New patterns of mixed-substrate utilization during batch growth of Escherichia coli K12

Microbial growth on mixtures of substrates is of considerable engineering and biological interest. Most of the work until now has dealt with microbial growth on binary mixtures of sugars or polyols. In these cases, it is often found that no matter how the inoculum is precultured, only one of the two substrates is consumed in the first growth phase, leading to the diauxic growth pattern. The goal of the experiments reported here is to investigate growth on mixtures containing at least one organic acid. These experiments show that the substrate utilization patterns in such mixtures are qualitatively different from the diauxic growth pattern. For instance, during growth of Escherichia coli K12 on certain binary mixtures of organic acids, the two substrates are utilized simultaneously, and the mixed-substrate maximum specific growth rate exceeds the single-substrate maximum specific growth rate on either one of the two constituent substrates. Furthermore, the very same mixed-substrate maximum specific growth and substrate uptake rates are observed no matter how the inoculum is precultured. On the other hand, in a mixture of glucose and pyruvate, the maximum specific growth rate seems to depend on the preculturing conditions, thus suggesting the existence of multiple physiological quasi-steady states. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 747-757, 1997.

Neonatal cytomegalovirus infection: diagnostic modalities available for early disease detection

CMV is a ubiquitous virus. In India, there is high seroendemicity with almost 99% adults showing IgG antibodies. Infection or re-activation becomes important in immunocompromised host (Transplant recipients, Cancer therapy patients and patients with HIV/AIDS). Neonates form a distinctive high risk population for congenital CMV infection and suffer disastrous sequlae of the same. Neonatal infections may be congenital in nature or may be acquired after birth during first month of life via infected breast milk or due to exposure to high risk blood products. The risk for transmission of the virus to the fetus is higher in primary infected mothers than in mothers with reactivated disease. Primary CMV infections are reported in 1-4% of seronegative women during pregnancy and the risk for viral transmission to fetus is 30-40%. Reactivation of a CMV infection during pregnancy is reported in 10-30% of seropositive women and the risk of transmitting the virus is about 1-3%. The adverse outcome of congenital neonatal CMV infection includes-microcephaly (70%), intellectual impairment (60%), sensineural hearing loss (35%), choriorenitis (22%), hepatosplenomegaly (70%), jaundice (68%), thrombocytopenia (65%), low birth weight (65%), pneumonitis (2-5%) and congenital heart disease (<5%). About 5-10% of congenitally infected asymptomatic infants will have neurological problems later in life the most common of which is unilateral or bilateral sensory neural hearing loss. All immunocompromised hosts, including pre-term neonates, mount weak antibody responses (IgM), making serological detection of CMV infection in them, fallacious. Thus, it is imperative to use antigen detection methods such as quantitative PCR or PP65 Antigenaemia assays to detect CMV infection in immunocompromised host. Sakhuja et al and Minz et al have demonstrated that PP65 Antigenaemia assay is very good for diagnosing CMV disease in renal transplant recipients. The present review tends to highlight the role of newer diagnostic modalities in early CMV infection detection in neonatal population.

Prediction of feed intolerance and necrotizing enterocolitis in neonates with absent end diastolic flow in umbilical artery and the correlation of feed intolerance with postnatal superior mesenteric artery flow

OBJECTIVES

To evaluate the role of postnatal superior mesenteric artery (SMA) flow in predicting feed intolerance and NEC in the babies who had AEDF in comparison with gestation matched SGA and AGA with normal flow.

DESIGN

This was a prospective cohort study conducted in 62 eligible babies admitted in NICU. Babies were enrolled in 3 groups. Group 1 (n = 23) was SGA and AEDF, group 2 (n = 20) was SGA and group 3 (n = 19) was AGA and both with normal UA flow. In all babies baseline SMA flow was measured before test feed (0.5 ml) and repeated every 15 minutes for 1 hour after the feed.

