Gelatin neutralization of the inhibitory effect of sodium polyanethol sulfonate on Neisseria meningitidis in blood culture media

Development of o.a.s.i.s., a new automated blood culture system in which detection is based on measurement of bottle headspace pressure changes

o.a.s.i.s. (Unipath Ltd., Basingstoke, United Kingdom) is a new automated blood culture system. The metabolism of microorganisms is detected by measuring changes in the pressure of the headspace of blood culture bottles. These changes are measured by monitoring the position of a flexible sealing septum, every 5 min, with a scanning laser sensor. This noninvasive system can detect both gas absorption and production and does not rely solely on measuring increasing carbon dioxide levels. A research prototype instrument was used to carry out an evaluation of the media, the detection system, and its associated detection algorithm. In simulated blood cultures, o.a.s.i.s. supported growth and detected a range of clinical isolates. Times to positivity were significantly shorter in o.a.s.i.s. than in the BACTEC 460 system. Results of a clinical feasibility study, with a manual blood culture system as a control, confirmed that o.a.s.i.s. was able to support the growth and detection of a variety of clinically significant organisms. On the basis of these findings, full-scale comparative clinical trials of o.a.s.i.s. with other automated blood culture systems are warranted.

Assessment of gelatin supplementation of PEDS Plus BACTEC blood culture medium

Gelatin supplementation of blood culture media has been shown to neutralize the effects of sodium polyanetholesulfonate and enhance detection of Neisseria species. We evaluated the effect of 1.2% gelatin supplementation of nonradiometric Peds Plus Bactec blood culture medium on the rate and speed of recovery of pathogens from pediatric patients. From June 1991 to June 1992, a total of 6451 paired comparisons of blood cultures in Peds Plus medium and gelatin-supplemented Peds Plus medium were done: 465 organisms were isolated, of which 338 were significant. There were no significant differences in recovery of organisms or the speed of detection of microbial growth between the two media. In particular, the recovery of Neisseria meningitidis (eight isolates) was not improved with gelatin supplementation. In conclusion, gelatin supplementation of Peds Plus Bactec medium does not offer any advantage over the regular Peds Plus Bactec medium.

Methods used in the United Kingdom for the culture of micro-organisms from blood

AIMS

To survey blood culture methods in use in the United Kingdom.

METHODS

A questionnaire was distributed to the 415 United Kingdom laboratories participating in the clinical bacteriology subscheme of the UK National External Quality Assessment Scheme for Microbiology.

RESULTS

Two hundred and eighty seven laboratories completed the questionnaire. The responses indicated wide variations in methods used including considerable differences among laboratories using the same basic methods. The most widely used techniques were the Bactec and conventional broth systems.

CONCLUSIONS

Although many published comparisons have failed to show that any basic method is outstandingly successful in the isolation of all organisms, there is evidence that several factors can contribute to good performance. In some laboratories suboptimal conditions were in use. The variations in technique probably reflect differences in practical suitability of a system for any particular laboratory, costs, and personal preferences.

Assessment of gelatin-supplemented BACTEC blood culture medium in a pediatric hospital

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 BACTEC system, 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 BACTEC aerobic 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.

Performance of a BACTEC nonradiometric medium for pediatric blood cultures

A BACTEC aerobic nonradiometric medium, PEDS Plus, designed for diagnosis of pediatric bacteremia was evaluated in three hospital centers. Equivalent blood volumes (up to 5 ml) were inoculated into and incubated in BACTEC NR-6A (6A) and PEDS Plus broths. Among 4,581 compliant sets, 289 clinically significant organisms, representing more than 20 bacterial and two Candida species, were isolated. One hundred eighty-one isolates were recovered in both bottles, 75 in PEDS Plus only, and 33 in 6A only (P less than 0.001). Time to detection when both bottles were positive was the same for 129 isolates, detection with PEDS Plus was earlier for 39, and detection with 6A was earlier for 13 (P less than 0.005). Staphylococcus aureus was recovered significantly more often in PEDS Plus than in 6A (P less than 0.01), and more coagulase-negative staphylococci and pediatric pathogens (pneumococci, Haemophilus influenzae, and Streptococcus agalactiae) were recovered in PEDS Plus than in 6A. Coagulase-negative staphylococci and H. influenzae were detected significantly earlier in PEDS Plus (P less than 0.05 and less than 0.01, respectively). When the eight species of the family Enterobacteriaceae isolated were considered together, recovery in PEDS Plus was better than in 6A (P less than 0.05). For 66 of the 143 isolates from patients known to be on antimicrobial therapy at the time blood was drawn, PEDS Plus was superior to 6A. In 45 cases, organisms were isolated from PEDS Plus only (P less than 0.001) and in 21 cases they were isolated from PEDS Plus before 6A (P less than 0.01). PEDS Plus broth aids diagnosis of pediatric bacteremia by increasing recovery of etiologic agents and decreasing the time required for detection.

