A genetic mechanism for deletion of the ser2 gene cluster and formation of rough morphological variants of Mycobacterium avium.

A major phenotypic trait of the Mycobacterium avium complex is the ability to produce rough and smooth colony variants. The chemical basis of this morphological variation is the loss of an antigenic surface structure, termed glycopeptidolipid (GPL), by rough variants. Using M. avium serovar 2 strain 2151 as a model system, this laboratory previously reported that rough variants arise via the deletion of large genomic regions encoding GPL biosynthesis. One such deletion encompasses the gene cluster (ser2) responsible for production of the serovar 2 GPL haptenic oligosaccharide. In this study, nucleotide sequencing revealed that both ends of the ser2 gene cluster are flanked by a novel insertion sequence (IS1601) oriented as direct repeats. Detailed analyses of the site of deletion in the genome of M. avium 2151 Rg-1 demonstrated that a single copy of IS1601 remained and that the ser2 gene cluster was deleted by homologous recombination. This same deletion pattern was observed for 10 out of 15 rough colony variants tested. Additionally, these studies revealed that IS1601 contains portions of three independent insertion sequences. This report is the first to define the precise genetic basis of colony variation in Mycobacterium spp. and provides further evidence that homologous recombination between insertion sequence elements can be a primary determinant of genome plasticity in these bacteria.

Identification and recombinant expression of a Mycobacterium avium rhamnosyltransferase gene (rtfA) involved in glycopeptidolipid biosynthesis.

The Mycobacterium avium complex is a source of disseminated infections in patients with advanced AIDS. This group of mycobacteria is distinguished by the presence of highly antigenic, surface-exposed glycopeptidolipids, and these glycolipids possess variant oligosaccharide structures that are the chemical basis of the 28 distinct serovars of the M. avium complex. We previously described the ser2 gene cluster, encoding the synthesis of the haptenic oligosaccharide (2, 3-dimethylfucose-rhamnose-6-deoxytalose-) of the serovar 2-specific glycopeptidolipid, and revealed a locus (ser2A) encoding a putative rhamnosyltransferase. Sequencing of the ser2A locus demonstrated the presence of three open reading frames, two of which yielded significant homology to several glycosyltransferases, and the deduced amino acid sequences of these two putative glycosyltransferases had 63% identity. These two genes were expressed in Mycobacterium smegmatis, and the resulting recombinant glycopeptidolipids were characterized by thin-layer chromatography and gas chromatography-mass spectrometry. These analyses demonstrated that only one of these genes, termed rtfA, encoded the rhamnosyltransferase responsible for the transfer of rhamnose to 6-deoxytalose. The identification of rtfA will permit further evaluation of glycopeptidolipid biosynthesis and the construction of isogenic mutants of multiple M. avium complex serovars. Moreover, such mutants will help define the role of glycopeptidolipids in the intracellular survival of these bacteria.

Specific and nonspecific lymphadenitis in childhood: etiology, diagnosis, and therapy.

Over a period of 4 years, 39 children with lymphadenitis were treated surgically; in 31 cases cervical lymph nodes were the main location. In 9 cases the lymphadenitis was caused by mycobacterial infection. Staphylococcus aureus was the most frequent causative organism of unspecific lymphadenitis (11 cases). The therapy of choice appears to be surgical treatment and medical care after operation. Especially in mycobacterial lymphadenitis, complete surgical excision of the lymph node is decisive for definitive healing. There was only 1 case of therapy-resistant, relapsing cervical lymphadenitis that needed a second operation. Causative organisms in this case were Mycobacterium avium and Mycobacterium intracellulare. All other patients showed an uneventful postoperative clinical course. We believe that a consequent diagnostic process and cooperation between the pediatric surgeon and pediatrician are necessary for effective therapy.

Cholecystolithiasis and infection of the biliary tract with Salmonella Virchow--a very rare case in early childhood.

In early childhood gallstones are rare. However, in the last years the number of patients has increased. A possible cause for calculous and acalculous cholecystitis are infections with Salmonella species. The following report describes a case of perforated cholecystitis and cholecystolithiasis accompanied by microbiological finding of Salmonella Virchow in the gallbladder in a three-and-a-half-year-old boy. A combination of symptomatic cholecystolithiasis and Salmonella Virchow has not yet been described in the literature. The belated diagnosis resulted in a sealed perforation of the gallbladder with local biliary peritonitis. After cholecystectomy and antimicrobial therapy, the patient could be discharged without any complaints. Diseases of the biliary tract are part of the differential diagnosis of unclear abdominal pain in early childhood.