RESULTS

Feed intolerance was seen in 69.5% of babies in group1 (p = <0.001) as compared to 20% and 17.5% in group 2 and 3. Four (17.3%) babies developed NEC in group1 (p = 0.02) but none in other 2 groups. Baseline peak systolic velocity (PSV) and time average mean velocity (TAMV) at 60 min post feed were significantly (p = 0.01 and 0.028 respectively) lower in group1 than group3. TAMV and PSV at 60 min post feed were significantly lower (p = 0.028 and 0.03) in babies with feed intolerance as compared to no feed intolerance group. Absent end diastolic flow and hypoglycemia were independent risk factors for feed intolerance.

CONCLUSION

SGA babies with AEDF had higher incidence of feed intolerance and NEC. Serial SMA flow studies specially the 60 min post feed study may help in differentiating which babies are likely to develop feed intolerance.

Hepatitis B Prevalence during pregnancy

In order to determine the efficacy of a new hepatitis B immune globulin (HBIG), a phase 3, vertical transmission (mother to child) clinical interventional trial of hepatitis B virus (HBV) post exposure prophylaxis (PEP) was conducted at selected sites (n=15) throughout India. This required a large screening program for HBsAg positivity at prenatal clinics located in tertiary care hospitals. 36,379 pregnant women consented to be tested for Hepatitis B surface antigen (HBsAg) by Rapid Test and if positive-confirmed by ELISA. The weighted mean prevalence was 0.82% (95% CI, 0.72, 0.91). In conclusion, the prevalence of HBV carrier state during pregnancy in India in this study was low compared to previous reports.

Clinical risk factors associated with extubation failure in ventilated neonates

We conducted this study to find out the incidence of extubation failure (EF) in ventilated neonates and associated clinical risk factors. Eighty two ventilated neonates were followed up to 48 hours post extubation to look for EF. Twenty two babies (26.8%) had EF. The common risk factors for EF were presence of patent ductus arteriosus, post-extubation lung collapse and acquired pneumonia. The duration of ventilation, and maximum and pre-extubation alveolar arterial oxygen gradients (AaDO2) were significantly higher (P<0.05) in EF group. The incidence of sepsis (P=0.034), anemia (P=0.004) and pneumonia (P=0.001) were significantly higher in EF group. Detection of significant PDA and adequate post extubation care may help to reduce rate of extubation failure in neonates.

Validity of New Ballard Score until 7th day of postnatal life in moderately preterm neonates

OBJECTIVE

The New Ballard Score (NBS) has been evaluated only until 96 h of age. We studied the validity and reliability of NBS for gestational age (GA) assessment on days 1, 5 and 7 of postnatal age (PNA).

DESIGN AND SETTING

This prospective, analytical study was conducted in a level III neonatal unit.

PATIENTS

Neonates born at a GA of 29-35 weeks (based on accurate last menstrual period (LMP)) were eligible. Encephalopathy, malformations, and unstable vitals were exclusion criteria. LMP-based GA was the gold standard. NBS was assessed within 24 h of birth by one rater, and two raters assessed NBS on days 5 and 7. All were blinded to LMP and one anothers' ratings. Recruitment continued until >100 subjects were enrolled with > or =25 in each LMP-based GA group: 29-30 weeks, 31-32 weeks, 33-34 weeks and 35 weeks.

MAIN OUTCOME

Correlation of GA assessed on day 7 with gold standard.

RESULTS

129 neonates were studied. NBS-based GA on days 5 or 7 did not differ from the gold standard GA by more than 2 weeks in any subject. On day 7, NBS overestimated GA in 26.7% and underestimated GA in 19.8% cases; all discrepancies were < or =2 wks. Compared to gold standard GA, the intra-class correlations (ICCs) of the gold standard GA and the NBS-based GA of the day 1 rater, day 5 rater and day 7 rater were 0.94, 0.94 and 0.92, respectively. ICCs for inter-rater reliability on day 5 and day 7 were 0.97 and 0.96, respectively. Compared to the day 1 rater's raw NBS, the ICCs of day 5 and day 7 raters' total scores were 0.98 and 0.97, respectively; of day 5 and day 7 raters' neurological scores were 0.98 and 0.97; and of day 5 and day 7 raters' physical scores were 0.92 and 0.88. All ICCs mentioned above had p values <0.001.

