| The most frequent cause of bacterial meningitis in older adults is: | View Page |
| The Quelling test is useful for which of the following : | View Page |
| Which of the following organisms are gram positive: | View Page |
| Group A beta-hemolytic streptococci are best characterized by which of the following: | View Page |
| Which of the following is a presumptive test for the identification of Lancefield group A Streptococcus: | View Page |
| Which of the following organisms is best visualized by use of a darkfield microscope: | View Page |
| Which of the following streptococcus exhibits a positive bile solubility test: | View Page |
| Which of the following species are gram positive: | View Page |
| Sheep blood agar contains inhibitors to which of the following organisms: | View Page |
| Which one of the following organisms is sensitive to bacitracin: | View Page |
| The grow seen here on PPLO agar is most likely caused by: | View Page |
| Match the illustrations with corresponding cocci classification: | View Page |
| Based on the gram stain morphology observed before, the possible presumptive identifications might include "gram positive cocci consistent with... | View Page |
| The patient was admitted to the hospital. The sputum specimen was inoculated to sheep blood agar. Based on the colony morphology and the alpha hemolysis seen in the accompanying photograph, the most likely identification is: | View Page |
| Streptococcus pnemoniae is the most common cause of fatal community-acquired pneumonia. | View Page |
| The colonies shown in the blood agar (upper) and MacConkey agar (lower) biplate are a 24 hour growth from an aerobic blood culture bottle that became positive at 12 hours after inoculation. The appearance of the colonies on MacConkey agar rules out the following two bacterial species: | View Page |
| PYR Differential As mentioned before, the spot PYR test is commonly performed to separate Enterococcus species (positive reaction) from the Group D streptococci (S. bovis, S. equinus), which are negative.It should be remembered that Streptococcus pyogenes (group A) also produces PYR; therefore, additional characteristics such as beta hemolysis are important.Some species of Aerococcus and Gemella are also PYR-positive; however, they can be suspected if large cocci in tetrads or clusters are observed on gram stain.These species are rare isolates in most clinical practices. | View Page |
| Most strains of S. milleri (anginosus) carry the F antigen (see photograph). Rare strains that carry the group A antigen can be differentiated from S. pyogenes by which of the following laboratory tests: | View Page |
| A clinical condition often associated with Streptococcus milleri (anginosus) is: | View Page |
| Review 1 Piscitelli SC., Shwed J., Schreckenberger P., Danziger LH.
Streptococcus milleri group: renewed interest in an elusive pathogen.
European Journal of Clinical Microbiology & Infectious Diseases.11:491-8, 1992The following review examines the bacteriological characteristics, epidemiology, pathogenicity and antimicrobial susceptibility of the "Streptococcus milleri group". "Streptococcus milleri group" is a term for a large group of streptococci which includes Streptococcus intermedius, Streptococcus constellatus and Streptococcus anginosus.Usually considered commensals, these organisms are often associated with various pyogenic infections including cardiac, intra-abdominal, subcutaneous and central nervous system infections, particularly with the formation of abscesses.Organisms of the "Streptococcus milleri group" are often unrecognized pathogens due to the lack of uniformity in classifications and difficulties in microbiological identification. Penicillin G, cephalosporins, clindamycin and vancomycin all possess activity against these streptococci.Use of agents with poor activity may promote infections with "Streptococcus milleri group" and allow it to exhibit its pathogenicity. An understanding of these organisms may aid in their recognition and proper treatment. | View Page |
| The Gram stain prepared from the positive blood culture is shown in the photograph. The appropriate report is: | View Page |
