MRSA isolates that are extremely hetero-resistant and phenotypically oxacillin-susceptible mecA-positive S. aureus (OS-MRSA) are likely to be missed by the oxacillin/cefoxitin DDT (disk diffusion test) or oxacillin agar screening methods.

Because treatment with a β-lactam antibiotic is likely to be used for infections with MSSA, this could result in treatment failure. Therefore, it is important for these isolates be reported to the clinician as MRSA so that appropriate treatment and isolation precautions can be initiated.

Approximately 1% of MRSA are being misclassified as methicillin-susceptible S. aureus (MSSA) based on routinely used phenotypic tests.

In facilities that do not have specific infection control staff, the laboratory should notify the ward staff about the MRSA isolate and the report should include a comment code indicating isolation precautions are required.

If evidence of more than one morphotype exists, both should be identified so that susceptibilities on each can be performed. In such cases it may occur that one is quite susceptible and the other multi-resistant. Picking the susceptible one only could have significant consequences for treatment, outcome and spread of the organism in hospital.

In most cases the MIC of ertapenem is suggestive of the probable mechanism of carbapenem resistance: low or intermediate level resistance to ertapenem is usually indicative of an altered porin or efflux mechanism where the strain is susceptible using gradient endpoint or broth dilution methods to other carbapenems (imipenem, meropenem, or doripenem). When the MIC to ertapenem is high (> 16 mg/L) there is a greater likelihood that the isolate has a carbapenemase and that imipenem and meropenem will also be resistant.

Resistance to carbapenems can be caused by various mechanisms: production of carbapenemases (carbapenem-specific β-lactamases), efflux pumps, and decreased expression or function of porins and PBPs.

Gram stain of vaginal fluid is an objective method of diagnosis of bacterial vaginosis that correlates well with the clinical criteria described by Amsel and colleagues.

It is important to differentiate women with DSIV from BV because the treatment is different

The reporting of the Gram stain without reference to the presence of RBCs is inaccurate, potentially confusing and misleading because the report will be discordant with the CSF cell count.

Most infectious conjunctivitis are of viral etiology, although bacterial conjunctivitis is more common in children than in adults.

Systemic therapy is the mainstay with Neisseria infections since primary meningococcal conjunctivitis has been known to precede invasive disease

The clinical spectrum of disease caused by group G streptococcus resembles infections caused by group A streptococcus (S. pyogenes). Both group A & G streptococci are associated with upper respiratory tract infections and invasive infections such as necrotizing fasciitis, STSS, bacteremia, and endocarditis.

Morganella are opportunistic pathogens that are found commonly in soil, water and sewage.

Urinary tract infections (UTIs) among elderly are very common and are considered within the context of complicated UTI

Most strains are also resistant to nitrofurantoin but are usually susceptible to aminoglycosides, trimethoprimsulfamethoxazole, quinolones and carbapenems

If the clinician suspects Neisseria infection, a bacterial Gram stain and culture should be obtained immediately. The diagnosis of meningococcal conjunctivitis should be considered when gram-negative diplococci are observed.

Neisseria species, including N. meningitidis, can cause a hyperacute bacterial conjunctivitis that is severe and sight-threatening.

Treatment of conjunctivitis should include systemic therapy in view of the potential for invasiveness of N meningitidis, with topical antibiotics as an adjunct. The risk of invasive disease in those treated initially with topical therapy alone was estimated to be 19 times greater than for those receiving systemic antibiotic.

Chromogenic agars have been developed which allow for detection of sorbitol and non-sorbitol fermenting isolates.

Antimicrobial therapy is not recommended and has been linked to an increased risk of HUS in children.

Bacteremia is rare as STEC are not invasive but they secrete ribosome inactivating toxins which are responsible for the organ damage

Although O157:H7 is the serotype most frequently isolated from humans, a recent CDC surveillance report showed that O157 serotypes comprised 41.1% of all the STEC isolated.

Granulicatella adiacens and other nutritionally variant streptococci (e.g. Abiotrophia defectiva, other Granulicatella species) are infrequent but important isolates from blood cultures. It is important for a laboratory to have the ability to cultivate and recognize a nutritionally variant streptococci.

Their Gram stain appearance varies depending on the culture media. In liquid media containing pyridoxal (e.g. thioglycolate broth), they appear as gram positive cocci in chains, indistinguishable from other streptococci. More commonly, when the Gram stain is performed on colonies from agar plates, especially those poor in pyridoxal, they may appear pleomorphic and even gram variable. Extremely elongated forms may be mistaken for bacilli, and swollen cells may resemble spores, leading to confusion in interpretation of the stain.

From a clinical standpoint, recognition that an isolate belongs to the group of Abiotrophia/Granulicatella spp. is more important than identification to the species level, as there may be ramifications in pathogenicity and antibiotic susceptibilities.

Susceptibility testing methods and interpretation guidelines for Abiotrophia and Granulicatella species have been published by the CLSI in the document M45-A3.

Penicillin resistance is relatively uncommon but still is seen in up to 20% of isolates, but isolates appear to more likely be resistant to ceftriaxone (13 – 60%).13 Macrolide resistance, mediated by mefA and ermB,13 is common: one study reported an azithromycin resistance rate of over 90%.14 Clindamycin resistance has also been observed; however, no vancomycin resistant isolates have been reported

M. chelonae causes sporadic diseases, which include cellulitis, abscess, and disseminated disease; skin trauma may be the primary cause for cutaneous illness

Although C. albicans is the predominant species that causes invasive candidiasis, C. glabrata has emerged as the most common non-albicans Candida in North America