CONCLUSIONS

NBS is a valid and reliable clinical tool for GA assessment until day 7. It slightly overestimates the GA with increasing PNA. Neurological signs are more reliable than physical ones.

Clinico-epidemiological profile and validation of symptoms and signs of severe illness in young infants (< 60 days) reporting to a district hospital

OBJECTIVES

To describe the clinical and epidemiological profile of infants less than 2 months of age reporting to a district hospital and to assess the ability of simple clinical symptoms and signs used by health workers to detect severe illness warranting hospital admission.

METHODS

It was an observational study done at a general district hospital at Chandigarh, North India. Infants less than 2 months of age presenting to this hospital were enrolled. All infants were first evaluated by an auxiliary nurse midwife (ANM) to record a pre-determined set of symptoms and signs. A pediatrician who was blinded to the findings of the ANM did an independent assessment for severe illness needing urgent hospitalization.

RESULTS

A total of 1268 infants were enrolled. Of these, 356 (28%) were below 7 days of age. Overall, regurgitation, vomiting and stool problems (25%) were the most common presenting complaints in the first 2 months of life, followed by jaundice (22%) and respiratory symptoms (15%). 112 (8.8%) infants were classified as having "severe illness requiring urgent hospital management" by the pediatrician. Nearly half (46%) of the admissions were because of jaundice while 17% each were due to sepsis and pneumonia / lower respiratory tract infection (LRTI). A history of not feeding well (OR 14.7, 8.0 and 11.3 in 0-6, 7-27 and 28-59 days age groups, respectively) and a respiratory rate >60/min (OR 21.5, 6.2 and 10.5 in 0-6, 7-27 and 28-59 days age groups, respectively) had significant positive predictive value to predict severe illness (except jaundice) in all the 3 age groups studied. In the second month of life, severe chest in-drawing (OR 4.6) was also a significant predictor.

CONCLUSIONS

Simple clinical signs are useful in hands of health worker for identifying neonates with serious illness warranting hospital admission. These will be of use in the further development of clinical algorithms for the national integrated management of childhood illnesses.

Randomized controlled trial of 7-Day vs. 14-Day antibiotics for neonatal sepsis

There are no evidence-based guidelines available regarding the duration of antibiotics in neonatal septicemia. We compared the effectiveness of a 7-day intravenous antibiotic regimen with the standard 14-day regime in blood-culture-proven sepsis in neonates. This was a controlled, blinded, randomized trial with stratification (for birth weight). Blood-culture-positive septic babies > or =32 weeks and/or > or =1500 g were enrolled if meningitis and other deep-seated focal infections were ruled out. Parental consent was obtained. Randomization to either 7-day or 14-day therapy was done on day 7 of antibiotics if the baby had clinically remitted by day 5. Blood culture was repeated 24 h after antibiotic completion. Subjects were observed in the hospital for at least 72 h, and followed-up for 28 days by weekly visits and telephonic contacts. The primary outcome was treatment failure within 28 days defined as a positive blood culture, or clinical signs accompanied by either positive CRP or adjudicated to be a relapse by an expert committee. A total of 120 babies were eligible, 51 were excluded (no consent: 12; non-remission: 39), and 69 were randomized to receive either a 7-day course (n = 34) or a 14-day course (n = 35) of antibiotics. Baselines variables were comparable in the two groups. Primary outcome assessment could be done in 33 cases in either group. There was a trend to greater treatment failures in the 7-day group compared with 14-day group (5 vs. 1, respectively; P = 0.19). On subgroup analysis of subjects with Staphylococcus aureus infection, those who received 7-day therapy (n = 7) had significantly more treatment failure than 14-day therapy (n = 7) (four and zero, respectively; P = 0.022), whereas on sub-group analysis of babies with non-S. aureus infections, treatment failure rates were identical (3.8% in both groups). On comparing the organisms isolated in the group of subjects which was not randomized by virtue of being symptomatic (n = 39) vs. the group which was randomized (n = 69), it was found that S. aureus infections were significantly commoner in the former group (61.5 vs. 21.3%, respectively; P < 0.001). Neonates > or =32 weeks and/or > or =1500 g with S. aureus sepsis require 14 days of antibiotics. S. aureus infection is also associated with failure to achieve clinical remission by the 5th day of antibiotic therapy. Larger trials are required to confirm whether neonates with non-S. aureus sepsis, whose symptoms remit by 5 days, can be treated with 7 days of antibiotics.

