Diagnosis of mycobacterial infections by PCR and restriction enzyme digestion

A method for the diagnosis of mycobacterial infections by PCR amplification followed by selective restriction enzyme digestion of the PCR product was developed. The amplified DNA sequence used in this study occurs within the gene encoding for the mycobacterial 65 kDa heat shock protein (Hance et al. 1989), which is found in all mycobacteria. However, there are minute differences in the amplified sequence from the Mycobacterium tuberculosis complex compared with the corresponding sequence from the Mycobacterium avium complex. These differences made it possible to rapidly identify to which mycobacterial complex a particular sample belonged by restriction enzyme digestion of the PCR product. A total of 66 samples were tested and all of them were correctly identified. This and similar methods should provide a sensitive, specific and rapid (within 12 h) way of diagnosing mycobacterial infections to the species level.

Human immunodeficiency virus type 1 enhances intracellular growth of Mycobacterium avium in human macrophages

Disseminated Mycobacterium avium infections are common in patients with AIDS and result in a reduced life expectancy. Human monocytes/macrophages are important target cells for both human immunodeficiency virus (HIV) and M. avium. We have studied the interaction in vitro of M. avium and HIV type 1 (HIV-1) in human macrophages. Human monocytes isolated from the peripheral blood of healthy individuals were infected with HIV-1, M. avium, or both. The intracellular growth of M. avium and the replication of HIV-1 were monitored for up to 5 weeks. Intracellular mycobacterial growth was seen in all M. avium infected cell cultures and was paralleled by increased production of interleukin 1 alpha and beta. Preinfection of the macrophages with HIV-1 reduced the interleukin 1 production and accelerated the intracellular growth of M. avium. These findings may explain in part the impaired control of mycobacterial infections seen with patients with AIDS.

Mycobacterium malmoense: an easily missed pathogen

The BACTEC system (Becton Dickinson, Sparks, Md.) was compared with culture on Löwenstein-Jensen egg medium for the detection of Mycobacterium malmoense in lymph node samples from children with lymphadenitis. It was found to be significantly more sensitive and rapid. The use of the BACTEC system is thus recommended as a complement to culture on solid media for the primary isolation of atypical mycobacteria, such as M. malmoense.

Serovars of Mycobacterium avium complex isolated from patients in Sweden

The serovars of clinical isolates of Mycobacterium avium complex from 24 acquired immunodeficiency syndrome (AIDS) and 140 non-AIDS patients in Sweden were studied by using type-specific antisera. A wide distribution of serovars was seen. Serovar 6 was predominant in both groups of patients, isolated from 33 and 16% of the AIDS and non-AIDS patients, respectively. The results indicate geographical as well as disease-related differences in the distribution of M. avium complex serovars of clinical importance.

Prospective study of mycobacterial infections in patients with cystic fibrosis

Fifty four patients with cystic fibrosis, aged 3-67 years, were studied prospectively for pulmonary mycobacterial infection. Sputum smears and cultures were carried out and intradermal skin tests performed. Mycobacteria were cultured from six patients in association with clinical deterioration; four patients had positive direct smears. Mycobacterium tuberculosis, M aviumintracellulare, M kansasii, and M gordonae were isolated. There were no deaths and all improved with chemotherapy. A third of the other 48 patients had positive skin test responses (greater than 6 mm) to purified protein derivative (PPD) tuberculin and 21 to one or more antigens prepared from non-tuberculous mycobacteria. Sensitisation increased with age; before the age of 11 only one patient had a positive response to PPD tuberculin and none to any other antigen. This was less than in healthy control subjects of similar age. After age 11 the reactions in sensitised patients were stronger than in positive healthy control subjects. Our study indicates that it is important to consider mycobacterial infection in patients with cystic fibrosis who deteriorate without obvious cause.

Susceptibility of mycobacteria to fusidic acid

Fusidic acid was shown to be effective in vitro against 30 clinical isolates of Mycobacterium tuberculosis at concentrations of 32-64 mg/l, concentrations which are readily achieved in serum. All but one of 17 Mycobacterium avium complex strains were resistant to fusidic acid at concentrations up to 64 mg/l. However, synergistic effects were shown for 11 of the 17 strains when fusidic acid was combined with ethambutol. Five of the strains were fully susceptible to the combination of fusidic acid (64 mg/l) and ethambutol (4 mg/l). It is suggested that fusidic acid should be evaluated clinically as a potential supplementary drug for treatment of mycobacterial infections.