Evaluation of modified trypticase soy broth versus supplemented peptone broth in the detection of bacteremia and fungemia

In vitro, 1.2% gelatin counteracts the inhibition of growth of bacterial species by sodium polyanetholsulfonate in blood culture media. Additionally, 1% yeast extract has been used to promote bacterial growth. We compared the performance of supplemented peptone broth and Trypticase soy broth, both of which contained sodium polyanetholsulfonate, gelatin and yeast extract. Trypticase soy broth with gelatin and yeast extract inhibited (p less than 0.001) and delayed growth, especially of gram-positive (p less than 0.01) and gram-negative (p less than 0.005) anaerobic bacteria. Although the recovery of organisms usually inhibited by sodium polyanetholsulfonate was similar in supplemented peptone and Trypticase soy broths, supplemented peptone broth clearly was superior in the recovery of other organisms commonly found in blood cultures.

Controlled evaluation of blood culture medium containing gelatin and V-factor-analog for detection of septicemia in children

Both Neisseria meningitidis and Haemophilus influenzae are important isolates recovered in blood cultures from septicemic children. Sodium polyanetholsulfonate is present in most blood culture media and can inhibit the growth of certain bacteria, including N. meningitidis. The addition of gelatin to blood culture media neutralizes this inhibition. The growth of H. influenzae is enhanced by specific growth factors such as hemin and NAD. The addition of gelatin and V-factor-analog (a proprietary supplement for enhancing the growth of H. influenzae) might have a positive effect on the yield and on the speed of detection of septicemia in children. To evaluate this possibility, we did 4,565 paired comparisons of blood cultured in BACTEC 6B (aerobic) medium with and without the addition of both 1.2% gelatin and V-factor-analog. More aerobic and facultative bacteria grew in the 6B than in the 6B-gelatin-V-factor-analog medium (P less than 0.01). Only seven isolates of Neisseria spp. were recovered during this study period, with the 6B medium performing as well as the supplemented medium. When microorganisms grew in both bottles, they did so at the same time except for H. influenzae and Candida albicans. H. influenzae was recovered earlier from the 6B-gelatin-V-factor-analog bottle (P less than 0.01), with a mean time to detection of 8.5 h compared with 15.9 h for the 6B bottle. C. albicans was recovered earlier from the 6B bottle (P less than 0.02), with a mean time to detection of 34.9 h compared with 71.6 h for the 6B-gelatin-V-factor-analog bottle. We conclude that the 6B medium in its present formulation is superior to bB supplemented with gelatin and V-factor-analog.

Controlled evaluation of trypticase soy broth with and without gelatin and yeast extract in the detection of bacteremia and fungemia

The addition of gelatin to blood culture media has been suggested to prevent the inhibition of Neisseria meningitidis, Neisseria gonorrhoeae, Gardnerella vaginalis, and Peptostreptococcus anaerobius that is caused by sodium polyanetholsulfonate. To determine the effect of such supplementation on the overall yield of microorganisms, we compared the yield and speed of detection of clinically important microorganisms from 5422 paired 10-ml samples of blood cultured in Trypticase soy broth (TSB) containing 0.03% sodium polyanetholesulfonate (SPS) and TSB/SPS containing 1.2% gelatin and 1.0% yeast extract (mTSB). The atmosphere of incubation (open venting unit) and ratio of blood to broth (1:5) were the same for both samples. Only cultures with adequate blood sample (greater than or equal to 80% of stated volume) were compared statistically. Addition of gelatin and yeast extract resulted in inhibited growth of Enterobacteriaceae (p less than 0.001), Pseudomonas aeruginosa (p less than 0.01), fungi (p less than 0.05), and the overall set of microorganisms encountered (p less than 0.001). It delayed growth of Enterobacteriaceae (p less than 0.001) but reduced the time to recover staphylococci (p less than 0.02). Of 12 isolates of species usually inhibited by SPS, seven grew only with the addition of gelatin and yeast extract, none grew only without supplementation, and five grew in both media. Although gelatin and yeast extract may improve the yield of some specific bacteria, the routine use of these additives cannot be recommended for all blood culture media.

