ABSTRACT
Cryptococcus neoformans (Cn) is a pathogenic yeast that is the leading cause of fungal meningitis in immunocompromised patients. Various Cn virulence factors, such as the enzyme laccase and its product melanin, phospholipase, and capsular polysaccharide have been identified. During a screen of knockout mutants, the gene resistance to aminocholesterol 1 (RTA1) was identified, the function of which is currently unknown in Cn. Rta1 homologs in S. cerevisiae belong to a lipid-translocating exporter family of fungal proteins with transmembrane regions and confer resistance to the antimicrobial agent 7-aminocholesterol when overexpressed. To determine the role of RTA1 in Cn, the knock-out (rta1Δ) and reconstituted (rta1Δ+RTA1) strains were created and phenotypically tested. RTA1 was involved in resistance to 7-aminocholesterol, and also in exocyst complex component 3 (Sec6)-mediated secretion of urease, laccase, and the major capsule component, glucuronoxylomannan (GXM), which coincided with significantly smaller capsules in the rta1Δ and rta1Δ+RTA1 strains compared to the wild-type H99 strain. Furthermore, RTA1 expression was reduced in a secretory 14 mutant (sec14Δ) and increased in an RNAi Sec6 mutant. Transmission electron microscopy demonstrated vesicle accumulation inside the rta1Δ strain, predominantly near the cell membrane. Given that Rta1 is likely to be a transmembrane protein located at the plasma membrane, these data suggest that Rta1 may be involved in both secretion of various fungal virulence factors and resistance to 7-aminocholesterol in Cn.
ABSTRACT
This study investigated the cause of recent outbreaks of septicaemia in neonatal pigs in Australia (Victoria and Queensland). Septicaemia in neonatal pigs is commonly caused by enterotoxigenic E. coli, extraintestinal pathogenic E. coli and beta-haemolytic streptococci. Infrequent causes of septicaemia are Actinobacillus suis and Citrobacter freundii. Therefore, it was quite unexpected when Klebsiella pneumoniae was isolated in predominant growth from multiple organs of pigs dying of septicaemia from six days of age. Two cases in Victoria were associated with multilocus sequence type 25 (ST25), whereas the cases on a single farm in Queensland were associated with two different sequence types (ST278 and ST1978). Similar outbreaks of septicaemia have also occurred in England, but all were associated with K. pneumoniae ST25. The K. pneumoniae sequence types did not cluster phylogenetically into groups of isolates from the same geographical location or into groups which caused either septicaemia or pneumonia. Antibiotic resistance also varied between isolates and showed neomycin resistance in Queensland. These results suggest that several sequence types of K. pneumoniae are involved in causing outbreaks of septicaemia in neonatal pigs, in addition to its previously recognised role in pneumonia and mastitis.