In-vitro synergistic activity between ethambutol and fluorinated quinolones against Mycobacterium avium complex

Ciprofloxacin, ofloxacin and norfloxacin were ineffective at clinically relevant concentrations against the Mycobacterium avium complex (MAC) in vitro as measured by radiometric respirometry. Only two of 30 clinical isolates of MAC were susceptible to any of the tested quinolones. By contrast good antibacterial activity was obtained when any of the quinolones was combined with ethambutol. The synergistic effect was most pronounced for the combination of ethambutol and ciprofloxacin, to which 76 of 100 strains were susceptible. It is suggested that the synergism is based on an enhanced penetration of the quinolones by ethambutol.

Pneumocystis carinii is not a major cause of pneumonia in HIV infected patients in Lusaka, Zambia

The clinical occurrence of Pneumocystis carinii and Mycobacterium tuberculosis was investigated in patients infected with human immunodeficiency virus (HIV) who had clinical pneumonia of unknown aetiology in Lusaka, Zambia. The results were compared with a similar group of patients in Stockholm, Sweden. Induced sputum samples were stained for Pneumocystis by indirect immunofluorescence using monoclonal antibody 3F6 and toluidine blue O. Mycobacterial culture and acid fast stain were performed on the specimens from Lusaka. P. carinii cysts were detected in none of 27 Lusaka patients, compared to 10 of 33 Stockholm patients. M. tuberculosis was identified in 11 of 22 Lusaka patients tested. In conclusion, P. carinii could not be incriminated as the aetiological agent of HIV-associated pneumonia in Zambia in contrast to the situation in Sweden, where Pneumocystis is the dominating aetiological agent.

Does vaccination with bacille Calmette-Guérin protect against AIDS?

In the United States a majority of patients with AIDS are infected with bacteria of the Mycobacterium avium complex (MAC), while in Sweden only approximately 10% of AIDS patients are so infected. It is proposed that general vaccination with bacille Calmette-Guérin (BCG) in Sweden may have induced protection not only against tuberculosis but also against infections with MAC, accounting for the lower incidence of MAC infection in Swedish patients with AIDS. The current AIDS pandemic may indicate a need for reevaluation of national BCG vaccination policies.

Influence of age on faecal carriage of P-fimbriated Escherichia coli and other gram-negative bacteria in hospitalized neonates

The aerobic faecal flora of 953 infants aged over 5 days was studied on discharge from 22 neonatal wards in Swedish hospitals. Klebsiella/enterobacter was isolated from 74% of infants and dominated the aerobic gram-negative flora in 19 wards. Escherichia coli was carried by 42% and showed a slight dominance in two wards. Initially klebsiella/enterobacter dominated the flora but became increasingly mixed with and taken over by E. coli, carriage increasing from 21% in infants discharged after 5-7 days to 57% after 3 weeks or later. Among infants with E. coli, P-fimbriated strains were demonstrated in 23% (range 0-67) and were independent of age. Occasional clustering of such strains was observed in 3/22 wards during the study period. It is postulated that the general and local colonization patterns observed reflect differences between individual strains of E. coli and klebsiella in both their capacity for transmission and their persistence in the newborn gut. The role of P-fimbriae in intestinal colonization of neonates by E. coli was, however, not supported.

P-fimbriae receptors in patients with chronic pyelonephritis

The adherence of fluorescein isothiocyanate-labeled P-fimbriated Escherichia coli to uroepithelial cells from 19 women with chronic pyelonephritis was determined with the fluorescence-activated cell sorting technique. The application of this method has made it possible to study bacterial binding to a large number of cells. Renal function was determined in all patients and the recurrences of P-fimbriated Escherichia coli bacteriuria, cystitis and acute pyelonephritis during a 3-year followup were studied. We found a significant correlation between the P-fimbriae receptor accessibility on uroepithelial cells and glomerular filtration rate (r equals -0.75, p less than 0.001). Uroepithelial cells from the patients with chronic pyelonephritis and renal insufficiency had a higher binding capacity of P-fimbriated Escherichia coli than uroepithelial cells from patients with a normal glomerular filtration rate. There was no correlation between kidney function and the availability of P-fimbriae receptors in a control group of patients with polycystic kidney disease.