Controlled evaluation of modified radiometric blood culture medium supplemented with gelatin for detection of bacteremia and fungemia

Although the addition of 1.2% gelatin to broth blood culture media containing sodium polyanetholesulfonate has been shown to enhance detection of certain bacteria, including Neisseria meningitidis, N. gonorrhoeae, Peptostreptococcus anaerobius, and Gardnerella vaginalis, the effect of such supplementation on the detection of other microorganisms causing bacteremia and fungemia is not known. Therefore, we studied BACTEC 6B medium with and without gelatin in 6,833 paired comparisons to examine the effects of supplementation on both the yield and the speed of detection of sepsis. More aerobic and facultative bacteria grew in the 6B than in the 6B-gelatin medium (P less than 0.001), especially staphylococci (P less than 0.01), Escherichia coli (P less than 0.01), other members of the family Enterobacteriaceae (P less than 0.05), and Acinetobacter spp. (P less than 0.05). When microorganisms grew in both bottles, they did so earlier in 6B than in 6B-gelatin (P less than 0.001). We conclude that the 6B medium in its present formulation is superior to 6B medium supplemented with 1.2% gelatin.

Blood-culture techniques. A survey in Australasian laboratories

The blood-culture methods of participants in the Microbiology Quality Assurance Programme were surveyed in late 1983; 183 participants from Australasia and S.E. Asia completed a questionnaire, the results of which are discussed. The choice of skin disinfectants varied widely. Conventional broth media were used by 85 participants; one or more diphasic bottles by 56; Roche Septi-Chek was used by 25; and BACTEC by 17. Only 80% of respondents reported the use of sodium polyanethol sulfonate. Contamination rates ranged from 0 to greater than 10%. Cultures were kept for as little as five days or as long as three weeks and were examined by inspection and/or Gram stain and/or subculture at widely varying intervals. While a great diversity of methods was used, in most cases these were adequate. The workload involved in some of the more laborious routines was considerable. It would be desirable to evaluate the cost-effectiveness of many blood culture practices.

Effect of sodium polyanetholesulfonate and gelatin on the recovery of Gardnerella vaginalis from blood culture media

Sodium polyanetholesulfonate (SPS) is used as a routine supplement to blood culture media to enhance recovery of microorganisms, but it inhibits the growth of Peptostreptococcus anaerobius, Neisseria meningitidis, Neisseria gonorrhoeae, and Streptobacillus moniliformis. Comparative clinical blood culture studies at the University of Colorado Hospital suggested that SPS also inhibits the growth of Gardnerella vaginalis. We inoculated 16 blood culture isolates of G. vaginalis into 11 blood culture media containing SPS or sodium amylosulfate, with and without gelatin. In the absence of gelatin, only brain heart infusion and thiol broths with SPS supported the growth of more than five strains of G. vaginalis, whereas all media except Bactec 6B and 7C and brucella broths recovered most isolates with SPS and gelatin or with sodium amylosulfate alone. We conclude that SPS inhibits the growth of G. vaginalis in blood culture media but that this inhibition is medium dependent and can be overcome by supplementation of most media with gelatin.

Neutralization of the inhibitory effect of sodium polyanetholesulfonate on Neisseria meningitidis in blood cultures processed with the Du Pont Isolator System

The inhibitory and bactericidal effects of sodium polyanetholesulfonate on Neisseria meningitidis were neutralized by blood lysis which occurs within the pediatric Isolator 1.5 Microbial tube (E. I. du Pont de Nemours & Co., Inc., Wilmington, Del.). Lysed blood was more effective than 2.5% gelatin in preventing the inhibitory effect. All but 1 of 16 N. meningitidis strains were killed by 0.06% sodium polyanetholesulfonate in the absence of lysed blood, whereas none were killed by 1.0% sodium polyanetholesulfonate when lysed blood was present. The possible clinical relevance of these results was reflected in the improved detection of meningococcemia in children when the Isolator 1.5 Microbial tube was compared with a conventional broth system.

