Bascom F. Anthony

Importance of bacterial growth phase in determining minimal bactericidal concentrations of penicillin and methicillin.

The minimal inhibitory concentrations of penicillin against 96 strains of group B streptococci and of methicillin against 10 strains of Staphylococcus aureus were unrelated to the growth phase of test bacteria. However, the minimal bactericidal concentrations were significantly higher in the stationary phase than the logarithmic phase for both organisms (P less than 0.001 and less than 0.05, respectively).

Importance of Medium in Demonstrating Penicillin Tolerance by Group B Streptococci

A total of 30 clinical isolates of group B streptococci were studied for penicillin tolerance in vitro. Minimal inhibitory and bactericidal concentrations of penicillin were determined simultaneously in three test media which have been used for group B streptococci, tryptose phosphate, Mueller-Hinton, and Todd-Hewitt broths, using a logarithmic-phase inoculum of 105 colony-forming units per ml. Minimal inhibitory concentrations in the three media did not differ significantly. However, minimal bactericidal concentrations were significantly higher in tryptose phosphate broth (mean, 1.04 μg/ml) than in Mueller-Hinton broth (0.22 μg/ml) or Todd-Hewitt broth (0.15 μg/ml). Similarly, ratios of minimal bactericidal to minimal inhibitory concentrations were significantly greater in tryptose phosphate broth than in Mueller-Hinton or Todd-Hewitt broth. After incubation in tryptose phosphate broth for an additional 24 h, the minimal bactericidal concentration consistently fell to levels which were only twice or equal to the minimal inhibitory concentration. This study illustrates the importance of the medium in the demonstration of penicillin tolerance and of controlling laboratory variables in the susceptibility testing of group B streptococci with penicillin.

Comparison of group B streptococcal hyperimmune globulin and standard intravenously administered immune globulin in neonates

Standard intravenously administered immune globulin (IVIG) contains varying amounts of group B streptococcus (GBS) antibody. A GBS hyperimmune IVIG was produced by immunizing plasma donors. The GBS type-specific opsonic activity was > or = 90% in the hyperimmune IVIG at a 1280 dilution-1 versus at a 10 dilution-1 in standard IVIG. Suckling rat survival after GBS type-specific infection was 100% when the rats were treated with hyperimmune IVIG versus < or = 20% with standard IVIG. To evaluate the effect of this product on GBS antibody levels and clinical toxic effects, we randomly administered either GBS hyperimmune IVIG, 500, 250, or 100 mg/kg, or standard IVIG, 500 mg/kg, to 20 neonates with suspected sepsis. No adverse effects were observed. Total and subclass serum IgG levels reflected only the dose; serum GBS type-specific IgG and opsonic activity reflected both the product and dose of IVIG administered. Standard IVIG did not significantly increase serum GBS type-specific IgG, whereas hyperimmune IVIG, 500 mg/kg, produced a fourfold rise for > 6 weeks; more variable increases were observed after 250 and 100 mg/kg doses were given. Serum GBS type-specific opsonic activity correlated with serum GBS type-specific IgG levels (R2 = 0.74; p < 0.0001). Further studies of this or similar products will be necessary to determine whether GBS type-specific antibody improves the outcome of GBS-infected neonates.

Solid-phase antigen density and avidity of antibodies detected in anti-group B streptococcal type III IgG enzyme immunoassays

Two enzyme immunoassays which measure anti-group B streptococcal type III capsular carbohydrate IgG antibodies were compared. One utilised poly-L-lysine conjugated coating antigen while the other used tyraminated coating antigen. Both carbohydrate antigens appeared to be antigenically identical but the poly-L-lysine based assay gave significantly lower values for some sera. Sera were identified which had low and high avidity anti-group B streptococcal type III IgG antibodies by the thiocyanate elution method. These antibodies gave results on a dilution range of coating concentrations consistent with their relative avidity. Comparison of dilution ranges of the two conjugates used for coating suggests that the poly-L-lysine conjugate coats with a ten-fold lower efficiency than the tyramine conjugate and therefore detects only higher avidity antibodies. Four fractions containing different relative avidities of affinity-purified IgG were produced from a single serum. These fractions behaved in the same manner as sera containing antibodies of different avidities. The results of this study suggest that the method of polysaccharide conjugation in enzyme immunoassays may affect the antigen concentration on the solid phase and thence the detection of antibodies of various avidities.

Demonstration of Opsonic and Protective Activity of Human Cord Sera against Type III Group B Streptococcus that Are Independent of Type-Specific Antibody

ABSTRACT: In an effort to further understand the host defense against group B streptococcus (GBS), we examined 71 human cord sera for their content of type III GBS IgG antibody by enzyme-linked immunosorbent assay and correlated the results with opsonic and protective activity against type III GBS. Most cord sera (67%) containing >0.1 μg/ml of type III GBS IgG antibody promoted phagocytosis and killing in vitro and protection against type III GBS in neonatal rats. However, 26% of cord sera containing <0.1 tig/ml of type III IgG antibody exhibited similar activity in vitro and in vivo against type III GBS. This opsonic and protective activity was retained in IgG fraction of whole serum, and was not directly associated with complement activity or with fibronectin. Further studies are needed to understand the mechanisms responsible for the opsonic and protective activity of some cord sera against type III GBS that may be independent of antibody to the type-specific polysaccharide antigen.

