The spectrum of antibacterial activity of human amniotic fluid determined by scanning electron microscopy

Use of the 'ex vivo' test to study long-term bacterial survival on human skin and their sensitivity to antisepsis

AIMS

To determine bacterial survival on human skin and their sensitivity to antisepsis.

METHODS AND RESULTS

An 'ex vivo' protocol which uses human skin samples placed into diffusion cells, and electron microscopy (EM), were used to study the growth of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa inoculated onto skin samples over a 46-h incubation period at 32 degrees C. Concurrently variation in skin pH was evaluated at different time intervals during this period. In addition the antimicrobial activity of three antiseptics against the incubated micro-organisms was assessed quantitatively with the 'ex vivo' test, while their detrimental effects against bacteria were observed by EM. All three bacteria were still present in high number after 46 h inoculation on skin, although the concentration of E. coli and S. aureus were reduced by 2.74 and 1.58 log(10) reduction, respectively, over this period of time. Electron micrographs showed clear evidence of cell division and some bacteria appeared to be embedded into the skin layers. The antiseptics tested had some antibacterial activity against bacteria incubated on skin for 3 and 10 h, and EM evidence showed some morphological damages including cellular blebbing and the presence of fibrillar material around the cells. All micro-organisms had an acidifying effect on skin samples.

CONCLUSIONS

Here, it was shown that bacterial pathogens can survive and grow when incubated on human skin. In addition, it is possible that they can penetrate the stratum corneum, which can provide some protection against antisepsis.

SIGNIFICANCE AND IMPACT OF THE STUDY

The apparent low bactericidal activity of biocides attributed in part to bacterial protection from skin layers is particularly important to assess in order to ensure antisepsis efficacy.

The effect of meconium staining of amniotic fluid on the growth of Escherichia coli and group B streptococcus

OBJECTIVE

To compare the effect of meconium staining on the growth rate of Escherichia coli and group B streptococci (GBS) in amniotic fluid.

STUDY DESIGN

Sterile meconium was added in different concentrations to pooled sterile amniotic fluid obtained from term mothers. Meconium concentration was equal to: 1, 1.5, 3, 6, and 12 mg meconium/ml amniotic fluid. Amniotic fluid was quantitatively inoculated with E. coli and GBS type II and type III organisms (10(3) organisms/ml). Clear amniotic fluid and Todd-Hewitt broth served as controls. Growth rates of organisms were measured at 2, 4, 6, 8, and 24 hours after inoculation.

RESULTS

Clear amniotic fluid was completely inhibitory for growth of E. coli even after 24 hours of incubation. In contrast, after 6 hours of incubation, significantly increased growth of GBS occurred (10(5) organisms/ml) (p<0.0001). The inhibitory effect on E. coli was observed even with meconium concentration of up to 1.5 mg/ml. In contrast, even the smallest concentration of meconium (1 mg/ml) resulted in a 2-log fold increase of GBS within 4 hours. The more rapid growth rate of GBS compared to E. coli persisted even at moderate staining of amniotic fluid (6 mg/ml) in the first 8 hours of incubation (p<0.005). In the presence of thick meconium (12 mg/ml), during the first 6 hours of incubation, the growth rates of GBS and E. coli were nearly similar.

CONCLUSIONS

GBS (type II and III) growth, in contrast to E. coli, was less inhibited by amniotic fluid, occurred at a more rapid rate, and was enhanced at lower concentrations of meconium. As such, the presence of even light meconium staining in cases of rupture of membranes of even less than 6 hours in a mother who is a GBS carrier should be considered as a risk factor for the development of perinatal GBS infection.

Perinatal mortality associated with intrauterine infection due to pseudomonads

Pseudomonads are common causes of nosocomial infections but are rarely implicated in perinatal disease. In a retrospective autopsy study we found that 9% of all acute congenital bacterial infections were due to Pseudomonas species. Premature rupture of membranes occurred in half the cases and clinical maternal amnionitis in two-thirds. One case was apparently nosocomial in origin. No known risk factors were implicated in any other case. Seven infants were stillborn and two died within a few hours. Congenital pneumonia, funisitis, and chorioamnionitis were found at autopsy. Intrauterine infection due to the pseudomonads poses a serious problem that has not been previously recognized.