Controlled evaluation of the effect of atmosphere of incubation on detection of bacteremia and fungemia in supplemented peptone broth

To evaluate the role of atmosphere of incubation in the detection of clinically important bacteremia and fungemia in adults, we compared the yield of microorganisms from 10,541 paired 5-ml samples of blood incubated aerobically and anaerobically. The medium, supplemented peptone broth (SPB) with 0.03% sodium polyanetholesulfonate, and the ratio of blood to broth (1:10) were the same for all cultures. Only cultures with adequate blood samples (greater than or equal to 80% of stated volume) were compared statistically. More fungi (P less than 10(-7) ) grew in continuously vented bottles of SPB. Aerobic incubation also favored (P less than 0.01) isolation of Neisseria gonorrhoeae and Eubacterium; more than 80% of these bacterial organisms were detected only in vented bottles. Anaerobic incubation (plugged venting units) did not significantly favor the isolation of any genus of microorganisms, although an estimated 11% more Bacteroidaceae grew in the unvented bottle of SPB. By comparison of our data with published results for other media, we conclude that the need for both aerobic and anaerobic incubation of blood cultures is dependent upon the medium used and the microorganisms likely to be encountered. Vented incubation of blood cultured in SPB is crucial for detection of fungi and some bacteria. Routine use of an unvented bottle of SPB may not be worthwhile for patients in whom Bacteroidaceae cause bacteremia infrequently. However, when Bacteroidaceae are suspected as the cause of sepsis, use of an unvented bottle of SPB is prudent.

Influence of a blood culture inoculation technique on detection of bacteremia by the BACTEC system

A 2-year study compared the influence of blood culture inoculation technique on the detection of bacteremia by an automated radiometric system (BACTEC; Johnston Laboratories, Inc.). A total of 4,690 specimens (20 ml each) were collected. Of each sample, 10 ml was inoculated into a pair of Bactec bottles at the bedside (BACTEC system). The remaining 10 ml was placed in an evacuated blood collection tube (VACUTAINER; Becton Dickinson VACUTAINER Systems) and transported to the laboratory for subsequent inoculation into an identical set of vials (VACUTAINER-BACTEC system). A total of 309 cultures grew organisms considered to be clinically significant. The recovery rate, time to positivity, and spectrum of isolates were similar for the two methods. There were substantially more sporeforming "contaminants" isolated in the VACUTAINER-BACTEC system.

Comparative evaluation of supplemented peptone broth with sodium polyanetholesulfonate and trypticase soy broth with sodium amylosulfate for detection of septicemia

We compared the yield and speed of detection of clinically important microorganisms from 10,156 paired 5-ml samples of blood cultured in supplemented peptone broth (SPB) with 0.03% sodium polyanetholesulfonate (SPS) or Trypticase soy broth (TSB) with 0.5% sodium amylosulfate (SAS). The atmosphere of incubation (open venting units) and ratio of blood to broth (1:10) were the same for both samples. Only cultures with adequate blood samples (greater than or equal to 80% of stated volume) were compared statistically. Overall, SPB/SPS outperformed TSB/SAS. Bacteroidaceae and Eubacterium were found more often (P less than 0.05) and viridans streptococci were found sooner (P less than 10(-4)) in SPB/SPS than in TSB/SAS. Most importantly, staphylococci were found both more often (P less than 0.03) and sooner (P less than 10(-7)) in SPB/SPS than in TSB/SAS. In a separate experiment, SAS slowed the growth of a clinical strain of Staphylococcus aureus in TSB. Unless important advantages can be confirmed for SAS in controlled clinical trials, SAS cannot be recommended for routine use as an anticoagulant in blood culture media.

Evaluation of sucrose and magnesium sulfate as additives in aerobic blood culture medium

Clinical blood cultures were made in duplicate in brain heart infusion broth with sodium polyanetholsulfonate and gelatin (P broth) and in the same medium with 20% sucrose (S broth). In part of the study, 0.1% magnesium sulfate was also included in the medium with sucrose (SMg broth). The results from 1,287 positive blood cultures are reported. Significant differences among the rates and speeds of isolations from these media were found in Enterobacteriaceae and Staphylococcus aureus, which were isolated more frequently from S broth and SMg broth than from P broth; in addition, recoveries were accomplished earlier (1 or more days) from S broth and SMg broth than from P broth more often than the reverse growth patterns. An additional effect of magnesium sulfate upon recoveries could not be concluded. The possible mechanisms by which sucrose promotes recoveries from clinical blood cultures are discussed.