A randomized controlled trial of sodium bicarbonate in neonatal resuscitation—effect on immediate outcome

Very little evidence is available that supports or disproves the use of medications in neonatal resuscitation. In this randomized controlled trial, we evaluated the effect of sodium bicarbonate given during neonatal resuscitation, on survival and neurological outcome at discharge.

SUBJECTS AND METHODS

Consecutively born asphyxiated neonates continuing to need positive pressure ventilation at 5min of life received either sodium bicarbonate or 5% dextrose. The study group was given intravenous sodium bicarbonate solution 4ml/kg (1.8meq./kg) over 3-5min. This solution was prepared by diluting 7.5% sodium bicarbonate (0.9meq./ml) with distilled water in a 1:1 ratio. The placebo group received 4ml/kg of undiluted 5% dextrose at a similar rate. The surviving neonates were evaluated for their neurological status at discharge. Primary outcome variable: Death or abnormal neurological examination at discharge. Secondary outcome variables: Encephalopathy, multi-organ dysfunction, intraventricular haemorrhage (IVH) and arterial pH at 6h.

RESULTS

Twenty-seven babies were randomized to receive sodium bicarbonate (bicarb group) and 28 to receive 5% dextrose. Eighteen of the 27 (66.7%) babies in the bicarb group and 19 of the 28 babies (68%) in the dextrose group survived to discharge ( P=0.84 ). Twenty-eight percent of the survivors in the bicarb group and 32% of the survivors in the dextrose group were neurologically abnormal at discharge ( P=0.10 ). The composite primary outcome of death or abnormal neurological examination at discharge was similar in both groups (52% versus 54%, P=0.88 ). The incidence of encephalopathy (74% versus 63%), cerebral oedema (52% versus 30%), need for inotropic support (44% versus 29%), intraventricular haemorrhage (IVH) and the mean arterial pH at 6hrs were similar between the two groups.

CONCLUSION

Administration of sodium bicarbonate during neonatal resuscitation did not help to improve survival or immediate neurological outcome.

Rapid detection of Haemophilus influenzae by hel gene polymerase chain reaction

AIMS

To evaluate the efficiency of hel gene polymerase chain reaction (PCR) to detect Haemophilus influenzae in various clinical/non-clinical samples.

METHODS AND RESULTS

Seventy-four clinical samples (cerebrospinal fluid, blood, sputum, throat and nasal swabs) and throat swabs of 17 asymptomatic carriers were collected. Primers were used to amplify the hel gene of H. influenzae encoding P4 outer membrane protein directly from the processed samples. The samples were also examined by conventional culture methods and the results were compared with those of PCR. The culture methods showed positive results in 60 (65.9%) of 91 samples in contrast to 62 (68.12%) samples tested positive by PCR. None of the culture-positive samples were PCR-negative while two of the culture-negative samples were PCR-positive. The specificity of the products was confirmed by Southern hybridization and failure of various other organisms to amplify the hel gene product. The sensitivity of the PCR assay was found to be 50 pg of DNA.

