Michael G. Caparon

Urinary tract infections: epidemiology, mechanisms of infection and treatment options

Urinary tract infections (UTIs) are a severe public health problem and are caused by a range of pathogens, but most commonly by Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Enterococcus faecalis and Staphylococcus saprophyticus. High recurrence rates and increasing antimicrobial resistance among uropathogens threaten to greatly increase the economic burden of these infections. In this Review, we discuss how basic science studies are elucidating the molecular details of the crosstalk that occurs at the host–pathogen interface, as well as the consequences of these interactions for the pathophysiology of UTIs. We also describe current efforts to translate this knowledge into new clinical treatments for UTIs.

Cytolysin-Mediated Translocation (CMT): A Functional Equivalent of Type III Secretion in Gram-Positive Bacteria

Type III secretion for injection of effector proteins into host cells has not been described for Gram-positive bacteria despite their importance in disease. Here, we describe an injection pathway for the Gram-positive pathogen Streptococcus pyogenes that utilizes streptolysin O (SLO), a cholesterol-dependent cytolysin. The data support a model in which an effector is translocated through the SLO pore by a polarized process. The effector, SPN (S. pyogenes NAD-glycohydrolase), is capable of producing the potent second messenger cyclic ADP-ribose, and SLO and SPN act synergistically to trigger cytotoxicity. These data provide a novel paradigm for the function of the cholesterol-dependent cytolysin family and its wide distribution suggests that cytolysin-mediated translocation (CMT) may be the equivalent of type III secretion for Gram-positive pathogens.

Streptococcus-Zebrafish Model of Bacterial Pathogenesis

ABSTRACT Due to its small size, rapid generation time, powerful genetic systems, and genomic resources, the zebrafish has emerged as an important model of vertebrate development and human disease. Its well-developed adaptive and innate cellular immune systems make the zebrafish an ideal model for the study of infectious diseases. With a natural and important pathogen of fish, Streptococcus iniae, we have established a streptococcus- zebrafish model of bacterial pathogenesis. Following injection into the dorsal muscle, zebrafish developed a lethal infection, with a 50% lethal dose of 103 CFU, and died within 2 to 3 days. The pathogenesis of infection resembled that of S. iniae in farmed fish populations and that of several important human streptococcal diseases and was characterized by an initial focal necrotic lesion that rapidly progressed to invasion of the pathogen into all major organ systems, including the brain. Zebrafish were also susceptible to infection by the human pathogen Streptococcus pyogenes. However, disease was characterized by a marked absence of inflammation, large numbers of extracellular streptococci in the dorsal muscle, and extensive myonecrosis that occurred far in advance of any systemic invasion. The genetic systems available for streptococci, including a novel method of mutagenesis which targets genes whose products are exported, were used to identify several mutants attenuated for virulence in zebrafish. This combination of a genetically amenable pathogen with a well-defined vertebrate host makes the streptococcus-zebrafish model of bacterial pathogenesis a powerful model for analysis of infectious disease.

A role for Trigger Factor and an Rgg‐like regulator in the transcription, secretion and processing of the cysteine proteinase of Streptococcus pyogenes

The ability of numerous microorganisms to cause disease relies upon the highly regulated expression of secreted proteinases. In this study, mutagenesis with a novel derivative of Tn4001 was used to identify genes required for the expression of the secreted cysteine proteinase (SCP) of the pathogenic Gram‐positive bacterium Streptococcus pyogenes. Designated as Rop loci (regulation of proteinase), ropB is a rgg‐like transcriptional activator required for transcription of the gene which encodes the proteinase. In contrast, ropA contributes post‐transcriptionally to the secretion and processing of SCP and encodes a homologue of Trigger Factor, a peptidyl‐prolyl isomerase and putative chaparone which is highly conserved in most bacterial species, but of unknown function. Analysis of additional ropA mutants demonstrated that RopA acts both to assist in targeting SCP to the secretory pathway and to promote the ability of the proprotein to establish an active conformation upon secretion. This latter function was dependent upon the peptidyl‐prolyl isomerase domain of RopA and mutants that lacked this domain exhibited a bipartite deficiency manifested as a kinetic defect in autologous processing of the proprotein to the mature proteinase, and as a catalytic defect in the mature proteinase. These results provide insight into the function of Trigger Factor, the regulation of proteinase activity and the mechanism of secretion in Gram‐positive bacteria.

Visualizing pneumococcal infections in the lungs of live mice using bioluminescent Streptococcus pneumoniae transformed with a novel gram-positive lux transposon.

ABSTRACT Animal studies with Streptococcus pneumoniae have provided valuable models for drug development. In order to monitor long-term pneumococcal infections noninvasively in living mice, a novel gram-positive lux transposon cassette, Tn4001 luxABCDE Kmr, that allows random integration oflux genes onto the bacterial chromosome was constructed. The cassette was designed so that the luxABCDE and kanamycin resistance genes were linked to form a single promoterless operon. Bioluminescence and kanamycin resistance only occur in a bacterial cell if this operon has transposed downstream of a promoter on the bacteriums chromosome. S. pneumoniae D39 was transformed with plasmid pAUL-A Tn4001 luxABCDEKmr, and a number of highly bioluminescent colonies were recovered. Genomic DNA from the brightest D39 strain was used to transform a number of clinical S. pneumoniae isolates, and several of these strains were tested in animal models, including a pneumococcal lung infection model. Strong bioluminescent signals were seen in the lungs of the animals containing these pneumococci, allowing the course and antibiotic treatment of the infections to be readily monitored in real time in the living animals. Recovery of the bacteria from the animals showed that the bioluminescent signal corresponded to the number of CFU and that the lux construct was highly stable even after several days in vivo. We believe that thislux transposon will greatly expand the ability to evaluate drug efficacy against gram-positive bacteria in living animals using bioluminescence.