Enhancement of recovery of Neisseria meningitidis by gelatin in blood culture media

The efficacy of gelatin for the recovery of Neisseria meningitidis from blood cultures was evaluated in a clinical setting. The organism was isolated from seven patients with meningococcal infections in blood culture media containing 1% gelatin. In contrast, only two blood cultures from these patients were positive in media without gelatin (P less than 0.05). Gelatin did not influence the recovery of other organisms isolated during this study. Conventional blood culture media may be supplemented with gelatin when meningococcemia is suspected.

Inhibition of Neisseria gonorrhoeae by sodium polyanetholesulfonate

Sodium polyanetholesulfonate (SPS), in concentrations commonly used in blood culture media, inhibited the growth of a significant number of isolates of Neisseria gonorrhoeae in an agar dilution system. This SPS toxicity, shown to be bactericidal when examined in broth culture, could be reversed by hemoglobin and gelatin. Gelatin in 1% concentration allowed optimal growth of SPS-sensitive isolates in the presence of 0.025% SPS. Of 50 clinical isolates of N. gonorrheae tested under simulated blood cultures conditions with SPS, 16 isolates failed to grow on subculture at days 1, 3, and 10 after inoculation. Recovery was delayed with eight isolates as compared to controls. Early subcultures at 4, 8, and 12 h failed to recover SPS-sensitive isolates, whereas 1% gelatin, added even as late as 8 h after inoculation, reversed the SPS toxicity. The data reported suggest that SPS at concentrations routinely used in blood cultures can delay or prevent isolation of N. gonorrhoeae, but 1% gelatin can eliminate this adverse effect.

An in vitro evaluation of two commercial blood culture media--supplemented peptone broth and supplemented tryptone soya broth

Two commercial blood culture--supplemented peptone broth and supplemented tryptone soya broth--were compared by an in vitro method. The two media were inoculated with microorganisms suspended in fresh human blood in an attempt to mimic the clinical situation. The two media differed completely in their ability to support the growth of Neisseria meningitidis and Neisseria gonorrhoeae. Macroscopic evaluation of the blood culture medium during the incubation period was difficult when using supplemented tryptone soya broth in contrast to supplemented peptone broth. The former medium remained turbid whether microorganisms were growing or not. No other important differences between the two media were detected. Our findings indicate a need for both in vitro and in vivo studies to evaluate blood culture media and also a need for quality control of microbiological diagnostic devices before they are released for clinical use.

Neutralization of human serum beta-lysin by sodium polyanetholsulfonate and sodium amylosulfate

Normal fresh and heat-inactivated (56 degrees C, 30 min) human sera (80 vol%, i.e., 80% [vol/vol] of a 2-ml assay volume) killed Bacillus subtilis ATCC 6633 cell inocula of 1.5 x 10(4) colony-forming units per ml within 1 to 2 h after exposure. The B. subtilis assay strain proved slightly and reversibly susceptible to 5 mug of egg white lysozyme per ml. Seitz filtration of fresh human serum completely removed beta-lysin activity; significant amounts of serum lysozyme were removed as well, as determined with the bioassay strain Micrococcus lysodeikticus ATCC 4698. However, bactericidal activity of human serum via classical or alternative complement pathway activation remained intact. Addition of 0.01 M dithiothreitol to fresh human serum abolished beta-lysin activity, but not that of serum lysozyme. Chelation of fresh and heat-inactivated human serum with 0.01 M MgCl(2) + 0.01 M ethylene glycol tetraacetic acid, but not with 0.01 M ethylenediaminetetraacetic acid, markedly retarded beta-lysin activity; however, lysozyme activity remained unaffected. Chelation of serum with 0.01 M MgCl(2) + 0.01 M ethylene glycol tetraacetic acid + 0.01 M CaCl(2) completely abrogated beta-lysin activity, but not that of lysozyme. Absorption of human serum with 10 mg of bentonite per ml (10 min, 37 degrees C) completely removed beta-lysin and lysozyme activity, but failed to affect serum bactericidal activity against Escherichia coli control strain C. Reconstitution of 50 vol% of bentonite-absorbed serum with 40 vol% of heat-inactivated human serum restored both beta-lysin and lysozyme activity. Addition of either 63 to 500 mug of sodium polyanetholsulfonate per ml or 63 to 500 mug of sodium amylosulfate per ml to 80 vol% of fresh human serum completely neutralized beta-lysin activity for the entire observation period of 22 h.