Susceptibility of streptomycin-resistant Mycobacterium tuberculosis strains to amikacin

A total of 585 Mycobacterium tuberculosis strains isolated during a three-year period in Sweden were tested for in vitro susceptibility to amikacin in comparison with streptomycin. Resistance to streptomycin was seen in 27 of the isolates (4.6%). These isolates had been obtained from 22 patients, a majority of which were non-European immigrants. All but one of the streptomycin-resistant isolates were susceptible to amikacin. None of 263 streptomycin-susceptible isolates tested was resistant to amikacin. Amikacin appears to be an alternative to streptomycin in the treatment of patients with streptomycin-resistant Mycobacterium tuberculosis.

Faecal colonization with P-fimbriated Escherichia coli between 0 and 18 months of age

A prospective study of faecal colonization with P-fimbriated Escherichia coli between 0 and 18 months of age was conducted in 751 healthy infants. The influence of breast-feeding and treatment with antibiotics on this colonization was studied. Colonization with P-fimbriated E. coli increased with age from 10% at 6 days to 30% at 18 months of age (P less than 0.01). Breast-feeding influenced colonization at 6 weeks of age when breast-fed children harboured fewer bacterial species (P less than 0.001) and fewer P-fimbriated E. coli (P = 0.06) than bottle-fed infants. Treatment with antibiotics increased the colonization rate with P-fimbriated E. coli at the age of 11 months (P less than 0.05). However, this was not true for treatment with ampicillin, which increased colonization rate with Gram-negative species other than E. coli (P less than 0.05). Fifty per cent (378) of all children were colonized and a quarter (183) had pure cultures of P-fimbriated E. coli in at least one faecal sample. The clinical importance of this colonization remains to be shown.

Synergistic effects of antimycobacterial drug combinations on Mycobacterium avium complex determined radiometrically in liquid medium

A technique to determine the effects of combining antimycobacterial drugs in liquid medium employing the radiometric growth readings in the Bactec system was tested using 20 Mycobacterium avium complex strains. Ten of the strains had been isolated from children with lymphadenopathy and ten from adults with pulmonary disease. All isolates were resistant to streptomycin, rifampicin, isoniazid and ethambutol when tested with a conventional resistant ratio technique on Löwenstein-Jensen medium. Synergistic interactions were shown for the two-drug combinations streptomycin + ethambutol and ethambutol + rifampicin against all 20 strains. Good efficacy was also found for all three-drug combinations containing ethambutol. Thus, although most isolates of the Mycobacterium avium complex are resistant to first-line antituberculous drugs when tested individually, they are susceptible in vitro to certain combinations of these drugs. This rapid radiometric assay is an efficient means for detecting such synergy.

The use of biochemical markers, serotype and fimbriation in the detection of Escherichia coli clones

Biochemical reactions, O and K serotypes and presence of P-fimbriae were analysed in 116 Escherichia coli strains isolated in blood cultures from patients with bacteraemia and in 99 faecal strains isolated from healthy individuals. By using biochemical typing, the strains could be grouped into six main clusters with similarity index less than 0.8 (Gower, 1971) and altogether 16 subclusters with similarity index 0.82-0.89. The most discriminating tests between the clusters were fermentation of D-tagatose, saccharose, salicin and sorbose. No single biochemical property could differentiate bacteraemic isolates from faecal strains, although strains isolated from blood were significantly more often found in certain subclusters, whereas other subclusters contained mainly control strains. Bacteraemic strains possessed P-fimbriae more often, especially strains isolated from patients with E. coli in the urine concomitantly with bacteraemia. Equally, no single reaction could separate P-fimbriated from non-P-fimbriated strains. D-Tagatose was fermented more often by the P-fimbriated strains; on the other hand, melibiose and lactose fermentation tests were less often positive. Certain O serotypes (O1, O4, O6, O7, O18 and O25) were more common among bacteraemic isolates than controls. K serotypes such as K1, K5 and K52 were also more frequent among blood isolates. We conclude that a combination of biochemical tests, fimbriation and serotyping might be used to identify potentially pathogenic clusters of E. coli.

