Capsule production promotes Group B Streptococcus intestinal colonization

Late-onset disease is the most common clinical presentation of Group B Streptococcus (GBS) infection during infancy, and gastrointestinal (GI) colonization is an important precursor. Previously, we described a murine model of postnatal GBS GI colonization that resulted in sustained colonization and progression to invasive disease. Capsular polysaccharide is an important GBS virulence factor. Vaccines based on a subset of capsular serotypes are in clinical trials. However, little is known regarding the role of specific GBS capsular serotypes in GI colonization. We examined the role of GBS capsule in GI colonization using capsule-producing and acapsular strains derived from GBS strain A909 (serotype Ia) in a murine model. Using isogenic GBS strains differing only in capsular serotypes, we explored the role of specific serotypes in GI colonization by determining competitive indices during cocolonization. We found that GBS A909 colonizes the murine GI tract without causing invasive disease. In monocolonization experiments, there was colonization persistence with the capsule-producing strain (100%) compared to the acapsular mutant strain (13%). In cocolonization experiments, the capsule-producing strain outcompeted its isogenic acapsular mutant, with a geometric mean competitive index of 8, 95% confidence interval (CI) [1.7, 38.9] in the colon at 7 days post-colonization. A909 expressing its native serotype Ia capsule outcompeted an isogenic mutant that expresses serotype III capsule, with a geometric mean competitive index of 2.5, 95% CI [1.2, 5.1] in the colon at 7 days post-colonization. Thus, polysaccharide capsule production enhances GBS GI colonization in vivo. In an A909 genetic background, the production of a serotype Ia capsule provides a competitive advantage over an isogenic strain producing type III capsule. The murine model is a valuable tool to understand the role of GBS capsule types in GI colonization. IMPORTANCE The establishment of GBS intestinal colonization is believed to be a critical precursor to late-onset disease in neonates, which has a significant impact on neurodevelopment outcomes in this population. Our prior work described a murine model of postnatal Group B Streptococcus (GBS) acquisition and invasive disease. Using this model, we explored the importance of GBS polysaccharide capsule production on gastrointestinal colonization. We found that the expression of capsule (compared to isogenic acapsular strains) provides an advantage in intestinal colonization and, importantly, that capsule type Ia has an advantage over capsule type III in a GBS A909 strain background. We speculate that specific serotypes may differ in colonization fitness, which may play a role in serotype distribution in neonatal disease.

A 24-year longitudinal study of Klebsiella pneumoniae isolated from patients with bacteraemia and urinary tract infections reveals the association between capsular serotypes, antibiotic resistance, and virulence gene distribution

Longitudinal studies on the variations of phenotypic and genotypic characteristics of K. pneumoniae across two decades are rare. We aimed to determine the antimicrobial susceptibility and virulence factors for K. pneumoniae isolated from patients with bacteraemia or urinary tract infection (UTI) from 1999 to 2022. A total of 699 and 1,267 K. pneumoniae isolates were isolated from bacteraemia and UTI patients, respectively, and their susceptibility to twenty antibiotics was determined; PCR was used to identify capsular serotypes and virulence-associated genes. K64 and K1 serotypes were most frequently observed in UTI and bacteraemia, respectively, with an increasing frequency of K20, K47, and K64 observed in recent years. entB and wabG predominated across all isolates and serotypes; the least frequent virulence gene was htrA. Most isolates were susceptible to carbapenems, amikacin, tigecycline, and colistin, with the exception of K20, K47, and K64 where resistance was widespread. The highest average number of virulence genes was observed in K1, followed by K2, K20, and K5 isolates, which suggest their contribution to the high virulence of K1. In conclusion, we found that the distribution of antimicrobial susceptibility, virulence gene profiles, and capsular types of K. pneumoniae over two decades were associated with their clinical source.

Nutrient conditions are primary drivers of bacterial capsule maintenance in Klebsiella

The fitness cost associated with the production of bacterial capsules is considered to be offset by the protection provided by these extracellular structures against biotic aggressions or abiotic stress. However, it is unknown if the capsule contributes to fitness in the absence of these. Here, we explored conditions favouring the maintenance of the capsule in Klebsiella pneumoniae, where the capsule is known to be a major virulence factor. Using short-term experimental evolution on different Klebsiella strains, we showed that small environmental variations have a strong impact on the maintenance of the capsule. Capsule inactivation is frequent in nutrient-rich, but scarce in nutrient-poor media. Competitions between wild-type and capsule mutants in nine different strains confirmed that the capsule is costly in nutrient-rich media. Surprisingly, these results also showed that the presence of a capsule provides a clear fitness advantage in nutrient-poor conditions by increasing both growth rates and population yields. The comparative analyses of the wild-type and capsule mutants reveal complex interactions between the environment, genetic background and serotype even in relation to traits known to be relevant during pathogenesis. In conclusion, our data suggest there are novel roles for bacterial capsules yet to be discovered and further supports the notion that the capsule's role in virulence may be a by-product of its contribution to bacterial adaptation outside the host.

Prevalence of virulence factor, antibiotic resistance, and serotype genes of Pasteurella multocida strains isolated from pigs in Vietnam

AIM

The study was conducted to determine the prevalence and characterization of the Pasteurella multocida isolates from suspected pigs in Vietnam.

MATERIALS AND METHODS

A total of 83 P. multocida strains were isolated from lung samples and nasal swabs collected from pigs associated with pneumonia, progressive atrophic rhinitis, or reproductive and respiratory symptoms. Isolates were subjected to multiplex polymerase chain reaction (PCR) for capsular typing, detection of virulence-associated genes and antibiotic resistance genes by PCR. The antimicrobial sensitivity profiles of the isolates were tested by disk diffusion method.

RESULTS

All the isolates 83/83 (100%) were identified as P. multocida by PCR: serogroup A was obtained from 40/83 (48.19%), serogroup D was detected from 24/83 strains (28.91%), and serogroup B was found in 19/83 (22.35%) isolates. The presence of 14 virulence genes was reported including adhesins group (ptfA - 93.97%, pfhA - 93.97%, and fimA - 90.36%), iron acquisition (exbB - 100%, and exbD - 85.54%), hyaluronidase (pmHAS - 84.33%), and protectins (ompA - 56.62%, ompH 68.67%, and oma87 - 100%). The dermonecrotoxin toxA had low prevalence (19.28%). The antimicrobial susceptibility testing revealed that cephalexin, cefotaxime, ceftriaxone, ofloxacin, pefloxacin, ciprofloxacin, and enrofloxacin were the drugs most likely active against P. multocida while amoxicillin and tetracycline were inactive. The usage of PCR revealed that 63/83 isolates were carrying at least one of the drug resistance genes.

CONCLUSION

Unlike other parts of the word, serotype B was prevalent among Vietnamese porcine P. multocida strains. The high antibiotic resistance detected among these isolates gives us an alert about the current state of imprudent antibiotic usage in controlling the pathogenic bacteria.