Variable neutralization of several nonspecific antibacterial systems in fresh, defibrinated human blood by sodium polyanetholsulfonate and sodium amylosulfate

Fresh, defibrinated human blood (80 vol%, i.e., 80% [vol/vol] of a 2-ml final assay volume) from two healthy adult donors killed "delayed serum-sensitive" (DSS) and "promptly serum-sensitive" (PSS) strains of Serratia marcescens, PSS control strain Escherichia coli C, Bacillus subtilis strain ATCC 6633, and Micrococcus lysodeikticus ATCC 4698 in a kinetic manner comparable to that of fresh human serum (80 vol%). However, heat-inactivated (56 degrees C, 30 min), defibrinated human blood revealed markedly reduced or a total lack of beta-lysin activity against the B. subtilis assay strain. Similarly, lysozyme activity of defibrinated blood was diminished somewhat by heat treatment, as determined with the M. lysodeikticus assay strain. Addition of 500 mug of sodium polyanetholsulfonate (SPS) per ml to 80 vol% of fresh, defibrinated human blood completely neutralized blood bactericidal activity against all assay strains of S. marcescens, E. coli C, and B. subtilis; however, SPS at this concentration failed to abolish lysozyme activity for prolonged periods of incubation. Addition of 500 mug of sodium amylosulfate (SAS) per ml to 80 vol% of fresh defibtinated human blood resulted in protection of cell inocula of DSS strains of S. marcescens only; SAS failed to protect cell inocula of the PSS strains of S. marcescens, E. coli C, B. subtilis, and M. lysodeikticus for extended periods of observation. Based on these data, it is recommended that blood culture specimens that are first drawn into specimen containers (such as Vacutainer tubes or the like) at the patient's bedside, and which contain >/=250 mug of SPS per ml, be diluted into suitable broth media with at least >/=250 mug of SPS per ml by the receiving laboratory within 2 to 4 h after procurement of the specimen. This procedure would ensure continued, adequate neutralization of the specimen's inherent beta-lysin, lysozyme, and complement- and antibody-mediated bactericidal activities.

Neutralization of human serum lysozyme by sodium polyanethol sulfonate but not by sodium amylosulfate

Sodium polyanethol sulfonate (SPS) at 500 microgram/ml, but not sodium amylosulfate (SAS) at 500 microgram/ml, precipitated egg white lysozyme (1 mg and 50 microgram of lysozyme per ml) as determined with the assay strain Micrococcus lysodeikticus ATCC 4698. Fresh and heat-inactivated (56 degrees C, 30 min) human serum (80%, vol/vol) killed M. lysodeikticus (10(4) bacteria per ml at zero time) within 1 to 2 h after exposure. Addition of 250 to 500 microgram of SPS per ml to fresh human serum protected M. lysodeikticus for 22 h as effectively as absorption of either fresh or heat-inactivated human serum with bentonite (10 mg/ml of serum, 10 min, 37 degrees C); the latter procedure is known to remove serum lysozyme. In contrast, SAS at 250 and 500 microgram/ml of serum retarded killing of the assay bacteria for periods of 4 h; after overnight (22 h) incubation, however, the number of M. lysodeikticus survivors had decreased significantly. The finding that SPS, but not SAS, at 250 to 500 microgram/ml effectively neutralized serum lysozyme-mediated killing of a lysozyme-sensitive assay strain may be of relevance with respect to laboratory processing of human blood culture specimens.

Effects of two blood culture anticoagulants on growth of Neisseria meningitidis

Tests of 25 strains of Neisseria meningitidis for sensitivity to sodium polyanethol sulfonate (SPS) showed that the sensitivity of strains varied with both inoculum size and SPS concentration. In Trypticase soy broth (TSB), 2 out of 13 strains were sensitive to 0.05% SPS, whereas 8 out of 13 strains were sensitive to the same concentration of SPS in brain heart infusion (BHI). In artificial blood cultures with six strains of meningococci, the addition of 10% defibrinated blood was found to eliminate the sensitivity of all six strains to SPS in BHI, but not of the two strains in TSB. Addition of 1.2% gelatin to artificial blood cultures eliminated the inhibitory effect of 0.05% SPS, whereas the addition of 1% yeast extract to blood cultures containing 0.025% or 0.05% SPS enhanced the inhibitory effect of this anticoagulant. None of the 13 strains tested was inhibited by 0.05% sodium amylosulfate in TSB or BHI alone or in artificial blood cultures with these media.