 1975) and Neisseria gonorrhoeae (Staneck a n d Vincent, 1981) from blood cultures. Eng and H o l t e n (1977) r e p o r t e d that the effect of From the Department of Microbiology, Montreal Children's Hospital, McGill University, Montreal, Quebec, Canada. Address reprint requests to Dr. J. C. McDonald, Department of Microbiology, Room C-1339, Montreal Children's Hospital, 2300 Tupper Street, Montreal, PQ H3H 1P3, Canada. Received 2 October 1990; revised and accepted 1 July 1991. © 1992 Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010 0732-8893/92/$5.00
MATERIALS AND METHODS C o l l e c t i o n of S a m p l e s From A u g u s t 1988 to A u g u s t 1989, all blood cultures from patients seen at the Montreal Children's Hos-
278
pital were inoculated into two 30-ml BACTECbottles: one aerobic NR6A medium (tryptic soy broth base containing 0.035% SPS) and the same medium (NR6A analogue), but with 0.025% SPS and 1.2% gelatin (prepared by Johnston Laboratories). Blood cultures were obtained after preparation of the skin with povidone iodine and isopropyl alcohol. The protocol includes equal division of the blood obtained into the two bottles.
Processing of Samples Both bottles were incubated in a shaking air incubator within 30 min of sampling, shaken for the first 48 hr of incubation, and incubated aerobically for a total of 7 days. All bottles were examined macroscopically and read by infrared spectrophotometry (BACTEC NR730 system) twice daily for the first 2 days and then once daily through day 7. Blind subcultures of all bottles onto chocolate agar were made at 24 hr and incubated in 5% CO2 for 48 hr. Bottles with a growth index of 15 or more or an increase of 10 or more index units between consecutive readings were examined by Gram stain and subcultured. The companion bottle was always subcultured and placed back in the tray to complete the protocol. All microorganisms isolated were identified by standard procedures.
Analysis of Data Isolation rates were evaluated by the McNemar modification of the X2 test (McNemar, 1962) and times to positivity were evaluated by paired t test.
RESULTS During the study period, 6045 blood culture sets were received. A total of 396 (6.5%) were positive in either the NR6A and/or the NR6A analogue medium. Clinically important bacteria and fungi were isolated in 370 (6.1%). Of these, 230 (62.2%) isolates grew in both, 80 (21.6%) grew in the NR6A medium only, and 60 (16.2%) grew in the NR6A analogue only. A comparison of the frequency of isolation of these organisms from the two media is shown in Table 1. Of particular note is the finding that N. meningitidis was isolated more frequently in the NR6A analogue than in the NR6A medium. Only three of eight isolates grew in the NR6A medium, whereas all eight isolates grew in the NR6A analogue. Thus there is a trend for better isolation in the media with gelatin (X2 = 3.2, p = 0.07). This did not reach statistical significance probably because of the small numbers. There was no significant difference in the eventual recovery of other bacteria or of Candida species.
J.C. McDonald et al.
Charts of all cases with positive meningococcal isolates were reviewed. It was apparent that the isolation of the organism was important in at least one instance where meningococcemia was not suspected clinically. This patient presented with a 2-day history of headache and fever. He had no rash, and a lumbar puncture showed no white blood cells. He was discharged from emergency after a blood culture was drawn with a diagnosis of probable viral infection. The patient was contacted when the NR6A analogue blood culture was reported as positive on day 1, admitted, and treated with penicillin for 7 days. He subsequently developed a reactive arthritis of his left knee. In two other patients, meningococcal infection was not suspected because of the absence of a typical rash or clinical signs on presentation. These two patients had positive blood cultures only in NR6A analogue. However, as the cerebrospinal fluid from these patients also grew meningococci, the blood culture results did not influence the final management. Table 2 shows the speed of detection of blood culture isolates in the two media by growth index flagging. It should be noted that the growth of Haemophilus influenzae was significantly delayed in the NR6A analogue medium at 24 hr.