Amniotic fluid activity against Bacteroides fragilis and group B streptococci

The antimicrobial capacity of amniotic fluid (AF) against B. fragilis, group B streptococci and Escherichia coli, the latter as a reference indicator, was investigated in samples from 30 patients. In order to study trimester as well as individual variations in the antibacterial activity, 10 individual samples from each trimester of pregnancy (AF1, AF2, AF3), were separately tested. With B. fragilis all trimester samples showed initial inhibition lasting for 8 h, the bacteria then regaining growth capacity in all AF1, and the majority of AF2 and AF3 specimens. However, 4 AF2 and 3 AF3 samples showed continued bacteriostatic activity for up to 24 h. Group B streptococci exhibited uninhibited growth in all trimester samples. The growth of E. coli in AF1 and AF2 was not inhibited, whereas in AF3 a temporary arrest was observed at 8 h, this being followed by growth to control levels at 24 h. The findings may explain the frequent isolation of B. fragilis from cases of septic abortions during the first trimester. Individual variation in the effectiveness of the antibacterial activity against B. fragilis in AF2 and AF3 may explain why this microorganism, which is often implicated in severe maternal and neonatal infections, is occasionally recovered from the mother's endocervix without signs of disease. The inefficacy of AF in defence against group B streptococci correlates well with the frequent isolation of these bacteria from cases of severe congenital infections associated with premature delivery.

Clinical significance of amniotic fluid, amniotic membranes, and endometrial biopsy cultures at the time of cesarean section

When we compared amniotic fluid and amniotic membranes, as a source of organisms at the time of cesarean section, amniotic membranes proved to be superior. During labor, intact membranes do not protect the amniotic cavity from contamination with pathogenic anaerobes and commensals. Ruptured membranes in the presence of prolonged labor predisposes the amniotic cavity to contamination with pathogenic anaerobes, commensals, and pathogenic aerobes. Cultures of the endometrial biopsy specimens taken from the site of incision at the time of cesarean section showed the presence of pathogens in 50% of the women with prolonged labor and ruptured membranes.

Antimicrobial activity of amniotic fluid obtained vaginally

Twenty-nine amniotic fluid samples were aspirated from pregnant women at term (38-40 weeks' gestation) by tapping the bulging membrane vaginally, and their effects on Escherichia coli, Staphylococcus aureus and Candida albicans were studied. Inhibition rates were 72.41% for E coli, 68.96% for S aureus and 79.31% for C albicans. Two samples (6.90%) affected only a single organism, 18 (62.07%) affected two organisms and eight (27.59%) affected all three. Only one sample (3.45%) had no inhibitory effect on the microorganisms studied. Thus, 28 of 29 samples (96.55%) inhibited the growth of at least one of the microorganisms tested. These results are also significant because there is a high risk of contamination of amniotic fluid samples obtained through the vaginal route, although they can be obtained easier that way than through amniocentesis.

Antimicrobial effect of amniotic fluid against anaerobic bacteria

Amniotic fluid samples were obtained at term and tested for their antimicrobial effect on anaerobes, Peptostreptococcus (Ps.) anaerobius, Peptococcus (Pc.) prevotii, Bacteroides (B.) fragilis, and B. coagulans with facultative Escherichia (E.) coli serving as control. Amniotic fluid had only temporary bacteriostatic effect on Pc. prevotii and B. fragilis for 8 to 16 hours. This effect lasted for only 8 hours on Ps. anaerobius. On the contrary, the bacteriostatic effect of amniotic fluid was well sustained on E. coli and B. coagulans, lasting for the entire test periods of 20 and 32 hours, respectively. At the end of the time intervals mentioned, Ps. anaerobius, Pc. prevotii, and B. fragilis exhibited logarithmic growth, confirming the earlier reports that it is not nutritionally deficient. Amniotic fluid exhibited temporary bacteriostatic effect on Ps. anaerobius, P. prevotii, and B. fragilis, but this effect was well sustained against B. coagulans.