Group G streptococcal infections on a dermatological ward.

Groups A, B, C and G streptococci were cultured from 63 consecutive in-patients recruited between November 1987 and April 1988 and monitored until the end of July 1988. Chronic leg ulcers were present in 34 patients. Group G was found in 34 patients, 25 of whom had pyoderma and 3 had sepsis. Six of the patients had no signs of clinical infection, and treatment with antibiotics was therefore withheld. Recurrent phlegmon or erysipelas developed in 2 of 28 patients with clinical Group G infections. Erysipelas developed some 1-7 months later in 3 of the 6 patients who were not initially treated. No significant difference in severity or additional medical conditions was found between the patients with either Group G or Group A streptococci. In comparison, data on all streptococcal cultures at the Department indicated that Group G was isolated 2.6 times as often as Group A streptococci for the in-patients, compared with 1.1 for all patients seen. It is concluded that Group G streptococcal skin infections must be regarded with the same clinical vigilance as Group A infections.

Streptococcal throat infection: calculation of test standards and a comparison between an antigen detection test and culture.

The standard minimum sensitivity (94%) and minimum specificity (89%) of a group A streptococcus (GAS) test were calculated, assuming that no more than 10% false positive and no more than 2% false negative test results should be allowed. The clinical judgement of the need for immediate antibiotic treatment in tonsillitis/pharyngitis was an unreliable indicator of a GAS aetiology, 20-29% of the results being false positive and 2-10% false negative. The rapid antigen detection test Tandem Icon Strep A was not sensitive enough to be used as a single test, though it was specific enough. The sensitivity of culture almost reached the standard demand. Two combinations of rapid test and culture (sequence testing) were superior to the rapid test, but were not significantly better than culture.

Septicemia in patients with hematological disorders and neutropenia. A retrospective study of causative agents and their resistance profile.

In order to identify the cause of septicemia and the resistance patterns of bacteria in Swedish patients with hematological disorders, all positive blood cultures collected at a hematological ward during 1980-1986 were evaluated retrospectively. 198 episodes of septicemia in 129 patients were recorded. 54% were males and 46% women with a median age of 67 years (range 16-88). Patients with acute leukemia (46%), lymphoma (19%) and myeloma (19%) dominated. The absolute neutrophil count (ANC) was less than 0.5 x 10(9)/l in 76% of the bacteremic episodes. A total of 253 consecutive isolates were found with 53% Gram-negatives and 47% Gram-positives. The dominating pathogens were Escherichia coli (27%), klebsiella/enterobacter (15%), pseudomonas (7%), coagulase negative staphylococci (13%), alpha-streptococci (13%), Staphylococcus aureus (10%) and anaerobes (6%). Coagulase negative staphylococci showed a significant increase in isolation rate during the study period. The majority of E. coli were resistant to ampicillin. The susceptibility of klebsiella/enterobacter to ceftazidime and cefuroxime was reduced, while no imipenem resistant strains occurred. Among coagulase negative staphylococci 61% were resistant to isoxazolylpenicillin, none to vancomycin. No dramatic changes in the etiology of septicemia or the susceptibility pattern during the study period were noticed. Coagulase negative staphylococci, S. epidermidis in particular, constitute an increasing problem among granulocytopenic patients.

Bacteria on stumps of amputees and the effect of antiseptics.

Amputees get stump infections usually from the natural inhabitants of the healthy skin and probably due to the unnatural environment of tight fitting sockets. The aim of the present study was to investigate the natural stump bacteria and the effect of antiseptics as well as the amputees' evaluation of such treatment. Fifteen amputees using their prostheses all day were investigated. Bacterial samplings were taken by swab technique with respect to bacteria and fungi from the stumps in the morning before prosthetic application and in the evening after a whole day's prosthetic use without antiseptic cleaning; after antiseptic cleaning with a combination of Isopropanol 45%. N-propanol 30% and N-cetyl-pyridiniumchloride 0.2% for one day: after fourteen days continuous use. The patients were asked if they liked the antiseptic and if they would like to continue to use it. Two patients did not submit bacteriological samples after the cleaning period. Before cleaning S. epidermidis, S. aureus and alpha-hemolytic streptococci were commonly found. In two instances gram negative rods were found. After the cleaning period there was a reduction of bacteria in 11 out of 13 patients. All patients liked the antiseptic and the simplicity by which the stumps and the sockets could be kept clean. The authors feel that the use of antiseptics to increase stump and socket hygiene is justified.

Types of interpretive errors in susceptibility testing. Zone breakpoints for norfloxacin disk diffusion testing.