DISCUSSION
Hemophilus influenzae and N. meningitidis are important pathogens in the pediatric age group. The rapid isolation of these organisms with the BACTECsystem has in the past been relatively poor. Delayed yield of these organisms was shown by Meadow and Schwartz (1986) with only 12% of 33 N. meningitidis isolates and 7% of 289 H. influenzae isolates detected by 24 hr in a radiometric BACTEC system. Schnur et al. (1989) demonstrated that the nonradiometric BACTEC NR730 blood culture system using bottles with and without SPS, but no gelatin supplement, was also poor in the early detection (24 hr) of N. meningitidis. Interestingly, this did not appear to be related to the presence or absence of SPS in the culture medium in that study. The mechanism whereby gelatin seems to counter the effect of SPS on the recovery of Neisseria spp. in blood culture medium is not fully understood. It may be related to interference with complement inactivation by the SPS or to protective stabilization of the cell membrane. A study by Weinstein et al. (1987), which did not include any isolates of N. meningitidis, reported a lower yield and slower growth of several aerobic and facultative bacteria in 1% gelatin-supplemented, 0.025% SPS BACTECmedia used in a radiometric system. Another study by the same group (Stratton et al., 1988) did not show a difference in
Gelatin-Supplemented Blood Culture Medium
TABLE 1
279
C o m p a r i s o n of Yield of Clinically I m p o r t a n t Bacteria a n d Fungi f r o m BACTEC N R 6 A M e d i u m a n d A n a l o g u e M e d i u m (with Gelatin) No. Isolates Recovered by
Organism Streptococcus groups A and B Enterococcus Streptococcus pneumoniae Haemophilus influenzae Neisseria meningitidis Staphylococcus aureus Coagulase-negative staphylococci Escherichia coli Klebsiella Enterobacter Salmonella Pseudomonas aeruginosa Bacteroides fragilis Candida albicans
Total
TABLE 2
Total No. Isolated
Analogue Only
Both
NR6A Only
5
3
1
1
6 38 25 8 13 132
4 23 20 3 6 64
1 6 2 5 2 28
1 9 3 0 5 40
27 21 9 10 18 1 47
17 18 8 5 15 0 36
4 3 0 2 0 1 4
6 0 1 3 3 0 7
370
230
60
80
C o m p a r i s o n of Detection Times for Clinically Significant M i c r o o r g a n i s m s Isolated f o r m BACTEC NR6A M e d i u m a n d A n a l o g u e M e d i u m (Gelatin) No. Isolates Detected by
Microogranism Streptococcus groups A and B Streptococcus pneumoniae Enterococcus Haemophilus influenza Neisseria meningitidis Staphylococcus aureus Coagulase-negative staphylococci Escherichia coli Klebsiella Enterobacter Salmonella Pseudomonas aeruginosa Pseudomonas maltophilia Candida albicans
Total
Total No. Isolates in Both Bottles
NR6A + Analogue at Same Time
NR6A Earlier
Analogue Earlier
3
2
1
0
23 4 20 3 6 64
21 4 9 1 5 50
0 0 11 0 1 4
2 0 0" 2 0 10
17 18 8 5 15 2 36
16 15 7 3 10 2 28
1 0 0 2 4 0 4
0 3 1 0 1 0 4
230
178
29
23
aSignificantly increased time to positivity (15.61 hr; 95% confidence intervals, 9.63, 20.69 hr).
280
the recovery of N. meningitidis (seven isolates) w h e n comparing 1.2% gelatin and V-factor-supplemented versus n o n s u p p l e m e n t e d BACTEC media (6B) for the radiometric system (SPS concentration, 0.025%). In this study, more aerobic and facultative bacteria and Candida albicans were r e c o v e r e d earlier from the nons u p p l e m e n t e d m e d i u m . H o w e v e r , H. influenzae was recovered earlier in the gelatin and V-factor-supplemented medium. The n u m b e r of meningococcal isolates in our study is small, but a trend was f o u n d in favor of better recovery from the NR6A analogue m e d i u m containing 1.2% gelatin and 0.025% SPS than from the NR6A routine m e d i u m w i t h o u t gelatin, but with 0.035% SPS. The lower concentration of SPS in this m e d i u m might have contributed to this effect. Unlike the other studies cited, in our s t u d y the addition of gelatin did not significantly affect the recovery of other bacteria or yeasts. H o w e v e r , the detection of H. influenzae was delayed in the NR6A analogue m e d i u m
J.C. McDonald et al.
at 24 hr, although the eventual rate of recovery was not different. This was not o b s e r v e d in the previous s t u d y by Pal and Sorger (1981) As H. influenzae is an i m p o r t a n t pediatric p a t h o g e n , a delay in detection of e v e n 1 day is significant. Therefore we do not advocate using NR6A analogue m e d i u m blood culture media alone, and our institution continues to use both a regular BACTEC NR6A m e d i u m and a gela t i n - s u p p l e m e n t e d analogue for the collection of routine blood cultures. More studies are n e e d e d to establish the efficacy of gelatin in the recovery of N. meningitidis and its effect on the recovery of other p a t h o g e n s from blood cultures using the a u t o m a t e d BACTEC system.
We thank the laboratory staff for their technological support, and Ms. Carole Fisher for her expert assistance in the preparation of the manuscript.
REFERENCES Eng J (1975) Effect of sodium polyanetholesulfonate in blood cultures. J Clin Microbiol 1:119-123. Eng J, Ivelard H (1975) Inhibitory effect in vitro of sodium polyanetholesulfonate on the growth of Neisseria meningitidis. J Clin MicrobioI 1:444-447. Eng J, Holton E (1977) Gelatin neutralization of the inhibitory effect of sodium polyanetnol sulfonate on Neisseria meningitidis in blood culture media. J Clin Microbiol 6:13. McNemar Q (1962) Psychological Statistics, 3rd ed. New York: John Wiley and Sons, pp 209-239. Meadow W, Schwartz 1 (1986) Time course of radiometric detection of positive blood cultures in childhood. Pediatr Infect Dis J 5:333-336. Pai CH, Sorger S (1981) Enhancement of recovery of Neisseria meningitidis by gelatin in blood culture media. J Clin Microbiol 14:20-23. Reller LB, Murray PR, MacLowery JD (1982) Cumitech 1A
Blood Culture II. Coord ed, JA Washington II. Washington, DC: American Society for Microbiology. Schnur ER, Azini PH, Bilchis DA (1989) Poor performance of the BACTECNR730 blood culture system in early detection of Neisseria meningitidis. J Clin Microbiol 27:654656. Staneck JL, Vincent S (1981) Inhibition of Neisseria gonorrhea by sodium polyanetholesulfonate. J Clin Microbiol 13:463-467. Stratton CW, Weinstein MP, Mirrett S, Paisley J, Lauer BA, Reller LB (1988) Controlled evaluation of blood culture medium containing gelatin and V-factor-analog for detection of septicemia in children. J Clin Microbiol 26:747-749. Weinstein MP, Reller LB, Mirrett S, Reisner LG, Wang WL, Stratton CW (1987) Controlled evaluation of modified radiometric blood culture medium supplemented with gelatin for detection of bacteremia and fungemia. J Clin Microbiol 25:1373-1375.
