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.

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.

A geographical study of antibodies to membrane antigens of HSV-2-infected cells and HSV-2-specific antibodies in patients with cervical cancer.

Sera was obtained from patients with squamous carcinoma of the cervix from Great Britain (29), Sri Lanka (32), Malawi (27), and Sudan (27), and from controls from all countries except Sudan. Controls were matched for ethnic origin, age and social class. Sera were tested by indirect immunofluorescence (IF) for IgG and IgA antibodies to membrane antigens (MA) and IgA antibodies to VCA of HSV-2 infected cells. Compared with controls, IgA antibodies to MA (IgA anti-MA) were detected more frequently and at higher titres in all groups of patients. However, there was no significant difference in prevalence of these antibodies at titres greater than or equal to 1:4 between Malawian patients and controls, although a significantly higher proportion of patients had IgA anti-MA titres of greater than or equal to 1:16. In contrast, IgA anti-VCA did not distinguish patients from controls. More than 90% of both patients and controls from all countries had IgG antibodies to MA (IgA anti-MA). Malawian patients had a significantly higher geometric mean titre (GMT) of IgG anti-MA than controls and both patients and controls had significantly higher GMTs than their counterparts from other countries. The variation between herpes IgG anti-MA titres in subjects from different countries did not reflect differences in serum immunoglobulin levels and similar variations in titre were not seen in rubella and measles HAI titres. Among the patients there was a geographical variation in the prevalence of HSV-2 specific antibodies detected by ELISA, which varied from 52% among British and Sudanese patients to 73% among Malawian patients. Even when adjustment was made for possible false negative results, there were between 10 and 31% patients without HSV-2-specific antibodies, although only 2 of 103 (1.9%) patients had neither HSV-1 nor HSV-2 antibodies. The association of HSV-2 with cervical carcinoma appeared to vary with age.