Genetic manipulation of pathogenic streptococci

Publisher Summary This chapter discusses genetic manipulation of pathogenic streptococci. The streptococci are a diverse class of gram-positive bacterial species containing many human pathogens. Suppurative diseases, including pharyngitis, scarlet fever, cellulitis of the skin, impetigo, erysipelas, and the recently recognized toxic shock-like syndrome, are associated with infection by Streptococcus pyogenes , which is also responsible for the serious non suppurative diseases of acute glomerulonephritis and rheumatic fever. Streptococcus mutans plays a central role in the development of dental plaque and dental caries, and Streptococcus agalactiae (group B) has become a very important cause of neonatal meningitis. Streptococcus pneumoniae remains one of the major causes of morbidity and mortality among debilitated individuals despite the widespread use of antibiotics, and it is an important cause of otitis media in infants. No effective vaccines exist for streptococcal diseases, with the possible exception of the pneumococcal capsule vaccine.

Mutation of luxS affects growth and virulence factor expression in Streptococcus pyogenes

Adaptive responses of bacteria that involve sensing the presence of other bacteria are often critical for proliferation and the expression of virulence characteristics. The autoinducer II (AI‐2) pathway has recently been shown to be a mechanism for sensing other bacteria that is highly conserved among diverse bacterial species, including Gram‐positive pathogens. However, a role for this pathway in the regulation of virulence factors in Gram‐positive pathogens has yet to be established. In this study, we have inactivated luxS, an essential component of the AI‐2 pathway, in the Gram‐positive pathogen Streptococcus pyogenes. Analyses of the resulting mutants revealed the aberrant expression of several virulence properties that are regulated in response to growth phase, including enhanced haemolytic activity, and a dramatic reduction in the expression of secreted proteolytic activity. This latter defect was associated with a reduced ability to secrete and process the precursor of the cysteine protease (SpeB) as well as a difference in the timing of expression of the protease. Enhanced haemolytic activity of the luxS strain was also shown to be linked with an increased expression of the haemolysin S‐associated gene sagA. Disruptions of luxS in these mutants also produced a media‐dependent growth defect. Finally, an allelic replacement analysis of an S. pyogenes strain with a naturally occurring insertion of IS1239 in luxS suggested a mechanism for modulation of virulence during infection. Results from this study suggest that luxS makes an important contribution to the regulation of S. pyogenes virulence factors.

Protein F2, a novel fibronectin‐binding protein from Streptococcus pyogenes, possesses two binding domains

Binding of the group A streptococcus (GAS) to respiratory epithelium is mediated by the fibronectin (Fn)‐binding adhesin, protein F1. Previous studies have suggested that certain GAS strains express Fn‐binding proteins that are different from protein F1. In this study, we have cloned, sequenced, and characterized a gene (prtF2) from GAS strain 100076 encoding a novel Fn‐binding protein, termed protein F2. Insertional inactivation of prtF2 in strain 100076 abolishes its high‐affinity Fn binding. prtF2‐related genes exist in most GAS strains that lack prtF1 (encoding protein F1) but bind Fn with high affinity. These observations suggest that protein F2 is a major Fn‐binding protein in GAS. Protein F2 is highly homologous to Fn‐binding proteins from Streptococcus dysgalactiae and Strep‐tococcus equisimilis, particularly in its carboxy‐terminal portion. Two domains are responsible for Fn binding by protein F2. One domain (FBRD) consists of three consecutive repeats, whereas the other domain (UFBD) resides on a non‐repeated stretch of approximately 100 amino acids and is located 100 amino acids amino‐terminal of FBRD. Each of these domains is capable of binding Fn when expressed as a separate protein. In strain 100076, protein F2 activity is regulated in response to alterations in the concentration of atmospheric oxygen.

A tale of two pili: assembly and function of pili in bacteria

Bacterial pili have long been recognized as mediators of initial host-pathogen interactions important for the progression of Gram-negative bacterial diseases. An appreciation of the role of pili on virulence in Gram-positive bacteria and the unique properties of their biogenesis is a rapidly emerging area of research. In this review, we focus on recent advances in one of the longest-studied Gram-negative pilus systems, the chaperone/usher assembled pili, along with the newcomer to the field, the sortase-assembled pili of Gram-positive bacteria. In both systems, a wealth of new structural and molecular details has emerged recently. In light of this, we explore similarities between chaperone/usher and sortase-assembled pilus biogenesis and highlight paradigms unique to each, with the goal of using knowledge of each system to raise new questions and inform future studies of the other.

Patterns of virulence gene expression differ between biofilm and tissue communities of Streptococcus pyogenes

The ability of Streptococcus pyogenes to form biofilm‐like bacterial communities during infection of soft tissue has suggested that the capacity to produce biofilm may be important for pathogenesis. To examine this relationship, a panel of mutants was evaluated for their ability to form biofilm on abiotic surfaces in several assays. Several established virulence factors were crucial for biofilm formation, including the M protein, required for initial cell‐surface interactions, and the hyaluronic acid capsule, required for subsequent maturation into a three‐dimensional structure. Mutants lacking the transcription regulators Mga and CovR (CsrR) also failed to form biofilm. Comparison of transcriptional profiles revealed differential regulation of approximately 25% of the genome upon adaptation to biofilm. During infection of zebrafish, several virulence factors (notably cysteine protease and streptokinase) were regulated in a biofilm‐like manner. However, the overall profile of virulence factor expression indicated that tissue communities have a pattern of gene expression different from biofilm. Taken together, these data show that while biofilm and tissue communities have many characteristics in common, that biofilm reproduces only a subset of the myriad cues used by tissue communities for regulation of virulence.