CONCLUSIONS

These findings suggest that the hel gene PCR is a rapid, sensitive and a specific new method for direct identification of H. influenzae.

SIGNIFICANCE AND IMPACT OF THE STUDY

Thus, this PCR test can improve the detection rate of H. influenzae in suspected clinical samples as compared with that of conventional culture methods.

Oral health and related factors in cystic fibrosis and other chronic respiratory disorders

AIM

To compare the prevalence of dental caries, dental calculus, and enamel defects in children with cystic fibrosis (CF) and children with other chronic respiratory disorders.

METHODS

A cross sectional observational survey. One examiner (AN) undertook oral examinations to assess dental caries, periodontal health, and enamel defects in children attending respiratory outpatient clinics.

RESULTS

A total of 74 patients with CF (35 male; mean age 10.7 years, range 2.5-16.5) were compared with a control group of 106 patients with other chronic respiratory disorders (52 male; mean age 9.1 years, range 3.0-16.5). There were significantly more defects of enamel in the permanent teeth of CF patients, compared with the teeth of those children with other chronic respiratory disorders. In addition, non-significant trends towards a lower caries prevalence in both dentitions, increased numbers of sextants with calculus deposits, and a reduced number of healthy gingival sextants were observed in the patients with cystic fibrosis.

CONCLUSIONS

Enamel defects, particularly enamel opacities, which can be disfiguring, are more common in CF patients. Early, regular dental visits may prevent such defects becoming dentally disabling and would also permit the removal of dental calculus deposits. The use of long term antibiotics and pancreatic enzymes may confer some protection against the development and progression of dental caries in patients with cystic fibrosis. The inclusion of a specialist paediatric dentist, as part of the multiprofessional team managing the care of these children, would be an advantage.

Resuscitation of asphyxiated newborns with room air or 100% oxygen at birth: a multicentric clinical trial

OBJECTIVE

To compare the short-term efficacy of room air versus 100% oxygen for resuscitation of asphyxic newborns at birth.

DESIGN

Multicentric quasi randomized controlled trial.

SETTING

Teaching hospitals.

INCLUSION CRITERIA

Asphyxiated babies weighing greater than 1000 grams, with heart rate less than 100 per min and/or apnea, unresponsive to nasopharyngeal suction and tactile stimuli and having no lethal abnormalities.

INTERVENTION

Asphyxiated neonates born on odd dates were given oxygen and those on even dates room air for resuscitation.

OUTCOME MEASURES

Primary: Apgar score at 5 minutes; Secondary: Mortality and Hypoxic ischaemic encephalopathy (HIE) during first 7 days of life.

RESULTS

A total of 431 asphyxiated babies, 210 in the room air and 221 in 100% oxygen group were enrolled for the study. Both the groups were comparable for maternal, intrapartum and neonatal characteristics. The heart rates in room air and 100% oxygen groups were comparable at 1 minute (94 bpm and 88 bpm), 5 minutes (131 bpm and 131 bpm) and 10 minutes (135 bpm and 136 bpm). Median apgar scores at 5 min [7 versus 7] and 10 minutes [8 versus 8 ], in the room air and oxygen groups respectively, were found to be comparable. Median time to first breath (1.5 versus 1.5 minutes) was similar in the room air and oxygen group. Median time to first cry (2.0 versus 3.0 minutes) and median duration of resuscitation (2.0 versus 3 minutes) were significantly shorter in the room air group. The number of babies with HIE during first seven days of life in the two treatment groups (35.7% babies in room air and 37.1% in the 100% oxygen group) were similar. There was also no statistically significant difference in the overall and asphyxia related mortality in the two treatment groups (12.4% and 10.0% in room air versus 18.1% and 13.6% in oxygen group).

CONCLUSION

Room air appears as good as 100% oxygen for resuscitation of asphyxic newborn babies at birth.