Efficacy of Trimethoprim/Sulfamethoxazole in Experimental Escherichia coli Bacteremia and Meningitis

We evaluated the activity of trimethoprim/sulfamethoxazole (TMP/SMZ) against a K1 Escherichia coli strain. Minimal inhibitory and bactericidal concentrations were 0.06/1.14 and 0.25/4.75 micrograms/ml, respectively. In vivo studies using an infant rat model of bacteremia and meningitis revealed that TMP/SMZ penetrated well into the cerebrospinal fluid (CSF) and that 37% of serum levels were achieved. The efficacy of TMP/SMZ was compared with that of ampicillin, chloramphenicol, cefotaxime and lamoxactam. Bacterial clearance from blood and CSF was significantly greater with TMP/SMZ than with ampicillin or chloramphenicol and mortality was significantly less than with chloramphenicol (p less than 0.01). However, 3 of 21 (14%) and 2 of 8 animals (25%) still had positive blood and CSF cultures after 3 days of treatment with TMP/SMZ. None of the survivors in the cefotaxime and lamoxactam groups were bacteremic after 1 day of therapy. Furthermore, 5 of 13 animals (38%) treated with TMP/SMZ developed meningitis during therapy, in contrast with none in the cefotaxime and lamoxactam groups. These findings indicate that although the activity of TMP/SMZ is bactericidal in vitro and in vivo against E. coli, TMP/SMZ may not provide optimal therapy for gram-negative bacillary meningitis in this model.

The effect of hexachlorophene on staphylococcal colonization rates in the newborn infant: a controlled study using a single-bath method.

Three hundred and thirty-two infants admitted to the normal newborn nursery at Harbor General Hospital during January and February, 1972, were divided into two groups. Half received a single bath with 3 per cent hexachlorophene at 2 to 4 hours of age followed by thorough rinsing with water. The other half was bathed with water only. Cohort system and careful hand-washing technique with hexachlorophene were observed during the study period. Cultures of the anterior nares and cord were taken on the third day of life prior to discharge from the hospital. Twenty-one (12.6 per cent) of those bathed with water and nine (5.4 per cent) of those bathed with hexachlorophene were colonized with Staphylococcus aureus on discharge. Follow-up cultures 2 to 4 weeks after discharge showed that 6 of the 9 hexachlorophene-bathed infants and 14 of the 21 water bathed infants were still positive. An acceptably low staphylococcal carrier rate (9 per cent) was found in the infants discharged from the nursey during this study. It appears that a single bath with 3 per cent hexachlorophene in the early hours of life followed by thorough rinsing can be expected to effect an additional, significant reduction in the rate of staphylococcal colonization.

Paradox between the responses of Escherichia coli K1 to ampicillin and chloramphenicol in vitro and in vivo.

We evaluated the activity of ampicillin and chloramphenicol in vitro and in vivo against an Escherichia coli K1 strain. In vitro, the strain was relatively susceptible to both antibiotics (MIC and MBC of ampicillin, 2 and 4 micrograms/ml; MIC and MBC of chloramphenicol, 4 and 64 micrograms/ml). Checkerboard determinations of MBCs of drug combinations were consistent with antibiotic antagonism. Killing curves with concentrations of antibiotics similar to in vivo levels in blood and cerebrospinal fluid of infected rats indicated antagonism within the first 4 h and an indifferent effect of the combination at 24 h. Paradoxically, the combination was significantly more effective than ampicillin or chloramphenicol alone in vivo in infant rats. This was shown by (i) more rapid bacterial clearance from the blood and cerebrospinal fluid, (ii) a decreased incidence of meningitis in bacteremic animals, and (iii) improved survival. These findings illustrate a divergence between the effects of ampicillin and chloramphenicol against E. coli in vitro and in vivo and suggest that this combination is an effective synergistic regimen in this experimental model of E. coli bacteremia and meningitis.

1122 TREATMENT OF EXPERIMENTAL E. COLI (EC) INFECTION WITH THE COMBINATION OF CHEMOTHERAPY AND IMMUNOTHERAPY

The morbidity and mortality associated with neonatal EC infection have remained significant despite advances in antimicrobial chemotherapy. In a search for more effective therapy, we evaluated combination therapy against a K1 EC with cefotaxime (Ct) and two different antibody (Ab) preparations, rabbit J5 antiserum (J5 Ab) and murine IgM monoclonal antibody to the lipopolysaccharide of the infecting EC serotype (LPS Ab). EC bacteremia and meningitis.were induced in 5-day-old rats by sc inoculation. At 6 days of age, each litter was divided into 3 groups to receive Ct (50 mg/kg sc twice daily), one of the Ab preparations (50 μl/10 gm ip) or combination therapy. A control rat from each litter received saline. Bacterial counts in blood and CSF were determined daily before and during therapy and mortality recorded. All animals receiving saline died. Bacterial clearance was inversely related to the mortality, which is summarized below:As noted, LPS Ab enhanced the efficacy of Ct while J5 Ab was not beneficial. These findings suggest that the combination of antibiotics and LPS Ab have enhanced efficacy in this model.

Genital and intestinal carriage of group B streptococci during pregnancy

To evaluate the relative importance of genital and gastrointestinal carriage of group B streptococci, repeated semiquantitative and qualitative cultures were obtained from 64 patients during pregnancy. Carriage was documented in 20% of the women at the first visit, in 41% of the women cumulatively, and at 24% of 295 visits. Group B streptococci were isolated from 20% of genital, 17% of rectal, and 17% of stool cultures. Concordance of carriage among these body sites was high (87%-93%) for cultures collected simultaneously. Counts of streptococci ranged between 10(2) and 10(7) colony-forming units per gram of dry stool (geometric mean, 2.3 x 10(5)) and varied widely among repeated samples from chronic carriers. The group B streptococci tended to appear, persist, and disappear simultaneously in genital, rectal, and stool cultures of individuals, although some women appeared to harbor the organism in the birth canal or lower bowel alone.