Comparison of minimum inhibitory concentrations to methicillin in heterogeneous and homogeneous methicillin resistant Staphylococcus aureus.

OBJECTIVE: To determine the minimum inhibitory concentration (MIC) to methicillin and compare it with the type of methicillin resistance in methicillin resistant Staphylococcus aureus (MRSA) isolated from clinical samples, and to evaluate the usefulness of beta-lactamase resistant penicillins such as cloxacillin for treatment of minor MRSA infections. DESIGN: Sixty-five strains of MRSA isolated from clinical samples were studied. Homogeneous and heterogeneous resistance to methicillin of these strains was determined by an efficiency of plating technique. The MICs to methicillin of all homogeneously resistant strains and an equal number of heterogeneously resistant strains were determined by the 'E' test. SETTING: General Hospital, Colombo; De Soysa Maternity Hospital for Women; Lady Ridgeway Hospital for Children. RESULTS: 171 strains of S aureus were isolated from specimens processed in the laboratory of the Department of Microbiology, Faculty of Medicine Colombo, during a 14-month period. Seventy (40.9%) were methicillin resistant. Fifty-three MRSA strains (81.5%) were heterogeneously resistant to methicillin. Only 12 of 65 strains were homogeneously resistant. Nine of 12 of the homogeneously resistant strains were from surgical wards. MICs for methicillin in the two groups were compared. Six of 12 (50%) homogeneously resistant strains had very high levels of resistance to methicillin (MIC > 200 micrograms/ml). In contrast the MICs of all the heterogeneously resistant strains ranged from 16 micrograms/ml to 96 micrograms/ml. CONCLUSIONS: The majority of clinical isolates of MRSA from hospitals in Colombo, Sri Lanka were heterogeneously resistant to methicillin with lower MICs for methicillin than the homogeneously resistant strains. Thus, beta-lactamase resistance penicillins such as cloxacillin may have a place in the treatment of minor MRSA infections. Surveillance studies to determine if there is an increase of homogeneously methicillin resistant MRSA are required.

Emergence of penicillin resistant pneumococci in Sri Lanka.

Two strains of penicillin resistant (PR) pneumococci were isolated recently from cerebrospinal fluid of two children with meningitis. Penicillin resistance was detected by using a lug disc of oxacillin in the Stokes disc diffusion method. The strains were tested quantitatively for sensitivity to penicillin by an agar dilution technique. The minimum inhibitory concentration (MIC) to penicillin of these strains were 2 micrograms/ml and 0.12 microgram/ml, indicating that respectively they were of frank and intermediate resistance to penicillin. However these strains were sensitive to other antibiotics tested, namely, erythromycin, tetracycline, chloramphenicol, amoxycillin, cephalexin and cefotaxime. Penicillin resistant pneumococci are here in Sri Lanka. Though one strain was of intermediate resistance, therapeutic failure during treatment with penicillin was evident in this case.

Bacteria, viruses, yeasts and protozoans associated with diarrheal disease in Singapore.

Labile toxin producing enterotoxic E. coli (ETEC) were the commonest pathogen isolated from diarrheal stools of hospitalized children (21%) and adults (26%) in Singapore. Salmonellas ranked a close second in children (19%). Other bacterial pathogens were isolated from less than 5% of subjects. Blastocystis hominis was detected in 4.3% of diarrheal stools when a simple sedimentation technique was used. Cryptosporidium was not detected at all. An analysis of yeast counts in smears of diarrheal and non-diarrheal stools suggested they were etiologically associated with at least 6% of diarrhea in children and 19% in adults. Testing for rotaviruses by Latex agglutination and for adenovirus by electronmicroscopy showed an association with 6 per cent and 3 per cent diarrhea respectively. The study highlighted a need for: case control studies on ETEC and B. hominis; studies on the epidemiology of diarrhea by yeasts; establishing the true incidence of adenovirus diarrhea; studies on the prevalence and seasonality of rotavirus infection in Singapore.

Serum and coproantibody responses to rotavirus infection in children during the first two years of life.