Neonatal hyperbilirubinemia and its association with thyroid hormone levels and urinary iodine excretion

OBJECTIVE

To investigate, if, urinary iodine contents as a marker of iodine deficiency and hypothyroidism are associated with the incidence of neonatal hyperbilirubinemia.

METHODS

One hundred neonates with total serum bilirubin > or = 15 mg/dl and with no known cause of jaundice were included in the study as a jaundice group. An equal number (n = 100) of non-jaundiced neonates (bilirubin < or = 14.9 mg/dl) with matching for age, gestation period and weight were enrolled in the study as a control group.

RESULTS

Thirteen neonates (13%) in the study group had urinary iodine levels < 100 mg/dl as against only 2 (2%) in the control group (p < 0.05). Thirty-four (34/200-17%) neonates i.e. 17 each in the study and control groups had serum TSH > 5 mU/ml and hence an indirect indicator of iodine deficiency in the study population. The mean serum levels of total T3, T4 and TSH in the study neonates were 1.52 +/- 1.23 ng/ml, 15.8 +/- 12.0 micrograms/dl & 3.13 +/- 3.0 mU/ml respectively and did not differ significantly from the mean levels in the control group. Only one neonate in the study group had serum TSH > 20 mU/ml which was suggestive of hypothyroidism, but had normal T3 & T4. Seven neonates in the study group and 8 in the control group had low T4. There was no significant correlation between the maternal and neonatal urine iodine levels, thyroid functions and the bilirubin levels (p > 0.01).

CONCLUSION

The jaundiced babies had lower urine oidine levels than the control population. Since, there was no significant difference in the levels of the thyroid hormones, no cause and effect relationship could be inferred between iodine deficiency and jaundice.

A preliminary study on pharmacokinetics of oral indomethacin in premature infants in north India

BACKGROUND & OBJECTIVES

Patent ductus arteriosus (PDA) is a frequent complication in premature infants. Intravenous indomethacin is the standard mode of medical therapy and has been shown to be efficacious in closing the ductus. In our setup, oral indomethacin is being regularly used for medical treatment of suspected or clinically diagnosed PDA. Non-availability of the parenteral preparation and lack of information regarding the pharmacokinetic disposition of indomethacin in the premature infants in north Indian population led us to conduct this pharmacokinetic study with oral indomethacin.

METHODS

Twenty premature infants with gestational age 30.3 +/- 0.3 wk and birth weight, 1209.8 +/- 39.5 g; admitted to the neonatal unit of the Nehru Hospital, Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh were enrolled in the study. Indomethacin was administered in a single oral dose of 0.2 mg/kg and blood samples were collected through an indwelling vascular catheter at 0 and 1, 2, 4, 8 and 12 h after administration of indomethacin. Plasma indomethacin concentrations were assayed by spectrofluorometric technique.

RESULTS

Large interindividual variability was observed for peak plasma concentrations (Cmax; 137.9 +/- 14.0 ng/ml), elimination half-life (t1/2 el; 21.4 +/- 1.7 h) and area under the plasma concentrations time curve (AUC0-infinity;4172 +/- 303 ng.h/ml) in these infants. Variables like birth weight, and sex did not have any sigiificant effect on indomethacin pharmacokinetics. However, the plasma t1/2 el of indomethacin was significantly (P < 0.01) larger in older infants (gestational age > 30 wk) in comparison to younger ones (gestational age < or = 30 wk). There was a negative correlation between gestational age and elimination t1/2 (r = -0.77).

INTERPRETATION & CONCLUSION

In conclusion, indomethacin pharmacokinetics showed a wide variability in premature infants. In view of these findings it can be suggested that infants of smaller gestational age are at greater risk of cumulative toxicity if more than one dose of indomethacin is given. With advancing age, metabolism as well as elimination of drug is faster that may require modification in indomethacin dose to achieve therapeutic response. These preliminary results may be of use in designing future pharmacokinetic studies of oral indomethacin in preterm neonates on a larger sample.

