Chapter 19 : Gram-Positive Uropathogens, Polymicrobial Urinary Tract Infection, and the Emerging Microbiota of the Urinary Tract

S. saprophyticus virulence factors. (A) Secreted surface proteins: Aas, possesses N-terminal signal sequence, but no motifs such as a transmembrane domain, LPXTG sortase-recognition motif, or proline/glycine-rich cell wall-spanning domain to indicate the mode of attachment to the cell surface after translocation across the membrane (indicated by the purple question marks) ( 72 ). Immuno-electron microscopy shows Aas as part of a fuzzy surface layer that is absent when Aas is not expressed ( 75 ). Ssp has a YSIRK-containing signal sequence but no sortase-recognition motif so its mode of attachment to the cell surface is uncertain (indicated by the red question mark); it is easily sheared from the cell surface. Electron microscopy and immuno-electron micrographs also show Ssp to exist as part of fuzzy surface layer, apparently consisting of 50–75nm fibrillar structures; the nature of these fibers in not known ( 75 , 76 ). (B) UafA, SdrI, SssF, and UafB contain an LPXTG motif and are predicted to be covalently attached to the cell wall ( 78 , 79 , 81 ). The small arrows near the membrane-anchored sortase enzymes indicate the two-step transpeptidation reaction whereby sortase substrates are first cleaved within the LPXTG motif to create a sortase-substrate intermediate (and releasing the membrane domain and positively charged cytoplasmic tail, indicated by the straight line in the membrane) that is then resolved, resulting in covalent linkage of the substrate to the cell wall ( 328 ). UafB is genetically linked to accessory secretion genes secA2 and secY2 that are predicted to encode a dedicated accessory secretion system for UafB ( 79 ). (C) Cytoplasmic enzymes that promote S saprophyticus survival in urine ( 329 , 330 ).

Gram-positive inhabitants and pathogens of the human urinary tract. Approximate phylogenetic relationships between Gram-positive bacteria are illustrated in this schematic representation. Please refer to the text and Table 1 for additional information and references describing these genera as uropathogens or inhabitants of the human urinary tract. On the left, Bifidobacterium and Gardnerella belong to the order Bifidobacteriales, which together with the orders Propionibacteriales, Actinomycetales, and Corynebacteriales belong to the class Actinobacteria (a.k.a. “high-GC Gram-positive bacteria”). Atopobium belongs to the order Coriobacteriales and the class Coriobacteriia. The classes Coriobacteriia and Actinobacteria both belong to the phylum Actinobacteria. The remaining genera, with the exception of Mycoplasma, belong to the phylum Firmicutes. Whereas Peptostreptococcus, Anaerococcus, Finegoldia, and Peptoniphilus belong to the order Clostridiales and the class Clostridia, Staphylococcus and Gemella belong to the order Bacillales and the class Bacilli. Members of the order Lactobacillales (Lactobacillus, Aerococcus, Enterococcus, and Streptococcus), are also classified as Bacilli. The genus Veillonella is also a member of the Firmicutes, but belongs to the class and order Negativicutes and Selenomonadales, respectively. On the other hand, Mycoplasma belongs to the phylum Tenericutes, the class Mollicutes, and the order Mycoplasmatales.

Transmission-electron micrographs of several urogenital isolates from the phylum Actinobacteria. Strains grown for 24–48 hours underwent negative staining with uranyl acetate and were examined by TEM. These strains were isolated from the urine or vaginas of pregnant or nonpregnant women and are available through BEI resources. Strain names are as follows: Actinomyces neuii, MJR8396A; Alloscardovia omnicolens, CMW7705A; Atopobium vaginae, CMW7778A; Bifidobacterium bifidum, MJR8628B; Gardnerella vaginalis, PSS7772B; Propionibacterium avidum, MJR7694. Scale bars are 500 nm. Shaded backgrounds contain images of the same strain.