Chromosomal diversity and relationships among 126 Streptococcus pyogenes strains expressing M1 protein from 13 countries on five continents were analyzed by multilocus enzyme electrophoresis and restriction fragment profiling by pulsed-field gel electrophoresis. All isolates were studied for the presence of the gene encoding streptococcal pyrogenic exotoxin A by PCR. Strain subsets were also examined by automated DNA sequencing for allelic polymorphism in genes encoding M protein (emm), streptococcal pyrogenic exotoxin A (speA), streptokinase (ska), pyrogenic exotoxin B (interleukin-1␤ convertase) (speB), and C5a peptidase (scp). Seven distinct emm1 alleles that encode M proteins differing at one or more amino acids in the N-terminal variable region were identified. Although substantial levels of genetic diversity exist among M1-expressing organisms, most invasive disease episodes are caused by two subclones marked by distinctive multilocus enzyme electrophoretic profiles and pulsed-field gel electrophoresis restriction fragment length polymorphism (RFLP) types. One of these subclones (ET 1/RFLP pattern 1a) has the speA gene and was recovered worldwide. Identity of speA, emm1, speB, and ska alleles in virtually all isolates of ET 1/RFLP type 1a means that these organisms share a common ancestor and that global dispersion of this M1-expressing subclone has occurred very recently. The occurrence of the same emm and ska alleles in strains that are well differentiated in overall chromosomal character demonstrates that horizontal transfer and recombination play a fundamental role in diversifying natural populations of S. pyogenes.

Based on strong evidence, blood cultures usually recover the causative organism of bacterial meningitis in children not pretreated with antibiotics. Based on moderate evidence, pretreatment does not adversely affect the cerebrospinal fluid cell count, but it decreases the positive test result for cerebrospinal fluid culture, especially for meningococcal meningitis. Based on some research evidence as well as consensus, children with suspected bacterial meningitis and no clinical signs of brain herniation do not need neuroimaging as part of their initial clinical evaluation. Dexamethasone adjunctive therapy in children with pneumococcal meningitis is controversial. Some experts recommend neuroimaging toward the end of therapy for all neonates with bacterial meningitis. Based on some research evidence as well as consensus, home intravenous antimicrobial therapy may be an option in selected cases of pediatric bacterial meningitis.

To develop a strategy for rapid species assignment and strain differentiation of Mycobacterium avium complex (MAC) organisms, the sequence of a 360-bp region of the gene (hsp65) encoding a 65-kDa heat shock protein was determined for 56 isolates, including 21 patient isolates and 35 reference strains. Eleven hsp65 alleles were identified, and there was no sharing of alleles between strains classified as M. avium and Mycobacteriurn intracellulare based on serovar and species-specific DNA hybridization probes. Phylogenetic analysis showed that 30 strains had one of two hsp65 alleles which were found in known M. avium organisms, 23 strains had one of six alleles allied with known M. intracellulare organisms, and three MAC isolates had one of three hsp65 alleles that differed substantially from the consensus M. avium and M. intracellulare hsp65 sequences. Estimates of strain relationships based on the sequences of hsp65 and the 16s-23s ribosomal DNA internal transcribed spacer were similar. Automated DNA sequencing of a 360-bp region of the hsp65 gene from MAC organisms provides a rapid and unambiguous marker system for strain differentiation and permits specific assignment of these acid-fast organisms for diagnostic purposes.The bacteria of the Mycobacterium avium complex (MAC) are a group of related acid-fast organisms that are abundant in nature (21, 51). This complex is comprised of two principal species (Mycobacterium avium and Mycobacterium intracellulare) containing morphologically and biochemically indistinguishable organisms (21). Members of the MAC are opportunistic pathogens of animals and humans that can be isolated from environmental sources, such as water, soil, plants, and house dust (12, 20, 33, 46, 521. These bacteria have long been known to cause pulmonary infections in adults and cervical lymphadenitis in children. More recently, they have gained considerable importance as a frequent cause of disseminated disease and death in AIDS patients (15, 22,51). For example, 25 to 50% of adult AIDS patients and 10 to 15% of pediatric AIDS patients in the United States are infected with MAC (19, 21, 27, 30). These individuals have much lower survival rates than AIDS patients without MAC infections (4, 17, 18).The epidemiology of MAC infections is poorly defined, in part due to a lack of unambiguous and rapid strain-specific molecular markers. The standard technique used for MAC strain differentiation has been serologic typing of surface molecules, and 28 serovars have been described. Nucleic acid and antibody probes and high-performance liquid chromatography (HPLC) analysis have been used to assign serovars 1 to 6, 8 to 11, and 21 to M. avium and serovars 7, 12 to 20, and 25 to M. intracellulare (36). Serovar 27 and perhaps serovar 26 are considered to be Mycobacterium scrofulaceum serovars (50). The specific status of the remaining serovars is undetermined (36,50).Several other strategies have been utilized for differentiating MAC strains. These strategies include phage typing (5, 7), analysis of restricti...

A surge in news stories regarding GAS disease was associated with an increase in testing for GAS in a pediatric ED.

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