Postasphyxial encephalopathy in preterm neonates

OBJECTIVE

Perinatal asphyxia is an important determinant of infant neurological outcome. There are very few studies looking exclusively at postasphyxial encephalopathy in preterm neonates.

METHODS

We studied the neurologic and sonographic abnormalities in 40 preterm babies with severe birth asphyxia during their hospital stay and till 3 months corrected age.

RESULT

87.5 % of the asphyxiated preterm babies had neonatal neurologic abnormality, compared to only 17% of the control babies (p<0.0001). Generalised hypotonia and reduced activity were the commonest abnormalities (observed in 85% of asphyxiated babies) while depressed sensorium (60%) and seizures (35%) were seen in more severe cases. White matter disease (WMD-including periventricular flare, cerebral edema and periventricular leucomalacia) was significantly more frequent in the study cases (34.5% in study cases vs 7.5% in controls, p<0.0001) as was grade 3/4 intraventricular hemorrhage(IVH) (25% in study cases vs 2.5% in controls, p<0.0001). There was 11 fold higher mortality among the asphyxiated babies (23 deaths in study cases vs 2 in controls, p<0.0001).

CONCLUSION

The survivors had a significantly higher incidence of both mild and severe neurological abnormalities at corrected age of 3 months among the asphyxiated babies. There was a good correlation between the severity of the neonatal encephalopathy as well as the sonographic findings and the outcome.

Melanotic neuroectodermal tumour of infancy: a case report

Melanotic Neuroectodermal Tumour of Infancy is a rare tumour. Prompt recognition of such a case is essential for the Pediatric Dentist Presented here is a case of a four and a half month old child who reported in the dental out patient department of Guru Teg Bahadur Hospital with a swelling in the right anterior maxillary ridge region.

A mathematical model for chemoattractant gradient sensing based on receptor-regulated membrane phospholipid signaling dynamics

The crawling movement of cells in response to a chemoattractant gradient is a complex process requiring the coordination of various subcellular activities. Although a complete description of the mechanisms underlying cell movement remains elusive, the very first step of directional sensing, enabling the cell to perceive the imposed gradient, is becoming more transparent. A fundamental problem of directional sensing is its exquisite sensitivity. Even in the presence of relatively shallow chemoattractant gradients, cell projections are extended precisely in the region exposed to the highest chemoattractant concentration. This reflects the existence of a mechanism for amplifying the external signal. Recent experiments have identified a potential candidate for the seat of this amplification-membrane phosphoinositides such as PI4,5P2 and PI3,4,5P3 appear to be the first components of the signal transduction pathway to be amplified. Perturbing the cell with various chemoattractant gradients reveals a rich spectrum of phosphoinositide dynamics (Parent, C. A., and P. N. Devreotes. Science 284:765, 1999). The goal of this work is to develop a mathematical model of these phosphoinositide dynamics. Specifically, we address the following questions: (a) Which signaling pathway could lead to the localized accumulation of membrane phosphoinositides? (b) Why is this accumulation independent of the slope and mean value of the chemoattractant gradient? The model is based on the phosphoinositide cycle that transfers phosphoinositides between the plasma membrane and endoplasmic reticulum. We show that a mathematical model taking due account of receptor desensitization and the reaction-diffusion processes of the phosphoinositide cycle captures many of the experimentally observed dynamics. Having shown the plausibility of the model with respect to directional sensing, we discuss its implications for lamellipod extension, the process that follows directional sensing.

Early onset mixed Morganella and Klebsiella sepsis in a neonate

A premature baby girl was delivered vaginally to a mother who had an otherwise normal pregnancy, and spontaneous premature onset of labour. She had early onset neonatal sepsis with pneumonia. The baby's blood culture as well as the amniotic membrane culture grew Morganella and Klebsiella. She recovered on appropriate antibiotics. This is only the second reported case of early onset neonatal sepsis due to Morganella. The literature is reviewed.