| Group A Strep A Disk/SXT In follow up to the previous question, the upper image again illustrates the colonies recovered from the blood culture bottle. The colonies are small, transluscent, gray-yellow, and surrounded by a wide zone of beta hemolysis.The size of the colonies compared to the zones of hemolysis suggests a group A streptococcus.The susceptibility to bacitracin (zone of inhibition around the "A" disk)(lower photograph) is virtually diagnostic of a group A streptococcus.The absence of a zone of inhibition around the SXT disk indicates resitance to sulfamethoxazole/ trimethoprim. SXT resistance is also shared by group B streptococci, which are, however, resistant to bacitracin.The resistance to SXT is used for the primary recovery of groups A and B streptococci from specimens with mixed culture. Their resistance allows them to selectively grow out from contaminating bacteria that are inhibited by this antibiotic. | View Page |
| Thus, in follow-up to the previous discussion, the reaction shown in the photograph establishes the identification of a group A, beta hemolytic streptococcus. | View Page |
| Review 1 Spencer RC.:
Invasive streptococcEuropean Journal of Clinical Microbiology & Infectious Diseases. 14 Suppl. 1:S26-32, 1995.Before the introduction of antibiotics, serious infections caused by Streptococcus pyogenes (Lancefield Group A streptococci) were common. Before World War II, this bacterium was responsible for as many as 50% of postpartum deaths and was the major cause of death in patients with burns. Also common were the sequelae of streptococcal infections-rheumatic fever and post-streptococcal glomerulonephritis.With the use of penicillin, however, Streptococcus pyogenes was believed to be virtually eliminated as a pathogen. The organism was consigned to the history books, but not for long.In the mid-1980s, focal resurgences of rheumatic fever began to be reported from different areas in the USA, such as Salt Lake City, Utah. In such communities, where increases in cases of rheumatic fever had been reported, the serotypes M-1, 3, 5, 6 and 18 were isolated which, on culture, produced characteristic mucoid colonies. At the same time, reports of increases in invasive streptococcal disease began to surface in both the USA and Europe.Two syndromes were described; invasive streptococcal infection, occurring in previously healthy children and adults, commonly associated with septicaemia resulting from a deep focus of infection such as bone or lung; and streptococcal toxic shock syndrome, involving a cutaneous focus, accompanied by necrotizing or bullous soft tissue changes. Septicaemia is rare in streptococcal toxic shock syndrome, but the most characteristic feature is one of rapidly progressing multi-organ failure. A high proportion of the strains of Streptococcus pyogenes associated with this condition are serotype M-1, and fatality rates approaching 50% have been reported. | View Page |
| Review 2 Cunningham MW.:
Pathogenesis of group A streptococcal infections.
Clinical Microbiology Reviews. 13):470-511, 2000Group A streptococci are model extracellular gram-positive pathogens responsible for pharyngitis, impetigo, rheumatic fever, and acute glomerulonephritis. A resurgence of invasive streptococcal diseases and rheumatic fever has appeared in outbreaks over the past 10 years, with a predominant M1 serotype as well as others identified with the outbreaks.Emm (M protein) gene sequencing has changed serotyping, and new virulence genes and new virulence regulatory networks have been defined. The emm gene superfamily has expanded to include antiphagocytic molecules and immunoglobulin-binding proteins with common structural features.At least nine superantigens have been characterized, all of which may contribute to toxic streptococcal syndrome. An emerging theme is the dichotomy between skin and throat strains in their epidemiology and genetic makeup. Eleven adhesions have been reported, and surface plasmin-binding proteins have been defined.The strong resistance of the group A streptococcus to phagocytosis is related to factor H and fibrinogen binding by M protein and to disarming complement component C5a by the C5a peptidase. Molecular mimicry appears to play a role in autoimmune mechanisms involved in rheumatic fever, while nephritis strain-associated proteins may lead to immune-mediated acute glomerulonephritis. Vaccine strategies have focused on recombinant M protein and C5a peptidase vaccines, and mucosal vaccine delivery systems are under investigation. | View Page |
| A Brown and Brenn gram stain was performed on one of the tissue biopsy specimens. Organisms were seen as shown in the photograph. Based on the history and the appearance of the bacteria, the most likely identification is: | View Page |
| Shown in the photograph is a close-in view of the colony growth after 48 hours incubation. Possible presumptive identifications suggested by the colonies observed include: | View Page |