The serum and coproantibody response (IgG and IgA) to naturally acquired rotavirus infections and reinfections in the first two years of life were studied in 13 cases and 12 control children using enzyme-immunoassay. A 100% IgG seroconversion and coproconversion occurred after tertiary and quaternary infections respectively. Unlike the IgA coproantibody response, serum IgG was detected more frequently after symptomatic (89%) than asymptomatic (50%) infections, and its duration and titre were boosted by reinfections. The durations of both responses was prolonged when reinfection occurred at 15 months versus 8 months. Both responses were observed after primary infection in the first two months of life. Higher instances of virus reinfections were detected serologically (72.5%) than virologically (27%). The results suggest that at least 3 doses of a rotavirus vaccine will be required before 4 months plus boosters around the 10th and 15th months. Further, during vaccine trials, virus infections should be monitored virologically and serologically.

Concentrations of interleukin 6 and tumour necrosis factor in serum and stools of children with Shigella dysenteriae 1 infection.

Serum interleukin 6 (IL-6) and tumour necrosis factor (TNF) were measured in children with dysentery during an epidemic caused by Shigella dysenteriae 1. IL-6 and TNF were also measured in fresh stool filtrates from children with acute gastroenteritis. The median serum IL-6 concentration was raised significantly in the children with complications (haemolytic uraemic syndrome, leukemoid reaction, thrombocytopenia, thrombocytosis, and severe colitis lasting more than one week) during the first week (n = 18, 9-7728 pg/ml; median 107) and in the second week (n = 13, 5-312 pg/ml; median 77), compared with convalescent sera (n = 10, < 3-85 pg/ml; median 39; p < 0.02 and < 0.05 respectively). The median IL-6 concentration during the first week was significantly higher in the group with complicated disease than in those with no complications (n = 8, < 3-37 pg/ml; median 5; p < 0.001). Although serum TNF concentrations were significantly raised in the complicated group during the first and second weeks of the illness and in the uncomplicated group compared with convalescence, there was no significant difference in the TNF concentrations between the complicated and uncomplicated groups. IL-6 was detectable in stool filtrates from eight of 13 children with S dysenteriae 1 infection and four of eight children with S flexneri infection. It was not detectable in Cryptosporidia, rotavirus, or adenovirus infections, those with pathogen-negative acute diarrhoea or controls. Seven of 13 children with S dysenteriae 1 and three of nine children with S flexneri infections had TNF detectable in stools. None of the children with Salmonella, Cryptosporidia, rotavirus of children with pathogen-negative diarrhoea and controls had detectable TNF in stool filtrates. It is postulated that the local and generalised vasculitis observed in shigellosis may be related to a direct effect of Shiga toxin on endothelial cells or caused by cytokine production stimulated by endotoxin, or both.

Serological diagnosis of infection by Shigella dysenteriae-1 in patients with bacillary dysentery.

A total of 192 samples of serum from 113 Sri Lankan patients with clinical dysentery was examined for antibodies of the IgM class to the lipopolysaccharides (LPSs) of Shigella dysenteriae-1 and Escherichia coli O157:H7. By means of ELISA and immunoblotting, 59 patients were found to have serum antibodies to the LPS of S. dysenteriae-1 only. Four samples from one patient were found to contain serum antibodies to the LPSs of both S. dysenteriae-1 and E. coli O157:H7. Antibodies to the LPS of S. dysenteriae-1 were also detected in 16 samples from 25 children, from Sri Lanka, with no previous history of dysentery; one of these children also had antibodies to the LPS of E. coli O157:H7. Analysis of 16 samples from apparently healthy children in the U.K. showed that only one serum contained antibodies to the LPS of S. dysenteriae-1. This patient had a history of recent travel to Pakistan. The isolation of S. dysenteriae-1 remains the preferred test for the diagnosis of bacillary dysentery. The use of serology as a means of providing evidence of infection with S. dysenteriae-1, however may prove to be a useful adjunct to cultural techniques but needs to be validated in an area where this organism is endemic.

