Transmission of group A streptococci. III. The effect of drying on the infectivity of the organism for man

To harm or not to harm? On the evolution and expression of virulence in group A streptococci

Group A streptococci (GAS) cause three different types of infection (sensu lato) with distinct levels of virulence: asymptomatic colonization, superficial symptomatic infection, and invasive infection. To address why this pattern with several infection types has evolved, we combine mechanistic understanding from infection medicine with recent theory from evolutionary ecology. We propose that asymptomatic colonization and superficial symptomatic infection exploit different states of the host epithelium to maximize transmission between hosts in different epidemiological conditions, whereas the ability of the bacteria to cause invasive infection is a non-adaptive side effect of traits required for superficial symptomatic infection.

Streptococcus pyogenes and re-emergence of scarlet fever as a public health problem

Explosive outbreaks of infectious diseases occasionally occur without immediately obvious epidemiological or microbiological explanations. Plague, cholera and Streptococcus pyogenes infection are some of the epidemic-prone bacterial infections. Besides epidemiological and conventional microbiological methods, the next-generation gene sequencing technology permits prompt detection of genomic and transcriptomic profiles associated with invasive phenotypes. Horizontal gene transfer due to mobile genetic elements carrying virulence factors and antimicrobial resistance, or mutations associated with the two component CovRS operon are important bacterial factors conferring survival advantage or invasiveness. The high incidence of scarlet fever in children less than 10 years old suggests that the lack of protective immunity is an important host factor. A high population density, overcrowded living environment and a low yearly rainfall are environmental factors contributing to outbreak development. Inappropriate antibiotic use is not only ineffective for treatment, but may actually drive an epidemic caused by drug-resistant strains and worsen patient outcomes by increasing the bacterial density at the site of infection and inducing toxin production. Surveillance of severe S. pyogenes infection is important because it can complicate concurrent chickenpox and influenza. Concomitant outbreaks of these two latter infections with a highly virulent and drug-resistant S. pyogenes strain can be disastrous.

Clustering of group A streptococcal infections on a burns unit: important lessons in outbreak management

In a 12-month period 37 patients and four members of staff on a burns unit were infected or colonized by Streptococcus pyogenes (Group A streptococcus). One patient became septicaemic and died. Serotyping revealed five distinct clusters against a low background level of infection. Infection control measures included isolation, screening of patients, staff and environment and the use of prophylactic antibiotics for uninfected patients. We discuss the role of staff and patient carriers and the environment as a continuing source of infection, and the importance of serotyping in outbreak epidemiology.

Genetic instability of M protein and serum opacity factor of group A streptocci: evidence suggesting extrachromosomal control

The M antigen, a primary determinant of virulence in group A streptococci that is expressed biologically as resistance to phagocytosis, is known to undergo a variety of phenotypic changes both in vivo and in vitro. These changes are nonrandom and can occur at a high frequency. Using the previously described relationship between the serum opacity reaction (associated with certain strains) and the presence of the M antigen, the phenotypic instability of the M antigen was analyzed. The results support the conclusion that M protein synthesis and the serum opacity reaction are directly or indirectly controlled by the same gene or by genes which are linked and can segregate as a unit. Moreover, growth conditions and the curing agents rifampin and ethidium bromide had a discernible influence on the segregation of clones unable to exhibit serum opacity factor and to resist phagocytosis by human leukocytes. Serial transfer of stationary-phase cultures of four strains of group A streptococci significantly increased the number of colonies negative for the serum opacity reaction and the M antigen. For two of four strains both ethidium bromide and rifampin also increased the segregation of colonies with this phenotype. In light of these experiments and the necessary controls, the possible influence of plasmids or bacteriophage in regulating M protein synthesis is discussed.

The recovery of smallpox virus from patients and their environment in a smallpox hospital

Attempts had been made in 1961 to recover smallpox virus by air sampling in smallpox wards and close to the mouths of smallpox patients, but these had been largely unsuccessful, possibly owing to the air sampling method used. Further attempts were therefore made in 1963, with a fluid impinger for air sampling and with Petri dishes placed below the orifice of the impinger to collect large droplets or particulate matter that the impinger might miss.Air samples from near the patients' mouths yielded little virus, this being more readily recovered from the settling-plates. Patients' bedclothes sampled with the impinger yielded rather more virus, but again even more was obtained from the Petri dishes.The results suggest that contamination of the air in the vicinity of smallpox patients is due to relatively large particles of infected dust from the patients' bedclothes rather than from fine droplets or droplet nuclei coming from the upper respiratory tract. Secretions from the mouth and upper respiratory tract appear to be responsible for the early contamination of pillows and bedclothes.