No abstract

In 1990, a new type of erythromycin resistance phenotype, designated NR, was found in group A streptococcus (GAS) in Finland. In the present study, the distribution of GAS isolates with this and other erythromycin-resistance phenotypes was surveyed in Finland, and the clonality of the isolates was explored. Of 4179 GAS isolates collected from all over Finland, 695 (17%) were resistant to erythromycin, and 82% of these had the NR phenotype. Of a group of 96 isolates with the NR phenotype from different areas, 91% was T4 serotype, opacity factor-positive. The majority of these isolates were studied further: All were M4 serotype and 88% were of one clonal origin in genetic analyses. Thus, one single clone predominates among erythromycin-resistant GAS in Finland. This clone is of T4M4 serotype and mediates the new type of erythromycin resistance, characterized by the NR phenotype.

Patients diagnosed as suffering from erysipelas or cellulitis were subjected to bacteriological and serological investigations. The serological tests used included the anti-streptolysin O reaction (ASO), the anti-deoxyribonuclease B test (ADB) and the anti-hyaluronidase tests (AHT) that are specific both for the group A streptococcus (Streptococcus pyogenes) and for the human pyogenic streptococci of group C or group G. Antibody tests to the 3!-lysin and the nuclease of Staphylococcus aureus were also employed. Conventional bacteriological culture methods were used plus needle aspiration of injected saline in most patients with erysipelas, but recognized pathogens were isolated in only 42",, of cases. Our results indicate the limitations of these tests for making initial diagnoses and deciding treatment.

SUMMARYOne hundred and seventy-nine isolates of Legionella pneumophila serogroup 1, obtained from a site associated with an outbreak of Legionnaires' disease, were examined by monoclonal antibody subgrouping, restriction fragment length polymorphism typing, restriction endonuclease analysis and plasmid content. Nine distinct phenotypes were detected but at the genotypic level all strains were closely related. The data presented indicate that phenotypic variation of a single parent strain can occur within an environmental site. The implications of these findings are discussed in relation to the investigation of outbreaks of Legionnaires' disease.

An oligonucleotide probe microarray for investigation of the evolution of epidemic Staphylococcus aureus strains has been constructed. The array comprises 383 probes based on virulence-associated genes present in four key strains. Twelve strains including seven for which the complete chromosomal nucleotide sequence was available were tested on the array. Twenty-six per cent of the probes were able to differentiate between strains to give a minimum of two gene differences between pairs. A gene difference distance tree based on the array data had approximately the same topology as one prepared using concatenated MLST sequences. Differences in the topologies of these trees were found to indicate that large-scale recombination events had occurred during the evolution of the species. One such occurrence appears to have been a key event in the genesis of the EMRSA-15 clone (ST22) that currently represents the most prevalent methicillin-resistant S. aureus (MRSA) in the UK. INTRODUCTIONStaphylococcus aureus is an important human pathogen responsible for bacterial infections seen both in the community and in hospitals. Over the last decades the emergence of multi-drug resistant strains has greatly increased the economic and health importance of staphylococcal infection (Chambers, 2001;Stefani & Varaldo, 2003;Wenzel, 1982). S. aureus is a highly adapted and extremely successful colonizer of the human nasopharynx, other mucosal surfaces and skin (Kluytmans et al., 1997;Williams, 1963). Colonization is generally asymptomatic but occasionally results in disease with a wide variety of signs and symptoms. These range from mild self-limiting infections of the skin to fulminating septicaemia (Lowy, 1998;Projan & Novick, 1997). Staphylococcal disease appears to result from an imbalance between the bacterium and the immune system and is associated with tissue invasion or unchecked growth. S. aureus is able to maintain its colonist status by producing a variety of proteins that interact with host-cell components (Baba et al., 2002;Kuroda et al., 2001). These proteins are described as virulence-associated and have functions such as extracellular matrix binding and host cell lysis. Expression of the S. aureus virulence-associated proteins is very carefully controlled by means of a network of regulatory genes including the agr and sar operons (Chien & Cheung, 1998;Sabersheikh & Saunders, 2004). Strain variation in these regulatory mechanisms may be an important factor influencing the switch from colonization to disease. Such variations may also contribute towards the success of the species by helping to minimize the emergence of immunity to essential S. aureus-specific antigens.Genome sequencing has shown that the species maintains a large number of virulence-associated genes but that not all are carried by each individual strain (Baba et al., 2002;Holden et al., 2004;Kuroda et al., 2001). Pairwise comparisons show as much as 20 % variation in the gene inventory of different S. aureus with most of the difference contributed by virule...