A total of 548 strains of the eleven most common urinary tract pathogens were investigated for possible errors in norfloxacin susceptibility tests comparing MIC determinations with disk diffusion assays. Most strains were found to be sensitive with MIC-90 values below 1.0 for the Enterobacteriaceae while the classical nalidixic acid resistant species, the gram-positive bacteria and Pseudomonas aeruginosa, were less susceptible to norfloxacin with MIC-90 above 1.0 mg/l. MIC-values close to interpretive MIC-limits were recorded for S. faecalis and S. agalactiae using the recommendations of the national Committee for Clinical Laboratory Standards (NCCLS) (susceptible, S less than or equal to 4.0) and for P. aeruginosa and S. aureus using the Swedish Reference Group for Antibiotics (SRGA) standards (S less than or equal to 1.0). Susceptibility interpretations for these species showed a lack of accuracy consistent with methodological problems of reproducibility, an error called type I. The changes in the MIC-limits required for these strains to correct the error would be S less than or equal to 4 for P. aeruginosa and S. aureus, S less than or equal to 8 for S. agalactiae and S less than or equal to 0.5 for S. faecalis. A type II error, occurring when a bacterial species shows a regression line different from the regular line, was also identified for S. saprophyticus. The use of breakpoints derived from single strains regression analysis corrected this error and also reduced the frequency of similar misinterpretations in other species. The term "species-specific MIC-limits" should be introduced along with the established concept of "species-specific interpretive zone breakpoints" to allow for the correction of type I interpretive errors. Type II errors can be corrected by using species-specific interpretive breakpoints, either issued by reference laboratories or derived by calculations from single-strain regression analysis in the individual laboratory.

Species-specific interpretive breakpoints for ciprofloxacin disk diffusion susceptibility testing.

When ciprofloxacin was introduced on the Swedish market the recommended interpretive standards for disk diffusion susceptibility testing using a 10 microgram disk were: Sensitive greater than or equal to 24 mm (MIC less than or equal to 1 mg/l) and Resistant less than 18 mm (MIC greater than 4 mg/l), except for enterococci where S greater than or equal to 18 mm and R less than 14 mm were recommended. A quality control study revealed that the accuracy of the routine susceptibility testing of ciprofloxacin was low. 50% of the strains of Staphylococcus aureus and 90% of Streptococcus agalactiae strains were falsely assigned to the intermediate instead of the sensitive category, and the test missed to detect true resistance in Pseudomonas maltophilia. New species-specific breakpoints were determined by the SRA method. Separate breakpoints were required only for the pseudomonas species. Streptococcus faecalis was found to belong mainly to the intermediate group and it is suggested that these strains are not categorized as sensitive. The breakpoints that gave acceptable accuracy in routine susceptibility testing of ciprofloxacin were S greater than or equal to 20 mm, R less than 13 mm for all relevant bacteria except Pseudomonas aeruginosa for which S greater than or equal to 27 mm, R less than 18 mm is proposed, and Pseudomonas maltophilia where S greater than or equal to 30 mm, R less than 23 mm are adequate breakpoints. The 10 microgram disk gave acceptable inhibition zones for all strains with MICs within the clinically interesting MIC range.

Role of exotoxin A and elastase in the pathogenicity of Pseudomonas aeruginosa strain PAO experimental mouse burn infection.

We examined the virulence of Pseudomonas aeruginosa strain PAO and xcp (extracellular proteins deficient) and xch (extracellular proteins hyperproducing) mutants derived from strain PAO in an experimental mouse burn infection model. The results showed that xcp mutants, which produced little or no extracellular elastase and exotoxin A, were as virulent as their corresponding xcp+ strains. The xch mutants produced more elastase and exotoxin A than the wild type strain, however, they had significantly lower virulence, probably due to reduced ability of these strains to take up iron. Treatment of mice with ferric ammonium citrate had no effect on the wild type strain but enhanced mortality in mice challenged with xch mutants. Neither elastase nor exotoxin A seem to play any role in burn infections with P. aeruginosa strain PAO. However, ability for iron uptake is an important virulence factor.

Genetic mapping and characterization of Pseudomonas aeruginosa mutants that hyperproduce exoproteins.

We isolated two mutants of Pseudomonas aeruginosa PAO with defective iron uptake. In contrast to the wild-type strain, the mutants produced extracellular protease activity in media containing high concentrations of salts or iron and hyperproduced elastase, staphylolytic enzyme, and exotoxin A in ordinary media (Xch mutants). The mutations were located in the 55' region of the chromosome, between the markers met-9011 and pyrD.