P-fimbriated Escherichia coli in children with acute cystitis

P-fimbriation of Escherichia coli is an important factor in the pathogenesis of childhood pyelonephritis. The present study investigates children with single episodes of symptomatic non-febrile urinary tract infection, i.e. cystitis, with respect to clinical appearance and bacteriology, especially the frequency of P-fimbriated E. coli. The study included 75 children, 57 of whom had their first attack of urinary tract infection. E. coli was the causative agent in 88% (66/75) of the infections, and 48% (32/66) of E. coli strains were P-fimbriated. No association was found between identification of P-fimbriated E. coli at index infection and proneness to reinfection during the following six-month period. It is suggested that P-fimbriated E. coli is a virulence factor even in lower urinary tract infections, when occurring in single, symptomatic episodes.

Epidemiological aspects of P-fimbriated Escherichia coli. IV. Extraintestinal E. coli infections before the age of one year and their relation to fecal colonization with P-fimbriated E. coli

In two retrospective studies we have found outbreaks of E. coli pyelonephritis and septicemia to be due to nosocomial spread and fecal colonization with virulent E. coli strains in the neonatal ward of Danderyd Hospital. The incidence of extraintestinal E. coli infections before the age of one year was therefore prospectively studied in all children born at Danderyd Hospital during two and a half years (n = 7963). The number of infections was correlated to the previous fecal colonization with P-fimbriated E. coli. During this study we found no outbreaks of E. coli infections. The incidence of E. coli pyelonephritis before the age of one year was 0.6-0.7%, which we propose to be a baseline incidence. This corresponds well with the low incidence of fecal colonization with P-fimbriated E. coli found among these children. Fecal colonization with P-fimbriated E. coli during this non-epidemic period had no predictive value for the individual child for the later development of pyelonephritis.

Symptomatic recurrent urinary tract infections in patients with renal scarring in relation to fecal colonization with P-fimbriated Escherichia coli

We evaluated prospectively 49 women with renal scarring and a history of febrile urinary tract infections in regard to the incidence of recurrent symptomatic urinary tract infection and fecal colonization with P-fimbriated Escherichia coli. During a 3-year followup 26 patients (53 per cent) had symptomatic urinary tract infection (0.036 infections per patient-month), including 8 (16 per cent) who had 9 new episodes of febrile urinary tract infection, while 33 (67 per cent) had Escherichia coli bacteriuria (10(5) bacteria per ml. urine in pure culture). Thus, patients with previous febrile urinary tract infections and renal scarring have a high risk for recurrent infections. For comparison, the incidence of symptomatic urinary tract infection also was determined in 35 women with a recent episode of acute nonobstructive pyelonephritis and with normal kidneys on excretory urography. These patients had 0.031 symptomatic infections per patient-month. The fecal flora were examined twice a year for P-fimbriated Escherichia coli in 48 patients with renal scarring. Of these patients 21 (44 per cent) had at least 1 fecal colonization with a P-fimbriated Escherichia coli strain. However, in only 1 instance was a relationship detected between the presence of P-fimbriated Escherichia coli in the fecal flora and the development of subsequent febrile urinary tract infection. The findings indicate that fecal sampling twice a year is not of value to predict future urinary tract infections in adults with renal scarring.

Epidemiological aspects of fecal colonization with P-fimbriated Escherichia coli in neonates

Fecal colonization with P-fimbriated Escherichia coli has caused epidemic outbreaks of extraintestinal E. coli infections in the neonatal unit of Danderyd Hospital. The aerobic fecal flora was therefore studied in 1,955 newborn children born at Danderyd Hospital during a period of 2.5 years. E. coli was found in 58% of the maternity ward children and in 57% of the neonatal unit children. A P-fimbriated strain was found in 12% and 17% of the children, respectively (p less than 0.01). There was a significant increase in the frequency of children colonized with E. coli, and especially P-fimbriated E. coli, with length of stay in the neonatal unit. There was a statistical correlation between bed occupancy and colonization with P-fimbriated E. coli (r = 0.46, p less than 0.01) during this study period. We found an incidence of P-fimbriated E. coli of 10 to 20% among the E. coli strains isolated from the fecal specimens which we regard as the baseline incidence.