Population-based analysis of ocular Chlamydia trachomatis in trachoma-endemic West African communities identifies genomic markers of disease severity.

BACKGROUND: Chlamydia trachomatis (Ct) is the most common infectious cause of blindness and bacterial sexually transmitted infection worldwide. Ct strain-specific differences in clinical trachoma suggest that genetic polymorphisms in Ct may contribute to the observed variability in severity of clinical disease. METHODS: Using Ct whole genome sequences obtained directly from conjunctival swabs, we studied Ct genomic diversity and associations between Ct genetic polymorphisms with ocular localization and disease severity in a treatment-naïve trachoma-endemic population in Guinea-Bissau, West Africa. RESULTS: All Ct sequences fall within the T2 ocular clade phylogenetically. This is consistent with the presence of the characteristic deletion in trpA resulting in a truncated non-functional protein and the ocular tyrosine repeat regions present in tarP associated with ocular tissue localization. We have identified 21 Ct non-synonymous single nucleotide polymorphisms (SNPs) associated with ocular localization, including SNPs within pmpD (odds ratio, OR = 4.07, p* = 0.001) and tarP (OR = 0.34, p* = 0.009). Eight synonymous SNPs associated with disease severity were found in yjfH (rlmB) (OR = 0.13, p* = 0.037), CTA0273 (OR = 0.12, p* = 0.027), trmD (OR = 0.12, p* = 0.032), CTA0744 (OR = 0.12, p* = 0.041), glgA (OR = 0.10, p* = 0.026), alaS (OR = 0.10, p* = 0.032), pmpE (OR = 0.08, p* = 0.001) and the intergenic region CTA0744-CTA0745 (OR = 0.13, p* = 0.043). CONCLUSIONS: This study demonstrates the extent of genomic diversity within a naturally circulating population of ocular Ct and is the first to describe novel genomic associations with disease severity. These findings direct investigation of host-pathogen interactions that may be important in ocular Ct pathogenesis and disease transmission.

Follicular trachoma and trichiasis prevalence in an urban community in The Gambia, West Africa: is there a need to include urban areas in national trachoma surveillance?

OBJECTIVES: Urban areas are traditionally excluded from trachoma surveillance activities, but due to rapid expansion and population growth, the urban area of Brikama in The Gambia may be developing social problems that are known risk factors for trachoma. It is also a destination for many migrants who may be introducing active trachoma into the area. This study aimed to determine the prevalence and risk factors for follicular trachoma and trichiasis in Brikama. METHODS: A community-based cross-sectional prevalence survey including 27 randomly selected households in 12 randomly selected enumeration areas (EAs) of Brikama. Selected households were offered eye examinations, and the severity of trachoma was graded according to WHO's simplified grading system. Risk factor data were collected from each household via a questionnaire. RESULTS: The overall prevalence of trachomatous inflammation-follicular (TF) in children aged 1-9 years was 3.8% (95% CI 2.5-5.6), and the overall prevalence of trichiasis in adults aged ≥15 years was 0.46% (95% CI 0.17-1.14). EA prevalence of TF varied from 0% to 8.4%. The major risk factors for TF were dirty faces (P < 0.01, OR = 9.23, 95% CI 1.97-43.23), nasal discharge (P = 0.039, OR = 5.11, 95% CI 1.08-24.10) and residency in Brikama for <1 year (P = 0.047, OR = 7.78, 95% CI 1.03-59.03). CONCLUSIONS: Follicular trachoma can be considered to have been eliminated as a public health problem in Brikama according to WHO criteria. However, as the prevalence in some EAs is >5%, it may be prudent to include Brikama in surveillance programmes. Trichiasis remains a public health problem (>0.1%), and active case finding needs to be undertaken.

Pseudomonas chlororaphis strain JF3835 reduces mortality of juvenile perch, Perca fluviatilis L., caused by Aeromonas sobria.

Motile aeromonad septicaemia caused by Aeromonas sobria is a cause of disease in farmed perch, Perca fluviatilis L., in Switzerland. We have evaluated the potential of a Pseudomonas chlororaphis isolate, obtained from perch intestine, to control A. sobria infection. Inoculation of juvenile perch with P. chlororaphis strain JF3835 prior to infection with A. sobria caused a reduction in A. sobria associated mortalities. Infection of perch with xylE-labelled P. chlororaphis indicated the bacterium is able to transiently colonize juvenile fish and fingerlings.

Identification of bacteria from the normal flora of perch, Perca fluviatilis L., and evaluation of their inhibitory potential towards Aeromonas species.

Pathogenic Aeromonas sobria has been identified as a causative agent of ulcerative disease in farmed European perch, Perca fluviatilis L. To study the effect of the normal intestinal bacterial flora of perch against A. sobria, we sampled 193 bacterial isolates from the perch digestive tract. The isolates were identified by sequence analysis of the 16S rRNA gene and their inhibitory potential against A. sobria was evaluated in vitro. Nineteen of the strains isolated showed inhibition and were also tested against other aeromonad and non-aeromonad fish pathogens including Yersinia ruckeri and Vibrio anguillarum. Isolates showing inhibition were primarily Pseudomonas spp.; however, inhibitory Shewanella spp., and Delftia sp. were also identified. A Pseudomonas chlororaphis isolate showed inhibition against all fish pathogens tested.

Aeromonas sobria, a causative agent of disease in farmed perch, Perca fluviatilis L.

Significant numbers of perch, Perca fluviatilis, raised on a pilot fish farm in Switzerland presented focal skin lesions on the lateral sides and fin rot. Mortality rates reached levels of up to 1% of the total fish on the farm per day. Virtually pure cultures of Aeromonas sobria were isolated from the liver, kidney, spleen and skin lesions of affected fish. Aeromonas sobria isolated from the farmed perch had a haemolytic effect on sheep and trout erythrocytes, autoaggregated, was cytotoxic for cultured fish cells and possessed genes involved in type III protein secretion. Experimental infection of naive perch with a single colony isolate of A. sobria from an affected farm fish resulted in the development of clinical signs identical to those seen on the farm. The results indicate that A. sobria can act as a primary pathogen of perch.

Type II secretion by Aeromonas salmonicida: evidence for two periplasmic pools of proaerolysin.

Aeromonas salmonicida containing the cloned gene for proaerolysin secretes the protein via the type II secretory pathway. Here we show that altering a region near the beginning of aerA led to a dramatic increase in the amount of proaerolysin that was produced and that a large amount of the protein was cell associated. All of the cell-associated protein had crossed the cytoplasmic membrane, because the signal sequence had been removed, and all of it was accessible to processing by trypsin during osmotic shock. Enlargement of the periplasm was observed by electron microscopy in overproducing cells, likely caused by the osmotic effect of the very large concentrations of accumulated proaerolysin. Immunogold electron microscopy localized nearly all of the proaerolysin in the enlarged periplasm; however, only half of the protoxin was released from the cells by osmotic shocking. Cross-linking studies showed that this fraction contained normal dimeric proaerolysin but that proaerolysin in the fraction that was not shockable had not dimerized, although it appeared to be correctly folded. Both periplasmic fractions were secreted by the cells; however, the nonshockable fraction was secreted much more slowly than the shockable fraction. We estimated a rate for maximal secretion of proaerolysin from the bacteria that was much lower than the rates that have been estimated for inner membrane transit, which suggests that transit across the outer membrane is rate limiting and may account for the periplasmic accumulation of the protein. Finally, we show that overproduction of proaerolysin inhibited the release of the protease that is secreted by A. salmonicida.