Rotavirus infection in children hospitalised with diarrhoea in Sri Lanka.

Seasonal and clinical aspects of rotavirus-associated diarrhoea in 98 of the 326 children hospitalised for diarrhoea are described. Rotavirus infection was detected (30% overall) throughout the year from May 1980 to April 1981, but the prevalence was higher during the rainy season (40-50%). The age group in which rotavirus was detected most frequently was from 4 months to 2 years (34.6%). Watery diarrhoea and vomiting were significantly commoner in children with rotavirus diarrhoea (75% and 71% respectively) than those with non-rotavirus diarrhoea (54.2% and 60.8% respectively; p less than 0.05). Although about 15% of the children with rotavirus-associated diarrhoea showed blood or mucus in stools, the invasive nature of rotavirus infection cannot be drawn since the study did not include tests to detect other diarrhoeal pathogens.

Susceptibility to rubella virus among Sri Lankan women.

Immunity to the rubella virus was tested in 534 women in the childbearing age by the haemolysis-in-gel test, and 228 (43%) were found to be susceptible. This level of susceptibility is higher than that found in most temperate countries and mainland populations, and similar to descriptions in a few island and rural populations in the tropics. Although rubella epidemics do not occur in Sri Lanka, cases of congenital rubella and rubella complicating pregnancy are diagnosed. But the risk of congenital deformity in the foetus is not sufficient cause for a legal abortion in Sri Lanka. Under the circumstances it appears appropriate to use the measles--mumps--rubella vaccine rather than the measles vaccine for vaccination of infants or to introduce rubella vaccination of teen-age girls or female school leavers. Furthermore wherever possible, primipara could be screened by inexpensive methods such as the haemolysis-in-gel test and offered rubella vaccination after partus.

Comparative evaluation of the WHO and DAKOPATTS enzyme-linked immunoassay kits for rotavirus detection.

Faeces obtained from 1,163 children (including 66 newborn babies) were analysed in parallel for the presence of rotavirus particles using two enzyme-linked immunosorbent assay kits. The kits had been formulated by the WHO Collaborating Centre for Reference and Research on Rotavirus (WHO-ELISA kit) and by DAKOPATTS (DAKO-ELISA kit) to be suitable for use in laboratories in developing countries. The kits were evaluated in laboratories in Burma, Chile, India, Mexico, Pakistan, Sri Lanka and the United Kingdom. Comparison of the results obtained with the two kits indicated that the DAKO-ELISA had an overall sensitivity of 97% and a specificity of 97% relative to the WHO-ELISA. In individual laboratories the DAKO-ELISA (K349) kit had a sensitivity in the range 90-100%, and a specificity of 85-100%. The kit showed a sensitivity of 100% and a specificity of 98% in assays on faeces obtained from newborn babies. We conclude that the DAKO-ELISA is as sensitive and specific as the WHO-ELISA for the detection of rotavirus antigen in faeces.

Comparative evaluation of the WHO and DAKOPATTS enzyme-linked immunoassay kits for rotavirus detection

Faeces obtained from 1163 children (including 66 newborn babies) were analysed in parallel for the presence of rotavirus particles using two enzyme-linked immunosorbent assay kits. The kits had been formulated by the WHO Collaborating Centre for Reference and Research on Rotavirus (WHO-ELISA kit) and by DAKIPATIS (DAKO-ELISA kit) to be suitable for use in laboratories in developing countries. The kits were evaluated in laboratories in Burma, Chile, India, Mexico, Pakistan, Sri Lanka and the United Kingdom. Comparison of the results obtained with the two kits indicated that the DAKO-ELISA has an overall sensitivity of 97 per cent and a specificity of 97 per cent relative to the WHO-ELISA. In individual laboratories the DAKO-ELISA (K349) kit had a sensitivity in the range 90-100 per cent in assays on faeces obtained from newborn babies. We conclude that the DAKO-ELISA is as sensitive and specific as the WHO-ELISA for the detection of rotavirus antigen in faeces(AU)